Communication Satellite Antennas

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Robert Dybdal

Communication Satellite Antennas: System Architecture, Technology, and Evaluation Robert Dybdal

New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto

Robert Dybdal

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Library of Congress Cataloging-in-Publication Data Dybdal, Robert. Communication satellite antennas : system architecture, technology, and evaluation / Robert Dybdal. p. cm. Includes bibliographical references and index. ISBN-13:978-0-07-160918-0 (alk. paper) ISBN-10:0-07-160918-0 1. Artificial satellites—Radio antennas. 2. Satellite dish antennas. 3. Artificial satellites in telecommunication. I. Title. TL3035.D93 2009 621.382’54—dc22 2009017847 McGraw-Hill books are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs. To contact a special sales representative, please visit the Contact Us page at www.mhprofessional.com. Communication Satellite Antennas: System Architecture, Technology, and Evaluation Copyright © 2009 by The McGraw-Hill Companies. All rights reserved. Printed in the United States of America. Except as permitted under the Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher. All trademarks or copyrights mentioned herein are the possession of their respective owners and McGraw-Hill makes no claim of ownership by the mention of products that contain these marks. 1 2 3 4 5 6 7 8 9 0 FGR FGR 0 1 9 ISBN 978-0-07-160918-0 MHID 0-07-160918-0 Sponsoring Editor Wendy Rinaldi Editorial Supervisor Jody McKenzie Project Manager Madhu Bhardwaj, International Typesetting and Composition Acquisitions Coordinator Joya Anthony Copy Editor Michael McGee Proofreader Andy Saff Indexer Steve Ingle Production Supervisor George Anderson Composition International Typesetting and Composition Illustration International Typesetting and Composition Art Director, Cover Jeff Weeks Cover Designer 12E Design Information has been obtained by McGraw-Hill from sources believed to be reliable. However, because of the possibility of human or mechanical error by our sources, McGraw-Hill, or others, McGraw-Hill does not guarantee the accuracy,

adequacy, or completeness of any information and is not responsible for any errors or omissions or the results obtained from the use of such information.

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ABOUT THE AUTHOR BOB DYBDAL has supported a broad base of military and commercial communication satellite programs and is affiliated with The Aerospace Corporation. His interest in antennas and RF systems developed at the ElectroScience Laboratory at Ohio State University, where he received a BSEE, MSc, and PhD in Electrical Engineering. He has been involved in a wide range of IEEE technical activities and is a past president of the Antenna Measurement Techniques Association. He holds patents in instrumentation, adaptive antennas, antenna tracking, satellite transponder designs, interferometry, and microwave components.

Professional Engineering 6X9 / Communication Satellite Antennas / Bob Dybdal / 918-0 / Front Matter

Contents at a Glance

Chapter 1. Fundamental Parameters

1

Chapter 2. Technology Survey

25

Chapter 3. Communication Satellite System Architectures

73

Chapter 4. Propagation Limitations and Link Performance

105

Chapter 5. Interference Susceptibility and Mitigation

137

Chapter 6. Space Segment Antenna Technology

167

Chapter 7. User Segment Antennas

197

Chapter 8. Antenna Test Facilities and Methodologies

225

Chapter 9. Satellite Antenna System Evaluation

277

Index

311

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Contents

Preface ix Introduction

xi

Chapter 1. Fundamental Parameters 1.1 Overview 1.2 Antenna Parameters References

Chapter 2. Technology Survey 2.1 2.2 2.3 2.4 2.5 2.6

Overview Wide Coverage Antennas Earth Coverage Antennas Narrow Coverage Antennas Array Antennas Antenna Tracking References

Chapter 3. Communication Satellite System Architectures 3.1 3.2 3.3 3.4

Overview Space Segment Architectures User Segment Architectures Orbital Alternatives References

Chapter 4. Propagation Limitations and Link Performance 4.1 4.2 4.3 4.4

Overview Propagation Limitations Modulation and Multiple Access Link Analyses References

1 1 1 23

25 25 26 32 35 41 49 70

73 73 74 95 98 102

105 105 106 125 129 133

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viii

Contents

Chapter 5. Interference Susceptibility and Mitigation 5.1 5.2 5.3 5.4

Overview Interference Environment Deﬁnition Susceptibility Analyses Interference Mitigation Techniques References

Chapter 6. Space Segment Antenna Technology 6.1 6.2 6.3 6.4 6.5 6.6

Overview Spot Beam Antennas Multiple-Beam Designs Adaptive Uplink Antennas Active Aperture Antennas Point-to-Point Antennas References

Chapter 7. User Segment Antennas 7.1 7.2 7.3 7.4 7.5

Overview User Antenna Technology Antenna Sidelobe Control Adaptive User Antennas Mission Control Assets References

Chapter 8. Antenna Test Facilities and Methodologies 8.1 8.2 8.3 8.4 8.5 8.6 8.7

Overview General-Purpose Test Facilities Radio Source Techniques Adaptive Antenna Evaluation Evaluation of Antennas Having Integrated Electronics Antenna Tracking Evaluation System Evaluation References

Chapter 9. Satellite Antenna System Evaluation 9.1 9.2 9.3 9.4 9.5

Index

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Overview Space Segment Antenna Testing Space Segment Test Issues User Segment Antenna Testing User Segment Test Issues References

137 137 138 149 159 165

167 167 168 171 180 188 192 194

197 197 198 201 207 212 223

225 225 226 244 257 262 266 272 274

277 277 278 291 296 304 309

311

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Preface Antenna systems are a fundamental part of communication satellite systems. Antenna technology has a long development history beginning with the fundamental experiments performed by Hertz in the 1880s, the development of broadcast antennas in the 1920s where fundamental concepts of antenna pattern shaping and array synthesis began, the microwave technology demonstrated during World War II, and today’s technology and analysis capabilities. Antenna technology has had a significant impact not only on communication systems but also in radar, remote sensing, and other applications. Antenna technology is extensively documented in IEEE publications and those of other organizations, including the Antenna Measurement Techniques Association. A number of excellent textbooks are available to educate future antenna developers, and a variety of books address specific antenna technologies. This book describes the way in which antenna technology is used in communication satellite systems. The book is motivated by a belief that practicing system designers and technology developers would benefit from a system view of antenna applications, a description of antenna technology, and guidance on methodologies needed in their evaluation. On an educational level, the material would be suitable for academic courses on applications of antenna technology to systems that have a major importance worldwide. The material in this book has evolved from an innumerable collection of people spanning the development history and application of anten-nas. The technology heritage is very rich, spanning a variety of system applications, innovative designs, well-developed analysis capabilities, and instrumentation and measurement facilities. Future system development and application likewise depend on the efforts of a large number of people. Clearly, this publication is indebted to the efforts of many. On a personal level, the author is likewise indebted to many people, including peers, members of professional organizations, and the contractor and customer communities. One of life’s riches is the opportunity to benefit from lively

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technical debate, learn and teach, collaborate, and create and evolve in a technology area as vibrant as antennas and their system applications. The enthusiasm and encouragement of Wendy Rinaldi of McGraw-Hill and the careful editing of Madhu Bhardwaj and her colleagues are gratefully acknowledged.

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Introduction Satellite systems have had a profound effect on worldwide information dissemination. Early systems provided proof-of-concept demonstrations and established an initial operating capability. System capabilities have greatly extended beyond these early system designs in ways that were not foreseen at the inception of satellite systems. Early systems and technology available at that time provided limited service to large ground terminals and then dissemination by terrestrial means to system users. Today, a wide ranging number of services are available to individual system users having relatively modest user equipment requirements. Future system designs will continue to extend the services available to system users in ways that are not grasped today. Existing satellite system maturity has been made possible by a wide range of enabling technologies. Today’s launch vehicle, solar power arrays, and attitude stability technologies have resulted in satellite capabilities that could not have been imagined by early satellite developers. Today’s satellite lifetimes greatly exceed those of the early satellites and often their own projected lifetimes. Electronic technologies likewise have made possible the development of capable systems for both the space and user segments comprising satellite systems. The development and demonstration of modulation formats and multiple access techniques that allow a collection of users to share satellite resources have had major roles in providing efficient and reliable communications for a multitude of system users and applications. Antenna systems have greatly increased in sophistication. Space segment antennas provide high gain capabilities to ease user requirements; can spatially isolate different portions of the field of view allowing the available spectra to be reused; and can mitigate interference. Of all the technologies used in the space segment, antenna systems are the most diverse as a result of different operating frequencies and system requirements. User segment antenna designs are also diverse, ranging from handheld designs for low data rate applications to very large ground terminals for high data rate transfer. The escalating

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number of system users demand attention to cost-effective designs and economies of production to control system acquisition costs. Future satellite systems will not only replenish existing capabilities but also provide capabilities that cannot be clearly envisioned today. While today’s satellite system technologies are highly capable, future designs will benefit by development and further refinements and efficiencies. Technology evolution will continue to contribute to systems having additional capabilities and flexibilities, as well as reduced weight and power requirements and acquisition costs. This evolution will extend over all the diverse technologies used in satellite systems. In addition to component evolution, other developments in modulation, multiple access, and network techniques can also be envisioned. Utilization of software and digital technologies will also increase in future system designs. Like these other technologies, satellite antenna systems will continue to evolve to satisfy the objectives of future system designs. Communication satellites have been developed for both commercial and military applications and the objectives of their applications differ. Commercial systems are configured to serve particular market segments and are intended to provide as much system capacity from the available frequency allocation as possible. These considerations result in system designs that have relatively fixed coverage requirements and techniques to expand system capacity by reusing the same frequency spectra. Serving the required coverage with multiple beams to isolate users in different portions of the coverage area and reusing the same frequency subband when sufficient spatial isolation is available is one technique. Another commonly used technique uses orthogonal polarizations to communicate independent data channels. Military systems, by contrast, require the capability to respond to capacity and coverage needs that change over the satellite’s lifetime because of evolving geopolitical requirements. Additionally, military users have long had concerns regarding intentional interference or jamming. Techniques to protect systems from interference have been developed and used operationally. While commercial and military systems have differing objectives, both share common development requirements. Independent of the application, SWaP, size, weight, and power, are of paramount importance for the space segment. Reliability is also essential and extensive system testing and redundant components are required to assure satisfying orbital lifetime objectives. Acquisition cost is another critical factor. As the number of system users continues to increase, providing sufficient performance to reduce user requirements and permitting the development of cost-effective user segment designs are the most important areas of system design and planning. Testing is an essential part of system development, and as the number of users continues to

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increase, techniques to test on a production basis must be developed. These issues will have increased importance for future system designs as the level of complexity increases and the number of system users continues to grow. System design is an iterative process, and the amount of iteration will grow as system complexity and the number of users continues to increase. The system design process illustrated in Fig. 1 indicates the iterative nature that must be addressed by system planners. At a top level, system-level objectives define the user data transfer and coverage requirements, the frequency allocations to be used, and preliminary assessments of G/T and ERP (effective radiated power) constraints for both the space and user segments. These top-level requirements are used to develop system design concepts based on preliminary assessments of performance capabilities for the space and user segments. A most important and fundamental part of system definition is questioning and understanding the impacts of system requirements. As the system definition proceeds, the requirements will evolve as necessary to configure viable system designs. The importance of questioning system requirements cannot be overstated. The system design concepts are compared with launch vehicle constraints for the space segment and compared with production costs for the user segment. Technology estimates play a major role in these preliminary system designs and development risk for implementation must be addressed. Other choices that are examined at this time are modulation formats to be used in user communications and multiple access techniques that allow users to share the space segment resources. A significant number of system tradeoffs exist and the process iterates multiple times in developing an

Figure 1 The system design process

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acceptable system design. System design development and definition clearly must provide a balance between the space and user segment performance requirements in deriving system-viable implementations. As system capabilities increase and afford increased service requirements to service a greater number of system users, this iterative process becomes more complex and extensive. While the system planning and development process is ongoing, the capabilities of many different technologies are also assessed in support of the system definition. The scope of this effort likewise becomes more extensive as system design complexity increases. Design implementation choices, such as the fabrication alternatives of MMIC (monolithic microwave integrated circuits) and ASIC (application-specific integrated circuits) implementations to support specialized needs of the system design and the use of digital technology, are addressed in selecting the system electronics. System design choices for space and user antenna requirements become extensive with the complexity of requirements and technology alternatives. Antenna systems in particular afford opportunities for creative solutions because the system requirements for each application differ and “standard” designs are nonexistent. In addition to the component selection, this preliminary system definition phase needs to address testing requirements and the associated facilities needed to evaluate not only components but integrated subsystems and systems. While many technology choices and technical issues must be addressed, acquisition costs must also be examined and tradeoffs in system design evaluated on a cost basis. System definition is a multifaceted undertaking that requires careful assessments of requirements, technology alternatives, the allocation of resources, and economic impacts. Antenna technology to support system definition and development has a major role in devising viable system designs. System development, to date, has demonstrated a diverse antenna technology base to meet requirements for specific system applications. This antenna technology base has greatly contributed to existing system capabilities. Future system designs will continue to generate even more diverse antenna designs and extend component-level antennas to antennas integrated into system-level designs. Much opportunity exists here to develop creative solutions for future system needs. This book was prepared to provide guidance for future communication satellite antenna developments and endeavors to provide a system background to assist system planners and technology developers. Such development requires insight into system architectures, antenna technology alternatives, and methods to evaluate both their component- and system-level performance. The organization of the book has the following format. An overview of the parameters that characterize antennas is presented to provide a basis to quantify antenna performance. Antenna technology required

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in communication satellite systems is described in some detail. System architectures for both the space and user segment are reviewed so that antenna interfaces with system designs are understood. Practical system designs must assess propagation limitations and link analyses that determine the capabilities afforded by candidate system designs. The increased number of communication, radar, and navigation services and the substantial increase in user demands for these services result in potential interference between systems. Future system designs therefore will require increased design attention to interference susceptibility and include techniques to mitigate interference. Space and user segment antenna technologies are separately addressed, and technology applications to satisfy typical system requirements are discussed. Antenna performance evaluations must address facility alternatives and techniques to provide meaningful assessments of their performance. The processes used in the development and characterization of antenna systems are then reviewed.

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APERTUREANDTHEFARFIELDPATTERNS4HEPATTERNCHARACTERISTICSOFREFLEC TORANTENNASARESOMETIMESREPRESENTEDFORPHAVINGAVALUEOF4HESE SIMPLEANALYTICFORMSLENDTHEMSELVESTOSIMULATIONACTIVITIES ANDAS THESIMULATIONISREFINED CHARACTERISTICSOFTHEACTUALANTENNACANBE USEDTOINCREASETHESIMULATIONFIDELITY 4HEANTENNAGAINANDTHEANTENNABEAMWIDTHDEPENDONTHEELECTRI CALSIZEOFTHEANTENNA THATIS THESIZEINWAVELENGTHS4HEANTENNA GAININCREASESWITHTHESQUAREOFTHEELECTRICALSIZEWHILETHEBEAMWIDTH ISINVERSELYRELATEDTOTHEELECTRICALSIZE"OTHVALUESCLEARLYDEPENDON THESPECIFICSOFTHEANTENNASDESIGN&ORPRELIMINARYSYSTEMSIZING AN O EFFICIENCYOFANDABEAMWIDTHFACTOROF AREOFTENUSED!STHE DESIGNEVOLVES SUCHVALUESAREUPDATED5SINGTHESEPARAMETERVALUES THEGAINANDBEAMWIDTHAREPLOTTEDIN&IG FORVARIOUSAPERTURESIZES INWAVELENGTHS6ALUESOFANTENNAGAINANDBEAMWIDTHFORSPECIFICCASES ASAFUNCTIONOFFREQUENCYAREGIVENIN&IGS AND RESPECTIVELY )NPRACTICE DETAILEDCOMPUTERCODESAREAVAILABLETOACCURATELYPROJECT THEPERFORMANCEOFAWIDEVARIETYOFANTENNATECHNOLOGYUSEDINCOM MUNICATIONSATELLITESYSTEMS3UCHANALYSESPROVIDETHEMEANSOFREFIN INGTHEVALUESOFTHENOMINALPARAMETERSUSEDINPRELIMINARYSYSTEM SIZINGS ASINDICATEDHERE4HESENOMINALVALUESCANALSOBEUSEFULFOR hMENTALESTIMATESvOFANTENNAPERFORMANCE.OTICETHATTHESPEEDOFLIGHT ISAPPROXIMATELYFTNSECANDTHEREFORETHENUMBEROFWAVELENGTHSPER FOOTEQUALSTHEFREQUENCYIN'(Z&OREXAMPLE A FTANTENNAAT'(Z HASADIAMETEROFWAVELENGTHS5SINGABEAMWIDTHFACTOROF THE BEAMWIDTHEQUALSABOUTO&ORACIRCULARAPERTURE THEANTENNAGAIN

&IGURE .OMINALANTENNAGAINANDBEAMWIDTHVALUES


&IGURE !NTENNAGAINVARIATIONWITHFREQUENCY

&IGURE !NTENNABEAMWIDTHVARIATIONWITHFREQUENCY

EQUALS G O $K 4HE PRODUCT GO CORRESPONDS TO ABOUT D" FOR A ANTENNAEFFICIENCY4HEAPERTUREDIAMETEREQUALSWAVELENGTHS ANDTIMESTHELOGOFEQUALSD"4HEANTENNAGAINTHUSEQUALS ABOUTD"ITHISINDICATESANTENNAGAINRELATIVETOANISOTROPICGAIN LEVEL 4HISPROCESSMAYPROVEUSEFULWHENROUGHESTIMATESOFANTENNA PARAMETERSAREREQUIREDANDDETAILEDCALCULATIONISUNAVAILABLE

#HAPTER/NE

0OLARIZATION

4HEVECTORNATUREOFELECTROMAGNETICWAVESISSPECIFIEDBYTHEPOLARIZA TIONPRODUCEDBYANANTENNA ANDPROPAGATINGINFREESPACE0OLARIZATION SPECIFIESTHEORIENTATIONOFTHEELECTRICFIELDDURINGONE2&CYCLE4HE MOSTGENERALPOLARIZATIONSTATEISELLIPTICALWHERETHEELECTRICFIELDTRACES OUTANELLIPSE&OREVERYPOLARIZATION AUNIQUEORTHOGONALPOLARIZATION EXISTS WHERE ORTHOGONAL DENOTES IDEAL ISOLATION BETWEEN A RECEIVING ANTENNA AND AN INCIDENT FIELD HAVING ORTHOGONALLY POLARIZED STATES 0OLARIZATIONISCHARACTERIZEDBYTHREEPARAMETERS/NEISANAXIALRATIO EQUALTOTHERATIOOFTHEMAJORANDMINORAXESOFTHEPOLARIZATIONELLIPSE 4HESECONDISTHETILTANGLESPECIFIEDBYTHEALIGNMENTOFTHEMAJORAXIS OFTHEELLIPSEINAREFERENCEFRAME4HETHIRDISTHEPOLARIZATIONSENSE SPECIFIEDBYTHEFAMILIARRIGHT ORLEFT HANDROTATION ASVIEWEDINTHE DIRECTIONOFPROPAGATION 4HENOMINALORTHOGONALPOLARIZATIONSARELINEARANDCIRCULAR,INEAR POLARIZATIONSARETYPICALLYINDICATEDASVERTICALANDHORIZONTAL ANDIDEAL LINEARPOLARIZATIONCONFINESTHEELECTRICFIELDTOAPLANE,INEARVERTICALLY POLARIZEDANTENNASDONOTRESPONDTOHORIZONTALLYPOLARIZEDFIELDSAND THUSTHELINEARPOLARIZATIONSMUSTBESPATIALLYALIGNEDINUSE#IRCULAR POLARIZATIONISCOMPRISEDOFTWOORTHOGONALLINEARCOMPONENTSHAVING AOPHASEDIFFERENCE/VERONE2&PERIOD THEELECTRICFIELDTRACESOUTA CIRCLE#IRCULARPOLARIZATIONDOESNOTREQUIRETHEPOLARIZATIONALIGNMENT THATLINEARPOLARIZATIONDOES ANDFORTHATREASONCIRCULARPOLARIZATIONIS WIDELYUSEDINSATELLITECOMMUNICATIONSYSTEMS#IRCULARPOLARIZATION COMPONENTSAREORTHOGONALWHENTHEIRSENSEDIFFERS2IGHT HANDCIRCU LARPOLARIZATIONSENSEISORTHOGONALTOLEFT HANDCIRCULARPOLARIZATION SENSE4HESEPOLARIZATIONSENSESFOLLOWTHEFAMILIARRIGHT ANDLEFT HAND RULESWHENVIEWEDINTHEDIRECTIONOFPROPAGATION 0RACTICALANTENNASARENOTIDEALLYPOLARIZEDANDAREMIXTURESOFTHE TWO ORTHOGONAL COMPONENTS 4HE CROSS POLARIZED ANTENNA RESPONSE QUANTIFIES THE DEGREE TO WHICH THE ANTENNA DEVIATES FROM THE IDEAL POLARIZATION!TASYSTEMLEVEL TWOISSUESRESULTFROMTHEFINITECROSS POLARIZEDCOMPONENTS 7HAT SIGNAL LOSS RESULTS FROM THE CROSS POLARIZED COMPONENTS A PARAMETERREFERREDTOASPOLARIZATIONMISMATCHLOSS 7HEN ORTHOGONALLY POLARIZED SIGNALS ARE USED TO COMMUNICATE INDEPENDENTDATASTREAMSINPOLARIZATIONREUSEDESIGNS WHATISTHE ISOLATIONBETWEENORTHOGONALPAIRS 4HE AXIAL RATIO R CAN BE EXPRESSED ;= IN TERMS OF THE CIRCULARLY POLARIZEDCOMPONENTSAS

R%2%, %2n%,


WHERE%2AND%,ARETHEAMPLITUDESOFTHERIGHT ANDLEFT HANDPOLAR IZATIONCOMPONENTS RESPECTIVELY.OTICETHATTHENUMERICVALUEOFAXIAL RATIOISPOSITIVEFORRIGHT HANDCOMPONENTSANDNEGATIVEFORLEFT HAND COMPONENTS.ORMALLY AXIALRATIOISGIVENINALOGARITHMICVALUETHAT INVOLVESTHEMAGNITUDEOFTHEAXIALRATIO4HELEVELOFTHECROSS POLARIZED COMPONENT RELATIVE TO THE PRINCIPALLY POLARIZED COMPONENT CAN BE CALCULATEDASPRESENTEDIN&IG .ORMALLY THE AXIAL RATIO OF INCIDENT FIELDS AND ANTENNA SYSTEMS ARE KNOWN BUT THE RELATIVE ORIENTATION OF THE TILT ANGLES OF THEIR RESPECTIVEPOLARIZATIONELLIPSESAREUNKNOWN"OTHTHEPOLARIZATION MISMATCHLOSSANDPOLARIZATIONISOLATIONDEPENDONTHERELATIVEORIEN TATIONOFTHETWOPOLARIZATIONELLIPSESOFTHEINCIDENTFIELDANDRECEIV ING ANTENNA! STATISTICAL APPROACH ;= IS PRESENTED AS A MEANS OF UNDERSTANDING THE VARIATIONS RESULTING FROM UNKNOWN POLARIZATION ELLIPSEALIGNMENT 4HE POLARIZATION EFFICIENCY HAS BEEN DEFINED IN TERMS OF THE AXIAL RATIOSANDORIENTATIONOFTHEPOLARIZATIONELLIPSESOFTHEINCIDENTFIELD ANDRECEIVINGANTENNA0OLARIZATIONMISMATCHLOSSISDETERMINEDFROM POLARIZATIONEFFICIENCYWHENTHEINCIDENTFIELDANDRECEIVINGANTENNA HAVETHESAMEPOLARIZATIONSENSE0OLARIZATIONISOLATIONISDETERMINED FROM POLARIZATION EFFICIENCY WHEN THE INCIDENT FIELD AND RECEIVING ANTENNAHAVEOPPOSITEPOLARIZATIONSENSES0OLARIZATIONEFFICIENCY;= EQUALS

GP !"COS$

&IGURE #ROSS POLARIZEDLEVELVERSUSAXIALRATIO

#HAPTER /NE

WHERE

! RW RR ¨ª RW RR ·¹

" RW RR ¨ª RW RR ·¹

WHERETHESUBSCRIPTShWvANDhRvREFERTOTHEAXIALRATIOSOFTHEINCI DENTWAVEANDTHERECEIVINGANTENNA RESPECTIVELY7HENTHESENSEOF INCIDENTFIELDANDTHERECEIVINGANTENNAHAVETHESAMEPOLARIZATION SENSE !ISPOSITIVEBECAUSETHEPRODUCTOFTHENUMERICVALUEOFAXIAL RATIOSISPOSITIVEWHENBOTHSENSESARETHESAME7HENTHESENSESOF THE INCIDENT FIELD AND RECEIVING ANTENNA HAVE OPPOSITE POLARIZATION SENSES ! IS NEGATIVE4HE ANGLE $ IS THE PHASE DIFFERENCE BETWEEN THEPOLARIZATIONCOMPONENTSANDEQUALSTWICETHEDIFFERENCEINTHETILT ANGLEORIENTATIONSOFTHEELLIPSES 4HECOMMONLYUSEDBOUNDSONPOLARIZATIONEFFICIENCYARE !" 4HE STATISTICAL VARIATION OF THE POLARIZATION EFFICIENCY IS DERIVED BY ASSUMINGTHERELATIVEORIENTATIONSOFTHETILTANGLEOFTHEINCIDENTFIELD ANDRECEIVINGANTENNAAREEQUALLYLIKELYANDUNIFORMLYDISTRIBUTEDOVER TOO CORRESPONDINGTO$BEINGEQUALLYLIKELYANDUNIFORMLYDISTRIBUTED OVERTOO4HEFIRSTORDERMEAN STATISTICSAREDETERMINEDFROM

%P O °GD$

! WHERE THE INTEGRATION EXTENDS OVER TO O7HEN BOTH THE INCIDENT FIELDANDRECEIVINGANTENNAHAVETHESAMEPOLARIZATIONSENSE THEMEAN EFFICIENCYIS ANDWHENTHEIRPOLARIZATIONSENSESAREOPPOSITE THE EFFICIENCYIS !DDITIONALLY IFEITHERTHEINCIDENTFIELDORTHERECEIVING ANTENNAORBOTHISIDEALLYLINEAR THEMEANPOLARIZATIONEFFICIENCYIS ORTHEFAMILIARD"LOSS 3IMILARLY THESECONDORDERVARIANCE STATISTICSAREDETERMINEDFROM

6PO°Gn%P D$

" WHEREAGAINTHEINTEGRATIONEXTENDSOVERTOO4HESTANDARDDEVIA TIONOFTHEPOLARIZATIONEFFICIENCY R ABOUTITSMEANVALUEEQUALS" 4HEPOLARIZATIONEFFICIENCYSTATISTICSHAVEANON ZEROMEANVALUE SO THESECOND ORDERSTATISTICSAREGENERALLYEXPRESSEDASTHER SPREAD ABOUT THE MEAN VALUE &URTHER THE POLARIZATION EFFICIENCY STATISTICS ARE NOT 'AUSSIAN4HE PEAK TO PEAK BOUNDS ARE " FOR THESE STATIS TICS WHILETHERMSSPREADIS"4HEBOUNDSEQUALTIMES


THESTANDARDDEVIATION"YCONTRAST PEAK TO PEAKVARIATIONSFOR'AUSSIAN STATISTICSAREOFTENTAKENASR WELLINEXCESSOFTHEPOSSIBLEPEAK TO PEAK EXCURSIONFORTHEPOLARIZATIONEFFICIENCY %XAMPLEVALUESILLUSTRATETHESTATISTICALVARIATIONSANDTWODIFFERENT CASES ONEFORANINCIDENTFIELDHAVINGAD"AXIALRATIOANDTHESECOND WITHAD"AXIALRATIO4HEPOLARIZATIONMISMATCHLOSSLEVELSIN&IG

&IGURE 0OLARIZATIONMISMATCHLOSSSTATISTICS

#HAPTER /NE

ILLUSTRATE THE MEAN THE MINIMUM THE MAXIMUM AND THE MEAN R VALUES4HETWOEXAMPLESILLUSTRATETHEVARIATIONINTHESTATISTICAL VALUESINCREASEASTHEAXIALRATIOOFTHEINCIDENTFIELDINCREASESANDAS THEAXIALRATIOOFTHERECEIVINGANTENNAINCREASES&URTHER NOTICETHAT THEMATCHEDPOLARIZATIONCONDITIONWHENTHEINCIDENTFIELDANDRECEIV INGANTENNAHAVETHESAMEAXIALRATIOVALUEANDTHEIRPOLARIZATIONTILT ANGLESARECOINCIDENTHASAFINITEPROBABILITYOFHAVINGNOPOLARIZATION MISMATCHLOSS3YSTEMAPPLICATIONSFORPOLARIZATIONREUSEREQUIREHIGH POLARIZATIONPURITYANDINCIDENTFIELDSHAVINGAXIALRATIOVALUESONTHE ORDEROFD"/THERAPPLICATIONSTHATSEEKREASONABLEPOLARIZATION MISMATCHLOSSGENERALLYLIMITAXIALRATIOVALUESTOABOUTD"&OREXAM PLE IFBOTHTHEAXIALRATIOSOFTHEINCIDENTFIELDANDRECEIVINGANTENNA ARELIMITEDTOD" THEMAXIMUMPOSSIBLEPOLARIZATIONMISMATCHLOSS ISLESSTHAND" ANDONAVERAGETHEPOLARIZATIONMISMATCHLOSSIS ABOUTD" CORRESPONDINGTOTHEMEANVALUE 4HEPOLARIZATIONISOLATIONVALUESIN&IG SIMILARLYILLUSTRATETHE STATISTICALVARIATIONSWHENTHEINCIDENTFIELDHASAANDD"AXIAL RATIO7HENORTHOGONALLYPOLARIZEDCOMPONENTSAREUSEDINFREQUENCY REUSEDESIGNSTOINCREASESYSTEMCAPABILITY HIGHLEVELSOFPOLARIZATION PURITYAREREQUIREDOFBOTHTHEINCIDENTFIELDANDTHERECEIVINGANTENNA &OREXAMPLE IFTHEINCIDENTFIELDANDTHERECEIVINGANTENNABOTHHAVE D"AXIALRATIOS THEMINIMUMPOLARIZATIONISOLATIONISABOUTD" 7HENDESIGNATTENTIONISNOTPAIDTOPOLARIZATIONPURITY THEISOLATION SIGNIFICANTLYDEGRADES)DEALPOLARIZATIONISOLATIONREQUIRESTHEINCIDENT FIELDANDRECEIVINGANTENNATOHAVETHESAMEAXIALRATIOANDORTHOGONAL POLARIZATIONTILTANGLEORIENTATIONS4HERESULTSINDICATEAFINITEPROB ABILITYOFTHATCONDITIONBEINGSATISFIED /FTEN CIRCULARPOLARIZATIONISPRODUCEDBYCOMBININGORTHOGONALLINEAR COMPONENTSWITHAQUADRATUREHYBRIDTOPRODUCECIRCULARPOLARIZATION 4HE AXIAL RATIO RESULTING FROM AMPLITUDE AND PHASE IMBALANCE ;= IN COMBININGTWOORTHOGONALLINEARLYPOLARIZEDCOMPONENTSISILLUSTRATED IN &IG !S THE AUTHORS POINT OUT THE INHERENT CROSS POLARIZATION INTHELINEARCOMPONENTSISNOTINCLUDEDINTHISANALYSISANDMUSTBE CONSIDEREDINPRACTICALDESIGNS )MPEDANCE

4HE INTERFACE BETWEEN THE ANTENNA AND THE SYSTEM ELECTRONICS MUST ALSOBESPECIFIED-AXIMUMPOWERTRANSFERREQUIRESMATCHEDIMPEDANCE CHARACTERISTICS ANDDEVIATIONSFROMIDEALMATCHEDIMPEDANCERESULTIN REDUCEDPOWERTRANSFERREFERREDTOASMISMATCHLOSS-EASUREDTERMINAL PARAMETERS ARE GENERALLY PERFORMED USING NETWORK ANALYZER INSTRU MENTATION ANDSUCHMEASUREMENTSAREEXPRESSEDINSCATTERINGMATRIX PARAMETERS4HE REFLECTED COMPONENTS ARE EXPRESSED IN THE VOLTAGE


&IGURE 0OLARIZATIONISOLATIONSTATISTICS

REFLECTION COEFFICIENT DENOTED BY 3 WHILE THE VOLTAGE TRANSMISSION PROPERTIESAREDENOTEDBY34HEINSERTIONLOSSFORPASSIVECOMPONENTS EQUALS¸3¸ BETWEENTERMINALSANDANDFORACTIVEELECTRONICS ¸3¸ ISTHEINSERTIONGAIN4HEMISMATCHLOSSIS ¸3¸ !NTENNAIMPEDANCE

#HAPTER /NE

&IGURE (YBRIDIMBALANCEIMPACTSONAXIALRATIO;=Ú)%%%

VALUESARECOMMONLYSPECIFIEDBYTHEVOLTAGEREFLECTIONCOEFFICIENT3 THERETURNLOSS2, ORTHE6372VOLTAGESTANDINGWAVERATIO ANDARE EXPRESSEDAS

2,LOG¸3¸

AND

6372¸3¸ ¸3¸

WHERE PHYSICALLY6372 IS THE RATIO OF THE MAXIMUM AND MINIMUM VALUESOFTHEVOLTAGESALONGATRANSMISSIONLINE4HERETURNLOSSTHAT EQUALSLOG¸3¸ISCOMMONLYUSEDWHENNETWORKANALYZERMEASURE MENTS ARE USED4HE MISMATCH LOSS IS n ¸ 3¸ %XAMPLE VALUES OF IMPEDANCE MISMATCH LOSS FOR THE THREE COMMON WAYS OF EXPRESSING MISMATCHAREGIVENIN&IG )NSPECIFICATIONS 6372ANDRETURNLOSS AREMOSTCOMMONLYUSED ANDTHERELATIONSHIPBETWEENTHESEPARAM ETERSISGIVENIN&IG )N PRACTICAL SYSTEM DESIGNS NEITHER THE ANTENNA NOR THE INTERFACE ELECTRONICSAREIDEALLYMATCHED!SARESULT MULTIPLEREFLECTIONSBETWEEN THEANTENNAANDELECTRONICSOCCURGIVINGRISETOAMPLITUDEANDPHASE RIPPLESOVERTHESYSTEMSOPERATINGBANDWIDTH4YPICALLY THEAMPLITUDES OFTHEREFLECTIONCOEFFICIENTSAREKNOWN BUTTHEPHASEVALUESANDTHEIR


&IGURE )MPEDANCEMISMATCHLOSSVERSUSCOMMONIMPEDANCEPARAMETERS

&IGURE 2ELATIONSHIPBETWEENRETURNLOSSAND6372

VARIATIONWITHFREQUENCYARENOT!MPLITUDEANDPHASERIPPLEDEGRADES SIGNAL DETECTION PERFORMANCE AND GENERALLY A SPECIFICATION IS PLACED ON THE TOLERABLE RIPPLE /NE APPROACH TO ADDRESSING THE RIPPLE USES COHERENT ERROR STATISTICS ;= /THER APPLICATIONS OF THESE STATISTICS

#HAPTER /NE

BESIDES ASSESSING 6372 INTERACTIONS INCLUDE ASSESSING THE EFFECTS OF MULTIPATH FACILITY REFLECTION ERRORS AND ANTENNA CROSS POLARIZATION ERRORS 4HECOHERENTERRORSTATISTICSCANBEVISUALIZEDBYTHEPHASORDIAGRAM IN&IG 4HETRUEVALUEASSUMESAUNITLEVEL ANDTHECOHERENTERROR ISREPRESENTEDBYAPHASORHAVINGANAMPLITUDEAANDAPHASEA3INCE THEPHASEISASSUMEDTOBEUNKNOWN THEERRORSTATISTICSAREDERIVED BYASSUMINGANYPHASEVALUEISEQUALLYLIKELYANDUNIFORMLYDISTRIB UTEDBETWEENANDO4HERESULTINGFIRST ANDSECOND ORDERSTATISTICAL VALUESFORPOWER VOLTAGE ANDPHASEAREGIVENIN4ABLE 4HESTATIS TICSFORPOWERCANBEEXACTLYINTEGRATED WHILESERIESEXPRESSIONSARE DERIVEDFORBOTHVOLTAGEANDPHASESTATISTICS4HEMAXIMUMERRORSFOR A6372 2,nD" AREINDICATEDANDAPPLYTOMOSTPRACTI CALCASES4HEPOWERANDVOLTAGESTATISTICSARENON ZEROMEANANDTHE PEAK TO PEAKERRORBOUNDSHAVEFINITEVALUES4HERMSSPREADABOUTTHE MEANERRORANDTHEPEAK TO PEAKERRORSAREPRESENTEDIN&IG 4HE COHERENT ERROR STATISTICS ARE CLEARLY NOT A 'AUSSIAN DISTRIBUTION AND HAVEFINITEBOUNDSWHOSEVALUESAREMUCHLESSTHANTHATTHATWOULDBE ANTICIPATEDFROMRCONFIDENCEVALUESFOR'AUSSIANSTATISTICS)NTHE CASEOFLIMITINGTHEAMOUNTOFAMPLITUDERIPPLERESULTINGFROM6372 INTERACTIONS THEPRODUCTOFTHERETURNLOSSVALUESFORBOTHIMPEDANCE INTERFACESMUSTBELESSTHANVALUESINDICATEDIN&IG &OREXAMPLE IFTHERIPPLEISTOBELESSTHAND" THEPRODUCTOFTHERETURNLOSSVALUES MUSTBELESSTHANABOUTnD")NSOMECASESEG ACABLERUNFROM AN,.!OUTPUTTOADOWNCONVERTERINPUT THEADDITIONOFLOSSCANBE ADVANTAGEOUSINREDUCINGTHERIPPLEANDTHEPRODUCTOFTHERETURNLOSS 4!",% #OHERENT%RROR3TATISTICS

0OWER -EAN %RRORA 3TANDARD$EVIATION %RRORA

A .! A .!

6OLTAGE

zA zA nA

&IGURE 0HASORDIAGRAMFORCOHERENTERRORS;=Ú)%%%

0HASE .! zAA


&IGURE #OHERENTERRORSTATISTICALVALUES;=Ú)%%%

#HAPTER /NE

&IGURE %RRORCOMPONENTLEVELVERSUSPEAK TO PEAKRIPPLE

VALUESISINCREASEDBYTWICETHEATTENUATIONVALUEBECAUSETHE6372 INTERACTIONCOMPONENTINCURSATWO WAYPATHTHROUGHTHEATTENUATION 4HEINSERTIONOFATTENUATORSWHENMEASURINGANTENNASTHATHAVESIG NIFICANT MISMATCH IS COMMONLY DONE TO REDUCE ERRORS RESULTING FROM 6372INTERACTIONS4OBEEFFECTIVE THEATTENUATORSMUSTHAVEAGOOD IMPEDANCEMATCH 3YSTEM.OISE4EMPERATURE

4HESYSTEMFIGUREOFMERITFORRECEIVINGANTENNASIS'4 THEANTENNA GAIN DIVIDED BY THE TOTAL SYSTEM NOISE TEMPERATURE 4 4HE SYSTEM NOISE TEMPERATURE HAS TWO COMPONENTS4HE ANTENNA NOISE TEMPERA TURE INCLUDES NOISE COMPONENTS FROM THE ENVIRONMENT SURROUNDING THEANTENNAANDTHENOISEGENERATEDBYLOSSESWITHINTHEANTENNA! COMMONREFERENCETERMINALMUSTBESPECIFIEDWHEREANTENNAGAINAND SYSTEM NOISE FIGURES ARE BOTH ESTABLISHED '4 IS INDEPENDENT OF THE LOCATION OF THE REFERENCE TERMINAL PLANE BUT BOTH ANTENNA GAIN AND SYSTEMNOISETEMPERATUREVALUESVARYWITHTHELOCATIONOFTHETERMINAL PLANEUSEDFOR'4DETERMINATION&OREXAMPLE THEINPUTTERMINALOFAN ,.!ISOFTENCONVENIENTINMEASURINGTHERECEIVERNOISETEMPERATURE 'ENERALLY CABLINGAND2&FILTERINGFOLLOWTHEANTENNATERMINALSWHERE THEANTENNAGAINVALUESHAVEBEENESTABLISHED4HELOSSESINSUCHCOM PONENTSMUSTBEUSEDTOADJUSTTHEANTENNAGAINVALUEANDANTENNA NOISETEMPERATURESOTHATTHEANTENNAGAINLEVELISREFERENCEDTOTHE ,.!SINPUTTERMINAL!LTERNATIVELY THERECEIVERNOISETEMPERATURECAN


BEMEASURED INCLUDINGTHEFILTERANDCABLINGLOSS SOTHATTHE'4IS DETERMINEDATTHEANTENNATERMINAL 4HE ANTENNA NOISE TEMPERATURE CAN BE MEASURED AS DESCRIBED IN #HAPTER OR CALCULATED IN THE FOLLOWING WAY7HEN CALCULATING THE ANTENNANOISETEMPERATURE THEANTENNAISINITIALLYASSUMEDTOBELOSS LESS ANDTHENOISETEMPERATUREISCALCULATEDFROM

4ANT°°0PnPO InIO 4EP I SINPDPDI

WHERE 0 P n PO I n IO IS THE POWER PATTERN OF THE ANTENNA POINTED WITHITSBEAMMAXIMAINTHEDIRECTIONPO IOANDNORMALIZEDTOAUNITY VALUEATTHEBEAMPEAK 4EP I ISTHEEMISSIONBACKGROUNDTEMPERA TURETHATISDESCRIBEDINFURTHERDETAILIN#HAPTER4HEPOWERPATTERN INCLUDES BOTH PRINCIPAL AND CROSS POLARIZED COMPONENTS!N EXAMPLE OFSUCHACALCULATIONFORAREFLECTORANTENNAISGIVENIN&IG 4HE ANTENNAISAN FTREFLECTORFEDWITHALOW LOSSCONICALHORNILLUMINATING A#ASSEGRAINSUBREFLECTORATAFREQUENCYOF'(Z4HEANALYSISWAS PERFORMEDUSING.%#2%&;= AGEOMETRICALTHEORYOFDIFFRACTIONCODE 4HEMEASUREMENTSANDANALYTICRESULTSAGREEWELL 4HEEXAMPLEIN&IG HASALOW LOSSFEEDTHATCONTRIBUTESLITTLETOTHE ANTENNANOISETEMPERATURE(OWEVER PRACTICALANTENNASGENERALLYHAVE LOSSESINTHEANTENNAFEED THEINTERCONNECTINGCABLING ANDTHEFILTERSARE

&IGURE %XAMPLEANTENNATEMPERATUREVALUES;=

#HAPTER /NE

REQUIREDTOLIMITTHESIGNALSPECTRATOTHEOPERATINGBANDWIDTH4HELOSS LESSANTENNATEMPERATURE;=ISTHENCORRECTEDFORTHENOISECONTRIBUTED BYTHESELOSSES4HEANTENNANOISETEMPERATUREATTHEOUTPUTOFTHEFILTER ANDINPUTTOTHERECEIVERS,.!ISGIVENBY

4ANTn' ;4ANT,n, =

WHERE' ISTHEMAGNITUDEOFTHEREFLECTIONCOEFFICIENT;FORWELL MATCHED SYSTEMS n' ISVERYCLOSETO= 4ANTISTHEANTENNANOISETEMPERA TUREATTHEANTENNATERMINALS AND,ISTHEOHMICLOSS0HYSICALLY THE NOISEPOWERRECEIVEDBYALOSSLESSANTENNAISREDUCEDBYOHMICLOSS BUT ADDITIONALNOISEISGENERATEDBYTHELOSS7HENIMPEDANCEMISMATCH LOSS IS SIGNIFICANT THE ANTENNA NOISE TEMPERATURE IS REDUCED BY THE IMPEDANCEMISMATCHLOSSn' 4HERECEIVERNOISETEMPERATUREATTHE,.!INPUTTERMINALINCLUDES CONTRIBUTIONSFROMTHE,.!ANDOTHERRECEIVERCOMPONENTSFOLLOWING THE,.!4HERECEIVERNOISETEMPERATUREATTHE,.!INPUT TAKINGINTO ACCOUNT THE ,.! AND RECEIVER COMPONENTS FOLLOWING THE ,.! IS THE CASCADENOISETEMPERATURE WHICHEQUALS

4REC4LNA¤4I 'I

WHERE4IISTHENOISETEMPERATUREOFTHEI THCOMPONENTINTHERECEIVER AND'I ISTHEINSERTIONGAINATTHEINPUTTOTHATCOMPONENT3YSTEM DESIGNSGENERALLYSTRIVETOMAKETHE,.!NOISETEMPERATUREDOMINATE THERECEIVERNOISETEMPERATURE BUTCONTRIBUTIONSFROMTHEOTHERRECEIVER COMPONENTS CAN BECOME SIGNIFICANT WHEN THE RECEIVER IS REQUIRED TO HAVEAWIDELINEARDYNAMICRANGE4HENOISEPERFORMANCEOFRECEIVER COMPONENTSISGENERALLYSTATEDINTERMSOFNOISEFIGURE .& WHICHIS RELATEDTOTHENOISETEMPERATURE 4N BY

4N.&n

.OISEFIGUREISDEFINEDASTHEINPUT3.2SIGNAL TO NOISERATIO DIVIDED BYTHEOUTPUT3.24HETOTALINPUTNOISECANHAVEMANYDIFFERENTVALUES DEPENDINGONHOWTHECOMPONENTISUSED3PECIFYINGTHECOMPONENTS NOISEFIGURETOASTANDARD+REFERENCETEMPERATUREALLOWSTHENOISE TEMPERATURETOBECALCULATEDANDUSEDINAPPLICATIONSWHERETHEINPUT NOISETEMPERATUREDIFFERSFROM+)NTHISAPPLICATION THEANTENNA NOISETEMPERATUREGENERALLYDIFFERSFROM+ FOREXAMPLE.UMERICAL VALUESOFTHECONVERSIONBETWEENNOISEFIGUREANDNOISETEMPERATURE AREGIVENIN&IG 4HESYSTEMNOISETEMPERATUREISTHESUMOFTHEANTENNAANDRECEIVER NOISETEMPERATUREANDEQUALS

44ANT4REC


&IGURE .OISETEMPERATUREVERSUSNOISElGURE

4HESYSTEMNOISETEMPERATUREDEPENDSONTHETERMINALSINTHESYSTEM USED FOR THE SPECIFICATION AND BOTH THE ANTENNA AND RECEIVER NOISE TEMPERATUREVALUESMUSTBESPECIFIEDFORTHESAMETERMINAL )NCOMMUNICATIONSATELLITEAPPLICATIONS THESPACESEGMENTANTENNAS FORUPLINKRECEIVINGSERVICEVIEWTHEEARTHSSURFACEANDGENERALLYHAVE ANAMBIENT+ANTENNATEMPERATURE5SERSEGMENTANTENNASLOOK OUTTOWARDSSPACEBUTINCURATMOSPHERICLOSSASDISCUSSEDIN#HAPTER ANDASILLUSTRATEDIN&IG THEIRANTENNANOISETEMPERATUREVARIES WITHELEVATIONANGLEANDFREQUENCYOFOPERATION#ROSSLINKANTENNASTHAT PROVIDECONNECTIVITYBETWEENSATELLITESVIEWA+COSMICBACKGROUND TEMPERATURE2ECEIVINGSYSTEMPERFORMANCE HOWEVER DEPENDSONTHE SYSTEMNOISETEMPERATURE4ODAYS,.!TECHNOLOGYOFFERSVERYLOWNOISE PERFORMANCE(OWEVER THESYSTEMNOISEPERFORMANCECANBEDOMINATED BYTHEANTENNANOISETEMPERATURE4HISISILLUSTRATEDIN&IG WHERE AN IDEAL NOISELESS RECEIVER IS USED AS A REFERENCE VALUE4HE LOSS IN RECEIVINGSENSITIVITYORSYSTEMTEMPERATUREFORVARIOUSANTENNANOISE TEMPERATUREVALUESISPARAMETRICALLYPLOTTEDASAFUNCTIONOFRECEIVER NOISETEMPERATURE!STHEANTENNANOISETEMPERATUREINCREASES THELOSS INSENSITIVITYISLESSSENSITIVETOTHERECEIVERNOISETEMPERATURE4HUS LOWNOISERECEIVERTEMPERATURESCANBEEFFECTIVELYUSEDIFALOWANTENNA NOISETEMPERATUREEXISTS WHEREASHIGHERANTENNANOISETEMPERATURE VALUESDERIVELESSBENEFITFROMLOWNOISERECEIVERTECHNOLOGY

#HAPTER /NE

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4ECHNOLOGY3URVEY

/VERVIEW 4HE ANTENNA TECHNOLOGY USED FOR COMMUNICATION SATELLITE SYSTEMS IS QUITEVARIEDBECAUSEOFDIFFERINGPROGRAMREQUIREMENTSANDFREQUEN CIESOFOPERATION!SARESULT ANTENNADESIGNSAREARGUABLYTHEMOST DIVERSE TECHNOLOGY USED IN SATELLITE COMMUNICATION SYSTEMS &UTURE ANTENNASYSTEMSCANBEANTICIPATEDTOBECOMEEVENMOREDIVERSEASTHE COMPLEXITYOFSYSTEMREQUIREMENTSCONTINUESTOINCREASEANDASANTEN NASBECOMEMOREINTEGRATEDWITH2&RADIOFREQUENCY ELECTRONICS4HIS DIVERSITYOFANTENNATECHNOLOGYPRESENTSAPROBLEMINTHISDISCUSSION! DETAILEDCOMPREHENSIVEDESCRIPTIONOFEXISTINGANTENNADESIGNSWOULD BEOFIMPRACTICALLENGTHANDWOULDSOONBECOMEOUTDATEDASTECHNOL OGYISDEVELOPEDFORFUTURESYSTEMDESIGNS)NMANYCASES THEDETAILED DESIGNSAREPROPRIETARYTOTHESYSTEMDEVELOPERS ANDINOTHERCASESTHE DESIGNDESCRIPTIONSARESUBJECTTO)4!2)NTERNATIONAL4RAFFICIN!RMS 2EGULATIONS RESTRICTIONS&URTHERMORE THEVARIEDSYSTEMREQUIREMENTS THATRESULTINTHEEXISTINGDESIGNDIVERSITYPREVENTAPPLYINGDESIGNSFOR ONEAPPLICATIONDIRECTLYTOOTHERAPPLICATIONS&UTUREANTENNADESIGNS WHILEDRAWINGONTHEEXISTINGTECHNOLOGYBASE WILLCONTINUETOEVOLVE ASREQUIREMENTSFORFUTUREPROGRAMSANDAPPLICATIONSAREDEFINED !NOVERVIEWOFTHEGENERICANTENNATECHNOLOGYUSEDINCOMMUNICA TIONSATELLITEAPPLICATIONSISPROVIDED4HEDISCUSSIONDESCRIBESTECHNOL OGYASTHEIRBEAMWIDTHVALUESDECREASEANDAPERTURESIZESINCREASE 7IDE COVERAGE ANTENNAS ARE REQUIRED IN APPLICATIONS SUCH AS44# 4ELEMETRY 4RACKING AND#ONTROL SERVICESTHATAREUSEDONEVERYSATEL LITE/THERAPPLICATIONSEXISTFORWIDECOVERAGEANTENNAS PARTICULARLY FORSATELLITESINLOWEARTHORBITS%ARTHCOVERAGEANTENNASAREALSOA COMMONREQUIREMENTANDONETHATWILLHAVEADDITIONALFUTUREAPPLI CATIONTOALLOWUSERSTOACCESSSATELLITERESOURCESIRRESPECTIVEOFTHEIR

#HAPTER 4WO

LOCATIONWITHINTHEAVAILABLEFIELDOFVIEW!PERTUREANTENNASPROVIDING HIGHERGAINLEVELSARETHEBACKBONETECHNOLOGYFORBOTHTHESPACEAND USERSEGMENTS!RRAYANTENNATECHNOLOGYALSOHASITSAPPLICATIONSFOR BOTHSPACEANDGROUNDSEGMENTS&INALLY ANTENNATRACKINGTECHNIQUES THAT SPATIALLY ALIGN THE ANTENNAS WITH THE SIGNAL SOURCE ARE USED IN BOTHSPACEANDUSERSEGMENTANTENNADESIGNS&URTHERDISCUSSIONOF ANTENNATECHNOLOGYAPPLICATIONSISCONTAINEDIN#HAPTERSANDFOR SPACESEGMENTANDUSERSEGMENTTECHNOLOGIES RESPECTIVELY 7IDE#OVERAGE!NTENNAS 7IDECOVERAGESPACESEGMENTANTENNASAREREQUIREDINAPPLICATIONSFOR 44#SUBSYSTEMSANDSATELLITESHAVINGLOWALTITUDEORBITS7IDECOVER AGEANTENNASARENEEDEDTOSATISFY44#CAPABILITIESREQUIREDBYEVERY SATELLITE/THERAPPLICATIONSFORWIDECOVERAGEANTENNASARISEPARTICU LARLYFORLOWEARTHORBITINGSATELLITESSUCHASTHEPOLARSATELLITESUSEDIN METEOROLOGICALREMOTESENSINGPROGRAMS7IDECOVERAGEANTENNASARE ALSOUSEDINUSERSEGMENTDESIGNSFORLOWDATARATEAPPLICATIONS4HE INTERACTIONSOFSUCHANTENNASWITHTHEIRSURROUNDINGENVIRONMENTARE LIKEWISEAWELL KNOWNPROBLEM!FAMILIAREXAMPLEIS'03USERANTEN NAS WHEREMULTIPATHCOMPONENTSAREONELIMITATIONONTHEACCURACYOF NAVIGATIONALSOLUTIONS ! PRINCIPAL DESIGN ISSUE FOR WIDE COVERAGE ANTENNAS IS THE ABILITY TOMAINTAINTHEIRWIDECOVERAGECHARACTERISTICSINTHEPRESENCEOFTHE SURROUNDING ENVIRONMENT &OR EXAMPLE THE WIDE COVERAGE ACHIEVED BYSPACESEGMENTANTENNASINAFREESPACEENVIRONMENTUNAVOIDABLY ILLUMINATESTHESPACECRAFTSTRUCTURE4HERADIATEDSCATTERINGFROMTHE SPACECRAFTSTRUCTUREDEGRADESTHEWIDECOVERAGECHARACTERISTICSOFTHE ANTENNA4HE CHALLENGE IS TO ISOLATE THE ANTENNA FROM THE SPACECRAFT STRUCTURE4HEFREESPACEPATTERNOFTHEANTENNAITSELFDIFFERSFROMTHE ANTENNASPATTERNWHENTHEANTENNAISLOCATEDONTHESPACECRAFT4HE SCATTERINGFROMTHESPACECRAFTSTRUCTURERESULTSINPATTERNRIPPLESAND CROSS POLARIZATIONCOMPONENTSTHATDISTORTANDDEGRADETHEPATTERNOF THEANTENNAINAFREESPACEENVIRONMENT ! COMMON APPLICATION FOR WIDE COVERAGE ANTENNAS RESULTS FROM THE REQUIREMENTSIMPOSEDBY44#APPLICATIONSTHATAREREQUIREDBYEVERY SATELLITE/FTEN THESE44#SUBSYSTEMSOPERATEATLOWERMICROWAVEFRE QUENCIESTHATHAVERELATIVELYLONGWAVELENGTHS)NOTHERCASES SUCHWIDE COVERAGEANTENNASAREUSEDDURINGLAUNCHOPERATIONS ANDON ORBIT THE 44#FUNCTIONSUSETHEPAYLOADANTENNASTHATOPERATEATHIGHERFREQUEN CIES4HISOPERATIONUSINGHIGHERMICROWAVEFREQUENCIESCANBEANTICIPATED INFUTUREDESIGNSASSOFTWAREBECOMESMOREHEAVILYUSEDINSPACESEGMENT DESIGNS"ECAUSEFUTURESPACESEGMENTDESIGNSWILLNEEDTOUPLOADSOFT WAREREVISIONSANDAUGMENTATIONS THESEDESIGNSWILLREQUIREHIGHERDATA

4ECHNOLOGY3URVEY

RATESERVICESTHANARENECESSARYFORCOMMANDINGANDHEALTHANDSTATUS SERVICES4HE GENERAL REQUIREMENTS FOR44# ANTENNAS DURING LAUNCH OPERATIONSARETOPROVIDECOMPLETESPHERICALCOVERAGETOALLOWACCESSTO THE44#SUBSYSTEMREGARDLESSOFTHESATELLITESORIENTATION TOUSECIR CULARPOLARIZATIONWITHSUFFICIENTPOLARIZATIONPURITYTOAVOIDEXCESSIVE SIGNALLOSSANDALLOWRELIABLEANTENNATRACKINGWITHCLOSED LOOPTRACKING SYSTEMS ANDTOHAVEACOMPACTSIZEPROVIDINGBOTHUPLINKANDDOWNLINK OPERATION)NADDITION THERELIABILITYOFTHE44#SUBSYSTEMISMORECRITI CALTHANTHATOFALLTHEOTHERSUBSYSTEMSINTHESATELLITETOENSURETHATTHE SATELLITECANBECONTROLLEDOVERITSLIFETIME 44#ANTENNASHAVETWOCOVERAGEREQUIREMENTS4HELAUNCHPHASE OF THE PROGRAM IMPOSES A REQUIREMENT TO PROVIDE COVERAGE OVER THE COMPLETESPHERESOTHATIFTHESATELLITESTARTSTOTUMBLEORHASOTHER LAUNCHANOMALIES COMMANDSFORCORRECTION ORWORSEYETDESTRUCTION CAN BE INJECTED IRRESPECTIVE OF THE SATELLITES ORIENTATION !DEQUATE COVERAGE OVER THE COMPLETE SPHERE REQUIRES MORE THAN ONE ANTENNA BECAUSEOFTHEINHERENTBLOCKAGEOFTHESPACECRAFT4YPICALLY TWOSEPA RATEANTENNASAREUSEDTHATPROVIDECOVERAGEOVERINDEPENDENTHEMI SPHERES AhFOREANTENNAvTHATISEARTHFACINGANDANhAFTANTENNAvTHAT IS FACING AWAY FROM THE EARTH! SECOND COVERAGE REQUIREMENT EXISTS WHEN THE SPACECRAFT IS ESTABLISHED IN ITS DESIRED ORBITAL POSITION )N THISCASE THEREQUIREMENTISTOPROVIDECOVERAGEONLYOVERTHEEARTHS FIELDOFVIEW7HILESUCHACOVERAGEREQUIREMENTCANBESATISFIEDBYAN EARTHCOVERAGEANTENNAHAVINGAHIGHERGAINLEVELTHANAHEMISPHERIC COVERAGE ANTENNA THE COST AND ADDITIONAL COMPLEXITY AND RELIABILITY ISSUESOFANOTHERANTENNAANDASSOCIATEDSWITCHINGCIRCUITRYAREGENER ALLYNOTWARRANTED&URTHERMORE THELOWDATARATESTYPICALLYUSEDFOR 44#APPLICATIONSTOGETHERWITHGROUNDTERMINALSCONFIGUREDFORLARGE SIGNALMARGINSRESULTINADECISIONSIMPLYTOUSETHEEARTH FACING44# ANTENNA $URINGTHELAUNCHTRAJECTORY ACCESSTOBOTHHEMISPHERICANTENNASIS REQUIRED/NEAPPROACHASSIGNSDIFFERENTFREQUENCYALLOCATIONSDURING LAUNCH WHERE ONE FREQUENCY IS ASSIGNED TO THE FORE ANTENNA AND THE SECONDTOTHEAFTANTENNA)NTHISWAY THEREQUIREDSPHERICALCOVERAGEIS ACHIEVEDBYINDEPENDENTTELEMETRYSUBSYSTEMS4HISAPPROACHREQUIRES SEPARATETELEMETRYTRANSPONDERSFOREACHOPERATINGFREQUENCYHOWEVER SUCHANAPPROACHADVANTAGEOUSLYPROVIDESAREDUNDANTTRANSPONDERFOR RELIABILITYOVERTHESATELLITESLIFETIME)NOPERATION THEMISSIONGROUND LINK USES BOTH TELEMETRY FREQUENCIES AND BASES THE COMMANDING ON THE SYSTEM HAVING THE HIGHEST SIGNAL LEVEL !NOTHER APPROACH USES SWITCHINGTECHNIQUESTOSELECTTHEAPPROPRIATEANTENNADEPENDINGON THEVEHICLESORIENTATION2ECEIVEDSIGNALSTRENGTHISINDICATEDBYTHE 44#TRANSPONDERS!'#!UTOMATIC'AIN#ONTROL LEVELS)FTHE!'# LEVELOFONETRANSPONDERISLOWERTHANAPREDETERMINEDTHRESHOLDVALUE

#HAPTER 4WO

THE44#TRANSPONDERISSWITCHEDTOTHESECONDANTENNA WHERETHE RECEIVEDSIGNALLEVELSHOULDEXCEEDTHETHRESHOLDSIGNALLEVELBECAUSE HIGHERANTENNAGAINISAVAILABLEFORTHATSIGNALDIRECTION )N MANY INSTANCES PROPOSALS ARE MADE SIMPLY TO COMBINE THE TWO ANTENNAS AND ROUTE THEIR COMBINED SIGNAL TO THE44# TRANSPONDER (OWEVER THEPHYSICALSEPARATIONOFTHETWOANTENNASONTHEFOREAND AFTSIDESOFTHESATELLITEANDTHEIRWIDEPATTERNCHARACTERISTICSRESULTS INAGRATINGLOBESTRUCTUREWHERETHETWOFOREANDAFTANTENNAPATTERNS OVERLAP4HECOHERENTCOMBINATIONOFTWOWIDELYSEPARATEDANTENNAS RESULTSINADDITIONANDSUBTRACTIONOFTHETWOOVERLAPPINGANTENNAPAT TERNS CREATINGASETOFPEAKSANDNULLSASTHESIGNALDIRECTIONCHANGES 4HE TWO ANTENNAS WHEN COHERENTLY COMBINED FORM A TWO ELEMENT ANTENNAARRAY ANDTHESEPARATIONBETWEENTHETWOELEMENTSPRODUCES ALOBESTRUCTURERESULTINGFROMTHEADDITIONANDSUBTRACTIONOFTHETWO ANTENNAPATTERNS4HERESULTINGLOBESTRUCTUREISREFERREDTOASAGRAT INGLOBESPECTRA4HEDIFFERENTUPLINKANDDOWNLINKFREQUENCIESRESULT INGRATINGLOBESTRUCTURESTHATGENERALLYDONOTOVERLAPIE THEGRAT INGLOBEPEAKSOFTHEUPLINKFREQUENCYGENERALLYDONOTCOINCIDEWITH THOSEOFTHEDOWNLINKFREQUENCY 4HERESULTINGPATTERNSSIGNIFICANTLY DEGRADE THE SUBSYSTEMS ANTENNA GAIN COVERAGE4HE UPLINK PATTERN CANBEALIGNEDTOAPEAKLEVELPROVIDINGGOODUPLINKPERFORMANCEWHILE THEDOWNLINKCOULDBEALIGNEDTOAPATTERNNULL SIGNIFICANTLYDEGRADING DOWNLINKSIGNALRECEPTION3IMILARLY THEUPLINKCOULDBEINAPATTERN NULLWHILETHEDOWNLINKISINAPATTERNPEAK#OHERENTLYCOMBININGTHE FOREANDAFTANTENNASISSPECIFICALLYNOTRECOMMENDEDFORTHISREASON 4HEPRINCIPALDEVELOPMENTPROBLEMISISOLATINGTHE44#ANTENNAS FROMTHESATELLITETOACHIEVETHESPHERICALCOVERAGENEEDEDDURINGTHE LAUNCH PHASE4HE COMPLEX STRUCTURE OF A TYPICAL SATELLITE RESULTS IN BLOCKAGEANDDIFFRACTIONMECHANISMSTHATDEGRADEHEMISPHERICCOVER AGEREQUIREMENTS#ONSEQUENTLY AMOUNTINGLOCATIONWITHACLEARFIELD OFVIEWOVERAHEMISPHEREISTYPICALLYDIFFICULTTOFINDWITHTHELARGE COMPLEXSATELLITESTRUCTURESUSEDTODAY4HEINTERACTIONWITHTHESATEL LITECANBEEXAMINEDEITHERANALYTICALLYWITHDIFFRACTIONCODES;=ORBY MEASUREMENT.EITHERAPPROACHISASIMPLEUNDERTAKING4HEANALYTIC CHALLENGEISMODELINGACOMPLEXSTRUCTUREANDVALIDATINGTHERESULTS )NPRACTICE SATELLITESARECOVEREDWITHTHERMALBLANKETMATERIALTHAT MAYNOTBESMOOTHATTHE44#FREQUENCYOFOPERATION WHICHADDSTO THEMODELINGCHALLENGE$IRECTMEASUREMENTOFTHEANTENNASMOUNTED ONTHESPACECRAFTISGENERALLYIMPRACTICAL"ECAUSETHERADIATIONARISES FROMBOTHTHEANTENNAANDTHESPACECRAFTSTRUCTURE EXCESSIVEFARFIELD DISTANCES ARE INVOLVED 3UCH MEASUREMENTS WOULD ALSO NEED TO BE PERFORMED DURING SPACECRAFT ASSEMBLY AND CONCERNS OF RISK TO FLIGHT HARDWARE WOULD LIKELY PRECLUDE SUCH MEASUREMENTS /THER FEATURES OFTHESPACECRAFTTHATIMPACTANTENNACOVERAGE SUCHASSOLARARRAYS

4ECHNOLOGY3URVEY

GENERALLYCANNOTBEDEPLOYEDFORMEASUREMENT&INALLY MEASUREMENTS OFTHEVEHICLEMOUNTEDANTENNASOVERTHESPHERICALVOLUMEREQUIREDIN THISAPPLICATIONAREGENERALLYIMPRACTICAL #LEARLY ANEEDEXISTSTODEVELOPVALIDATEDTECHNIQUESTOESTABLISHTHE 44#ANTENNACOVERAGECHARACTERISTICS/NEAPPROACHMIGHTUSESCALE MODELTECHNIQUESANDMEASUREMENTATASCALEDFREQUENCY3CALEMODEL MEASUREMENTSAREBASEDONTHETHEOREMOFSIMILITUDE;=4HEDIMEN SIONSOFASCALEMODELPRESERVETHEELECTRICALSIZEOFACTUALDESIGNIN WAVELENGTHSANDTHEMEASUREMENTISPERFORMEDATTHESCALEDFREQUENCY )NTHISAPPLICATION ASCALEFACTOROFATLEASTISREQUIREDIE A SCALE MODEL OF THE SATELLITE IS MEASURED AT TEN TIMES THE OPERATIONAL FREQUENCY 4HE SMALLER SCALED TEST ARTICLE IS REQUIRED TO RESULT IN A POTENTIALLYPRACTICALMEASUREMENT 7HENTHESATELLITEREACHESITSON ORBITPOSITION THEANTENNACOVERING THEEARTH FACINGHEMISPHERECANBEUSED)NTHEORY SOMEWHATHIGHER GAINPERFORMANCECANBEOBTAINEDBYSWITCHINGTOANANTENNAMATCHED TOTHEEARTHSFIELDOFVIEWFORTHEOPERATIONALPHASEOFTHESATELLITE)N PRACTICE THEADDITIONALCOMPLEXITIESOFTWOSETSOFANTENNASANDTHERELI ABILITYOFNECESSARYSWITCHESLIMITTHEATTRACTIVENESSOFTHISAPPROACH -OREOVER 44#SYSTEMSAREPURPOSELYSIZEDTOACHIEVELARGEMARGINS FORRELIABLECOMMUNICATIONSINTHEEVENTOFPERFORMANCESHORTFALLSIN THESPACESEGMENT4HUS THESAMEANTENNAISGENERALLYUSEDFORBOTH LAUNCHANDON ORBITOPERATIONS 4HEEXISTING44#FREQUENCYALLOCATIONSATLOWMICROWAVEFREQUEN CIESAREOFTENSEPARATEDBYALARGEPERCENTAGEBANDWIDTH ANDCONSE QUENTLY SIMPLEFREQUENCYINDEPENDENTANTENNAS;=SUCHASSPIRALS ARE COMMONLY USED7HILE THESE DESIGNS ARE SIMPLE AND RELATIVELY LIGHTWEIGHT PATTERNCONTROLBEYONDTHEREQUIREDCOVERAGEAREAWITH A COMPACT DESIGN IS DIFFICULT TO ACHIEVE FOR THE EXISTING LOW MICRO WAVEFREQUENCIESANDRELATIVELYHIGHBACKLOBELEVELSARECOMMONFOR THESE DESIGNS4HESE HIGH BACKLOBES ILLUMINATE NOT ONLY THE UNDE SIREDCOVERAGEHEMISPHEREREDUCINGTHEANTENNASGAININTHEDESIRED HEMISPHERE BUT ALSO THE SATELLITE STRUCTURE4HE RESULTING REFLECTED ANDDIFFRACTEDCOMPONENTSFROMTHESATELLITESTRUCTUREINTHEDESIRED COVERAGE HEMISPHERE DEGRADE MINIMUM GAIN VALUES4HE IRREGULAR SHAPES IN THE SATELLITE STRUCTURE AND REFLECTIONS FROM SMOOTH SUR FACESALSORESULTINCROSS POLARIZEDCOMPONENTS4HESECROSS POLARIZED COMPONENTSCANRESULTINREGIONSOFTHEDESIREDHEMISPHERICCOVER AGEWHERETHESENSEOFTHESIGNALSPOLARIZATIONISREVERSED#LOSED LOOP ANTENNA TRACKING TECHNIQUES CAN RESULT IN TRACKING SHORTFALLS INSITUATIONSWHERESUCHPOLARIZATIONDIVERSITYEXISTS ASWILLBEDIS CUSSEDLATERINTHISCHAPTER&URTHER THEPOLARIZATIONDIVERSITYINTHE DESIREDCOVERAGEHEMISPHEREREQUIRESDIVERSITYCOMBININGTECHNIQUES TOMAINTAINSIGNALRECEPTION

#HAPTER 4WO

!COMPACTANTENNAHAVINGGOODPOLARIZATIONPURITY SUFFICIENTBAND WIDTH ANDLOWBACKLOBESISDESIREDFOR44#APPLICATIONS/NEDESIGN APPROACHISTHEROLLEDEDGECAVITYANTENNA;=SHOWNIN&IG 4HIS DESIGN USES A CROSS DIPOLE IN A CAVITY WHOSE EDGES ARE ROLLED IN A SEMICIRCULAR SHAPE! VARIETY OF TECHNIQUES CAN BE USED TO INCREASE THEBANDWIDTHOFTHEDIPOLESSUCHASBOWTIECONFIGURATIONSANDTHE SLEEVELOADINGUSEDINTHISDESIGN4HECAVITYEXTENDSTOSCREWHEADS VISIBLEBELOWTHEROLLEDEDGETERMINALANDTHEREMAININGPORTIONOF THE CYLINDRICAL HOUSING WAS USED TO ENCLOSE THE ELECTRONICS USED IN THE ANTENNAS APPLICATION4HE OVERALL ELECTRICAL DIAMETER INCLUDING THEROLLEDEDGEISABOUTWAVELENGTHS4HECALCULATEDPATTERNSIN &IG WERE PERFORMED USING A COMMERCIAL (&33 HIGH FREQUENCY STRUCTURAL SIMULATOR FINITE ELEMENT MODELING CODE AND REVEAL LOW BACKLOBELEVELSPRODUCINGHIGHGAINLEVELSINTHEDESIREDFORWARDHEMI SPHERE4HEGOODPATTERNSYMMETRYANDLOWCROSS POLARIZEDPATTERN LEVELSARENECESSARYTOACHIEVEGOODAXIALRATIOPERFORMANCEINTHEFOR WARDHEMISPHERE4HEMEASUREDPATTERNS;=CLOSELYAGREEWITHTHESE CALCULATEDRESULTS

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4ECHNOLOGY3URVEY

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#HAPTER 4WO

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4ECHNOLOGY3URVEY

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#HAPTER 4WO

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4ECHNOLOGY3URVEY

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#HAPTER 4WO

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4ECHNOLOGY3URVEY

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#HAPTER 4WO

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4ECHNOLOGY3URVEY

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#HAPTER 4WO

AWAVELENGTHORIFTHETOLERANCELOSSISLIMITEDTOD" THEREQUIRED TOLERANCEISRELAXEDTOAVALUEOFABOUTOFAWAVELENGTH 3PACESEGMENTANTENNAREQUIREMENTSCANRESULTINAPERTUREDIAM ETERS WHOSE VALUE EXCEEDS THE LAUNCH VEHICLES FAIRING DIMENSIONAL LIMITATIONS)NSUCHCASES REFLECTORANTENNADESIGNSHAVINGDEPLOYABLE SURFACES ARE USED4HESE SURFACES ARE COMPRISED OF A WOVEN METALLIC MESHANDADEPLOYABLESTRUCTURE!NEARLYEXAMPLEOFDEPLOYABLEREFLEC TORANTENNATECHNOLOGY;=WASFLOWNONTHE!43 SATELLITE! FT DIAMETERPRIMEFOCUSREFLECTORWASDEMONSTRATEDFOROPERATIONUPTO # BANDFREQUENCIES$EVELOPMENTOFDEPLOYABLEDESIGNSCONTINUES;= AND APPLICATION OF DEPLOYABLE ANTENNAS CAN BE ANTICIPATED IN FUTURE SYSTEMSASNARROWBEAMWIDTHSPACESEGMENTANTENNASAREREQUIRED TOFURTHERINCREASELINKPERFORMANCE$EPLOYABLEANTENNATECHNOLOGY HASTHREEDESIGNISSUES4HEFIRSTISSUEISTHEREFLECTIVITYOFTHEMESH SURFACE'ENERALLYATLEASTTHREEOPENINGSPERWAVELENGTHAREREQUIRED 4HE SECOND ISSUE ARISES IN MULTICARRIER COMMUNICATION APPLICATIONS WHERE0)-0ASSIVE)NTERMODULATION PRODUCTSDISCUSSEDIN#HAPTER DEGRADE COMMUNICATION PERFORMANCE #ONTAMINATION BETWEEN MESH ELEMENTSCANPRODUCENONLINEARRECTIFICATION PRODUCINGTHEINTERMODU LATIONPRODUCTS4HETHIRDISSUEISTHEMECHANICALACCURACYOFTHESUR FACE4HERMSTOLERANCEERRORSDISCUSSEDEARLIERMUSTBEMET(OWEVER SUCH ANALYSES ARE BASED ON RANDOM SURFACE ERRORS $ESIGN ATTENTION MUSTBEPAIDTOASSURETHATSYSTEMATICPHASEERRORSDONOTRESULTFROM PRODUCINGTHESURFACEFROMTHEMESHMATERIAL 7HILE REFLECTOR ANTENNAS ARE COMMONLY USED TO SATISFY HIGH GAIN REQUIREMENTS LENS ANTENNAS OFFER AN ALTERNATIVE TECHNOLOGY ,ENS ANTENNASHAVETHEADVANTAGETHATTHEFEEDDOESNOTPRODUCEBLOCKAGE 4HEINNERANDOUTERLENSSURFACESPROVIDEDESIGNFREEDOMTOOPTIMIZE THEBEAMSCANNINGPERFORMANCEOFTHEDESIGN$IELECTRICLENSDESIGNS ARELIMITEDBYTHEWEIGHTOFTHEDIELECTRICANDTHEPRACTICALPROBLEMOF OBTAININGASUFFICIENTDIELECTRICSIZEWITHUNIFORMDIELECTRICPROPERTIES $IELECTRICLENSAPPLICATIONSARELIMITEDTODESIGNSATHIGHERFREQUENCIES THATREQUIRERELATIVELYSMALLLENSDIAMETERS4HEDIELECTRICWEIGHTCAN BEREDUCEDBYZONINGTECHNIQUES)NTHISCASE THEDIELECTRICAPERTURE ISDIVIDEDINTORADIALZONESANDTHEDIELECTRICTHICKNESSISREDUCEDBY SATISFYINGTHEAPERTUREPHASEDISTRIBUTIONONAMODULOOSENSERATHER THANTHETRUETIMEDELAYOFANUNZONEDLENS:ONINGTECHNIQUESRESULTIN BANDWIDTHLIMITATIONSSINCETHEAPERTUREPHASEDISTRIBUTIONSSATISFYTHE REQUIREDUNIFORMPHASECHARACTERISTICSATTHEDESIGNFREQUENCYCHOSEN FORZONESTEPSIZE !NOTHER ALTERNATIVE IS A WAVEGUIDE LENS ; = WHERE THE PHASE VELOCITY OF WAVEGUIDE FUNCTIONS LIKE A DIELECTRIC $IELECTRIC SLOWS THE PHASEVELOCITYSOTHATTHETHICKERSURFACEATTHECENTEROFTHELENSSLOWS THE WAVE TO COMPENSATE FOR THE LONGER PATH LENGTHS TO THE EDGES OF

4ECHNOLOGY3URVEY

THELENSSURFACE"YCONTRAST THEPHASEVELOCITYOFWAVEGUIDEINCREASES THEPHASEVELOCITYSOTHELENSISTHICKERATTHEEDGESTHANTHECENTERTO COMPENSATEFORTHELONGERPATHLENGTHATTHEEDGESOFTHELENS7AVEGUIDE IS A DISPERSIVE MEDIA SINCE THE PHASE VELOCITY VARIES WITH FREQUENCY )N THIS CASE ZONING TECHNIQUES CAN ACTUALLY INCREASE THE BANDWIDTH BECAUSESHORTERLENGTHSOFWAVEGUIDEREDUCETHEAPERTUREPHASEVARIA TIONRESULTINGFROMDISPERSION !RRAY!NTENNAS !RRAY ANTENNAS ;= MAY BE THOUGHT OF AS DIGITAL REPRESENTATIONS OF ANALOG APERTURE DISTRIBUTIONS4HEIR OVERALL ELECTRICAL CHARACTERISTICS SUCHASBEAMWIDTHAREDICTATEDBYTHESAMECONSIDERATIONS4HEANTENNA EFFICIENCYOFARRAYDESIGNSDEPENDSONTHESPECIFICIMPLEMENTATION4HE ARRAY GAIN PERFORMANCE EQUALS THE GAIN OF THE ARRAY ELEMENT TIMES THENUMBEROFELEMENTSTOFIRSTORDER!RRAYANTENNAS HOWEVER HAVE FUNDAMENTAL LIMITATIONS ,IKE ANY DIGITAL REPRESENTATION THE ANALOG APERTUREDISTRIBUTIONHASMINIMUMSAMPLINGREQUIREMENTS4OAVOID ALIASING THESAMPLINGOFTHEANALOGAPERTUREDISTRIBUTIONMUSTBELESS THAN WAVELENGTH!LIASINGINTHISCASERESULTSINADDITIONALLOBESIN THEARRAYSPATTERNS REFERREDTOASGRATINGLOBES4HEARRAYELEMENTS COMBINE TOGETHER TO PRODUCE A MAIN BEAM WHEN THE ARRAY ELEMENTS PRODUCEANIN PHASECONDITIONINAPLANENORMALTOTHEMAINBEAMS DIRECTION )F THE ELEMENT SPACING EXCEEDS WAVELENGTHS THIS SAME PHASINGCONDITIONRESULTSATANGLESOTHERTHANTHEMAINBEAMDIREC TIONANDGRATINGLOBESAREPRODUCED0RACTICALARRAYDESIGNSENDEAVOR TOMINIMIZETHEREQUIREDNUMBEROFARRAYELEMENTSTOREDUCEDESIGN COMPLEXITY ANDTHESPACINGOFTHEARRAYELEMENTSISOFTENSELECTEDSO THATGRATINGLOBESAREREMOVEDFROMTHEEARTHSSURFACE3UCHDESIGNS ARESOMETIMESREFERREDTOAShTHINNEDvARRAYSSINCETHENUMBEROFELE MENTSISLESSTHANTHATOFANARRAYWHOSEELEMENTSPACINGISSELECTED TOAVOIDGRATINGLOBES'RATINGLOBESREDUCETHEDIRECTIVITYOFTHEARRAY COMPROMISINGTHEANTENNAEFFICIENCY 4HEGAINOFANARRAYANTENNATOFIRSTORDEREQUALS.'E WHERE.IS THENUMBEROFARRAYELEMENTSAND'EISTHEANTENNAGAINOFANARRAY ELEMENT4HEELEMENTSARECOMBINEDTOGETHERWITHAMPLITUDECOEFFI CIENTSTHATDICTATETHESIDELOBECHARACTERISTICSANDPHASECOEFFICIENTS THATDICTATETHEARRAYSBEAMDIRECTION4HEARRAYELEMENTSAREGENER ALLYIDENTICAL SOINTHEPATTERNANALYSESTHEARRAYELEMENTISSEPARABLE FROMTHEARRAYEXCITATIONCOEFFICIENTSTHATCOMBINETOGETHERTOFORM ANhARRAYFACTORv4HISARRAYFACTORISTHEARRAYPATTERNIFTHEARRAY ELEMENTSHADISOTROPICGAINCHARACTERISTICS4HEOVERALLELECTRICALSIZE OFTHEARRAYANDTHEARRAYELEMENTAMPLITUDECOEFFICIENTSDETERMINE THEARRAYSBEAMWIDTH4HEARRAYPHASECOEFFICIENTSARESETTOPRODUCE

#HAPTER 4WO

THEARRAYBEAMSDIRECTION(OWEVER THEELEMENTPHASECOEFFICIENTSARE ADJUSTEDBYPHASESHIFTERS4HESEPHASEADJUSTMENTSAREADJUSTEDON AMODULOOBASISATADESIGNFREQUENCYRATHERTHANANANALOGLINEAR PHASEGRADIENT ASPRODUCEDBYOTHERTECHNOLOGIES!SACONSEQUENCE THEARRAYSBEAMSTEERINGHASAFREQUENCYDEPENDENCE SOTHEFARTHER THEARRAYBEAMISSCANNEDFROMTHENORMALTOTHEARRAYSURFACE THE FASTERTHEBEAMSCANSWITHFREQUENCYCHANGES !RRAYDESIGNSGENERALLYCONNECTACTIVEELEMENTSDIRECTLYTOTHEARRAY ELEMENTSTOAVOIDTHEEFFECTSOFLOSSINPHASESHIFTERSANDELEMENTCOM BININGCIRCUITRY0REAMPLIFIERSAREGENERALLYCONNECTEDDIRECTLYTOARRAY ELEMENTS TO ESTABLISH THE SYSTEM NOISE TEMPERATURE!RRAY TRANSMIT MODULES ARE DIRECTLY ATTACHED TO THE ARRAY ELEMENTS SO THAT PHASE SHIFTER AND COMBINING CIRCUITRY LOSSES DO NOT REDUCE %20 LEVELS4HE %20OFANACTIVETRANSMITARRAYEQUALS. 'E0E WHERE0EISTHEPOWER OUTPUTOFTHEARRAYSTRANSMITMODULES4HEFACTOROF. RESULTSBECAUSE THEARRAYSANTENNAGAINIS.TIMESTHENUMBEROFARRAYELEMENTSAND THETRANSMITTEDPOWEREQUALS.TIMESTHEPOWEROFASINGLEARRAYTRANS MITMODULE4HEACTIVETRANSMITARRAYSCANBETHOUGHTOFASASPATIAL POWERCOMBINER 4HEARRAYELEMENTSARECOMBINEDBYACORPORATEFEEDSTRUCTUREWHOSE TOPOLOGY RESEMBLES AN ORGANIZATION CHART )F THE ARRAY IS REQUIRED TO GENERATE MULTIPLE BEAMS TO SERVICE DIFFERENT COVERAGE AREAS THE CORPORATEFEEDSTRUCTUREMUSTBEREPLICATEDTOCONTROLTHEINDIVIDUAL BEAMS/PERATIONATSEPARATEDFREQUENCYBANDSISDIFFICULTFORARRAY DESIGNS SINCE THE ELEMENT CHARACTERISTICS AND SPACING ARE SELECTED FOR OPERATION AT A SINGLE FREQUENCY BAND!RRAY ELEMENT PHASE SET TINGSREQUIREDFORBEAMSTEERINGCAPABILITIESAREGENERALLYPRODUCED BY PHASE SHIFTERS )N ADDITION TO THE DESIGN COMPLEXITY POWER CON SUMPTION FOR ARRAY DESIGNS IS MUCH GREATER THAN REFLECTOR ANTENNA SYSTEMS4HEINDIVIDUALACTIVEELEMENTSINTHEARRAYMUSTBEPOWERED ANDTHEPHASESHIFTERSALSOREQUIREPOWERFORBOTHTHEIRSETTINGANDA CONTROLSYSTEMTHATCOMMANDSTHEIRPHASESHIFTVALUES)NADDITION SPECIALTHERMALCONTROLDESIGNSARENEEDEDTOMAINTAINTHEAMPLITUDE ANDPHASETRACKINGREQUIREMENTSOFTHEACTIVEELEMENTSINTHEARRAY DESIGN4HE INHERENT DESIGN COMPLEXITY INCREASES TESTING SCHEDULES 4HECOMBINATIONOFDESIGNCOMPLEXITY POWERCONSUMPTION ANDTHER MALCONTROLLIMITSTHEAPPLICATIONATTRACTIVENESSOFARRAYTECHNOLOGY ANDINCREASESTHECOSTCOMPAREDTOOTHERTECHNOLOGIES#ONSEQUENTLY ARRAYDESIGNSAREGENERALLYUSEDINTHOSEAPPLICATIONSWHEREREQUIRE MENTSCANNOTBEEASILYSATISFIEDBYOTHERTECHNOLOGIES&OREXAMPLE CONFORMALARRAYSINAIRCRAFTANTENNAAPPLICATIONSAREUSEDTOSATISFY AERODYNAMICREQUIREMENTS 3PACESEGMENTAPPLICATIONSOFARRAYANTENNATECHNOLOGYARESUBJECTTO THEUSUAL37A0SIZE WEIGHT ANDPOWER LIMITATIONSOFSPACESYSTEMS

4ECHNOLOGY3URVEY

'EOSYNCHRONOUS SATELLITE ANTENNAS GENERALLY REQUIRE NARROW BEAM WIDTHS AND AN EXCESSIVE NUMBER OF ARRAY ELEMENTS ARE REQUIRED TO ACHIEVEACCEPTABLEPERFORMANCE!SACONSEQUENCE HIGH GAINSPACESEG MENTANTENNAAPPLICATIONSARECOMMONLYSATISFIEDBYREFLECTORANTENNA TECHNOLOGY'EOSYNCHRONOUSSATELLITESHAVEALIMITEDFIELDOFVIEWEQUALTO O ANDTHISFIELDOFVIEWISCOMPATIBLEWITHTHELIMITEDBEAMSCANCAPA BILITIESOFREFLECTORANTENNADESIGNS!RRAYDESIGNSFORLOWORBITINGSATEL LITES; =ARECAPABLEOFPROVIDINGBEAMSOVERTHEMUCHWIDERFIELDOF VIEWTHATEXISTSATLOWORBITALALTITUDESTHANTHENARROWERFIELDOFVIEW FORGEOSYNCHRONOUSORBITS ASDISCUSSEDIN#HAPTER4HEWIDERANGULAR FIELDOFVIEWFORLOWORBITINGSATELLITESRESULTSINANTENNAREQUIREMENTSFOR BROADERBEAMWIDTHSANDCORRESPONDINGSMALLERANTENNAAPERTURESTHAT RESULTINTHEARRAYDESIGNHAVINGAREASONABLENUMBEROFELEMENTS4HIS ISANEXAMPLEWHEREARRAYDESIGNSCANBEEFFECTIVELYUSEDBECAUSETHE REQUIREDFIELDOFVIEWISINCOMPATIBLEWITHREFLECTORANTENNATECHNOLOGY !NADVANTAGEOFARRAYTECHNOLOGYTHATISCOMMONLYTOUTEDISGRACEFUL DEGRADATION7ITHINREASON ELEMENTFAILURESRESULTINASMALLREDUC TIONINTHEANTENNAGAINLEVEL(OWEVER ELEMENTFAILURESALSODEGRADE SIDELOBEPERFORMANCE ANIMPORTANTFACTORWHENISOLATIONISTOBEMAIN TAINEDBETWEENSEPARATEDCOVERAGEAREAS3IDELOBEDEGRADATIONDEPENDS ONTHENUMBEROFFAILEDELEMENTSANDTHEIRDISTRIBUTIONWITHINTHEARRAY 3IDELOBEDEGRADATIONWHENELEMENTFAILURESHAVEARANDOMDISTRIBUTION INTHEARRAYISLESSPRONOUNCEDTHANWHENADJACENTARRAYELEMENTSFAIL 4HEPATTERNWHENADJACENTELEMENTSFAILCANBEVIEWEDASTHESUBTRAC TIONOFTHEARRAYPATTERNOFTHEFAILEDELEMENTSFROMTHEARRAYPATTERN WITHALLELEMENTSFUNCTIONAL3INCETHEFAILEDELEMENTSINTHISCASEHAVE ASMALLER LOWERGAINPATTERNTHATHASADIRECTIVEPATTERN ITSSUBTRAC TIONFROMTHEPATTERNWITHOUTFAILURESRESULTSINADDITIONANDSUBTRAC TIONWITHTHESIDELOBESTRUCTUREOFTHEARRAYPATTERNWITHOUTELEMENT FAILURES7HENTHEDISTRIBUTIONOFELEMENTFAILURESISRANDOM THECOR RESPONDINGPATTERNOFFAILEDELEMENTSISLESSDIRECTIVETHANTHEPATTERN OFFAILEDADJACENTELEMENTSANDGENERALLYHASGRATINGLOBESTHATREDUCE DIRECTIVITY #ONSEQUENTLY THE PATTERN WHEN ELEMENTS FAIL HAS A MORE RANDOMDISTRIBUTIONHASALESSPRONOUNCEDEFFECTONTHEARRAYPATTERN WITHOUTELEMENTFAILURES )FTHELOCATIONOFTHEFAILEDARRAYELEMENTSCANBEDETERMINED APOS SIBILITY ;= EXISTS TO REPHRASE THE ARRAY TO ATTEMPT TO MAINTAIN THE REQUIRED SIDELOBE PERFORMANCE4HE DESIGN SIDELOBE PERFORMANCE CAN BEMAINTAINEDIFASMALLNUMBEROFELEMENTSFAIL BUTASTHENUMBEROF FAILEDELEMENTSINCREASES THEDESIGNSIDELOBECANNOTBERECOVERED)F THISTECHNIQUEISUSED AMEANSOFIDENTIFYINGFAILEDELEMENTSON ORBITIS REQUIRED ACAPABILITYTHATCANUSEADDITIONALDEVELOPMENTATTENTION ! WELL KNOWN APPLICATION OF ARRAY TECHNOLOGY IS THE ANTENNA USED INTHE'03SATELLITES;=4HE'03SATELLITESPROVIDEEARTHCOVERAGE

#HAPTER 4WO

FROM NMIORBITSANDUSEARRAYSOFHELICALELEMENTSTOSHAPETHE ANTENNAPATTERN;=SOTHATUSERSDISTRIBUTEDOVERTHEEARTHSSURFACE WILLRECEIVECOMPARABLEINCIDENTPOWERDENSITYVALUESINDEPENDENTOF THEUSERSELEVATIONANGLETOTHESATELLITE4HE'03ARRAYDESIGNISCOM PRISEDOFTWOCIRCUMFERENTIALARRAYSTHATARECOMBINEDBYSUBTRACTING ASMALLPORTIONOFTHEMOREDIRECTIVEOUTERARRAYFROMTHELESSDIRECTIVE INNER ARRAY4HE PATTERN LEVEL ON AXIS IS REDUCED BY THE SUBTRACTION WHILETHEPATTERNREDUCTIONATWIDERANGLESFROMTHESUBSATELLITEDIREC TIONISSMALLERBECAUSEOFTHEMOREDIRECTIVEPATTERNOFTHEOUTERCIRCUM FERENTIALARRAY4HERESULTISAPATTERNVARIATIONWHOSEGAININCREASES TOWARDSTHEEDGEOFTHEEARTH4HISGAININCREASEOFFSETSTHELONGERRANGE TOWARDSTHEEDGEOFTHEEARTHSOTHATTHEPOWERDENSITYUSERSRECEIVEHAS COMPARABLELEVELSWITHINTHEEARTHSFIELDOFVIEW4HEARRAYTECHNOLOGY PROVIDESAPATTERNSHAPINGCAPABILITYANDTHESIMPLEARRAYDESIGNDOES NOTREQUIREPHASESHIFTERSFORBEAMSTEERINGANDHASSUFFICIENTLYLOW LOSSTHATACTIVEELEMENTSARENOTREQUIRED !RRAYSOF(IGH 'AIN!NTENNAS

.ORMALLY ARRAYANTENNASARECONFIGUREDWITHRELATIVELYSMALLANTENNA ELEMENTSTOREDUCETHEEFFECTSOFGRATINGLOBES"ECAUSETHESMALLARRAY ELEMENTSHAVERELATIVELYLOWGAINPERFORMANCE ALARGENUMBEROFELE MENTS MUST BE COMBINED TO ACHIEVE HIGH GAIN LEVELS SINCE THE ARRAY GAINTOFIRSTORDEREQUALSTHEANTENNAELEMENTGAINMULTIPLIEDBYTHE NUMBEROFELEMENTS(IGHGAINLEVELSREQUIRESOMANYELEMENTSTHAT THE ARRAY DESIGN BECOMES IMPRACTICAL!N ALTERNATIVE APPROACH IS TO COMBINEANUMBEROFHIGH GAINANTENNAELEMENTSCOHERENTLYTOACHIEVE HIGHERGAINLEVELS/NEAPPLICATIONOFTHISAPPROACHISBEINGEXPLORED ASAREPLACEMENTFORMREFLECTORANTENNASUSEDIN*0,S$EEP3PACE .ETWORK ;=!NOTHER POTENTIAL APPLICATION IS COMBINING HIGH GAIN ARRAYELEMENTSONAIRCRAFTTOACHIEVEHIGHERGAINLEVELSNEEDEDFORHIGH DATARATEAPPLICATIONSWHILECONTROLLINGTHEPHYSICALSIZEOFTHEARRAY ELEMENTSTOSATISFYAERODYNAMICREQUIREMENTS 4HECOHERENTCOMBINATIONOFHIGH GAINARRAYELEMENTSIMPOSESSEV ERALREQUIREMENTS4HEELEMENTSMUSTBESITEDWITHSUFFICIENTSEPARA TIONTHATARRAYELEMENTSDONOTBLOCKOTHERARRAYELEMENTS,IKEANY ARRAYDESIGN THEELEMENTELECTRONICSMUSTHAVEMATCHEDAMPLITUDEAND PHASERESPONSESSOTHATTHECOHERENTCOMBININGRESPONSEISMAINTAINED OVERTHEREQUIREDBANDWIDTH4HEARRAYELEMENTSEPARATIONSRESULTIN SIGNAL ARRIVAL TIME DIFFERENCES AT THE INDIVIDUAL ARRAY ELEMENTS THAT REQUIRENOTONLYPHASECOMPENSATIONBUTTIMEDELAYCOMPENSATIONTO MAINTAINCOHERENTCOMBININGOVERABANDWIDTH4HEHIGH GAINANTENNA ELEMENTSHAVENARROWBEAMWIDTHSSOTHATANTENNATRACKINGMUSTBE USEDTOALIGNTHEANTENNAELEMENTSWITHTHESIGNALSDIRECTION

4ECHNOLOGY3URVEY

4HEREQUIREDSEPARATIONOFTHEARRAYDEPENDSONTHEMINIMUMELEVA TION ANGLE ANTICIPATED IN SYSTEM OPERATION ! SIMPLE EXPRESSION CAN BEDERIVEDIFITISASSUMEDTHESIGNALSCANARRIVEATANYANGLEABOVE THEMINIMUMELEVATIONANGLEANDTHATTHEANTENNASHAVEACOMMON DIAMETER$ANDARELOCATEDONAPLANARSURFACE4HEMINIMUMANTENNA ELEMENTSEPARATIONIN&IG EQUALS$SIND WHERE$ISTHEANTENNA ELEMENTDIAMETERANDDISTHEREQUIREDMINIMUMELEVATIONANGLE&OR EXAMPLE THEREQUIREDANTENNASEPARATIONMUSTBEATLEASTANTENNA O DIAMETERSFORA MINIMUMELEVATIONANGLE 4HECOHERENTCOMBINATIONOFARRAYELEMENTSINTHISCASEMUSTCOM PENSATEFORTHESIGNALARRIVALTIMEDIFFERENCESATEACHANTENNAELEMENT 6ERYNARROWBANDWIDTHSIGNALSREQUIREPHASECOMPENSATION BUTWIDER BANDWIDTH SIGNALS REQUIRE BOTH PHASE AND TIME DELAY COMPENSATION 4HE TOLERANCES FOR THESE COMPENSATION REQUIREMENTS CAN BE DERIVED BYCONSIDERINGATWO ELEMENTANTENNAARRAY; =THATHASANIDEAL COHERENTCOMBINATIONEFFICIENCYTHATINCREASESTHEPEAKANTENNAGAIN LEVELBYAFACTOROFD" GREATERTHANTHEGAINOFASINGLEANTENNA ELEMENT4HECOMBININGEFFICIENCYOFTWOANTENNAELEMENTSIS

#P V ;COS[;V 3C SINPnS n@ =]=

&IGURE !RRAYELEMENTSEPARATIONREQUIREMENTS;=Ú)%%%

#HAPTER 4WO

WHEREPISTHESIGNALDIRECTION 3ISTHESEPARATIONBASELINE BETWEEN ANTENNAELEMENTS VISTHERADIANFREQUENCY SISTHETIMEDELAYADJUST MENT IN THE ARRAY COMBINING CIRCUITRY AND @ IS THE INSERTION PHASE DIFFERENCE BETWEEN THE ANTENNA ELEMENTS AT A CENTER FREQUENCY4HE ADJUSTMENT TOLERANCES CAN BE EXPRESSED AS AN UNCOMPENSATED TIME DELAY $S3C SINP nS ANDANUNCOMPENSATEDPHASECEVO$Sn@ ATTHECENTERFREQUENCY4HESETOLERANCESARETHEDEVIATIONSFROMIDEAL COMPENSATION4HECOMBININGEFFICIENCYBECOMES

#COSCV$SCE

WHERETHERADIANFREQUENCYHASBEENEXPANDEDABOUTTHECENTERFRE QUENCYASVVOCV)DEALCOMPENSATIONISACHIEVEDWHEN$SEQUALS CORRESPONDINGTOADJUSTINGSTOEQUAL3C SINPANDADJUSTINGTHE INSERTION PHASE AT THE CENTER FREQUENCY SO THAT @ O .OTICE THAT IDEALCOMPENSATIONISINDEPENDENTOFFREQUENCYANDTHUSHASUNLIMITED BANDWIDTH 0RACTICALSYSTEMSCOMMUNICATEFINITEBANDWIDTHSIGNALSTHATHAVE LESSSTRINGENTTOLERANCEREQUIREMENTSFORCOMPENSATIONTHANTHEIDEAL VALUESTHATAREFREQUENCYINDEPENDENT4HESETOLERANCESAREDERIVEDBY EXAMININGTHEAVERAGECOMBININGEFFICIENCYFORTHEREQUIREDBANDWIDTH "7 4HEAVERAGECOMBININGEFFICIENCYISCOMPUTEDBYINTEGRATINGTHE COMBININGEFFICIENCYOVERTHEFINITEBANDWIDTHANDDIVIDINGTHERESULT BYTHEBANDWIDTHTHATYIELDS

#AVESIN 88 COSCE

WHERE8O"7$S#OMPENSATIONTOLERANCELOSSVALUESDEPENDONALLOW ABLELOSS ANDINTHISCASEAD"LOSSISUSEDFORBOTHTHEUNCOMPENSATED TIMEDELAYANDTHEPHASETOLERANCES4HETIMEDELAYTOLERANCEDEPENDS ON 8 THAT IS DIRECTLY PROPORTIONAL TO THE SIGNAL BANDWIDTH! D" COMBININGLOSSLIMITS8TOAVALUEOF4IMEDELAYTOLERANCEVALUES PLOTTED IN &IG ILLUSTRATE THAT THE REQUIRED TIME DELAY TOLERANCE BECOMESINCREASINGLYSTRINGENTASTHESIGNALBANDWIDTHINCREASES4HE TIMEDELAYTOLERANCEFORA-(ZBANDWIDTHSIGNALEQUALSNSEC BUT A-(ZBANDWIDTHSIGNALIMPOSESANSECTOLERANCE4HETOLER ANCEPRECISIONBECOMESMORECHALLENGINGFORLARGESIGNALBANDWIDTHS 3INCETHESPEEDOFLIGHTISABOUTFTNEC THECOMBINATIONOFTHEARRAY GEOMETRYANDTHESIGNALSELEVATIONANGLECANBEADEQUATETOSETTIME DELAY VALUESFOR NARROWBANDWIDTHSIGNALS! MOREPRECISE MEANSOF DETERMININGANDMAINTAININGTHETIMEDELAYCOMPENSATIONISREQUIRED FORWIDEBANDWIDTHCOHERENTCOMBINING 4HETOLERANCEFORARRAYELEMENTPHASECOMPENSATIONATTHECENTER FREQUENCY DOES NOT DEPEND ON THE SIGNAL BANDWIDTH )F THE PHASE COMPENSATIONTOLERANCELOSSISASSUMEDTOBED"LOSS THEPHASE

4ECHNOLOGY3URVEY

&IGURE 4IMEDELAYCOMPENSATIONTOLERANCEVERSUSBANDWIDTH;=Ú)%%%

COMPENSATIONTOLERANCEEQUALSAOVALUE/THERVALUESOFCOHER ENTCOMBININGEFFICIENCYLOSSDUETOPHASEERRORCOMPENSATIONACCU RACYAREILLUSTRATEDIN&IG 7HENTHEUNCOMPENSATEDPHASEERROR EXCEEDSO THECOMBININGEFFICIENCYISLESSTHANANDTHECOMBINED GAINOFTHEARRAYISLOWERTHANTHATOFASINGLEARRAYELEMENT

&IGURE #OMBININGEFlCIENCYSENSITIVITYTOPHASECOMPENSATIONERRORS;=

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#HAPTER 4WO

0HYSICALLY THEOVERALLARRAYANGULARRESPONSECONTAINSALARGENUMBER OFGRATINGLOBES!SFREQUENCYVARIES THEGRATINGLOBESSCANINANGLE 4HETIMEDELAYCOMPENSATIONLIMITSTHEAMOUNTOFFREQUENCYSCANFOR GRATING LOBES CLOSE TO THE SIGNALS DIRECTION 'OOD ARRAY PERFORMANCE OVERABANDWIDTHREQUIRESALIGNINGAGRATINGLOBEWITHSUFFICIENTTIME DELAY COMPENSATION WITH THE SIGNALS DIRECTION4HE ALIGNMENT OF THE GRATINGLOBEPEAKWITHTHESIGNALDIRECTIONISACCOMPLISHEDBYTHEPHASE COMPENSATION )N OPERATION COHERENTLY COMBINING HIGH GAIN ANTENNA ELEMENTS REQUIRESAQUICK RELIABLEMETHODTOALIGNTHEANTENNAWITHTHESIGNALS DIRECTION4HISALIGNMENTREQUIRESTHEARRAYANTENNAELEMENTSTOTRACK THESIGNALDIRECTIONANDAMEANSTODETERMINE IMPLEMENT ANDMAINTAIN THETIMEDELAYANDPHASECOMPENSATION4HETIMEDELAYCOMPENSATION FORWIDEBANDWIDTHSIGNALISAPARTICULARCHALLENGE!PROPOSEDMEANS OF IMPLEMENTING THIS ARRAY ALIGNMENT ; = USES A BEACON SIGNAL FORARRAYALIGNMENTPURPOSESTHATISTRANSMITTEDALONGWITHTHEDATA SIGNAL! WIDE BANDWIDTH PSEUDORANDOM CODE WOULD BE USED FOR THE BEACONSIGNAL4HECODEDSIGNALANDITSPROCESSINGGAINPROVIDESUFFI CIENTSIGNALSTRENGTHTOALLOWANTENNAELEMENTTRACKINGUSINGPSEUDO MONOPULSETRACKINGTECHNIQUESDESCRIBEDLATERINTHISCHAPTER,IKEWISE AN ADEQUATE LEVEL OF THE PSEUDORANDOM BEACON SIGNAL IS NEEDED FOR ARRAYELEMENTTIMEDELAYANDPHASEALIGNMENT4HISBEACONSIGNALLEVEL BECAUSEOFPROCESSINGGAIN WOULDNOTINTERFEREWITHTHEDATASIGNALAND WOULDCONSUMEONLYAFRACTIONOFTHETRANSMITTEDSIGNALPOWER4IME DELAY COMPENSATION VALUES AT EACH ARRAY ELEMENT ARE DETERMINED BY CORRELATIONWITHAREPLICAOFTHECODEDSIGNAL4HEARRAYOUTPUTSIGNALS AREALSOCORRELATEDWITHAREPLICAOFTHEBEACONSIGNALTOVERIFYAPPRO PRIATECOMPENSATIONVALUES4HEBEACONCARRIERFREQUENCYWOULDALSO BEUSEDTODETERMINETHEREQUIREDPHASECOMPENSATION ANDIFRELATED TOTHEDATASIGNALSCARRIERFREQUENCY WOULDADVANTAGEOUSLYASSISTIN DATASIGNALACQUISITION BUTWITHASIGNALLEVELTHATDOESNOTINTERFERE WITHTHEDESIREDSIGNALRECEPTION !NIMPLEMENTATIONOFTHEBEACONALIGNMENTTECHNIQUEILLUSTRATEDIN &IG HASANARCHITECTURECOMPRISEDOFTHEANTENNAELEMENTSWITH

&IGURE !RRAYARCHITECTUREFORHIGH GAINANTENNAELEMENTS;=Ú)%%%

4ECHNOLOGY3URVEY

CALIBRATIONTESTSIGNALSCORRELATIONRECEIVERSTODETERMINETHEELEMENT TIME DELAY VALUES ELEMENT COMPENSATION CIRCUITRY WITH TIME DELAY AMPLITUDE ANDPHASEADJUSTMENTCAPABILITIESASUMMERFORTHEINDI VIDUALARRAYELEMENTSIGNALCOMPONENTSACORRELATIONRECEIVERTODETER MINEANDMAINTAINTHEPHASEALIGNMENTBETWEENARRAYELEMENTSAND ADATARECEIVER4HEINDIVIDUALARRAYELEMENTSUSEACALIBRATIONSIGNAL TODETERMINETHEIRINSERTIONAMPLITUDEANDPHASEVALUES ANDTHECOM PENSATIONCIRCUITRYISADJUSTEDSOTHATTHEARRAYELECTRONICRESPONSES MATCHELEMENTTOELEMENT4HEINTERCONNECTINGCABLINGALSOISMEASURED ANDANYVARIATIONINTHEIRRESPONSEISADJUSTEDWITHTHECOMPENSATION CIRCUITRYTOPROVIDEMATCHEDRESPONSESATTHEARRAYELEMENTSUMMING CIRCUITRY4HEGOALOFTHISCALIBRATIONISTOHAVEMATCHEDRESPONSESFOR THEELEMENTELECTRONICSOVERTHEBANDWIDTH$ESIGNATTENTIONSHOULDBE PAIDTOCOMPONENTSELECTIONANDTHERMALSTABILITYREQUIREMENTSDURING SYSTEM DEVELOPMENT SO THAT THE DESIRED ACTIVE COMPONENTS TRANSFER FUNCTIONSMATCHANDTHATTHISMATCHISMAINTAINEDFORREASONABLETIME PERIODS4HEELEMENTCALIBRATIONSIGNALSMIGHTUSEONESIGNALSPECTRA FORINITIALALIGNMENTANDOUT OF BANDTONESFORMONITORINGDURINGARRAY OPERATIONTOAVOIDINTERFERENCEWITHTHEDESIREDDATASIGNALS3UCHCALI BRATIONSIGNALSALSOPROVIDEABUILT INTESTANDDIAGNOSTICCAPABILITYFOR ARRAYELECTRONICS 4HEOVERALLOBJECTIVEFORARRAYTIMEDELAYCOMPENSATIONISTOACHIEVEA SIN88VALUEINTHEAVERAGECOMBININGEFFICIENCYTHATISCLOSETO)FTHE DATASIGNALISCORRELATED ITSTIMEDELAYRESOLUTIONISONTHEORDEROF"7 4HETIMEDELAYOFTHEPSEUDORANDOMCODEISONTHEORDEROF"7 ASSUMINGTHECODEBANDWIDTHEQUALSTHEDATASIGNALSBANDWIDTH)FTHE DELAYTOLERANCESAREEQUALTOTHETIMERESOLUTIONOFTHESIGNALS THESIGNAL CORRELATIONRESULTSINAN8VALUEOFOSOTHATSIN88EQUALS4HEAVER AGECOMBININGEFFICIENCYINTHISCASEEQUALSANDCOHERENTCOMBINING AFFORDSTHESAMEPERFORMANCEASASINGLEARRAYELEMENT"YCONTRAST THE CORRELATIONOFTHEBEACONSIGNALRESULTSINAN8VALUEO ASSUMINGTHE TIMEDELAYCOMPENSATIONERRORISAGAINTHETIMEDELAYRESOLUTIONOFTHE PSEUDORANDOMBEACONSIGNAL4HEVALUEOFSIN88INTHISCASEISVERYCLOSE TOANDRESULTSINACOMBININGEFFICIENCYTHATISWITHIND"OFTHE IDEALVALUE4HETIMERESOLUTIONPERFORMANCEOFTHECODEDBEACONSIGNAL ALLOWSACCURATEDETERMINATIONOFTHETIMEDELAYCOMPENSATIONREQUIRE MENTS#OMBININGEFFICIENCYPERFORMANCECLOSETOIDEALVALUESSHOULDBE ACHIEVABLEWITHPROPERPHASECOMPENSATIONATTHECENTERFREQUENCY !NTENNA4RACKING 4HE MAIN BEAM OF THE RECEIVING ANTENNA MUST BE ALIGNED WITH THE INCIDENTSIGNALDIRECTIONTOAVOIDREDUCEDSIGNALLEVELS4HISREDUCTION ISCOMMONLYREFERREDTOASANTENNAPOINTINGLOSS!NTENNAALIGNMENT

#HAPTER 4WO

REQUIREMENTSDEPENDONTHEANGULARBEAMWIDTHOFTHEANTENNAANDTHE UNCERTAINTYOFTHEKNOWLEDGEOFTHESIGNALSDIRECTION6ERYBROADBEAM WIDTHANTENNASREQUIREONLYAGENERALORIENTATIONINTHESIGNALDIRECTION WHEREASNARROWANTENNABEAMWIDTHSMUSTBEALIGNEDWITHPRECISION 4HEPROCESSOFCOMMANDINGANANTENNATOAGIVENANGULARLOCATIONIS REFERREDTOASANTENNAPOINTINGWHILEDYNAMICALLYMAINTAININGALIGN MENT WITH THE SIGNAL DIRECTION IS REFERRED TO AS ANTENNA TRACKING! VARIETYOFUSERSEGMENTNEEDSEXISTTHATRANGEFROMSIMPLEORIENTATION TOCLOSED LOOPTRACKINGSYSTEMSCAPABLEOFHIGHANGULARPRECISION4HE SPACE SEGMENT CAN ALSO IMPOSE ANTENNA TRACKING REQUIREMENTS &OR EXAMPLE CROSSLINKSYSTEMSGENERALLYUSEVERYNARROWBEAMWIDTHS AND CLOSED LOOPANTENNATRACKINGTECHNIQUESARENEEDEDTOCOMPENSATEFOR THESATELLITESATTITUDEVARIATIONS!NTENNATRACKINGTECHNIQUES;=ARE BASED ON OPEN LOOP OR CLOSED LOOP DESIGNS DEPENDING ON THE REQUIRED ACCURACYANDDYNAMICSOFTHESIGNALSDIRECTION !NTENNAPOINTINGINFORMATIONFORUSERSEGMENTANTENNASISDERIVED FROM KNOWLEDGE OF THE USERS GEOGRAPHIC LOCATION AND THE SATELLITES EPHEMERIS4HE SATELLITES ORBITAL LOCATION POSITION IS DEFINED BY THE EPHEMERISDATA WHICHSPECIFIESTHEORBITALTITUDE ECCENTRICITY INCLINA TIONANGLE ANDTIME OF EPOCHPARAMETERSININERTIALSPACE4HEUSERS LOCATIONANDTHESATELLITESEPHEMERISAREUSEDTODEFINETHEREQUIRED TIME VARIATION OF THE ANTENNAS AZIMUTH AND ELEVATION VARIATION 5NCERTAINTIESANDINACCURACIESINTHISINFORMATIONDICTATETHEREQUIRE MENTSFORANTENNATRACKINGTHATCANRANGEFROMOPEN LOOPPOSITIONING TOCLOSED LOOPTRACKINGDESIGNS !NALYSES OF ANTENNA TRACKING PERFORMANCE GENERALLY ARE CONCERNED WITHTHEANTENNASMAINBEAMALIGNMENT!CONVENIENTREPRESENTATION OFTHEHIGH LEVELPORTIONSOFTHEANTENNASMAINBEAMISA'AUSSIANFUNC TIONTHATISAGOODFITFORPRACTICALANTENNADESIGNSANDISGIVENBY

F P EXP;n+P P HP =VOLTAGE

WHEREP ISTHEANGLEMEASUREDFROMTHEMAINBEAMBORESIGHT P HPISTHE ANTENNASHALF POWERBEAMWIDTH AND+ ASCANBEDETERMINED BYEVALUATINGTHEEXPRESSIONATTHEHALF POWERPOINT P HP 4HEANGULARACCURACYOFANTENNATRACKINGANALYSESISGENERALLYNOR MALIZED;=TOTHEANTENNASHALF POWERBEAMWIDTH4HISNORMALIZATION RESULTSINEXPRESSIONSTHATAREINDEPENDENTOFTHEANTENNASBEAMWIDTH ANDARESUITABLEFORUSEWITHERRORBUDGETASSESSMENTSOFTHEFACTORS THATLIMITANTENNATRACKINGUNCERTAINTY4HEANTENNAPOINTINGLOSSTHAT RESULTSFROMTHEANTENNATRACKINGUNCERTAINTYCANBEDERIVEDFROMTHE 'AUSSIANPATTERNREPRESENTATIONGIVENIN&IG 4HEREQUIREDTRACK INGACCURACYFORCOMMUNICATIONSYSTEMSISGENERALLYACCEPTEDASOF THEANTENNASBEAMWIDTH4HISANGULARUNCERTAINTYLIMITSTHEANTENNA POINTINGLOSSTOABOUTD""ETTERANGULARACCURACYFORCOMMUNICATION

4ECHNOLOGY3URVEY

&IGURE !NTENNAPOINTINGLOSSVERSUSMISALIGNMENT;=

APPLICATIONSWOULDHAVEANINSIGNIFICANTIMPACTONLINKPERFORMANCE /THERAPPLICATIONS SUCHASTRACKINGRADARS REQUIREASMUCHTRACKING ACCURACYASPOSSIBLEINORDERTOLOCATETARGETSWITHPRECISION REQUIRING MORECOMPLEXIMPLEMENTATIONS !NTENNATRACKINGTECHNIQUESCANBESEPARATEDINTOOPEN ANDCLOSED LOOP SYSTEM DESIGNS /PEN LOOP SYSTEMS PRINCIPALLY REQUIRE SOFTWARE CONTROL OF THE ANTENNA POINTING WHILE CLOSED LOOP SYSTEMS REQUIRE A MORECOMPLEXANTENNADESIGN ADDITIONALRECEIVERELECTRONICS ACONTROL SYSTEM ANDSUPPORTINGSOFTWARE /PEN ,OOP!NTENNA4RACKING

7HEN THE ANTENNAS BEAMWIDTH SIGNIFICANTLY EXCEEDS THE UNCERTAINTY IN THE SIGNALS DIRECTION EITHER FIXED POINTING OR PROGRAM TRACK TECH NIQUESAREUSED!TYPICALEXAMPLEOFTHEFIXEDPOINTINGISUSERSATELLITE 46ANTENNAS WHOSEBEAMWIDTHSARESUFFICIENTLYBROADTOPERMITFIXED MOUNTINGAFTERALIGNMENTWITHTHEDESIREDSATELLITE0ROGRAMTRACKFOR USERAPPLICATIONSUSESTHESATELLITESEPHEMERISVALUESANDTHEGEOGRAPHIC LOCATIONOFTHETERMINALTOCALCULATETHETIMEVARIATIONOFTHEANTENNAS AZIMUTHANDELEVATIONPOSITIONS)NMOSTPROGRAMTRACKAPPLICATIONS AN !#5ANTENNACONTROLUNIT ISPROGRAMMEDWITHTHESATELLITESEPHEMERIS ANDUSERLOCATIONTOCOMMANDOPEN LOOPANTENNAPOINTINGTOTHESIGNALS DIRECTION'EOSYNCHRONOUSALTITUDESATELLITESHAVERELATIVELYLITTLEMOTION ANDDEVIATIONSINTHESATELLITESINCLINATIONRESULTINASMALLFIGURE EIGHT

#HAPTER 4WO

VARIATIONOVERA HOURPERIOD4HEEXTENTOFTHISMOTIONISCONTROLLED BY OCCASIONAL THRUSTER ADJUSTMENTS TO THE ORBIT A PROCESS REFERRED TO ASSTATIONKEEPING0OLARORBITSAREUSEDBYMETEOROLOGICALSATELLITES FOR EXAMPLE ANDHAVEMUCHMOREDYNAMICANTENNATRACKINGREQUIREMENTS 4HIS ORBITAL CHOICE ALLOWS REMOTE SENSING WITH HIGH RESOLUTION PERFOR MANCE BECAUSE OF THE SHORT RANGE TO THE EARTHS SURFACE AND BECAUSE GLOBAL SAMPLING OF METEOROLOGICAL CONDITIONS RESULTS FROM THE INCLINED ORBIT5SERANTENNATRACKINGFORSUCHORBITSISMUCHMOREDYNAMICTHAN GEOSTATIONARYANTENNATRACKING !NEXAMPLESYSTEMIN&IG THATUSESPROGRAMTRACKCANRECEIVE DATAFROMBOTHPOLARANDGEOSYNCHRONOUSMETEOROLOGICALSATELLITES4HIS CAPABILITYISATTRACTIVETOMETEOROLOGISTSBECAUSETHERESOLUTIONOFLOW ALTITUDESATELLITESISAVAILABLEWHENTHEYAREINVIEW ANDWHENPOLAR SATELLITESARENOTINVIEW hRAPIDREFRESHvDATACANBECOLLECTEDFROMGEO SYNCHRONOUSSATELLITESTHATSCANTHEVISIBLEEARTHSSURFACECONTINUOUSLY PROVIDINGINFORMATIONONWEATHERDYNAMICS$ATAFROMMETEOROLOGICAL SATELLITES IN BOTH ORBIT ARE THEREFORE COMPLEMENTARY4HIS PROTOTYPE DESIGN FOR METEOROLOGICAL SATELLITE READOUT TERMINALS PROVIDES BOTH , AND3 BANDRECEIVECAPABILITIESBYUSINGASCALEDVERSIONOFTHEROLLED EDGECAVITYPREVIOUSLYDESCRIBEDIN&IG ! FTDIAMETERREFLECTOR ISUSEDFORHIGH RESOLUTIONGEOSTATIONARYSATELLITEDATAANDHASBEAM WIDTHVALUESOFOANDOAT, AND3 BAND RESPECTIVELY4HETER MINALSLOCATIONANDTHESATELLITESEPHEMERISPERMITDETERMINATIONOF THEREQUIREDTIMEHISTORYOFTHENECESSARYAZIMUTHANDELEVATIONANGLE VARIATIONS4HEANTENNABEAMWIDTHSARESUFFICIENTLYBROADINTHISCASE

&IGURE !NTENNATHATUSESPROGRAMTRACKTECHNIQUES

4ECHNOLOGY3URVEY

TOALLOWRELIABLETRACKINGPERFORMANCEUSINGPROGRAMTRACK5SINGTHE BEAMWIDTHACCURACYREQUIREMENTTHATLIMITSTHEPOINTINGLOSSTO D" THEREQUIREDPOSITIONINGACCURACYISONTHEORDEROFO WHICHIS ACHIEVEDTHROUGHANTENNALEVELING POSITIONERALIGNMENTTOTRUENORTH ANDTHEREADOUTACCURACYOFABSOLUTEENCODERSINTHEAZIMUTHANDELEVA TIONAXESOFTHEANTENNASPOSITIONER 3TEP4RACK

)FUNCERTAINTYEXISTSREGARDINGTHEACCURACYOFPROGRAMTRACK ANOTHER OPEN LOOPTRACKINGTECHNIQUE REFERREDTOASSTEPTRACK;= CANBEUSED TO VERIFY CORRECT ANTENNA TRACKING4HE ANTENNA BEAM IS POSITIONED BASEDONPROGRAMTRACKINFORMATION ANDISDISPLACEDFROMTHISPOSI TIONBYEQUALANDOPPOSITEANGULARINCREMENTS ASINDICATEDIN&IG 4HERECEIVEDPOWERLEVELSAREMEASUREDATBOTHANGULAROFFSETS)FTHE ANTENNASBORESIGHTAXISISALIGNEDWITHTHESIGNALSDIRECTION THEPOWER LEVELSATBOTHANGULAROFFSETPOSITIONSWILLBEIDENTICAL$IFFERENCESIN THEPOWERLEVELSATEACHANGULAROFFSETINDICATEMISALIGNMENTWITHTHE SIGNALDIRECTION)FTHEMAINBEAMSPATTERNISREPRESENTEDBYA'AUSSIAN FUNCTION THEREQUIREDANGULARCORRECTIONQECANBESHOWNTOEQUAL PDnP HP +PO LN2

WHERE PHP IS THE ANTENNAS BEAMWIDTH PO IS THE ANGULAR OFFSET USED IN THE MEASUREMENT AND 2 IS THE AMPLITUDE RATIO OF THE SIGNALS AT

&IGURE 3TEPTRACKOPERATION;=

#HAPTER 4WO

THEANGULAROFFSETPOSITIONS4HUS THEANTENNASMISALIGNMENTWITHTHE SIGNALDIRECTIONPDCANBEDETERMINEDFROMTHEMEASUREDSIGNALLEVEL ATEQUALANDOPPOSITEANGULAROFFSETS 4HE ANGULAR ACCURACY FOR STEP TRACK HAS BEEN DERIVED USING THE 'AUSSIAN REPRESENTATION OF THE ANTENNA PATTERN !NTENNA TRACKING ACCURACY ;= IS DEFINED BY THE RMS ANGULAR ERROR NORMALIZED BY THE ANTENNASHALF POWERBEAMWIDTH4HISNORMALIZATIONISDIRECTLYRELATED TOTHEANTENNAPOINTINGLOSSEG ABEAMWIDTHTRACKINGACCURACY RESULTSINAD"ANTENNAPOINTLOSS 4HEANGULARACCURACYCANBE SHOWNTOEQUAL RP P HPP HP+PO R!

WHERERP ISTHERMSANGULARERRORANDR!ISTHERMSAMPLITUDEMEASURE MENT ACCURACY!MPLITUDE MEASUREMENT ACCURACY IS LIMITED BY 3.2 SIGNAL TO NOISERATIO ANDTHERMSAMPLITUDEMEASUREMENTACCURACY EQUALS3.2 4HEANTENNATRACKINGACCURACYCANBEEXPRESSEDAS KST3.2 WHEREKSTISTHESTEPTRACKACCURACYCOEFFICIENT.UMERICAL VALUESFORTHISCOEFFICIENTIN&IG ARESHOWNASAFUNCTIONOFTHE PATTERNLEVELSUSEDINTHEANGULAROFFSETVALUES 4HESELECTIONOFANANGULAROFFSETVALUEFORSTEPTRACKMEASUREMENTS ISBASEDONHAVINGASMALLVALUEOFTHESTEPTRACKACCURACYCOEFFICIENT 4HEBEHAVIOROFKSTRESULTSFROMTHEFOLLOWINGFACTORS3MALLANGULAROFF SETSHAVELIMITEDMEASUREMENTSENSITIVITYBECAUSETHEANTENNAPATTERN

&IGURE 3TEPTRACKCOEFlCIENT;=

4ECHNOLOGY3URVEY

NEARTHEMAINBEAMPEAKISRELATIVELYFLATANDHIGHAMPLITUDEMEASURE MENTACCURACYISREQUIREDTODISCERNAMPLITUDEDIFFERENCESATTHETWO OFFSET ANGLES ,ARGE ANGULAR OFFSETS BENEFIT FROM THE LARGER ANTENNA PATTERNSLOPEATTHELARGEANGULAROFFSETANGLESHOWEVER THISINCREASED MEASUREMENTSENSITIVITYISALSOACCOMPANIEDBYREDUCED3.2VALUES BECAUSE THE OFFSET ANGLES ARE SAMPLED AT LOWER ANTENNA GAIN LEVELS 4HESEFACTORSAREINDICATEDINALARGEANGULARDISPLACEMENTTHEABILITY TOMEASURETHEAMPLITUDEATBOTHANGULARDISPLACEMENTSISDEGRADED BY THE LOSS IN 3.2 FROM THE ANTENNA PATTERN REDUCTION AT THE LARGE ANGULARDISPLACEMENT4HESEFACTORSRESULTINTHEVALUESSHOWNIN&IG WHERETHEDESIREDSMALLVALUESOFKSTHAVEABROADMINIMAREGION AROUNDTHEMINIMAATAPATTERNLEVELOFD"LOWERTHANTHEPEAKGAIN ONTHEANTENNASBORESIGHTAXIS)NPRACTICE SYSTEMSNORMALLYHAVEA SYSTEMMARGINVALUERELATIVETOTHEIRTHRESHOLDSENSITIVITY/NESTRATEGY SELECTSTHEANGULAROFFSETVALUEBASEDONTHEAVAILABLESYSTEMMARGIN )NTHISWAY THERECEIVEDDATAARENOTIMPACTEDDURINGTHESTEPTRACKS ANGULARSAMPLINGBYANTENNAPATTERNLEVELSTHATWOULDBELOWERTHAN THEGAINLEVELREQUIREDTORECEIVETHETHRESHOLDSIGNALPOWER &ORMANYCOMMUNICATIONSYSTEMS ANTENNATRACKINGISBASEDONPRO GRAMTRACKANDVERIFIEDANDREFINEDBYSTEPTRACKMEANS'EOSYNCHRONOUS SATELLITESHAVERELATIVELYLITTLEMOTIONINORBIT ANDSTATIONKEEPINGUSING OCCASIONALSPACECRAFTTHRUSTINGLIMITSTHEAMOUNTOFORBITALMOVEMENT 4HIS MOVEMENT FOLLOWS A NORTHnSOUTH FIGURE EIGHT PATH &OR NARROW BEAMWIDTHS SOMEANGULARTRACKINGMAYBEREQUIRED ANDSTEPTRACK VERIFICATIONMIGHTBEPERFORMEDFOURTIMESADAYTOFOLLOWTHEFIGURE EIGHTTRACE&OROTHERSATELLITEORBITS THEUSERANTENNAMUSTDYNAMI CALLYFOLLOWTHESATELLITESORBITALTRAJECTORY)NTHISCASE THESATELLITES EPHEMERISANDUSERSLOCATIONCANBEUSEDTOPREDICTTHETIMEHISTORY OFTHEREQUIREDAZIMUTHANDELEVATIONVARIATION ASISDONEINPROGRAM TRACK#ONVENTIONALSTEPTRACKTECHNIQUESASSUMETHESIGNALDIRECTION REMAINSCONSTANTOVERTHETIMEREQUIREDTOOFFSETTHEANTENNATOPER FORM THE RECEIVED POWER MEASUREMENTS NECESSARY IN THE STEP TRACK PROCEDURE4HE CONVENTIONAL STEP TRACK PROCEDURE HAS BEEN EXTENDED TOAPPLYTOSITUATIONSWHERETHESIGNALDIRECTIONISVARYINGDURINGTHE MEASUREMENT PROCESS A TECHNIQUE REFERRED TO AS RATE CORRECTED STEP TRACK;= 2ATE CORRECTED STEP TRACK INITIALLY REQUIRES ACQUIRING THE SIGNAL AS THE SATELLITE CLEARS THE LOCAL HORIZON AND THEN VERIFIES THE PREDICTED TIMEHISTORYVARIATIONOFAZIMUTHANDELEVATION0RIORTOTHEESTIMATED SATELLITEARRIVALTIME THEPRECALCULATEDAZIMUTHANGLEISUSEDTOPOSI TIONTHEANTENNA4YPICALLY EPHEMERISERRORSAREOFFSETSINTIMEDUETO SATELLITEDRAGPERTURBATIONSOFTHESATELLITEINITSORBITALPLANEREQUIRE MOMENTUM CHANGES!T LOW ELEVATION ANGLES THE RECEIVING ANTENNA IS TYPICALLY LIMITED BY MULTIPATH ERRORS SO IT IS RECOMMENDED THAT

#HAPTER 4WO

THEANTENNABORESIGHTBEPOSITIONEDSOMEWHATABOVETHEHORIZONAND THATTHEANTENNABESWEPTBACKANDFORTHINAZIMUTHOVERANANTICI PATEDUNCERTAINTYVALUEMAINTAININGACONSTANTELEVATIONANGLEUNTIL THE RECEIVER ACQUISITION OCCURS "Y MAINTAINING A CONSTANT ELEVATION ANGLE THEEFFECTOFMULTIPATHCHANGESONTHERECEIVEDSIGNALLEVELWITH ELEVATIONANGLEINCREASESISMINIMIZED)FTHERECEIVERHASNOTACQUIRED BYTHEANTICIPATEDTIMEPERIOD AWIDERAZIMUTHSEARCHISREQUIRED4HE AZIMUTHANDELEVATIONRATESOFTHEORBITALTRAJECTORYAREMODESTASTHE SATELLITECLEARSTHEHORIZONANDALLOWSTIMETOSEARCHFORTHESATELLITE 4HE ANTENNAS SPATIAL ALIGNMENT PROCEEDS AFTER THE RECEIVER HAS ACQUIRED THE SIGNAL4HE ALIGNMENT IN AZIMUTH IS PERFORMED FIRST SO THATMULTIPATHVARIATIONSINTHEELEVATIONDIRECTIONDONOTPERTURBTHE RECEIVEDSIGNALLEVEL#OMMANDEDANGULAROFFSETSAREPROCESSEDINTHE SAME WAY AS CONVENTIONAL STEP TRACK PROCEDURES SINCE ONLY AZIMUTH VARIATIONSARESAMPLED!LTERNATIVELY IFTHERECEIVEDSIGNALLEVELSARE RECORDEDDURINGTHEAZIMUTHSWEEP AFITBETWEENTHEKNOWNANTENNA PATTERNANDTHEMEASUREDSIGNALPOWERVARIATIONSCANBEMADETODETER MINETHECORRECTAZIMUTHPOSITION)NTHISWAY AZIMUTHMULTIPATHVARIA TIONSCANBEAVERAGEDINALIGNINGTHEANTENNASAZIMUTHAXIS 4HROUGHOUTTHISPERIOD THEELEVATIONANGLEOFTHEANTENNAREMAINS FIXED!STHESATELLITEINCREASESINELEVATION THERECEIVEDSIGNALVARIES INACCORDANCEWITHTHEANTENNAPATTERN3INCETHISPORTIONOFTHETRAJEC TORYISATLOWELEVATIONANGLESWHEREMULTIPATHISANISSUE MEASURING THERECEIVEDSIGNALDURINGTHEELEVATIONRISEANDFITTINGTHEDATATOTHE ANTENNAPATTERNISANAPPROPRIATEAVERAGINGTECHNIQUE&ROMSUCHDATA THE ANTENNA BORESIGHT CAN BE REALIGNED WITH THE SATELLITES ELEVATION ANGLE!TTHISPOINT THERECEIVERHASACQUIREDTHESIGNALANDTHEANTENNA ISCORRECTLYALIGNEDINBOTHAZIMUTHANDELEVATIONCOORDINATES &OLLOWINGTHISINITIALACQUISITIONOFTHESIGNALANDANTENNABORESIGHT AXISALIGNMENT THEESTIMATEDTRAJECTORYISCOMPAREDWITHTHEMEASURED VALUESFORTHISTIMEPERIODOFTHESATELLITESTRAJECTORY$ISCREPANCIESIN THISCOMPARISONAREGENERALLYTIMEOFFSETS USEDWITHVALIDATIONTOFOLLOW THESATELLITE4HEACCURACYOFTHISTRAJECTORYDERIVEDFROMTHEEPHEMERIS ISINDICATEDINPARTBYTHECORRESPONDENCEBETWEENTHEANTICIPATEDAND ACTUALACQUISITIONPARAMETERSIE THEAZIMUTHANGLEANDTIMEOFACQUI SITION COMPARISON )NITIALLY THE ANTENNA IS POSITIONED IN ACCORDANCE WITHTHEESTIMATEDTRAJECTORY ANDTHECORRECTNESSOFTHISPOSITIONINGIS VALIDATEDBYTHERATE CORRECTEDSTEPTRACKPROCEDURE 7HILE THE CONVENTIONAL STEP TRACK TECHNIQUE PROVIDES ANGULAR DIS PLACEMENTSINAZIMUTHANDELEVATIONDIRECTIONS SINCETHESIGNALSOURCE ISMOVINGINBOTHCOORDINATES SUCHCONVENTIONALSTEPTRACKSAZIMUTH ANDELEVATIONSAMPLINGRESULTSINCOUPLEDMEASUREMENTSBETWEENTHE ANGULARCOORDINATES4HEMOTIONFORTHESAMPLINGFORTHERATE CORRECTED STEPTRACKISINTHECROSSTRACKANDIN TRACKDIRECTIONS ANDTHESAMPLING

4ECHNOLOGY3URVEY

TIMES ALSO VARY IN ACCORDANCE WITH THE AZIMUTH AND ELEVATION RATES !TLOWELEVATIONANGLESAFTERINITIALACQUISITION THEANGULARRATESARE MODESTBUTINCREASEATHIGHERELEVATIONANGLES-OREFREQUENTSAMPLING IS PERFORMED AT HIGHER ELEVATION ANGLES WHERE THE ANGULAR RATES ARE MOREDYNAMIC 4HECROSSTRACKSAMPLINGISMADEBYCOMMANDINGEQUALANDOPPOSITE ANGULAROFFSETSINTHECROSSTRACKDIRECTION4HEMOTIONOFTHEANTENNA IS ANhS SHAPEDv CURVE ABOUT THE TRAJECTORY AND BASED ON THE POWER MEASUREMENTSAMPLESDURINGTHEEXCURSIONOFTHEhS vTHEANTENNACAN BEREALIGNEDFROMTHEESTIMATEDTRAJECTORYTOTHEACTUALTRAJECTORY4WO ALTERNATIVESEXISTFORTHEIN TRACKALIGNMENT/NEALTERNATIVEISTOCOM MANDTHEANTENNABYEQUALANDOPPOSITEAMOUNTSINTHEIN TRACKDIREC TION4HE REALIGNMENT IS THEN BASED ON THE SIGNAL DIFFERENCES AT THE COMMANDEDPOSITIONS4HESECONDALTERNATIVEACCELERATESTHEANTENNA IN THE IN TRACK DIRECTION AND THEN SLOWS THE ANTENNA IN THE IN TRACK DIRECTIONTOALLOWTHESIGNALTODRIFTTHROUGHTHEMAINBEAMPEAK!GAIN LIKETHEPROCEDURERECOMMENDEDFORTHEELEVATIONALIGNMENTININITIAL ACQUISITION THE MEASURED SIGNAL VARIATION CAN BE FIT TO THE ANTENNA PATTERNANDREALIGNMENTTOTHEBEAMPEAKCANBEMADEBASEDONTHIS PATTERNFIT #LOSED ,OOP4RACKING

7HENTHEUNCERTAINTYINOPEN LOOPTRACKINGPERFORMANCEEXCEEDSTHE REQUIREDANGULARUNCERTAINTY CLOSED LOOPANTENNATRACKINGSYSTEMSARE USEDTODYNAMICALLYTRACKTHESIGNALSDIRECTION#LOSED LOOPTECHNIQUES TRACKTHEDYNAMICSOFTHESIGNALSDIRECTIONVARIATIONS COMPENSATEFOR PLATFORMMOTION ANDOROFFSETWINDLOADINGDISTURBANCESTOMAINTAIN ANTENNATRACKINGACCURACY4HECLOSED LOOPANTENNATRACKINGISREFERRED TOASMONOPULSETRACKING WHICHWASDEVELOPEDFORRADARAPPLICATIONS WHERE VARIATIONS IN THE RECEIVED SIGNAL LEVEL LIMITED OTHER TRACKING TECHNIQUES4HETERMDERIVESFROMTHEABILITYTODETERMINETHESIGNALS DIRECTIONFROMASINGLERADARPULSE)NPRACTICALRADARSYSTEMDESIGNS A TRACKING CAPABILITY THAT IS INVARIANT TO SIGNAL LEVEL FLUCTUATIONS IS REQUIRED #OMMUNICATION APPLICATIONS HAVE WELL BEHAVED RECEIVED SIGNALLEVELSINCOMPARISONTORADARSYSTEMS ALLOWINGDESIGNSIMPLI FICATION -ONOPULSESYSTEMSOPERATEBYFORMINGTWOANTENNABEAMSASUM BEAMTHATISTHENORMALANTENNAMAINBEAMTHATRECEIVESTHESIGNAL WITH HIGHEST SENSITIVITY AND A DIFFERENCE BEAM USED BY THE TRACKING SYSTEM THAT HAS A PATTERN NULL ALIGNED WITH THE ANTENNAS BORESIGHT AXIS)NOPERATION ACLOSED LOOPSYSTEMISCONFIGUREDTOALIGNTHEDIFFER ENCENULLWITHTHESIGNALDIRECTION4HERATIOOFTHEDIFFERENCEANDSUM BEAM OUTPUT LEVELS IS REFERRED TO AS THE ERROR RESPONSE WHICH IS THE

#HAPTER 4WO

CLOSED LOOPSYSTEMSINPUTSIGNAL!SWILLBESHOWN THEERRORRESPONSE ISZEROONTHEANTENNASBORESIGHTAXISANDHASALINEARVARIATIONFOR ANGULAR DEVIATIONS FROM THE BORESIGHT AXIS THAT ARE POSITIVE ON ONE SIDEOF THEAXISAND NEGATIVEONTHEOTHER SIDEOFTHE AXIS4HUS THE ERRORSIGNALRESPONSEERRORFOLLOWSTHECLASSICVARIATIONUSEDINCONTROL SYSTEMS -INIMIZING THE ERROR RESPONSE ALIGNS THE ANTENNA WITH THE SIGNAL DIRECTION THE MAGNITUDE OF THE ERROR RESPONSE IS PROPORTIONAL TOTHESEPARATIONOFTHESIGNALDIRECTIONFROMTHEANTENNASBORESIGHT AXIS ANDTHESIGNOFTHEERRORRESPONSEINDICATESWHICHSIDEOFTHEAXIS CORRESPONDSTOTHESIGNALDIRECTION 2ADARSYSTEMSCOMMONLYUSETHREERECEIVERS ONEFORTHESUMBEAM AND TWO MORE THAT SEPARATELY DETECT THE AZIMUTH AND ELEVATION DIF FERENCE BEAMS 4HE RECEIVER OUTPUTS ARE SIMULTANEOUSLY PROCESSED SO THAT ANTENNA TRACKING IS UNAFFECTED BY CHANGES IN SIGNAL LEVEL #OMMUNICATIONSIGNALLEVELSDONOTHAVETHESAMEDYNAMICVARIATIONS ASRADARSYSTEMSSIGNALSSOTHATAZIMUTHANDELEVATIONAXESARESEQUEN TIALLYSAMPLEDBYASINGLERECEIVERANDAVERAGED4HETRACKINGFORCOM MUNICATIONAPPLICATIONSISREFERREDTOASPSEUDO MONOPULSESINCEBOTH AZIMUTHANDELEVATIONCHANNELSARENOTSIMULTANEOUSLYANDCONTINU ALLYRECEIVED4HEDIFFERENCEPATTERNCHANNELSARESEQUENTIALLYCOUPLED ONTOTHEDATACHANNELBYASWITCHINGCIRCUIT ANDSYNCHRONOUSDETECTION OFTHERESULTING!-AMPLITUDEMODULATION ONTHEDATACHANNELPRO VIDESTHETRACKINGINFORMATION4HE!-LEVELVARIESLINEARLYWITHTHE SIGNALSDISPLACEMENTFROMTHEANTENNABORESIGHT COMMONLYREFERRED TOASTHEhMONOPULSEERRORSLOPEv4HECONTROLSYSTEMFUNCTIONSTOMINI MIZETHE!-VALUEASANhERRORSIGNALvTOALIGNTHEANTENNASBORESIGHT AXISWITHTHESIGNALDIRECTION 4HETRACKINGACCURACYFORTHEMONOPULSETECHNIQUECANBEDERIVED ; =USING'AUSSIANFUNCTIONSSUCHASTHESTEPTRACKANALYSIS4WO 'AUSSIANBEAMSAREDISPLACEDFROMTHEBORESIGHTAXISANDOVERLAPAT THEIRHALF POWERPOINTS7HENTHESETWOBEAMSAREADDEDTOGETHER A SUMBEAMRESULTS ANDWHENTHETWOBEAMSARESUBTRACTED ADIFFERENCE BEAMRESULTS ASILLUSTRATEDIN&IG 4HERATIOOFTHESEDIFFERENCE AND SUM BEAM PATTERNS GIVES THE ERROR RESPONSE SHOWN IN &IG 4HEANGULARACCURACYOFTHEMONOPULSEDESIGNUSINGTHESEBEAMREP RESENTATIONSBECOMES

RP P HP3.2

4HE MONOPULSE ACCURACY COEFFICIENT IS SMALLER THAN THE STEP TRACK ACCURACY COEFFICIENT AND GENERALLY MONOPULSE DESIGNS HAVE BETTER ANGULARACCURACYTHANSTEPTRACKDESIGNS4HEERRORSINTHISDISCUSSION CONSIDERTHE2&TRACKINGOUTPUTS0RACTICALDESIGNSHAVEOTHERERRORS RESULTINGFROMMECHANICALIMPERFECTIONSSUCHASBACKLASH WINDGUSTS

4ECHNOLOGY3URVEY

&IGURE 3UMSOLID ANDDIFFERENCEDASHED PATTERNS;=

&IGURE %RRORRESPONSECORRESPONDINGTOTHESUMANDDIFFERENCEBEAMSIN

&IGURE ;=

CONTROLSYSTEMOFFSETS AND2&NULLOFFSETSFORMONOPULSEDESIGNS AND POSITIONALENCODERERRORSFOROPEN LOOPTRACKINGTECHNIQUES4HEOVERALL TRACKING ACCURACY REQUIRES EXAMINATION OF THESE OTHER ERROR SOURCES ANDFROMTHEIRCOMPONENTERRORSANERRORBUDGETISCONSTRUCTEDFROM

#HAPTER 4WO

THERSSSUMOFTHEINDIVIDUALRMSVALUESOFTHECOMPONENTERRORS&OR ANTENNASTHATARENOTENCLOSEDINRADOMESTOPROTECTTHEANTENNAFROM WINDGUSTS THEERRORBUDGETGENERALLYCONSIDERSTRACKINGPERFORMANCE INCALMCONDITIONSANDUNDERWINDLOADINGCONDITIONSSEPARATELY4HE ANALYSESOFANTENNATRACKINGVARIATIONSWITHWINDLOADING;=FOLLOW COMMONLY ESTABLISHED PROCEDURES THAT ASSESS BOTH STEADY STATE AND GUSTYCONDITIONS -ONOPULSE&EED$ESIGNS

7HILEMONOPULSEDESIGNSPROVIDEACCURATETRACKINGANDCANDYNAMICALLY FOLLOWCHANGESINSIGNALDIRECTION THEIRIMPLEMENTATIONCOSTISHIGHER BECAUSEOFTHECONTROLSYSTEMANDADDITIONALRECEIVERREQUIREMENTS BUT IN LARGE PART BECAUSE OF A MORE COMPLEX ANTENNA FEED DESIGN %ARLY MONOPULSESYSTEMSUSEDAFEEDDESIGNCOMPRISEDOFMULTIPLEHORNSCEN TEREDONTHEBORESIGHTAXIS-ORERECENTLY MULTIMODEFEEDDESIGNSHAVE BEENDEVELOPED4HESUMBEAMUSESTHEUSUALWAVEGUIDEMODEEXCITA TION WHILETHEDIFFERENCEBEAMSAREFORMEDFROMHIGHER ORDERWAVEGUIDE MODEEXCITATION4HESETWODESIGNAPPROACHESAREDISCUSSEDINTURN 4HEMULTIPLEHORNTRACKINGFEEDSFORMTHESUMBEAMBYADDINGTHE HORNS TOGETHER TO PRODUCE AN ANTENNA PATTERN THAT HAS A PEAK MAIN BEAM LEVEL COINCIDENT WITH THE ANTENNAS BORESIGHT AXIS4HE DIFFER ENCE BEAMS THAT PROVIDE ANTENNA TRACKING CAPABILITIES ARE PRODUCED BYSUBTRACTINGTHEHORNSONOPPOSITESIDESOFTHEBORESIGHTAXIS4HE SUBTRACTEDANTENNAPATTERNHASANULLON AXISANDISPOSITIVEONONE SIDE OF THE BORESIGHT AXIS AND NEGATIVE ON THE OTHER SIDE4HIS PRO CESSWASUSEDTODETERMINETHESUMANDDIFFERENCEPATTERNSSHOWNIN &IG AND THE ERROR RESPONSE SHOWN IN &IG WHERE THE OFF AXISBEAMSTHATAREFORMEDBYTHEFEEDCLUSTERINTHEFOCALREGIONUSE 'AUSSIANFUNCTIONSFORTHEIRREPRESENTATION4HEERRORRESPONSEISTHE INPUTTOTHEANTENNASPOSITIONCONTROLSYSTEMANDISTHERATIOOFTHE DIFFERENCE AND SUM PATTERNS7HEN THE ANTENNA IS IDEALLY TRACKING THEERRORRESPONSEEQUALSZERO4RACKINGDEVIATIONSFROMTHEANTENNAS BORESIGHTAXISHAVEALINEARDEVIATIONTHATISPOSITIVEONONESIDEOFTHE AXISANDNEGATIVEONTHEOTHER4HUSTHEMONOPULSECIRCUITRYRESULTSIN ACLASSICCONTROLSYSTEMRESPONSE MINIMIZINGTHEERRORRESPONSEAND AWELL BEHAVEDLINEARRESPONSEWHENTHEERRORISNON ZERO4HISLINEAR RESPONSEPERSISTSFORASIGNIFICANTPORTIONOFTHEANTENNASMAINBEAM ANGULAREXTENTBUTDEVIATESFORLARGERVALUES4HUS THEINITIALANTENNA POINTINGMUSTHAVESUFFICIENTACCURACYTOALIGNTHEANTENNAWITHTHE SIGNALDIRECTIONSOTHECONTROLSYSTEMFUNCTIONSPROPERLY&URTHERDISCUS SIONFOLLOWSREGARDINGTHEACQUISITIONISSUES /NEPROBLEMWITHTHISSIMPLECOMBINATIONOFOFF AXISANTENNABEAMS ISTHATTHESUMANDDIFFERENCEPATTERNSCANNOTBESEPARATELYOPTIMIZED ;= )F THE OFF AXIS BEAMS ARE SUMMED TO FORM A DESIRED APERTURE

4ECHNOLOGY3URVEY

AMPLITUDETAPER THEINDIVIDUALBEAMSTHATFORMTHEDIFFERENCEBEAM WOULDHAVEHIGHCROSSOVERLEVELSANDTHERESULTINGDIFFERENCEPATTERNS WOULDHAVEASHALLOWLINEARSLOPE)FTHEOFF AXISBEAMSARESELECTEDTO PROVIDEDIFFERENCEPATTERNSWITHAHIGHERLINEARSLOPEBYINCREASINGTHE ANGULARSEPARATIONOFTHECOMPONENTBEAMSFROMTHEBORESIGHTAXIS THE BEAMWIDTHOFTHEFEEDCLUSTERSUMWOULDBECOMENARROWER INCREASING THE AMPLITUDE TAPER OF THE REFLECTOR ILLUMINATION AND THUS REDUCING ANTENNA EFFICIENCY !N ALTERNATIVE APPROACH IS TO USE A NORMAL FEED DESIGNFORTHESUMBEAMANDINTEGRATESMALLERANTENNAELEMENTSINTO THETHROATORPERIMETEROFTHESUMPATTERNFEED/NEEXAMPLE;=USED FOUR POLYROD RADIATORS LOCATED WITHIN THE THROAT OF A SUM BEAM FEED HORN4HESEELEMENTSAREARRANGEDINFOURQUADRANTSSURROUNDINGTHE CENTRALHORN ANDOPPOSINGPAIRSOFELEMENTSCANBESUBTRACTEDTOFORM VERTICALANDHORIZONTALDIFFERENCEBEAMS (YBRIDNETWORKSAREGENERALLYUSEDTOCOMBINETHEANTENNAELEMENTS INMULTIPLEAPERTUREMONOPULSEFEEDDESIGNS4HEAMPLITUDEANDPHASE ACCURACYREQUIREMENTS;=HAVEBEENEXAMINEDFORSUCHHYBRIDCOMBIN INGCIRCUITRY4WODISTINCTMONOPULSECOMBININGCIRCUITRYNETWORKSARE ADDRESSEDUSING'AUSSIANBEAMREPRESENTATIONSOFTHEINDIVIDUALBEAMS BEINGCOMBINEDTOPRODUCETHEMONOPULSETRACKINGFEEDPATTERNS4HEFIRST COMBININGCIRCUITRY REFERREDTOAShHYBRIDCOMBINED vPRODUCESTHESUM ANDDIFFERENCEBEAMPATTERNSBYCOMBININGMULTIPLEHORNS4HESECOND REFERREDTOAShSEPARATESUMBEAM vUSESASINGLECENTRALFEEDTOFORMTHE SUMBEAMANDHYBRIDNETWORKSTOCOMBINEFOURANTENNAELEMENTSTOFORM DIFFERENCEBEAMS4HEPATTERNCHARACTERISTICSANDERRORRESPONSESFORTWO HYBRIDCOMBININGCIRCUITDESIGNSAREPRESENTEDIN4ABLE 4!",% 0ATTERNSAND%RROR2ESPONSEFOR(YBRID-ONOPULSE#IRCUITS

3UM"EAM $IFFERENCE"EAM %RROR2ESPONSE

(YBRID#OMBINED

3EPARATE3UM"EAM

;EXPn8+ =;COSH8 C = ;EXPn8 + =;SINH8 nC = SINH8 nC COSH8 C

EXPn8 + ;EXPn8+ =;SINH8 nC = ;SINH8 nC =

WHERE8+P P HPANDC!n EXPn8 WHENP OP HP 4HEIDEAL HYBRIDCIRCUITRYRESULTSWHENTHEPARAMETER!EQUALS!MPLITUDEAND PHASEDEVIATIONSFROMTHISIDEALVALUEOFRESULTINTHEHYBRIDCIRCUIT IMPERFECTIONSEXPRESSEDBYTHEPARAMETERCANDTHECOMBININGTOLER ANCE WHERE!ISTHEAMPLITUDEANDORPHASETOLERANCEDEVIATIONFROM IDEALCOMBININGWHERE!EQUALS4HEERRORRESPONSEISTHERATIOOFTHE DIFFERENCEANDSUMBEAMSANDISTHECONTROLSYSTEMINPUT !MPLITUDEERRORSINMONOPULSECOMBININGCIRCUITRYRESULTINANGULAR SHIFTSINTHEBORESIGHTAXESOFTHEDIFFERENCEANDSUMBEAMS4HEDIFFER ENCEPATTERNNULLSHIFTDDEQUALS

DD;LN!+=P HP

#HAPTER 4WO

4HISERRORSHIFTSTHEDIFFERENCEPATTERNNULLTOWARDTHECOMPONENT BEAMHAVINGTHELOWERVALUE!MPLITUDEERRORSINTHEHYBRIDCOMBINED DESIGNALSOSHIFTTHESUMBEAMPOSITION BUTINADIRECTIONTOWARDTHE COMPONENTBEAMWITHTHEHIGHERLEVEL4HESUMBEAMSHIFTISDERIVED BYSETTINGTHEDERIVATIVEOFTHESUMBEAMTOZERO WHICHYIELDSASUM ERRORDSTHATEQUALS DS[n!n+ ;!n+ n!n += ]P HP+

4HEBORESIGHTSHIFTSFORTHEDIFFERENCEBEAMANDTHESUMBEAMAND TOTAL BORESIGHT SHIFT FOR THE HYBRID COMBINED CASE ARE PRESENTED IN &IG !MPLITUDEERRORSALSORESULTINAMINORVARIATIONOFTHEERROR RESPONSESLOPEVALUES 0HASEERRORSINTHECOMBININGCIRCUITRYRESULTINFILLINGINTHEDIFFER ENCEPATTERNNULLBECAUSETHEQUADRATUREERRORCOMPONENTCANNOTBE CANCELLED4HEDIFFERENCEPATTERNNULLDEPTH .$ EQUALS .$;nCOSI =

WHERE I IS THE PHASE IMBALANCE RELATIVE TO THE ZERO IDEAL VALUE AS ILLUSTRATEDIN&IG 4HEDIFFERENCEPATTERNNULLFILLINGALSORESULTS INANON ZEROERRORRESPONSEATBORESIGHTASINDICATEDIN&IG FOR THE33"CASEWITHAOPHASEERROR4HEIDEALERRORRESPONSEMAKESA OPHASETRANSITIONATTHEBORESIGHTAXIS BUTTHISPHASETRANSITIONIS ROUNDEDWHENPHASEERRORISPRESENT

&IGURE "ORESIGHTSHIFTSWITHAMPLITUDEIMBALANCE;=Ú)%%%

4ECHNOLOGY3URVEY

&IGURE .ULLDEPTHVERSUSPHASEIMBALANCE;=Ú)%%%

&IGURE .ULLlLLINGWITHoPHASEIMBALANCE;=Ú)%%%

4HEALLOWABLEAMPLITUDEANDPHASEIMBALANCESINPRACTICALDESIGNS DEPENDSONTHESPECIFICAPPLICATION4YPICALLY THEOVERALLTRACKINGACCU RACYOFONE TENTHOFTHEANTENNASBEAMWIDTHLIMITSTHEANTENNAPOINT ING LOSS TO D" BUT THIS PERFORMANCE INCLUDES OTHER ERROR SOURCES

#HAPTER 4WO

BESIDESHYBRIDCIRCUITRYIMBALANCES!REPRESENTATIVEERRORCOMPONENT ALLOCATIONFORCOMBININGCIRCUITRYIMBALANCESMIGHTLIMITTHEVALUESTO BEAMWIDTHS4HEAMPLITUDEIMBALANCEVALUESFORABEAMWIDTH ERROR ARE ABOUT D" FOR THE SEPARATE SUM BEAM DESIGN AND ABOUT D"FORTHEHYBRIDCOMBINEDDESIGN ASILLUSTRATEDIN&IG 4HE TIGHTERHYBRIDCOMBINEDTOLERANCERESULTSFROMTHEOPPOSITELYDIRECTED ANDROUGHLYDOUBLEDMAGNITUDEERRORSFORTHESUMBEAMINTHEHYBRID COMBINEDCASE4HENULLDEPTHLIMITATIONCANBEUSEDTODERIVEAPHASE TOLERANCEVALUEFORABEAMWIDTHDEVIATION7ITHOUTPHASEERROR ANIDEALPATTERNHASAnD"NULLDEPTHATABEAMWIDTHDEVIA TIONFROMTHEBORESIGHTAXIS!D"NULLDEPTHLIMITATIONFROMPHASE IMBALANCEISASSUMEDADEQUATEANDRESULTSINANULLDEPTHTHATIS D"LOWERTHANTHEIDEALNULLDEPTHOFD"ATABEAMWIDTHOFFSET 4HED"NULLDEPTHVALUECORRESPONDSTOAPHASEIMBALANCEOFABOUT O ASILLUSTRATEDIN&IG !NOTHERMONOPULSEANTENNAFEEDTECHNOLOGY; =USESAMULTI MODE APERTURE DESIGN4HE DOMINANT MODE PRODUCES THE SUM BEAM AND HIGHER ORDER WAVEGUIDE MODES PRODUCE THE DIFFERENCE PATTERNS 4HEDOMINANTMODEHASANIN PHASEAPERTUREDISTRIBUTION WHILETHE DIFFERENCEMODEPATTERNHASAOPHASEPROGRESSIONTHATRESULTSIN A PATTERN NULL ON THE BORESIGHT AXIS4HE SAME O PHASE PROGRES SIONEXISTSINTHEFARFIELDANTENNAPATTERN)NTHISCASE THEANTENNAS ANGULARMISALIGNMENTISEXPRESSEDINAPOLARQ IFORMRATHERTHANTHE X YFORMPREVIOUSLYDISCUSSED4HEMAGNITUDEOFTHEERRORRESPONSE Q INDICATESTHERADIALDISTANCEFROMTHEANTENNASBORESIGHTAXISANDTHE PHASEITHATISMEASUREDRELATIVETOTHESUMBEAMPATTERNINDICATES THE AZIMUTH POSITION OF THE ANTENNAS ANGULAR MISALIGNMENT4HESE FEEDDESIGNSREQUIREHIGHER ORDERMODECOUPLERSTOSEPARATEDOMINANT ANDHIGHER ORDERMODECOMPONENTS3UCHFEEDSGENERALLYSEQUENTIALLY SAMPLETHEHIGHER ORDERMODECOMPONENTSINANGULARQUADRANTSAND ADDTHESAMPLEDSIGNALCOMPONENTSTOTHERECEIVEDSUMBEAMSIGNAL 4HESEQUENTIALSAMPLINGRESULTSINANAMPLITUDEMODULATIONPATTERN ONTOTHERECEIVEDSUMBEAMSIGNALLEVEL4HEHEIGHTOFTHEAMPLITUDE MODULATIONINDICATESTHEANGULARDISPLACEMENTFROMTHEANTENNASBORE SIGHTAXIS4HEHIGHANDLOWVALUESOFTHEAMPLITUDEMODULATIONWHERE THECOUPLEDHIGHER ORDERMODEADDSANDSUBTRACTSWITHTHESUMSIGNAL RESPECTIVELYINDICATETHEAZIMUTHPLANEWHERETHEANTENNAMISALIGN MENTOCCURS )NSUCHDESIGNS INACCURACIESINTHEPHASEOFTHESUMBEAMANDDIF FERENCEBEAMSRESULTINTRACKINGERRORSTHATAREREFERREDTOAShCROSS TALKv &OR EXAMPLE IF THE ANTENNA IS DISPLACED A HORIZONTAL DISTANCE FROMTHEANTENNASBORESIGHTAXIS THECONTROLSYSTEMSHOULDRESPOND WITHMOTIONWITHINTHEHORIZONTALPLANE)FTHEANTENNAFOLLOWSBOTHA HORIZONTALANDVERTICALTRAJECTORYINRETURNINGTOTHEBORESIGHTPOSITION

4ECHNOLOGY3URVEY

THEVERTICALMOTIONREFERREDTOASCROSSTALKRESULTSFROMPHASEOFFSETS BETWEEN THE SUM AND DIFFERENCE CHANNELS THAT NEED TO BE CORRECTED FORPROPERTRACKINGOPERATION&ORNARROWBANDWIDTHAPPLICATIONS THE PHASEBETWEENTHESUMANDDIFFERENCEBEAMSISADJUSTEDWITHAPHASE SHIFTER TO MINIMIZE ANTENNA CROSSTALK ERRORS7HEN WIDE BANDWIDTH REQUIREMENTSMUSTBESATISFIED THEGROUPDELAYDIFFERENCESRATHERTHAN THEPHASESHIFTBETWEENTHESUMANDDIFFERENCEBEAMSMUSTBEEQUAL IZEDTOMINIMIZECROSSTALK4HEEVALUATIONOFANTENNATRACKINGSYSTEMS ISDISCUSSEDIN#HAPTER 3IGNAL!CQUISITION)SSUES

7HENANTENNATRACKINGTECHNIQUESAREUSED THEANTENNAISINITIALLY POINTEDUNDERCOMMANDTOANOMINALAZIMUTHANDELEVATIONPOSITION BASEDONAPRIORIKNOWLEDGESUCHASEPHEMERISDATA)FTHEINITIALPOINT INGKNOWLEDGEISSUFFICIENTLYACCURATE THERECEIVERSHOULDACQUIRETHE SIGNAL4HE ACCURACY REQUIRED OF THE INITIAL POINTING DIRECTION CLEARLY DEPENDSONTHEANTENNASBEAMWIDTH'ENERALLY ANTENNATRACKINGPER FORMANCEISLIMITEDTOAPORTIONOFTHEANGULARWIDTHOFTHEANTENNAS MAINBEAMTHATISREFERREDTOASTHESIGNALACQUISITIONANGULARWIDTHOF THEANTENNASTRACKINGDESIGN)FTHERECEIVERDOESNOTACQUIRETHESIGNAL ASEARCHFORTHESIGNALSDIRECTIONISPERFORMEDBYVARYINGTHEANTENNAS POINTINGABOUTTHENOMINALPOINTINGDIRECTIONUNTILTHERECEIVERACQUIRES THESIGNAL"OTHRASTERANDSPIRALSCANPATTERNSAREUSEDINPRACTICEIN SEEKINGSIGNALACQUISITION .ARROWBEAMWIDTHANTENNASAREREQUIREDTOSATISFYHIGHDATARATE APPLICATIONS AND REQUIRE ACCURATE A PRIORI KNOWLEDGE OF THE SIGNALS LOCATIONTOMINIMIZESEARCHTIME4WOTECHNIQUESCANBEUSEDTOEXTEND THEACQUISITIONFIELDOFVIEWFORNARROWBEAMWIDTHANTENNAS"OTHOF THESETECHNIQUESCAPITALIZEONTHESENSITIVITYOFTHETRACKINGRECEIVER 'ENERALLY TRACKINGRECEIVERSUSECARRIERTRACKINGTECHNIQUESWHEREHIGH SENSITIVITYISACHIEVEDBYANARROWBANDWIDTHRECEIVERRESPONSEAND AVERAGINGTECHNIQUESTOREDUCETHEVARIANCEOFTHERECEIVERSIGNALLEVEL "YCONTRAST ADATARECEIVERREQUIRESHIGHERSIGNALLEVELSTODEMODULATE THESIGNALWITHADEQUATEFIDELITY /NE TECHNIQUE FOR NARROW BEAMWIDTH SIGNAL ACQUISITION USES A SMALLERANTENNAHAVINGABROADERBEAMWIDTHTHANTHEANTENNAUSED FORDATARECEPTIONTOACQUIRETHESIGNALANDMEASUREITSDIRECTION4HE GAINOFTHESMALLERANTENNAMUSTBESUFFICIENTTOALLOWRELIABLEANTENNA TRACKING PERFORMANCE "OTH STEP TRACK OR MONOPULSE TRACKING TECH NIQUESCANBEUSEDBYTHEBROADERBEAMWIDTHANTENNATOMEASURETHE SIGNALSDIRECTIONWITHSUFFICIENTACCURACYTOALLOWPOINTINGALIGNMENT WITHINTHEDATAANTENNASTRACKINGACQUISITIONWIDTH4HISTECHNIQUE RESULTS IN THE ADDITIONAL COMPLEXITY OF A SEPARATE SMALLER ANTENNA

#HAPTER 4WO

3INCEHIGH GAINANTENNASCOMMONLYUSEDDUALREFLECTORDESIGNS THE SMALLERSIGNALACQUISITIONANTENNACANBELOCATEDBEHINDTHESUBREFLEC TORSOTHATBORESIGHTCOINCIDENCEOFTHESMALLERANDDATAANTENNASIS ESTABLISHEDBYDESIGN 4HESECONDTECHNIQUE;=EXTENDSTHEANGULARACQUISITIONWHILEUSING THENARROWBEAMWIDTHANTENNASREFLECTOR)NADDITIONTOACENTRALFEED SYSTEMFORNORMALTRACKINGANDDATARECEPTION ADDITIONALFEEDELEMENTS AREPLACEDINTHEFOCALREGIONANDEACHOFTHESEFEEDELEMENTSARECON NECTEDTOATRACKINGRECEIVER$URINGSIGNALACQUISITION THESIGNALARRIVAL DIRECTIONISIDENTIFIEDBYTHETRACKINGRECEIVERHAVINGTHEHIGHESTSIGNAL LEVEL3INCETHEBORESIGHTAXESFOREACHANTENNABEAMISESTABLISHEDBY DESIGN KNOWLEDGE OF THE REQUIRED POINTING CORRECTION IS OBTAINED BY THEANGULARSEPARATIONOFTHEFEEDWITHTHEHIGHESTSIGNALLEVELANDTHE CENTRAL FEED 4HIS ACQUISITION TECHNIQUE REQUIRES ADDITIONAL ANTENNA FEEDSANDTRACKINGRECEIVERSBUTAVOIDSTHEREQUIREDADDITIONALSMALLER ANTENNA NEEDED BY THE FIRST TECHNIQUE 4RADEOFFS EXIST REGARDING THE NUMBEROFANTENNAFEEDSANDTHEIRSEPARATIONFROMTHECENTRALFEED AND THESETRADEOFFSDEPENDONTHESENSITIVITYOFTHETRACKINGRECEIVERS 4HEHIGHSENSITIVITYOFTHETRACKINGRECEIVERCANRESULTINSITUATIONS WHERETHEANTENNAISTRACKINGONANANTENNASIDELOBERATHERTHANTHE MAIN BEAM 3OME INDICATION OF SIDELOBE ALIGNMENT RESULTS WHEN THE DATARECEIVEREITHERDOESNOTACQUIRETHESIGNALORHASEXCESSIVENOISE (OWEVER MAIN BEAM ALIGNMENT VERIFICATION ;= IS DESIRED IN MANY APPLICATIONS AND ALIGNMENT VERIFICATION BEFORE INITIATING CLOSED LOOP TRACKING OPERATION IS ALSO DESIRED4HREE TECHNIQUES FOR MAIN BEAM ALIGNMENTVERIFICATIONAREDESCRIBED /NETECHNIQUEUSESASEPARATESMALLERANTENNAINADDITIONTOTHELARGER MAINANTENNAREQUIREDFORSIGNALRECEPTION4HESMALLERANTENNA GENER ALLYREFERREDTOASAGUARDANTENNA ISDESIGNEDSOTHATITSMAINBEAM GAINLEVELISCOMPARABLETOTHESIDELOBEANTENNAGAINVALUESOFTHEMAIN ANTENNA4RACKINGSIGNALLEVELSARECOMPAREDFORBOTHANTENNAS)FTHE TRACKINGSIGNALLEVELINTHEMAINANTENNAISSIGNIFICANTLYLARGERTHANTHAT FORTHEGUARDANTENNA THESIGNALISALIGNEDWITHTHEANTENNASMAINBEAM )FTHESIGNALLEVELSINEACHTRACKINGRECEIVERARECOMPARABLE ASIDELOBE OFTHEMAINANTENNAISPOSSIBLYALIGNEDWITHTHESIGNALDIRECTION/PEN LOOPCOMMANDSARETHENMADETOREPOSITIONTHEANTENNASEQUENTIALLYIN EQUALANDOPPOSITEANGULAROFFSETSINAZIMUTHANDELEVATION4HEANGULAR OFFSETSIZESAREONTHEORDEROFONE HALFOFTHEANTENNASBEAMWIDTH! COMPARISONOFTHETRACKINGRECEIVEROUTPUTSISMADEATEACHOFFSETPOSI TION)FTHESIGNALLEVELOFTHEMAINANTENNASTRACKINGRECEIVERATONE OFTHEFOURCOMMANDEDOFFSETSISSIGNIFICANTLYHIGHERTHANTHETRACKING RECEIVERS OUTPUT LEVEL OF THE GUARD ANTENNA THE REQUIRED MAIN BEAM ALIGNMENTISINTHEDIRECTIONOFTHATOFFSETDIRECTION&URTHEROPEN LOOP COMMANDSUSINGSMALLERANGULAROFFSETVALUESPROVIDEADDITIONALCONFI DENCEOFMAINBEAMALIGNMENTANDTHUSNORMALTRACKINGOPERATIONCAN

4ECHNOLOGY3URVEY

BEINITIATED)FNONEOFTHEFOURANGULAROFFSETSRESULTSINTRACKINGRECEIVER SIGNALLEVELSINTHEMAINANTENNATHATEXCEEDTHEGUARDANTENNASTRACK INGRECEIVEROUTPUT THEANTENNABORESIGHTAXISISMORETHANONESIDELOBE REMOVEDFROMTHESIGNALDIRECTION&URTHEROPEN LOOPCOMMANDINGUSING STEPSIZESBASEDONTHEANTENNASSIDELOBERESPONSEAREREQUIREDTOALIGN THEANTENNASMAINBEAMWITHTHESIGNALDIRECTION !SECONDTECHNIQUEAPPLIESTOANTENNASYSTEMSTHATUSEOPEN LOOP TRACKINGTECHNIQUES!NEXAMINATIONOFANTENNAPATTERNCHARACTERISTICS REVEALS THE ANGULAR WIDTH OF THE MAIN BEAM IS CONSIDERABLY GREATER THANTHEANGULARWIDTHOFASIDELOBE)NTHISCASE STEPTRACKCOMMANDS AREMADEANDTHEMEASUREDVALUESATTHEANGULAROFFSETSAREFITTOTHE KNOWNMAINBEAMSANGULARRESPONSE)FTHEMEASUREDVALUESDONOTFIT THEANTICIPATEDRESPONSE ANANTENNASIDELOBEISALIGNEDWITHTHESIGNAL DIRECTION!GAINOPEN LOOPCOMMANDINGUSINGTHEKNOWNANTENNAPAT TERNTOSELECTPOINTINGOFFSETSASDESCRIBEDEARLIERISUSEDTOLOCATETHE SIGNALDIRECTION)FTHECOMMANDEDANGULAROFFSETRESULTSINASIGNIFI CANTINCREASEINTHETRACKINGRECEIVERSOUTPUTLEVEL THEANTENNASMAIN BEAMALIGNMENTISINTHEVICINITYOFTHESIGNALDIRECTION ANDSMALLER ANGULAROFFSETSAREUSEDTODETERMINETHESIGNALDIRECTION&INALLY THE NORMAL STEP TRACK OPERATION IS INITIATED4HE OPEN LOOP COMMANDING USEDINTHISPROCESSCANALSOBEUSEDASAMEANSOFALIGNINGCLOSED LOOP ANTENNATRACKINGDESIGNSWITHTHESIGNALDIRECTION 4HE THIRD TECHNIQUE IS BASED ON THE CLOSED LOOP ANTENNA RESPONSE #LOSED LOOPANTENNATRACKINGISBASEDONALINEARVARIATIONANDPRE DETERMINED SLOPE OF THE MONOPULSE ERROR SLOPE4HIS ERROR RESPONSE BEHAVIOR HOWEVER PERSISTSONLYOVERALIMITEDPORTIONOFTHEANTENNAS MAINBEAM ANDDEPARTSSIGNIFICANTLYFROMTHATLINEARRESPONSEBEYOND THEMAINBEAMREGION%RRORRESPONSEVARIATIONSFORWIDERANGLESARE ILLUSTRATED IN &IG 3INCE THE ANGLES IN &IG EXTEND INTO THE

&IGURE -ONOPULSEERRORSLOPEVARIATION

#HAPTER 4WO

ANTENNAS SIDELOBE REGION THE ERROR RESPONSE WAS COMPUTED FROM COMPOSITE BEAMS HAVING A SIN88 FUNCTION TO REPRESENT THE SIDELOBE RESPONSE)FAVAILABLE MEASUREMENTSOFTHEERRORRESPONSEVALUESFOR THEACTUALANTENNACANBEUSED)FSIDELOBEALIGNMENTWITHTHESIGNALIS APROGRAMCONCERN MEASUREMENTSOFTHEERRORRESPONSEWELLBEYONDTHE DESIGNLINEARREGIONARERECOMMENDED4HEERRORFUNCTIONSARESHOWN FORBOTHAPRINCIPALLYPOLARIZEDRESPONSEANDACROSS POLARIZEDRESPONSE TOBEDISCUSSEDLATER -AINBEAMALIGNMENTVERIFICATIONFORCLOSED LOOPANTENNATRACKING DESIGNS CAN BE BASED ON TWO FACTORS CONCERNING THE MONOPULSE ERROR RESPONSE4HEFIRSTFACTORISTHEDETERMINATIONOFEXCESSIVEAMPLITUDE MODULATION RESULTS AT THE ANTENNAS INITIAL POINTING DIRECTION -OST TRACKING RECEIVERS CAN MEASURE A LIMITED AMOUNT OF AMPLITUDE MOD ULATION AND EXCESSIVE AMPLITUDE MODULATION OR RECEIVER MODULATION SATURATIONINDICATESANTENNASIDELOBEALIGNMENTWITHTHESIGNALDIREC TION!SILLUSTRATEDIN&IG ATTHEEDGESOFTHEMAINBEAMTHELEVEL OFTHEDIFFERENCEPATTERNEXCEEDSTHATOFTHESUMPATTERN RESULTINGIN OVERMODULATIONANDDEVIATIONFROMTHEERRORRESPONSESLINEARSLOPE! SECONDFACTORCONCERNSTHESLOPEOFTHEMONOPULSEERRORRESPONSE!S ILLUSTRATEDIN&IG THEERRORRESPONSESLOPEINTHELINEARREGIONIS SIGNIFICANTLYSTEEPERINTHESIDELOBEREGIONTHANTHEDESIGNERRORSLOPE INTHEMAINBEAM/PEN LOOPCOMMANDEDANGULAROFFSETSCANBEUSED TOMEASURETHEERRORSLOPETODETERMINEIFTHEANTENNASMAINBEAMOR ASIDELOBEISALIGNEDWITHTHESIGNALSDIRECTION!GAINOPEN LOOPCOM MANDED ANGULAR OFFSETS AND TRACKING RECEIVER OUTPUT MEASUREMENTS AREUSEDTOLOCATETHEMAINBEAM#LOSED LOOPTRACKINGISINITIATEDONCE MAINBEAMALIGNMENTISVERIFIED 4HE ERROR RESPONSE IN &IG ALSO ILLUSTRATES THE BEHAVIOR WHEN THE RECEIVED SIGNAL HAS THE DESIGN POLARIZATION SENSE AND WHEN THE RECEIVEDSIGNALISCROSS POLARIZED7ITHINTHEDESIGNACQUISITIONLIMITS THE ERROR RESPONSE FOR THE CORRECT POLARIZATION SENSE HAS THE DESIRED BEHAVIOR NAMELYZEROERRORONTHEBORESIGHTAXISANDALINEARGRADIENT FORSMALLANGULARDISPLACEMENTSFROMTHEBORESIGHTAXIS(OWEVER THE ERRORRESPONSEFORTHECROSS POLARIZEDSIGNALSHASADECIDEDLYDIFFERENT BEHAVIOR THEREGIONNEARTHEBORESIGHTAXISHASTHEWRONGSLOPEWITH ANEXCEEDINGLYHIGHVALUE ANDZEROERRORPOINTSARELOCATEDAWAYFROM THEBORESIGHTAXISATANGLESCORRESPONDINGTOABOUTD"BELOWTHESUM BEAMPEAKLEVELFORTHEDESIGNPOLARIZATION4HEERRORRESPONSEFORCROSS POLARIZEDSIGNALSCANRESULTINUNSTABLETRACKING ASWILLBEILLUSTRATED WITHMEASUREDRESPONSESTOCROSS POLARIZEDSIGNALSIN#HAPTER !NTENNATRACKINGDESIGNS;=CANBEIMPLEMENTEDWITHDIFFERENCE ANTENNAELEMENTSHAVINGEITHERLINEARORCIRCULARPOLARIZATION7HENTHE DIFFERENCEELEMENTSARELINEARLYPOLARIZED THEANTENNAPROPERLYTRACKS SIGNALS HAVING THE DESIGN LINEAR POLARIZATION AND FOR BOTH SENSES OF

4ECHNOLOGY3URVEY

CIRCULARPOLARIZATION(OWEVER THEANTENNADOESNOTTRACKSIGNALSHAVING THEORTHOGONALLINEARPOLARIZATION SIMPLYBECAUSENOSIGNALCOMPONENT ISRECEIVED7HENTHEDIFFERENCEELEMENTSARECIRCULARLYPOLARIZED THE ANTENNAPROPERLYTRACKSSIGNALSHAVINGDESIGNSENSECIRCULARLYPOLARIZED SIGNALSANDLINEARLYPOLARIZEDSIGNALSHAVINGANYORIENTATION(OWEVER ANTENNATRACKINGCANBECOMEUNSTABLEWHENCIRCULARLYPOLARIZEDSIGNALS HAVINGTHEOPPOSITESENSETOTHEDESIGNSENSEARERECEIVED 7HENANTENNATRACKINGSYSTEMSAREOPERATEDINAPPLICATIONSWHERE THE RECEIVED SIGNAL HAS VARYING POLARIZATION PROPERTIES TWO REQUIRE MENTSMUSTBESATISFIEDBYTHESYSTEMDESIGN3UCHPOLARIZATIONDIVERSE APPLICATIONS REQUIRE A MEANS TO MAINTAIN THE RECEIVED SIGNAL LEVEL WITHOUTINCURRINGSIGNIFICANTPOLARIZATIONMISMATCHLOSSANDMAINTAIN ANTENNATRACKINGPERFORMANCEFORVARYINGPOLARIZATIONCONDITIONS4HE FIRSTREQUIREMENTOFCONTROLLINGPOLARIZATIONMISMATCHLOSSISSATISFIED BYANANTENNADESIGNWHOSESUMCHANNELHASORTHOGONALLYPOLARIZED OUTPUTSANDBYTHECOMBININGOFTHETWOORTHOGONALLYPOLARIZEDSUM CHANNELOUTPUTSINAPOLARIZATIONDIVERSITYCOMBINERTHATDYNAMICALLY TRACKSTHERECEIVEDSIGNALSPOLARIZATION/NEIMPLEMENTATIONFORPOLAR IZATIONDIVERSITYCOMBINERDESIGNSCOMBINESTHEORTHOGONALLYPOLARIZED ANTENNAOUTPUTSINAVECTORMODULATORTHATCANCOMBINETHETWOSIGNALS INANYCOMBINATIONOFAMPLITUDEANDPHASE/NEOFTHEVECTORMODULA TORSOUTPUTSISCONNECTEDTOTHEDATARECEIVER4HEPOWERLEVELINTHE SECONDVECTORMODULATOROUTPUTISUSEDASANINPUTTOACONTROLSYSTEM THATMAINTAINSTHEADJUSTMENTOFTHEVECTORMODULATORBYMINIMIZING THEPOWERATTHATSECONDVECTORMODULATOROUTPUTUSEDBYTHECONTROLLER 4HISSECONDVECTORMODULATOROUTPUTISTHEERRORSIGNALTOTHECONTROL SYSTEM ANDBYMINIMIZINGTHATERROR THEPOLARIZATIONOFTHERECEIVED SIGNALISDYNAMICALLYMATCHEDBYTHERECEIVINGANTENNATOMINIMIZE POLARIZATIONMISMATCHLOSS 4HESECONDREQUIREMENTISTOMAINTAINANTENNATRACKINGWHENTHE RECEIVEDSIGNALSPOLARIZATIONISVARYING3EVERALALTERNATIVESEXISTIN ADDRESSINGDIVERSEPOLARIZATIONISSUESINANTENNATRACKING!SWITHTHE SUMCHANNELFORDATARECEPTION TRACKINGELEMENTSWITHORTHOGONALPOLAR IZATIONOUTPUTAREREQUIRED/NEMEANSTOMAINTAINANTENNATRACKINGIN POLARIZATIONDIVERSEENVIRONMENTSISTOCOMMANDTHEPOLARIZATIONOFTHE TRACKINGELEMENTSFROMTHEPOLARIZATIONWEIGHTINGOFTHESUMCHANNEL BASEDONTHEPOLARIZATIONDIVERSITYCOMBINER4HISAPPROACHREQUIRES ANADDITIONALVECTORMODULATORCOMBINER!NALTERNATIVEAPPROACH; =ISTOSEQUENTIALLYDETECTTHEORTHOGONALLYPOLARIZEDTRACKINGCHANNEL OUTPUTSANDSUMTHEM4HISSUMCANBESHOWNTOBEDOMINATEDBYTHE TRACKINGCHANNELOUTPUTTHATISMOSTCLOSELYMATCHEDTOTHEPOLARIZATION OFTHEINCIDENTSIGNAL)NCOMPARISONTOADESIGNWHOSETRACKINGCHAN NELSDYNAMICALLYMATCHTHERECEIVEDSIGNALSPOLARIZATION THEIMPLE MENTATIONOFTHISALTERNATIVEAPPROACHISLESSCOMPLEXANDCOSTLYBUT

#HAPTER 4WO

RESULTSINASOMEWHATREDUCEDTRACKINGSENSITIVITYSINCETHETRACKING RESPONSEOFTHECHANNELWITHTHEDOMINANTPOLARIZATIONRESPONSEISMEA SUREDONLYONE HALFOFTHETIMEANDINCURSSOMEPOLARIZATIONMISMATCH LOSS (OWEVER AS DISCUSSED THE SENSITIVITY OF THE TRACKING CHANNELS EXCEEDSTHESENSITIVITYOFTHEDATACHANNELSSOTHATTHELOSSOFTRACKING SENSITIVITYINTHISALTERNATIVEAPPROACHCANBEACCOMMODATED 2EFERENCES 7$"URNSIDEAND2*-ARHEFKA h!NTENNASON!IRCRAFT 3HIPS OR!NY/THER ,ARGE #OMPLEX%NVIRONMENT vIN94,OAND37,EEEDS !NTENNA(ANDBOOK .EW9ORK#HAPMANAND(ALL *!3TRATTON %LECTROMAGNETIC4HEORY.EW9ORK-C'RAW (ILL $3&ILIPOVICAND4#ENCICH h&REQUENCY)NDEPENDENT!NTENNAS v*,6OLAKISED !NTENNA%NGINEERING(ANDBOOK.EW9ORK-C'RAW (ILL $%0ING *43HAFFER ,5"ROWN AND2"$YBDAL h!"ROADBAND2OLLED%DGED #AVITY!NTENNA v)%%%!0 33YMPOSIUM$IGEST -ONTEREY#! *UNE 0$0OTTER h!.EW(ORN!NTENNAWITH3UPPRESSED3IDELOBESAND%QUAL "EAMWIDTHS v-ICROWAVE*OURNAL VOL6)*UNE n 2%,AWRIEAND,0ETERS h-ODIlCATIONSOF(ORN!NTENNASFOR,OW3IDELOBE ,EVELS v)%%%4RANS!NTENNASAND0ROPAGATION VOL!0 3EPTEMBER n !7,OVEED (ORN!NTENNAS.EW9ORK)%%%0RESS #'RANET ',*AMES 2"OLTON AND'-OOREY h!3MOOTH 7ALLED3PLINE0ROlLE (ORNASAN!LTERNATIVETOTHE#ORRUGATED(ORNFOR7IDE"AND-ILLIMETER7AVE !PPLICATIONS v)%%%4RANS!NTENNASAND0ROPAGATION VOL!0 -ARCH n 7$"URNSIDEAND#7#HUANG h!PERTURE-ATCHED(ORN$ESIGN v)%%%4RANS !NTENNASAND0ROPAGATION VOL!0 *ULY n *43HAFFER $%0ING AND2"$YBDAL h!3IMPLE(IGH0ERFORMANCE(ORN $ESIGN v)%%%!0 33YMPOSIUM$IGEST*UNE 3AN!NTONIO48 *$-ICHAELSONAND2"$YBDAL h$EVELOPMENT$EMONSTRATIONOFA4ACTICAL2$3 4ERMINAL v-!8)$IGEST/CTOBER 3ILVER3PRING-$ !7,OVEED 2EmECTOR!NTENNAS.EW9ORK)%%%0RESS 7642USCH 3CATTERINGFROMA(YPERBOLOIDAL2EmECTORINA#ASSEGRAIN&EED 3YSTEM )%%%4RANS!NTENNASAND0ROPAGATION VOL!0 *ULY n #$RAGONEAND$#(OGG h4HE2ADIATION0ATTERNAND)MPEDANCEOF/FFSETAND 3YMMETRIC.EAR&IELD#ASSEGRAINIANAND'REGORIAN!NTENNAS v)%%%4RANS !NTENNASAND0ROPAGATION VOL!0 -AY n '7#OLLINS h3HAPINGOF3UBREmECTORSIN#ASSEGRAIN!NTENNASFOR-AXIMUM !PERTURE%FlCIENCY v)%%%4RANS!NTENNASAND0ROPAGATION VOL!0 -AY n 33ILVER -ICROWAVE!NTENNA4HEORYAND$ESIGN.EW9ORK-C'RAW (ILL 43#HUAND2(4URRIN h$EPOLARIZATION0ROPERTIESOF/FFSET2EmECTOR!NTENNAS v )%%%4RANS!NTENNASAND0ROPAGATION VOL!0 -AY n 7!)MBRIALE 0')NGERSON AND7#7ONG h,ARGE,ATERAL&EED$ISPLACEMENTS INA0ARABOLIC2EmECTOR v)%%%4RANS!NTENNASAND0ROPAGATION VOL!0 .OVEMBER n 2*ORGENSEN 0"ALLING AND7*%NGLISH h$UAL/FFSET2EmECTOR-ULTIBEAM !NTENNAFOR)NTERNATIONAL#OMMUNICATIONS3ATELLITE!PPLICATIONS v)%%%4RANS !NTENNASAND0ROPAGATION VOL!0 $ECEMBER n #-2APPAPORTAND70#RAIG h(IGH!PERTURE%FlCIENCY3YMMETRIC2EmECTOR !NTENNASWITHUPTOO&IELDOF6IEW v)%%%4RANS!NTENNASAND0ROPAGATION VOL-ARCH n "!-UNK &REQUENCY3ELECTIVE3URFACES.EW9ORK7ILEY

4ECHNOLOGY3URVEY +5NEO 4)TANAMI (+UMAZAWA AND)/HTOMO h$ESIGNAND#HARACTERISTICSOF A-ULTI BAND#OMMUNICATION3ATELLITE!NTENNA3YSTEM v)%%%4RANS!EROSPACE AND%LECTRONIC3YSTEMS VOL!PRIL n *2UZE h!NTENNA4OLERANCE4HEORY!2EVIEW v0ROC)%%% VOL!PRIL n *0#ORRIGAN h!43 %XPERIMENT3UMMARY v)%%%4RANS!EROSPACEAND%LECTRONIC 3YSTEMS VOL!%3 .OVEMBER n -74HOMSON h4HE!STROMESH$EPLOYABLE2EmECTOR v)%%%!0 3 3YMPOSIUM$IGEST*UNE /RLANDO&, !2$IONAND,*2ICARDI h!6ARIABLE#OVERAGE3ATELLITE!NTENNA3YSTEM v0ROC )%%% VOL&EBRUARY n (%+ING *,7ONG 2"$YBDAL AND-%3CHWARTZ h%XPERIMENTAL%VALUATION OFA#IRCULARLY0OLARIZED-ETALLIC,ENS!NTENNA v)%%%4RANS!NTENNASAND 0ROPAGATION VOL!0 -AY n 2*-AILLOUX 0HASED!RRAY!NTENNA(ANDBOOK.ORWOOD-!!RTECH &*$IETRICH 0-ETZEN AND0-ONTE h4HE'LOBALSTAR#ELLULAR3ATELLITE3YSTEM v )%%%4RANS!NTENNASAND0ROPAGATION VOL!0 *UNE n **3CHUSS *5PTON "-EYERS 43IKINA !2OHWER 0-AKRIDAKAS 2&RANCOIS ,7ARDLE AND23MITH h4HE)2)$)5--AIN-ISSION!NTENNA#ONCEPT v)%%% 4RANS!NTENNASAND0ROPAGATION VOL!0 -ARCH n 4*0ETERS h!#ONJUGATE'RADIENT BASED!LGORITHMTO-INIMIZETHE3IDELOBE,EVEL OF0LANAR!RRAYSWITH&AILED%LEMENTS v)%%%4RANS!NTENNASAND0ROPAGATION VOL!0 /CTOBER n 3PECIAL)SSUEON'034HE'LOBAL0OSITIONING3YSTEM 0ROC)%%% VOL *ANUARY #4"RUMBAUGH !7,OVE '-2ANDALL $+7AINEO AND3(7ONG h3HAPED "EAM!NTENNAFORTHE'LOBAL0OSITIONING3ATELLITE v)%%%!0 33YMPOSIUM $IGEST/CTOBER $3"AGRI *)3TATMAN AND-3'ATTI h0ROPOSED!RRAY BASED$EEP3PACE .ETWORKFOR.!3! v0ROC)%%% VOL/CTOBER n +-3OO(OOAND2"$YBDAL h4OLERANCESFOR#OMBINING(IGH'AIN!NTENNAS v )%%%!0 33YMPOSIUM$IGEST*UNE 2"$YBDALAND+-3OO(OO h!RRAYING(IGH'AIN!NTENNAS v)%%%30 3 3YMPOSIUM$IGEST*ULY 2"$YBDALAND3*#URRY h!RRAYING,ARGE!NTENNAS v)%%%!0 3 3YMPOSIUM$IGEST*UNE 2"$YBDAL h#OHERENTLY#OMBINING(IGH'AIN!NTENNAS v)%%%-),#/- 3YMPOSIUM$IGEST.OVEMBER 2"$YBDAL h!NTENNA4RACKING v#HAPTERIN*,6OLAKISED !NTENNA %NGINEERING(ANDBOOK.EW9ORK -C'RAW (ILL $+"ARTONAND(27ARD (ANDBOOKOF2ADAR-EASUREMENT%NGLEWOOD#LIFFS.* 0RENTICE(ALL 2"$YBDAL h3TEP4RACKING0ERFORMANCEAND)SSUES v)%%%!0 33YMPOSIUM $IGEST*UNE 2"$YBDALAND$$0IDHAYNY h2ATE#ORRECTED3TEP4RACK v)%%%!0 3 3YMPOSIUM$IGEST*UNE SEEALSO2"$YBDALAND$$0IDHAYNY h-ETHOD OF4RACKINGA3IGNALFORA-OVING3IGNAL3OURCEv-AY 530ATENT 2"$YBDAL h-ONOPULSE2ESOLUTIONOF)NTERFEROMETRIC!MBIGUITIES v)%%%4RANS !EROSPACEAND%LECTRONIC3YSTEMS VOL!%3 -ARCH n %LECTRICALAND-ECHANICAL#HARACTERISTICSOF%ARTH3TATION!NTENNASFOR 3ATELLITE#OMMUNICATIONS %LECTRONIC)NDUSTRIES!LLIANCE4ELECOMMUNICATIONS )NDUSTRY2EPT4)!%)! 2EVISON!3EPTEMBER 07(ANNAN h/PTIMUM&EEDSFOR!LL4HREE-ODESOFA-ONOPULSE!NTENNA v)2% 4RANS!NTENNASAND0ROPAGATION VOL!0 3EPTEMBER n *$I4ULLIO h!(IGH0ERFORMANCE&EEDFOR%ARTH3TATION3ATELLITE#OMMUNICATIONS v TH!NNUAL53!&!NTENNA2$3YMPOSIUM$IGEST/CTOBER 2OBERT!LLERTON 0ARK ),

#HAPTER 4WO 2"$YBDAL h-ONOPULSE!NTENNA4OLERANCE%RRORS v)%%%!0 33YMPOSIUM $IGEST *UNE 9(#HOUNG +2'OUDEY AND,/"RYANS h4HEORYAND$ESIGNOFA+U BAND 4%-ODE#OUPLER v)%%%4RANS-ICROWAVE4HEORYAND4ECHNIQUES VOL-44 .OVEMBER n 9(#HOUNG h7IDEBAND4- MODE4RAVELING7AVE#OUPLER v0ROC)%% VOL /CTOBER 2"$YBDAL h%XTENDED3PATIAL!CQUISITIONFOR4RACKING!NTENNAS v)%%% !0 33YMPOSIUM$IGEST*ULY SEEALSO2"$YBDAL h%XTENDED3PATIAL !CQUISITIONFOR4RACKING!NTENNAS v3EPTEMBER 530ATENT 2"$YBDALAND$$0IDHAYNY h-AIN"EAM!LIGNMENT6ERIlCATION v)%%% !0 33YMPOSIUM$IGEST*UNE SEEALSO 2"$YBDALAND$$0IDHAYNY h-AIN"EAM!LIGNMENT6ERIlCATIONFOR4RACKING!NTENNASv!UGUST 53 0ATENT 2"$YBDALAND$$0IDHAYNY h0OLARIZATION/PTIMIZATIONFOR4RACKING!NTENNAS v )%%%!0 33YMPOSIUM$IGEST*UNE 2"$YBDAL h0OLARIZATION,IMITATIONSIN!NTENNA4RACKING v)%%%!0 3 3YMPOSIUM$IGEST*UNE 2"$YBDALAND$$0IDHAYNY h-ETHODSAND3YSTEMSFOR4RACKING3IGNALSWITH $IVERSE0OLARIZATIONv*ULY 530ATENT

#HAPTER

#OMMUNICATION3ATELLITE 3YSTEM!RCHITECTURES

/VERVIEW 4HEOVERALLCOMMUNICATIONSATELLITESYSTEMISCOMPRISEDOFTHEORBITING SPACE SEGMENT PAYLOAD AND THE USER SEGMENT TERMINALS4HE SYSTEM DESIGNSFORSPECIFICAPPLICATIONSVARYGREATLYBECAUSEOFDIFFERINGSYSTEM OBJECTIVES AND REQUIREMENTS 4HIS TREND WILL CONTINUE TO EXPAND IN FUTURE SYSTEMS AS DEMAND INCREASES FOR ADDITIONAL SATELLITE SERVICES ANDASFURTHEREXTENSIONSAREMADETOPROVIDEPERSONALSERVICES 4HESPACESEGMENTHASSEVERALALTERNATIVEARCHITECTURES4HEMOST COMMON COMMUNICATION SATELLITE SYSTEM SIMPLY RELAYS INFORMATION BETWEENUSERSUSINGTHESATELLITEPAYLOAD4HESPACESEGMENTISREFERRED TO AS A TRANSPONDER WHICH RECEIVES THE UPLINK INFORMATION FROM THE USERS AND THEN BROADCASTS THE INFORMATION TO USERS ON A FREQUENCY TRANSLATEDDOWNLINK)NOTHERCASES THESAMEINFORMATIONISBROADCAST FROM THE SATELLITES TO NUMEROUS USERS AN ARCHITECTURE REFERRED TO AS ADIRECTBROADCASTDESIGN3ATELLITETELEVISIONBROADCASTDESIGNSAREA PARTICULARLY POPULAR EXAMPLE OF THIS ARCHITECTURE /THER SERVICES ARE POINT TO POINTDESIGNS SUCHASSATELLITECROSSLINKSTHATPROVIDECOMMU NICATIONSBETWEENADJACENTSATELLITESWITHOUTANYRELAYTHROUGHGROUND ASSETS#ROSSLINKSTHUSPROVIDECONNECTIVITYTOUSERSWHODONOTHAVE MUTUALVISIBILITYTOACOMMONSATELLITE&INALLY ALLSATELLITESREQUIREA 44#4RACKING 4ELEMETRY AND#ONTROL SUBSYSTEM ANOTHERCOMMU NICATION SYSTEM THAT ASSISTS IN VERIFYING THE SATELLITES ON ORBIT POSI TION PROVIDESDATAREGARDINGTHESATELLITESON ORBITHEALTHANDSTATUS USINGTELEMETRYMULTIPLEXEDONTHE44#DOWNLINK ANDCONTROLSTHE SATELLITESOPERATIONTHROUGHCOMMANDINGANDAUTHENTICATION

#HAPTER 4HREE

4HEUSERSEGMENTLIKEWISEHASVARIEDARCHITECTURES%ARLYSATELLITE SYSTEMSWITHVERYLIMITEDSPACEBORNERESOURCESNEEDEDLARGEGROUND TERMINALSTOACHIEVEADEQUATEPERFORMANCEANDDISSEMINATEDDATATO INDIVIDUALUSERSVIATERRESTRIALLINKSINAhHUBANDSPOKEvARRANGEMENT 7ITHMORECAPABLESATELLITEDESIGNS DIRECTDISTRIBUTIONOFMOREINFORMA TIONTOAWIDERCLASSOFUSERSBECAMEPOSSIBLE ATRENDTHATCONTINUES TOEXTENDCOMMUNICATIONSBETWEENINDIVIDUALUSERTERMINALS0RESENT SYSTEM DESIGNS INCLUDE THE PROLIFERATION OF USER TERMINALS FOR DIRECT BROADCASTSERVICESTHATREQUIRECOST EFFECTIVETERMINALDESIGNSHAVING RECEIVE ONLY CAPABILITIES AND COMMUNICATION NETWORKS USING MODEST SIZED TERMINAL REFERRED TO AS63!4 VERY SMALL APERTURE TERMINALS TO LINK TERRESTRIAL USERS4HESE SYSTEM DESIGNS ARE MADE POSSIBLE BY INCREASED SATELLITE CAPABILITIES AND IMPROVED USER TERMINAL DESIGNS 4HUS LINKINGINDIVIDUALUSERSTOEXTENDPERSONALCOMMUNICATIONSBY USING SATELLITE LINKS IS ACCOMPLISHED AND WILL BE EXTENDED IN FUTURE DEVELOPMENTSTOADDITIONALSERVICESAVAILABLETOUSERSWITHHANDHELD EQUIPMENT#ONNECTIVITYWITHOTHERASSETSSUCHASTERRESTRIALCOMMU NICATIONNETWORKS AFEATUREREQUIREDBYTHEEARLYSATELLITES CONTINUES TOBEANOBJECTIVEOFFUTURESYSTEMS PARTICULARLYINEXPANDING)NTERNET SERVICES4HISEVOLUTIONFROMLIMITEDNETWORKSANDTERRESTRIALRELAYOF LOWDATARATESERVICESTOINDIVIDUALUSERSFOUNDINEARLYSYSTEMSTOAN EXPLODINGNUMBEROFUSERTERMINALSWITHINCREASEDSERVICECAPABILITIES IS A KEY REASON FOR EXISTING AND FUTURE SATELLITE SYSTEM GROWTH4HIS SAMEEXPANSIONTOINDIVIDUALUSERSREQUIRESINCREASEDEMPHASISOFCOST EFFECTIVEUSERTERMINALSTOCONTROLOVERALLSYSTEMACQUISITIONCOSTS 4HEOVERALLSATELLITECOMMUNICATIONARCHITECTURESHAVEMANYVARIA TIONS FOR SPECIFIC PROGRAM APPLICATIONS BUT THE NUMBER OF GENERIC ARCHITECTURALDESIGNSISLIMITED0RACTICALDESIGNSVARYSIGNIFICANTLYAS REQUIREDTOMEETTHEIRPROGRAMOBJECTIVESHOWEVER THEGENERICDESIGNS ARE REPEATED TO PROVIDE CHANNELIZED SERVICES TO SERVE NEEDS OVER THE SATELLITESFIELDOFVIEW,IKEWISE AWIDEVARIETYOFUSERDESIGNSEXIST TOSUPPORTDIVERSESERVICES3PACEANDUSERSEGMENTARCHITECTURESARE DESCRIBEDATATOPLEVELANDORBITALALTERNATIVESANDTHEIRIMPACTONLINK REQUIREMENTSAREDISCUSSED 3PACE3EGMENT!RCHITECTURES 3EVERALARCHITECTURESARECOMMONLYUSEDINTHESPACESEGMENT4HREEDIF FERENTTRANSPONDERARCHITECTURESCANBEDISTINGUISHEDFORSPACESEGMENT APPLICATIONSTHATPROVIDECONNECTIVITYBETWEENINDIVIDUALUSERS4HEFIRST ANDMOSTWIDELYUSEDDESIGNISALINEARFREQUENCYTRANSLATINGTRANSPON DER WHERETHERECEIVEDSIGNALSONTHEUPLINKARETRANSLATEDINFREQUENCY ANDAMPLIFIEDFORRETRANSMISSIONONTHEDOWNLINK ATRANSPONDERARCHI TECTURECOMMONLYREFERREDTOASABENTPIPEREPEATER4HESECONDTYPE

#OMMUNICATION3ATELLITE3YSTEM!RCHITECTURES

OFTRANSPONDERDESIGNISREFERREDTOASTHEREGENERATIVEREPEATER WHERE THEUPLINKSIGNALSAREPARTIALLYORCOMPLETELYDEMODULATED REFORMATTED ANDREMODULATED ANDRETRANSMITTED3OMESYSTEMARCHITECTURESPERFORM THEDEMODULATION REMODULATION ANDROUTINGONTHEGROUNDBYTRANSMIT TINGTHERECEIVEDUPLINKSIGNALSTOTHEGROUND BASEDGATEWAYTERMINALS PROCESSINGTHEM ANDRETRANSMITTINGTHEPROCESSEDSIGNALSTOTHESATELLITE FORBROADCASTTOTHEUSERSONTHEDOWNLINK4HEGROUNDSEGMENTWHERETHE PROCESSINGISPERFORMEDISCOMMONLYREFERREDTOASAGATEWAYTERMINAL 4HE ADVANTAGES OF THE MORE COMPLEX REGENERATIVE REPEATER TRAN SPONDERARETHECAPABILITYTOREDUCETHEDOWNLINKBROADCASTOFUPLINK INTERFERENCEPOWER THEREBYINCREASINGTHEEFFECTIVENESSOFTHEDOWNLINK POWERADDEDFLEXIBILITYINROUTINGINFORMATIONTOAVARIETYOFDESTINA TIONSANDMAINTAININGUSERDOWNLINKPOWERCONTROL7ITHADVANCESIN DIGITALTECHNOLOGY ATHIRDTYPEOFTRANSPONDERDESIGNISDISTINGUISHED ANDFUTUREDESIGNSWILLCAPITALIZEONDIGITALTECHNOLOGYTOFARGREATER EXTENTS$IGITALTECHNOLOGYHASTHEPOTENTIALFLEXIBILITYTOTAILORSATELLITE ASSETSTOCHANGINGDEMANDSFORSATELLITERESOURCESTHATEVOLVEOVERTHE SATELLITESLIFETIME-EMORYTECHNOLOGYCANBEUSEDTOAVERAGEOUTTHE PEAKCAPACITYDEMANDSBYSTORINGDATATHATARENOTTIMECRITICALWHEN CAPACITYDEMANDSAREATTHEIRPEAKLEVELSANDBROADCASTINGSTOREDDATA ASCAPACITYBECOMESAVAILABLE$IGITALTECHNOLOGYCANALSOBEUSEDIN FREQUENCYTRANSLATINGREPEATERSWHERETHETRANSPONDERUSESADIGITAL CHANNELIZERTOSEPARATEUSERSRECEIVEDINAGIVENFREQUENCYSUBBAND ENABLINGTHEROUTINGOFINDIVIDUALUSERSTODIFFERENTDOWNLINKSUBBANDS THATSERVEDIFFERENTCOVERAGEAREAS4HISUSERSIGNALSEPARATIONCAPABIL ITYPROVIDESADDEDFLEXIBILITYINROUTINGUSERTRAFFIC /THERSPACESEGMENTARCHITECTURESPROVIDESERVICESFORDIRECTBROAD CAST POINT TO POINT LINKS FOR CROSSLINK AND EARTH LINK CAPABILITIES AND 44#REQUIREMENTS$IRECTBROADCASTSERVICESCANEITHERBROADCASTSIG NALSRECEIVEDFROMANUPLINKTRANSMISSION ASISTHECASEFORSATELLITE46 BROADCAST ORBROADCASTINFORMATIONDERIVEDONBOARDTHESATELLITE0OINT TO POINTARCHITECTURESPROVIDECONNECTIVITYBETWEENSATELLITESINCROSSLINK DESIGNSORINEARTHLINKSERVICESSUCHASSATELLITE TO GATEWAYCOMMUNICA TIONS#ROSSLINKCAPABILITIESALLOWGLOBALCOMMUNICATIONSBETWEENUSERS THATDONOTHAVEMUTUALVISIBILITYTOACOMMONSATELLITEANDINTHISWAY ADDITIONALRELAYSTHROUGHGROUNDRELAYSTATIONSARENOTREQUIRED%VERY SATELLITEREQUIRESA44#SUBSYSTEMTHATASSISTSINDETERMININGTHESAT ELLITESORBITALLOCATION REPORTSTHEHEALTHANDSTATUSOFTHESATELLITE AND PROVIDESACOMMANDINGCAPABILITYFORSATELLITEOPERATION &REQUENCY4RANSLATING4RANSPONDER

4HE FREQUENCY TRANSLATING TRANSPONDER ARCHITECTURE DESCRIBED IN &IG ISASIMPLEARCHITECTUREANDTHEMOSTWIDELYUSED4HEUPLINK SIGNALSCOLLECTEDBYTHERECEIVEANTENNASAREPREAMPLIFIEDTOESTABLISH

#HAPTER 4HREE

&IGURE &REQUENCYTRANSLATINGTRANSPONDER

THEUPLINKSYSTEMNOISELEVEL4HEUPLINKSIGNALCOLLECTIONISTRANSLATED TOTHEDOWNLINKFREQUENCYASSIGNMENTBYAFREQUENCYCONVERTERS )N PRACTICE THEFREQUENCYCONVERTERISSIMPLYAMIXER ASTABLELOCALOSCILLA TOR AFILTERTOREJECTTHEIMAGEFREQUENCY ANDANAMPLIFIER)NSOMECASES THEFREQUENCYCONVERSIONISPERFORMEDINMORETHANONESTEP)NTHIS WAY THEUPLINKFREQUENCIESAREMAPPEDINTOTHEDOWNLINKFREQUENCIES BYAFIXEDFREQUENCYOFFSETFOLLOWINGTHISTRANSPONDERSNAME3UITABLE AMPLIFICATION IS THEN PROVIDED TO MEET THE TRANSMITTED POWER LEVELS 4HEAMPLIFICATIONCANBEVARIEDBYGROUNDCOMMANDTHROUGHTHE44# SUBSYSTEMTOOPTIMIZETHEPOWERLEVELOFTHETRANSMITTER 3ATELLITE TRANSMITTERS ARE TYPICALLY OPERATED NEAR THEIR SATURATED OUTPUTLEVELTOOBTAINTHEMOSTPOWER EFFICIENTTRANSMITTEROPERATION (OWEVER THENONLINEARBEHAVIOROFTHETRANSMITTERNOTONLYRESULTSIN INTERMODULATIONPRODUCTSFROMMULTIPLEUSERSSHARINGTHETRANSPONDER BUTITALSODISTORTSTHESIGNALMODULATION THUSDEGRADINGCOMMUNICA TIONPERFORMANCE4HEOUTPUTPOWEROFTHETRANSMITTERMUSTTHEREFOREBE CONTROLLEDTOACHIEVETHEMAXIMUMLEVELSCONSISTENTWITHANACCEPTABLE DEGRADATIONINUSERSIGNALRECEPTION4HETRANSPONDERSPOWEROUTPUTIS CONTROLLEDBYTHETRANSPONDERSANALOGGAINNOTONLYTOCOMPENSATEFOR ON ORBITTRANSPONDERGAINVARIATIONSBUTALSOTOMAINTAINTHEDESIRED TRANSMITTEROPERATINGPOINTUNDERDIVERSEUSERLOADINGCONDITIONS4HE 44#SUBSYSTEMNOTONLYCOMMANDSTHETRANSPONDERGAINSETTINGBUT ALSOSELECTSANTENNABEAMSANDPOINTINGDIRECTIONS COMMANDSREDUN DANTELEMENTSTOREPLACEFAILURES ANDMONITORSTHEHEALTHANDSTATUS VIATELEMETRYOUTPUTS 3IMPLICITYISTHEPRINCIPALADVANTAGEOFTHISTRANSPONDERAND ATTHE SAME TIME ITS PRINCIPAL DISADVANTAGE4HESE TRANSPONDERS ARE EASILY CONSTRUCTED AND THUS MINIMIZE THE VERY IMPORTANT 37A0 IN SATELLITE SYSTEMS"ECAUSEOFTHIS THEFREQUENCYTRANSLATINGDESIGNISTHEMOST COMMON TRANSPONDER ARCHITECTURE! GENERIC OPERATIONAL PROBLEM IS MAINTAININGPOWERCONTROLAMONGTHEINDIVIDUALUSERSSOEACHUSERHAS ITSEQUABLESHAREOFTHESATELLITEDOWNLINKTRANSMITTER4HEGOALOFOPER ATING THE TRANSPONDER TRANSMITTER NEAR ITS SATURATED OUTPUT LEVEL TO MAXIMIZEPOWEREFFICIENCYREQUIRESPOWERCONTROLAMONGTHEINDIVIDUAL USERS!FREQUENCYTRANSLATINGTRANSPONDERDOESNOTDISTINGUISHBETWEEN


DESIREDSIGNALSANDINTERFERENCEANDITSOPERATIONCANBEDEGRADEDBY STRONGINTERFERENCE&INALLY SINCEINDIVIDUALUSERSARENOTSEPARATEDIN AFREQUENCYTRANSLATINGTRANSPONDER USERCONNECTIVITYINDIFFERENTCOVER AGEAREASREQUIRESDIVIDINGTHEFREQUENCYINTOSUBBANDSSOCONNECTIVITY TODIFFERENTCOVERAGEAREASCANBEPROVIDED 4RANSMITTERS;=HAVEALIMITEDPOWEROUTPUT)FTHEINPUTPOWERLEVELS TOTHETRANSMITTERAREALLOWEDTOINCREASE EVENTUALLYTHEPOWEROUTPUT OFTHETRANSMITTERWILLNOTINCREASEABOVEAMAXIMUMLEVEL COMMONLY REFERREDTOASTHESATURATEDOUTPUTPOWER4HEAMPLIFICATIONATSATURATION ISNONLINEAR WHICHDEGRADESCOMMUNICATIONRECEPTIONASARESULTOFINTER MODULATIONPRODUCTSBETWEENMULTICARRIERSIGNALS SIGNALSUPPRESSION ANDSIGNALDISTORTIONTHATINCLUDESSPECTRALREGROWTHOFTHESIGNALSMOD ULATIONSIDELOBES THUSINCREASINGCO CHANNELINTERFERENCELEVELS 4WOALTERNATIVESPECIFICATIONSAREUSEDBYVENDORSTOCHARACTERIZETHE SIGNALLEVELSTHATRESULTINANONLINEARRESPONSEFROMTHEIRDEVICES4HE FIRSTALTERNATIVESPECIFICATIONISAD"COMPRESSIONPOINTDEFINEDBYA D" DEVIATION FROM THE DEVICES LINEAR GAIN RESPONSE AT SMALL SIGNAL INPUTPOWERS&OREXAMPLE ATYPICAL,.!HASAD"COMPRESSIONPOINT WHENITSOUTPUTLEVELISABOUTTOD"M!SECONDALTERNATIVESPECIFI CATIONISTHETHIRD ORDERINTERCEPTPOINT4HETHIRD ORDERINTERMODULATION PRODUCTISDETERMINEDBYEXCITINGTHEDEVICEWITHTWOEQUALAMPLITUDE #7CONTINUOUSWAVE TONESANDINCREASINGTHEINPUTPOWERLEVELSOFTHE TONESWHILEOBSERVINGTHEGROWTHOFTHEINTERMODULATIONPRODUCTLEVELOF THETONES4HESMALLSIGNALLEVELGAINRESPONSEISLINEARLYEXTRAPOLATEDTO REGIONSWHERETHEDEVICESPOWERISNONLINEAR4HISLINEARGAINRESPONSE HAS A ONE TO ONE CORRESPONDENCE BETWEEN THE OUTPUT AND INPUT SIGNAL LEVELS4HEINTERMODULATIONPRODUCTHASACUBICVARIATIONWITHINPUTPOWER LEVELS4HETHIRD ORDERINTERCEPTLEVELISTHESIGNALINPUTLEVELWHERETHE EXTRAPOLATEDLINEARRESPONSEOFTHESMALLSIGNALGAINANDTHEEXTRAPOLATED CUBICRESPONSEOFTHETHIRD ORDERINTERMODULATIONRESPONSEINTERCEPTAND AREEQUAL )N OPERATION SATELLITE TRANSPONDERS GENERALLY SUPPORT A MULTICAR RIERSIGNALCOLLECTION ANDTHEINTERMODULATIONPRODUCTSPECTRAISMORE VARIED THAN THAT FOR TWO #7 TONES SO THAT MULTIPLE CARRIER DISTORTION SIDEBANDSARENOTFULLYADDRESSED!NALTERNATIVEMEASUREMENTAPPROACH REPLACESTHETWO#7TONESBYTWOSEPARATEDNOISESPECTRAHAVINGSUF FICIENTFILTERINGTOALLOWOBSERVINGTHELINEARNOISEPOWERLEVELSBETWEEN THETWOSPECTRAFORLINEARSMALLSIGNALOPERATION4HEPOWERLEVELSOFTHE TWONOISESPECTRAAREINCREASEDTOVALUESRESULTINGINNONLINEAROPERA TIONANDTHEINTERMODULATIONSPECTRABETWEENNOISECOMPONENTSRESULT IN INCREASED POWER LEVELS IN THE BANDWIDTH OCCUPIED BY NOISE POWER WHENTHESYSTEMRESPONSEISLINEAR4HE.02NOISEPOWERRATIO ISTHE POWERDIFFERENCEBETWEENTHEAMPLIFIEDNOISELEVELANDTHEPOWERLEVEL WITHINTHEBANDWIDTHBETWEENTHEORIGINALTWONOISESPECTRA4HE.02

#HAPTER 4HREE

CHARACTERIZATIONMAYBETHOUGHTOFASAGENERALIZATIONOFTHESTANDARD TWO#7TONECHARACTERIZATIONUSEDTOOBTAINTHETHIRD ORDERINTERCEPT PARAMETER BUTACHARACTERIZATIONTHATISMOREREALISTICINREPRESENTING THEINTERMODULATIONSPECTRAFORMULTICARRIEROPERATION&URTHEREVALUA TIONOF.02TECHNIQUES;=EXPRESSESCONCERNREGARDINGSIGNALDISTORTION CHARACTERIZATIONS BY SUCH TECHNIQUES AND PROPOSES OTHER MEASURES TO CHARACTERIZECO CHANNELDISTORTIONEFFECTS 7HILETHESEALTERNATIVESPECIFICATIONSOFNONLINEARDEVICERESPONSEARE COMMONLYUSEDTOQUANTIFYDEVICENONLINEARPERFORMANCE THEIMPACT ONCOMMUNICATIONSIGNALSREQUIRESAREPRESENTATIONOFTHEDEVICESNON LINEAR RESPONSE .ONLINEAR AMPLIFIER CHARACTERISTICS ARE SPECIFIED BY !- !-DISTORTIONTHATDESCRIBESTHEAMPLIFIERSGAINCOMPRESSIONAND THE!- 0-DISTORTIONTHATDESCRIBESTHEAMPLITUDE PHASEDISTORTION )NPRACTICE SATELLITETRANSMITTERSGENERALLYOPERATEATAPOWEROUTPUT LEVELhBACKEDOFFvFROMTHEIRNONLINEARSATURATEDPOWEROUTPUTLEVELTO MAINTAINOPERATIONTHATISSUFFICIENTLYLINEARTOCONTROLTHEDEGRADATION TOUSERSIGNALRECEPTION4HEREQUIREDAMOUNTOFBACKOFFDEPENDSONTHE AMPLIFIERSNONLINEARRESPONSEANDTHESENSITIVITYOFTHEUSERSMODULA TIONFORMATSTODISTORTION 4HENONLINEARRESPONSEOFTHEAMPLIFIERISCHARACTERIZEDBYMEASURE MENTTECHNIQUESTHATAREUSEDTODEVELOPNONLINEARMODELSTOASSESSTHE IMPACTSONCOMMUNICATIONSYSTEMPERFORMANCE6ECTORNETWORKANA LYZERMEASUREMENTSPROVIDEONEMEANSOFMEASURINGTHE!-!-AND !-0-PARAMETERSASAFUNCTIONOFTHEINPUTSIGNALLEVEL-OREACCURATE MEASUREMENTTECHNIQUES; =HAVEBEENDEVELOPEDANDDEMONSTRATED TODYNAMICALLYCHARACTERIZEBOTHSOLIDSTATEAND474AMPLIFIERS4HE RESULTINGMEASUREMENTSWEREUSEDTODEVELOPAhBOXvMODELINGREPRE SENTATIONOFANONLINEARAMPLIFIER4HEIMPACTSOFAMPLIFIERNONLINEARI TIESONSIGNALRECEPTIONPERFORMANCEHAVEBEENADDRESSED;=ANDTHE TOLERANCES FOR NONLINEAR AMPLIFIER RESPONSES TO DIFFERENT MODULATION FORMATSAREQUANTIFIED&INALLY RECENTDEVELOPMENTATTENTIONHASBEEN PAIDTOLINEARIZERS; =THATMODIFYTHEINPUTSIGNALSUSINGFEEDFOR WARD PREDISTORTION ORADAPTIVETECHNIQUESTOALLOWOPERATIONCLOSERTO THEAMPLIFIERSSATURATEDOUTPUTLEVEL)NTHISWAY SOMEWHATINCREASED TRANSMITTERPOWEROUTPUTLEVELSCANBEOBTAINEDWHILEMAINTAININGSUF FICIENTLINEARITYTOSATISFYSIGNALFIDELITYREQUIREMENTS 4HEPRECEDINGCONSIDERATIONSANDDESIGNAPPROACHESFORMTHEBASISOF ESTABLISHINGADESIGNTRANSMITTEROPERATINGPOINTTHATDETERMINESTHE AMOUNTOFTRANSMITTERBACKOFFTOBEMAINTAINEDDURINGSYSTEMOPERA TION4YPICALLY THE TRANSPONDER CONTAINS AN ANALOG GAIN CONTROL THAT CANBECOMMANDEDTOMAINTAINTHEDESIREDOPERATINGPOINT4HISGAIN CONTROLISGENERALLYINTHEDRIVEELECTRONICSANDESTABLISHESTHEINPUT POWER TO THE FINAL TRANSMIT AMPLIFIER &OR THE FREQUENCY TRANSLATING TRANSPONDER INDIVIDUAL USER SIGNALS ARE NOT SEPARATED AND THUS THE


INPUTSIGNALPOWERISSUBJECTTOVARIATIONSINTHEUPLINKUSERSIGNALSAS WELLASTHENUMBEROFSYSTEMUSERS $ISCIPLINEAMONGTHEINDIVIDUALUSERSISREQUIREDTOMEETTHEGOALS OFOPERATINGTHETRANSMITTERNEARSATURATEDCONDITIONSANDMAINTAIN INGANEQUABLEDISTRIBUTIONOFTHEDOWNLINKPOWER5SERSWITHHIGHER SIGNALPOWERSWITHINTHETRANSPONDERHAVEAGREATERSHAREOFTHELIMITED DOWNLINKTRANSMITTERPOWER)FANINDIVIDUALUSERINCREASESITSUPLINK POWERLEVELTOENHANCEITSOWNLINKPERFORMANCE AGREATERSHAREOFTHE DOWNLINKPOWERISAVAILABLETOTHATUSERTOTHEDETRIMENTOFTHEOTHER USERS)FTHEENTIREUSERCOLLECTIONINCREASESTHEUPLINKSIGNALPOWEROR IF ADDITIONAL USERSACCESS THE SATELLITE THE UPLINK INPUTPOWER LEVELS INCREASE3INCETHEELECTRONICSGAINTHROUGHTHETRANSPONDERHASAFIXED BUTSELECTABLELEVEL THEINCREASEDUPLINKINPUTPOWERLEVELRESULTSIN TRANSMITTEROPERATIONMORECLOSELYLOCATEDTOTHENONLINEARREGION4HE TRANSPONDERGAININTHISCASEMUSTBEREDUCEDBYCOMMANDTOMAINTAINTHE DESIGNOPERATINGPOINTOFTHEFINALAMPLIFIERINTHETRANSMITTER4HUS THE TRANSMITTED LEVELS AMONG THE INDIVIDUAL USERS AND VARIATIONS IN THETOTALUPLINKSIGNALPOWERMUSTBECONTROLLEDTOACHIEVETHEPROPER POWERBALANCESOEACHUSERHASITSEQUABLESHAREOFSATELLITERESOURCES ANDTHETRANSMITTERDESIGNOPERATINGPOINTISMAINTAINEDTOPROVIDEAS MUCHDOWNLINKPOWERASPOSSIBLEWHILESATISFYINGTHELINEARITYREQUIRED FORUSEROPERATION4HERESPONSIBILITYTOMAINTAINTHEDOWNLINKTRANS MITTERDESIGNOPERATINGPOINTRESTSWITHTHEMISSIONCONTROLSEGMENTS SELECTIONOFTHETRANSPONDERGAINSETTING 7HILEDISCIPLINEAMONGUSERSISREQUIRED INSOMEAPPLICATIONS LINK IMPAIRMENTSFURTHERCONFOUNDTHEPROBLEM!SDISCUSSEDIN#HAPTER %(&EXTREMELYHIGHFREQUENCY SYSTEMSAREIMPACTEDBYWEATHER PAR TICULARLYRAINFALLTHATATTENUATESUPLINKANDDOWNLINKSIGNALS3IMILARLY AVARIETYOFLINKIMPAIRMENTSIMPACT5(&ULTRAHIGHFREQUENCY SYS TEMS )N SUCH CASES USER POWER CONTROL TECHNIQUES ARE ADDRESSED TO MAINTAINUSERLINKPERFORMANCE%XPERIMENTSUSINGTHE.!3!!#43 PROGRAM;=PROVIDEANEXPERIMENTALDEMONSTRATIONOFOPEN LOOPTECH NIQUES )N THESE EXPERIMENTS POWER CONTROL OVER AN D" DYNAMIC RANGEWASEXERCISEDANDTHEPOWERCONTROLACCURACYDURINGRAINEVENTS WASBELIEVEDTOBEABOUTD"!NOTHERAPPROACHINTEGRATESARADIO METRICSENSORINTOAFREQUENCYHOPPED%(&SYSTEM;=TOPROVIDEACOST EFFECTIVEMEANSOFPOWERCONTROL&INALLY ASATELLITEBEACONSYSTEMFOR 5(&COMMUNICATIONS;=ANDAUSERRECEIVERUSINGTHISBEACONSIGNAL HAVEBEENPROPOSEDTOPROVIDEAREAL TIMEINDICATIONOFTHESEVERITYOF SEVERALLINKIMPAIRMENTS TOINDICATECOMMUNICATIONCAPABILITIES AND TOPROVIDETHEBASISOFPOWERCONTROLTECHNIQUES 3TRONG INTERFERENCE IS AN EVEN MORE SEVERE PROBLEM FOR FREQUENCY TRANSLATINGTRANSPONDERSANDDEGRADESTHEIRDOWNLINKPERFORMANCEIN SEVERAL WAYS )NTERFERENCE OBSCURES DESIRED USER SIGNALS THAT OCCUPY

#HAPTER 4HREE

THESAMESPECTRAASTHEINTERFERENCEDEGRADINGUSERRECEPTION3INCETHE TRANSMITTERISOPERATEDCLOSETOITSSATURATEDLEVELUNDERINTERFERENCE FREE CONDITIONS STRONG INTERFERENCE DRIVES THE TRANSMITTER INTO ITS NONLINEARREGION SUPPRESSINGTHEDESIREDSIGNALSASWELLASDISTORTING THEMANDGENERATINGUNDESIREDINTERMODULATIONPRODUCTS/PERATIONAT THETRANSMITTERSDESIGNOPERATINGPOINTCANBERESTOREDBYSELECTINGAN APPROPRIATETRANSPONDERGAINLEVELTOALLOWUSERRECEPTIONINSPECTRAL REGIONSNOTOBSCUREDBYINTERFERENCE(OWEVER DOWNLINKRESOURCESARE WASTEDBECAUSEINTERFERENCEPOWERISBEINGTRANSMITTED REDUCINGTHE DOWNLINKPOWERAVAILABLETOUSERSIGNALS4HUS AFUNDAMENTALLIMITA TIONOFTHEFREQUENCYTRANSLATINGTRANSPONDERDESIGNISITSSUSCEPTIBILITY TOINTERFERENCESIGNALS !SIDEFROMTHEINHERENTPROBLEMSOFUSERPOWERCONTROLANDINTERFER ENCESUSCEPTIBILITY ANADVANTAGEOFFREQUENCYTRANSLATINGTRANSPONDERS INADDITIONTOTHEIRDESIGNSIMPLICITYISTHATITISTRANSPARENTTOITSUSE 5SERFREQUENCYASSIGNMENTSWITHININDIVIDUALTRANSPONDERBANDWIDTHS CANBEVARIED MULTIPLEACCESSTECHNIQUESAMONGTHESYSTEMUSERSCAN BECHANGED ANDDIFFERENTMODULATIONFORMATSCANBEUSED4HUS THEFRE QUENCYTRANSLATINGTRANSPONDERHASASIGNIFICANTAMOUNTOFFLEXIBILITYIN THEWAYINWHICHITSRESOURCESAREUSEDDURINGTHESATELLITESLIFETIME 4HEBASICTRANSPONDERDESIGNHASBEENAPPLIEDTOAVARIETYOFPROGRAM APPLICATIONSANDDIFFERINGFREQUENCYPLANSTHATDIVIDETHEALLOCATEDFRE QUENCYBANDINTODIFFERENTCHANNELSANDCOVERAGEAREASTHATSUBDIVIDE THESATELLITESFIELDOFVIEWINTODIFFERENTREGIONSSERVEDBYTHEANTENNA SYSTEMDESIGN3MALLANTENNABEAMWIDTHS ORTHOGONALPOLARIZATIONS AND DIVISIONOFTHEBANDWIDTHINTOSUBBANDSISOLATESEPARATEDCOVERAGEAREAS WITHINTHEFIELDOFVIEW4HEISOLATIONBETWEENCOVERAGEAREASALLOWSREUS ING THE SAME FREQUENCY SUBBANDS FOR INDEPENDENT DATA STREAMS THUS INCREASINGTHETHROUGHPUTCAPACITYANDEFFICIENTLYUSINGTHEFREQUENCY ALLOCATIONS4HESETECHNIQUESAREREFERREDTOASFREQUENCYANDPOLARIZA TIONREUSE RESPECTIVELYANDWILLBEDISCUSSEDINMOREDETAILLATER 0RACTICAL SATELLITE SYSTEMS PROVIDE COVERAGE TO DIFFERENT PORTIONS OFTHEAVAILABLEFIELDOFVIEW ANDUSETHEFREQUENCYANDPOLARIZATION REUSE TECHNIQUES TO ISOLATE COMMUNICATIONS BETWEEN COVERAGE AREAS 'ENERALLY COMMUNICATIONCONNECTIVITYWITHUSERSISREQUIREDNOTONLY WITHINTHESAMECOVERAGEAREABUTALSOBETWEENCOVERAGEAREAS!SA RESULTTHEAVAILABLEFREQUENCYALLOCATIONSAREDIVIDEDINTOSUBBANDSTO PROVIDETHECONNECTIVITYFLEXIBILITY!SIMPLEEXAMPLEIN&IG ILLUS TRATESTHESETECHNIQUESWHERETWOCOVERAGEAREAS !AND" ARELOCATED WITHIN THE FIELD OF VIEW4HE ALLOCATED BANDWIDTH IN THIS EXAMPLE IS DIVIDEDINTOFOURSUBBANDSASILLUSTRATEDIN&IG WHERE!AND" PROVIDECONNECTIVITYWITHINTHEIRRESPECTIVECOVERAGEAREASAND!AND "PROVIDECONNECTIVITYBETWEENTHETWOCOVERAGEAREAS!FUNCTIONAL DESCRIPTION OF THE TRANSPONDER FOR THIS CASE IS ILLUSTRATED IN &IG DESCRIBINGTHESUBBANDCHANNELIZATION


&IGURE %XAMPLECOVERAGEAREAS

&IGURE %XAMPLE&REQUENCYPLAN

&IGURE #HANNELIZEDTRANSPONDERFUNCTIONDIAGRAM

4HE).4%,3!46))6))!TRANSPONDERARCHITECTURE;=DESCRIBESA REPRESENTATIVECOMMERCIALDESIGN4HISTRANSPONDEROPERATESINTWO FREQUENCYBANDS # AND+U BAND"OTHFREQUENCYREUSEANDPOLARIZA TIONREUSETECHNIQUESAREUSEDTOEXPANDSYSTEMCAPACITY!TOTALOF

#HAPTER 4HREE

# BAND TRANSPONDERS AND SIX +U BAND TRANSPONDERS ARE USED IN THIS DESIGN THAT ILLUSTRATE THE PROLIFERATION OF THE FREQUENCY TRANS LATINGTRANSPONDERARCHITECTURESWITHINASINGLESATELLITETOPROVIDE COMMUNICATIONCAPABILITIESTOTHEVARIOUSCOVERAGEAREAS4HEANTENNA SYSTEMDESIGNPROVIDESGLOBAL HEMISPHERIC ZONEANDSPOTBEAMS4HE ANTENNADESIGNISBASEDONREFLECTORTECHNOLOGYANDDESIGNATTENTION HASBEENPAIDTOPOLARIZATIONPURITYTOMAINTAINISOLATIONINTHEPOLAR IZATION REUSE PLAN4HE # BAND ANTENNAS PROVIDE HEMISPHERIC AND GLOBALCOVERAGEAREASBYCOMBININGFEEDHORNS WHILETHE+U BAND ANTENNASPROVIDESTEERABLESPOTCOVERAGEAREAS"OTHFREQUENCYAND POLARIZATIONREUSETECHNIQUESDESCRIBEDMOREFULLYIN#HAPTER ARE USEDBYTHISTRANSPONDERARCHITECTURETOUSETHEAVAILABLEFREQUENCY ALLOCATIONEFFICIENCYBYUSINGTHESAMEFREQUENCYSIMULTANEOUSLYIN DIFFERENTCOVERAGEAREASANDINORTHOGONALPOLARIZATIONS4HEABILITY TOSERVICEDIFFERENTCOVERAGEAREASINDEPENDENTLYANDSIMULTANEOUSLY ANDTOOPERATEUSINGORTHOGONALPOLARIZATIONSILLUSTRATESTHESIGNIFI CANTROLETHATPAYLOADANTENNASPLAYINMODERNSATELLITESYSTEMS4HE TRANSPONDER ARCHITECTURE DESCRIBED IN THIS REFERENCE ILLUSTRATES THE USEOFSUBBANDSANDPOLARIZATIONANDFREQUENCYREUSETECHNIQUESTHAT INCREASETHEFLEXIBILITYTOPROVIDECOMMUNICATIONNETWORKSLINKING DIFFERENTCOVERAGEAREAS 2EGENERATIVE2EPEATER4RANSPONDERS

4HESECONDTYPEOFTRANSPONDERDESIGN THEREGENERATIVEREPEATERILLUS TRATEDIN&IG ADDRESSESSOMEOFTHELIMITATIONSOFTHEFREQUENCY TRANSLATINGTRANSPONDERARCHITECTUREATTHEEXPENSEOFINCREASEDIMPLE MENTATIONCOMPLEXITY,IKETHEFREQUENCYTRANSLATINGTRANSPONDER THE SYSTEMNOISETEMPERATUREISESTABLISHEDBYTHEPREAMPLIFIERANDFRE QUENCYCONVERSIONISUSED4HISTYPEOFTRANSPONDERDEMODULATESTHE UPLINKSIGNALCOLLECTIONTOSEPARATEINDIVIDUALUSERS4HEDEMODULATED SIGNALSWITHINTHISCOLLECTIONAREINDIVIDUALLYROUTEDANDMULTIPLEXED WITHOTHERUPLINKSIGNALSTOFORMDOWNLINKCHANNELSTHATAREREMODU LATED AMPLIFIED AND RETRANSMITTED4HUS THE UPLINK INFORMATION IS hREGENERATEDvFORDOWNLINKTRANSMISSION)NSOMECASES THEDEMODULA TIONWITHINTHETRANSPONDERMAYNOTBECOMPLETELYDONE&OREXAMPLE IN SYSTEMSUSINGSPREADSPECTRUMMODULATION;= THETRANSPONDERMIGHT

&IGURE !REGENERATIVEREPEATERTRANSPONDER


ONLYDESPREADTHEUPLINKSIGNALSRATHERTHANFULLYDEMODULATETHEM 4HESE DESPREAD SIGNALS CAN BE REMODULATED RESPREAD AND RETRANS MITTED!NY UPLINK INTERFERENCE IS DESPREAD AND THEREBY REDUCED BY THESPREADSPECTRUMPROCESSINGGAINTOREDUCETHERADIATEDDOWNLINK INTERFERENCERADIATEDPOWER4HEREDUCEDDOWNLINKINTERFERENCEPOWER RESULTSINANINCREASEDAMOUNTOFDOWNLINKPOWERBEINGAVAILABLETO THEDESIREDUSERS6ARIATIONSOFTHISTRANSPONDERARCHITECTUREANDTHEIR BENEFITS HAVE BEEN KNOWN FOR A LONG TIME HOWEVER IMPLEMENTATION OFTHESEARCHITECTURESAWAITEDTHETECHNOLOGYDEVELOPMENTOFSUITABLE PAYLOAD CAPABILITIES AND MANUFACTURING TECHNIQUES FOR THE REQUIRED PROCESSINGEQUIPMENTWITHINREASONABLEWEIGHTANDPOWERRESTRICTIONS 4HECAPABILITIESRELYON!3)#!PPLICATION3PECIFIC)NTEGRATED#IRCUIT AND--)#-ONOLITHIC-ICROWAVE)NTEGRATED#IRCUIT TECHNOLOGIESTO ACHIEVEPRACTICALDESIGNSWITHREASONABLE37A0 4HE REGENERATIVE REPEATER TRANSPONDER ARCHITECTURE ADDRESSES THE PRINCIPAL DISADVANTAGES OF THE FREQUENCY TRANSLATING TRANSPONDER AND PROVIDESROUTINGFLEXIBILITYFORINDIVIDUALUSERSANDREDUCEDSUSCEPTIBILITY TO INTERFERENCE 3INCE THE INDIVIDUAL USERS ARE SEPARATED IN THE TRAN SPONDER FLEXIBILITY TO ROUTE INDIVIDUAL USERS TO DESIRED COVERAGE AREAS ANDPOWERLEVELINGFOREACHUSERCANALSOBEPERFORMEDWITHINTHETRAN SPONDERSOEACHUSEROBTAINSAFAIRSHAREOFTHESATELLITEDOWNLINK4HE INTERFERENCEPOWERISREDUCEDBYTHEDEMODULATIONPROCESSPRIORTOTRANS MISSIONSOTHATTHEDOWNLINKRESOURCESARENOTWASTEDBYTRANSMITTING INTERFERENCE POWER4HUS THE INDIVIDUAL USERS ENJOY REDUCED INTERFER ENCETHROUGHPROCESSINGANDRECEIVINGMOREOFTHEDOWNLINKPOWERSINCE INTERFERENCE POWER IS NOT BEING TRANSMITTED )N FUTURE SYSTEM DESIGNS FORPERSONALCOMMUNICATIONS SOMEOFTHEPOTENTIALCHANNELSMAYNOTBE OCCUPIEDCONTINUOUSLY ANDBYDEMODULATINGANDRETRANSMITTINGONLYTHE OCCUPIEDCHANNELS THEDOWNLINKTRANSMITTERRESOURCESARENOTWASTEDBY TRANSMITTINGTHENOISEPOWERINUNOCCUPIEDCHANNELS 7HILETHEREGENERATIVEREPEATERTRANSPONDERADDRESSESTHEINHERENT LIMITATIONSOFTHEFREQUENCYTRANSLATINGTRANSPONDERDESIGN THEREGEN ERATIVE REPEATER IS INHERENTLY MORE COMPLEX4HIS INHERENT COMPLEX ITYTRANSLATESINTOADDITIONALWEIGHTANDPOWERREQUIREMENTSFORTHE SATELLITETRANSPONDER WHICHISNOTDESIRABLE)NADDITION THEINHERENT FLEXIBILITYOFTHEFREQUENCYTRANSLATINGTRANSPONDERDESIGNSINUSINGTHE CHANNEL BANDWIDTHS WITH DIFFERENT MULTIPLE ACCESS TECHNIQUES MOD ULATION FORMATS AND NUMBER OF USERS IS LIMITED BY THE REGENERATIVE REPEATER DESIGN7HEN THE DEMODULATION AND REMODULATION CIRCUITRY OF THE REGENERATIVE REPEATER IS IMPLEMENTED USING ANALOG TECHNOL OGY OPTIONSTOCHANGEMODULATION MULTIPLEACCESSFORMATS ANDSOON DISCUSSEDIN#HAPTER DURINGTHESATELLITESLIFETIMEAREUNAVAILABLE $IGITALIMPLEMENTATIONSPROVIDEPOTENTIALFLEXIBILITYTOALTERMODULA TIONANDMULTIPLEACCESSSCHEMESON ORBIT4HEADDITIONALCOMPLEXITYOF

#HAPTER 4HREE

THEREGENERATIVEREPEATERTRANSPONDERISTHEREFOREJUSTIFIEDWHENTHE SYSTEMREQUIREMENTSDEMANDPROTECTIONFROMINTERFERENCEORWHENTHE FLEXIBILITYISREQUIREDINROUTINGINDIVIDUALUSERSTOAVARIETYOFCOVER AGEAREAS 4HETRANSPONDERDESIGNFORTHEREGENERATIVEREPEATERILLUSTRATEDIN &IG INDICATESTHEMANNERINWHICHCONNECTIVITYISPROVIDEDFORUSERS WITHINTHESAMECOVERAGEAREAANDFORUSERSINDIFFERENTCOVERAGEAREAS !GAINTHESAMEEXAMPLECOVERAGEAREASILLUSTRATEDIN&IG WILLBE USEDANDISOLATIONBETWEENCOVERAGEAREASWILLAGAINBEPROVIDEDBY FREQUENCY AND POLARIZATION REUSE PLANS %ACH ANTENNA SEPARATES ITS RECEIVEDSIGNALCOLLECTIONINTOINDIVIDUALUSERDATASTREAMSANDDEMOD ULATESTHOSEDATASTREAMS!SWITCHNETWORKROUTESTHEDEMODULATED DATASTREAMSTOTHEAPPROPRIATEDOWNLINKBEAMWHERETHECOLLECTIONOF MULTIPLEXEDDATASTREAMSISREMODULATEDFORDOWNLINKTRANSMISSIONS )N COMPARISON TO THE FREQUENCY TRANSLATING TRANSPONDER ARCHITECTURE DISCUSSED EARLIER THE REGENERATIVE REPEATER TRANSPONDER REQUIRES DIVIDING THE ALLOCATED FREQUENCY INTO SUBBANDS FOR FREQUENCY REUSE PURPOSES5NLIKETHEFREQUENCYTRANSLATINGTRANSPONDER SUBBANDSARE NOT REQUIRED TO PROVIDE USER CONNECTIVITY BETWEEN DIFFERENT COVERAGE AREAS4HEREDUCEDNUMBEROFSUBBANDSPROVIDESSOMESIMPLIFICATION OF THE TRANSPONDERS ANALOG CIRCUITRY AT THE EXPENSE OF CHANNELIZERS DEMODULATORS SWITCH MATRICES MULTIPLEXERS AND REMODULATORS4HE ADVANCES IN DIGITAL TECHNOLOGY ANTICIPATED IN FUTURE YEARS WILL MAKE THEREGENERATIVEREPEATERARCHITECTUREMOREATTRACTIVE 4HE)4!,3!4MULTIPLEBEAMTRANSPONDER;=ISANEXAMPLEOFTHE REGENERATIVEREPEATERARCHITECTUREANDSERVICESSIXDIFFERENTCOVERAGE AREASCOVERINGTHE)TALIANNATION4HEFREQUENCYPLANPROVIDESSIXSUB BANDSTOISOLATETHEBEAMSANDEACHBEAMHASA-(ZBANDWIDTH 4HESIXCOVERAGEAREASAREPRODUCEDBYUSINGTWOREFLECTORANTENNAS ANDEACHANTENNAPROVIDESTHREEINDEPENDENTBEAMS4HESYSTEMOPER ATESAT+A BANDFREQUENCIES ANDTHEANTENNABEAMWIDTHSFORTHESER VICEAREASARESUFFICIENTLYSMALLTHATACTIVETRACKINGOFGROUNDBEACONS IS REQUIRED TO MAINTAIN COVERAGE ALIGNMENT IN THE PRESENCE OF SATEL LITEATTITUDEVARIATIONS4HEUPLINKDATAISDEMODULATEDONBOARDAND

&IGURE 2EGENERATIVEREPEATERARCHITECTUREFORMULTIPLEBEAMS


SWITCHEDANDROUTEDTOTHEAPPROPRIATESERVICEAREA4HISSYSTEMUSES A SPREAD SPECTRUM TIME DIVISION MULTIPLE ACCESS WAVEFORM AND USER ASSIGNMENTTOTHESATELLITERESOURCESSOTHATHIGHCAPACITYANDFLEXIBIL ITYISACHIEVED/THEREXAMPLESOFREGENERATIVEARCHITECTUREAREUSEDIN MILITARYAPPLICATIONSTOACHIEVEHIGHLEVELSOFINTERFERENCEPROTECTION $IGITAL4RANSPONDER$ESIGNS

$IGITALTECHNOLOGYHASPROGRESSEDTOTHEPOINTTHATSUFFICIENTTECHNOL OGY IS AVAILABLE TO PRESENT SERIOUS ALTERNATIVES TO TRADITIONAL ANALOG IMPLEMENTATIONS4HEPRECEDINGTRANSPONDERARCHITECTURESAREBASED ONANALOGDESIGNCONCEPTS7HILEDIGITALSYSTEMSCANBECONFIGUREDAS REPLACEMENTSFORANALOGDESIGNS THEADDITIONALFLEXIBILITYAFFORDEDBY DIGITALCIRCUITRY THEDIFFERENCESINDESIGNPHILOSOPHIESBETWEENDIGITAL ANDANALOGCIRCUITRY ANDINTERFACESWITHOTHERDIGITALTECHNOLOGIESSUCH ASMEMORYDEVICESRESULTINTRANSPONDERARCHITECTURESTHATFUNDAMEN TALLYDIFFERFROMTHEIRANALOGCOUNTERPARTS4HESEDIFFERENCESJUSTIFYA SEPARATEDISCUSSIONOFTRANSPONDERSTHATAREIMPLEMENTEDWITHDIGITAL TECHNOLOGY 4HE FUNCTIONAL BLOCK DIAGRAM OF A DIGITAL TRANSPONDER IN &IG ASSUMESARRAYANTENNASAREUSEDWITHDIGITALBEAMFORMINGTECHNIQUES $IGITALBEAMFORMINGTECHNIQUES; =HAVELONGBEENKNOWN0RACTICAL APPLICATIONSINTHEPASTHAVEBEENLIMITEDBYDIGITALTECHNOLOGYCAPABILI TIES ANDOTHERSYSTEMSENSORSSUCHASSONARTHATHAVESUFFICIENTLYSMALL BANDWIDTHREQUIREMENTSTHATCOULDBEACCOMMODATEDBYEARLIERDIGITAL TECHNOLOGY HAVE CAPITALIZED ON DIGITAL BEAMFORMING4HE SUBSTANTIAL INCREASEINDIGITALTECHNOLOGYCAPABILITIESRESULTSINCOMMUNICATIONSAT ELLITESYSTEMDESIGNSBASEDONDIGITALTECHNOLOGY!DDITIONALAPPLICATION OFDIGITALTECHNOLOGYINFUTURESYSTEMDESIGNSISAPPARENT 4HE TRANSPONDER DESIGN IN &IG PROCESSES THE ANALOG OUTPUTS OF THE RECEIVE ARRAY ELEMENTS USING ANALOG TECHNOLOGY TO PROVIDE A SUITABLEINPUTTOTHE! $SANALOG TO DIGITALCONVERTERS THATCONVERT

&IGURE !DIGITALTRANSPONDER

#HAPTER 4HREE

THE ANALOG ARRAY ELEMENT INPUT SIGNALS TO THE DIGITAL DOMAIN4HE ANALOGPROCESSINGINCLUDESPREAMPLIFICATIONTOESTABLISHTHESYSTEM NOISETEMPERATUREANDFREQUENCYCONVERSIONTOTHESPECTRAWHERETHE ! $TRANSFORMSTHEANALOGDATARECEIVEDBYEACHARRAYELEMENTINTO ADIGITALDATASTREAMFOREACHARRAYELEMENT4HECOLLECTIONOFDIGI TIZEDBASEBANDSIGNALSFROMEACHRECEIVEARRAYELEMENTISPROCESSED BYTWO DIMENSIONAL&OURIERTRANSFORMSTOPRODUCETHEANTENNAARRAY PATTERNS 4HE INDIVIDUAL USERS IN THESE BEAMS CAN BE SEPARATED BY DIGITALDEMULTIPLEXERSAND IFDESIRED DEMODULATED$IGITALDEMULTI PLEXINGANDMULTIPLEXING;=MAYBEACCOMPLISHEDBYCAPITALIZINGON HARDWARENORMALLYUSEDTOIMPLEMENT&&4FAST&OURIERTRANSFORM OPERATIONS4HEINDIVIDUALDATASTREAMSAREREMODULATEDIFREQUIRED ANDROUTEDTOMULTIPLEXERS!TWO DIMENSIONAL&OURIERTRANSFORMIS THEN USED TO PRODUCE THE DIGITAL EXCITATIONS FOR THE DOWNLINK ARRAY ELEMENTS!NALOGSIGNALPROCESSINGISAPPLIEDANDISCOMPRISEDOFTHE $!SANALOGUPCONVERSIONTOTHE2&TRANSMITTERFREQUENCY ANDAMPLI FICATIONTOTHEREQUIREDARRAYELEMENTPOWERLEVELANDTHENRADIATIONBY THEARRAY&ORNARROWBANDWIDTHAPPLICATIONS COMPLEXMATRIXMULTIPLI CATIONOFMULTIPLEXEDSAMPLESOFTHESAMEINFORMATIONSTREAM;=CANBE PERFORMEDINPLACEOFTHETWO DIMENSIONAL&OURIERTRANSFORMTOPERFORM THEBEAMSTEERINGINTHESAMEMANNERASANALOGPHASESHIFTERS )NSOMECASES THEDIGITALPROCESSINGFUNCTIONSWOULDBEPERFORMED WITHINTHESATELLITETRANSPONDER WHILEINOTHERCASES THEUPLINKSIGNAL COLLECTIONISRELAYEDTOAGATEWAYGROUNDTERMINALWHERETHEPROCESS INGISPERFORMEDANDTHEPROCESSEDDATAARETRANSMITTEDTOTHESATELLITE FORREBROADCASTTOUSERS/NBOARDPROCESSINGWITHINWEIGHTANDPOWER RESTRICTIONSOFPRACTICALSPACESEGMENTDESIGNSISLIMITEDTOAPPLICATIONS WITHLIMITEDBANDWIDTHANDUSERCHANNELS&URTHERDIGITALEXPLOITATION IN SPACE SEGMENT TRANSPONDER DESIGNS CAN BE ANTICIPATED AS DIGITAL TECHNOLOGYCONTINUESTOMATURE !NOTHER DIGITAL APPLICATION APPLIES DIGITAL MEMORY TECHNOLOGY TO STORE SELECTED UPLINK SIGNALS FOR LATER REBROADCAST TO THE USER TERMI NALS!NETWORKDESCRIPTIONOFTHISTECHNIQUE;=ILLUSTRATESPOTENTIAL IMPLEMENTATIONS4WODISTINCTAPPLICATIONSEXISTFORSUCHACAPABILITY 4HEFIRSTAPPLICATIONSTORESUPLINKSIGNALSWHENDOWNLINKCAPACITYISNOT AVAILABLEANDREBROADCASTSTHESIGNALSATALATERTIMEWHENTHECAPACITY ISAVAILABLE)NTHISWAY THEPEAKDEMANDSFORSPACESEGMENTCAPACITY AREAVERAGEDTOALLOWEFFICIENTSATELLITEOPERATION!SECONDAPPLICATION APPLIESTOSATELLITESINALOW ALTITUDECONSTELLATION;=7HENUSERSOF SUCHSYSTEMSDONOTHAVEMUTUALVISIBILITYANDCROSSLINKRESOURCESARE NOTAVAILABLETORELAYTHEIRCOMMUNICATIONSBETWEENSATELLITES MEMORY TECHNOLOGYCANBEUSEDTOREBROADCASTTHEINFORMATIONWHENTHESATEL LITEISVISIBLETOTHERECEIVINGUSERINASUBSEQUENTPARTOFTHEORBITAL TRAJECTORY


/NE EXAMPLE OF 2& DIGITAL BEAMFORMING DESIGNS ;= HAS BEEN REPORTEDTHATILLUSTRATESTHEHARDWAREIMPLEMENTATIONANDACHIEVED PERFORMANCE)NTHISCASE MULTIPLEBEAMSPRODUCEDBYDIGITALBEAM FORMING HAVE BEEN USED WITH A MOBILE USER PLATFORM TO MAINTAIN ALIGNMENTWITHAN, BANDSATELLITE4HEARRAYISCOMPRISEDOFELE MENTSARRANGEDINAsGEOMETRY)NTHISEXPERIMENT &0'!&IELD 0ROGRAMMABLE 'ATE!RRAY DIGITAL DEVICES WERE USED FOR THE DIGITAL PROCESSING!NADAPTIVEPROCESSINGTECHNIQUEWASEMPLOYEDTOIMPLE MENTTHEBEAMSTEERINGANDADAPTIVECO CHANNELINTERFERENCECANCEL LATION AS PROPOSED IN THIS DESIGN )N OPERATION THE SATELLITE SIGNAL ALIGNMENTWASPERFORMEDBYSUMMINGTHEIN PHASEANDQUADRATURE POWERLEVELSANDUSINGTHEBEAMWITHTHEHIGHESTLEVEL4HEARRAYWAS MOUNTEDONAVANANDDRIVENINANURBANAREA)NTHISWAY SEVERAL BEAMPOSITIONSWEREUSEDTOMAINTAINALIGNMENTWITHTHESATELLITEAS THEVANMANEUVEREDTHROUGHANURBANAREAANDTHEEFFECTSOFSHADOW INGBYOVERPASSESANDBUILDINGSWEREOBSERVEDINTHERECEIVEDSIGNAL LEVELS!DDITIONALDEVELOPMENTANDTECHNOLOGYEXPERIENCEWITHDIGITAL BEAMFORMINGCANBEANTICIPATED $IGITAL TRANSPONDER DESIGNS AND ARCHITECTURES CONTAIN INHERENT IMPLEMENTATIONTRADEOFFSTHATADDRESSCRITICALSYSTEMPARAMETERSSUCH AS WEIGHT AND POWER REQUIREMENTS &OR EXAMPLE THE ARCHITECTURE IN &IG PERFORMSBEAMFORMINGOVERTHEOPERATINGBANDWIDTHANDTHEN DEMULTIPLEXINGORMULTIPLEXING 4HISAPPROACHADVANTAGEOUSLYRESULTS INPOTENTIALPOWERSAVINGSINSYSTEMSTHATPERMITTURNINGOFFBEAMS WHENUSERSARENOTPRESENT!NOTHERALTERNATIVEISTODEMULTIPLEXOR MULTIPLEX INDIVIDUAL FREQUENCY CHANNELS AT EACH ARRAY ELEMENT AND PERFORMNARROWBANDWIDTHBEAMFORMINGONTHEMULTIPLEXEDCHANNELS 4RADEOFFSINPOWERCONSUMPTIONINTHESETWOAPPROACHESDEPENDONTHE NUMBEROFCHANNELSANDTHEUSERTRAFFICMODELS 4WOIMPLEMENTATIONALTERNATIVESEXISTFORTHEDIGITALHARDWARETECH NOLOGY /NE ALTERNATIVE USES &0'! TECHNOLOGY THAT PROVIDES FLEXIBIL ITYINCONFIGURINGTHEPROCESSING4HESECONDALTERNATIVEUSESCUSTOM !3)#TECHNOLOGY WHOSEDESIGNISTAILOREDTOMEETTHESYSTEMSDESIGN REQUIREMENTS4HISSECONDALTERNATIVEISMORECOSTLYTHANTHEFIRSTBUT RESULTSINLOWERPOWERCONSUMPTION4HETRADEOFFSBETWEENTHESETWO APPROACHESDEPENDONTHESPECIFICREQUIREMENTSOFTHEAPPLICATION COST DIFFERENCES ANDREQUIREDSCHEDULEIMPACTS7HEN!3)#TECHNOLOGYIS DEVELOPED SUFFICIENTTIMESHOULDBEALLOWEDTOPRODUCETWO!3)#VER SIONSSOTHATANYREQUIREDUPDATESTOTHEFIRSTVERSIONCANBEPRODUCED INTHESECONDVERSIONFORFLIGHTAPPLICATION !SURPRISINGVARIETYOFDIGITALTECHNOLOGYFORTRANSPONDERAPPLICATIONS ISAVAILABLEANDPROGRESSINDEVELOPINGMORECAPABLEDIGITALTECHNOLOGY WILLCONTINUEINTHEFUTURE"OTHTHESAMPLINGRATESANDTHEQUANTIZA TION LEVELS OF DIGITAL HARDWARE CAN BE EXPECTED TO INCREASE IN FUTURE

#HAPTER 4HREE

YEARSANDDECREASEDPOWERCONSUMPTIONCANBEANTICIPATED4YPICALLY THESAMPLINGRATESARESELECTEDTOPROVIDEOVERSAMPLING4HEDIGITAL QUANTIZATION IS SELECTED TO ACCOMMODATE THE UPLINK SIGNAL COLLECTION DYNAMICRANGE%ACHBITOFQUANTIZATIONPROVIDESD"OFDYNAMICRANGE SOTHAT BITQUANTIZATIONPROVIDESAD"DYNAMICRANGE4HEEFFEC TIVE NUMBER OF BITS IS SOMEWHAT LOWER BECAUSE THE LEAST SIGNIFICANT BITSNEEDTOCORRESPONDTOSIGNALINPUTLEVELSSOMEWHATBELOWTHETHER MALNOISELEVELSOQUANTIZATIONNOISEDOESNOTIMPACTTHESYSTEMNOISE TEMPERATURE4HEDYNAMICRANGEMUSTACCOUNTFORNOTONLYTHEPOWER VARIATIONSANTICIPATEDINTHESIGNALSRECEIVEDFROMTHEUSERSBUTALSOTHE POSSIBILITYOFINTERFERINGSIGNALS4HEEFFECTSOFINTERFERENCEON!$CON VERTERSUSEDINDIGITALBEAMFORMERS;=ILLUSTRATEANTENNAPATTERNDIS TORTIONTHATRESULTSINHIGH LEVELINTERFERENCE4HESYSTEMDESIGNNEEDS TOADDRESSTHEANALOGGAINDISTRIBUTIONSOTHEAPPROPRIATESIGNALLEVELS ARE PRESENT AT THE!$ INPUTS AND SO SUFFICIENT ANALOG ANTI ALIASING FILTERING IS PROVIDED INSURING THAT OUT OF BAND INTERFERENCE DOES NOT DEGRADETHEDESIREDSIGNALRECEPTION $IGITALIMPLEMENTATIONSNEEDTOBECOMPAREDWITHANALOGALTERNATIVES TO DEVELOP SYSTEMS WITH ACCEPTABLE 37A0 &OR EXAMPLE WITHIN THE GENERICTRANSPONDERDESIGNIN&IG THEALTERNATIVESOFANALOGBEAM FORMINGANDDIGITALBEAMFORMINGNEEDTOBEADDRESSEDPARTICULARLYIN REGARD TO 37A0 $IGITAL BEAMFORMING TECHNIQUES HAVE MANAGEABLE ARRAYCOMPLEXITYLEVELSFORTHEWIDEFIELDOFVIEWREQUIREMENTSFORLOW ALTITUDESATELLITEDESIGNS)NSUCHAPPLICATIONS THEOVERALLAPERTURESIZE ISMODESTANDANARRAYDESIGNCANBEIMPLEMENTEDWITHAREASONABLE NUMBEROFELEMENTS COMPLEXITY ANDPOWERCONSUMPTION&ORGEOSTA TIONARY SATELLITES HOWEVER THE ARRAY COMPLEXITY BECOMES EXCESSIVE ANDANALOGANTENNADESIGNSAREMOREAPPROPRIATE$IGITALPROCESSING INTHEFORMOFCHANNELIZERSTOSEPARATEANDROUTEINDIVIDUALUSERSISA REASONABLEALTERNATIVETOPURSUE4RANSPONDERAPPLICATIONSOFDIGITAL TECHNOLOGYARERAPIDLYDEVELOPINGATTHISWRITING ANDFARGREATERUSE OFTHESETECHNOLOGIESANDDESIGNIMPLEMENTATIONSCANBEANTICIPATED INTHEFUTURE 4HE FLEXIBILITY OF FUTURE TRANSPONDER DESIGNS IMPOSES GREATER BUR DENS FOR MANAGING THE SPACE SEGMENT RESOURCES THAT GREATLY EXCEED THEREQUIREMENTSOFROUTINECOMMANDINGASUSEDBYEARLIERSATELLITES !NADAPTIVECONTROLTECHNIQUE;=IN&IG HASBEENPROPOSEDASA MEANSOFMANAGINGTHERESOURCES4HEUPLINKANDDOWNLINKANTENNA DESIGNSPROVIDEUSERCOMMUNICATIONCAPABILITIESANDTHEUPLINKCOLLEC TIONOFINDIVIDUALUSERSIGNALSISDEMULTIPLEXEDANDROUTEDTODOWNLINK DESTINATIONSWHERETHEUSERSIGNALSAREMULTIPLEXEDFORDOWNLINKTRANS MISSION4HEDIGITALTECHNOLOGYPROVIDESROUTINGCOMPLEXITYUNAVAILABLE INFIXEDANALOGSUBBANDSTORESPONDTOVARYINGCOMMUNICATIONNEEDS ANDTRAFFICVARIATIONS$IGITALTECHNOLOGYPROVIDESTHEFLEXIBILITYTOVARY


&IGURE !DAPTIVETRANSPONDERCONTROL;=

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!VARIETYOFDIRECTBROADCASTARCHITECTURESEXISTTHATUSESATELLITESTO RELAYTHESAMEINFORMATIONTOAMULTITUDEOFUSERS!TPRESENT DIRECT BROADCASTISCOMMONLYTHOUGHTOFASRELAYINGTELEVISIONCOVERAGEOVER WIDEAREAS4HEPROGRAMINFORMATIONISRELAYEDTOTHESATELLITEFROMA SINGLEGROUNDTERMINALANDTHEDOWNLINKTRANSMISSIONISRECEIVEDBYA VARIETYOFUSERS/THERFORMSOFDIRECTBROADCASTSERVICESRESULTINNAVI GATION AND REMOTE SENSING SATELLITES 4HE INFORMATION FOR NAVIGATION SATELLITESISDERIVEDFROMANONBOARDCLOCKANDPSEUDORANDOMCODESTHAT ALLOWUSERSTODETERMINETHETIMEDIFFERENCEOFARRIVALVALUESNEEDEDTO

#HAPTER 4HREE

CALCULATEANAVIGATIONALSOLUTION;=4HEONBOARDSENSORSINREMOTE SENSINGSATELLITESGATHERDATATHATAREBROADCASTTOUSERTERMINALSTO BEPROCESSEDINTOMETEOROLOGICALDATAANDOTHERREMOTESENSINGPARAM ETERS4HECOMMONFEATUREINALLCASESISTHATINFORMATIONISDELIVERED TOAMULTITUDEOFUSERSBYDIRECTSATELLITEBROADCASTWITHOUTANYRETURN LINKFROMTHEUSERSTHEMSELVES 4HEDIRECTBROADCASTTRANSPONDERDESIGNILLUSTRATEDIN&IG ISLESS COMPLEXTHANOTHERTRANSPONDERARCHITECTURES4HESIGNALSOURCEISWELL CONTROLLEDSOTHATPOWERCONTROLAMONGUSERSISNOTANISSUE2ELATIVELY SIMPLESPACESEGMENTANTENNASAREREQUIREDTOMEETTHEREQUIREMENTS FORUSERBROADCASTSERVICE5SEREQUIPMENTFORDIRECTBROADCASTSERVICES REQUIRES ONLY A RECEIVING CAPABILITY SIMPLIFYING THEIR DESIGN REQUIRE MENTSANDPROVIDINGOPPORTUNITIESFORCOST EFFECTIVEUSEREQUIPMENT )NRECENTYEARS THESIZEOFUSERSATELLITE46TERMINALSHASSHRUNK ASSATELLITESWITHINCREASEDPERFORMANCEHAVECOMEINTOSERVICE-ORE PROGRAMALTERNATIVESCONTINUETOBEAVAILABLETOSYSTEMUSERS4HEPRO DUCTION VOLUME AND DEVELOPMENT OF THE COMMERCIAL USER EQUIPMENT RESULTINAWIDEVARIETYOFCOST EFFECTIVEALTERNATIVESFORUSERS!SIMILAR SITUATIONEXISTSWITHNAVIGATIONSATELLITESSUCHAS'03 WHERELOW COST TERMINALSHAVEBECOMEWIDELYAVAILABLE5SERAPPLICATIONSFORNAVIGA TIONALSIGNALSHAVEEXPANDEDWELLBEYONDTHEAPPLICATIONSENVISIONED ORIGINALLY#OMMERCIALEQUIPMENTFORPRECISIONSURVEYINGANDAIRPORT TRAFFICCONTROLAREREPRESENTATIVEEXAMPLEAPPLICATIONSTHATEXTENDFAR BEYOND THE OBJECTIVES OF THE ORIGINAL NAVIGATIONAL FUNCTION 2EMOTE SENSINGSATELLITESAREANOTHERCLASSOFDIRECTBROADCASTSATELLITESTHAT HAVEALSOENJOYEDCOMMERCIALAPPLICATIONANDUSERSYSTEMDEVELOPMENT FORWEATHERDATARECEIVEDBYINEXPENSIVETERMINALSFORLOW RESOLUTION SERVICES TO MORE CAPABLE TERMINALS FOR HIGHER RESOLUTION SERVICES! WIDE VARIETY OF COMMERCIAL ALTERNATIVES FOR USER RECEPTION ARE AVAIL ABLE4HESEEXAMPLESWILLENJOYGREATERUSERINTERESTINFUTUREYEARS 3YSTEMPLANNERSFORDIRECTBROADCASTSERVICESNEEDTOPROVIDESATELLITES WITHADEQUATE%20PERFORMANCETOALLOWTHEDEVELOPMENTOFCOST EFFECTIVE USERTERMINALS!STHENUMBEROFUSERSANDAVAILABLEAPPLICATIONSCON TINUESTOINCREASE THETOTALSYSTEMACQUISITIONCOSTRESULTSINAGREATER

&IGURE !DIRECTBROADCASTTRANSPONDER


PROPORTION OF THE COST IN THE USER SEGMENT )NCREASED SPACE SEGMENT PERFORMANCEREDUCESUSERPERFORMANCEREQUIREMENTSANDCOST ASWELL ASPROVIDESADDITIONALAPPLICATIONSFORTHEUSERSEGMENT #ROSSLINKSAND%ARTH,INKS

#ROSSLINKSUBSYSTEMSAREPOINT TO POINTARCHITECTURESTHATPROVIDECOM MUNICATIONSERVICESBETWEENTWOSATELLITES4HESESYSTEMSACHIEVEGLOBAL USER CONNECTIVITY WITHOUT THE NEED TO RELAY COMMUNICATIONS THROUGH INTERMEDIARY GROUND TERMINALS 4HIS CAPABILITY PROVIDES COMMUNICA TIONSBETWEENUSERSTHATDONOTHAVEMUTUALVISIBILITYTOTHESAMESATEL LITE'ENERALLY SATELLITESHAVETWOCROSSLINKSUBSYSTEMS SOCONNECTIVITY BETWEENADJACENTSATELLITESISACHIEVED#ROSSLINKSYSTEMSCOMMONLYUSE '(ZBECAUSETHEOXYGENABSORPTIONSPECTRADESCRIBEDIN#HAPTER PROVIDEPROTECTIONFROMGROUND BASEDINTERFERENCE;=)NADDITION THE REQUIREDANTENNASIZEFORPOINT TO POINTSERVICESISREDUCEDBYINCREASING THE2&FREQUENCY AND'(ZCROSSLINKDESIGNSHAVECOMPACTHIGH GAIN ANTENNAS TRANSPONDERHARDWAREWITHAWELL ESTABLISHEDTECHNOLOGY AND AREASONABLEWEIGHTANDSIZEFACTORSTHATHAVERESULTEDINTHEPOPULARITY OF'(ZCROSSLINKOPERATION(IGHDATARATETRANSFERINCROSSLINKDESIGNS GENERALLYREQUIRESCLOSED LOOPANTENNATRACKINGCAPABILITIESDESCRIBEDIN #HAPTER TOCOMPENSATEFORSATELLITEATTITUDEVARIATIONS 4HISSUBSYSTEMDESCRIBEDIN&IG HASARELATIVELYSTRAIGHTFOR WARDARCHITECTURE4HECOMMUNICATIONINTERFACESAREWITHTHESATELLITE TRANSPONDERANDAREWELLDEFINEDBYTHESYSTEMDESIGN4HEFREQUENCY PLAN FOR CROSSLINK OPERATION WITH GEOSYNCHRONOUS SATELLITES REQUIRES FOURINDEPENDENTFREQUENCIESTOAVOIDMUTUALINTERFERENCEWHENANODD NUMBEROFSATELLITESAREINTHECONSTELLATIONAND ORWHENCROSSLINKSARE CONFIGUREDBETWEENSATELLITESTHATAREACROSSTHECONSTELLATIONRATHER THAN TO ADJACENT SATELLITES4HESE FREQUENCY PLANS ARE BASED ON NOT ALLOWINGAGIVENSATELLITETOHAVETOBOTHTRANSMITANDRECEIVEOPERATION ONTHESAMEFREQUENCYSUBBAND!NEXAMPLEFREQUENCYPLANIN&IG ILLUSTRATES THE CONNECTIVITY BETWEEN A CONSTELLATION OF FOUR SATELLITES WHERE FOUR FREQUENCIES ARE REQUIRED SO THAT CONNECTIVITY TO EITHER ADJACENTORCROSS CONSTELLATIONSATELLITESCANBEMADE4WOFREQUENCY

&IGURE !CROSSLINKTRANSPONDER

#HAPTER 4HREE

&IGURE !NEXAMPLEOFACROSSLINKFREQUENCYPLAN

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"

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&IGURE 'EOMETRICPARAMETERSFORCROSSLINKS


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4HE44#SUBSYSTEMPLAYSAVITALROLEINEVERYSATELLITE4HISSUBSYS TEMASSISTSINDETERMININGTHEPRECISELOCATIONOFTHESATELLITEINORBIT REPORTSTHEHEALTHANDSTATUSOFTHESATELLITEBYGATHERINGDATAFROM SUBSYSTEMSENSORSTOFORMTELEMETRYMESSAGES ANDCOMMANDSCHANGES INTHESATELLITEOPERATION4HE44#SUBSYSTEMISOPERATEDINBOTHTHE SATELLITELAUNCHPHASEANDDURINGITSOPERATIONALLIFEINORBIT$URING THELAUNCHPHASE TELEMETRYDATAAREUSEDTODETERMINETHECORRECTNESS OFTHEORBITALTRAJECTORY TOPROVIDECOMMANDINGINTHEORBITALINSER TIONASREQUIRED ANDTOCOMMANDTHEOPERATIONOFSATELLITESUBSYSTEM DEPLOYMENTS$URINGTHISPHASEOFTHEPROGRAM THE44#ANTENNAS MUSTPROVIDECOVERAGEOVERACOMPLETESPHERESOTHATIFTHESATELLITE BEGINSTOTUMBLEDURINGLAUNCHASCENT COMMANDSCANBEINJECTEDTO CONTROLTHESATELLITEORORDERITSDESTRUCTION/N ORBIT THE44#SUB SYSTEMISTHEONLYMEANSOFCONTROLLINGTHESATELLITEOPERATIONDURING ITSLIFETIME4HUS THERELIABILITYANDAVAILABILITYOFBOTHSPACESEGMENT ANDGROUNDSEGMENT44#SYSTEMELEMENTSRELIABILITYHASPARAMOUNT IMPORTANCE4HE44#SYSTEMDESIGNPURPOSELYPROVIDESGENEROUSLINK MARGINSANDATTENTIONTOREDUNDANCY 4HE SPACE SEGMENT44# SUBSYSTEM COMMUNICATES WITH SATELLITE MISSIONCONTROLTERMINALSTHATMONITORTHESATELLITEOPERATIONANDISSUE COMMANDSTOCHANGEITSOPERATION7ITHTHEEXCEPTIONOFREMOTESENSING SATELLITESTHATMULTIPLEXTHEIRMISSIONDATAONTOTHE44#DOWNLINK

#HAPTER 4HREE

44#SYSTEMSHAVENODIRECTINVOLVEMENTWITHTHEUSERSEGMENT !GENERICBLOCKDIAGRAMOFA44#SATELLITETRANSPONDERISPRESENTED IN&IG 3PACESEGMENTTRANSPONDERSFOR44#APPLICATIONS;= NOWRELYHEAVILYONDIGITALTECHNOLOGYANDTHUSHAVETHEFLEXIBILITYTO SERVEDIVERSE44#APPLICATIONS 4HEOVERALLDETERMINATIONOFTHESATELLITESORBITALPOSITIONRESULTSFROM COMPLYINGDATAFROMAVARIETYOFSOURCES TRACKINGRADARS BEACONSYSTEMS CARRIER$OPPLERVARIATIONS ANDSOON ANDTHE44#SUBSYSTEM WHICHCAN ASSISTINTHISPROCESSBYPROVIDINGARANGINGCODE0SEUDORANDOMCODES AREUSEDTOPROVIDEACCURATERANGEVALUES4HERANGEDATAANDDATAFROM THEREMAININGCOLLECTIONOFSOURCESAREPROCESSEDUSING+ALMANFILTERING TECHNIQUES;=TOOBTAINABESTESTIMATEOFTHESATELLITESORBITALPOSI TIONDEFINEDBYTHESATELLITESEPHEMERIS4HERANGINGCODEISTYPICALLY BROADCASTBYTHESATELLITECONTROLTERMINALANDCONVERTEDTOTHEDOWNLINK FREQUENCYONBOARDTHESATELLITEUSINGDIVIDINGANDMULTIPLYINGTECHNIQUES TOMAINTAINCODECOHERENCE4HERANGINGINFORMATIONALONGWITHANGULAR TRACKINGDATAFROMTHESATELLITECONTROLTERMINALANTENNASPROVIDESINFOR MATIONUSEDTOPROJECTTHESATELLITESORBITALPOSITION 4HETELEMETRYGATHEREDBYTHESATELLITESSUBSYSTEMSPROVIDESDATA TOMONITORTHESATELLITESHEALTHANDSTATUS4HISINFORMATIONTYPICALLY INCLUDESSATELLITEPRIMEPOWERDATA ATTITUDECONTROLDATA TEMPERATURE INFORMATION GATHERED FROM VARIOUS PARTS OF THE SATELLITE SUBSYSTEM VOLTAGESANDCURRENTDRAWS ANDOTHERS4HESEDATA TOGETHERWITHANY ONBOARDDIAGNOSTICS ARETHEONLYMEANSOFIDENTIFYINGCAUSESOFOPERA TIONALPROBLEMS4HEREFORE ITISCRITICALLYIMPORTANTEARLYINTHEDEVEL OPMENTOFASATELLITETOASSURETHATANADEQUATEAMOUNTOFTELEMETRY POINTSAREAVAILABLE THATTHEIRRESPONSECANBECLEARLYINTERPRETED AND THATTHETELEMETRYLINKHASADEQUATEDATACAPABILITYSOTHATTELEMETRY CANBERECEIVEDINATIMELYMANNER 3ATELLITECOMMANDINGISTHETHIRDFUNCTIONOFTHE44#SUBSYSTEM 4HISCOMMANDINGHASAVARIETYOFFORMS INCLUDINGDEPLOYINGSUBSYSTEMS DURINGTHEEARLYON ORBITLAUNCHPHASE CONTROLLINGATTITUDETHRUSTERS SWITCHING TO REDUNDANT COMPONENTS TO REPLACE FAILED ITEMS CHANGING

&IGURE !44#TRANSPONDER

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ANTENNACOVERAGEBYCOMMANDINGTHEOPERATIONOFBEAMFORMINGNET WORKSORREPOSITIONINGSPOTBEAMS ANDSOON)FPERFORMANCEANOMALIES ARISEOPERATIONALLY THE44#SYSTEMCANCOMMANDADDITIONALTELEM ETRY DATA INCLUDING DATA THAT ARE NOT ROUTINELY REPORTED TO PROVIDE ADDITIONALDIAGNOSTICDATA4HECOMMANDINGMUSTBEEXTREMELYRELIABLE BOTHINTERMSOFITSOPERATIONANDPERFORMANCE#OMMANDAUTHENTICATION TECHNIQUES ARE OFTEN USED IN CRITICAL COMMANDS TO AVOID MISTAKEN OR MISINTERPRETEDCOMMANDSTOTHEEXTENTPRACTICAL 5SER3EGMENT!RCHITECTURES 5SERSEGMENTTERMINALSHAVEHADMUCHDEVELOPMENTANDAREAVAILABLE INAWIDEVARIETYOFCONFIGURATIONSDEPENDINGONTHEAPPLICATIONAND DATARATES5SERTERMINALDESIGNSRANGEFROMHANDHELDTERMINALSTHAT EVOLVEFROMTECHNOLOGYUSEDINTERRESTRIALAPPLICATIONSTOVERYLARGETER MINALSFORHIGHDATARATESERVICES4ERMINALDESIGNSAREREQUIREDTOSAT ISFYUSERNEEDSINGROUND NAVAL ANDAIRBORNEAPPLICATIONS4ERMINALS FORDIRECTBROADCASTSERVICESDONOTREQUIREATRANSMITTINGCAPABILITY ANDTHEIRDESIGNANDCOSTAREMOREMODESTTHANTERMINALSREQUIRINGA TRANSMISSIONCAPABILITY2ATHERTHANDWELLONTERMINALDESIGNSFORDIF FERENTAPPLICATIONS ADESCRIPTIONOFAGENERICTERMINALANDITSOPERATING PRINCIPLESANDFEATURESISPROVIDED 4HE USER TERMINAL ARCHITECTURE ILLUSTRATED IN &IG DESCRIBES THEMOSTGENERALUSERTERMINALDESIGN4HETERMINALISCOMPRISEDOFTHE ANTENNA AN!#5ANTENNACONTROLUNIT ADIPLEXERTHATCONNECTSTHE RECEIVERANDTRANSMITTERTOTHEANTENNA ARECEIVER ANDATRANSMITTER 5SER TERMINALS GENERALLY USE A SINGLE ANTENNA FOR BOTH RECEIVE AND TRANSMITOPERATIONSANDADIPLEXERISOLATESTHETERMINALSRECEIVERAND

&IGURE !USERTERMINALFUNCTIONALDIAGRAM

#HAPTER 4HREE

TRANSMITTER4HEANTENNAISPOSITIONEDBYTHE!#5 WHICHTAKESAVARI ETYOFFORMSDEPENDINGONTHEANTENNASBEAMWIDTH0ERSONALSYSTEMS HAVE BROAD ANTENNA COVERAGE WITH NO POINTING REQUIREMENTS!T THE OTHEREXTREME LARGEGROUNDTERMINALSFORHIGHDATARATESYSTEMSUSE CLOSED LOOPTRACKINGSYSTEMSTOMAINTAINANTENNATRACKING ASDESCRIBED IN#HAPTER4HE!#5SUBSYSTEMUSESTHETERMINALSGEOGRAPHICLOCA TIONSANDTHESATELLITESEPHEMERISINFORMATIONTHATDESCRIBESTHESATEL LITESORBITTODERIVENOMINALANTENNAPOINTINGINFORMATION3IGNALSFROM THEANTENNAFEEDAREUSEDTOALIGNTHEANTENNAWITHTHESATELLITE AS DESCRIBEDIN#HAPTER#OMMONLY THE!#5ALSOCONTAINSSTARTRACKING INFORMATIONTHATISUSEDINRADIOSOURCEANTENNACALIBRATIONTECHNIQUES DESCRIBEDIN#HAPTER !DIPLEXERISADEVICETHATALLOWSCONNECTIONSBETWEENTHEANTENNA AND THE RECEIVER AND TRANSMITTER WHILE PROVIDING ADEQUATE ISOLATION SOTHATTHETRANSMITTEROPERATIONDOESNOTINTERFEREWITHTHERECEIVER 7HILESUCHISOLATIONCANBEACHIEVEDBYPHYSICALSEPARATIONBETWEEN THERECEIVERANDTRANSMITTERUSEDWITHSEPARATEANTENNAS GENERALLYTHE COSTANDREALESTATEREQUIREDFORSEPARATERECEIVEANDTRANSMITANTENNAS AREPROHIBITIVE4HEREQUIREDDIPLEXERISOLATIONISACHIEVEDBYPROVID INGADEQUATEFILTERINGINTHERECEIVEANDTRANSMITPATHS4HETRANSMIT FILTER MUST PASS THE IN BAND TRANSMITTED SIGNAL WITH MINIMUM LOSS WHILE SUPPRESSING THE OUT OF BAND TRANSMITTER NOISE OVER THE RECEIVE BANDWIDTH4HERECEIVEFILTERMUSTLIKEWISEPASSTHEIN BANDRECEIVED BANDWIDTHWITHMINIMUMLOSSANDSUPPRESSTHEOUT OF BANDTRANSMIT SPECTRASUFFICIENTLYTOMAINTAINLINEARRECEIVEROPERATION 4HEDIPLEXERISOLATIONREQUIREMENTSAREDERIVEDFROMTHEFACTORSILLUS TRATEDIN&IG 4HEFILTERINGREQUIREMENTINTHETRANSMITTERPATH MUSTSUPPRESSTHETRANSMITTERSPECTRAWITHINTHERECEIVEBANDWIDTH SUFFICIENTLYTOAVOIDPERTURBINGTHERECEIVERNOISETEMPERATURE4HEOUT OF BANDTRANSMITTERSPECTRACONTAINNOISE HARMONICS ANDSPURIOUSCOM PONENTS#OMMONLY THEOUT OF BANDTRANSMITTERSPECTRAAREREQUIREDTO BESUPPRESSEDTOALEVELD"LOWERTHANTHESYSTEMNOISETEMPERATURE 3UCH SUPPRESSION LIMITS THE INCREASE IN THE SYSTEM NOISE TEMPERA TURETOABOUTD")NCREASEDRECEIVERNOISELEVELSWITHTRANSMIT TEROPERATIONPROVIDEABASISOFTESTREQUIREMENTSTODETERMINETHE ADEQUACY OF THE DIPLEXER FILTER4HE RECEIVER NOISE LEVELS WITH AND WITHOUTTRANSMITTEROPERATIONARECOMPAREDTODETERMINECOMPLIANCE WITHTHEDIPLEXERREQUIREMENTS3IMILARLY THEFILTERINGINTHERECEIVE PATHMUSTBESUFFICIENTTOSUPPRESSTHETRANSMITTEROUTPUTTOAVOID EXCEEDING THE LINEAR DYNAMIC RANGE OF THE RECEIVER 4YPICALLY THE FILTERINGINTHERECEIVERDOWNCONVERSIONISOLATESTHATPORTIONOFTHE RECEIVERFROMTHETRANSMITTEDSPECTRA ANDATTENTIONMUSTBETYPICALLY FOCUSED ON MAINTAINING LINEARITY OF THE ,.! AND POSSIBLY THE FIRST DOWNCONVERTER'ENERALLY SUFFICIENTRECEIVERFILTERINGTOREDUCETHE


&IGURE $IPLEXERlLTERREQUIREMENTS

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#HAPTER 4HREE

THESATELLITEDOWNLINK THEMEANSTOSEPARATETHEUSEROFINTERESTIS REQUIRED "ECAUSE OF THE RELATIVE MOTION BETWEEN THE SATELLITE AND THEUSER $OPPLERVARIATIONSMUSTBECOMPENSATED4HELARGERANTEN NASOFTENUSEASEPARATETRACKINGRECEIVERTOMEASURETHEDOWNLINK POWER FOR ANTENNA TRACKING PURPOSES $IGITAL SIGNAL FORMATS AND SPREADSPECTRUMMODULATIONFORMATSHAVEAVARIETYOFSYNCHRONIZA TION REQUIREMENTS THAT THE RECEIVERS MUST SATISFY $IGITAL RECEIVER PROCESSING TECHNIQUES CAN PROVIDE BIT AND FRAME SYNCHRONIZATION DECODINGERRORCORRECTIONCODINGANDDEINTERLEAVING ANDDEMODULA TIONINSOFTWARERADIOIMPLEMENTATIONS 3IMILARLY THETRANSMITTERREQUIREMENTSDEPENDONTHEPROGRAM4HE INPUTDATAMUSTBEMODULATED AMPLIFIED ANDUPCONVERTEDTOTHETRANS MITFREQUENCYANDAMPLIFIEDTOTHEREQUIREDOUTPUTPOWER4HEDETAILS OFTHISPROCESSALSODEPENDONTHESPECIFICSYSTEM3YNCHRONIZATIONAS APPROPRIATETOTHEPROGRAMMUSTBEOBTAINEDTOAVOIDINTERFERINGWITH OTHERSYSTEMUSERS-ODULATIONFORMATSDIFFERFROMONEPROGRAMTOTHE NEXT4HETRANSMITTERPROVIDESTHEFINALAMPLIFICATIONANDITSOUTPUT LEVELISTYPICALLYVARIEDBYADJUSTINGTHELEVELOFTHEINPUTSIGNALPOWER TOTHETRANSMITTERSOTHATTHETRANSMITTEROUTPUTLEVELDOESNOTEXCEED ATHRESHOLDVALUEDICTATEDBYLINEARITYREQUIREMENTS4RANSMITTERPRO TECTIONCIRCUITRYANDPOWERMONITORINGTESTPORTSARETYPICALLYPROVIDED INTHETERMINALDESIGN )NADDITIONTOTHESEFUNCTIONALREQUIREMENTS LARGEGROUNDTERMINALS GENERALLYHAVEFURTHERREQUIREMENTSTOMAINTAINOPERATIONWHENCOM PONENTSFAIL,ARGERTERMINALSAREOFTENREQUIREDTOOPERATEREMOTELY TO THE EXTENT PRACTICAL WHILE BEING SUBJECT TO INCENTIVES TO MAINTAIN AVAILABILITY 3UCH REQUIREMENTS DEMAND ATTENTION TO EFFECTIVE ")4% BUILT INTESTEQUIPMENT CAPABILITIESTOIDENTIFYCOMPONENTSHORTFALLS RAPIDLYANDTOCOMMANDREDUNDANTREPLACEMENTSTOMAINTAINOPERATION 3IGNIFICANTDESIGNATTENTIONMUSTBEPAIDTODEVELOPSYSTEMSCAPABLEOF REMOTEOPERATIONANDHIGHAVAILABILITY /RBITAL!LTERNATIVES -OSTSATELLITECOMMUNICATIONPROGRAMSCONFIGUREACONSTELLATIONOFGEO STATIONARYSATELLITES;=SOTHATTHESATELLITEREMAINSSTATIONARYWITH RESPECTTOGROUNDUSERS4HEABILITYTOREMAINFIXEDWITHRESPECTTOTHE GROUNDUSERSISADVANTAGEOUSINMANYRESPECTS3YSTEMSTHATSERVICE ONLYONEGEOGRAPHICALAREABENEFITFROMGEOSYNCHRONOUSORBITSBECAUSE FIXEDANTENNACOVERAGEISPROVIDEDTOUSERCOMMUNITIES ANDTHEANTENNA BEAMSARENOTCONSTANTLYMOVINGTOMAINTAINCOVERAGETOFIXEDREGIONSOF THEEARTH7ITHTHEEXCEPTIONOFTHEPOLARREGIONS THREESATELLITESPROVIDE ALMOSTGLOBALCOVERAGE&ORTHESEREASONS GEOSYNCHRONOUSALTITUDESATEL LITESAREATRADITIONALCHOICEFORCOMMUNICATIONSATELLITES


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&IGURE )NSTANTANEOUSlELDOFVIEWVERSUSSATELLITEALTITUDE

#HAPTER 4HREE

ANGULARCOVERAGEASTHEALTITUDEDECREASES4HEANGULARFIELDOFVIEW SUBTENDEDBYTHEEARTH &/6 CANBECALCULATEDFROM

&/6SIN H

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&IGURE 3PACE LOSS RELATIVE TO THE NADIR FOR THE HORIZON SOLID LINE AND O A ELEVATIONANGLEDASHEDLINE

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#HAPTER 4HREE

ANDSATELLITESCANBECONFIGUREDFORLOWDATARATEAPPLICATIONS(IGHER DATARATEAPPLICATIONSFORUSERSLOCATEDOUTSIDEOFTHEPOLARREGIONSCAN BEANTICIPATEDTOUSEHIGHERALTITUDESATELLITEORBITALCONFIGURATIONS 2EFERENCES &(2AAB 0!SBECK 3#RIPPS 0"+ENINGTON 3"0OPOVIC .0OTECARY *&3EVIC AND./3OKAL h0OWER!MPLIlERSAND4RANSMITTERSFOR2&AND-ICROWAVE v)%%% 4RANS-ICROWAVE4HEORYAND4ECHNIQUES VOL-ARCH n *#0EDROAND."DE#ARVALHO h#HARACTERIZING.ONLINEAR2&#IRCUITSFOR4HEIR )N BAND3IGNAL$ISTORTION v)%%%4RANS)NSTRUMENTATIONAND-EASUREMENT VOL *UNE n #*#LARK #03IVA !!-OULTHROUP AND-3-UHA h0OWER!MPLIlER #HARACTERIZATION5SINGA4WO4ONE-EASUREMENT4ECHNIQUE v)%%%4RANS -ICROWAVE4HEORYAND4ECHNIQUES VOL*UNE n #*#LARK '#HRISIKOS -3-UHA !!-OULTHROP AND#03ILVA h4IME$OMAIN %NVELOPE-EASUREMENT4ECHNIQUEWITH!PPLICATIONTO7IDEBAND0OWER!MPLIlER -ODELING v)%%%4RANS-ICROWAVE4HEORYAND4ECHNIQUES VOL$ECEMBER n -#*ERUCHIM 0"ALABAN AND+33HANMUGAN 3IMULATIONOF#OMMUNICATION 3YSTEMS.EW9ORK+LUWER 0LENUM !+ATZ h,INEARIZATION2EDUCING$ISTORTIONIN0OWER!MPLIlERS v)%%%-ICROWAVE -AGAZINE VOL NO$ECEMBER n !7$ISSANAYAKE h!PPLICATIONOF/PEN,OOP5PLINK0OWER#ONTROLIN+A BAND 3ATELLITE,INKS v0ROC)%%% VOL*UNE n 2"$YBDAL h2ADIOMETER)NTEGRATEDWITH#OMMUNICATIONS4ERMINAL v)%%% 3YMPOSIUM$IGEST*UNE n 2"$YBDALAND-!2OLENZ h3ATELLITE"EACONFOR5(&3YSTEM5SERS v )%%%-),#/-3YMPOSIUM$IGEST/CTOBER SEEALSO2"$YBDALAND-! 2OLENZ h-ETHODOF$ETERMINING#OMMUNICATION,INK1UALITY%MPLOYING"EACON 3IGNALSv-AY 530ATENT $*#ORNELIUS !*(ERRIDGE 23ILK AND044HOMPSON h4HE).4%,3!46))) 6)))! 'ENERATIONOF'LOBAL#OMMUNICATION3ATELLITES v)NTER*OUR3ATELLITE#OMMUNICATIONS VOL*ANUARY &EBRUARY n 2,0ETERSON 2%:IEMER AND$%"ORTH )NTRODUCTIONTO3PREAD3PECTRUM #OMMUNICATIONS0RENTICE(ALL &#ARDUCCIAND-&RANCESI h4HE)4!,3!43ATELLITE3YSTEM v)NTERNATIONAL*OUR 3ATELLITE#OMMUNICATIONS VOL*ANUARYn&EBRUARY n $%$UDGEON h&UNDAMENTALSOF$IGITAL!RRAY0ROCESSING v0ROC)%%% VOL *UNE n 2*-AILLOUX 0HASED!RRAY!NTENNA(ANDBOOK 3ECOND%DITION.ORWOOD-! !RTECH -'"ELLANGERAND*,$AGUET h4$- &$-4RANSMULTIPLEXER$IGITAL0OLYPHASEAND &&4 v)%%%4RANSON#OMMUNICATIONS VOL#/- 3EPTEMBER n 4'EBAUERAND(''OEKLER h#HANNEL)NDIVIDUAL!DAPTIVE"EAMFORMINGFOR -OBILE3ATELLITE#OMMUNICATIONS v)%%%4RANS3ELECTED!REASON#OMM VOL3!# &EBRUARY n *0(AVLICEK *#-C+EEMAN AND072EMAKLUS *R h.ETWORKSOF,OW%ARTH /RBIT3TOREAND&ORWARD3ATELLITES v)%%%4RANS!EROSPACEAND%LECTRONIC3YSTEMS VOL!%3 !PRIL n 2-IURA 44ANAKA )#HIBA !(ORIE AND9+ARASAWA h"EAMFORMING%XPERIMENT WITHA$"&-ULTIBEAM!NTENNAINA-OBILE3ATELLITE%NVIRONMENT v)%%%4RANS !NTENNASAND0ROPAGATION VOL!%3 !PRIL n &!NANASSOAND&$0RISCOLI h4HE2OLEOF3ATELLITESIN0ERSONAL#OMMUNICATION 3ERVICES v)%%%*OURNAL3ELECTED!REASON#OMMUNICATIONS VOL3!# &EBRUARY n

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#HAPTER

0ROPAGATION,IMITATIONS AND,INK0ERFORMANCE

/VERVIEW #OMMUNICATIONSYSTEMPERFORMANCEDEPENDSONTHERECEIVERANDTRANS MITTER CAPABILITIES THE PROPAGATION MEDIUM AND THE MODULATION AND MULTIPLEACCESSTECHNIQUES4HEPROPAGATIONOFSATELLITELINKSATMICRO WAVEFREQUENCIESISRELATIVELYCLOSETOIDEALVACUUMCONDITIONS BUTTHE 5(& AND %(& EXTREMES ARE IMPACTED BY PROPAGATION IMPAIRMENTS ! USEFUL COMPENDIUM OF PROPAGATION DATA ;= COVERING BOTH 5(& AND %(& CHARACTERISTICS DESCRIBES PREDICTIVE TECHNIQUES TO ADDRESS THESE IMPAIRMENTS 5(& SYSTEMS ARE SUBJECT TO IONOSPHERIC EFFECTS AND THE RELATIVELYHIGHGALACTICANDMANMADENOISELEVELSTHATHAVEASIGNIFICANT IMPACTONSYSTEMPERFORMANCE)NADDITION THERELATIVELONGWAVELENGTHS ANDREASONABLESIZELIMITATIONSCONSTRAINTHEBENEFITSTHATANTENNASCAN PROVIDEATHIGHERFREQUENCIESWHEREAGIVENPHYSICALSIZECORRESPONDSTO AGREATERELECTRICALSIZE"OTHTHENORMALWATERVAPORANDOXYGENABSORP TIONCHARACTERISTICSWITHINTHEATMOSPHERERESULTINMODERATEATTENUATION AWAYFROMTHE%(&RESONANTFREQUENCIES WHILEHYDROMETEORS CLOUDS ICE CRYSTALS HAIL SNOW ANDPARTICULARLYRAINHAVEMOREPRONOUNCEDEFFECTS ON%(&PROPAGATION4HESIZEOFATMOSPHERICHYDROMETEORSBECOMESA SIGNIFICANT FRACTION OF THE %(& WAVELENGTHS RESULTING IN ATMOSPHERIC ATTENUATIONANDDEPOLARIZATIONTHATCANSIGNIFICANTLYCONSTRAINSYSTEM PERFORMANCE ,OWER MICROWAVE FREQUENCIES ARE RELATIVELY UNAFFECTED BECAUSE THE HYDROMETEORS ARE SMALLER COMPARED TO MICROWAVE WAVE LENGTHS)NCONFIGURINGSYSTEMDESIGNS SIGNALMODULATIONFORMATS CODING ANDINTERLEAVINGTECHNIQUES ANDMULTIPLEACCESSTECHNIQUESTHATALLOW MULTIPLEUSERSTOSHARESATELLITERESOURCESMUSTBEADDRESSEDANDTHEIR

#HAPTER &OUR

SELECTIONALSODICTATESTHECAPACITYOFSYSTEMS4HISCHAPTERDISCUSSES THEPROPAGATIONISSUESANDTHEPROCESSOFLINKANALYSES 0ROPAGATION,IMITATIONS 4HEIONOSPHERICPROPAGATIONISBUTONEOFTHELINKIMPAIRMENTSTHAT IMPACTTHEOPERATIONOF5(&SYSTEMS; =4HELONG5(&WAVELENGTH ANDREASONABLECONSTRAINTSONPHYSICALSIZELIMITSTHEELECTRICALSIZEOF THE5(&ANTENNAS&ORUSERS THERESULTINGBROADPATTERNCHARACTERIS TICSCREATEFURTHERIMPAIRMENTSARISINGFROMMULTIPATHANDBLOCKAGEBY MANMADEANDTERRESTRIALFEATURESINTHETERRAIN)NADDITION SPECTRAL CROWDINGANDDEMANDSFOROTHERSERVICESRESULTININTERFERENCEISSUES !DDITIONALLY THEBACKGROUNDNOISELEVELAT5(&RESULTSFROMNOTONLY THE NATURAL GALACTIC BACKGROUND THE RADIATION NOISE CREATED BY THE -ILKY7AY BUTALSOMANMADENOISETHATCONTINUESTOINCREASEWITH LEVELSTHATEXCEEDTHENATURALGALACTICBACKGROUND4HUS INADDITIONTO PROPAGATIONLIMITATIONS OTHERFACTORSRESULTINAVARIETYOFLINKIMPAIR MENTSTHATIMPACT5(&SYSTEMS&ORTHISREASON ABEACONHASBEEN PROPOSED;=TOPROVIDESYSTEMUSERSWITHAREAL TIMEINDICATIONOFTHE VALUESOFINDIVIDUAL5(&LINKIMPAIRMENTSANDAMEANSTODETERMINE THEAVAILABLECOMMUNICATIONCAPABILITIES 0ROPAGATIONAT%(&FREQUENCIESISSENSITIVETOWEATHER4HEPRINCIPAL CONCERNISRAINFALL BUTCLOUDSANDICECRYSTALSALSOIMPAIRPROPAGATION 4HREE MAJOR EFFECTS MUST BE ADDRESSED4HE FIRST IS ATTENUATION THAT BOTHREDUCESSIGNALLEVELSANDPRODUCESADDITIONALNOISE4HESECONDIS DEPOLARIZATIONTHATRESULTSSINCEHYDROMETEORSARENOTIDEALLYSPHERI CAL#ROSS POLARIZEDLEVELSINCREASEASRAINRATESINCREASE ANDFORSYS TEMS THAT OPERATE USING ORTHOGONAL POLARIZATION AND HAVE HIGH RAIN MARGINS PERFORMANCEISDEGRADEDBYNOTONLYSIGNALLOSSBUTALSOCO CHANNELINTERFERENCERESULTINGFROMINCREASEDCROSS POLARIZATION4HE THIRDFACTORISTHEhWETANTENNAvPROBLEM WHICHISOFTENOVERLOOKEDIN LINKANALYSES!SIGNIFICANTEFFORTTOUNDERSTANDTHESELIMITATIONSAND DEVELOPPREDICTIVETECHNIQUESHASEVOLVEDOVERTHELASTYEARS )ONOSPHERIC,IMITATIONS

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#HAPTER &OUR

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#HAPTER &OUR

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#HAPTER &OUR

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#HAPTER &OUR

4HEOUTPUTOFTHERADIOMETERISPROPORTIONALTOTHEINPUTNOISELEVEL THATDEPENDS INPART ONTHEANTENNASNOISETEMPERATURE ASILLUSTRATEDIN &IG 4HEANTENNASNOISETEMPERATUREDEPENDSONTHEPROPAGATION LOSS THEREBYPROVIDINGAMEANSOFDETERMININGTHEATTENUATION2ECALLTHAT THERAINATTENUATIONGENERATESNOISELIKEANYOTHERLOSSCOMPONENTAND AS EXPLAINEDIN#HAPTER HASANIMPACTONTHESYSTEMNOISETEMPERATURE OFTHERADIOMETER4HECHANGEINTHEEMISSIONTEMPERATUREWHENRAINFALL ISPRESENT INDICATEDBYTHERADIOMETER ISRELATEDTOTHEATTENUATION4HE EMISSIONTEMPERATUREINCREASE SHOWNIN&IG ILLUSTRATESTHISEFFECT 4HREEDIFFERENTEMPIRICALTEMPERATUREVALUESAREINDICATEDINTHISFIGURE +ISANAMBIENTVALUECOMMONLYUSEDFORHARDWARELOSS+IS COMMONLYUSEDBECAUSEOFTHETEMPERATUREDECREASEATHIGHALTITUDES CONTAININGRAINDROPSAND+ISANAVERAGEVALUEFORHIGHFREQUENCIES EG '(Z WHEREATHIGHRAINRATES SIGNALENERGYISSCATTEREDOUTOF THEBEAM4HEFIGUREINDICATESTHATTHEMEASUREMENTSDYNAMICRANGEIS LIMITEDBYTHEKNOWLEDGEOFTHEEMPIRICALTEMPERATURE THUSARADIOMETER ISMOSTUSEFULFORMEASURINGRAINATTENUATIONATLOWERRAINRATES ! NOVEL APPLICATION OF THIS TECHNIQUE ;= INTEGRATES A RADIOMETER WITHTHETERMINALRECEIVERTHATPROVIDESAREAL TIMEMEASUREMENTOFTHE DOWNLINKATTENUATION4HISDESIGNCONCEPTWASDEVELOPEDFORFREQUENCY HOPPEDSYSTEMSANDCANBEIMPLEMENTEDINEXPENSIVELY/THERRECEIVER MODULATIONSCANOFFSETTHERADIOMETRICMEASUREMENTCHANNELFROMTHE OPERATINGBANDWIDTHTOACHIEVETHISATTENUATIONMEASUREMENTCAPABILITY 4HE RADIOMETER AND THE SYSTEM RECEIVER SHARE THE EXPENSIVE SYSTEM

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#HAPTER &IVE

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3ECTORBLANKINGRESTRICTSTHEOPERATIONOFOFFENDINGSYSTEMSINTHEDIREC TION OF THE TERMINAL &OR EXAMPLE HIGH POWER DENSITIES PRODUCED BY RADARSYSTEMSCANBECONTROLLEDBYLIMITINGTHERADARSAZIMUTHAND ELEVATIONCOVERAGEWHENRADARINFORMATIONINTHOSEDIRECTIONSMAYNOT BE OF PARTICULAR INTEREST4HE SECTOR BLANKING CONSTRAINTS LIMIT RADAR ILLUMINATIONOVERPORTIONSOFTHERADARSSCANTOAVOIDINTERFERENCEWITH OTHER SYSTEMS AN EXAMPLE OF AN OPERATIONAL SOLUTION TO INTERFERENCE PROBLEMS 3ITE SURVEYS USE SPECTRUM ANALYZER INSTRUMENTATION TO MEASURE INTERFERENCE POWER4HE SYSTEM ILLUSTRATED IN &IG ;= USES A LOG PERIODIC ANTENNA TO SAMPLE THE INCIDENT INTERFERENCE PERFORMS THE MEASUREMENTSWITHAPORTABLESPECTRUMANALYZER COVERSA-(ZTO '(ZFREQUENCYRANGE ANDHASPREAMPLIFIERSWITHPROTECTIVEFILTERS TOOFFSETTHEINHERENTLYHIGHNOISEFIGUREOFTHESPECTRUMANALYZER4HE PHOTOGRAPHILLUSTRATESTHELOGPERIODICANTENNA THEPREAMPLIFIERSON THESHELFOFTHETRIPOD ANDTHESPECTRUMANALYZERLOCATEDONTOPOFTHE SYSTEMS SHIPPING CASES4HIS PARTICULAR SYSTEM PROVIDES HIGH MEA SUREMENTSENSITIVITYOVERAVERYBROADBANDWIDTHTOACCOMMODATEA VARIETYOFSURVEYTASKS'ENERALLY SITESURVEYEQUIPMENTREQUIRESHIGH

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#HAPTER &IVE

SENSITIVITYOVERTHEBANDWIDTHUSEDBYTHESYSTEM ANDAFILTERWHOSE RESPONSEEMULATESTHEACTUALSYSTEMSINPUTBANDPASSFILTERISUSEDTO DETERMINEINTERFERENCELEVELSATTHEOPERATIONALSYSTEMS,.!INPUT TERMINALS/UTSIDEOFTHEOPERATINGBANDWIDTHOFTHESYSTEM THEUSERS SYSTEMFILTERINGISEFFECTIVEINREDUCINGINTERFERENCELEVELS4HUS THE REQUIREDSENSITIVITYOFTHESURVEYEQUIPMENTISREDUCEDCOMPAREDTOITS IN BANDREQUIREMENTS ANDTHEPREAMPLIFICATIONISNOTREQUIRED 3EVERAL ISSUES MUST BE ADDRESSED IN CALIBRATING THE SURVEY EQUIP MENT4HE ANTENNA GAIN OF THE SURVEY ANTENNA MUST BE DETERMINED SO THAT THE RECEIVED SIGNALS CAN BE RELATED TO AN ISOTROPIC GAIN LEVEL FOR REFERENCE PURPOSES &OR EXAMPLE THE LOG PERIODIC ANTENNA HAS A BORESIGHTGAINVALUEOFD"IFORTHESYSTEMSHOWNIN&IG 7HEN PREAMPLIFIERSAREUSED THEIRGAINVALUESAREALSOREQUIREDTORELATETHE SPECTRUM ANALYZERS INDICATED LEVEL TO THE POWER AT THE TERMINALS OF THESURVEYANTENNA4HISSYSTEMUSESTWOPREAMPLIFIERSATEACHOFTWO LOWERFREQUENCYBANDSTHATCOVERTHE-(ZTO'(ZANDTO'(Z BANDWIDTHS RESPECTIVELY ANDASINGLEPREAMPLIFIERTHATCOVERSTHETO '(ZBANDWIDTH4HESYSTEMSSENSITIVITYEXPRESSEDINA'4GAIN OVERTEMPERATURE VALUESHOWNIN&IG ILLUSTRATESTHESENSITIVITY BENEFITSOFTHEPREAMPLIFIERSANDTHEBORESIGHTANTENNAGAINOFTHELOG PERIODICANTENNA&ORREFERENCEPURPOSES THE'4OFASYSTEMHAVINGA +SYSTEMNOISETEMPERATUREANDANISOTROPICANTENNAGAININTHE SIDELOBEREGIONISALSOINDICATED

&IGURE '4SENSITIVITYOFSURVEYEQUIPMENT;=


,IKETHEOPERATIONALSYSTEM THESURVEYEQUIPMENTREQUIRESLINEAR OPERATIONTOOBTAINVALIDRESULTS&ORTHISSYSTEM THED"COMPRESSION POINTSOFTHEPREAMPLIFIERSANDSPECTRUMANALYZERWEREUSEDTOINDICATE THE LINEARITY LIMITATIONS AND THE POWER LEVELS INDICATED AT THE SPEC TRUMANALYZERREFERENCEDTOTHED"COMPRESSIONPOINTAREINDICATEDIN &IG 4HEPREAMPLIFIERSINTHISCASEHAVED"COMPRESSIONLEVELSOF ABOUTD"MATTHEIROUTPUT WHILETHESPECTRUMANALYZERINTHISCASE HASAD"COMPRESSIONLEVELOFnD"MATITSINPUTTERMINALWITHOUT ATTENUATION4HEFILTERSELECTIVITYOFTHESPECTRUMANALYZERANDTHEUSE OFTHESPECTRUMANALYZERSATTENUATORSPROVIDELINEAROPERATIONWHEN THESPECTRUMANALYZERMEASURESSPECTRALCHARACTERISTICSWELLREMOVED FROMHIGH LEVELSOURCES!COMBINATIONOFFIXEDFILTERSANDVARIABLE9)' BANDREJECTFILTERSWEREALSOUSEDTOAVOIDSPECTRUMANALYZERAND,.! LOW NOISEAMPLIFIER COMPRESSIONTOMAINTAINSYSTEMLINEARITYINMEA SUREMENTSITUATIONSWHEREHIGH LEVELINTERFERENCEWASPRESENT)NADDI TION THE PREAMPLIFIERS COULD ALSO BE REMOVED TO INCREASE THE LINEAR DYNAMICRANGEFORHIGH LEVELSIGNALSATTHEEXPENSEOFSENSITIVITYFOR LOW LEVELSIGNALS ASINDICATEDIN&IG 3ITESURVEYSSHOULDALLOWSUFFICIENTMEASUREMENTTIMETOOBSERVEALL POTENTIALLYINTERFERINGSYSTEMSBECAUSESOMESYSTEMSARENOTOPERATED CONTINUOUSLY4HEIMPACTSOFFUTURENEARBYSYSTEMSMUSTBEADDRESSED

&IGURE ,INEARITYLIMITATIONSOFSURVEYEQUIPMENT;=

#HAPTER &IVE

BYSEPARATEANALYSES)NSOMECASES SITEFREQUENCYMANAGERSAREAVAIL ABLETOPROVIDEDATAONEXISTINGSYSTEMSANDTHEINSTALLATIONSOFFUTURE SYSTEMS4HESEDATAAREUSEDINANALYSESTHATACCOUNTFORTHESEPARA TIONBETWEENSYSTEMS ANYTERRAINBLOCKAGEINTHEPATHBETWEENSYS TEMS TRANSMITPOWERLEVELS ANDTHEGAINSOFTHEPOTENTIALLYINTERFERING TRANSMITANTENNAANDTHERECEIVERSANTENNAINTHEDIRECTIONSBETWEEN THETWOSITESANDTHEINTERFERENCESPECTRA 0OTENTIAL)NTERFERENCE3OURCES

! SECOND MEANS OF DEFINING THE INTERFERENCE ENVIRONMENT EXAMINES POTENTIALINTERFERENCESOURCESTHATOPERATENEARTHERECEIVERSDESIGN BANDWIDTH ANDOR HAVE POSSIBLE HARMONICS OR OUT OF BAND NOISE THAT FALLSWITHINTHERECEIVERSBANDWIDTH4HISAPPROACHISOFTENUSEDFOR MOBILERECEIVERSTHATHAVETOOPERATEINARBITRARYLOCATIONS4HEMOBILE EQUIPMENTDOESNOTEXPERIENCEEVERYPOSSIBLEINTERFERENCEENVIRONMENT BUT REPRESENTATIVE INTERFERENCE SOURCES CAN BE ADDRESSED /FTEN THE GOALOFTHESEANALYSESISTODETERMINETHEMINIMUMREQUIREDSEPARATION BETWEENTHEPOTENTIALINTERFERENCEANDTHERECEIVERNEEDEDTOACHIEVE ACCEPTABLERECEIVEROPERATION 3UCHANALYSESPROCEEDBYDETERMININGTHEPOWERDENSITYVARIATIONS OFTHEINTERFERINGSYSTEMASAFUNCTIONOFSEPARATIONFROMTHATSYSTEM 7HENTHESYSTEMSARESEPARATEDBYFARFIELDDISTANCES THEPOWERDEN SITYHASA2VARIATION4HEINTERFERENCEPOWERRECEIVEDBYTHESYSTEM BEING ANALYZED EQUALS THE INCIDENT POWER DENSITY MULTIPLIED BY THE EFFECTIVEAPERTUREOFTHESYSTEMBEINGANALYZED4HEEFFECTIVEAPERTURE EQUALSKOMULTIPLIEDBYTHEANTENNAGAIN BYDEFINITION'ENERALLY A WORST CASEANTENNAGAINLEVELISUSEDINITIALLYTODETERMINETHEPOTENTIAL OFAPROBLEM)FAPOTENTIALPROBLEMISIDENTIFIED THEASSESSMENTCAN BEREFINEDUSINGUPDATEDVALUES&ORTHESPACESEGMENT THEWORST CASE LEVELSARETHEPEAKGAINOFTHEANTENNAFORMAINBEAMILLUMINATION AND ASDISCUSSED FORTHEUSERSEGMENT ANISOTROPICGAINLEVELISCOMMONLY USED WHEN THE INTERFERENCE POWER IS RECEIVED THROUGH THE ANTENNAS SIDELOBESTHATAREWIDELYSEPARATEDFROMTHEMAINBEAM4HEEFFECTS OFANYTERRAINBLOCKAGEBETWEENTHEINTERFERENCESOURCEANDTHEUSERS ANTENNAMUSTALSOBEADDRESSEDTOOBTAINREALISTICRESULTS )NSOMECASES THEINTERFERINGANDVICTIMSYSTEMSARENOTSEPARATED BYFARFIELDDISTANCES4HEMUTUALCOUPLINGBETWEENPAYLOADANTENNAS ON A SPACECRAFT IS A COMMON EXAMPLE 5SER SYSTEMS OPERATING CLOSE TOLARGEGROUNDTERMINALSCANALSOBEWITHINTHEINTERFERENCESOURCES NEARFIELD7HILETHENEARFIELDANTENNACHARACTERISTICSCANBEANALYZED ANUNDERSTANDINGOFNEARFIELDBEHAVIORPROVIDESSUFFICIENTINSIGHTTO OBTAINFIRST ORDERPOWERDENSITYESTIMATES3UCHESTIMATESCANQUICKLY ASSESSTHEPOTENTIALOFAPROBLEM)FTHISPOTENTIALEXISTS MOREREFINED ANALYSESANDORMEASUREMENTSCANBEPERFORMED


4WODISTINCTNEARFIELDREGIONSEXIST4HENEARFIELDOFTHEAPERTURE FIELDSPROPAGATESASACOLLIMATEDDISTRIBUTIONLOCATEDAROUNDTHEANTEN NASBORESIGHT7HENTRANSMITTING THENEARFIELDPOWERDENSITYINTHIS REGIONISROUGHLYEQUALTOTHETRANSMITPOWERDIVIDEDBYTHEAPERTURE AREA4HISNEARFIELDREGIONISSELDOMOFINTERESTBECAUSEOTHERANTEN NASWITHINTHISREGIONWOULDBLOCKTHEANTENNASMAINBEAMANDCON SEQUENTLYREDUCETHEANTENNASGAINLEVEL&OREXAMPLE SEARCHRADARS COMMONLYSCANINAZIMUTHBUTSTRONGLYILLUMINATINGOBJECTSCLOSETOTHE MAINBEAMWOULDSHADOWMOREDISTANTTARGETSORRESULTINMULTIPATH ERRORS THUSREDUCINGDETECTIONPERFORMANCE-OSTSEARCHRADARSHAVE REDUCEDANTENNAGAINLEVELSATLOWELEVATIONANGLESTOMINIMIZETER RESTRIALILLUMINATIONSOTHERADARSOPERATIONISNOTLIMITEDBYCLUTTER RETURNSFROMTHESURROUNDINGTERRAIN4HEREDUCEDANTENNAGAINLEVEL ALSORESULTSINREDUCEDINTERFERENCEPOWERRECEIVEDBYUSERTERMINALS !WAY FROM THIS MAIN BEAM REGION THE FIELDS ARE PRODUCED BY THE SAMEMECHANISMSTHATPRODUCETHEWIDEANGLEFARFIELDSIDELOBES&OR EXAMPLE THEWIDEANGLESIDELOBESOFREFLECTORANTENNASAREPRODUCED BYTHECOMPLEXSUMOFDIRECTFEEDILLUMINATIONANDSPILLOVER BLOCKAGE FROMTHEFEEDSUPPORTS ANDEDGEDIFFRACTION.OTSURPRISINGLY THEHIGH ESTPOWERDENSITIESINTHISREGIONARETYPICALLYINTHESPILLOVERREGIONS ANDINREGIONSWHEREFEEDSUPPORTSTRUTSSCATTERTHESIGNAL4HESESAME MECHANISMS PRODUCE THE FAR FIELD WIDE ANGLE SIDELOBES4HE LEVELS OF THESESIDELOBESARETYPICALLYBOUNDEDBYANISOTROPICGAINLEVEL BECAUSE IFTHEIRLEVELWEREHIGHER THEANTENNASDIRECTIVITYWOULDBEREDUCED 4HESE SAME SIDELOBE MECHANISMS COMBINE IN A COMPLEX SUM IN THE NEAR FIELD BUT THEIR PHASING FINITE RANGE SEPARATIONS AND DIFFERENT ANGULARRELATIONSHIPSPRODUCEARANGEDEPENDENCEUNLIKETHEFARFIELD BEHAVIOR4HEPEAKPOWERDENSITIESINTHENEARFIELDARESTILLBOUNDED BYANISOTROPICGAINVALUE4HESEASSERTIONSHAVEBEENVERIFIEDBYANA LYTICPROJECTIONSOFNEARFIELDPOWERDENSITIESANDFURTHERVALIDATEDBY MEASUREMENT -EASUREMENTS CAN BE PERFORMED TO ESTABLISH THE NEAR FIELD POWER DENSITIESFROMATRANSMITTINGANTENNATHATISAPOTENTIALINTERFERENCE SOURCE4HESPECTRUMANALYZERINSTRUMENTATIONDESCRIBEDFORSITESUR VEYSCANBEUSEDFORSUCHMEASUREMENTS4HEPOWERLEVELSRECEIVEDBY THESURVEYANTENNACANBEPERFORMEDATVARIOUSLOCATIONSANDDISTANCES TOMEASURETHENEARFIELDANTENNATRANSFERFUNCTIONTHATCOULDBEEXPERI ENCEDBYAUSERTERMINALOPERATINGINTHEINTERFERINGANTENNASVICINITY 4HEANTENNASNEARFIELDDISTRIBUTIONSCANALSOBEPREDICTEDBYUSING ANALYTIC CODES AN EXAMPLE OF SUCH ANALYSES IS DESCRIBED IN &IG WHEREAPORTIONOFTHECOLLIMATEDNEARFIELDREGIONPROVIDESFIELDUNI FORMITYSUFFICIENTFORANTENNATESTING3UCHANALYTICTECHNIQUESALLOW IDENTIFICATIONOFNEARFIELDREGIONSHAVINGHIGH POWERDENSITYVALUESTO SAVEMEASUREMENTTIME

#HAPTER &IVE

4HE ANALYSIS ANDOR MEASUREMENT FOR TRANSMIT ANTENNAS CAN ALSO ADDRESSARELATEDPROBLEM(IGH POWERTRANSMITANTENNASCANPRODUCE POWERDENSITYLEVELSTHATRAISEBIOLOGICALCONCERNS THERADIATIONHAZARD PROBLEM!COMMONLYUSEDPOWERDENSITYVALUEFORRADIATIONHAZARD LEVELS;=ISM7CM-EASUREDNEARFIELDPOWERDENSITYLEVELSPRO VIDEDATANEEDEDTOASSESSRADIATIONHAZARDCONCERNS4HEPOWERDEN SITY VALUES OF CONCERN ARE VERY HIGH AND ALLOW MEASUREMENTS TO BE CONDUCTEDATREDUCEDTRANSMITPOWERLEVELS!SIGNALGENERATORCANBE USEDINPLACEOFTHEOPERATIONALHIGH POWERTRANSMITTERTOPROTECTPER SONNELWHILEPERFORMINGTHEMEASUREMENTS)NADDITION NARROWBAND WIDTHWAVEFORMSFROMTHESIGNALGENERATORANDTHESPECTRUMANALYZER SENSITIVITYAFFORDAMPLEDYNAMICRANGEINTHEMEASUREMENTS4HEEND OBJECTIVEISTODETERMINELOCATIONSTHATPERSONNELSHOULDAVOIDWHEN THESYSTEMISTRANSMITTINGATFULLPOWER 3TANDARDS

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MAGNETICFIELDSTRENGTHSAREREQUIREDTODEMONSTRATE%-)%-#COM PLIANCEATTHOSEFREQUENCYRANGES3UCHLOWFREQUENCIESAREABACKDOOR CONSIDERATION AND PRINCIPALLY CONCERN SYSTEM ELECTRONIC COMPONENTS %-)%-#COMPLIANCEANDATTENTIONTOSHIELDINGRECEIVERCOMPONENTS INTHEDESIGNRESULTINTHEPRINCIPALINTERFERENCECONCERNBEINGFRONT DOORILLUMINATIONTHROUGHTHEANTENNASYSTEM !TYPICALLEVELFORTHESUSCEPTIBILITYTESTINGATMICROWAVEFREQUENCIES ISVOLTSMETER4HISFIELDSTRENGTHCORRESPONDSTOAPOWERDENSITYOF 7M ORD"7M REQUIREDFORTESTPURPOSES!SANASIDE THE RADIATION HAZARD LEVEL PREVIOUSLY DISCUSSED EQUALS M7CM WHICH CORRESPONDSTOD"7M4HEVOLTMETERILLUMINATIONOF%-)%-# MEASUREMENTSISROUGHLYD"LOWERTHANTHERADIATIONHAZARDLEVEL 4HERADIATIONHAZARDLEVELWASDERIVEDFROMSOLARFLUXDENSITYVALUESSO THATTHERMALHEATINGFROM%-)%-#TESTINGISNOTACONCERN4HESUSCEP TIBILITYLEVELSAREUSEDINEVALUATIONPAYLOADCOMPONENTS BUTFORANTENNA SYSTEMS OTHERLIMITSSPECIFYTHEIN BANDSUSCEPTIBILITYLEVELSASWELLAS THE OUT OF BAND REJECTION REQUIREMENTS NEAR THE OPERATING BANDWIDTH 3UCHLIMITSSPECIFYTHELINEARDYNAMICRANGEREQUIREDOFTHERECEIVERAND FURNISHDESIGNGUIDANCEONFILTERINGREQUIREMENTS%-)%-#COMPLIANCE REQUIRESDEMONSTRATIONTHATTHECOMPONENTOPERATESWITHOUTMALFUNCTION ORPERFORMANCEDEGRADATION!NEXAMINATIONOFTHEVALUESUSEDINTHE STANDARDSASTHEYEVOLVEWITHTIMEINDICATETHATRECENTSTANDARDSHAVE MORESTRINGENTREQUIREMENTSTHANEARLIERSTANDARDS REFLECTINGINCREASED AWARENESSOFTHEGROWINGPROBLEMOFINTERFERENCE 4HETESTINGTOESTABLISH%-)%-#COMPLIANCENECESSARILYCOVERSTHE BROADBANDWIDTHSTIPULATEDINTHESTANDARDS#ALIBRATEDANTENNASFOR SUCHMEASUREMENTSAREAVAILABLEFROMSPECIALTYVENDORS)NMANYCASES SMALL PROBE ANTENNAS ARE USED INhSNIFF TESTSv TO BOTH RECEIVE EQUIP MENTEMISSIONSANDTOILLUMINATECOMPONENTPIECES-EASUREMENTSOF SPACECRAFTANTENNASMAYUSEPAYLOADANTENNAMODELSANDMOCKUPSOF PORTIONSOFTHESPACECRAFTININITIALSTUDIESASAMEANSOFREDUCINGTHE RISK OF COMPLYING DURING QUALIFICATION TESTS 3UCH MEASUREMENTS ARE GENERALLY WITHIN THE ANTENNAS NEAR FIELDS AND CONSIDERATION OF RADI ATEDHARMONICLEVELSMUSTBEADDRESSED'ENERALLY THEPAYLOADANTEN NASAREISOLATEDFROMTHEPAYLOADELECTRONICSWITHINTHEVEHICLESBUS STRUCTUREBYTHERMALBLANKETS PANELSTRUCTURE AND&ARADAYSHIELDING 4HEPRINCIPAL%-)%-#ATTENTIONFORSPACECRAFTANTENNASISTHEREFORE DIRECTED TOWARDS THE INTERACTION BETWEEN PAYLOAD ANTENNAS &OR THE ANTENNASYSTEMS ADDITIONALMEASUREMENTSATOUT OF BANDFREQUENCIES MAYBEREQUIREDTOEVALUATEPOTENTIALSUSCEPTIBILITIES0ERFORMINGSUCH MEASUREMENTS DURING DEVELOPMENT TESTING FOR THE IN BAND ANTENNA PERFORMANCEMAYBESCHEDULE ANDCOST EFFECTIVE 4HESESTANDARDSALSOPROVIDEDESIGNGUIDANCEDURINGSYSTEMDEVEL OPMENTTOAVOIDINTERNALLYGENERATEDINTERFERENCESUSCEPTIBILITIESAND

#HAPTER &IVE

TOREDUCEEMISSIONSFROMTHESYSTEMSTHATCOULDINTERFEREWITHOTHER SYSTEMS3YSTEMDESIGNGENERALLYINCLUDESEXTENSIVE%-)%-#ANALY SESFORTHEVARIOUSSUBSYSTEMSCOMPRISINGTHEDESIGNTOAVOIDINTERFER ENCEBETWEENSUBSYSTEMS4HISPROCESSSTARTSWITHFREQUENCYPLANNING WITHINTHESUBSYSTEMSTOMINIMIZETHEPOTENTIALINTERFERENCEEG THE SELECTIONOFLOCALOSCILLATORFREQUENCIES )&S ANDSOFORTH 4HEPOTENTIAL INTERMODULATIONPRODUCTS HARMONICS SPURIOUSOUTPUTS ANDNOISELEVELS FROM VARIOUS SYSTEM COMPONENTS ARE INCLUDED IN THESE DESIGN DEVEL OPMENT ACTIVITIES 3UCH ANALYSES ALSO ADDRESS FREQUENCY COMPONENTS CONDUCTEDONTHEPRIMEPOWER4HEPOTENTIALINTERFERINGPATHSINATYPI CAL SPACECRAFT CAN NUMBER IN THE THOUSANDS!T THE DESIGN LEVEL THE PLAUSIBILITYOFTHEPOTENTIALPATHSSHOULDBEASSESSED ANDTHOSEPATHS THAT APPEAR TROUBLESOME OR HAVE LITTLE MARGIN SHOULD BE SPECIFICALLY IDENTIFIEDFORFURTHERSTUDYANDEVALUATION)NMANYCASES %-)%-# SHORTFALLSARETHERESULTOFWORKMANSHIPERRORS0ARTOFTHE%-)%-# ANALYSESSHOULDADDRESSSYSTEMELEMENTSWHERESUCHERRORSCOULDLEAD TONONCOMPLIANCE#AREFULATTENTIONTOTHESEDETAILED%-)%-#ANALY SES BENEFITS SYSTEM TESTING AND IDENTIFIES FACTORS THAT MERIT SPECIAL ATTENTIONDURINGSUCHTESTS )NTERMSOFSUSCEPTIBILITYANALYSES THE%-#%-)REQUIREMENTLEVELS PROVIDEGUIDANCEININTERFERENCESTUDIESTODETERMINEPOTENTIALPROB LEMS#OMPLIANCEWITHTHE%-)%-#REQUIREMENTSINDICATESALEVELOF INCIDENTPOWERDENSITYTHATCANBETOLERATEDWITHOUTSYSTEMMALFUNC TION4HUS COMPLIANCEWITHSTANDARDSPROVIDESAhSAFEvLEVELTOADDRESS POTENTIALSYSTEMDEGRADATIONANDDEFINITIONOFINTERFERENCEPOWERDEN SITIESTHATMUSTBEEXCEEDEDTOPRODUCEPOTENTIALSYSTEMSHORTFALLS)N SOMECASES ACAPABILITYISREQUIREDTOMONITORTHEFIELDSTRENGTHOFINCI DENTSIGNALSANDIDENTIFYTIMEPERIODSWHERETHRESHOLDFIELDSTRENGTH LEVELSAREEXCEEDED!SIMPLEBROADBANDWIDTHRECEIVERFORTHISPURPOSE ISDESCRIBEDIN#HAPTER )NTERFERENCE3CENARIOS

)NTERFERENCEANALYSESOFTENUSESCENARIOSTODEFINEANTICIPATEDNUMBERS AND POWER LEVELS OF THE INTERFERENCE SOURCES THEIR LOCATIONS SPECTRAL CHARACTERISTICS AND OPERATION 3UCH SCENARIOS ARE COMMONLY USED TO ASSESSTHEEFFECTSOFINTENTIONALINTERFERENCEBUTAREALSOUSEFULINDEFIN ING A REPRESENTATIVE ENVIRONMENT TO DETERMINE THE SUSCEPTIBILITY OF MOBILESYSTEMS3YSTEMPERFORMANCEISTHENEVALUATEDUSINGADEFINED SCENARIOTODETERMINETHEDEGRADATIONCAUSEDBYINTERFERENCE 3CENARIOSUNAVOIDABLYINVOLVEALARGENUMBEROFPOSSIBLECASESTHAT RESULTINVARIATIONSOFTHEVARIOUSPARAMETERSDESCRIBINGTHEINTERFER ENCE4HE LARGE NUMBER OF POTENTIAL CASES IS TYPICALLY ADDRESSED BY SIMULATIONS4HESIMULATIONPROVIDESANSWERSPROJECTINGTHESYSTEMS


PERFORMANCEATASTATISTICALLEVEL4HESIMULATIONISEXERCISEDONA-ONTE #ARLOBASISTOSPANTHENUMBEROFSIMULATIONVARIABLES4HERESULTSOF THIS-ONTE#ARLOAPPROACHGENERATETHESTATISTICALMEASURESOFSYSTEM PERFORMANCE3UCHSIMULATIONSAREPRACTICALTOEXERCISEINSOFTWARE BUT WOULDINVOLVEANINORDINATETESTTIME4HESIMULATIONISVALIDATEDBY MEASURINGAREPRESENTATIVENUMBEROFTESTCASES)NTHISWAY APRACTICAL MEASUREMENTTIMEISACHIEVED4HEAGREEMENTBETWEENTHESEMEASURE MENTSANDTHESIMULATIONRESULTSAREUSEDTOVALIDATETHESIMULATION /NCEVALIDATED THESIMULATIONISEXERCISEDONA-ONTE#ARLOBASISTO DEFINESYSTEMPERFORMANCE 7HILESUCHAPROCEDUREISCOMMONLYUSED THEBASISOFTHESCENARIO IN MANY CASES HAS A SUBJECTIVE NATURE -OREOVER OVER THE SATELLITES LIFETIME THEBASISOFTHESCENARIOANDITSVALUESEVOLVESANDGENERALLY BECOMESMORESTRINGENT&URTHER WHILEASIMULATIONPROVIDESAMEANS TOQUANTIFYSYSTEMPERFORMANCE ITSHOULDBERECOGNIZEDTHATTHEOPERA TIONAL PERFORMANCE CAN DIFFER FROM THAT PROJECTED ON THE BASIS OF THE SIMULATION4HEREFORE THEEXAMINATIONOFTHESENSITIVITYOFTHERESULTS TOTHESCENARIOPARAMETERSISIMPORTANTANDRECOMMENDED!NIMPOR TANTPARTOFEVALUATINGTHEPERFORMANCEOFASYSTEMAGAINSTASPECIFIED SCENARIOISDETERMININGNOTONLYTHESYSTEMLIMITATIONSIMPOSEDINSAT ISFYINGTHESCENARIOREQUIREMENTSBUTALSOHOWPERFORMANCEISDEGRADED BYMORESTRINGENTSCENARIOPARAMETERS 3USCEPTIBILITY!NALYSES !WIDERANGEOFISSUESMUSTBEADDRESSEDTOEVALUATEASYSTEMSSUS CEPTIBILITYTOINTERFERENCE4HERANGEOFSUSCEPTIBILITYOUTCOMESCOVERS DAMAGE TO THE RECEIVER TO ONLY MINIMALLY DEGRADED OPERATION 4HE SUSCEPTIBILITY ANALYSES MUST ADDRESS BOTH THE ANTENNA AND RECEIVER RESPONSES TO INTERFERENCE4HE ANTENNA RESPONSE DEPENDS ON ITS GAIN LEVEL ') RELATIVETOTHEINTERFERENCESOURCEINBOTHDIRECTIONANDFRE QUENCY4HEINTERFERENCEPOWERRECEIVEDATTHEOUTPUTOFTHEANTENNAS TERMINALISTHEPRODUCTOFTHEINTERFERENCESOURCESINCIDENTPOWERDEN SITYANDEFFECTIVEAPERTUREOFTHEANTENNA2ECEIVERSUSCEPTIBILITIESTO INTERFERENCEINCLUDEDEGRADATIONTOTHEDESIREDSIGNALRECEPTIONLOSSOF SIGNALACQUISITIONDAMAGEFOREXTREMEINTERFERENCELEVELSAND INTHE CASEOFCLOSED LOOPANTENNATRACKING ERRORSINTHEANTENNASTRACKING PERFORMANCE4HERECEIVEROPERATIONFORACCEPTABLEPERFORMANCEISGEN ERALLYMEASUREDBYAN3.)2SIGNALTONOISEINTERFERENCE THRESHOLD VALUE THAT CAN BE TOLERATED IN ACHIEVING MINIMUM DATA FIDELITY AND LIMITATIONSONLINEARPERFORMANCEANDSIGNALACQUISITION7HENCLOSED LOOPANTENNATRACKINGISIMPLEMENTEDBYASEPARATETRACKINGRECEIVER THEASSESSMENTOFINTERFERENCESUSCEPTIBILITYMUSTBEEXTENDEDTOTHE

#HAPTER &IVE

TRACKING RECEIVER4WO QUESTIONS MUST BE ADDRESSED IN SUSCEPTIBILITY ANALYSES 7HATISTHE3.)2RELATIVETOITSTHRESHOLDVALUEFORACCEPTABLECOM MUNICATIONSERVICE 7HATISTHERECEIVEDINTERFERENCEPOWERLEVELRELATIVETOTHELIMITS OFLINEARRECEIVEROPERATION )NTERFERENCESUSCEPTIBILITYANALYSESAREBASEDONADEFINEDINTERFER ENCEENVIRONMENT THEANTENNARESPONSETOINTERFERENCESOURCESWITHIN THATENVIRONMENT ANDTHERECEIVERSRESPONSETOTHEINTERFERENCE !NTENNA2ESPONSETO)NTERFERENCE

4HEANTENNARESPONSEFORTHESPACESEGMENTISRELATIVELYSTRAIGHTFOR WARD 4HE IN BAND GAIN AND COVERAGE CHARACTERISTICS ARE WELL ESTAB LISHED IN ORDER TO VERIFY THE SYSTEM REQUIREMENTS AND REASONABLE ESTIMATES CAN BE MADE FOR SIDELOBE LEVELS BEYOND THE COVERAGE AREA ANDWITHINTHEEARTHSFIELDOFVIEW)NSOMECASES MULTIPLEBEAMSARE COMBINEDTHROUGHBEAMFORMINGNETWORKS4HEGAINLEVELSWITHINTHE COVERAGEAREAAREROUGHLYTHEGAINOFONEOFTHEBEAMSREDUCEDBYTHE NUMBER OF BEAMS COMBINED4HE SIDELOBE LEVELS BEYOND THE COVERAGE AREAINTHISCASEFOLLOWTHESIDELOBEVARIATIONOFANINDIVIDUALBEAM 'ENERALLY SUCHBEAMFORMINGNETWORKSAREPASSIVEANDTHEBEAMFORMER OUTPUT IS ROUTED TO AN INPUT BANDPASS FILTER AND ,.! )F THE BEAM FORMERCONTAINSACTIVEDEVICES THERESPONSEISTHESAMEASLONGASTHE BEAMFORMERSACTIVEELEMENTSAREINALINEAROPERATINGRANGE(OWEVER IFTHEINTERFERENCEISSUFFICIENTLYSTRONGTOSATURATEACTIVEDEVICESINONE ORMOREOFTHEMULTIPLEBEAMS THENTHEPERFORMANCEATTHOSEBEAMPOSI TIONSISDEGRADEDBYNOTONLYTHEINTERFERENCEBUTALSOBYTHENONLINEAR RESPONSEOFTHEELECTRONICS/THERBEAMSINTHECOMBINEDOUTPUTSCAN ALSOBEDEGRADEDBYINTERMODULATIONPRODUCTSFROMTHEBEAMSHAVING A NONLINEAR RESPONSE!CTIVE UPLINK ARRAY DESIGNS MUST ALSO ADDRESS NONLINEARRESPONSESINADDITIONTOINTERFERENCEDEGRADATIONWHENTHE ARRAYHASALINEARRESPONSE!CTIVEUPLINKARRAYSAREUSEDSOTHATTHE UPLINK'4ISESTABLISHEDWITHOUTBEINGIMPACTEDBYPHASESHIFTERAND COMBINERLOSSES!SLONGASTHEACTIVEARRAYELEMENTSREMAINLINEAR THE ARRAYBEAMPATTERNSAREUNAFFECTED4HEARRAYELEMENTPATTERNSCOVER THEENTIREEARTHFIELDOFVIEWANDTHEINTERFERENCEMUSTBESUFFICIENTLY STRONGTOSATURATETHEACTIVEELECTRONICSOFTHEELEMENT(OWEVER SUF FICIENTLYSTRONGINTERFERENCEWOULDSATURATEALLOFTHEARRAYELEMENTS ANDSOALLOFTHEBEAMPATTERNSFORMEDBYTHEARRAYWOULDBEAFFECTED 3INCETHEARRAYELEMENTPATTERNHASVERYBROADCOVERAGECHARACTERIS TICS THEINTERFERENCESOURCECANBELOCATEDANYWHEREINTHESATELLITES FIELDOFVIEW


4HEIN BANDANTENNARESPONSEFORSPACESEGMENTANTENNASISRELA TIVELY STRAIGHTFORWARD TO DETERMINE4HE OUT OF BAND PERFORMANCE IS MOREDIFFICULTTOADDRESS3PACESEGMENTUPLINKANTENNASHAVEINPUT BANDPASSFILTERSBEFORETHEACTIVEDEVICES!TAMINIMUM THERECEIVED OUT OF BANDPOWERISBOUNDEDBYTHEIN BANDANTENNAGAINLEVELSREDUCED BYTHEREJECTIONCHARACTERISTICSOFTHEINPUTFILTERING$EPENDINGONTHE ANTENNATECHNOLOGYANDTHEINTERFERENCESOURCESFREQUENCYRELATIVETO THEANTENNASDESIGNBANDWIDTH THEOUT OF BANDANTENNAGAINVALUES CANDIFFERFROMTHEIN BANDPERFORMANCE!NEXAMINATIONOFTHESPE CIFICANTENNATECHNOLOGYISREQUIREDINTHISCASE)NSOMECASESWHERE WAVEGUIDEISUSEDINTHEANTENNASINPUTCIRCUITRY INTERFERENCEATFRE QUENCIESBELOWTHEWAVEGUIDESCUTOFFFREQUENCYEXPERIENCESIGNIFICANT ATTENUATION 4HESITUATIONFORUSERSEGMENTANTENNASISMORECOMPLEX)NMANY CASES THEINTERFERENCESOURCEDOESNOTHAVEACLEARLINE OF SIGHTPATHTO THERECEIVINGANTENNAANDESTIMATESMUSTBEMADEOFTHETERRAINBLOCK AGELOSSESBETWEENTHEINTERFERENCESOURCEANDTHERECEIVINGANTENNA 3UCHLOSSESDEPENDONTHESPECIFICENVIRONMENTSSURROUNDINGTHEGROUND SEGMENTUSER4ERRESTRIALINTERFERENCEISRECEIVEDTHROUGHTHEANTENNAS SIDELOBESBECAUSETHEANTENNASMAINBEAMISPOINTEDATTHESATELLITE 'ENERALLY THEANTENNAGAINLEVELSCLOSETOTHEMAINBEAMAREDETER MINEDTOSPECIFYTHESYSTEMSPERFORMANCE ANDLESSATTENTIONISGIVEN TOTHEANTENNASSIDELOBERESPONSE/FTEN BOTHTHEANTENNAANDRECEIVER RESPONSESAREREQUIREDATOUT OF BANDFREQUENCIESWHENHIGH LEVELOUT OF BANDINTERFERENCECANIMPACTTHESYSTEMSPERFORMANCE4HUS ADDI TIONALANALYSESANDMEASUREMENTMAYBENEEDEDTOQUANTIFYTHEUSER ANTENNASRESPONSE&URTHER THEEXACTANGULARLOCATIONOFTHEINTERFER ENCEISGENERALLYUNKNOWNTHEREFORE THEANTENNASSIDELOBELEVELSTOBE USEDINLINKANALYSESSPANALARGEDYNAMICRANGE2EPRESENTATIVELEVELS INTHESIDELOBEREGIONSMUSTBEDETERMINEDINDEFININGTHERECEIVERS SUSCEPTIBILITY)NSOMEINSTANCES SIDELOBEENVELOPEVALUESDISCUSSEDIN #HAPTERAREACONVENIENTMEANSTOESTABLISHTHEWIDEANGLESIDELOBE VALUES4HUS ATTENTIONISREQUIREDTOMAKEREASONABLEESTIMATESOFTHE BOUNDINGANTENNAGAINLEVELSTOASSESSTHESUSCEPTIBILITYTOINTERFERENCE FORSPECIFICAPPLICATIONS 2ECEIVER2ESPONSETO)NTERFERENCE

4HEENDOBJECTIVEOFDEFININGTHEINTERFERENCESUSCEPTIBILITYISSPECIFY INGTHEINTERFERENCEPOWERANDSPECTRUMATTHERECEIVERSINPUTTERMI NALANDDETERMININGTHEIMPACTOFRECEIVEDINTERFERENCEPOWER;=ON RECEIVEROPERATION4HETWODISTINCTPROBLEMS THE3.)2FORACCEPTABLE COMMUNICATIONPERFORMANCEANDTHERECEIVEDPOWERLEVELSRELATIVETO THERECEIVERSLINEARITYLIMITATIONS MUSTBEADDRESSED4HERECEIVERS INPUTTERMINALISACONVENIENTREFERENCEPLANETOSEPARATETHEANTENNA

#HAPTER &IVE

FROMTHERECEIVERELECTRONICSANDISALSOCONVENIENTINEVALUATINGSYSTEM HARDWAREBYINJECTINGBOTHTHEDESIREDSIGNALANDINTERFERINGSIGNALS INTO THE RECEIVER TO EVALUATE RECEIVER OPERATION 3OME USER SEGMENT DESIGNSPROVIDECOUPLERSFORTESTSIGNALINJECTIONASAPARTOFTHE")4% BUILT INTESTEQUIPMENT CAPABILITIESTOMAINTAINANDDIAGNOSESYSTEM PERFORMANCE3UCHCOUPLERSALSOPROVIDEAMEANSOFINJECTINGSIGNALS REPRESENTINGTHEINTERFERENCEPOWERLEVELANDSPECTRALCHARACTERISTICS TOEVALUATESUSCEPTIBILITY)NMOSTCASES HOWEVER BENCHTESTSAREUSED TOEVALUATERECEIVERPERFORMANCE 2ECEIVERRESPONSESTOARANGEOFSIGNALLEVELSAREILLUSTRATEDIN&IG FORTHERECEIVERSDESIGNBANDWIDTH4HERECEIVEROPERATIONFORINTERFERENCE FREECONDITIONSISESTABLISHEDBYATHRESHOLDSIGNALLEVEL4HISTHRESHOLD VALUEISGENERALLYDERIVEDBYMEASURINGTHERECEIVERS"%2BITERRORRATE PERFORMANCE 4HE SYSTEM REQUIREMENTS STIPULATE THE ACCEPTABLE "%2 VALUE ANDTHERELATIONBETWEENTHETHRESHOLDSIGNALLEVELANDTHESYSTEM NOISELEVELISESTABLISHEDBYTHISPROCESS4HERECEIVERSIMPLEMENTATION LOSSISTHEDIFFERENCEBETWEENTHEMEASUREDANDIDEAL%B.OVALUESTHAT CANBECONVERTEDINTO3.VALUES)NCREASEDINPUTPOWERLEVELSCANRESULT INSATURATIONOFTHEANALOGCIRCUITRY PRODUCINGDESIREDSIGNALSUPPRESSION DISTORTION ANDINTERMODULATIONPRODUCTSTHATDEGRADERECEIVERPERFORMANCE &URTHERINPUTPOWERINCREASESRESULTINLOSSOFTHERECEIVERACQUISITION AND STILLMOREINCREASESININPUTPOWERDAMAGETHERECEIVER $IGITAL CIRCUITRY IN THE RECEIVER DESIGN MUST ALSO BE CONSIDERED 'ENERALLY SUFFICIENT DIGITAL QUANTIZATION MUST BE PROVIDED IN THE

&IGURE 2ECEIVERRESPONSESVERSUSINPUTPOWER


DESIGNTOSATISFYTWOOBJECTIVES4HEDRIVELEVELFORTHE!$ANDLEAST SIGNIFICANTBITISSELECTEDSOTHATTHEDIGITALQUANTIZATIONNOISEISLOWER THANTHETHERMALNOISEFLOORTOAVOIDDEGRADINGTHESYSTEMNOISETEM PERATURE4HEREQUIREDNUMBEROFBITSOFQUANTIZATIONISTHENDETER MINED BY THE OBJECTIVE OF HAVING SUFFICIENT LINEARITY TO EXTEND FROM THE LEAST SIGNIFICANT BIT TO A LEVEL SOMEWHAT HIGHER THAN THE D" COMPRESSIONPOINTOFTHEANALOGCIRCUITRY4HEQUANTIZATIONPROVIDESA DYNAMICRANGEOFD"BITSOTHAT BITQUANTIZATIONSPANSAD" DYNAMICRANGE FOREXAMPLE!DDITIONALATTENTIONMUSTALSOBEGIVEN TOANALOGANTI ALIASINGFILTERINGSOTHATOUT OF BANDINTERFERENCEDOES NOTFOLDINTOTHEDESIREDSIGNALSPECTRA4HELINEARDYNAMICRANGEFOR USERSIGNALSEXTENDSFROMTHETHRESHOLDSIGNALPOWERTOALEVELSOME WHATSHORTOFTHED"COMPRESSIONPOINTTHATHASSUFFICIENTLINEARITY TOAVOIDSIGNALDISTORTION)NSYSTEMSTHATREQUIREVERYHIGHDYNAMIC RANGE !'# AUTOMATIC GAIN CONTROL CIRCUITRY CAN VARY THE RECEIVER GAINLEVELSINRESPONSETOSIGNALINPUTPOWER)NINTERFERENCEENVIRON MENTS HOWEVER CAREMUSTBEEXERCISEDSOTHATINTERFERENCESIGNALSDO NOTCAPTURETHE!'#CIRCUITRYANDSUPPRESSTHEDESIREDSIGNALCOMPO NENTSINTOTHETHERMALNOISE 4HEOPERATIONOFCARRIERTRACKINGLOOPSANDORFRAMEORBITSYNCHRO NIZATIONCANALSOBEDISRUPTEDBYINTERFERENCE4YPICALLY SUCHDISRUP TIONRESULTSFROMAHIGH LEVELPULSE BUTLOSSOFLOCKORSYNCHRONIZATION CANALSOOCCURWHENANOTHERSIGNALWITHSIMILARCHARACTERISTICSTOTHE DESIREDSIGNALANDASLIGHTLYHIGH POWERLEVELhCAPTURESvTHELOOPANDOR SYNCHRONIZATION4HERECEIVERMUSTREACQUIRETHEDESIREDSIGNALAFTER THEINTERFERENCEISPAST ANDTHERECEIVERISDISRUPTEDFORTHEINTERFER ENCEPERIOD THETIMEFORTHEINTERFERENCETOPASSTHROUGHTHERECEIVERS FILTERS ANDTHEREACQUISITIONTIMEFORTHEDESIREDSIGNAL ,IKETHEANTENNARESPONSE THERECEIVERRESPONSETOOUT OF BANDINTER FERENCE MUST ALSO BE ADDRESSED )N COMPARISON TO THE IN BAND SIGNAL LEVELSDEPICTEDIN&IG THEOUT OF BANDRECEIVERSRESPONSETOINTER FERENCEPOWERISIMPACTEDBYTHERECEIVERSFILTERINGINTHEANALOGCIR CUITRY4HEFILTERINGBEFORETHE,.!DICTATESTHESPECTRUMTHATCANENTER THERECEIVERCIRCUITRY4HELEVELOFOUT OF BANDINTERFERENCEISREDUCED BYTHEFILTERSELECTIVITYPERFORMANCE3IMILARLY FILTERINGATTHE)&LEVEL FURTHER REJECTS OUT OF BAND INTERFERENCE 3UCH FILTERING IS EVEN MORE EFFECTIVE THAN 2& FILTERING BECAUSE OF INCREASED SELECTIVITY AND MORE SELECTIVEFILTERSHAPESBECAUSE)&INSERTIONLOSSISNOTASSIGNIFICANTAN ISSUE AS 2& INSERTION LOSS !DDITIONALLY ADEQUATE FILTERING AT THE )& LEVELMUSTBEPROVIDEDTOAVOIDALIASINGOUT OF BANDINTERFERENCEINTO THERECEIVERSDESIGNBANDWIDTH)NTERFERENCESOMEWHATOUTSIDEOFTHE RECEIVERSOPERATINGBANDWIDTHISREJECTEDBYTHERECEIVERSPROCESSING ANDDOESNOTDEGRADETHERECEIVERSPERFORMANCEASLONGASTHERECEIVER MAINTAINSALINEARRESPONSE

#HAPTER &IVE

4HE RECEIVER DESIGN HAS TWO CONFLICTING REQUIREMENTS 4HE FIRST REQUIREMENTISTOMINIMIZETHERECEIVERNOISETEMPERATURE4HESECOND REQUIREMENTISTOMAXIMIZETHELINEARDYNAMICRANGE4HEFIRSTREQUIRE MENTIMPLIESMINIMAL2&FILTERINGANDAHIGHGAIN LOWNOISE,.!SO THATTHECASCADEDNOISECONTRIBUTIONSOFTHEREMAINDEROFTHERECEIVER ELECTRONICSAREMINIMIZED(IGHLINEARDYNAMICRANGEREQUIRESMINI MUMANALOGGAINTOINCREASETHEINPUTSIGNALPOWERTORESULTINSATURA TIONANDSIGNIFICANTFILTERINGTOREJECTOUT OF BANDINTERFERENCE4HESE CONFLICTSARERESOLVEDINAPROCESSKNOWNAShGAINANDFILTERINGPARTITION INGvTHATEXAMINESTHEINTERFERENCEENVIRONMENTFORASPECIFICAPPLICA TIONANDTRIESTOSATISFYTHELINEARDYNAMICRANGEREQUIREMENTSWHILE MAINTAININGALOWRECEIVERNOISETEMPERATURE 'AINPARTITIONINGEXAMINESTHENOISEFIGUREANDSATURATIONCHARACTERIS TICSOFCANDIDATEANALOGCOMPONENTSFORARECEIVER!TYPICALSPECIFICATION FORRECEIVERSATURATIONISTHED"COMPRESSIONPOINTATTHERECEIVERINPUT !TTHISINPUTLEVEL THERECEIVEROUTPUTDIFFERSFROMITSLINEARRESPONSE BYD"4HISRECEIVERSATURATIONCANOCCURATFREQUENCIESWELLREMOVED FROMTHEDESIGNBANDWIDTHSOTHATTHEDISTRIBUTIONOFTHERECEIVERFILTER INGREQUIRESEXAMINATION4HESELECTIONOFTHEFILTERSHAPEFORTHE2&FILTER ANDTHEGAINOFTHE,.!REQUIRESEXAMINATIONOFTHEANTICIPATEDLEVELS OFTHEOUT OF BANDINTERFERENCE )NCREASED FILTER SELECTIVITY IS ACCOMPA NIEDBYINCREASEDINSERTIONLOSS2EDUCINGTHEGAINOFTHE,.!INCREASES THEPOWERLEVELATTHERECEIVERINPUTNEEDEDTOSATURATETHE,.! BUT THENOISECONTRIBUTIONSFORTHECOMPONENTSFOLLOWINGTHE,.!AREALSO INCREASED4HEFILTERINGATTHE)&LEVELSPROVIDESADDITIONALSELECTIVITY AND REJECTION OF IMAGE COMPONENTS 3ELECTIVITY TRADEOFFS AND THE GAIN SELECTIONATTHE)&LEVELSREQUIREEXAMINATIONOFANANTICIPATEDINTERFER ENCEENVIRONMENTCLOSETOTHEDESIGNBANDWIDTHANDANALYSESTOASSURE SUFFICIENTANTI ALIASINGFILTERINGISPROVIDEDFORTHEDIGITALCIRCUITRY7HILE THEGOALISTOASSURETHERECEIVERNOISETEMPERATUREISDOMINATEDBYTHE INITIALPREAMPLIFICATION REQUIREMENTSFORLINEARDYNAMICRANGECANRESULT INSOMEINCREASESINTHERECEIVERNOISETEMPERATURE 4HEEVALUATIONOFRECEIVERSBEGINSWITHQUANTIFYINGTHEIRPERFORMANCE ININTERFERENCE FREECONDITIONS4ESTINGGENERALLYSTARTSBYUSINGNET WORKANALYZERINSTRUMENTATIONTOVERIFYTHEGAINANDFILTERINGDISTRIBU TIONINTHEANALOGCIRCUITRY4HELINEARITYISALSOMEASUREDUSINGSIGNAL GENERATORMEASUREMENTS4HERECEIVERNOISETEMPERATUREISMEASURED BYUSING9FACTORTECHNIQUESORNOISEFIGUREINSTRUMENTATIONDESCRIBED IN #HAPTER 4HE ANALOG CIRCUITRY AFTER ITS EVALUATION IS CONNECTED WITHTHEDIGITALCIRCUITRYANDTHEDEMODULATIONEVALUATIONISSTARTED 2ECEIVERDEVELOPMENTTESTINGGENERALLYINCLUDES"%2TESTSTOEVALUATE RECEIVERPERFORMANCEANDTOQUANTIFYRECEIVERIMPLEMENTATIONLOSSES RELATIVE TO AN IDEAL RECEIVER FOR PURPOSES OF DETERMINING LINK BUDGET LOSSES )MPLEMENTATION LOSS IS DEFINED AS THE DIFFERENCE BETWEEN THE


IDEAL%B.OANDTHEVALUEREQUIREDOFTHEACTUALRECEIVERTOMEETTHE "%2 SPECIFIED FOR THE SYSTEM4HESE MEASUREMENTS ARE MADE USING STANDARD "%2 TEST SETS OR THE MODEMS TO BE USED OPERATIONALLY4HE RECEIVEREVALUATIONWHENINTERFERENCEISPRESENTISTHENSTARTED 4HEREQUIRED3.)2MUSTBEESTABLISHEDANDDEPENDSNOTONLYONTHE RECEIVEDINTERFERENCEPOWERBUTALSOTHESPECTRALCHARACTERISTICSOFTHE INTERFERENCE'ENERALLY MEASURINGINTERFERENCEEFFECTSUSINGTHESPECIFIC RECEIVERHARDWAREISTHEMOSTSATISFACTORYMEANSOFEVALUATINGINTERFER ENCEEFFECTS"OTHDESIREDSIGNALSANDINTERFERINGSIGNALSAREREQUIRED 4HE "%2 TEST SET OR OPERATIONAL MODEMS ARE USED FOR DESIRED SIGNAL REPRESENTATIONSSINCE3.)2LEVELSAREALSOEVALUATEDUSING"%2MEA SURED!DDITIONALSIGNALGENERATIONISREQUIREDTOREPRESENTINTERFERENCE SIGNALS!DDITIONALTESTINGTOQUANTIFYINTERFERENCELIMITATIONSSHOULD BEMADESINCESUCHTESTINGCANBEEASILYPERFORMEDINACOST EFFECTIVE MANNERATTHISTIME4HEINTERFERENCECANBEINJECTEDINTOTHERECEIVER ALONGWITHTHEBITSTREAMUSEDFOR"%2EVALUATIONSANDDIFFERENTTYPES OFINTERFERENCEEG NOISE #7TONES PULSES ANDSOONCANBEREADILY OBTAINEDFROMSIGNALGENERATORS 4HEGOALSOFSUCHMEASUREMENTSARE TODETERMINEATHRESHOLD3.)2THATACHIEVESTHESPECIFIEDDATAFIDEL ITY EXPRESSED BY A REQUIRED "%2 VALUE AND TO EVALUATE INTERFERENCE LEVELSNEEDEDTORESULTINLOSSOFLOCKANDORSYNCHRONIZATIONALONGWITH THEREQUIREDRECEIVERACQUISITIONTIME4HEUSERRECEIVERSHOULDHAVE INDICATORSFORLOSSOFLOCKANDORSYNCHRONIZATIONANDFORINTERFERENCE PRESENCE ANDTHEOPERATIONOFTHESEINDICATORSCANALSOBEEVALUATED 7HILETHESEMEASUREMENTSARERECOMMENDEDDURINGRECEIVERDEVELOP MENT SIMILARMEASUREMENTSAREOFTENPERFORMEDONEXISTINGRECEIVERS TOEVALUATETHEEFFECTSOFINTERFERENCEEXPERIENCEDINOPERATIONALCONDI TIONS4HEEFFECTSOFSPECIFICINTERFERENCESOURCESCANBEEVALUATEDBY OPERATINGTHERECEIVERINTHATENVIRONMENTANDMEASURINGINTERFERENCE VALUESWITHASPECTRUMANALYZER 4HEENDGOALFORTHERECEIVEREXAMINATIONISTODETERMINELIMITSOF THEEXISTINGRECEIVERDESIGNASWELLASPOSSIBLEIMPACTSTORECEIVERPER FORMANCEOFPOSSIBLECHANGESTOFURTHERREDUCERECEIVERVULNERABILITYTO INTERFERENCE&OREXAMPLE MORESTRINGENTFILTERINGATTHERECEIVERINPUT INCREASES THE FILTERING LOSS AND DEGRADES THE RECEIVER NOISE TEMPERA TUREANDCONSEQUENTLYSENSITIVITY4HERECEIVERDYNAMICRANGEMAYBE INCREASEDBYREDUCEDPREAMPLIFIERGAINANDMORESELECTIVEFILTERINGIN THEDOWNCONVERTERAND)&LIFIERSATTHEEXPENSEOFINCREASEDRECEIVER NOISE!DDITIONALQUANTIZATIONINDIGITALRECEIVERDESIGNSINCREASESTHE DYNAMICRANGEBUTMAYBELIMITEDBYCOMPONENTTECHNOLOGY!UTOMATIC GAINCONTROLTECHNIQUESMIGHTBEEMPLOYED BUTPRACTICALTIMECONSTANTS IN SUCH CIRCUITRY MAY LIMIT EFFECTIVENESS FOR PULSE INTERFERENCE 3UCH TRADEOFFSINTHERECEIVERDESIGNNEEDTOBEUNDERSTOODTOADDRESSTECH NIQUESFORPOSSIBLEREDUCTIONSTORECEIVERINTERFERENCEVULNERABILITY

#HAPTER &IVE

4HISDISCUSSIONCONCERNSAGENERALRECEIVERARCHITECTURETHATWOULD BEUSEDINUSERSEGMENTAPPLICATIONS4HESPACESEGMENTDESIGNSUSING LINEARFREQUENCYTRANSLATORSCONTAINTHEANALOGPORTIONSOFTHERECEIVER BUTNOTTHEDEMODULATIONCIRCUITRY!DDITIONALANALOGCIRCUITRYEXISTS INFREQUENCYTRANSLATIONANDTRANSMISSIONCIRCUITRY4HEFILTERINGAND DYNAMICRANGEISSUESOFTHEANALOGTRANSPONDERFOLLOWTHEPREVIOUSDIS CUSSION2EGENERATIVEREPEATERARCHITECTURESDOHAVEDEMODULATIONAND SIGNALSEPARATIONCIRCUITRYTHATFOLLOWSTHEPREVIOUSDISCUSSION#LOSED LOOPANTENNATRACKINGDESIGNSOFTENHAVESEPARATETRACKINGRECEIVERS )F INTERFERENCE DEGRADES THE TRACKING RECEIVER PERFORMANCE ANTENNA POINTLOSSINCREASES)NSOMECASES THEPRESENCEOFINTERFERENCEISINDI CATEDBY!'#LEVELSINTHETRACKINGRECEIVERORSEPARATETHRESHOLDING CIRCUITRY SUCHASUSEDINTHERECEIVERDESCRIBEDIN#HAPTER PROVIDING IDENTIFICATIONOFEXCESSIVEINTERFERENCEPOWER/NEAPPROACHTOINTERFER ENCEMITIGATIONFORTRACKINGRECEIVERSSIMPLYCOMMANDSTHEANTENNATO PROGRAMTRACKWHENTHEPRESENCEOFINTERFERENCEISIDENTIFIED 2ECEIVER$AMAGE

,OW NOISERECEIVERSHAVEGONETHROUGHMUCHDEVELOPMENT AND,.!S WITH VERY LOW NOISE TEMPERATURES ARE WIDELY AVAILABLE OVER A BROAD FREQUENCYRANGE4HELOWNOISETEMPERATURES HOWEVER REQUIREDEVICES HAVING VERY SMALL SUBMICRON DIMENSIONS7HILE THESE DIMENSIONS ARENECESSARYTOACHIEVETHELOW NOISEPERFORMANCE THEENDRESULTIS ADEVICETHATISLIMITEDBYITSTHERMALDISSIPATION#ONSEQUENTLY SUF FICIENTLYHIGH LEVEL2&INPUTS; =CANEXCEEDTHETHERMAL DISSIPATIONLIMITS CAUSETHEDEVICESSUBSTRATETOMELT ANDIRREVERSIBLY DAMAGETHEDEVICE4HIShBURNOUTvRESULTSINATTENUATIONRATHERTHAN THEAMPLIFICATIONTHEDEVICEISINTENDEDTOPROVIDE4YPICALPOWERINPUT VALUESFORDEVICEBURNOUT SHOWNIN&IG ILLUSTRATETHESEPOINTS&OR VERYSHORTEXPOSURETIMES THEREQUIREDBURNOUTPOWERVARIESAST ABEHAVIORTYPICALOFTHERMALDISSIPATIONLIMITS6ERYSHORTLY ROUGHLY NANOSECONDSAFTERPULSEINITIATION THEREQUIREDINPUTPOWERLEVEL FORDEVICEBURNOUTREACHESASTEADYSTATELIMIT7HENTHEPOWERLEVELIS LESSTHANTHISTHRESHOLDVALUE THEDEVICESURVIVESNOMATTERHOWLONG THEPOWERISAPPLIED4HUS THEPOWERLEVELRATHERTHANTHEAMOUNTOF ENERGYISTHECRITICALFACTORINBURNOUT4HE2&POWERNEEDEDFORBURN OUTEXCEEDSTHEDCBIASSOBURNOUTOCCURSWHETHERORNOTTHEDEVICEIS POWERED3INCELOW NOISEDEVICESHAVEONLYORD"OFGAIN TYPICAL ,.!SHAVESEVERALDEVICESINSERIESTOACHIEVETHEOVERALLAMPLIFIER GAINPERFORMANCE4HEDEVICESTYPICALLYSATURATEATATOD"MLEVEL ATTHEIROUTPUT3UFFICIENTLYHIGHPOWERLEVELINPUTSWILLDAMAGETHE FIRSTDEVICEOFTHEAMPLIFIERBUTTHEDEVICESFOLLOWINGTHEFIRSTDEVICE


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ARE PROTECTED BECAUSE OF THE LIMITED SATURATED OUTPUT LEVELS OF THE DEVICES ,OW NOISEDEVICESHAVEAWIDEBANDWIDTHRESPONSEANDWHENTHEY AREINTEGRATEDINTOTHELOW NOISEAMPLIFIER DEVICEMATCHINGTECHNIQUES AREUSEDTOMEETTHESPECIFIEDNOISEFIGUREANDGAINFLATNESSREQUIRE MENTSOVERTHEIRDESIGNBANDWIDTH4HEBROADBANDWIDTHOFTHEDEVICE PERSISTSAFTERMATCHINGISPERFORMED7HILENOTCOMPLIANTWITHNOISE FIGUREANDGAINFLATNESSPERFORMANCEINTHEOPERATINGBANDWIDTH THE AMPLIFIERHASAHIGHGAINRESPONSEOVERACONSIDERABLEBANDWIDTH&OR THISREASON ADEQUATEFILTERINGMUSTBEPROVIDEDTOMAINTAINRECEIVER LINEARITYWHENHIGH LEVELOUT OF BANDSIGNALSAREPRESENT )FSYSTEMSAREREQUIREDTOOPERATEINENVIRONMENTSWHEREBURNOUTISA POTENTIALCONCERN DIODELIMITERSCANBEPLACEDBEFORETHE,.!TOPROTECT THE,.!FROMHIGHPOWERINPUTLEVELS4HEINPUT2&FILTERISREQUIREDTO PRECEDETHELIMITERSOTHATHIGH LEVELOUT OF BANDINTERFERENCEDOESNOT ACTIVATETHELIMITERNEEDLESSLY4HEINSERTIONLOSSOFHIGHLYSELECTIVEFIL TERSANDPROTECTIVELIMITERSTHATARENECESSARYINADVERSEENVIRONMENTS DEGRADESTHERECEIVERNOISETEMPERATURE0RACTICALLIMITERDESIGNSFOR THESE APPLICATIONS HAVE A FEW TENTHS OF A D" INSERTION LOSS4HE LIM ITER REQUIRES SERIES AND SHUNT DIODES TO ACHIEVE RESPONSE TIMES SHORT ENOUGHINCOMPARISONTOTHESHORTTIMESTHATDEVICESCANBEDAMAGED /THERPARAMETERSSPECIFYLIMITERPERFORMANCEBESIDESINSERTIONLOSSAND RESPONSETIME4HEACTIVATIONLEVELDESCRIBESTHEINPUTPOWERLEVELTHAT INITIATESLIMITEROPERATION3PIKELEAKAGEISTHEPEAKPOWERLEVELLEAKED

#HAPTER &IVE

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4HESUSCEPTIBILITYOFRECEIVINGSYSTEMSTOINTERFERENCEISANALYZEDBY LINKANALYSESANDANEXAMINATIONOFTHERECEIVERRESPONSETOTHEINTER FERENCESOURCESSPECTRUM4HELINKANALYSESGENERALLYEXAMINERECEIVED INTERFERENCELEVELSRELATIVETOTHEREQUIRED3.)2VALUEANDTHERECEIVED POWERLEVELRELATIVETOTHELINEARITYLIMITATIONSOFTHERECEIVERSDESIGN 4HESEANALYSESAREEXAMINEDINTURN 4HE3.)2CANBEWRITTENINTHEFOLLOWINGMANNER

3.)2-;.3)3=

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#HAPTER &IVE

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#HAPTER &IVE

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!DAPTIVE)NTERFERENCE#ANCELLATION

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#HAPTER &IVE

INDICATETHATTOLERANCESBECOMEINCREASINGLYSTRINGENTASTHEREQUIRED CANCELLATIONLEVELINCREASES4HISAMPLITUDEANDPHASE MATCHINGPER FORMANCEMUSTBEMAINTAINEDOVERTHESYSTEMSOPERATINGBANDWIDTH TOACHIEVEEFFECTIVECANCELLATION#ANCELLATIONPERFORMANCEISDEGRADED BYMANYFACTORS INCLUDINGDISPERSIONCONTRIBUTIONSFROMTHEANTENNA AMPLITUDEANDPHASETRACKINGIMPERFECTIONSINTHESYSTEMELECTRONICS UPTOTHEPOINTATWHICHADAPTIVECOMBINATIONOCCURS ANDTHEPRECISION OFTHEDETERMINATIONANDADJUSTMENTOFTHEADAPTIVEWEIGHTVALUESUSED TOCOMBINETHEANTENNAELEMENTS4HEDESIGNCOMPLEXITYALSOINCREASES WITHTHEREQUIREDNUMBEROFPATTERNNULLSEG INTERFERENCESOURCESAND THECANCELLATIONBANDWIDTH 4HE ADAPTIVE WEIGHTING VALUES ARE DERIVED TO SATISFY AN OPTIMIZA TIONCRITERION;=ANDARECONVENTIONALLYDETERMINEDINTHREEALTERNA TIVEWAYS4HEMOSTCOMMONLYUSEDTECHNIQUEISAN,-3LEASTMEAN SQUARE ALGORITHM4HEWEIGHTINGVALUESAREDETERMINEDBYTHEADAP TIVEPROCESSORTHATFUNCTIONSASACONTROLSYSTEM4HEERRORINTHISCASE ISTHEINTERFERENCE ANDITCANBESHOWNTHEWEIGHTINGSOLUTIONISA QUADRATIC PROCESS SO THAT A SIMPLE RECURSIVE ALGORITHM CAN BE USED 3UCHASOLUTIONRAPIDLYPROVIDESASOLUTIONTHATMAXIMIZESTHE3.)2 !NOTHERTECHNIQUEISANITERATIVEWEIGHTADJUSTMENTPROCESSTHATVARIES THEWEIGHTINGWHILEMONITORINGTHEINTERFERENCEPOWERLEVELS4HISPRO CESSISRELATIVELYSLOWANDSUBJECTTODYNAMICVARIATIONSINTHEINTER FERENCE!THIRDTECHNIQUEISREFERREDTOASASAMPLEMATRIXINVERSION WHERETHEPROCESSINGFORMSANINTERFERENCECORRELATIONMATRIXTHATIS INVERTEDTOYIELDASOLUTION4HISTECHNIQUEISLIMITEDBYTHEACCURACY INDETERMININGTHECORRELATIONMATRIXVALUES !FOURTHTECHNIQUEHASBEENDEVELOPED; =ANDISDESCRIBEDAS $%!$%.$%TERMINISTIC!$APTIVE%NVIRONMENTAL.ULLER 4HISTECH NIQUEDEPARTSFROMCONVENTIONALALGORITHMSBYMEASURINGTHEINTERFER ENCESOURCESDIRECTIONSANDUSINGAPRIORIANTENNADESIGNINFORMATION TO COMMAND PATTERN NULLS ! SIMPLE EXAMPLE USING ARRAY ANTENNA TECHNOLOGYASSUMESTHEINTERFERENCEISRECEIVEDTHROUGHTHEANTENNA SIDELOBES4HE ARRAY FORMS ANOTHER ANTENNA BEAM THAT SEQUENTIALLY SAMPLESTHEANTENNASIDELOBESTOIDENTIFYTHOSESIDELOBESTHATCONTAIN INTERFERENCEPOWER)NTHISWAY THEDIRECTIONOFTHEINTERFERENCESOURCE CAN BE DETERMINED /NCE THE ARRAY SIDELOBE CONTAINING INTERFERENCE POWER IS IDENTIFIED ANOTHER ARRAY BEAM IS STEERED TO THAT SIDELOBES LOCATION COMMANDED TO MATCH THE KNOWN LEVEL OF THE SIDELOBE AND SUBTRACTEDFROMTHESIDELOBETOPRODUCEANULLCANCELINGTHEINTERFER ENCE4HEEXTENSIONOF$%!$%.TECHNIQUESTOADAPTIVEUPLINKMULTIPLE BEAMSHASBEENEXPLORED !DAPTIVE SYSTEM DEVELOPMENT IS GENERALLY GUIDED BY SIMULATION EFFORTSTOIDENTIFYTHEPERFORMANCECAPABILITIESOFTHEDESIGN4HESIMU LATIONPROGRAMCANADDRESSTHEPARAMETERSDESCRIBINGTHEINTERFERENCE


SOURCESONA-ONTE#ARLOBASISANDCANMAKEASTATISTICALPROJECTION OFADAPTIVESYSTEMPERFORMANCE!STHESYSTEMDEVELOPMENTPROCEEDS MEASUREDHARDWAREPERFORMANCEOFTHESYSTEMCANBEINCORPORATEDINTO THESIMULATIONTOIMPROVEITSFIDELITY4ESTINGTHEADAPTIVESYSTEMONA -ONTE#ARLOBASISWOULDREQUIREANIMPRACTICALAMOUNTOFTESTTIME)N PRACTICE THETESTINGUSESTHESIMULATIONPROGRAMTODEVELOPALIMITED NUMBEROFTESTCASES4HISLIMITEDNUMBEROFTESTCASESISMEASUREDTO VALIDATETHESIMULATION(AVINGVALIDATEDTHESIMULATION -ONTE#ARLO RESULTSFROMTHESIMULATIONPROGRAMAREUSEDTOESTABLISHSYSTEMCOM PLIANCEOFTHEDESIGN4HUS THEDEVELOPMENTOFADETAILEDSIMULATION IS A VERY IMPORTANT PART OF ADAPTIVE SYSTEM DEVELOPMENT 'ENERALLY ADAPTIVESYSTEMDESIGNSMUSTADDRESSTWOSYSTEM LEVELQUESTIONS 7HATISTHESTEADYSTATEPERFORMANCEWHENINTERFERENCEISPRESENT !FTERTHEINITIATIONOFINTERFERENCE WHATLENGTHOFTIMEISREQUIRED TOACHIEVESTEADYSTATEPERFORMANCE &ORTHESPACESEGMENT THESTEADYSTATEPERFORMANCEISMEASUREDBY THEPERCENTOFTHEDESIGNCOVERAGEAREAREMAININGAFTERTHEADAPTIVE WEIGHTSCONVERGE WHERECOMMUNICATIONSAREPOSSIBLEWHENINTERFER ENCE IS PRESENT &OR THE USER SEGMENT THE STEADY STATE PERFORMANCE ISJUDGEDONTHEBASISOFTHE3.)2ACHIEVEDUNDERSTEADYSTATECONDI TIONS4HETIMEAFTERTHEINITIATIONOFTHEINTERFERENCETOREACHSTEADY STATEPERFORMANCEISGENERALLYMEASUREDBYTHETIMEFORCONVERGENCE OFTHEADAPTIVEWEIGHTVALUESTOTHEIRSTEADYSTATELEVELS4HEUSERSEG MENTEVALUATIONMUSTADDRESSBOTHTHETIMEFORTHEADAPTIVESYSTEM RESPONSEANDTHETIMEFORRECEIVERREACQUISITIONIFINTERFERENCECAUSES THERECEIVERTOBREAKLOCK 2EFERENCES 2"$YBDAL '-3HAW AND44-ORI h!2&)-EASUREMENT3YSTEMFOR&IELD 3ITES v!-4!3YMPOSIUM$IGEST.OVEMBER )%%%3TANDARD4EST0ROCEDURESFOR!NTENNAS.EW9ORK7ILEY )NTERSCIENCE 2"$YBDAL h!NALYZING2ECEIVER6ULNERABILITYTO)NTERFERENCE v)%%% -),#/-3YMPOSIUM$IGEST.OVEMBER 2"$YBDAL *&(ENEY --C#OLL AND(*7INTROUB h4HE4ECHNOLOGYOF THE%LECTROMAGNETIC4HREATTO3PACE3YSTEM2ECEIVERS v)%%%-),#/- 3YMPOSIUM$IGEST/CTOBER 2"$YBDAL +-3OO(OO AND(*7INTROUB h,IMITATIONSOF-ULTIPLE3OURCE #OMBINING!GAINST3URVIVABLE#OMMUNICATION3YSTEMS v)%%%-),#/- 3YMPOSIUM$IGEST/CTOBER !!-OULTHROUP -(-UHA 2"$YBDAL AND(*7INTROUB h(0-$AMAGE 4HRESHOLDSOF,OW.OISE'A!S&%4SAND(%-04S v&IFTH.ATIONAL(0- #ONFERENCE*UNE -!*OHNSON 2"$YBDAL 33OKOLSKY AND-(OPKINS h(IGH0OWER2ADIO &REQUENCY7EAPON4HREAT!NALYSISFOR'EOSYNCHRONOUS3ATELLITES v)%%% -),#/-3YMPOSIUM$IGEST/CTOBER

#HAPTER &IVE

**7HALEN -##ALCATERA AND-,4HORN h-ICROWAVE.ANOSECOND0ULSE "URNOUT0ROPERTIESOF'A!S-%3&%43 v)%%%4RANS-ICROWAVE4HEORYAND 4ECHNIQUES VOL-44 $ECEMBER n **7HALEN 24+EMBERLEY AND%2ASTEFANO h8 "AND"URNOUT#HARACTERISTICS OF'A!S-%3&%43 v)%%%4RANS-ICROWAVE4HEORYAND4ECHNIQUES VOL-44 $ECEMBER n 2"$YBDAL h!SSESSMENTOF!NTENNA)NTERFERENCE2EDUCTION4ECHNIQUESFOR #OMMUNICATION3ATELLITE3YSTEMS v)%%%-),#/-3YMPOSIUM$IGEST .OVEMBER 2,0ETERSON 2%:IEMER AND$%"ORTH )NTRODUCTIONTO3PREAD3PECTRUM #OMMUNICATIONS.EW9ORK0RENTICE(ALL ,(3IBUL !DAPTIVE3IGNAL0ROCESSING.EW9ORK)%%%0RESS 2!-ONZINGOAND47-ILLER )NTRODUCTIONTO!DAPTIVE!RRAYS.EW9ORK 7ILEY 2"$YBDALAND2(/TT h!PPARATUSAND-ETHODFOR%MPLOYING!DAPTIVE )NTERFERENCE#ANCELLATIONOVERA7IDE"ANDWIDTHv!UGUST 530ATENT $*(INSHILWOOD 2"$YBDAL AND+-3OO(OO h4HE#ANCELLATIONOF)NTERFERENCE BY3IDELOBE!NNIHILATION v)%%%!0 33YMPOSIUM$IGEST*UNE 2"$YBDALAND$*(INSHILWOOD h$%!$%.!.EW!DAPTIVE#ANCELLATION 4ECHNIQUE v)%%%-),#/-3YMPOSIUM$IGEST.OVEMBER

#HAPTER

3PACE3EGMENT !NTENNA4ECHNOLOGY

/VERVIEW !NTENNAS GREATLY CONTRIBUTE TO THE PERFORMANCE AND CAPABILITIES OF THESPACESEGMENT;=ANDAREVISUALLYPROMINENTFEATURESOFSATELLITE DESIGNS4HE DIFFERING REQUIREMENTS FOR SATELLITE SYSTEMS RESULT IN A WIDERANGEOFSATELLITEANTENNATECHNOLOGIES ANDANEVENMOREDIVERSE TECHNOLOGYRANGEHASBEENCARRIEDTHROUGHDEVELOPMENT4HESPACESEG MENTANTENNATECHNOLOGYHASMOREDIVERSITYTHANANYOTHERPAYLOAD SUBSYSTEMBECAUSEOFTHEDIFFERENCESINPROGRAMREQUIREMENTS 3PACESEGMENTANTENNASCANBEBROADLYSEPARATEDINTOTECHNOLOGIES THAT SUPPORT DIFFERENT COVERAGE AREAS %ARLY SATELLITE ANTENNAS WERE NECESSARILYCONSTRAINEDBYLIMITEDPAYLOADCAPABILITIES SATELLITEATTI TUDESTABILITY ANDLOWFREQUENCYOPERATION THUSSIMPLEANTENNADESIGNS PROVIDED VERY BROAD COVERAGE!S DESCRIBED IN #HAPTER BROAD COV ERAGEANTENNASANDEARTHCOVERAGEANTENNASCONTINUETOHAVEAPPLI CATIONS BUT THE NARROW COVERAGE ANTENNAS DESCRIBED IN THIS CHAPTER PROVIDE SYSTEM DESIGNS THAT ARE LARGELY RESPONSIBLE FOR PRESENT DAY COMMUNICATIONCAPABILITIES4HESENARROWCOVERAGEANTENNASYSTEMS BECAMEPRACTICALASSATELLITEPAYLOADCAPABILITIESANDATTITUDESTABIL ITY INCREASED AND AS LAUNCH CAPABILITIES TO GEOSYNCHRONOUS ALTITUDES BECAME AVAILABLE4ODAYS SYSTEMS BENEFIT FROM OPERATION AT HIGHER FREQUENCIES WHERE BROAD BANDWIDTH FREQUENCY ALLOCATIONS ARE AVAIL ABLEANDCOMPACTANTENNASYSTEMSCANBEIMPLEMENTED!TTHESAME TIME INCREASEDDEMANDFORSATELLITESERVICES PARTICULARLYINCOMMERCIAL DESIGNS ISMADEPOSSIBLEBYFREQUENCYANDPOLARIZATIONREUSETECHNIQUES THATACHIEVEGREATLYINCREASEDCOMMUNICATIONCAPACITY!COMPENDIUM

#HAPTER 3IX

THAT DESCRIBES THE VARIETY OF SATELLITE PROGRAMS ;= AND THE TOP LEVEL CHARACTERISTICSOFTHETECHNOLOGIESUSEDINTHEIRIMPLEMENTATIONILLUS TRATESTHEDIVERSITYOFTECHNOLOGYTHATHASBEENDEVELOPEDTOSATISFYA VARIETYOFSYSTEMREQUIREMENTSANDAPPLICATIONS 3POTBEAMANTENNATECHNOLOGIESTHATCOMMUNICATETHESAMEINFORMA TIONTOASINGLECOVERAGEAREA ANDMULTIPLE BEAMANTENNATECHNOLOGIES THATPROVIDEINDEPENDENTBEAMSTHATINDIVIDUALLYSERVICEPORTIONSOF A COMPOSITE COVERAGE AREA HAVE BEEN WIDELY USED IN SPACE SEGMENT ANTENNA DESIGNS 3POT COVERAGE ANTENNAS AND MULTIPLE BEAM ANTEN NASAREWIDELYUSEDFORBOTHCOMMERCIALANDMILITARYSPACEAPPLICA TIONS )N RECENT YEARS THE TREND TOWARDS INTEGRATING ANTENNAS WITH SYSTEM ELECTRONICS HAS INCREASED RESULTING IN ANTENNA SYSTEMS THAT PROVIDEPERFORMANCEBENEFITSWHILEIMPOSINGADDITIONALCHALLENGESIN DEVELOPMENTANDTESTING!DAPTIVEANTENNASYSTEMSTOREDUCEUPLINK INTERFERENCE AND ACTIVE APERTURE DOWNLINK ANTENNAS TO COMBINE THE OUTPUTSOFMANYLOW LEVELSOLIDSTATETRANSMITTERSILLUSTRATEANTENNA SYSTEMS WHOSE PERFORMANCE STRONGLY DEPENDS ON SYSTEM ELECTRONICS 3PACE SEGMENT ANTENNAS THAT PROVIDE POINT TO POINT CONNECTIVITY ARE USEDINCROSSLINKSUBSYSTEMSANDFOREARTHLINKSHAVINGHIGHDATARATE REQUIREMENTS 3POT"EAM!NTENNAS 3POT COVERAGE ANTENNAS SERVICE ONLY A PORTION OF THE EARTHS FIELD OF VIEWANDHAVESEVERALDISTINCTBENEFITS3POTANTENNASPROVIDEHIGHER GAINPERFORMANCETHANEARTHCOVERAGEANTENNASTHATSERVICETHEENTIRE EARTHFIELDOFVIEW4HISINCREASEDANTENNAGAINPERFORMANCEFORSPOT ANTENNASSMALLERCOVERAGEREQUIREMENTENHANCESUSERSSYSTEMCOM MUNICATIONCAPACITIESANDORREDUCESUSERSPERFORMANCEREQUIREMENTS 4HE ANTENNA BEAMWIDTH NECESSARY TO COVER A PORTION OF THE EARTH IS GENERALLYDEFINEDBYTHEANTENNASFOOTPRINT WHICHOUTLINESTHEANTENNA COVERAGEPROJECTEDONTHEEARTHSSURFACE2EPRESENTATIVEVALUESOFSPOT COVERAGEFORGEOSYNCHRONOUSSATELLITESSHOWNIN&IG ILLUSTRATETHE MINIMUMFOOTPRINTVALUESATTHESUBSATELLITEPOINTANDTHELONGESTFOOT PRINTDIMENSIONFORUSERSATAOELEVATIONANGLEWHERETHEFOOTPRINT SPREADSOUTOVERTHEEARTHSSURFACE3EPARATINGDIFFERENTPORTIONSOFTHE EARTHFIELDOFVIEWINTODIFFERENTCOVERAGEAREASAFFORDSTHEPOSSIBILITY OFREUSINGTHEFREQUENCYANDORPOLARIZATIONTOOBTAINGREATERCAPACITY FROMTHEALLOCATEDFREQUENCYSPECTRUM4HESEBENEFITSAREACCOMPANIED BYLARGERANTENNADIMENSIONSCOMPAREDWITHEARTHCOVERAGEDESIGNS MORENUMEROUSANTENNASTOSERVICETHESATELLITESFIELDOFVIEW ANDTHE NEED FOR ROUTING SIGNALS BETWEEN ANTENNA COVERAGE AREAS WITHIN THE TRANSPONDER3POTBEAMCOVERAGEISWIDELYEXPLOITEDINBOTHCOMMER CIAL AND MILITARY SPACE SEGMENT DESIGNS TO INCREASE SYSTEM CAPACITY

3PACE3EGMENT!NTENNA4ECHNOLOGY

&IGURE 3POTCOVERAGEVERSUSANTENNABEAMWIDTH

ANDTHESESPACESEGMENTANTENNASFORSPOTCOVERAGEREQUIREMENTSARE PROMINENTFEATURESOFPRESENTANDFUTURESATELLITEDESIGNS !VARIETYOFDIFFERENTANTENNATECHNIQUESAREUSEDFORSPOTCOVERAGE REQUIREMENTS!VERYSIMPLEDESIGNFORSPOTCOVERAGEUSESAREFLECTOR ANTENNATOGENERATEANARROWBEAMWIDTH WHICHISSELECTEDTOCONFORM TOTHESPECIFIEDCOVERAGEAREAANDISMECHANICALLYPOSITIONEDTOPOINT ATTHECENTROIDOFTHEDESIREDCOVERAGEAREA!SCOMMUNICATIONNEEDS CHANGEDURINGTHESATELLITELIFETIME THEANTENNACANBEREPOSITIONED TO SERVICE OTHER COVERAGE AREAS4YPICALLY SATELLITE DESIGNS USE MORE THAN ONE SPOT BEAM ANTENNA TO PROVIDE COMMUNICATIONS IN DIFFERENT LOCATIONS )F THE SPOT BEAM ANTENNAS COVERAGE AREAS ARE SUFFICIENTLY SEPARATED THESAMEFREQUENCYBANDANDPOLARIZATIONSCANBEREUSED INBOTHCOVERAGEAREASTOINCREASECOMMUNICATIONCAPACITYBECAUSEOF THESPATIALISOLATIONBETWEENCOVERAGEAREASAFFORDEDBYTHEANTENNAS SIDELOBERESPONSES )NSOMECOMMUNICATIONAPPLICATIONS GEOPOLITICALBOUNDARIESMUSTBE SERVICEDFORTHEENTIRESATELLITESLIFETIME/FTEN THESEAPPLICATIONSALSO HAVEREGULATORYREQUIREMENTSCONCERNINGTHEALLOWABLERADIATEDPOWER DENSITIESOUTSIDEOFTHEGEOPOLITICALBOUNDARIES)NSUCHSITUATIONS THE COVERAGEPROVIDEDBYASINGLESPOTBEAMMAYBEINADEQUATEBECAUSETHE COVERAGEOFIRREGULARGEOPOLITICALAREASISNOTUNIFORMORTHEREGULATORY REQUIREMENTSONPOWERDENSITYLEVELSOUTSIDETHECOVERAGEAREAARENOT SATISFIED!NTENNATECHNIQUESTOCONFORMMORECLOSELYTOSUCHIRREGULAR CONTOURSHAVEBEENDEVELOPED /NEMEANSOFSATISFYINGIRREGULARCOVERAGEREQUIREMENTSUSESALARGER APERTUREHAVINGACLUSTEROFFEEDSWITHINTHEFOCALREGIONINPLACEOFA SMALLER ANTENNA HAVING A SINGLE SPOT BEAM4HE INDEPENDENT BEAMS PRODUCEDBYTHEFEEDELEMENTSINTHEFOCALREGIONARETHENCOMBINED TOPRODUCEPATTERNCONTOURSTHATCONFORMMORECLOSELYTOTHEIRREGULAR

#HAPTER 3IX

COVERAGEBOUNDARY4HEANTENNADESIGNINTHISCASETYPICALLYUSESOFFSET REFLECTORTECHNOLOGY ANDTHEARRANGEMENTOFTHEINDIVIDUALFEEDHORNS WITHINTHECLUSTERMIMICSTHEBOUNDARIESOFTHEDESIREDCOVERAGEAREA SHAPE4HEFITTOTHEIRREGULARCOVERAGEBOUNDARYIMPROVESASALARGER NUMBEROFNARROWERANTENNABEAMSARECOMBINEDTOPRODUCETHECOV ERAGECONTOUR)NADDITION THEANTENNASIDELOBEREDUCTIONBEYONDTHE COVERAGEAREAINCREASESSINCETHESIDELOBEROLLOFFFOLLOWSTHEPATTERNOF ANARROWERINDEPENDENTANTENNABEAMPATTERN(OWEVER THISIMPROVED FIT TO THE COVERAGE AREA BOUNDARIES IS ACHIEVED AT THE EXPENSE OF AN INCREASEDNUMBEROFFEEDSINTHECLUSTERANDALARGEROVERALLAPERTURE SIZE!NEXAMPLEOFGENERATINGCOVERAGEAREASBYBEAMCOMBINING;= ANDMULTIPLE BEAMCOVERAGEISILLUSTRATEDINMULTIFREQUENCYDESIGNSFOR THE*APANESENATION4HECOVERAGECHARACTERISTICSCANBEVARIEDDURING THESATELLITESLIFETIMEIFPROVISIONISMADEINTHEDESIGNTOCHANGETHE COMBINATIONOFANTENNABEAMSTHATPRODUCECONTOURCOVERAGE ! SECOND MEANS OF SATISFYING COVERAGE REQUIREMENTS FOR IRREGULAR AREASALSOUSESALARGERAPERTURECOMPAREDTOASMALLERANTENNA PRO VIDINGCOVERAGEBYASINGLEBEAM)NTHISDESIGNAPPROACH;= THELARGER APERTUREISFEDBYASINGLEFEEDANDTHEREFLECTORSURFACEISDEFORMEDTO PRODUCETHEREQUIREDCOVERAGEAREA4HEDESIGNOFTHEDEFORMEDREFLECTOR SURFACECANBEDEVELOPEDUSINGASYNTHESISAPPROACH;=4HECOVERAGE CONTOURSAREFIXEDBYTHEPARTICULARDEFORMATIONCONFIGURATIONUSEDIN THEREFLECTORSURFACEANDCANNOTBECHANGEDON ORBIT 7HILEBOTHOFTHESEAPPROACHESTOPRODUCINGIRREGULARCOVERAGEAREAS REQUIRELARGERAPERTURESTHANTHATFORASINGLEANTENNATHATPRODUCESA SPOTBEAM THELARGERAPERTUREPROVIDESFOURBENEFITS 4HE SIDELOBE LEVELS BEYOND THE DESIGN COVERAGE AREA ARE LOWER THANTHOSEINASMALLERSPOTBEAMANTENNAUSINGASINGLECOVERAGE BEAM 4HESEREDUCEDSIDELOBELEVELSBEYONDTHEDESIGNCOVERAGEAREAREDUCE INTERFERENCEBOTHTOANDFROMSOURCESLOCATEDOUTSIDEOFTHEDESIGN COVERAGEAREA 4HESEREDUCEDSIDELOBELEVELSPROVIDEINCREASEDISOLATIONBETWEEN OTHERCOVERAGEAREASINFREQUENCYREUSEAPPLICATIONS ALLOWINGEITHER AN INCREASED NUMBER OF COVERAGE AREAS OR CLOSER ANGULAR SPACING BETWEENCOVERAGEAREAS 4HEREDUCEDSIDELOBELEVELSANDBEAMCOMBININGRESULTINAMORE DIRECTIVE PATTERN HAVING MORE UNIFORM COVERAGE THUS INCREASING COMMUNICATIONPERFORMANCE 7HILEPAYLOADDESIGNSGENERALLYENDEAVORTOREDUCEWEIGHTANDCOM PLEXITY THEPERFORMANCEADVANTAGESOFTHESESPOTANTENNADESIGNSFOR


IRREGULAR COVERAGE AREAS AND THE SYSTEM REQUIREMENTS FOR FREQUENCY REUSETOEXPANDSYSTEMCAPACITYDICTATETHEIRUSE -ULTIPLE "EAM$ESIGNS )NCONTRASTTOSPOTBEAMANTENNASTHATSERVICEACOVERAGEAREAWITHABEAM PATTERNTHATCOMMUNICATESASINGLECOLLECTIONOFSIGNALS AMULTIPLE BEAM ANTENNASERVICESITSCOVERAGEAREAWITHMULTIPLEBEAMSHAVINGINDEPEN DENTDATASTREAMSROUTEDTODIFFERENTPORTIONSOFTHECOMPOSITECOVERAGE AREA)NTHISWAY INCREASEDCAPABILITIESAREPROVIDEDTOTHECOMPOSITECOV ERAGEAREA3INCEEACHBEAMSERVICESONLYAPORTIONOFTHECOVERAGEAREA THESPACESEGMENTSANTENNAGAINLEVELINEACHPORTIONISGREATERTHANIT WOULDBEIFTHECOMPOSITECOVERAGEAREAWERESERVICEDBYASINGLEBEAM 4HISINCREASEDSPACESEGMENTANTENNAGAINLEVELRESULTSINHIGHERDATA RATESERVICESTOUSERSAND ORREDUCEDUSERPERFORMANCEREQUIREMENTS 'ENERALLY MULTIPLEBEAMSAREPRODUCEDFROMASINGLEAPERTURECAPA BLEOFSIMULTANEOUSLYGENERATINGMORETHANONEBEAM4HE)4!,3!4 DESIGN;=DISCUSSEDIN#HAPTERISANEXCEPTIONTHATUSESMORETHAN ONEAPERTURETOACHIEVETHETOTALMULTIPLE BEAMCOVERAGE4WOAPERTURES EACHPROVIDINGTHREEMULTIPLEBEAMSPRODUCETHESIXBEAMCOVERAGEOF THE)TALIANNATION7HENASINGLEAPERTUREISUSED EACHOFTHEMULTIPLE BEAMSHASACOMMONAPERTUREPHASECENTERLOCATEDATTHEAPERTURES CENTER4HEBENEFITOFTHISFEATUREISTHATBEAMSCANBECOHERENTLYCOM BINEDTOSERVEALARGERCOVERAGEAREAWITHOUTSUFFERINGGRATINGLOBES THATWOULDDEGRADEPERFORMANCE!NOTHERSIGNIFICANTBENEFITOFMULTIPLE BEAMDESIGNSISTHATTHEYAREMORECOMPACTANDLIGHTERTHANMULTIPLE DISCRETE ANTENNAS4HE AVAILABLE SPACE ON A SATELLITE PARTICULARLY ON ITSEARTH FACINGSIDE ISINHIGHDEMANDTHEREFORE SIMULTANEOUSLYGEN ERATINGMULTIPLEBEAMSFROMASINGLEAPERTUREISANATTRACTIVE37A0 FEATURE-ULTIPLE BEAMDESIGNSCANBECONFIGUREDTOCOVERTHESATELLITES AVAILABLEFIELDOFVIEWORONLYALIMITEDPORTIONOFIT 4HENOMINALPARAMETERSFORMULTIPLE BEAMANTENNASAREDERIVEDASA MEANSTOEXAMINEDESIGNCOMPLEXITYVERSUS2&PERFORMANCE'ENERALLY MULTIPLE BEAMANTENNASUSEREFLECTORANTENNADESIGNS ANDOFFSETREFLEC TORCONFIGURATIONSARETYPICALLYUSEDTOAVOIDEFFICIENCYLOSSFROMFEED CLUSTERBLOCKAGE-ULTIPLE BEAMANTENNASARECONFIGUREDBYSURROUND INGACENTRALBEAMBYANUMBEROFBEAMSARRANGEDWITHBEAMCENTERS LOCATED ON AN EQUILATERAL TRIANGULAR PATTERN4HE MINIMUM ANTENNA GAINLEVELINTHEFIELDOFVIEWFORMULTIPLE BEAMDESIGNSOCCURSATTHE POINT WHERE THREE ADJACENT BEAM PATTERNS OVERLAP AND IS REFERRED TO ASTHEhTRIPLEPOINTv4HEEQUILATERALTRIANGULARBEAMARRANGEMENT;= RESULTS IN A MAXIMUM VALUE OF THIS MINIMUM GAIN LEVEL AT THE ADJA CENT BEAM OVERLAPPING POINT COMPARED TO OTHER BEAM ARRANGEMENT CONFIGURATIONS4HE ADJACENT BEAMS IN THIS TRIANGULAR ARRANGEMENT

#HAPTER 3IX

&IGURE 4ANGENTIALCROSSOVER

ANDTRIPLEPOINTLOCATIONS

SHOWNIN&IG ILLUSTRATETHEMINIMUMGAINLEVELBETWEENADJACENT BEAMS INDICATED BY THE TRIPLE POINT 4HE TANGENTIAL CROSSOVER POINT BETWEENTWOADJACENTBEAMSISALSOINDICATEDINTHISFIGUREANDTHETAN GENTIALCROSSOVERLEVELCORRESPONDSTOTHEPATTERNLEVELWHEREADJACENT BEAMCONTOURSINTERSECTHALFWAYBETWEENTHEBEAMCENTERS 4HEMULTIPLE BEAMPATTERNARRANGEMENTSTARTSWITHACENTRALBEAM ALIGNED WITH THE ANTENNAS BORESIGHT AXIS4HE CENTRAL BEAM IS SUR ROUNDEDBYARINGOFSIXADDITIONALBEAMSTHISINTURNISSURROUNDED BY ANOTHER RING HAVING BEAMS WHICH IN TURN IS SURROUNDED BY ANOTHERRINGOFBEAMS ANDSOFORTH4HETOTALNUMBEROFBEAMS N FORAMULTIPLE BEAMANTENNAHAVING.RINGSOFBEAMSSURROUNDING THECENTRALBEAM EQUALS

N. .

!TYPICALANTENNABEAMARRANGEMENTFORAMULTIPLE BEAMANTENNA HASBEAMSSPACEDSOTHATTHEEDGEOFCOVERAGEISTANGENTIALTOTHEHALF POWERPOINTSANDTHETANGENTIALCROSSOVERLEVELBETWEENADJACENTBEAMS ISD"BELOWTHEBEAMPEAK4HEPATTERNLEVELD"LOWERTHANTHE BEAMPEAKCORRESPONDSTOANANGULARSEPARATIONFROMTHEBEAMPEAK EQUALTOBEAMWIDTHSUSINGA'AUSSIANPATTERNREPRESENTATION FORTHEANTENNABEAMS7ITHTHEEQUILATERALSEPARATIONBETWEENBEAM CENTERS THE TRIPLE POINT WHERE THE THREE BEAM PATTERNS INTERSECT IS D"LOWERTHANTHEPEAKGAINVALUEANDFORTHEINDIVIDUALBEAMSCOR RESPONDSTOTHEMINIMUMGAINLEVELOFTHEINDIVIDUALBEAMSWITHINTHE FIELDOFVIEW!SANEXAMPLE THEBEAMPATTERNGEOMETRYFORA BEAM ANTENNAISILLUSTRATEDIN&IG .OMINALCHARACTERISTICSFORMULTIPLE BEAMANTENNASCANBEDERIVED BYDEFININGTHEREQUIREDFIELDOFVIEWANDDETERMININGTHENUMBEROF BEAMSNEEDEDTOSERVICETHATCOVERAGEAREA4HEANTENNABEAMWIDTH P B TOSERVICEA&/6FIELDOFVIEW HAVINGASPECIFIEDANGULAREXTENT CANBEDETERMINEDFROM

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&IGURE "EAMARRANGEMENTFORBEAMS

4HEREQUIREDAPERTUREDIAMETER$CANTHENBEDETERMINEDFROMTHE BEAMWIDTHOFTHEINDIVIDUALBEAMS !SANEXAMPLETHATPROVIDESFULLEARTHCOVERAGEFROMAGEOSTATIONARY SATELLITE THEBEAMWIDTHOFANINDIVIDUALBEAMISASSUMEDTOEQUALK$ 4HE PEAK GAIN LEVEL OF AN INDIVIDUAL BEAM DEPENDS ON THE ANTENNA EFFICIENCY ANDTHISEXAMPLEASSUMESAANTENNAEFFICIENCY4HEMINI MUMANTENNAGAINLEVELWITHINTHEFIELDOFVIEWOCCURSATTHETRIPLEPOINT BETWEENADJACENTBEAMSANDISOBTAINEDBYSUBTRACTINGTHED"VALUE FROMTHEPEAKANTENNAGAINLEVEL4HESENOMINALPARAMETERASSUMPTIONS WEREUSEDTOCONSTRUCT4ABLE WHICHILLUSTRATESTHEGAINLEVELSAND

4!",% .OMINAL-ULTIPLE "EAM!NTENNA0ARAMETERS

.UMBER .UMBER "EAMWIDTH $IAMETER 0EAK -INIMUM )NCREMENTAL OF2INGS OF"EAMS DEGREES 7AVELENGTHS 'AIN D"I 'AIN D"I 'AIN D"

#HAPTER 3IX

BEAMWIDTHOFASINGLEBEAMWITHINTHECOLLECTION4HISTABLEASSUMESTHE SATELLITEISINAGEOSTATIONARYORBITTHATHASAOEARTHFIELDOFVIEW 4HELASTCOLUMNOFTHETABLEINDICATESTHEINCREMENTALGAINLEVELRELATIVE TOTHEVALUESACHIEVEDWHENONELESSRINGOFFEEDSISUSED4HEBEAMS BECOMEMOREDENSELYPACKEDASTHENUMBEROFRINGSINCREASESHOWEVER THEGAINADVANTAGEAFFORDEDBYANINCREASEDNUMBEROFBEAMSBECOMES LESSSIGNIFICANTASTHENUMBEROFRINGSINCREASES0RACTICALDESIGNSUSING MULTIPLE BEAMANTENNATECHNOLOGYARELIMITEDBYTHEREQUIREDAPERTURE SIZEATLOWFREQUENCIESANDBYTHETOLERABLESYSTEMCOMPLEXITYOFTHE SUPPORTINGELECTRONICSASTHENUMBEROFBEAMSINCREASES 4HEABILITYTOINDEPENDENTLYUSETHEMULTIPLEBEAMSREQUIRESACHIEV ING ISOLATION BETWEEN BEAM POSITIONS TO AVOID MUTUAL INTERFERENCE BETWEENINDEPENDENTDATASTREAMSCOMMUNICATEDONADJACENTBEAMS 4HIS ISOLATION IS ACHIEVED BY THE ANTENNA SIDELOBE RESPONSE AND BY POLARIZATION)NPRACTICE FREQUENCYANDPOLARIZATIONREUSETECHNIQUES AREDEVELOPEDTOPROVIDETHEREQUIREDISOLATION4HEREQUIREDISOLATION DEPENDSONTHESIGNALMODULATIONFORMATSUSEDBYTHESYSTEMANDTHE DYNAMICRANGEOFTHEUSERSIGNALLEVELS4HETOLERABLECO CHANNELINTER FERENCE LEVEL FOR A GIVEN MODULATION FORMAT IS GENERALLY DETERMINED THROUGH MEASUREMENTS USING THE OPERATIONAL SIGNAL MODEMS ONE OF WHICH REPRESENTS THE DESIRED SIGNAL AND THE OTHER REPRESENTING THE INTERFERINGCO CHANNELINTERFERENCE4HELEVELOFTHEINTERFERINGSIGNAL REPRESENTATIONISINCREASEDUNTILTHE3.)2SIGNAL TO NOISEPLUSINTER FERENCE FOR A SPECIFIED "%2 LEVEL IS DETERMINED4HE DYNAMIC RANGE OFTHEUPLINKUSERSIGNALSALSOMUSTBEADDRESSEDINDETERMININGTHE REQUIREDISOLATIONBETWEENBEAMSASSIGNEDTOTHESAMEFREQUENCYSUB BAND)NASIMPLEEXAMPLEOFAFREQUENCYREUSEPLAN;= ILLUSTRATEDIN &IG THEAVAILABLESPECTRUMISDIVIDEDINTOTHREESUBBANDSANDTHE

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SUBBANDSAREASSIGNEDTOBEAMPOSITIONSASINDICATEDSOTHATADJACENT BEAM POSITIONS DO NOT USE THE SAME SUBBAND -ORE COMMONLY A FRE QUENCYREUSEBASEDONSEVENFREQUENCYSUBBANDSISUSEDTOINCREASE THEANGULARSPACINGBETWEENCOVERAGEAREASUSINGTHESAMEFREQUENCY SUBBAND4HEINCREASEDANGULARSPACINGRESULTSINLOWERSIDELOBELEVELS INADJACENTBEAMPOSITIONSSHARINGTHESAMEFREQUENCYSUBBANDAND INCREASEDISOLATIONBETWEENBEAMSASARESULT ! PRINCIPAL DESIGN ISSUE FOR MULTIPLE BEAM ANTENNAS ;= IS HOW TO ACHIEVEINDIVIDUALBEAMSWITHLOWSIDELOBEPERFORMANCEWHILEMAIN TAININGHIGHTANGENTIALBEAMCROSSOVERLEVELSSOTHEMINIMUMANTENNA GAINLEVELSINTHEFIELDOFVIEWARENOTREDUCED,OWSIDELOBELEVELSAS DISCUSSEDIN#HAPTER REQUIREANAPERTUREHAVINGATAPEREDAMPLITUDE DISTRIBUTIONPRODUCEDBYTHEFEEDILLUMINATION4HETAPEREDAMPLITUDE DISTRIBUTIONREQUIRESMOREDIRECTIVEFEEDPATTERNS WHICHINTURNREQUIRE A LARGER FEED APERTURE!T THE SAME TIME THE MINIMUM GAIN WITHIN THE FIELD OF VIEW IS ALSO AN IMPORTANT SYSTEM PARAMETER 4HE AMPLI TUDETAPERNEEDEDFORLOWSIDELOBEBEAMSREQUIRESRELATIVELYLARGEFEED DIMENSIONS TO PRODUCE THE DESIRED ILLUMINATION TAPER (OWEVER THE DIMENSIONSOFTHESERELATIVELYLARGEFEEDSALSOIMPOSECORRESPONDINGLY LARGEANGULARSEPARATIONSBETWEENADJACENTBEAMPOSITIONS4HESELARGE SEPARATIONSBETWEENADJACENTBEAMPOSITIONSRESULTINTANGENTIALBEAM CROSSOVERLEVELSTHATRELATIVETOTHEANTENNABEAMSPEAKGAINLEVEL AREATALOWERLEVELTHANDESIRED 4WOWAYSHAVEBEENEXPLOREDTOADDRESSTHECONFLICTBETWEENHIGH TANGENTIALBEAMCROSSOVERLEVELSANDLOWANTENNASIDELOBELEVELS/NE WAY;=ISTOCOMBINEAGIVENFEEDWITHSMALLAMOUNTSOFTHEADJACENT SIX FEEDS WITH WEIGHTING CIRCUITRY TO ACHIEVE LOW SIDELOBES AND HIGH CROSSOVERLEVELS4HERESULTOFCOMBININGSMALLVALUESOFADJACENTBEAMS WITHACENTRALBEAMISTOINCREASETHEFEEDAPERTURESIZEELECTRICALLY PRODUCINGANAPERTUREAMPLITUDETAPER!SECONDWAY;=TOACHIEVE HIGHTANGENTIALBEAMCROSSOVERLEVELSANDLOWANTENNASIDELOBELEVELS USESACLUSTEROFFEEDSTHATISDISPLACEDFROMTHEFOCALREGIONTOALLOW LARGERFEEDAPERTURESANDUNDERILLUMINATESTHEAPERTURETOACHIEVELOW SIDELOBES4HISAPPROACHREQUIRESASOMEWHATLARGERAPERTURETHANIS NORMALLYUSED BUTITSPOTENTIALINACHIEVINGHIGHCROSSOVERLEVELSAND LOWSIDELOBESWARRANTSFURTHERDEVELOPMENT !NOTHER DIFFERENT APPROACH TO ACHIEVE BOTH LOW SIDELOBE ANTENNA BEAMSANDHIGHVALUESOFTHEMINIMUMANTENNAGAINLEVELINTHEFIELD OFVIEWCONFIGURESTHEANTENNADESIGNTOHAVELOWSIDELOBEBEAMSAND ARELATIVELYLOWCROSSOVERLEVEL4HEPROBLEMOFOBTAININGAHIGHVALUE OFTHEMINIMUMANTENNAGAINLEVELINTHEFIELDOFVIEWISADDRESSEDBY COMBININGTHETHREEADJACENTBEAMSTOPRODUCEANOTHERBEAMWHOSE AXISISCOINCIDENTWITHTHETRIPLEPOINTLOCATIONS!FINALAPPROACH MEN TIONEDEARLIERANDUSEDBYTHE)4!,3!4DESIGN;= EMPLOYSTWOSEPARATE

#HAPTER 3IX

APERTURESTOFORMSIXINDEPENDENTBEAMS WITHEACHAPERTUREFORMING THREEINDEPENDENTBEAMS4HEBEAMSFORMEDBYEACHAPERTUREHAVESUF FICIENTANGULARSEPARATIONTOPROVIDETHENECESSARYAPERTUREAMPLITUDE TAPER4HEANTENNAPOINTINGBYEACHAPERTUREALLOWSALTERNATIVEBEAMS FROMEACHAPERTURETOFORMANOVERALLMULTIPLE BEAMARRANGEMENTWITH CLOSELY SPACED ADJACENT BEAMS 4HIS APPROACH DOES NOT PERMIT COM BININGBEAMSFROMTHESEPARATEDAPERTURESBECAUSETHEPHASECENTER SEPARATION BETWEEN THE APERTURES WOULD RESULT IN GRATING LOBES4HE SEPARATE APERTURE APPROACH ALSO INCREASES THE NUMBER OF APERTURES NEEDEDTOPRODUCETHECOMPOSITEMULTIPLE BEAMARRANGEMENTBUTCAN BEANEFFECTIVESOLUTIONFORAPPLICATIONSLIKETHE)4!,3!4DESIGN -ULTIPLE BEAM ANTENNA TECHNOLOGY MUST PRODUCE BEAMS WITH HIGH FIDELITYOVERTHEREQUIREDFIELDOFVIEW$ESIGNATTENTIONMUSTBEPAIDTO MINIMIZINGTHESCANLOSSOVERTHEFIELDOFVIEWANDMAINTAININGSIDELOBE PERFORMANCEATTHEEDGESOFCOVERAGETHATISCOMPARABLEWITHTHECEN TRALBEAMS-ULTIPLE BEAMANTENNASFORGEOSYNCHRONOUSSATELLITESTHAT COVERTHEENTIREAVAILABLEFIELDOFVIEWMUSTPRODUCEMULTIPLEBEAMS O OVERABOUTAN FIELDOFVIEW2EFLECTORANTENNATECHNOLOGYISGENERALLY CONSIDEREDALIMITEDSCANDESIGNAND WITHPROPERDESIGNATTENTION CAN MAINTAINGOODPATTERNFIDELITYANDMINIMALSCANLOSSOVERTHEREQUIRED FIELDOFVIEW/FFSETREFLECTORTECHNOLOGYISCOMMONLYUSEDBECAUSEITS GEOMETRYAVOIDSBLOCKAGEEFFECTSOFRELATIVELYLARGEFEEDCLUSTERSUSEDTO PRODUCETHEMULTIPLEBEAMS,ONGF $VALUES DUALREFLECTORCONFIGURA TIONS ANDSHAPINGTECHNIQUES; =ARECOMMONLYUSED ANDANALYSIS CODESAREAVAILABLETODEVELOPDETAILEDDESIGNSTOSATISFYREQUIREMENTS FORSPECIFICAPPLICATIONS 7HEN MULTIPLE BEAMS ARE USED FOR LOWER ALTITUDE SATELLITES THE REQUIREDFIELDOFVIEWEXPANDSGREATLYASSHOWNIN&IG ANDEXCEEDS THECAPABILITYOFLIMITEDSCANREFLECTORDESIGNS!TTHESELOWERALTITUDES THEREQUIREDBEAMWIDTHTOACHIEVEFOOTPRINTDIMENSIONSCOMPARABLETO GEOSYNCHRONOUSSATELLITESISMUCHLARGERTHANTHEGEOSYNCHRONOUSCASE 4HESEFACTORSRESULTINARRAYANTENNASYSTEMSTHATARESMALLENOUGHTO HAVEAPRACTICALNUMBEROFELEMENTSANDCANACHIEVETHEREQUIREDFIELD OFVIEWWITHACCEPTABLESCANDEGRADATION-ULTIPLE BEAMGENERATIONIS ACCOMPLISHEDBYUSINGMULTIPLECORPORATEFEEDSTRUCTURES WHEREEACH FEEDSTRUCTURECONTAINSTHEMEANSTOSTEERTHEBEAMINDEPENDENTLYTO THEDESIREDLOCATION4HE'LOBALSTARDESIGN;=USESSEPARATEUPLINK AND DOWNLINK ARRAYS THAT PRODUCE BEAMS4HE UPLINK ARRAY OPER ATES AT , BAND AND FORMS BEAMS FROM ARRAY ELEMENTS AND THE DOWNLINKARRAYOPERATESAT3 BANDANDFORMSBEAMSFROMARRAY ELEMENTS4HE)2)$)5-ARRAYDESIGN;=ISCONFIGUREDINTHREEARRAY PANELSHAVINGACTIVETRANSMITRECEIVEMODULESFOREACHOFTHEMORETHAN ARRAYELEMENTS%ACHARRAYCOVERSAOANGULARSECTORANDTHE ARRAYPANELSARETILTEDAWAYFROMTHESATELLITESNADIRAXISTOIMPROVE


COVERAGEATWIDEANGLESTOWARDSTHEEARTHSHORIZON%ACHARRAYPANEL PRODUCESBEAMSSOTHATTHEFIELDOFVIEWFOREACHSATELLITEISSERVICED BYBEAMPOSITIONS !NEXAMPLEOFMULTIPLE BEAMOPERATIONWITHINASPOTSIZE;=HAS BEENAPPLIEDTOTHEATERCOVERAGEAPPLICATIONS7HENMULTIPLEBEAMS SERVICE A SMALLER SPOT SIZE THAN THE ENTIRE FIELD OF VIEW ELECTRICALLY LARGEAPERTURESAREREQUIRED3UCHAPERTURESIZESBECOMEPRACTICALAT %(&FREQUENCIESWHEREAREASONABLYCOMPACTANTENNADESIGNRESULTS 4HIS DESIGN IS PROPOSED FOR UPLINK OPERATION AT '(Z TO PROVIDE COMMUNICATIONS FOR MILITARY APPLICATIONS 6ERY HIGH ANTENNA GAIN PERFORMANCE IS ACHIEVED BY THE NARROW BEAMWIDTH IN THIS DESIGN AND ACTIVE TRACKING OF GROUND BEACONS AS HAS BEEN DEMONSTRATED BYTHE)4!,3!4PROGRAM;= ISREQUIREDTOCOMPENSATEFORSATELLITE ATTITUDE VARIATIONS )N COMPARISON WITH THE GAIN LEVELS FOR ANTENNA SYSTEMDESIGNSTHATFORMASINGLEANTENNABEAM THEGAINLEVELSARE INCREASED BY THE NUMBER OF ANTENNA BEAMS SERVICING THE SPOT SIZE &OR MILITARY APPLICATIONS THE NARROW ANTENNA BEAMWIDTHS ISOLATE INTERFERENCESOURCESTOAVERYSMALLPORTIONOFTHECOVERAGEAREASINCE THESIDELOBESOFOTHERNARROWBEAMSREMOVEDFROMTHEBEAMPOSITION CONTAININGINTERFERENCEREDUCERECEIVEDINTERFERENCEPOWERLEVELS4HE SYSTEMDESIGNALSOUSESSPREADSPECTRUMMODULATIONFORINTERFERENCE PROTECTIONANDTHEPRESENCEOFINTERFERENCETHATIMPACTSPERFORMANCE ISINDICATEDBYEXCESSIVERECEIVEDPOWERLEVELSINTHEBEAMPOSITIONS RECEIVING INTERFERENCE POWER )N SUCH CASES THE INTERFERENCE POWER THATIMPACTSDESIREDSIGNALCOMMUNICATIONPERFORMANCEMUSTEXCEED THESIGNALPOWERLEVELBYROUGHLYTHESPREADSPECTRUMPROCESSINGGAIN !DAPTIVEINTERFERENCECANCELLATIONCANALSOBEIMPLEMENTEDINTHESE DESIGNS 3INCE SPREAD SPECTRUM IS ALSO USED ADAPTIVE INTERFERENCE CANCELLATIONISREQUIREDONLYWHENTHESPREADSPECTRUMINTERFERENCE CANCELLATION PROTECTION IS INADEQUATE )N SUCH CASES INTERFERENCE IS IDENTIFIEDBYEXCESSIVEPOWERLEVELSINUPLINKBEAMPOSITIONS!SDIS CUSSEDINTHENEXTSECTION DIRECTIONFINDINGTECHNIQUESUSINGTHEMUL TIPLEBEAMSANDADAPTIVEINTERFERENCECANCELLATIONBASEDONMEASURED INTERFERENCESIGNALDIRECTIONSCANBEUSED %XAMPLEVALUESFORAOCOVERAGEAREA;=IN4ABLE ILLUSTRATETHE BEAMWIDTH GAINLEVELS SIZE ANDINTERFERENCESUPPRESSIONPERFORMANCE ACHIEVEDASTHENUMBEROFMULTIPLEBEAMSINTHESPOTCOVERAGEINCREASES 4HEINTERFERENCEPERFORMANCEASSUMESAPATTERNNULLISLOCATEDONTHE INTERFERENCESOURCE ANDCOMMUNICATIONCANBEPERFORMEDWHENUSERS AREWITHIND"OFTHEBEAMPEAK4HEANGULARSEPARATIONBETWEEN THE PATTERN NULL AND A PATTERN LEVEL D" BELOW THE BEAM PEAK IS BEAMWIDTHS%(&SYSTEMSREQUIRELINKMARGINFORRAINATTENUA TION ANDITISASSUMEDTHATTHISSIGNALMARGINISAVAILABLEWHENINTER FERENCEISPRESENT4HEREQUIREDSEPARATIONBETWEENINTERFERENCEAND

#HAPTER 3IX

4!",% .OMINAL-ULTIPLE "EAM!NTENNA0ARAMETERSFORA #OVERAGE!REA;=

.UMBER $ELTA2 $ELTA2 $ELTA2 OF"EAMS "EAMWIDTH DEG 'AIN D"I $IAMETER FT KM KM KM

ADESIREDUSERHASBEENCOMPUTEDINTHETABLEASTHEhDELTA2vPARAMETER 3EPARATIONVALUESAREINDICATEDFORTHESUBSATELLITEPOINT ANDUSERELEVA TIONANGLESOFOANDOWHERETHEWORST CASEVALUESAREPRESENTED CORRESPONDINGTOTHESATELLITE THECENTEROFTHEEARTH THEDESIREDUSER ANDTHEINTERFERENCESOURCEARELOCATEDONACOMMONPLANE -ULTIPLE BEAMDESIGNS PARTICULARLYWHENVERYNARROWBEAMWIDTHS ARE USED HAVE ISSUES IN DEALING WITH CAPACITY ALLOCATIONSAND FOR MILITARYSYSTEMS DEALINGWITHINTERFERENCE#APACITYDEMANDSFORCOM MUNICATIONSERVICESARENOTUNIFORMLYDISTRIBUTEDOVERTHECOLLECTIONOF BEAMSANDCANALSOBETIME VARYING4HISSUGGESTSAFREQUENCYREUSE PLAN;=THATPROVIDESABASICCAPABILITYWITHFIXEDSUBBANDALLOCATIONS ANDANOTHERSUBBANDTHATCANPROVIDEINCREASEDCOMMUNICATIONCAPA BILITIESINBEAMPOSITIONSWITHHIGH CAPACITYDEMANDS4HISADDITIONAL SUBBANDCANALSOBEUSEDINBEAMPOSITIONSWHEREINTERFERENCEISPRES ENT4HECHANGEOFFREQUENCYBETWEENTHEBASICFIXEDSUBBANDTOTHE ADDITIONALSUBBANDMAYBEADEQUATETOREDUCEINTERFERENCE ANDIFNOT ADAPTIVEINTERFERENCETECHNIQUESCANBEAPPLIEDWITHOUTIMPACTINGTHE BASICFREQUENCYREUSEPLAN !TYPICALMULTIPLE BEAMTRANSPONDERDESIGN;=DESCRIBEDIN&IG USESMULTIPLE BEAMANTENNASONTHEUPLINKANDDOWNLINKFREQUENCIES 4HIS SYSTEM MAPS + UPLINK BEAMS INTO . DOWNLINK BEAMS WHICH IS CONTROLLED BY WHAT IS CALLED AhMESSAGE ROUTERv4HE MESSAGE ROUTER CANHAVEAVARIETYOFFORMS4HESIMPLESTFORMISSIMPLYAHARDWIRED FIXEDMAPPINGOFUPLINK TO DOWNLINKBEAMS7HILESUCHADESIGNISVERY SIMPLE CONNECTIVITYBETWEENUSERSINDIFFERENTCOVERAGEAREASREQUIRES INCORPORATINGSWITCHINGNETWORKSANDFREQUENCYSUBBANDSINTOTHEMES SAGEROUTERDESIGN3UCHTECHNIQUESFOLLOWTHELINEARFREQUENCYTRANS LATINGTRANSPONDERARCHITECTUREANDHAVEMINIMALWEIGHTANDPOWER IMPACTSONTHESPACESEGMENTDESIGNS


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4HE MESSAGE ROUTER HAS OTHER FORMS THAT FOLLOW THE REGENERATIVE REPEATER TRANSPONDER ARCHITECTURE )N THIS CASE THE MESSAGE ROUTER INCLUDES DEMODULATION AND REMODULATION CAPABILITIES THAT SEPARATE INDIVIDUALSYSTEMUSERS!FTERSUCHUPLINKSIGNALSEPARATION THEINDI VIDUALUPLINKSIGNALSUSERCANBEROUTEDTOTHEAPPROPRIATEDOWNLINK BEAM POSITIONS 2EGENERATIVE REPEATER DESIGNS PROVIDE FLEXIBILITY IN USERROUTINGASWELLASREDUCINGTHEINTERFERENCEPOWERTRANSMITTEDON THESATELLITEDOWNLINK4HEMULTIPLE BEAMSYSTEMCANCONTAINDIGITAL DEMULTIPLEXINGANDMULTIPLEXINGCIRCUITRYTOSEPARATETHEUPLINKUSER SIGNALS WITHIN THE INDIVIDUAL BEAM CHANNELS AND COMBINE AND ROUTE THEMTOFORMTHEDOWNLINKSIGNALCOLLECTION4HISSIGNALSEPARATIONAND COMBININGISREFERREDTOASACHANNELIZERARCHITECTUREDISCUSSEDEAR LIERIN#HAPTER )NDIVIDUALBEAMSCANALSOBEASSIGNEDTOSUBBANDS WHOSESIGNALCOLLECTIONSCANBEROUTEDTODOWNLINKBEAMSASAGROUP THUSSIMPLIFYINGTHECHANNELIZERDESIGN4HEINDIVIDUALSIGNALORFRE QUENCY SUBBANDS CAN BE COMBINED FROM DIFFERENT BEAM POSITIONS TO FORMLARGERDOWNLINKCOVERAGEAREASTHANASINGLEBEAMSCOVERAGEFOR BROADCASTPURPOSES)NSOMECASES THEMESSAGEROUTINGISPERFORMED ONTHESATELLITEWHILEOTHERSYSTEMDESIGNSLOCATETHEMESSAGEROUTER ONTHEGROUND WHERETHESEPARATION SWITCHING ANDROUTINGOPERATIONS AREPERFORMED4HEUPLINKSIGNALCOLLECTIONISTRANSMITTEDTOAGATEWAY GROUNDTERMINALWHERETHEAPPROPRIATEPROCESSINGISPERFORMEDTOFORM THEDOWNLINKSIGNALCOLLECTION4HEINFORMATIONISTHENTRANSMITTEDTO THESATELLITEBYTHEGATEWAYTERMINAL ANDTHESATELLITEREBROADCASTSTHE INFORMATIONTOTHEUSERSEGMENTS'ATEWAYARCHITECTURESAREPRACTICAL FORLOWDATARATEAPPLICATIONSWHERETHEMULTIPLE BEAMSIGNALCOLLEC TIONSCANBEACCOMMODATEDTHROUGHTHEGATEWAYLINKSWITHREASONABLE DATATRANSFERRESOURCES 4HESPECIFICARCHITECTUREFORTHEMULTIPLE BEAMSYSTEMSDEPENDSLARGELY ON THE APPLICATION #OMMERCIAL SYSTEMS ARE COMMONLY CONFIGURED TO

#HAPTER 3IX

PROVIDE FIXED COVERAGE IN ORBIT4HUS THESE SYSTEMS TEND TO COMBINE FEED ELEMENTS IN A FIXED MANNER TO FOLLOW GEOPOLITICAL BOUNDARIES #HANNELIZATIONFORDIFFERENTUSERSEGMENTSISCOMMONLYPERFORMEDAND PROVIDESLINKINGNOTONLYWITHINAGIVENCOVERAGEAREABUTALSOBETWEEN COVERAGEAREAS4HENEED TO USE THE EXISTING SPECTRAL ALLOCATION TO THE FULLESTEXTENTPOSSIBLERESULTSINHIGHDEMANDSONFREQUENCYANDPOLARIZA TIONREUSETECHNIQUES4HESEFACTORSAREAPPARENTINTHEEXISTINGDESIGNS FORGEOSYNCHRONOUSSATELLITES-ILITARYSYSTEMSPLACEDIFFERENTDEMANDS ONTHEIRSYSTEMSTHANCOMMERCIALSYSTEMS0OLITICALSITUATIONSCANVARY GREATLYDURINGTHESATELLITESLIFETIME SOTHATFLEXIBILITYTORECONFIGURECOV ERAGEAREASISESSENTIAL6ARIATIONSINCOVERAGEAREALSONEEDEDTOCOVER NAVALFLEETMOTIONSANDSERVICETOTACTICALOPERATIONS-ILITARYUSERSARE CONCERNEDWITHTHEPOSSIBILITYOFINTENTIONALINTERFERENCE ORJAMMING AS WELLASPRIVACY ANDSPREADSPECTRUMMODULATIONUSEDWITHREGENERATIVE REPEATERTRANSPONDERSANDADAPTIVEINTERFERENCECANCELLATIONPROVIDEA POWERFULMEANSOFREDUCINGINTERFERENCEANDMINIMIZINGTHEAMOUNTOF DOWNLINKPOWERWASTEDBYTRANSMITTINGINTERFERENCE !STHEEXAMPLESINTHISDISCUSSIONINDICATE MULTIPLE BEAMANTENNA SYSTEMSCANBEUSEDINALARGEVARIETYOFWAYS ANDTHEIRDESIGNFLEXIBIL ITYISTHEREASONFORTHEIMPORTANCEOFMULTIPLE BEAMANTENNASYSTEMS 5PLINKRECEIVINGANTENNASUSEPREAMPLIFIERSBETWEENTHEANTENNAPORTS AND THE BEAMFORMER CIRCUITY TO ESTABLISH THE SYSTEM NOISE TEMPERA TUREANDAVOIDDEGRADINGSYSTEMPERFORMANCEWITHBEAMFORMINGLOSS "EAMFORMINGCANALSOBEACCOMPLISHEDAT)&FREQUENCIESWITHPOTENTIAL SAVINGSINWEIGHTANDCOST7HENACTIVECOMPONENTSAREUSEDBETWEEN THEANTENNAPORTSANDBEAMFORMINGNETWORKS DESIGNATTENTIONMUSTBE PAIDTOTHEUNIT TO UNITAMPLITUDEANDPHASETRACKINGCHARACTERISTICSOF THEACTIVEDEVICESTOMAINTAINIDEALBEAMFORMINGPERFORMANCE4HELOW WEIGHTANDINSENSITIVITYTOLOSSFORRECEIVEUPLINKBEAMFORMERSALLOW SIGNIFICANTFLEXIBILITYINTHEIROPERATION4HEDOWNLINKBEAMFORMINGHAS LESSFLEXIBILITYBECAUSEOFSYSTEMLOSSINBEAMFORMERS0RESENTPRACTICE ISTODISTRIBUTEAGROUPOFTRANSMITTERSTOTHEDOWNLINKMULTIPLE BEAM COLLECTION3IGNALROUTINGLOSSFROMTHETRANSMITTERSTOTHEBEAMPORTS OFTHEMULTIPLE BEAMANTENNASDEGRADES%20PERFORMANCE)DEALLY EACH ANTENNAPORTWOULDHAVEITSOWNTRANSMITTERTHATCANBEPOWEREDAS REQUIREDTOSERVICEPARTICULARCOVERAGEAREAS)NTHISWAY THETRANSMIT BEAMFORMINGCANBEACCOMPLISHEDPRIORTOTHEFINALTRANSMITAMPLIFIERS ANDBEAMFORMINGLOSSWOULDNOTREDUCEDOWNLINK%2&PERFORMANCE !DAPTIVE5PLINK!NTENNAS !DAPTIVEUPLINKANTENNADESIGNSHAVEBEENDEVELOPEDTOREDUCEINTERFER ENCERECEIVEDBYTHESATELLITEUPLINKANTENNA3YSTEMDEGRADATIONFROM INTERFERENCEHASLONGBEENACONCERNOFMILITARYUSERS-ORERECENTLY


ADAPTIVE TECHNIQUES ;= TO LOCATE USER SIGNALS REDUCE UNINTENTIONAL INTERFERENCEINMULTIPLE BEAMDESIGNS ANDINCREASEISOLATIONBETWEEN BEAMSINFREQUENCYREUSETECHNIQUESHAVEBEENADDRESSEDFORTHECOM MERCIALCOMMUNICATIONSSECTOR!DAPTIVEUPLINKANTENNADEVELOPMENT ;=INVOLVESMANYDISCIPLINES THEANTENNAHARDWARE ALGORITHMSELEC TION SOFTWAREIMPLEMENTATION ANDSYSTEMDESIGNSIMULATION!DAPTIVE ANTENNAS ARE AN EXAMPLE OF AN ANTENNA SYSTEM WHOSE PERFORMANCE STRONGLYDEPENDSONTHESYSTEMELECTRONICSTHATAREINTEGRATEDWITHTHE ANTENNA4ESTTECHNIQUESFORADAPTIVEANTENNADESIGNSAREDESCRIBED IN#HAPTER !DAPTIVEMULTIPLE BEAMDESIGNS;=HAVEBEENUSEDTOPROTECTUSERSIN SPOTCOVERAGEAREAS ASILLUSTRATEDIN&IG )NSUCHAPPLICATIONS ADAP TIVECANCELLATIONOFINTERFERENCEWITHINTHECOVERAGEAREAPROTECTSUSERS

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#HAPTER 3IX

AND SIDELOBE PROTECTION IS PROVIDED FROM INTERFERENCE SOURCES LOCATED BEYONDTHECOVERAGEAREA.ARROWBEAMWIDTHSPRODUCEDBYTHEMULTIPLE BEAMANTENNAPROVIDEBOTHRESOLUTIONBETWEENINTERFERENCEANDDESIRED USERSANDREDUCETHEAMOUNTOFTHEDESIGNCOVERAGEAFFECTEDWHENANULL ISFORMEDTOCANCELINTERFERENCE4HESYSTEMDESIGNGENERALLYUSESSPREAD SPECTRUMMODULATIONFORMATSSOTHATADAPTIVEINTERFERENCECANCELLATION OPERATIONISREQUIREDONLYWHENADEQUATEINTERFERENCEPROTECTIONFROM SPREADSPECTRUMPROCESSINGGAINISNOTPROVIDED)NTERFERENCEISTHUS INDICATEDWHENTHEPOWERLEVELINTHEBEAMEXCEEDSATHRESHOLDLEVEL ASMEASUREDBYPOWERMONITORINGANDWHENTHERECEIVEDSIGNALCOM PONENTSDONOTHAVETHESPREADSPECTRUMCODING3INCESUCHADESIGN PROVIDESSPOTCOVERAGE MECHANICALREPOSITIONINGISUSEDTOMOVETHECOV ERAGEAREAASCOMMUNICATIONNEEDSCHANGE"EYONDTHECOVERAGEAREA THESYSTEMISPROTECTEDFROMINTERFERENCEBYTHESIDELOBERESPONSEOFTHE ANTENNA ANDUNLESSVERYSTRONGINTERFERENCEISVERYCLOSETOTHEDESIGN COVERAGE ADAPTIVERESOURCESARENOTNEEDEDTOREDUCEINTERFERENCE !DAPTIVE ANTENNA DESIGNS FOR UPLINK SATELLITE APPLICATIONS CANCEL INTERFERENCESOURCES BUTATTHESAMETIMEMUSTPROVIDECOMMUNICATION SERVICESTOUSERSLOCATEDWITHINTHECOVERAGEAREA4HESYSTEMDESIGN MUSTADDRESSFOURPERFORMANCEMEASURES4HEFIRSTMEASUREISTHESTEADY STATEPERFORMANCEWHENINTERFERENCEISPRESENT!DAPTIVECANCELLATION PRODUCES NULLS WITHIN THE COVERAGE AREA /NE PERFORMANCE MEASURE CONCERNSTHEEFFECTIVENESSOFTHEINTERFERENCECANCELLATION4HESECOND PERFORMANCEMEASUREISTHEPERCENTCOVERAGEAREATHATISTHEPORTIONOF THEORIGINALCOVERAGEAREAWHEREEXISTINGANDPOTENTIALUSERSCANCOM MUNICATEAFTERADAPTIVECANCELLATION4HETHIRDPERFORMANCEMEASURE ISTHEMINIMUMANGULARSEPARATIONBETWEENINTERFERENCESOURCESAND SYSTEMUSERS4HEFOURTHPERFORMANCEMEASUREISTHETIMEREQUIREDFOR THEADAPTIVEWEIGHTINGTOCONVERGETOSTEADYSTATEVALUES -ULTIPLE BEAMANTENNASPRODUCEDBYREFLECTORANTENNATECHNOLOGY ARECOMMONLYUSEDINSUCHAPPLICATIONS-ULTIPLE BEAMDESIGNSPRO DUCEINDIVIDUALBEAMSFROMACOMMONAPERTURETHATHASTHEIMPOR TANT BENEFIT OF PHASE CENTER COINCIDENCE FOR ALL BEAMS 4HE PHASE CENTERCOINCIDENCEPERMITSANTENNABEAMCOMBININGWITHOUTDISPER SION WHICHLIMITSADAPTIVECANCELLATIONPERFORMANCE4HINNEDARRAY DESIGNSRECEIVEDCONSIDERATIONINTHEPAST; = BUTHAVESEVERAL INHERENTDISADVANTAGES)NPRINCIPLE THEARRAYANTENNAELEMENTSCAN BE MORE WIDELY SEPARATED THAN THE DIAMETER OF THE MULTIPLE BEAM APERTURES4HEWIDERELEMENTSPACINGHASTHEPOTENTIALOFBETTERRESO LUTIONOFINTERFERENCESOURCES(OWEVER THEELEMENTSPACINGRESULTSIN DISPERSION AS A CONSEQUENCE OF THE FREQUENCY SCANNING PROPERTIES OF ARRAYS3UCHDISPERSIONLIMITSTHECANCELLATIONBANDWIDTHOFTHEDESIGN 7HENADAPTIVECANCELLATIONISIMPLEMENTEDWITHARRAYELEMENTS THE PERIODICITYALSOPRODUCESADDITIONALNULLSREFERREDTOASGRATINGNULLS


WITHINTHEFIELDOFVIEW THUSREDUCINGTHEAVAILABLECOVERAGEAREA4HE THINNEDARRAYDESIGNHASLESS'4THANTHEMULTIPLE BEAMAPPROACH ANDTHEARRAYSIDELOBELEVELSOUTSIDETHECOVERAGEAREAAREHIGHERTHAN THEMULTIPLE BEAMDESIGNSOTHATPROTECTIONFROMINTERFERENCEOUTSIDE OFTHECOVERAGEAREAISNOTPROVIDED !SIMULATIONPROGRAMFORADAPTIVECANCELLATIONOPERATIONISDEVELOPED INCONJUNCTIONWITHTHESYSTEMSHARDWAREANDSOFTWAREDEVELOPMENTS TODEMONSTRATEDESIGNCOMPLIANCEWITHREQUIREMENTS4HESIMULATION PROGRAMISINITIALLYUSEDTOPROJECTTHESYSTEMPERFORMANCEINTERMSOF THEFOURPERFORMANCEMEASURESPREVIOUSLYDISCUSSED!STHEPROGRAM PROCEEDS THESIMULATIONISUPDATEDBYMEASUREDCOMPONENTPERFORMANCE AND USED TO DEMONSTRATE DESIGN COMPLIANCE WITH REQUIREMENTS4HE SIMULATIONADDRESSESTHESTEADYSTATEANDTRANSIENTRESPONSESOFTHE DESIGNANDUSES-ONTE#ARLOPERFORMANCEEVALUATIONSOFTHEINTERFER ENCESCENARIOPARAMETERSTOOBTAINSTATISTICALMEASURESOFCOMMUNICA TIONPERFORMANCE3INCETESTINGONA-ONTE#ARLOBASISISIMPRACTICAL ALIMITEDNUMBEROFCASESARESELECTEDFROMTHESIMULATIONRESULTS AND MEASUREMENTSFROMTHESECASESAREUSEDTOVALIDATETHESIMULATION 4HEMINIMUMSEPARATIONBETWEENINTERFERENCESOURCESANDSYSTEM USERS DEPENDS ON THE ANGULAR RESOLUTION OF ADAPTIVE MULTIPLE BEAM ANTENNAS 4HE ANGULAR RESOLUTION IS A FUNCTION OF THE SLOPE OF THE ANTENNAPATTERNBETWEENTHEDESIREDSIGNALANDTHEINTERFERENCETHAT INTURNDEPENDSONTHEANTENNASELECTRICALSIZE#ONSEQUENTLY THERESO LUTIONBETWEENDESIREDSIGNALSANDINTERFERENCEINCREASESASTHEBEAM WIDTHOFTHEINDIVIDUALBEAMSCOMPRISINGTHEANTENNADECREASES4HE REQUIREDSEPARATIONBETWEENINTERFERENCEANDSYSTEMUSERSILLUSTRATED IN&IG CONSIDERSTWODIFFERENTUSERELEVATIONANGLES OWHERETHE BESTANGULARRESOLUTIONOCCURS ANDOWHERETHEBEAMISSPREADBYTHE EARTHCURVATURE ANDTHEWORST CASEVALUECORRESPONDINGTOTHELONGEST FOOTPRINTDIMENSIONISINDICATED4HEANGULARRESOLUTIONALSODEPENDS ONTHEAMOUNTOFGAINPERFORMANCETHATCANBESACRIFICEDINACHIEVING THETHRESHOLD3.)24WODIFFERENTVALUESOFSIGNALLOSS ANDD" ILLUSTRATETHEDIFFERENCESINRESOLUTIONPERFORMANCETHATAREACHIEVED ANDILLUSTRATETHEIMPORTANCEOFDESIGNINGTHEANTENNATOACHIEVETHE MAXIMUMGAINWITHINTHEDESIGNCOVERAGEAREA4HEANGULARRESOLU TION IS CALCULATED BY ALIGNING THE ANGULAR SEPARATION OF THE PATTERN LEVELANDTHEPATTERNNULLBETWEENTHEMAINBEAMANDFIRSTSIDELOBE 4HISSIMPLEANALYSISHASBEENVERIFIEDBYMOREDETAILEDSIMULATIONS THATHAVETHEADDITIONALCAPABILITYOFQUANTIFYINGTHEPERCENTCOVERAGE AREAWHEREDESIREDUSERSCANCOMMUNICATE4HEIMPORTANTFACTORSFOR PRACTICALDESIGNSAREILLUSTRATEDINTHISFIGURE!NARROWBEAMWIDTHIS SELECTEDTOPROVIDEGOODRESOLUTIONOFINTERFERENCESUBJECTTOASYSTEM DESIGN WITH A PRACTICAL NUMBER OF BEAMS!NTENNA DESIGNS WITH THE HIGHEST PRACTICAL '4 ARE NEEDED SO THAT MINIMIZING SYSTEM LOSSES

#HAPTER 3IX

&IGURE -ULTIPLE BEAM ADAPTIVE ANTENNA RESOLUTION;=Ú)%%%

USINGLOW NOISEPREAMPLIFIERS ANDCONTROLLINGTHENOISECONTRIBUTIONS FROMOTHERSYSTEMELECTRONICSUPTOTHEPOINTOFBEAMCOMBININGARE REQUIREDTOPROVIDEASYSTEMMARGINTHATCANBESACRIFICEDDURINGADAP TIVEOPERATION4HESESYSTEMELECTRONICSMUSTHAVEADEQUATEAMPLITUDE ANDPHASETRACKINGPERFORMANCEOVERTHEDESIGNBANDWIDTHTOMEETTHE TOLERANCEREQUIREMENTSPREVIOUSLYGIVENIN&IG TOOBTAINEFFECTIVE CANCELLATION !NOVELADAPTIVEANTENNADESIGN; =HASBEENDEVISEDTHATDOES NOTREQUIRETHEUSUALADAPTIVEWEIGHTINGCIRCUITRY4HEDESIGNUSESA NARROWANTENNABEAMWIDTHTHATISREPOSITIONEDTOALOWERGAINLEVELOF THEMAINBEAMINTHEDIRECTIONOFTHEINTERFERENCE4HEBASICIDEAOFTHIS DESIGNILLUSTRATEDIN&IG ISTHATTHEANTENNABEAMISSHIFTEDAWAY FROMTHEINTERFERENCESOURCE"EAMREPOSITIONINGREDUCESTHEDESIRED


&IGURE #ONTOURANDPATTERNDESCRIPTIONOFADAPTIVEBEAMRESPOSITIONING;= Ú)%%%

SIGNAL LEVEL BUT BECAUSE OF THE SLOPE OF THE MAIN BEAM PATTERN THE INTERFERENCEPOWERISREDUCEDBYAGREATERAMOUNT4HEDESIGNASSUMES SIDELOBELEVELSAWAYFROMTHEMAINBEAMPROVIDESUFFICIENTINTERFERENCE PROTECTION)DEALLY THEBEAMISSHIFTEDSUFFICIENTLYTHATTHEINTERFERENCE SOURCE IS ALIGNED WITH THE PATTERN NULL BETWEEN THE MAIN BEAM AND THEFIRSTSIDELOBE4HELOSSOFTHEDESIREDSIGNALPOWERASAFUNCTIONOF THE ANGULAR SEPARATION BETWEEN THE DESIRED AND INTERFERENCE SIGNALS ILLUSTRATED IN &IG ASSUMES THE PATTERN NULL IS ALIGNED WITH THE INTERFERENCESOURCE 4HEBEAMREPOSITIONINGISIMPLEMENTEDBYCORRELATIONTECHNIQUES USINGTHECIRCUITRYSHOWNIN&IG 4HENARROWBEAMWIDTHANTENNA ISASSUMEDTOUSECLOSED LOOPANTENNATRACKINGTOMAINTAINALIGNMENT WITHTHEDESIREDSIGNALBYCOMPENSATINGFORSATELLITEATTITUDEVARIATIONS

#HAPTER 3IX

&IGURE -ARGIN LOSS VERSUS SIGNAL INTERFERENCE SEPARATION ; =

Ú)%%%

&IGURE #IRCUITRYFORADAPTIVEBEAMRESPOSITIONING; =Ú)%%%

ININTERFERENCE FREECONDITIONS4HEUPLINKSIGNALISALSOASSUMEDTO CONTAINALOW LEVELPSEUDORANDOMCODEFOROPERATIONOFTHETRACKING SYSTEM#ORRELATIONOFTHESUMANDDIFFERENCEWITHTHEPSEUDORANDOM CODEISUSEDTOTRACKTHEDESIREDSIGNAL7HENINTERFERENCEISPRESENT THE NORMAL ERROR RESPONSE INDICATES A RESPONSE COMPRISED OF BOTH DESIRED AND INTERFERENCE SIGNAL COMPONENTS4HIS ERROR RESPONSE IS USEDTOSTEERTHEANTENNAAWAYFROMTHEINTERFERENCESOURCE$URING THEBEAMSTEERING THEERRORRESPONSEINCREASESBECAUSEOFTHEMOVE MENTOFTHEDESIREDSIGNALAWAYFROMTHEANTENNASBORESIGHTAXISAND


DECREASESASTHEINTERFERENCEISALIGNEDWITHLOWERGAINPORTIONSOF THEMAINBEAM3INCETHEDESIREDSIGNALSERRORRESPONSEISMEASURED BYTHEERRORSIGNALCORRELATIONWITHTHEPSEUDORANDOMCODE THEMINI MIZATIONOFTHEINTERFERENCECANBEDETERMINEDBYCOMPENSATINGTHE UNCORRELATEDERRORRESPONSEFORTHEINCREASEDERRORRESPONSEOFTHE DESIREDSIGNALCOMPONENTS 4HIS BEAM REPOSITIONING TECHNIQUE HAS ALSO BEEN EXTENDED ;= TO OPERATIONWITHMULTIPLE BEAMANTENNAS)NTHISCASE POWERMONITORS AREUSEDTOIDENTIFYBEAMSHAVINGEXCESSIVERECEIVEDPOWERLEVELSTHAT RESULT FROM INTERFERENCE POWER4HE THREE BEAMS HAVING THE HIGHEST LEVELSOFEXCESSIVEPOWERAREPROCESSEDTOIDENTIFYTHELOCATIONOFTHE INTERFERENCE SOURCE 3INCE THE BEAMS ARE ARRANGED ON AN EQUILATERAL TRIANGULARBASIS THEDIRECTIONFINDINGTECHNIQUESAREBASEDONSUBTRACT INGPAIRSOFTHETHREEBEAMSTOIDENTIFYTHEINTERFERINGSIGNALSLOCATION /NCETHELOCATIONISIDENTIFIED ANULLCANBECOMMANDEDTOTHATDIREC TIONUSINGAPRIORIINFORMATIONONTHEANTENNASBEAMRESPONSE,IKETHE BEAMREPOSITIONINGTECHNIQUE THEUSERSIGNALSCONTAINAPSEUDORANDOM CODE AND CORRELATION TECHNIQUES ARE USED TO MONITOR THE RECEPTION OF DESIREDSIGNALCOMPONENTS !NOTHERSIMPLEADAPTIVESYSTEMDESIGN;=APPLIESTORELATIVELYWIDE SPOTBEAMANTENNADESIGNSANDISBASEDONhPUNCHINGAHOLEvINTHESPOT BEAM COVERAGE )N OPERATION THE SPOT COVERAGE ANTENNA BEAM AND A MUCHNARROWERANTENNABEAMAREAMPLITUDEWEIGHTEDANDSUBTRACTED ASINDICATEDIN&IG 4HESPOTCOVERAGEANTENNAISALIGNEDWITHTHE INTERFERENCE SOURCE USING TRACKING TECHNIQUES4HE DESIGN ENDEAVORS TOLOCATETHEPHASECENTERSOFBOTHANTENNASCLOSETOONEANOTHERAND TIMEDELAYCOMPENSATIONISUSEDTOMINIMIZETHELOCATIONDIFFERENCES !LTERNATIVESEXISTINSELECTINGTHESUBTRACTEDLEVELOFTHENARROWBEAM ANTENNA)FTHEGAINLEVELSOFTHETWOANTENNASAREIDENTICALWHENSUB TRACTED ARELATIVELYBROADPATTERNNULLRESULTS ASINDICATEDIN&IG )FTHESUBTRACTEDGAINLEVELOFTHENARROWERBEAMWIDTHANTENNAHASA

&IGURE !DAPTIVENULLINGWITHINSPOTBEAMS;=Ú)%%%

#HAPTER 3IX

&IGURE 2ESOLUTIONPERFORMANCEOFSPOTNULLTYPES;=Ú)%%%

HIGHERVALUETHANTHEGAINOFTHESPOTCOVERAGEANTENNAINTHEDIRECTION OFTHEINTERFERENCE ARINGNULLISFORMED ASSHOWNIN&IG 7HEN THESUBTRACTEDGAINLEVELOFTHENARROWERBEAMWIDTHEQUALSTHEGAIN LEVELOFTHESPOTBEAM THENULLISRELATIVELYBROAD4HEPATTERNLEVELOF THENARROWERBEAMWIDTHANTENNASMAINBEAMHASLITTLEGAINVARIATION NEARTHEANTENNASBORESIGHTAXIS SOTHESUBTRACTIONISEFFECTIVEOVER ARANGEOFANGLES"YCONTRAST WHENTHESUBTRACTEDGAINVALUEOFTHE NARROWERBEAMWIDTHANTENNAISHIGHERTHANTHESPOTBEAMANTENNAS GAINLEVELINTHEDIRECTIONOFTHEINTERFERENCE THESUBTRACTIONISEFFEC TIVEOVERASMALLERANGULARWIDTHSOTHATRESOLUTIONOFTHERINGNULLIS BETTER THAN BROADER PATTERN NULL WHEN THE SUBTRACTED GAIN LEVELS OF THETWOANTENNASAREEQUAL4HISRESOLUTIONISBENEFICIALWHENDESIRED SIGNALSARENEARTHEINTERFERENCESOURCE(OWEVER THERINGNULLEXTENDS TO OTHER PORTIONS OF THE COVERAGE AREA4HE CHOICE OF THE SUBTRACTION LEVELDEPENDSONTHESPECIFICINTERFERENCESITUATION)FTHEINTERFERENCE SOURCEISNEARTHEEDGEOFCOVERAGE FOREXAMPLE THEALIGNMENTOFTHE NARROW BEAMWIDTH ANTENNA AND A SUBTRACTION LEVEL HIGHER THAN THE SPOTCOVERAGEANTENNAMIGHTBEUSEDTOFORMARINGNULLTHATEXTENDS BEYONDTHECOVERAGEAREA !CTIVE!PERTURE!NTENNAS 7HILE MULTIPLE BEAM ARRAY DESIGNS HAVE BEEN PREVIOUSLY DISCUSSED ANOTHER ARRAY DESIGN FOR DOWNLINK SERVICE IS THE ACTIVE APERTURE DESIGN ILLUSTRATED IN &IG )N OPERATION ACTIVE APERTURE DESIGN WOULDSEQUENTIALLYSERVICELOWDATARATEUSERSTHATARESPARSELYBUT WIDELYDISTRIBUTEDOVERTHEEARTHFIELDOFVIEW4HEBEAMCANBERAPIDLY


&IGURE !CTIVEAPERTUREANTENNA

REPOSITIONEDTODIFFERENTUSERLOCATIONSWITHTHESPEEDOFELECTRONICALLY CHANGING THE PHASE SHIFTERS USED TO STEER THE BEAM4HE INDIVIDUAL ARRAYELEMENTSAREWAVEGUIDERADIATORSTHATARECONTIGUOUSTOACHIEVE THEMAXIMUMPOSSIBLEARRAYELEMENTGAINLEVELS3INCEONLYONEBEAM ISRADIATEDATANYGIVENTIME THESIDELOBEREQUIREMENTSAREMINIMAL ANDTHUSAUNIFORMAMPLITUDEDISTRIBUTIONCANBEUSEDTOACHIEVETHE MINIMUM BEAMWIDTH FOR THE APERTURE SIZE 5NIFORM AMPLITUDE ALSO PERMITSEACHAMPLIFIERTOBEDRIVENTOTHESAMENEAR SATURATIONOPERAT INGCONDITIONSFORMAXIMUMPOWEREFFICIENCY THUSACHIEVINGTHEHIGH EST%20LEVEL 4HEFIRST ORDERDESIGNPROCEEDSBYSELECTINGABEAMWIDTHFORCOVERAGE PURPOSES DIVIDINGTHEAPERTUREINTOASUFFICIENTNUMBEROFELEMENTSSO THATWITHTHESELECTEDELEMENTTRANSMITTERPOWEROUTPUT THEDESIRED %20ISACHIEVED4HESELECTIONOFTHEELEMENTSIZEALSONEEDSTOAVOID GRATING LOBES WITHIN THE EARTH FIELD OF VIEW AND TO ACHIEVE THE %20 REQUIREMENTS AT THE EDGES OF THE FIELD OF VIEW! MAXIMUM ELEMENT SPACINGOFWAVELENGTHSISREQUIREDTOKEEPTHEGRATINGLOBESAWAY FROMTHEEARTHSFIELDOFVIEWFORGEOSYNCHRONOUSORBITS4HEPEAK%20 LEVELTOFIRSTORDERISGIVENBY

%20G. 0E'E

WHERE G IS THE ANTENNA EFFICIENCY . IS THE NUMBER OF ELEMENTS 0E ISTHETRANSMITTEDPOWERPERELEMENT AND'EISTHEELEMENTGAININ THEARRAYENVIRONMENT4HEANTENNAEFFICIENCY ASUSEDHERE ISREALLY THEARRAYEFFICIENCY ANDINCLUDESTHEEFFECTOFAMPLITUDEANDPHASE TRACKINGANDTHEDIRECTIVITYLOSSCAUSEDBYTHEGRATINGLOBES/THER EFFICIENCYLOSSINCLUDESOHMICANDMISMATCHLOSSTHATISINCLUDEDIN

#HAPTER 3IX

THEANTENNAELEMENTGAIN3IMILARLY THEELEMENTPATTERNROLLOFFHAS NOT BEEN INCLUDED A WAVELENGTH ELEMENT SPACING YIELDS A D" PATTERNROLLOFFATTHEEDGEOFTHEEARTH$ESIGNATTENTIONMUSTBEPAID TOTHESYSTEMSGAINDISTRIBUTION4HESOLIDSTATEDEVICESHAVEBOTH LIMITEDPOWEREFFICIENCYANDGAIN4HEGAINDISTRIBUTIONTHROUGHTHE ANTENNANEEDSTOBEOPTIMIZEDTOMINIMIZETHEPRIMEPOWERCONSUMP TION!TTENTION MUST ALSO BE GIVEN TO THE THERMAL CONTROL DESIGN TO MAINTAIN THE DESIGN OPERATING TEMPERATURE AND PROVIDE SUFFICIENT TEMPERATURE UNIFORMITY TO MAINTAIN AMPLITUDE AND PHASE TRACKING PERFORMANCEOFTHEACTIVEDEVICES!MEANSOFCALIBRATIONMUSTALSO BEDEVISEDTODETERMINETHEELEMENTAMPLITUDEANDPHASETRACKING PERFORMANCEINORBIT SOTHATCOMPENSATIONCANBEPROVIDEDBYADJUST INGTHEPHASESHIFTERS 4HIS CONCEPT HAS MANY ATTRACTIVE ADVANTAGES4HE %20 LEVEL CAN BEINCREASEDBYINCREASINGTHENUMBEROFELEMENTSAND ORTHEPOWER PERELEMENTTHATMAYBEACCOMPLISHEDBYCOMBININGACTIVEDEVICES )NTHISWAY THE%20TOAGIVENSIZECOVERAGEAREACANBEINCREASED WITHOUT THE DEVELOPMENT OF A HIGHER POWER TRANSMITTER NEEDED IN ANTENNADESIGNSWITHASINGLETRANSMITTER4HEBEAMCANBESTEERED TOANARBITRARYLOCATIONSOTHATTHEPEAK%20CANBECENTEREDONTHE DESIRED COMMUNITY OF USERS4HE PATTERNS IN &IG USE AN ARRAY OFELEMENTSARRANGEDINANsCONFIGURATION4HEFIRSTPATTERN ILLUSTRATES A DIAGONAL PLANE RESPONSE WHEN THE BEAM IS SCANNED O OFF AXIS)NADDITION THESIZEOFTHECOVERAGEAREACANBEINCREASEDBY REPHASINGTHEAPERTUREDISTRIBUTION4HISCAPABILITYISALSOILLUSTRATED IN&IG WHEREAGAINTHEBEAMISSCANNEDOOFF AXISINADIAGONAL PLANEANDTHEBEAMISBROADENEDBYAFACTOROFTHREE!BEAMBROAD ENING TECHNIQUE IS OFTEN ACCOMPLISHED BY ADDING QUADRATURE PHASE ERRORTOTHEAPERTUREDISTRIBUTION)NTHISCASE THEQUADRATICPHASE ERRORSIMPLYRAISEDTHESIDELOBEWITHOUTAPPRECIABLEBEAMBROADENING 4HEPATTERNRESULTSWEREACHIEVEDBYTAKINGEVERYOTHERELEMENTTO FORMTHREESUBARRAYS4HECENTRALSUBARRAYWASSTEEREDTOTHEDESIRED SCANANGLEANDTHEOTHERSUBARRAYSWEREPHASEDTOSTEERTHEIRBEAMS TO OPPOSITE SIDES OF THE CENTRAL BEAM AND THE PATTERNS WERE ADDED TOGETHER TO PRODUCE THE BROADENED PATTERN 3INCE THE SUBARRAY ELE MENTS ARE MORE WIDELY SPACED THAN THE ADJACENT ARRAY ELEMENTS A GRATINGLOBEISAPPARENTIN&IG &INALLY THEACTIVEAPERTUREDESIGN CANBEVIEWEDASASPATIALCOMBININGTECHNIQUE#OMBININGCIRCUITRY THATFORMSASINGLEPOWEROUTPUTPORTISWELLKNOWN; = BUTTHE SPATIALCOMBININGTECHNIQUEAVOIDSTHELOSSINTHEOUTPUTCOMBINER ANDTHEHIGHISOLATIONBETWEENARRAYELEMENTSRESULTSINLITTLEEFFECT ONTHECOMBININGEFFICIENCYOFTHEREMAININGDEVICESWHENANACTIVE ARRAYDEVICEFAILS


&IGURE .ORMALANDBROADENEDDIAGONALPLANEPATTERNS;=Ú)%%%

#HAPTER 3IX

0OINT TO 0OINT!NTENNAS !NTENNASFORPOINT TO POINTCOMMUNICATIONLINKSAREREQUIREDFORCROSS LINK SUBSYSTEMS AND FOR GATEWAY APPLICATIONS HAVING HIGH DATA RATE REQUIREMENTS!NEXAMPLEANTENNASYSTEMDESIGNFORACROSSLINKSUB SYSTEMFORGEOSTATIONARYSATELLITESISDESCRIBED4HEOVERALLTRANSPONDER ARCHITECTURE ANTENNA BEAM STEERING REQUIREMENTS AND THE NEED FOR FOURFREQUENCYSUBBANDSWEREEXPLAINEDPREVIOUSLYIN#HAPTER4HE BEAMSTEERINGREQUIREMENTSAREPRINCIPALLYINTHEAZIMUTHPLANE WITH MODESTREQUIREMENTSFORELEVATIONSCANNINGTOACCOMMODATESATELLITE STATIONKEEPINGVARIATIONS4HISANTENNADESIGNEVOLVEDTOSATISFYSEV ERALDEVELOPMENTOBJECTIVES 0ROVIDEALOWLOSSMEANSOFANTENNABEAMSTEERINGWHILEAVOIDING BEAMWAVEGUIDEANDROTARYJOINTCOMPLEXITIES -INIMIZETHEMASSNEEDEDTOBEMOVEDFORBEAMSTEERING !LLOW A lXED LOCATION FOR THE FEED AND 2& ELECTRONICS TO PROVIDE ISOLATIONFROMTHEEXTERNALENVIRONMENT ACCESSTOTHESPACECRAFTS THERMALCONTROLSYSTEM ANDLOWLOSSTOTHE2&ELECTRONICS !CHIEVELOWINSERTIONLOSSINTHERECEIVEPATHTOCAPITALIZEONTHE LOW NOISE BACKGROUND TEMPERATURE TO ACHIEVE A LOW SYSTEM NOISE TEMPERATURE 0ROVIDEVERYHIGHPOLARIZATIONPURITYTOALLOWTHEUSEOFORTHOGO NALPOLARIZATIONSTOLIMITREQUIREDBANDWIDTHFORHIGHDATARATE APPLICATIONS 3ATISFYTHEREQUIREMENTSTOSELECTTWOOFTHEFOURFREQUENCYBANDS REQUIRED IN THE CROSSLINK OPERATION ONE FOR TRANSMITTING AND THE SECONDFORRECEIVING 4HEANTENNASYSTEMCONCEPTSHOWNIN&IG ISANOFFSETREFLECTOR DESIGNHAVINGAFEEDANDGEOMETRYTHATREQUIRESMOVINGONLYTHEMAIN REFLECTOR TO MEET THE AZIMUTH AND ELEVATION SCANNING REQUIREMENTS PREVIOUSLY DESCRIBED IN &IG 4HE WIDE AZIMUTH PLANE SCANNING REQUIREMENTISSATISFIEDBYROTATINGTHEOFFSETREFLECTORABOUTTHEAXIS CONTAINING THE REFLECTOR CENTER AND THE REFLECTOR FOCUS IMAGED BY THE SUBREFLECTOR4HE OPTICS AND SCAN MOTION FUNCTION LIKE A PERISCOPE TO ACHIEVETHEWIDEAZIMUTHSCANNINGREQUIREMENT4HEELEVATIONSCANIS PROVIDEDINTHEAXISORTHOGONALTOTHEAZIMUTHSCANAXISTOCOMPENSATE FORSATELLITEATTITUDEVARIATIONSANDSATELLITESTATIONKEEPINGVARIATIONS 4HELONGEFFECTIVEFOCALLENGTHFROMTHEREFLECTORFURTHERMAGNIFIEDBY THE SUBREFLECTOR PERMITS THE REQUIRED ELEVATION SCAN CAPABILITY4HIS APPROACHPERMITSTHEREQUIREDBEAMSTEERINGBYONLYPOSITIONINGTHE MAIN REFLECTOR AND THE REST OF THE SYSTEM COMPONENTS INCLUDING THE


&IGURE 4HECROSSLINKANTENNACONCEPT

'REGORIANSUBREFLECTOR ANDTHEFEEDASSEMBLYAREFIXEDTO ANDENCLOSED BY THESPACECRAFT4HISAPPROACHREDUCESTHEREQUIREDMASSTOBEPOSI TIONEDFORBEAMSTEERINGANDALLOWSTHEELECTRONICSTOBEINTEGRATEDWITH THESPACECRAFTTHERMALCONTROLSYSTEMANDTOBESHIELDEDFROMTHEEXTER NALSPACEENVIRONMENT 4HEFEEDSYSTEMANDTHESUBREFLECTORUSEANOPENINGINTHESPACECRAFT PANELTOILLUMINATETHEMAINREFLECTOR4HISOPTICSARRANGEMENTMINI MIZESTHEMASSTHATISREPOSITIONEDTOPROVIDETHENECESSARYBEAMSTEER ING&URTHER THEFEEDSYSTEMISFIXEDWITHINTHESPACECRAFTTOMINIMIZE THELOSSTOTHE2&ELECTRONICS ISOLATETHECOMPONENTSFROMTHEEXTERNAL ENVIRONMENT ANDPROVIDEANINTERFACETOTHEBUSTHERMALCONTROL4HE FEEDSYSTEMIN&IG ISCOMPRISEDOFTWOFEEDELEMENTSSEPARATEDBY AFREQUENCYSELECTIVESURFACETHATREFLECTSTWOOFTHEFEEDSANDTRANSMITS THEOTHERTWOFEEDS%ACHFEEDSERVICESTWOOFTHEFOURFREQUENCYBANDS REQUIREDINTHISAPPLICATION4HISARRANGEMENTPERMITSFEEDOPTIMIZA TIONFOROPERATIONOVERTHEBANDWIDTHENCOMPASSEDBYTWOOFTHEBANDS RATHERTHANFOURBANDS4HEFREQUENCYSELECTIVESURFACEALSOPROVIDES ADDITIONAL ISOLATION BETWEEN THE FREQUENCY BANDS 4HE POLARIZATION PURITYISPROVIDEDBYTHE'REGORIANSUBREFLECTOR BUTDESIGNATTENTION INTHEFREQUENCYSELECTIVESURFACEDEVELOPMENTISREQUIREDTOMATCHBOTH THEAMPLITUDEANDPHASEOFTHEREFLECTIONANDTRANSMISSIONPROPERTIES OFTHESURFACEFORORTHOGONALPOLARIZATIONCOMPONENTSOVERTHERANGE

#HAPTER 3IX

OFINCIDENTANGLESOFTHEFEEDILLUMINATION4HEMATCHEDPOLARIZATION RESPONSESOFTHESURFACEARENECESSARYTOAVOIDDEGRADINGTHEAXIALRATIO PERFORMANCEOFTHESIGNALSREFLECTEDFROM ORTRANSMITTEDTHROUGH THE FREQUENCYSELECTIVESURFACE4HEFEEDSYSTEMISANTICIPATEDTOUSEEITHER DUAL MODE OR CORRUGATED HORN TECHNOLOGY AND A HIGHER ORDER WAVE GUIDEMODENEEDSTOBEGENERATEDFORTHESYSTEMSAUTOTRACKFUNCTION "OTHFEEDTECHNOLOGIESARECAPABLEOFPROVIDINGLOWSIDELOBEROTATION ALLYSYMMETRICILLUMINATIONPATTERNSTHATAREREQUIREDTOACHIEVEHIGH POLARIZATIONPURITY4HISDESIGNATTENTIONTOTHEFEEDSYSTEM THELONG REFLECTORFOCALLENGTH ANDTHEPOLARIZATIONCORRECTIONOFTHE'REGORIAN SUBREFLECTORDESIGNRESULTSINTHECAPABILITYTOACHIEVETHEAXIALRATIO PERFORMANCENEEDEDTOISOLATETHEORTHOGONALPOLARIZATIONS4HESELEC TIONOFALARGEF $RATIOFURTHERMAGNIFIEDBYTHESUBREFLECTORMINIMIZES THEBEAMSCANNINGLOSS 2EFERENCES 2"$YBDAL h3ATELLITE!NTENNAS v#HAPIN*,6OLAKISED !NTENNA%NGINEERING (ANDBOOK.EW9ORK-C'RAW (ILL $(-ARTIN 02!NDERSON AND,"ARTAMIAN #OMMUNICATION3ATELLITES &IFTH %DITION%L3EGUNDO#!4HE!EROSPACE0RESS +5ENO 4)TANAMI )+UMAZAMA AND)/HTOMO h$ESIGNAND#HARACTERISTICSOFA -ULTIBAND#OMMUNICATION3ATELLITE!NTENNA3YSTEM v)%%%4RANS!EROSPACEAND %LECTRONIC3YSTEMS VOL!%3 !PRIL n !2#HERRETT 37,EE AND2*!COSTA h!-ETHODFOR0RODUCINGA3HAPED#ONTOUR 2ADIATION0ATTERN5SINGA3INGLE3HAPED2EmECTORANDA3INGLE&EED v)%%%4RANS !NTENNASAND0ROPAGATION VOL*UNE n /-"UCCI '$%LIA '-AZZARELLO AND'0ANARIELLO h!NTENNA0ATTERN3YNTHESIS !.EW'ENERAL!PPROACH v0ROC)%%% VOL-ARCH n &#ARDUCCIAND-&RANCESI h4HE)4!,3!43ATELLITE3YSTEM v)NTERNATIONAL*OUR 3ATELLITE#OMMUNICATIONS VOL*ANUARYn&EBRUARY n 2*-AILLOUX 0HASED!RRAY!NTENNA(ANDBOOK.ORWOOD-!!RTECH 2"$YBDAL h-ULTIPLE"EAM#OMMUNICATION3ATELLITE!NTENNA3YSTEMS v)%%% )###ONFERENCE$IGEST*UNE +32AO '!-ORIN -14ANG 32ICHARD AND++#HAN h$EVELOPMENTOFA '(Z-ULTIPLE"EAM!NTENNAFOR-ILITARY3ATELLITE#OMMUNICATIONS v)%%%4RANS !NTENNASAND0ROPAGATION VOL!0 /CTOBER n 0)NGERSONAND#!#HEN h4HE5SEOF.ON FOCUSING!PERTUREFOR-ULTIBEAM !NTENNAS v)%%%!0 33YMPOSIUM$IGEST-AY 2*ORGENSEN 0"ALLING AND7*%NGLISH h$UAL/FFSET2EmECTOR-ULTIBEAM!NTENNA FOR)NTERNATIONAL#OMMUNICATIONS3ATELLITE!PPLICATIONS v)%%%4RANS!NTENNASAND 0ROPAGATION VOL!0 $ECEMBER n #-2APPAPORTAND70#RAIG h(IGH!PERTURE%FlCIENCY3YMMETRIC2EmECTOR !NTENNASWITHUPTOO&IELDOF6IEW v)%%%4RANS!NTENNASAND0ROPAGATION VOL-ARCH n &*$IETRICH 0-ETZEN AND0-ONTE h4HE'LOBALSTAR#ELLULAR3ATELLITE3YSTEM v )%%%4RANS!NTENNASAND0ROPAGATION VOL!0 *UNE n **3CHUSS *5PTON "-EYERS 43IKINA !2OHWER 0-AKRIDAKAS 2&RANCOIS ,7ARDLE AND23MITH h4HE)2)$)5--AIN-ISSION!NTENNA#ONCEPT v)%%% 4RANS!NTENNASAND0ROPAGATION VOL!0 -ARCH n 2"$YBDAL 3*#URRY AND-!+ING h!N5PLINK-ULTIPLE"EAM#ONCEPTFOR 4HEATER#OVERAGE v)%%%-),#/-3YMPOSIUM$IGEST/CTOBER

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#HAPTER

5SER3EGMENT!NTENNAS

/VERVIEW 5SER SEGMENT ANTENNAS LIKE SPACE SEGMENT ANTENNAS HAVE UNIQUE REQUIREMENTS FOR COMMUNICATION SATELLITE APPLICATIONS 7HILE SPACE SEGMENTANTENNASMAINTAINCOVERAGEOVERASPECIFIEDFIELDOFVIEW USER SEGMENTANTENNASMUSTPOINTANDTRACKTHESATELLITEINORBIT4HESPACE SEGMENTANTENNASMUSTSERVICETHESAMECOVERAGEAREASFORBOTHTHE UPLINK AND DOWNLINK FREQUENCIES4HE DIFFERENCES IN THE UPLINK AND DOWNLINK FREQUENCIES OFTEN RESULT IN USING DIFFERENT SPACE SEGMENT ANTENNASFORTHEUPLINKANDDOWNLINKSERVICES4HEUPLINKANDDOWN LINKSPACESEGMENTANTENNASHAVEDIFFERENTSIZESASREQUIREDTOACHIEVE THE SAME BEAMWIDTH VALUES AT BOTH FREQUENCIES NEEDED TO PRESERVE THESAMEANGULARCOVERAGECHARACTERISTICS5SERSEGMENTANTENNASDO NOTHAVECOVERAGEREQUIREMENTSATBOTHUPLINKANDDOWNLINKFREQUEN CIES ANDCONSEQUENTLY THEDIFFERENTANTENNABEAMWIDTHVALUESATTHE TWO FREQUENCIES DO NOT PRESENT A PROBLEM 3INCE THE SAME APERTURE ISUSEDFORBOTHUPLINKANDDOWNLINKFREQUENCIES DESIGNCOMPLEXITY ANDCOSTAREREDUCED3PACESEGMENTANTENNASPOINTATAWARMEARTH BACKGROUND WHEREASTHEUSERSEGMENTANTENNASPOINTATTHECOLDSKY BACKGROUND #ONSEQUENTLY USER ANTENNAS REQUIRE PARTICULAR DESIGN ATTENTIONTO2&LOSSESTOCAPITALIZEONLOWNOISERECEIVERTECHNOLOGYTO ACHIEVEALOWSYSTEMNOISETEMPERATURETOENHANCETHEUSERSYSTEMS '4PERFORMANCEASDISCUSSEDIN#HAPTER 5SERSEGMENTANTENNAS ARESUSCEPTIBLETOINTERFERENCEFROMOTHERNEARBYTERRESTRIALSERVICES PARTICULARLY AT THE LOWER MICROWAVE FREQUENCIES AND THEIR SIDELOBE ENVELOPE REQUIREMENTS AND CONTROL TECHNIQUES WILL HAVE INCREASED IMPORTANCEINFUTUREYEARS5SERSYSTEMSFORMULTIPLEFREQUENCYOPER ATION ARE COMMONPLACE ALLOWING THE SAME ANTENNA TO OPERATE WITH

#HAPTER 3EVEN

DIFFERENTSATELLITEPROGRAMS ATRENDTHATWILLINCREASEINTHEFUTURE 4HENUMBEROFUSERTERMINALSCONTINUESTOINCREASEWITHDEMANDSFOR SATELLITESERVICE ATRENDTHATWILLCONTINUEINTHEFUTUREASCOMMUNICA TIONSCONTINUETOBEEXTENDEDTOINDIVIDUALUSERS &UTUREDEVELOPMENTOFUSERSEGMENTANTENNAS;=CANLOGICALLYBE ANTICIPATED IN SEVERAL AREAS ,OW SIDELOBE ANTENNA DESIGNS WILL BE REQUIREDTOPROVIDEINCREASEDPROTECTIONFROMINTERFERENCE0ACKAGING TECHNIQUESTOSATISFYUSERMOBILITYREQUIREMENTSARENEEDEDTOSATISFY USERMISSIONREQUIREMENTS5SERTERMINALDESIGNSCAPABLEOFSEQUEN TIALLYCOMMUNICATINGWITHDIFFERENTSATELLITESERVICESWILLREQUIREFUR THERDEVELOPMENTOFMULTIFREQUENCYCAPABILITIES!SSATELLITESERVICES EXTENDTOINDIVIDUALUSERSINCELLULARNETWORKS MUCHOFTHETERRESTRIAL CELLULARUSERANTENNADEVELOPMENTCANBEANTICIPATEDTOAPPLYTOSATEL LITECOMMUNICATIONSERVICES#OST EFFECTIVEDESIGNSFORUSERTERMINALS WILLBENECESSARYTOCONTROLOVERALLSYSTEMCOSTSAND ASDISCUSSEDIN #HAPTER EFFICIENTTECHNIQUESFORPRODUCTIONTESTINGWILLBEREQUIRED ASWELL 5SERSEGMENTDESIGNSINITIALLYREQUIREDLARGEDEDICATEDGROUNDTERMI NALSFORLINKCLOSUREPURPOSES3UCHTERMINALSSERVEDASAHUB ANDCOM MUNICATIONSTOINDIVIDUALUSERSWEREDISTRIBUTEDBYTERRESTRIALMEANS 4ODAY LARGETERMINALSARESTILLREQUIREDFORHIGHDATARATETRANSFERIN APPLICATIONSSUCHASGATEWAYSANDSATELLITEUPLOADS4YPICALLY SUCHTER MINALDESIGNSUSESHAPEDREFLECTORTECHNIQUESDESCRIBEDIN#HAPTER TOINCREASEANTENNAEFFICIENCY)NADDITION MANYSYSTEMSAREDESIGNED FOR USE WITH63!4 VERY SMALL APERTURE TERMINALS APPLICATIONS THAT HAVEMUCHMOREMODESTPERFORMANCEREQUIREMENTSTHANEARLIERDESIGNS BECAUSEOFINCREASEDSATELLITEPERFORMANCECAPABILITIES$IRECTBROADCAST TELEVISION SERVICES ARE AN EXCELLENT EXAMPLE OF WHERE INITIAL SERVICES REQUIRINGABOUTAN FTUSERANTENNAHAVETRANSITIONEDTOMUCHMORE COMPACT ANTENNAS &URTHER THESE TERMINALS ARE SURPRISINGLY AFFORD ABLEASARESULTOFTHEIRPRODUCTIONVOLUME&UTURESATELLITEDESIGNSARE BEINGDEVELOPEDFORHANDHELDPERSONALEQUIPMENT4HETRENDFORMORE DIVERSECOLLECTIONSOFTERMINALTECHNOLOGYWILLCONTINUEINTHEFUTURE ANDSYSTEMSIZINGMUSTACCOMMODATEAMULTITUDEOFSMALLINDIVIDUAL USERSANDTHEIRCOSTCONSTRAINTS 5SER!NTENNA4ECHNOLOGY 4HEREQUIREMENTSFORUSERANTENNASFAVORREFLECTORANTENNATECHNOLOGY ANDINDEED INTHEPUBLICSMIND LARGEREFLECTORANTENNASARECOMMONLY ASSOCIATEDWITHSATELLITECOMMUNICATIONS 2EFLECTOR ANTENNAS ARE COST EFFECTIVE HAVEABROADBANDWIDTHCAPABILITY ANDIMPOSEMINIMALPOWER CONSUMPTION AND DESIGN COMPLEXITY /THER ANTENNA TECHNOLOGIES ARE SELECTEDONLYWHENCOMPELLINGSYSTEMREQUIREMENTSEXISTEG CONFORMAL

5SER3EGMENT!NTENNAS

ARRAY DESIGNS NEEDED TO SATISFY AERODYNAMIC CONSTRAINTS FOR HIGH PERFORMANCEAIRCRAFT 3UCHARRAYDESIGNSHAVEASIGNIFICANTCOST ARE LIMITED IN BANDWIDTH INHERENTLY HAVE HIGH COMPLEXITY AND REQUIRE PRIMEPOWERFORACTIVEELEMENTSANDBEAMSTEERINGREQUIREMENTS 5SER ANTENNA SIZE IS CONSTRAINED FOR REASONS THAT DIFFER FROM THE SPACESEGMENT!COMPACTANTENNASIZEISLESSEXPENSIVETHANALARGER ANTENNA,ARGEANTENNASARESUSCEPTIBLETOANTENNAPOINTINGERRORSFROM WINDLOADING BOTHINTERMSOFTHEIRNARROWBEAMWIDTHANDTHETORQUE RESULTINGFROMWINDLOADINGFORALARGEAPERTURE!NTENNAPOINTINGSTA BILITYUNDERWINDCONDITIONSREQUIRESASTIFFREFLECTORDESIGNANDPOSI TIONERDRIVEPOWERTOOFFSETTHEWIND INDUCEDTORQUES-ETHODOLOGIESTO ADDRESSWINDLOADINGEFFECTSONANTENNAPOINTINGPERFORMANCE;=COM MONLYASSESSSTEADYSTATEANDGUSTINGWINDCONDITIONS!LTERNATIVELY A PROTECTIVERADOMEISCOMMONLYUSEDTOISOLATETHEANTENNAFROMWIND PERTURBATIONS/PERATIONWITHORWITHOUTARADOMEINVOLVESECONOMIC TRADEOFFSINVOLVINGNOTONLYSATISFYINGOPERATIONDURINGHIGHWINDLEVELS BUTALSOPROVIDINGPROTECTIONFROMWEATHERDETERIORATIONOFTHEEQUIP MENTENCLOSEDWITHINTHERADOME 5SERSEGMENTANTENNADESIGNSENDEAVORTOACHIEVEHIGHANTENNAEFFI CIENCYTOMINIMIZETHEREQUIREDANTENNASIZE ANDFORHIGHGAINANTENNAS USINGDUALREFLECTORCONFIGURATIONS REFLECTORSHAPINGTECHNIQUESHAVE BEENQUITESUCCESSFUL2EFLECTORSHAPINGTECHNIQUESANDHIGH EFFICIENCY FEEDSSUCHASCORRUGATEDHORNSHAVINGLOWSIDELOBEROTATIONALLYSYM METRICPATTERNS AREKEYREASONSTHATSUCHDESIGNSACHIEVEEFFICIENCY VALUESINEXCESSOF ASDISCUSSEDIN#HAPTER4HESHAPINGOFTHE MAINREFLECTORANDTHESUBREFLECTORSRESULTSINAMOREUNIFORMAPERTURE DISTRIBUTIONTHATOFFSETSTHEAMPLITUDETAPERLOSSTOACHIEVEINCREASED EFFICIENCY3MALLERANTENNASFOR63!4APPLICATIONSCOMMONLYUSEOFFSET REFLECTOR TECHNOLOGY THAT INCREASES ANTENNA EFFICIENCY BY ELIMINATING FEEDBLOCKAGE 5SERANTENNADESIGNSFORPOLARIZATIONREUSESATELLITESYSTEMSMUST ACHIEVETHENECESSARYPOLARIZATIONPURITYTOAVOIDCO CHANNELINTERFER ENCEFROM ANDTO OTHERUSERS!TYPICALREQUIREMENTISTOREDUCETHE CROSS POLARIZEDFIELDSTOD"BELOWTHEPRINCIPALPOLARIZATIONOVERTHE FIELDOFVIEWSUBTENDEDBYTHETRACKINGUNCERTAINTY4HISDESIGNATTEN TIONINCLUDESFEEDDESIGNSWITHLOWAXIALRATIOCAPABILITIESFORCIRCULAR POLARIZATION3UCHDESIGNSREQUIREROTATIONALLYSYMMETRICFEEDPATTERNS TOMAINTAINPOLARIZATIONPURITYOVERTHERADIATINGAPERTUREPLANE7HEN OFFSETREFLECTORANTENNATECHNOLOGYISUSED CORRECTIONTECHNIQUESDIS CUSSEDIN#HAPTER PROVIDETHEMEANSTOPRODUCEDESIGNSWITHHIGH POLARIZATIONPURITY 5SER ANTENNAS FOR COMMERCIAL # AND +U BAND FREQUENCIES OFTEN REQUIREOPERATIONATBOTHBANDSSOTHATMULTIPLEFREQUENCYFEEDDESIGNS ARE REQUIRED &REQUENCY SELECTIVE SURFACES THAT ALLOW TRANSMISSION

#HAPTER 3EVEN

THROUGHTHESURFACEATONEFREQUENCYBANDANDREFLECTIONFROMTHESUR FACEATANOTHERFREQUENCYBANDPERMITTHESEPARATIONOFFREQUENCYBANDS 4HEFEEDSAREPHYSICALLYSEPARATED GIVINGTHEDESIGNENOUGHFREEDOMTO OPTIMIZEANTENNAFEEDPERFORMANCEFOREACHBAND#OMMONLY THELOWER FREQUENCYISINAPRIMEFOCUSCONFIGURATIONANDAFREQUENCYSELECTIVE SUBREFLECTORISUSEDTOPROVIDEA#ASSEGRAINCONFIGURATIONATTHEHIGH FREQUENCY4HEOVERALLSUBREFLECTORSIZEISMINIMIZEDBYTHISAPPROACH ANDFORTRANSMITTINGAPPLICATIONS THEHIGHFREQUENCYBANDHASASHORT WAVEGUIDERUN WHEREASTHELONGERWAVEGUIDERUNTOTHEPRIMEFOCUS LOCATIONHASREDUCEDLOSSLENGTHCOMPAREDWITHTHEHIGHFREQUENCY4HE OVERALLAPERTURESIZEMUSTBESUFFICIENTTOSATISFY'4AND%20REQUIRE MENTSATBOTHBANDS 5SERANTENNASFORFUTURESATELLITE BASEDCELLULARCOMMUNICATIONSHAVE RELATIVELYLOWDATARATECAPABILITIESANDPRESENTFUTUREDESIGNCHALLENGES ANDDEVELOPMENTNEEDS/FNECESSITY SUCHANTENNASNEEDTOBECOMPACT FORPRACTICALDESIGNS)NADDITION THEIRPATTERNCOVERAGEMUSTBEBROAD TOAVOIDREQUIREMENTSFORPRECISEPOINTING WHICHWOULDREPRESENTAN ADDITIONALBURDENTOTHEUSERS4HEBROADPATTERNCOVERAGERESULTING FROMTHESEREQUIREMENTSTOGETHERWITHTYPICALOPERATINGENVIRONMENTS RESULTS IN SITUATIONS WHERE MULTIPATH LEVELS GENERATED BY REFLECTIONS FROMTHESURROUNDINGENVIRONMENTSIGNIFICANTLYDEGRADESYSTEMPER FORMANCE4HESECONCERNSAREEXPRESSED;=FOR#$-!SYSTEMSWHERE MULTIPATH CAN REDUCE THE ISOLATION BETWEEN USERS AND CONSEQUENTLY DEGRADE THE CAPACITY OF THE SYSTEM4HE REFERENCE ALSO COMPARES THE CAPACITYDIFFERENCESBETWEEN#$-!AND&$-!4$-!MULTIPLEACCESS TECHNIQUES IN MULTIPATH ENVIRONMENTS &URTHER RESEARCH IS REQUIRED ANDSUITABLEANTENNADESIGNSMUSTBEDEVELOPEDFORTHESEAPPLICATIONS THATEVOLVEFROMTERRESTRIALCELLULARDESIGNS!DDITIONALUNDERSTANDING ANDQUANTIFICATIONSOFTHEPROPAGATIONLIMITATIONSOFSUCHSYSTEMSARE REQUIREDINTHEDEVELOPMENTANDOPERATIONOFTHESESYSTEMS !DAPTIVE TECHNIQUES ARE COMMONLY PROPOSED AS A MEANS TO COPE WITH THE MULTIPATH ENVIRONMENTS WHEN BROAD COVERAGE USER ANTEN NASAREREQUIRED2AKERECEIVERSTHATPROVIDEEQUALIZATIONANDDIVER SITY COMBINING ;= CAN PROTECT RECEIVERS FROM MULTIPATH FADING4HE TIME DELAYEDMULTIPATHSIGNALSAREEQUALIZEDBYANhADAPTIVETRANS VERSAL FILTER v WHICH IS A SERIES OF TAPPED DELAY LINES WITH ADAPTIVE AMPLITUDEANDPHASEWEIGHTING3UCHCIRCUITRYALIGNSTHEDIRECTAND DELAYEDMULTIPATHSIGNALSINTIME4HEDELAYTIMESPREADISBOUNDED BY THE AUTOCORRELATION FUNCTION OF THE SIGNAL $IVERSITY COMBINING ISALSOINCORPORATEDINTOTHE2AKEDESIGNTOMAXIMIZESIGNALPOWER -ORERECENTLY ADAPTIVECONCEPTSHAVEBEENAPPLIED;=TOTRANSMIT TINGANTENNAS)NTHISCASE REFLECTEDCOMPONENTSOFTHETRANSMITTED SIGNALSFROMTERRAINFEATURESARESAMPLED4HESEREFLECTEDCOMPONENTS AREALSOMULTIPATHSOURCES"YTRANSMITTINGTHESIGNALTHROUGHADAPTIVE

5SER3EGMENT!NTENNAS

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#HAPTER 3EVEN

)NADDITION THE##)2RECOMMENDATION ADDRESSESTHE%20SPEC TRALDENSITY ANDTHEMOREDETAILEDREPORTPROVIDESGREATERDATA ANDEXPLANATION#OMPLIANCEWITHTHESESIDELOBEENVELOPEREQUIREMENTS ISCOMMONLYSPECIFIEDDURINGUSERANTENNAPROCUREMENTS 7HILEVENDORDESIGNSARECOMMONLYAVAILABLETHATARECOMPLIANTWITH SUCHANTENNASIDELOBEENVELOPEREQUIREMENTS DESIGNTECHNIQUESEXIST TODEVELOPANTENNASHAVINGMUCHLOWERWIDEANGLESIDELOBELEVELS4HE CONTROL OF SIDELOBE LEVELS NEAR THE ANTENNAS BEAM REQUIRES PROVIDING ANAPERTUREDISTRIBUTIONWITHSIGNIFICANTAMPLITUDETAPERANDAPLANAR APERTUREDISTRIBUTION ASDISCUSSEDIN#HAPTER4HEWIDEANGLESIDELOBE RESPONSEOFTYPICALREFLECTORANTENNASISCOMPRISEDOFTHECOHERENTSUMOF THEAPERTUREDISTRIBUTION THEFEEDRESPONSEEXCLUSIVEOFTHATPORTIONILLU MINATINGTHEREFLECTOR BLOCKAGEEFFECTSFROMTHEFEEDANDSTRUTS REFLECTOR EDGEDIFFRACTION ANDSPILLOVER4HREEEXAMPLESOFDESIGNAPPROACHESWILL BEUSEDTOILLUSTRATEHOWTHESERADIATIONMECHANISMSCANBECONTROLLED TOREDUCESIDELOBELEVELSWELLBELOWTHELEVELSOFCONVENTIONALREFLECTOR ANTENNATECHNOLOGY !NEARLYEFFORTTOCONTROLANTENNASIDELOBESFORSATELLITECOMMUNICA TIONS; =USESANOFFSETREFLECTORANTENNA ASILLUSTRATEDIN&IG 4HEANTENNAFEEDINTHISDESIGNISENCLOSEDBYSHROUDSTOREDUCEFEED RADIATIONCONTRIBUTIONSTOTHEANTENNAPATTERNWHILEALSOAVOIDINGFEED BLOCKAGEIMPACTTOANTENNASIDELOBES4HISGEOMETRYDIDNOTADDRESS FEEDSPILLOVERLOBESTHATAREPRESENTINTHEPATTERN BUTLATERDEVELOPMENT ;=ADDEDSERRATEDhBLINDERSvTOTHEDESIGNTOREDUCESUCHCONTRIBUTIONS 4HEORIGINALRATIONALEFORTHISEARLYDEVELOPMENTWASTOREDUCEANTENNA NOISETEMPERATURELEVELSBYSUPPRESSINGWIDEANGLESIDELOBELEVELSTHAT WOULD COUPLE GROUND EMISSION COMPONENTS INTO THE ANTENNA THEREBY INCREASINGTHEPERFORMANCEOFUSERSEGMENTANTENNADESIGNS4HISDESIGN INSTEADHASFOUNDTERRESTRIALCOMMUNICATIONAPPLICATIONSINMUNICIPAL TELEPHONESEXCHANGES WHERETHEYAREAFAMILIARSIGHT-UNICIPALTELE PHONEEXCHANGESHAVESEVERALLINKSCONVERGINGTOACOMMONLOCATION ANDTHEREDUCEDSIDELOBELEVELSPROVIDEISOLATIONBETWEENSUCHLINKS

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5SER3EGMENT!NTENNAS

! SECOND EXAMPLE OF LOW SIDELOBE ANTENNA TECHNOLOGY ;= FURTHER REDUCESTHEWIDEANGLESIDELOBESBYADDINGANABSORBER LINEDTUNNELTO THEAPERTUREANDUSESAMPLITUDETAPERINGTOREDUCETHENEAR INSIDELOBE LEVELSASWELL4HEPATTERNSIN&IG ILLUSTRATEEXTREMELYLOWSIDELOBE LEVELSATWIDEANGLESTHATAREWELLBELOWISOTROPICANTENNAGAINLEVELS 4HEABSORBER LINEDTUNNELISEFFECTIVEINELIMINATINGTHESPILLOVERLOBES THATAREAPPARENTIN&IG )NCONTRASTTOTHEPREVIOUSLOWSIDELOBE ANTENNA THE OFFSET REFLECTOR IS FED WITH A RELATIVELY LARGE CORRUGATED HORNTHATPROVIDESAROTATIONALLYSYMMETRICILLUMINATIONOFTHEREFLECTOR 4HECORRUGATEDHORNPRODUCESALOWILLUMINATIONOFTHEOFFSETREFLECTOR SURFACEEDGES WHEREASTHEANTENNAIN&IG EXTENDSTHEFEEDAPERTURE ANDILLUMINATESTHEREFLECTORSURFACEWITHBASICALLYAWAVEGUIDEMODE DISTRIBUTION4HELOWEDGEILLUMINATIONPRODUCESASIGNIFICANTAMPLITUDE TAPER IN THE APERTURE DISTRIBUTION SO THAT THE NEAR IN SIDELOBE LEVELS AREALSOREDUCED4HEPATTERNRESPONSEOFTHISDESIGNISLARGELYLIMITEDTO THEANTENNASAPERTUREDISTRIBUTION4HE##)2SIDELOBEENVELOPEVALUES HAVEBEENADDEDTOTHEPATTERNINTHISFIGUREANDSERVETOILLUSTRATETHAT SIDELOBELEVELSWELLBELOWTHEENVELOPEVALUESCANBEACHIEVED 4HETHIRDLOWSIDELOBEANTENNAEXAMPLE;=ALSOUSESABSORBER LINED TUNNELS ANDTHEAPERTUREDISTRIBUTIONHASASIGNIFICANTAMPLITUDETAPER

-EASURED0ATTERN;=Ú)%%%

&IGURE ,OWSIDELOBEOFFSETREmECTOR

#HAPTER 3EVEN

4HISDESIGNAPPLIESANABSORBER LINEDTUNNELTOADIAMETERREFLECTOR 0ATTERNMEASUREMENTSAT'(Z ASILLUSTRATEDIN&IG WEREMADE WITHANDWITHOUTTHEABSORBER LINEDTUNNELINPLACE!DIAGONALHORN FEEDINAPRIMEFOCUSCONFIGURATIONPROVIDESABOUTAD"EDGEILLUMI NATIONTAPER ANDTHUSLOWSIDELOBELEVELSNEARTHEANTENNASMAINBEAM RESULT4HEFEEDANDINPUTWAVEGUIDEBLOCKAGELIMITSTHEEFFECTSOFTHE AMPLITUDETAPERAND PARTICULARLYINTHE( PLANE THELEVELSOFTHENEAR IN SIDELOBESFLATTENRATHERTHANMONOTONICALLYDECREASE ASWOULDBEANTICI PATEDIFTHESIDELOBESWERETOTALLYDICTATEDBYTHEAPERTUREDISTRIBUTION

&IGURE !BSORBER LINEDTUNNELREmECTOR;=Ú)%%%

5SER3EGMENT!NTENNAS

&IGURE !BSORBER LINEDTUNNELREmECTOR;=Ú)%%% #ONTINUED

4HESPILLOVERLOBESFROMTHEREFLECTORSURFACEANDMOUNTINGPLATEOCCUR AT ABOUT O FROM THE MAIN BEAM 4HE PEAK PATTERN LEVELS OF THESE SPILLOVERLOBESAREABOUTnD"IANDARELOWERTHANTYPICALLEVELSASA RESULTOFTHELARGEILLUMINATIONTAPER4HEPATTERNSWITHTHEABSORBER LINEDTUNNELFURTHERREDUCETHEWIDEANGLESIDELOBES ANDBEYONDO FROMTHEMAINBEAM THELEVELSAREBELOWnD"I4HEMEASUREMENTS ILLUSTRATETHATTHETUNNELBECOMESEFFECTIVEWHENITBLOCKSTHERADIATION FROMTHEANTENNAREFLECTOR4HUS THEANGULARREGIONSWHERESIDELOBE

#HAPTER 3EVEN

REDUCTIONCANBEACHIEVEDCANBEDETERMINEDFROMSIMPLEGEOMETRIC OPTICSARGUMENTS4HETUNNELSEDGESAREALSOROUNDEDTOREDUCEWIDE ANGLESIDELOBESFURTHER4HEMEASUREDANTENNAGAINWITHANDWITHOUT THEABSORBERTUNNELISIDENTICALWITHINMEASUREMENTERROR ILLUSTRAT ING THAT WIDE ANGLE SIDELOBE REDUCTION DOES NOT IMPACT MAIN BEAM GAINPERFORMANCESINCETHERADIATIONMECHANISMSRESPONSIBLEFORTHE WIDEANGLESIDELOBESDONOTCONTRIBUTETOTHEMAINBEAM4HECONTROL OFANTENNASIDELOBESFORTERRESTRIALAPPLICATIONSISREQUIREDPRINCIPALLY INTHEAZIMUTHPLANE ANDPARTIALTUNNELSBLOCKINGAZIMUTHDIRECTIONS WHEREINTERFERENCECANACCESSSIDELOBESHAVEBEENSHOWNTOBEEFFEC TIVEINTHATCASE %ACH OF THESE LOW SIDELOBE ANTENNA EXAMPLES ILLUSTRATES DIFFERENT ASPECTS OF LOW SIDELOBE DESIGN4HE HORN REFLECTOR ANTENNA DESIGN IN &IG ILLUSTRATES THE EFFECTIVENESS OF OFFSET REFLECTOR ANTENNAS AND REDUCEDSIDELOBELEVELSRESULTINGFROMDIRECTFEEDRADIATION"OTHTHELOW SIDELOBEOFFSETREFLECTORIN&IG ANDTHEABSORBER LINEDTUNNELPRIME FOCUSREFLECTORIN&IG ILLUSTRATETHEBENEFITSOFREDUCINGTHEEDGE ILLUMINATIONOFTHEREFLECTORTHATINCLUDELOWERSIDELOBELEVELSNEARTHE MAINBEAM REDUCEDSPILLOVERLEVELS ANDWIDEANGLESIDELOBELEVELSTHAT ARESIGNIFICANTLYLOWERTHANANISOTROPICGAINVALUE4HEEFFECTSOFFEED BLOCKAGEAREALSOSHOWNTOLIMITTHESIDELOBESNEARTHEANTENNASMAIN BEAMINTHEABSORBER LINEDPRIMEFOCUSANTENNAIN&IG !BSORBER LINED TUNNELS ARE EFFECTIVE IN BLOCKING WIDE ANGLE SIDELOBES AND FEED SPILLOVER4HEANGLESATWHICHTUNNELSBECOMEEFFECTIVECANBEANTICI PATEDFROMGEOMETRICOPTICSCONSIDERATIONSATANGLESWHERETHETUNNEL BEGINSTOBLOCKTHEREFLECTORANTENNASWIDEANGLERADIATION!NTENNA GAINMEASUREMENTSWITHANDWITHOUTTHEABSORBER LINEDTUNNELILLUS TRATEDIN&IG INDICATETHATTHEREDUCTIONOFTHEWIDEANGLESIDELOBES DOESNOTHAVEANAPPRECIABLEIMPACTONTHEMAINBEAMGAIN7HILETHE PRINCIPLESOFREDUCINGANTENNASIDELOBESAREWELLUNDERSTOOD SATISFYING SYSTEMNEEDSFORLOWSIDELOBELEVELSWILLREQUIRECOMMERCIALDEVELOP MENT!NEXAMINATIONOFTHESEFACTORSREVEALSTHATSUCHSIDELOBECONTROL TECHNIQUESRESULTINANTENNAPATTERNRESPONSESTHATPRINCIPALLYRESULT FROMONLYTHEANTENNASAPERTUREDISTRIBUTION 7HILE SOME OF THESE LOW SIDELOBE LEVEL DESIGN TECHNIQUES ARE WELL KNOWNANDCANBEAPPLIEDTOANEXISTINGANTENNA SEVERALPRECAUTIONS MUST BE OBSERVED ,ARGE REFLECTOR ANTENNAS ARE TYPICALLY CONSTRUCTED FROMACOLLECTIONOFPANELS,EAKAGETHROUGHTHEPANELSCONTRIBUTESTO THESIDELOBELEVELSBEHINDTHEREFLECTOR3IMILARLY SOMEREFLECTORSURFACES CONTAIN HOLES OR CUTOUTS FOR THE SPARS SUPPORTING THE SUBREFLECTOR OR PRIMEFOCUSFEED2ADIATIONFROMTHESEOPENINGSALSOCONTRIBUTESTOTHE SIDELOBELEVELSBEHINDTHEREFLECTOR4HUS ANEXAMINATIONOFTHEEXISTING ANTENNAISNEEDEDTOIDENTIFYADDITIONALCONTRIBUTORSTOTHESIDELOBES 3IDELOBELEVELSNEARTHEMAINBEAMCANBECONTROLLEDBYREPLACINGTHE

5SER3EGMENT!NTENNAS

EXISTING ANTENNA FEED WITH A LARGER AND MORE DIRECTIVE FEED HORN TO INCREASE THE APERTURE AMPLITUDE TAPER 3UCH APPROACHES INHERENTLY REDUCEANTENNAEFFICIENCYANDWHENAPERTUREBLOCKAGEISPRESENT THE REDUCTIONOFTHESIDELOBESNEARTHEANTENNASMAINBEAMISNOTASEFFEC TIVE AS WOULD RESULT FROM AN UNBLOCKED ANTENNA APERTURE 3IDELOBE CONTROLUSINGTUNNELSSURROUNDINGTHEAPERTUREHAVELENGTHCONSTRAINTS WHEN RADOMES ENCLOSE THE ANTENNA )F THE RADOME HAS A SPACE FRAME CONSTRUCTION SCATTERING FROM THE SPACE FRAME MEMBERS THAT SUPPORT THE INDIVIDUAL RADOME PANELS ALSO CONTRIBUTES TO THE SIDELOBE LEVELS )FTHESIDELOBESARETOBEREDUCEDINTHEAZIMUTHPLANE ONLYAPORTION OFTHETUNNELISREQUIRED INAMANNERSIMILARTOBLINDERSONAHORSE &INALLY WHETHERANEXISTINGANTENNAISMODIFIEDORANEWANTENNA ISDEVELOPED ATTENTIONMUSTBEPAIDTOLEAKAGEFROMMICROWAVECOM PONENTSANDTRANSMISSIONLINEINTERFACES3UCHLEAKAGECANEXCEEDTHE RADIATION FROM THE ANTENNA ITSELF %LECTROFORMING TECHNIQUES ARE AN EFFECTIVE MEANS OF REDUCING LEAKAGE COMPONENTS BY MINIMIZING THE NUMBER OF COMPONENT JUNCTIONS4ERMINATING THE FEED APERTURE AND MEASURINGITSPATTERNANDGAINLEVELWHENTERMINATEDISAMEANSOF QUANTIFYINGTHELEAKAGELEVELSINCOMPARISONTOTHESIDELOBERESPONSE OFTHEANTENNAITSELF4HETUNINGSCREWSOFMICROWAVEFILTERS WAVEGUIDE JUNCTIONSPARTICULARLYATHIGHERFREQUENCIES ANDMIXERPORTSARETYPI CALSOURCESOFLEAKAGERADIATION,EAKAGECOMPONENTSAREALSOARESULTOF WORKMANSHIPERRORS$EVELOPINGEFFECTIVEENCLOSURESANDSEALSFORSUCH ENCLOSURESSHOULDBEADDRESSEDTOCONTROLCOMPONENTLEAKAGE !DAPTIVE5SER!NTENNAS !DAPTIVE INTERFERENCE CANCELLATION SYSTEMS FOR USER ANTENNAS MUST PROVIDE EFFECTIVE CANCELLATION OVER A MUCH WIDER FIELD OF VIEW THAN SPACESEGMENT)NPRINCIPLE INTERFERENCECANARRIVEOVERAHEMISPHERIC VOLUMEIFBOTHGROUNDANDAIRBORNEINTERFERENCESOURCESARECONSIDERED 0OINTINGVARIATIONSEITHERRESULTINGFROMSATELLITEMOTIONORUSINGTHE SAMETERMINALDESIGNINDIFFERENTLOCATIONSCANEXPANDTHISHEMISPHERIC ANGULARVOLUME4HELIMITEDFIELDOFVIEWFORSPACESEGMENTANTENNAS REQUIRES ADAPTIVE CANCELLATION IN THOSE ANGULAR REGIONS WHERE THE ANTENNARESPONSEISPRINCIPALLYDICTATEDBYTHEAPERTUREDISTRIBUTION "YCONTRAST USERSEGMENTANTENNASAREPOINTEDTOWARDSTHESATELLITE ANDTERRESTRIALINTERFERENCEISRECEIVEDTHROUGHAWIDERANGULARRANGE ANDSEPARATIONFROMTHEANTENNASMAINBEAM4HUS ADAPTIVEDESIGNS FORUSERANTENNASMUSTBEEFFECTIVEFORSIDELOBESDICTATEDBYPRINCIPALLY SECOND ORDER MECHANISMS SUCH AS FEED RADIATION AND BLOCKAGE EDGE DIFFRACTION ANDSOON 4HESEDIFFERENCESINANGULARCOVERAGEREQUIREMENTSANDINTHEMECH ANISMS THAT PRODUCE THE SIDELOBES HAVE A SIGNIFICANT IMPACT ON THE

#HAPTER 3EVEN

DESIGN REQUIREMENTS FOR ADAPTIVE INTERFERENCE CANCELLATION4HE SIDE LOBERESPONSEOFTHESPACESEGMENTANTENNASISPRINCIPALLYDICTATEDBY THE APERTURE DISTRIBUTION HAVING A WELL DEFINED PHASE CENTER "Y CON TRAST THERESPONSEOFUSERANTENNASATWIDEANGLESFROMTHEMAINBEAM RESULTSFROMTHECOHERENTSUMOFMANYDIFFERENTRADIATIONMECHANISMS THAT INDIVIDUALLY HAVE WIDELY SEPARATED PHASE CENTERS4HE ANTENNA SIDELOBERESPONSEISASUMMATIONOFTHESEINDIVIDUALCOMPONENTSAND EACHRADIATIONCOMPONENTHASACORRESPONDINGTIMEDELAYINITSARRIVAL TIME!NTENNAANALYSESFORTHEUSERSEGMENTANTENNAFORMTHEPHASOR SUMOFTHESERADIATIONMECHANISMSWITHAPPROPRIATEPHASEDELAYSTOA COMMONPHASEREFERENCE4HESEANALYSESPRODUCETHEFAMILIARPATTERNS DESCRIBINGANTENNAPERFORMANCEATASINGLEFREQUENCY)FADAPTIVECAN CELLATIONISREQUIREDATASINGLEFREQUENCY APHASORVALUECONTAININGAN INTERFERENCE SAMPLE COULD CANCEL THE INTERFERENCE (OWEVER PRACTICAL CANCELLATIONTECHNIQUESMUSTRESPONDTOBOTHTHEINTERFERENCEANDTHE DESIREDSIGNALSBANDWIDTHVALUES !DAPTIVECANCELLATIONREQUIRESTHEANTENNARESPONSEOVERTHEOPERAT INGBANDWIDTHATASPECTANGLESCORRESPONDINGTOINTERFERENCEDIRECTIONS 4HETIMEDELAYSPREADORDISPERSIONINTHEUSERANTENNARESPONSEAT AGIVENDIRECTIONMUSTBEMATCHEDTOTHERESPONSEOFTHEANTENNAELE MENTS USED IN THE ADAPTIVE CANCELLATION4HE FREQUENCY RESPONSES OF THEMAINANTENNAANDTHEANTENNAELEMENTSUSEDINTHECANCELLATION PROCESS MUST BE IDENTICAL WITHIN THE TOLERANCES PREVIOUSLY SHOWN IN &IG 4HESE ANTENNA AND CANCELLATION ANTENNA ELEMENT RESPONSES HAVEDIFFERENTFREQUENCYRESPONSES NOTONLYONACOMPONENTLEVELBUT ALSO AS A RESULT OF THE PHYSICAL SEPARATION AND THEIR COMBINING4HE ADAPTIVEWEIGHTINGMUSTPROVIDEAMEANSOFCOMPENSATINGFORTHEFRE QUENCYRESPONSEDIFFERENCESBETWEENTHEUSERANTENNAANDTHEANTENNA ELEMENTCOMBINATIONSUSEDINTHEADAPTIVECANCELLATION4HEADAPTIVE WEIGHTINGCIRCUITRYACCORDINGLYREQUIRESFREQUENCY DEPENDENTWEIGHTING VALUESTOACHIEVEEFFECTIVECANCELLATIONOVERTHEBANDWIDTH RESULTING INADAPTIVEEQUALIZATIONREQUIREMENTS4HEADAPTIVEWEIGHINGCIRCUITRY GENERALLY TAKES THE FORM OF ADAPTIVE TRANSVERSAL FILTERS COMPRISED OF TIME DELAY COMPONENTS AND AMPLITUDE AND PHASE WEIGHTING FOR EACH TIME DELAY TAP &INALLY INTERFERENCE IS MUCH CLOSER TO USER ANTENNAS THANSPACESEGMENTANTENNAS ANDPROTECTIONFORMUCHHIGHERPOWER LEVELSISREQUIRED4HELINEARITYOFTHEUSERRECEIVERBECOMESANISSUEFOR NEARBYHIGH LEVELINTERFERENCESOURCES ANDTHEPOSSIBILITYOFSATURATING THERECEIVERMUSTBEADDRESSED4HUS DESIGNATTENTIONTOTHESYSTEMS LINEARDYNAMICRANGEISALSOREQUIRED)FTHERECEIVERRESPONSEREMAINS NONLINEAR AFTER ADAPTIVE INTERFERENCE CANCELLATION THE USER RECEIVER PERFORMANCEISSTILLDEGRADED !DAPTIVEUSERANTENNADESIGNSFOLLOWASIDELOBECANCELLATIONCONFIGU RATION;= ONEOFTHEORIGINALADAPTIVEANTENNADESIGNS4HISDESIGN

5SER3EGMENT!NTENNAS

CONFIGURESAMAINANTENNATOOPERATEASAUSERTERMINALANTENNAIN INTERFERENCE FREE CONDITIONS 4HE INTERFERENCE IS ASSUMED TO ARRIVE THROUGHTHEMAINANTENNASSIDELOBESTRUCTUREBECAUSETHEANTENNAS MAIN BEAM IS DIRECTED AT THE SATELLITE!UXILIARY ANTENNAS TYPICALLY SMALLHORNANTENNAS AREUSEDDURINGADAPTIVECANCELLATIONANDSAMPLE THERECEIVEDINTERFERENCE4HEGAINLEVELOFTHESEAUXILIARYANTENNAS ARESELECTEDSOTHATTHEIRGAINLEVELSMEETOREXCEEDTHESIDELOBEGAIN OFTHEMAINANTENNAINTHEANGULARREGIONCOVEREDBYEACHAUXILIARY ANTENNAELEMENTINTHECOLLECTION(IGHERGAINANTENNAELEMENTSCOVER THESIDELOBESNEARTHEMAINBEAM ANDLESSDIRECTIVEAUXILIARYANTENNA ELEMENTS ARE USED TO COVER THE LOWER GAIN VALUES OF THE WIDE ANGLE SIDELOBES4HUS THE MAIN ANTENNA RECEIVES THE DESIRED SIGNAL LEVEL THROUGHTHEMAINBEAM THEINTERFERENCESIGNALSARERECEIVEDTHROUGH THE MAIN ANTENNAS SIDELOBES AND THE MAIN ANTENNA HAS A THERMAL NOISECOMPONENT4HEAUXILIARYANTENNASPREDOMINATELYRECEIVEINTER FERENCEPOWER ANINDEPENDENTTHERMALNOISECOMPONENT ANDAMUCH SMALLERDESIREDSIGNALPOWERTHANTHEMAINANTENNASINCETHEAUXILIARY ANTENNA DOES NOT HAVE A HIGH GAIN MAIN BEAM!N EXAMPLE SYSTEM DESIGN AND MEASURED RESULTS FOR REPRESENTATIVE INTERFERENCE SIGNALS ;=HAVEBEENDESCRIBED )NOPERATION THEADAPTIVESIDELOBECANCELLATIONDESIGNMEASURESTHE CORRELATIONBETWEENTHEMAINANTENNAANDTHEAUXILIARYANTENNAELE MENTS)FINTERFERENCEPOWERISNOTPRESENT THECORRELATIONISPRIMARILY THATOFINDEPENDENTTHERMALNOISESAMPLES WHICHEQUALSZERO)FINTER FERENCEISPRESENT THECORRELATIONOFTHEINTERFERENCELEVELSRECEIVEDBY THE MAIN ANTENNAS SIDELOBES AND THE INTERFERENCE LEVELS RECEIVED BY THEAUXILIARYANTENNAELEMENTISNON ZEROBECAUSETHEINTERFERENCEIS COHERENTUPONITSELF3INCETHEINTERFERENCESAMPLESARECOHERENT THE OUTPUTCORRELATIONOFTHEMAINANTENNAANDAUXILIARYANTENNAELEMENTS ARE NON ZERO7HILE THE DESIRED SIGNAL SAMPLES RECEIVED BY THE MAIN ANTENNAANDTHEAUXILIARYANTENNAELEMENTSAREALSOCOHERENT THEIRCOR RELATIONVALUESAREQUITELOWBECAUSETHEDESIREDSIGNALLEVELSRECEIVED BYTHEANTENNASMAINBEAMARESOMUCHHIGHERTHANTHEDESIREDSIGNAL LEVELSINTHEAUXILIARYANTENNAELEMENTS4HEEXISTENCEOFACORRELATION PRODUCT INDICATES THE PRESENCE OF INTERFERENCE4HE CLOSED LOOP ADAP TIVESYSTEMOPERATIONTYPICALLYUSESALEASTMEANSSQUAREALGORITHMTO DETERMINE ADAPTIVE WEIGHT VALUES ITERATIVELY4HE AUXILIARY ANTENNA ELEMENTS ADAPTIVELYWEIGHTED ARECOMBINEDWITHTHEMAINANTENNA OUTPUT4HEADAPTIVEWEIGHTVALUESAREUPDATEDUNTILTHECORRELATION VALUESBECOMEZERO:EROCORRELATIONISEQUIVALENTTOCANCELINGTHEINTER FERENCEATTHEANTENNASYSTEMOUTPUT )FTHEPATTERNOFTHEANTENNASYSTEMCOMPRISEDOFTHEMAINANTENNA COMBINED WITH THE WEIGHTED AUXILIARY ANTENNA OUTPUTS IS PLOTTED ANTENNAPATTERNNULLSINTHEINTERFERENCEDIRECTIONS WOULDBEOBSERVED

#HAPTER 3EVEN

INTHESIDELOBESOFTHEMAINANTENNA4HEMAINBEAMOFTHEANTENNA SYSTEMISNOTAFFECTEDBYTHECANCELLATIONPROCESSSINCETHEAUXILIARY ANTENNA ELEMENT GAIN IS MUCH LOWER4HE ADAPTIVE MODIFICATIONS TO THEANTENNASIDELOBESHAVEAMINIMALEFFECTONTHEANTENNAGAIN4HE SYSTEM NOISE LEVEL CAN INCREASE SOMEWHAT BECAUSE OF NOISE CONTRIBU TIONSFROMTHEAUXILIARYANTENNAS4HISNOISELEVELDEPENDSONTHEGAIN DIFFERENCEBETWEENTHEMAINANTENNASSIDELOBELEVELSANDTHEAUXILIARY ANTENNASGAIN4HEEARLIERDISCUSSIONINDICATEDTHEAUXILIARYANTENNAS GAINLEVELSSHOULDEXCEEDTHEMAINANTENNASSIDELOBEGAINVALUES4HE MORETHEAUXILIARYANTENNAGAINEXCEEDSTHEMAINANTENNASSIDELOBE GAINLEVELS THELESSNOISEISADDEDBYTHEAUXILIARYANTENNAELEMENTS &INALLY THEADAPTIVEWEIGHTVALUESARECONSTRAINEDSOTHATTHEDESIRED SIGNALISNOTATTACKEDINOTHERWORDS THEADAPTIVEWEIGHTVALUESARE BOUNDED SO THAT DESIRED SIGNAL CORRELATIONS CANNOT REDUCE THE MAIN BEAMGAIN!SAPPROPRIATE IFTHESYSTEMATTEMPTSTOCANCELTHEDESIRED SIGNAL THRESHOLDLEVELSINTHECORRELATIONPRODUCTSCANBEUSEDTOINHIBIT THECANCELLATIONCIRCUITRY 0ERFORMANCEMEASURESFORADAPTIVEUSERANTENNASARETHEACHIEVED 3.)2 AND THE TIME REQUIRED TO REACH STEADY STATE PERFORMANCE4HE 3.)2PRINCIPALLYDEPENDSONTHERESIDUALINTERFERENCELEVELSAFTERINTER FERENCECANCELLATION CHANGESINTHESYSTEMNOISETEMPERATURERESULT ING FROM NOISE CONTRIBUTIONS FROM THE ADAPTIVELY WEIGHTED AUXILIARY ANTENNAS ANDCHANGESINTHEOVERALLANTENNAGAINWITHADAPTIVEWEIGHT CONTRIBUTIONS4HERESIDUALINTERFERENCEPOWERDEPENDSONTHEEFFECTIVE NESSOFTHEADAPTIVEINTERFERENCECANCELLATIONTHATINTURNDEPENDSON THEINTERFERENCEPOWERLEVELS4HESYSTEMNOISETEMPERATURECONTRIBU TIONSAREGENERALLYSMALLIFTHEGAINOFTHEAUXILIARYANTENNAELEMENTS EXCEEDSTHEMAINANTENNASSIDELOBELEVELS#HANGESINTHEANTENNAGAIN ARESMALLBECAUSEPATTERNNULLSINTHEANTENNASSIDELOBESTRUCTUREHAVE AMINIMALIMPACTONTHEANTENNASDIRECTIVITY4HETIMETOREACHSTEADY STATE PERFORMANCE DEPENDS ON THE ALGORITHM USED AND ITS TRANSIENT PERFORMANCE)FTHEINTERFERENCEUPSETSTHERECEIVERSACQUISITIONOFTHE DESIREDSIGNAL THETIMETORECOVERCOMMUNICATIONINCLUDESTHETIMEFOR THERECEIVERTOREACQUIRETHEDESIREDSIGNAL !SDISCUSSED THEANTENNADISPERSIONISADDRESSEDBYUSINGANADAP TIVETRANSVERSALEQUALIZERTOGENERATEFREQUENCY DEPENDENTWEIGHTING VALUES4HETOTALDELAYINTHEEQUALIZERCORRESPONDSTOTHEDELAYSPREAD IN THE MAIN ANTENNA SIDELOBE RESPONSE /NE WAY OF DETERMINING THE REQUIREDDELAYSPREADISTOMEASURETHEANTENNARESPONSEOVERABAND WIDTHWITHAVECTORNETWORKANALYZER4HERESULTINGFREQUENCYDOMAIN DATAARETRANSFORMEDINTOTHETIMEDOMAINUSINGINTERNALNETWORKANA LYZER CAPABILITIES4HE TIME DOMAIN DATA DISPLAY THE ANTENNAS TIME DELAYSPREAD!SECONDWAYOFDETERMININGTHEREQUIREDDELAYSPREAD ANALYTICALLYESTIMATESTHETIMEDELAYSPREADUSINGDIFFRACTIONANALYSES

5SER3EGMENT!NTENNAS

4HEANALYTICALLYDERIVEDDATAOFTHEEQUALIZERREQUIREMENTSFORREFLECTOR ANTENNAS;=AREPRESENTEDIN&IG ;=4HEDESIREDCANCELLATION PERFORMANCEISPLOTTEDASAFUNCTIONOFATIMEBANDWIDTHPRODUCTWITH THENUMBEROFTAPSINTHETRANSVERSALEQUALIZERASPARAMETERS4HETIME BANDWIDTHPRODUCTEQUALSTHETIMEDELAYSPREADINTHEANTENNAMUL TIPLIEDBYTHECANCELLATIONBANDWIDTH4YPICALLY THETIMEDELAYSPREAD INREFLECTORANTENNASEQUALSTWOTOTHREETIMESTHETRANSITTIMEACROSS THEAPERTURE4HUS ACHIEVINGGOODCANCELLATIONPERFORMANCEINLARGE REFLECTORANTENNASREQUIRESALARGENUMBEROFTAPSINTHETRANSVERSAL FILTER ANDFORLARGEOPERATINGBANDWIDTHS THEREQUIREDCOMPLEXITYOF THEEQUALIZERBECOMESIMPRACTICAL 4ECHNIQUESTOINCREASETHECANCELLATIONBANDWIDTHHAVEHADLIMITED INVESTIGATION/NEPROPOSEDDESIGN;=RECOMMENDEDUSINGADDITIONAL FEED ELEMENTS IN THE FOCAL REGION OF THE MAIN ANTENNA AS AUXILIARY ANTENNAELEMENTS4HEREASONINGINTHISDESIGNCONCEPTWASTHATSUCH AUXILIARYANTENNAELEMENTSWOULDCONTAINSIMILARDISPERSIONCHARAC TERISTICSASTHEMAINANTENNA PROVIDINGTHENECESSARYEQUALIZATIONTO OBTAINBROADBANDWIDTHCANCELLATION!MOREDETAILEDEXAMINATION;= REVEALSTHATTHEDISPERSIONDIFFERENCESBETWEENTHEMAINANDAUXILIARY FEEDSWERESUFFICIENTENOUGHTHATBROADBANDWIDTHCANCELLATIONWOULD NOTBEACHIEVED

&IGURE %QUALIZATIONREQUIREMENTSFORREmECTORANTENNAS; =Ú)%%%

#HAPTER 3EVEN

!NTENNA DESIGN HAS ALSO BEEN INVESTIGATED IN TERMS OF ADAPTIVE SYSTEM PERFORMANCE4HE DIFFERENCES BETWEEN #ASSEGRAIN AND OFFSET REFLECTORANTENNADESIGNSWEREEXAMINED;=/FFSETREFLECTORDESIGNS HAVE A LESS COMPLEX ANTENNA RESPONSE THAN #ASSEGRAIN DESIGNS THAT HAVETHEFEEDANDSUBREFLECTORBLOCKAGECONTRIBUTIONS4HELESSCOMPLEX ANTENNARESPONSEOFTHEOFFSETREFLECTORDESIGNRESULTSINBETTERCANCEL LATIONBANDWIDTHPERFORMANCETHANTHE#ASSEGRAINDESIGN!DDITIONAL DEVELOPMENTEFFORTSSHOULDBEDEVOTEDTOANTENNADESIGNSWHOSETIME DOMAINRESPONSESIMPLIFIESADAPTIVEPROCESSINGREQUIREMENTS -ORETOTHEPOINT SYSTEMDESIGNSARECONFIGUREDTOPROVIDEASPECI FIED LEVEL OF INTERFERENCE MITIGATION!NTENNA INTERFERENCE MITIGATION TECHNIQUESINCLUDEBOTHPASSIVESIDELOBECONTROLTECHNIQUESANDADAP TIVEINTERFERENCECANCELLATION&URTHERDEVELOPMENTATTENTIONTOACHIEV INGSPECIFIEDLEVELSOFINTERFERENCEPROTECTIONBYACOMBINATIONOFBOTH ANTENNA TECHNIQUES IS BELIEVED TO BE PROFITABLE $ESIGN ATTENTION TO ANTENNASIDELOBECONTROLFORUSERANTENNASADDRESSESMANYOFTHESAME SECOND ORDERMECHANISMSTHATRESULTINTHEDISPERSIONTHATLIMITSADAP TIVE CANCELLATION PERFORMANCE )NDEED SUCH ANTENNA SIDELOBE CONTROL TECHNIQUESRESULTINANTENNAPATTERNRESPONSESWHOSESIDELOBELEVELS AREREDUCEDBYCONTROLLINGTHESECOND ORDERRADIATIONMECHANISMS4HE RESULTING ANTENNA PATTERN IS DOMINATED BY THE APERTURE DISTRIBUTION THATALSOISNOTDISPERSIVESINCEAWELL DEFINEDPHASECENTEREXISTS4HIS SAMEREASONINGALSORESULTSINANTENNARESPONSESHAVINGLESSDISPER SION SIMPLIFYINGTHEADAPTIVEEQUALIZATIONREQUIREMENTS4HECHALLENGE THENISTOCONFIGUREANTENNASYSTEMDESIGNSCAPABLEOFPROVIDINGTHE SPECIFIEDINTERFERENCEPROTECTIONWITHMINIMALDESIGNCOMPLEXITY4HIS DESIGNAPPROACHACHIEVESMUCHOFTHEINTERFERENCEPROTECTIONATWIDE ANGLESFROMTHEANTENNASMAINBEAMBYPASSIVESIDELOBECONTROLTECH NIQUES!DAPTIVE CANCELLATION PROTECTS THE SYSTEM FROM INTERFERENCE CLOSERTOTHEANTENNASMAINBEAM ANDSINCETHEANTENNADISPERSION ISREDUCEDBYTHESIDELOBECONTROL CANCELLATIONCIRCUITRYBECOMESLESS COMPLEXBECAUSEOFREDUCEDEQUALIZATIONREQUIREMENTS&URTHERSTUDY OF THIS APPROACH IS RECOMMENDED TO MEET INTERFERENCE REQUIREMENTS WITHPASSIVEANTENNADESIGNTECHNIQUESANDANADAPTIVEDESIGNWITHA PRACTICALLEVELOFCOMPLEXITYFORWIDEBANDWIDTHAPPLICATIONS -ISSION#ONTROL!SSETS 3ATELLITEOPERATIONSDEPENDONAVARIETYOFMISSIONCONTROLASSETSTHAT SUPPORTLAUNCHOPERATIONS 44#SERVICES GATEWAYSTATIONS ANDMONI TORINGFUNCTIONSSPECIFICTOPROGRAMNEEDS7HILETHESEASSETSDEPENDON THENEEDSOFAPARTICULARPROGRAM TYPICALREQUIREMENTSANDEXAMPLES CANBEDISCUSSED4HEMISSIONCONTROLASSETSHAVEINCREASEDEMPHASISON THEIRCALIBRATIONSOTHATTHEON ORBITPERFORMANCECANBEESTABLISHEDAND

5SER3EGMENT!NTENNAS

MONITOREDWITHMINIMALMEASUREMENTUNCERTAINTY)NSOMEINSTANCES SPECIALIZEDSYSTEMSARENEEDEDTOMEASUREPERFORMANCEORESTABLISH2& PARAMETERSANDTWOEXAMPLESILLUSTRATESUCHSYSTEMS4HEFIRSTEXAMPLE DESCRIBESATERMINALTOMONITORTHEON ORBITPERFORMANCEOF'03SAT ELLITES AND THE SECOND EXAMPLE DESCRIBES A WIDE BANDWIDTH MONITOR RECEIVERTOIDENTIFYTIMEPERIODSWHENINCIDENTSIGNALVALUESEXCEEDHIGH FIELDSTRENGTHSTHATCOULDPOTENTIALLYDAMAGESYSTEMS -ISSION#ONTROL3TATIONS

-ISSIONCONTROLASSETSAREANIMPORTANTPARTOFTHEGROUNDSEGMENTAND AREUSEDBYSATELLITEOPERATORSTOCOMMUNICATEWITHTHESATELLITE4HE MISSIONCONTROLSTATIONMUSTSATISFYSEVERALOBJECTIVESINITSOPERATION !PRIMARYOBJECTIVEISTOMONITORTHESATELLITESHEALTHTHATISINDICATEDBY THETELEMETRYDATA4HESEDATAROUTINELYMONITORSUCHPARAMETERSASTHE PRIMEPOWERVOLTAGEANDCURRENTCONSUMPTION THERMALMEASUREMENTS ATTITUDEVARIATIONS ANDOTHERPARAMETERSUSEDTODETERMINETHEON ORBIT STATUSOFTHESATELLITE!SECONDOBJECTIVEISTOPROVIDEACOMMANDING FUNCTIONTOCONTROLTHESATELLITESOPERATIONTHROUGHOUTITSLIFETIME3UCH COMMANDINGINCLUDESREQUESTINGADDITIONALDATATHATARENOTROUTINELY REPORTEDTOOBTAINFURTHERINSIGHTIFSHORTFALLSAREEXPERIENCED REPOSI TIONINGTHESPACESEGMENTANTENNASTOACCOMMODATEDESIREDCHANGES INTHEIRCOVERAGEREQUIREMENTS SUBSTITUTINGREDUNDANTCOMPONENTSFOR FAILEDITEMS ANDINSTITUTING AND MONITORING THRUSTERS TO MAINTAIN OR CHANGETHESATELLITESORBITALPOSITION#OMMANDINGISDONEWITHEXTREME CARE ANDSOCOMMANDAUTHENTICATIONTECHNIQUESAREUSEDTOVERIFYTHAT THEPROPERCOMMANDSHAVEBEENRECEIVEDPRIORTOTHEIREXECUTION!THIRD OBJECTIVE IS TO PROVIDE INFORMATION USED IN DETERMINING THE SATELLITES EPHEMERISDATA4HEANGULARLOCATIONPROVIDEDBYTHEMISSIONCONTROL ANTENNATRACKINGPROVIDESALIMITEDAMOUNTOFINFORMATION!SECOND SOURCEOFINFORMATIONISACAPABILITYTOTRANSMITARANGINGCODETHATIS REBROADCASTBYTHESATELLITE4HISINFORMATIONTOGETHERWITHDATAFROM TRACKING RADARS AND OTHER SOURCES AND ORBITAL MONITORING TECHNIQUES ISUSEDINA+ALMANFILTERINGALGORITHMTODEFINETHESATELLITESORBITAL POSITION!FOURTHOBJECTIVEOFTHEMISSIONCONTROLSTATIONISAMEASURE MENTCAPABILITYOFTHESATELLITESON ORBITPERFORMANCE7HENTHESATELLITE REACHESITSON ORBITPOSITIONANDISCONFIGUREDFOROPERATION MEASURE MENTSAREMADETOASSESSCOMPLIANCEWITHTHESATELLITESSPECIFICATION /FTEN SUCHMEASUREMENTSINVOLVEFINANCIALINCENTIVES ANDCALIBRATION ACCURACYFORTHEMEASUREMENTSISCAREFULLYASSESSED -ISSIONCONTROLREQUIREMENTSARESPECIFICTOPROGRAMNEEDSANDSPACE SEGMENT DESIGNS &UTURE MISSION CONTROL REQUIREMENTS WILL INCLUDE CAPABILITIESTOUPLOADSPACESEGMENTSOFTWAREWHOSEUSEWILLBECOME MOREEXTENSIVEINFUTUREDESIGNS,INKSWITHASUFFICIENTLYHIGHDATA

#HAPTER 3EVEN

RATECAPABILITYTOACCOMPLISHTHESOFTWARETRANSFERINATIMELYMANNER AREREQUIRED!NOTHERREQUIREMENTCONCERNSTHEAMOUNTOFLINKMARGIN NECESSARYFORLOWDATARATECOMMANDINGINTHEEVENTOFSPACESEGMENT 44#TRANSPONDERSHORTFALLS#LEARLY SUCHMARGINREQUIREMENTSINVOLVE SUBJECTIVE DECISIONS BUT MOST MISSION CONTROL SEGMENTS ARE HEAVILY MARGINEDSOTHATACOMMANDINGCAPABILITYREMAINSIFSPACESEGMENT SHORTFALLSNEEDTOBEOVERCOME/THERMISSIONCONTROLREQUIREMENTSARE MOREEXTENSIVE/NEEXAMPLEIS.!3!SMISSIONCONTROLINVOLVINGTHE 4$23 SATELLITES THAT SUPPORT A MULTITUDE OF OTHER SATELLITES FOR DATA RELAYSERVICES4HEREQUIREMENTSTOINTERFACEWITH4$23SATELLITESARE DESCRIBEDINDETAIL;= -ONITORFOR/N /RBIT'030ERFORMANCE

!CAPABILITYTOMONITOR'03ON ORBITSATELLITEPERFORMANCEISONEEXAMPLE OFGROUNDASSETSTHATUTILIZEEQUIPMENTDEVELOPEDTOSUPPORTMISSIONOPER ATIONS4HEGENERALREQUIREMENTSFORTHEMONITORINGCAPABILITYINCLUDEA DIRECTIVEANTENNATOISOLATEASINGLESATELLITEWITHINTHE'03CONSTELLA TIONANDAVOIDMULTIPATHERRORS ACAPABILITYTOMONITORRECEIVEDSIGNAL LEVELSANDTHEIRPOLARIZATIONACCURATELY AMEANSTOSEPARATEINDIVIDUAL NAVIGATIONCODESANDDETERMINETHEIRPOWERRATIO ANDAWAYTOMEASURE OTHERSIGNALPARAMETERSUSEDIN'03OPERATION!PROTOTYPEDESIGN; = ILLUSTRATEDIN&IG WASDEVELOPEDTODEMONSTRATECALIBRATIONTECH NIQUESUSEDINITSOPERATION4HEACHIEVABLEMEASUREMENTUNCERTAINTYIN RECEIVEDPOWERLEVELSISOFPARTICULARINTEREST ANDANERRORBUDGETPROJEC TIONBASEDONMEASUREDPERFORMANCEWASDEVELOPEDTOASSESSMEASURE MENTUNCERTAINTY 4HIS PROTOTYPE DESIGN USES A FT REFLECTOR ANTENNA WITH THE ROLLED EDGECAVITYDIPOLEFEED SHOWNIN&IG TOCOVERTHE,TO,, BAND

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5SER3EGMENT!NTENNAS

FREQUENCIESUSEDBY'034HEFEEDDESIGNHASBEENPREVIOUSLYDESCRIBED IN&IGS AND 4HEROTATIONALPATTERNSYMMETRYPROVIDEDBYTHIS FEEDDESIGNRESULTSINLOWANTENNAAXIALRATIOPERFORMANCE SOTHEAXIAL RATIOOFTHEINCIDENT'03SIGNALSANDSIGNALPOWERMEASUREMENTSCAN BEPERFORMEDWITHMINIMUMUNCERTAINTY4HERECEIVERUSESCORRELATION TECHNIQUESTOISOLATETHECODECOMPONENTSTHISPROTOTYPEDESIGNEXAM INEDONLYTHE,#!'03CODECOMPONENT4HERECEIVERIMPLEMENTA TIONISBASEDON&0'!TECHNOLOGYTHATWASALSOUSEDTOGENERATECODE COMPONENTSFORBOTHCORRELATIONPROCESSINGANDACALIBRATIONSIGNALTO DETERMINETHERECEIVERSELECTRONICRESPONSE 4HE'03SYSTEMISSPECIFIEDINPARTBYTHEPOWERLEVELSRECEIVEDBY ANIDEALIZEDREFERENCEUSERANTENNATHATHASAD"ILINEARLYPOLARIZED GAIN LEVEL4HE MONITOR CAPABILITY MUST ADDRESS TWO QUESTIONS IN ITS CALIBRATIONFORRECEIVEDPOWER 7HATISTHERELATIONSHIPBETWEENTHEMONITORINGANTENNASGAINAND THEREFERENCEANTENNAUSEDINTHE'03SPECIlCATION (OW DO THE CORRELATION RECEIVER OUTPUT LEVELS RELATE TO THE SIGNAL POWERRECEIVEDBYTHEMONITORINGANTENNA 4HE MONITORING ANTENNAS GAIN WAS MEASURED BY TWO INDEPENDENT METHODS!FARFIELDRANGEMEASUREMENTOFTHEANTENNAYIELDEDAGAIN LEVELOFD"I4HEAXIALRATIOTHATISREQUIREDTOADDRESSUNCERTAINTY INPOLARIZATIONPARAMETERSWASMEASUREDTOBED"!SECONDANTENNA GAINMEASUREMENTWASPERFORMEDUSINGSOLARRADIOSOURCETECHNIQUES DESCRIBED IN #HAPTER 4HE '4 VALUE FROM THE RADIO SOURCE MEA SUREMENTANDTHESYSTEMNOISETEMPERATUREDERIVEDFROMTHERECEIVER NOISETEMPERATUREANDMEASUREDANTENNANOISETEMPERATUREYIELDSAN ANTENNAGAINLEVELOFD"I 4HEMEASUREDANTENNAPERFORMANCEMUSTBERELATEDTOTHESPECIFIED REFERENCEANTENNA4HETOTALPOWEROFTHEINCIDENTSIGNALRECEIVEDFROM THESATELLITEISTHESUMOFTHEDETECTEDOUTPUTSFORTHETWOORTHOGONALLY POLARIZED ANTENNA TERMINALS4HE DIFFERENCES IN THE RECEIVED POWER OUTPUTLEVELSATTHESETWOTERMINALSAREUSEDTOCALCULATETHEINCIDENT SIGNALSAXIALRATIO4HETOTALPOWERRECEIVEDBYANISOTROPICANTENNA MATCHEDTOTHEINCIDENTSIGNALSPOLARIZATIONEQUALSTHESUMMEDOUTPUT POWERLEVELSREDUCEDBYTHEANTENNAGAINRELATIVETOANISOTROPICCIR CULARLYPOLARIZEDANTENNA4HEREFERENCEANTENNAISAD"ILINEARLY POLARIZEDANTENNA)FTHEINCIDENTSIGNALHADIDEALCIRCULARPOLARIZA TION THEISOTROPICCIRCULARLYPOLARIZEDANTENNAANDTHED"ILINEARLY POLARIZEDANTENNAWOULDHAVETHESAMESIGNALLEVELS(OWEVER WHEN THE INCIDENT SIGNAL HAS A FINITE AXIAL RATIO THE RECEIVED SIGNAL LEVEL FORLINEARPOLARIZATIONDEPENDSONTHEORIENTATIONOFTHEPOLARIZATION ELLIPSES OF THE INCIDENT SIGNAL AND RECEIVING ANTENNA &OR EXAMPLE

#HAPTER 3EVEN

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&IGURE 0OLARIZATIONCORRECTIONFORLINEARORIENTATION

5SER3EGMENT!NTENNAS

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#HAPTER 3EVEN

)NCIDENT3IGNAL,EVEL-ONITOR

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THEFREQUENCYRESPONSEOFTHEANTENNAGAINMUSTVARYASK SOTHAT INCIDENT FIELD LEVELS INDEPENDENT OF THEIR OPERATING FREQUENCY ARE RECEIVEDBYTHEDETECTORS7HILEAVARIETYOFNETWORKSCANBEUSEDTO PRODUCESUCHANANTENNAGAINRESPONSE ASIMPLEMEANSWASUSEDIN THISCASE4HEORTHOGONALANTENNAELEMENTSUSEDINTHISDESIGNWERE SIMPLELINEARPATCHANTENNAELEMENTSTHATAREORTHOGONALLYORIENTEDTO RESPONDTOORTHOGONALLINEARLYPOLARIZEDINCIDENTFIELDCOMPONENTS4HE MISMATCHLOSSOFSUCHANANTENNATOFIRSTORDERHASAFREQUENCYRESPONSE BELOWITSRESONANTFREQUENCYTHATFOLLOWSTHEDESIREDK DEPENDENCE 4HISBEHAVIORWASUSEDTOPROVIDETHEDESIREDFREQUENCYRESPONSEOF THEANTENNASYSTEM 4HEOVERALLRECEIVERIN&IG ILLUSTRATESTHETWOLINEARLYPOLARIZED MICROSTRIPPATCHANTENNAELEMENTSTHATAREPRINTEDONADUROIDBOARD HAVINGAN INCH SQUARESIZE4HESYSTEMISREQUIREDTOCOVERATO'(Z FREQUENCY RANGE FOR THIS APPLICATION TO DETECT THE POWER DENSITY FROM POTENTIAL HIGH POWER EMITTERS4HE ANTENNA PATTERN RESPONSES IN THE PRINCIPALPLANESIN&IG ILLUSTRATETHEBROADCOVERAGECHARACTERISTICS OFTHEDESIGNANDTHEDESIREDREDUCEDGAINLEVELSATTHELOWERFREQUENCIES 4HE( PLANEPATTERNSAREROUGHLYCOSINE DEPENDENT ASANTICIPATED4HE % PLANEPATTERNSCANBEVISUALIZEDASTWOEQUIVALENTSLOTRADIATORSLOCATED ATTHEENDSOFTHELINEARELEMENTS!TLOWFREQUENCIES THEEQUIVALENTSLOTS HAVEFIELDCOMPONENTSTHATAREOPPOSITELYDIRECTED ANDTHEIREXCITATION TENDS TOWARD AN EQUAL PHASING THAT PRODUCES A PATTERN BEHAVIOR THAT TENDSTOWARDSANULLON AXIS ASILLUSTRATEDBYTHE'(ZPATTERN!STHE FREQUENCYINCREASESTOWARDSTHERESONANCEVALUE THEPHASESHIFTFROMONE ENDOFTHEPATCHTOTHEOTHERINCREASESTOWARDSO4HEFIELDCOMPONENTS

&IGURE -ICROSTRIP ANTENNA ELEMENTS FOR INCIDENT SIGNAL LEVELMONITOR;=Ú)%%%

#HAPTER 3EVEN

&IGURE 0RINCIPALPLANEPATTERNSFORMICROSTRIPANTENNA;= Ú)%%%

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#HAPTER 3EVEN

&IGURE %LECTRONICSRESPONSEOFRECEIVER;=Ú)%%%

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#HAPTER

!NTENNA4EST&ACILITIES AND-ETHODOLOGIES

/VERVIEW !NTENNA TESTING IS A VERY IMPORTANT PART OF COMMUNICATION SATELLITE DEVELOPMENTANDQUALIFICATION!NTENNATESTTECHNIQUES INSTRUMENTATION ANDTESTFACILITIESAREWELLDEVELOPEDFORAWIDEVARIETYOFAPPLICATIONS ; =ANDFORMTHEBASISTOEVALUATESATELLITEANTENNAS4HE!-4! !NTENNA-EASUREMENT4ECHNIQUES!SSOCIATION HASLONGBEENAFORUM TODISCUSSMEASUREMENTFACILITIES METHODOLOGIES EVALUATIONTECHNIQUES ANDMEASUREMENTUNCERTAINTIESASDOCUMENTEDINSYMPOSIUMRECORDS 3ATELLITEANTENNAEVALUATIONS HOWEVER POSEUNIQUEREQUIREMENTSTHAT ARENOTNORMALLYPARTOFANTENNASYSTEMEVALUATION!CCORDINGLY TEST TECHNIQUES AND METHODOLOGIES INSTRUMENTATION AND FACILITY REQUIRE MENTSMUSTBETAILOREDTOMEETTHESPECIFICREQUIREMENTSFORSATELLITE ANTENNADESIGNS !NTENNATESTINGCHARACTERIZESBOTHTHEIRSPATIALANDTERMINALPROP ERTIES ANDCLEARLYSUCHTESTINGANDEVALUATIONCRITERIADEPENDONTHE APPLICATIONANDPROGRAMREQUIREMENTS!TASYSTEMLEVEL THESYSTEMS '4 AND %20 LEVELS DICTATE THE DESIGN COMMUNICATION PERFORMANCE BUTTHESEPARAMETERSINTURNDEPENDONTHEANTENNASCHARACTERISTICS 4HESPATIALPROPERTIESOFANTENNASINCLUDEGAIN PATTERN ANDPOLARIZA TION PARAMETERS AND THEIR VARIATION OVER THEIR OPERATING BANDWIDTH REQUIREMENTS3PACESEGMENTANTENNASPROVIDESERVICETOEARTH LOCATED COVERAGE AREAS THUS THE SYSTEM LEVEL PARAMETERS ARE THE MINIMUM VALUESWITHINTHECOVERAGEAREABURDENEDBYANTENNAPOINTINGERRORS ANDSATELLITEATTITUDEUNCERTAINTY5SERSEGMENTANTENNASMUSTPOINTTO THESATELLITEANDTHEIRPROJECTEDTRACKINGERRORSLIKEWISEBURDENTHEUSER

#HAPTER %IGHT

SEGMENT PARAMETERS4HE ANTENNAS POLARIZATION MUST ALSO BE ESTAB LISHED4HEANTENNASPOLARIZATIONCHARACTERISTICSANDTHEPOLARIZATION OFTHEINCIDENTFIELDTOGETHERDEFINEPOLARIZATIONMISMATCHANDPOLAR IZATION ISOLATION VALUES FOR OPERATIONAL SYSTEM DESIGNS AS DESCRIBED IN #HAPTER 4HE TERMINAL CHARACTERISTICS OF AN ANTENNA DEFINE THE INTERFACEIMPEDANCEWITHTHESYSTEMS2&ELECTRONICSANDTHERESULTANT SIGNALTRANSFERCHARACTERISTICS 4HECOMBINATIONOFINCREASEDDESIGNCOMPLEXITY THEEVOLUTIONFROM THEEVALUATIONOFPASSIVE2&PARAMETERSTOSYSTEM LEVELPERFORMANCE MEASURES ANDINCREASEDINTEGRATIONOFELECTRONICSWITHTHEANTENNAS PROVIDECHALLENGESFORBOTHSPACEANDUSERSEGMENTANTENNADESIGNS 4HESE CHALLENGES PLACE INCREASED EMPHASIS ON MEASUREMENT FACILITY REQUIREMENTS AND TECHNIQUES TO QUANTIFY MEASUREMENT UNCERTAINTY 2&EVALUATIONFACILITIESAREWELLDEVELOPEDBUTTHESPECIALIZEDNEEDSOF FUTURESATELLITEANTENNADESIGNREQUIREFURTHEREXTENSIONSOFEXISTING CAPABILITIES4ESTTECHNIQUESFORADAPTIVEANTENNATECHNOLOGY ANTENNAS INTEGRATED WITH SYSTEM ELECTRONICS AND ANTENNA TRACKING TECHNIQUES PROVIDE EXAMPLES OF SUCH EXTENDED TEST REQUIREMENTS 4HE SYSTEM LEVELEVALUATIONSFORTHESEEXAMPLESILLUSTRATETHENEEDFORINCREASED INSTRUMENTATION ANDFACILITYREQUIREMENTSANDPERFORMANCEMEASURES INTHEIREVALUATIONEXPANDFROMTHECONVENTIONALPARAMETERSUSEDFOR ANTENNATESTINGTOSYSTEMPERFORMANCEPARAMETERS)NCREASEDUSEOF COMPUTERTECHNIQUESFORINSTRUMENTATIONCONTROL DATAPROCESSING AND ARCHIVINGWILLBEREQUIRED 'ENERAL 0URPOSE4EST&ACILITIES !NTENNA PARAMETERS AS THEY ARE DEFINED ASSUME THAT THE ANTENNA RESPONDSTOAUNIFORMPLANEWAVE4ESTFACILITIESTHEREFOREMUSTPROVIDE UNIFORMTESTFIELDSTOEVALUATETHEANTENNASRESPONSETOAPLANEWAVE 4HEEXTENTOFTHEFACILITYSTESTREGIONTHATHASSUFFICIENTUNIFORMITYIS COMMONLYREFERREDTOASTHEQUIETZONE4HREEGENERICTESTFACILITIESHAVE BEENDEVELOPEDFORTHISPURPOSE FARFIELDRANGES COMPACTRANGES AND NEARFIELDSAMPLINGTECHNIQUES!SISTHECASEINMANYINSTANCES NOONETYPEOFFACILITYISUNIVERSALLYADVANTAGEOUS SOTHATTHESELECTION OFFACILITIESTOEVALUATETESTARTICLESMUSTADDRESSTHETECHNOLOGYTOBE EVALUATED THEAPPLICATIONSREQUIREMENTS ANDFACILITYAVAILABILITY4HE INSTRUMENTATION TO SUPPORT THE FACILITY IS EQUALLY IMPORTANT AND THE CALIBRATIONOFANTENNASTANDARDSTOESTABLISHABSOLUTEGAINVALUESAND POLARIZATIONPROPERTIESOFTESTARTICLESISALSOREQUIRED0RESENTGENERAL PURPOSE INSTRUMENTATION AND SUPPORTING SOFTWARE IS WELL DEVELOPED &UTUREANTENNADESIGNSTHATINTEGRATETHEANTENNAWITHSYSTEMELEC TRONICSWILLNEEDTOINTERFACEAT)&ORDIGITALLEVELS4HEEVALUATIONOF ADAPTIVESYSTEMSFURTHEREXPANDTESTREQUIREMENTSTOREPRESENTBOTH

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#HAPTER %IGHT

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#HAPTER %IGHT

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#HAPTER %IGHT

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#HAPTER %IGHT

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#HAPTER %IGHT

&IGURE '4ERRORSFORAD"9FACTORERROR

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#HAPTER %IGHT

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!DAPTIVE!NTENNA%VALUATION 4HE EVALUATION OF ADAPTIVE ANTENNA SYSTEMS ; = EXTENDS THE SCOPEOFCONVENTIONALANTENNATESTINGTOSYSTEM LEVELTESTINGTOQUAN TIFY THE EFFECTIVENESS OF ADAPTIVE INTERFERENCE REJECTION 3UCH TESTING EVALUATES THE DESIGN INTEGRATION WITH SYSTEM ELECTRONICS THE CONTROL AND WEIGHTING CIRCUITRY AND SYSTEM PERFORMANCE MEASURES4HE QUI ESCENT PERFORMANCE OF THE ANTENNA IN INTERFERENCE FREE CONDITIONS IS INITIALLYESTABLISHEDUSINGCONVENTIONALANTENNATESTTECHNIQUESTOCHAR ACTERIZETHECOVERAGE POLARIZATION BANDWIDTH AND'4PERFORMANCE !DDITIONALBENCHTESTINGISPERFORMEDTOEVALUATETHEPERFORMANCEOF THEADAPTIVEELECTRONICCOMPONENTSOFTHEDESIGN4HEEVALUATIONOFTHE ADAPTIVEOPERATIONOFTHESYSTEMISTHENINITIATEDANDQUANTIFIESTHE STEADYSTATEPERFORMANCEWHENINTERFERENCEISPRESENTANDTHETRANSIENT PERFORMANCETHATMEASURESTHETIMEREQUIREDFORTHESYSTEMTOADAPT TOTHEINTERFERENCEANDQUANTIFIESTHEDISRUPTIONOFUSERCOMMUNICA TIONS WHEN DISRUPTED BY INTERFERENCE !DAPTIVE ANTENNA EVALUATIONS THEREFOREADDRESSTWOSYSTEM LEVELISSUES 7HATISTHESTEADYSTATELOSSINPERFORMANCEWHENINTERFERENCEIS PRESENT (OWLONGDOESITTAKETOREACHSTEADYSTATECONDITIONSAFTERINTERFER ENCEINITIATION 4HEREQUIREMENTSOFTHEADAPTIVEANTENNADESIGNARESTATEDINTERMS OFSCENARIOSTHATDESCRIBETHEINTERFERENCEENVIRONMENT4HESEREQUIRE MENTSFORMTHEBASISOFBOTHTHEDESIGNANDTESTING!DAPTIVEANTENNA DEVELOPMENT PROCEEDS BY CONSTRUCTING A DETAILED SIMULATION OF THE PROPOSEDDESIGNANDEXERCISINGTHESIMULATIONTOEVALUATEDESIGNCOM PLIANCE!STHEDEVELOPMENTPROCEEDS THESIMULATIONISAUGMENTEDBY MEASUREDCOMPONENTPERFORMANCEOFTHEADAPTIVEDESIGNELEMENTSTO IMPROVETHESIMULATIONSFIDELITY4HESIMULATIONISEXERCISEDINA-ONTE #ARLOSENSEFOLLOWINGTHEPOSSIBLEVARIATIONSDEFINEDBYTHESCENARIOTO OBTAINTHEREQUIREDSTATISTICALANSWERSTOADAPTIVESYSTEMPERFORMANCE 7HILETHE-ONTE#ARLOAPPROACHISNECESSARYTOPROVIDETHESTATISTICAL ANSWERSTOADAPTIVESYSTEMPERFORMANCE A-ONTE#ARLOAPPROACHTO ADAPTIVE SYSTEM TESTING HAS IMPRACTICAL SCHEDULE REQUIREMENTS4HE SIMULATIONISUSEDTODEFINEALIMITEDNUMBEROFTESTCASES ANDADAPTIVE ANTENNATESTINGISCONDUCTEDASDEFINEDBYTHESETESTCASES4HETEST RESULTSARETHENCOMPAREDWITHTHESIMULATIONRESULTS ANDTHEIRAGREE MENTVALIDATESTHESIMULATION/NCETHESIMULATIONHASBEENVALIDATED THROUGHTHETESTCASEAGREEMENT THESIMULATIONISTHENEXERCISEDINA -ONTE#ARLOMANNERTOADDRESSSYSTEMCOMPLIANCEWITHREQUIREMENTS !DAPTIVEANTENNATESTINGISTHEREFOREASIGNIFICANTDEPARTUREFROMTHE

#HAPTER %IGHT

NORMALANTENNATESTINGANDCOMPLIANCEDETERMINATIONUSEDINCONVEN TIONALANTENNATESTING !DAPTIVE ANTENNA TESTING IS CONTRASTED WITH CONVENTIONAL ANTENNA TESTING IN &IG #ONVENTIONAL ANTENNA TESTING IS WELL SUPPORTED BYSTANDARDS ESTABLISHEDFACILITIESANDINSTRUMENTATION ANDANALYTIC COMPUTERCODESTHATALLOWINDEPENDENTVERIFICATIONOFMEASUREDRESULTS 4HETESTRESULTSFORCONVENTIONALTESTINGADDRESSTHECOMPONENT LEVEL PARAMETERSTHATDEFINETHEANTENNASPERFORMANCE"YCONTRAST ADAP TIVEANTENNAEVALUATIONSAREGUIDEDBYANINTERFERENCESCENARIOTHATIS SPECIFICTOTHEPROGRAM4HEDETAILEDSIMULATIONOFTHEADAPTIVESYSTEM DESIGNANDTHE-ONTE#ARLOTREATMENTOFSIMULATIONRESULTSAREUSED TOSELECTTESTCASESFORADAPTIVESYSTEMEVALUATIONS#OMPARISONOFTHE MEASURED AND SIMULATED SYSTEM PERFORMANCE IS USED TO VALIDATE THE SIMULATION"YCONTRAST CONVENTIONALANTENNATESTINGTYPICALLYCOMPARES MEASUREMENTSWITHTHECALCULATEDRESULTSFROMANALYSISCODESTOPRO VIDECONFIDENCEINTHEMEASUREDRESULTS !DAPTIVE FACILITY REQUIREMENTS HAVE MORE GENERAL REQUIREMENTS THANCONVENTIONALANTENNATESTINGSINCETHEDESIREDSIGNALCOLLECTION MUSTBEGENERATEDALONGWITHINTERFERENCESIGNALS REPRESENTINGTHE COLLECTIONOFINTERFERENCESOURCES4HECOLLECTIONOFDESIREDANDINTER FERENCESIGNALSALSOISREQUIREDTOHAVEDIFFERENTARRIVALDIRECTIONS4HE SIGNALS MUST REPLICATE OPERATIONAL AND INTERFERENCE WAVEFORMS AND

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USESPECIALIZEDINSTRUMENTATIONSUCHAS"%2TESTSETSSOTHATPARAM ETERSSUCHAS3.)2CANBEEVALUATED!VARIETYOFINTERFERENCESIGNAL SPECTRACANBEPOSTULATEDANDPERFORMANCEMEASURESRELATIVETOTHE INTERFERENCESPECTRAMUSTBEEVALUATED4HUS THETESTSIGNALSUSEDIN ADAPTIVESYSTEMEVALUATIONARECLEARLYMOREDIVERSEANDGENERALTHAN THESWEPTFREQUENCYMEASUREMENTSUSEDWITHNETWORKANALYZERSTHAT AREEMPLOYEDINCONVENTIONALANTENNATESTING4HELEVELSOFTHESETEST SIGNALSMUSTALSOBEVARIEDSOTHATTHEPERFORMANCEFORDIFFERENTSIGNAL ANDINTERFERENCELEVELSCANBEEVALUATED#LEARLY COMPUTERCONTROLIS NEEDEDFORTHESIGNALSANDINSTRUMENTATION ANDSTORAGEANDDISPLAY OFTHEDATAAREREQUIRED&INALLY THEOUTPUTSOFTHEADAPTIVESYSTEM EVALUATIONSARESYSTEM LEVELMEASURESOFPERFORMANCERATHERTHANTHE COMPONENT LEVELPARAMETERSUSEDINCONVENTIONALANTENNATESTING 5PLINKADAPTIVEANTENNASPROVIDEINTERFERENCEPROTECTIONOVERALIM ITED FIELD OF VIEW SUBTENDED BY THE EARTH4HE PERFORMANCE OF THESE DESIGNS; =MUSTBEESTABLISHEDFORBOTHQUIESCENTANDADAPTIVE CANCELLATIONCONDITIONS4HEQUIESCENTPERFORMANCEOFTHEANTENNAPRO VIDES SERVICE OVER THE DESIGN COVERAGE AREA WHEN INTERFERENCE IS NOT PRESENTANDTHETESTINGFOLLOWSCONVENTIONALANTENNAMEASUREMENTS 7HENINTERFERENCEISINITIATED THEADAPTIVECANCELLATIONRESPONDSBY DYNAMICALLYFORMINGPATTERNNULLSINTHEDIRECTIONOFINTERFERINGSOURCES 4HERESULTINGPATTERNNULLSIMPACTTHEPERFORMANCEAVAILABLETOUSERS WITHIN THE DESIGN COVERAGE AREA! THRESHOLD VALUE OF THE ACCEPTABLE 3.)2VALUEMUSTBEESTABLISHEDTODEFINEUSERREQUIREMENTSFORCOM MUNICATION4HE PERFORMANCE MEASURE FOR ADAPTIVE SYSTEM EFFECTIVE NESSOFUPLINKANTENNASISTHEPERCENTCOVERAGEAREA4HEPERCENTAREA COVERAGEISDEFINEDBYTHEAMOUNTOFTHEDESIGNCOVERAGEAREAWHERE THE THRESHOLD 3.)2 IS EXCEEDED AFTER ADAPTIVE CANCELLATION DIVIDED BYTHEDESIGNCOVERAGEAREAWHERECOMMUNICATIONSERVICEISPROVIDED UNDERQUIESCENTCONDITIONS4HEPERCENTAREACOVERAGEVARIESWITHTHE PRECISELOCATIONOFINTERFERENCESOURCES#UMULATIVESTATISTICSGATHERED ASSCENARIOPARAMETERSANDTREATEDONA-ONTE#ARLOBASISAREUSEDTO MEASUREADAPTIVECANCELLATIONEFFECTIVENESS4HETRANSIENTPERFORMANCE ISESTABLISHEDBYMEASURINGTHETIMEREQUIREDAFTERINTERFERENCEINITIA TIONFORTHEADAPTIVEWEIGHTSTOCONVERGETOTHEIRSTEADYSTATEVALUES !DAPTIVEANTENNASFORUSERAPPLICATIONSGENERALLYFOLLOWTHESIDELOBE CANCELLER ARCHITECTURE DESCRIBED IN #HAPTER )NTERFERENCE ARRIVES THROUGHTHEANTENNASIDELOBESWHILETHEMAINBEAMISDIRECTEDTOWARDS THE SATELLITE4HE SIDELOBE CANCELLER DESIGN PURPOSELY CONSTRAINS THE AUXILIARYANTENNACOLLECTIONTOAVOIDCANCELINGTHEMAINANTENNASMAIN BEAM4HE AUXILIARY ANTENNAS ARE CONFIGURED SO THAT THEIR ANTENNA GAINEXCEEDSTHESIDELOBEGAINOFTHEMAINANTENNASOTHATNOISECON TRIBUTIONSFROMTHEAUXILIARYANTENNASWHENADAPTIVECANCELLATIONIS EXERCISED HAVE A MINIMAL IMPACT ON THE SYSTEM NOISE TEMPERATURE

#HAPTER %IGHT

4HEPRIMARYOBJECTIVESOFADAPTIVEEVALUATIONSOFTHESEDESIGNSARETO DETERMINERESIDUALINTERFERENCELEVELSANDCHANGESINTHESYSTEMNOISE TEMPERATUREFORSTEADYSTATEOPERATIONANDTHETRANSIENTPERFORMANCE OFTHEADAPTIVECIRCUITRY!GAIN ATHRESHOLD3.)2VALUEISUSEDASA MEANSOFEVALUATINGTHEEFFECTIVENESSOFSIDELOBECANCELLERDESIGNS &ACILITY REQUIREMENTS FOR ADAPTIVE TESTING DIFFER FROM CONVENTIONAL TESTING'ENERAL PURPOSEANTENNATESTFACILITIESAREBASEDONASINGLE ILLUMINATION SOURCE THAT PRODUCES FIELDS OF SUFFICIENT FIDELITY IN THEIR QUIET ZONES TO PERMIT ANTENNA MEASUREMENTS "Y CONTRAST ADAPTIVE SYSTEMEVALUATIONSREQUIREBOTHDESIREDSIGNALANDINTERFERENCESIGNAL COMPONENTSFROMDIFFERINGDIRECTIONSTOILLUMINATETHEADAPTIVEANTENNA UNDER TEST 3PACE SEGMENT ADAPTIVE ANTENNAS FOR UPLINK ANTENNA APPLICATIONSRECEIVESIGNALSANDINTERFERENCEFROMTHELIMITEDFIELDOF VIEWSUBTENDEDBYTHEEARTH%XTENSIONSOFCOMPACTRANGETECHNOLOGY DESCRIBEDEARLIERHAVEBEENFOUNDTOBEANATTRACTIVEWAYTOGENERATE THEDESIREDANDINTERFERINGSIGNALSOVERALIMITEDFIELDOFVIEW 5SERANTENNASWITHADAPTIVECANCELLATIONCAPABILITIESAREGENERALLY IMPACTED BY TERRESTRIAL INTERFERENCE4ESTING ADAPTIVE USER ANTENNAS REQUIRESSETTINGUPACOLLECTIONOFINTERFERENCESOURCESFORTESTPURPOSES SURROUNDINGTHEANTENNA!SDISCUSSEDIN#HAPTER SIDELOBECANCELLATION PERFORMANCEISIMPACTEDBYMULTIPATHFROMTERRAINFEATURESSURROUNDING THEANTENNA4HESELECTEDCONFIGURATIONOFINTERFERENCESOURCESTOEVALU ATESIDELOBECANCELLERADAPTIVEDESIGNSMUSTBESENSITIVETOSITINGSO THATTHESYSTEMRESPONDSTOTHEINTERFERENCEILLUMINATORSANDMEASURED RESULTSARENOTOBSCUREDBYMULTIPATH!SIMPLEEXAMPLEILLUSTRATEDTHE MEASUREMENTSENSITIVITYTOMULTIPATH!TWO ELEMENTADAPTIVEARRAY ILLUSTRATEDIN&IG ISPERTURBEDBYAMULTIPATHCOMPONENTINDICATED BY THE DASHED ELEMENT 4HE MULTIPATH COMPONENT IS ASSUMED TO BE D"LOWERTHANTHEDIRECTSIGNALCOMPONENTSRECEIVEDBYTHETWOARRAY ELEMENTS4HEEFFECTOFTHISMULTIPATHERRORONTHEARRAYSANTENNAPAT TERNMEASUREMENTININTERFERENCE FREECONDITIONSISMINOR D"IN AMPLITUDEANDOINPHASEUSINGTHECOHERENTERRORSTATISTICSDESCRIBED IN#HAPTER4HEEFFECTOFTHISMULTIPATHCOMPONENTONTHEADAPTIVE CANCELLATIONPERFORMANCEISILLUSTRATEDIN&IG WHERETHEMULTIPATH COMPONENTHASIN PHASEANDOUT OF PHASECONDITIONS 3EPARATEMEASUREMENTSOFTHEILLUMINATORSREPRESENTINGINTERFERENCE SOURCESCANBEMADETODETERMINETHEPRESENCEOFMULTIPATH)FSUFFICIENT BANDWIDTHISAVAILABLE NETWORKANALYZERMEASUREMENTSOFTHESIGNAL RECEIVEDBYTHEMAINANTENNAFROMTHEINTERFERENCEILLUMINATORCANBE PROCESSED IN THE TIME DOMAIN TO IDENTIFY MULTIPATH COMPONENTS AND THEIRLEVEL7HENTHEBANDWIDTHISTOONARROW THEILLUMINATORSLOCATION CANBEVARIED ANDDIFFERENCESINTHEPOWERTRANSFERBETWEENTHEILLUMI NATORANDTHEANTENNACANBEUSEDTOIDENTIFYTHEPRESENCEOFMULTIPATH 'ENERALLY LOCATINGTHEILLUMINATORSRELATIVELYCLOSETOTHEANTENNABEING


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#HAPTER %IGHT

EVALUATEDISDESIRED)NTHISCASE FARFIELDREQUIREMENTSARECONSIDERED 4HESIDELOBERESPONSEOFTHEMAINANTENNAARISESFROMTHECOLLECTION OF SECOND ORDER RADIATION COMPONENTS THAT HAVE A DIFFERENT FAR FIELD REQUIREMENTTHANTHATDICTATEDBYTHEMAINANTENNASAPERTURESIZE 4HEPHASINGBETWEENTHESECONDARYRADIATIONCOMPONENTSCLOSETOTHE MAINANTENNAMAYBESOMEWHATDIFFERENTTHANTHEIRFARFIELDVALUES BUT THEIRTIMEDELAYDIFFERENCESARECOMPARABLETOFARFIELDVALUES4HEDIS PERSIONRESULTINGFROMTHETIMEDELAYDIFFERENCESISTHELIMITINGFACTORIN ADAPTIVECANCELLATIONPERFORMANCESOTHATANILLUMINATORLOCATIONCLOSER THANTHEANTENNASFARFIELDDOESNOTIMPACTMEASUREMENTRESULTS4HE PRINCIPALREQUIREMENTFORTHESOURCEILLUMINATORISASEPARATIONTHAT ISSUFFICIENTENOUGHTHATTHEMAINANTENNAANDAUXILIARYELEMENTSARE UNIFORMLYILLUMINATEDBYTHEINTERFERENCEILLUMINATOR %VALUATIONOF!NTENNAS(AVING )NTEGRATED%LECTRONICS 4HE EVALUATION OF ANTENNAS HAVING INTEGRATED ELECTRONICS AND ACTIVE ARRAYANTENNASTYPICALLYPOSESPROBLEMSBECAUSEATERMINALTHATSEPA RATESTHEANTENNAANDTHEELECTRONICSISNOTAVAILABLEFORTESTPURPOSES 4WOEXAMPLESOFINTEGRATEDANTENNATECHNOLOGYWILLBEDISCUSSED4HE FIRST EXAMPLE IS ANTENNA DESIGNS WHERE THE ANTENNA FEED ,.! AND DOWNCONVERTERAREINTEGRATEDINTOASINGLEPACKAGE3UCHDESIGNSARE COMMONLYFOUNDINREFLECTORANTENNASYSTEMSFORUSERSEGMENTAPPLICA TIONS4HESECONDEXAMPLEISTHEEVALUATIONOFACTIVEARRAYDESIGNSBOTH RECEIVEANDTRANSMITARRAYSWILLBEDISCUSSED)NBOTHCASES THEACTIVE ELECTRONICSSHOULDRECEIVEANADEQUATEBURN INTIMETOSCREENOUTINFANT MORTALITYFAILURESPRIORTOASSEMBLINGTHEINTEGRATEDANTENNA 7HEN THE ANTENNA ,.! AND DOWNCONVERTER ARE AN INTEGRATED ASSEMBLY THERELATIVEPATTERNLEVELSANDPOLARIZATIONPROPERTIESCANBE MEASUREDBYUSINGTHE)&INTERFACE)FASAMPLEOFTHELOCALOSCILLATOR OUTPUTCANBEOBTAINED MIXINGTECHNIQUESCANBEUSEDSOTHATNETWORK ANALYZER INSTRUMENTATION CAN BE USED )F THE PERFORMANCE OF AhFIRST ARTICLEvMODELFORHIGHPRODUCTIONDESIGNSISBEINGTESTEDTODETERMINE DESIGNCOMPLIANCE MODIFICATIONSOFTHEFIRSTARTICLETOSAMPLETHEOUTPUT OFTHESYSTEMS,.!CANBEUSEDTOOBTAINAN2&SAMPLE)NTHISWAY DESIGNCOMPLIANCECANBEESTABLISHED ANDOTHERTESTTECHNIQUESCANBE USEDINPRODUCTIONTESTINGTOASSUREPROPEROPERATIONONAQUALITATIVE BASIS 0RODUCTION UNITS CAN BE TESTED BY SIGNAL INJECTION TECHNIQUES WHERE TEST SIGNALS ARE INJECTED INTO THE ANTENNA FEED APERTURE MUCH LIKEHATCOUPLERSAREUSEDINTHERMALVACUUMTESTING 4HE '4 OF THE USERS INTEGRATED ANTENNA CAN BE ESTABLISHED BY RADIOSOURCETECHNIQUES4HISASSUMESTHEANTENNAAPERTUREISLARGE ENOUGHTOALLOWSOLARRADIOSOURCEMEASUREMENTS)FTHISISNOTTHECASE


COMPARATIVE '4 MEASUREMENTS CAN BE MADE USING AN ANTENNA THAT CANBEMEASUREDBYRADIOSOURCETECHNIQUESANDBYSEPARATELYCOMPAR INGTHE3.2VALUESWHENBOTHANTENNASAREILLUMINATEDBYTHESAME SIGNALSOURCE)NSOMECASES THEMEASURED'4ISADEQUATETOEVALUATE PERFORMANCE)NOTHERCASES THEANTENNAGAINANDTHERECEIVERNOISE FIGUREAREDESIREDMEASUREMENTPARAMETERS3UCHMEASUREMENTSCAN BEPERFORMEDUSINGSYSTEMNOISETEMPERATUREMEASUREMENTTECHNIQUES PREVIOUSLYDISCUSSED3PECIFICALLY THERECEIVERNOISETEMPERATURECANBE MEASUREDBYTERMINATINGTHEFEEDAPERTUREWITHANABSORBERANDMEA SURINGTHEOUTPUTNOISEPOWERLEVELSWHENTHEABSORBERISATANAMBIENT TEMPERATURE AND WHEN THE ABSORBER IS IMMERSED IN LIQUID NITROGEN PROVIDINGA+REFERENCETEMPERATURE4HISMEASUREMENTCONSTITUTES AHOTCOLDLOADMEASUREMENTOFTHERECEIVERWITHTHEREFERENCETERMI NALBEINGTHEAPERTUREPLANEOFTHEFEEDHORN4HERESULTING9FACTOR MEASUREMENTALLOWSDETERMINATIONOFTHERECEIVERNOISETEMPERATURE 4HE FEED CAN BE ASSEMBLED INTO THE REFLECTOR AND THE ANTENNA NOISE TEMPERATURETHENMEASURED4HENOISEPOWERLEVELSAREMEASUREDWHEN THEANTENNAFEEDISENCLOSEDBYTHEABSORBERATANAMBIENTTEMPERATURE ANDWHENTHEANTENNAISPOINTEDATTHEELEVATIONANGLEWHERETHE'4 MEASUREMENTSWEREPERFORMED 4HEMEASUREMENTOFACTIVEANTENNAARRAYSISACONSIDERABLYMORE INVOLVEDANDCOSTLYENDEAVOR4HEINDIVIDUALACTIVEELEMENTSCOMPRISING THEARRAYDESIGNMUSTSATISFYAMPLITUDEANDPHASETRACKINGTOLERANCES TOMAINTAINARRAYPERFORMANCE4HEELEMENTSFOROPERATIONALUSEARE TYPICALLYSELECTEDFROMALARGERLOTOFELEMENTSBASEDONTHEIRAMPLITUDE ANDPHASETRACKINGTOLERANCES4HEREQUIREDNUMBEROFELEMENTSINTHIS SELECTIONMUSTEXCEEDTHENUMBERINTHEARRAYTOACCOUNTFORREPLACE MENTSOFELEMENTSTHATDEVELOPSHORTFALLSINTHESUBSEQUENTASSEMBLY ANDTESTINGPHASES4HESELECTEDACTIVEELECTRONICDEVICESARESUBJECTED TOTHEREQUIREDBURN INPERIODANDTESTINGISPERFORMEDTOASSUREAN ADEQUATE NUMBER OF DEVICES EXIST AT THAT POINT NOT ONLY TO POPULATE THEARRAYBUTALSOTOPROVIDEREPLACEMENTSFORFAILEDUNITSUNCOVERED INSUBSEQUENTTESTING !SIMILARPROCESSISUSEDTOSELECTTHEPHASESHIFTERELEMENTSUSEDIN THEDESIGN4HETOLERANCEREQUIREMENTSATEACHBITPOSITIONAREEXAM INEDALONGWITHINSERTIONLOSSTOSELECTANADEQUATENUMBEROF UNITS FORBOTHTHEARRAYOPERATIONANDANALLOWANCEFORREPLACEMENTOFUNITS SUBSEQUENTLYDETERMINEDTOHAVESHORTCOMINGS4HECONTROLCIRCUITRY NEEDEDFORPHASESHIFTERCOMMANDINGSHOULDBEMEASUREDANDVERIFIED ATTHISTIME 4HEASSEMBLYOFTHEARRAYBEGINSBYINTEGRATINGTHESELECTEDUNITSINTO SUBASSEMBLIESTHATWILLCOMPRISETHEOVERALLARRAYDESIGN4ESTINGOFTHE ARRAY SUBSYSTEMS INCLUDES EVALUATING NOT ONLY THEIR 2& PERFORMANCE BUTALSOTESTINGENVIRONMENTALSUITABILITY/PERATIONAFTERVIBRATIONAND

#HAPTER %IGHT

THERMALCYCLINGCANBEUSEDTOIDENTIFYSHORTCOMINGSATTHESUBSYSTEM LEVEL4HEOBJECTIVEISTODETERMINEPOTENTIALSHORTFALLSINTHESUBSYSTEMS ATTHELOWESTPOSSIBLELEVELTOREDUCETHEPOSSIBILITYOFLATERREPLACEMENTS THATDELAYTHESCHEDULEASARESULTOFCOMPONENTREPLACEMENTANDPENALTY TESTINGNEEDEDTOASSURETHATTHEINTEGRATEDASSEMBLYAFTERCOMPONENT REPLACEMENTCOMPLIESWITHREQUIREMENTS!SURPLUSOFSUBSYSTEMSTHAT HAVECOMPLETEDTHEREQUIREDTESTINGISNEEDEDSOTHATUNITREPLACEMENTS ARENOTDELAYEDBYADDITIONALTESTINGATTHESUBSYSTEMLEVEL&URTHERINTE GRATIONOFTHESUBSYSTEMUNITSISTHENPERFORMED ANDTESTINGATEACHPOINT OFTHEINTEGRATIONISREQUIREDTOREDUCETHEPOSSIBLENEEDFORREPLACEMENT ELEMENTS!GAIN ENVIRONMENTALTESTINGASTHEARRAYASSEMBLYINTEGRATION PROCEEDSISRECOMMENDEDTOIDENTIFYPOTENTIALSHORTFALLS)NDEPENDENTOF THEIRAPPLICATION CABLESANDCONNECTORSARETHELEASTRELIABLEELEMENTS OFSATELLITESYSTEMS!RRAYANTENNASREQUIREALARGENUMBEROFINTERFACES BETWEENSUBASSEMBLIES ANDTHUSTHEINTEGRITYOFTHEIRINTERCONNECTIONS MUSTBEVERIFIEDATEACHSTAGEOFTHEASSEMBLYPROCESS-ECHANICALAND THERMALTESTINGPROVIDESAMEANSOFIDENTIFYINGINTERCONNECTIONSHORTFALLS ANDREDUCESTHERISKOFSUBSEQUENTREPLACEMENTANDREQUIREDRETESTING 0ERFORMINGSOMEENVIRONMENTALTESTINGDURINGTHEPROCESSOFASSEMBLING THEARRAYISPRUDENTBECAUSETHEREPLACEMENTOFFAILEDARRAYCOMPONENTS ATTHEASSEMBLYLEVELISGENERALLYEASIERANDMOREEFFICIENTCOMPAREDTO DISASSEMBLINGAFULLYCOMPLETEDARRAYTOREPLACEFAILEDELEMENTSINLOWER ARRAYASSEMBLIES !RRAYDESIGNSDEPENDONTHEAMPLITUDEANDPHASETRACKINGPERFOR MANCEOFTHEELECTRONICS ANDPOTENTIALVARIATIONSMUSTBEEVALUATEDIN THEIRTESTING4HEAMPLITUDEANDPHASETRACKINGOFTHEARRAYELECTRONICS DEPENDINPARTONTHEIRTHERMALENVIRONMENT WHICHFORTHESPACESEG MENTDEPENDSONTHEPERFORMANCEOFTHETHERMALCONTROLSYSTEMFORTHE ARRAY2ECEIVEANDTRANSMITARRAYSALSOHAVEDIFFERENTTESTISSUES 2ECEIVE ARRAYS REQUIRE ATTENTION TO ESTABLISHING THE SYSTEM NOISE TEMPERATURE4HE RECEIVE ARRAYS ARE OPERATED IN THE LINEAR REGION OF THEDEVICES4HERMALCONTROLVARIATIONSANDPOWERSUPPLYFLUCTUATIONS ALLAFFECTTHEAMPLITUDEANDPHASETRACKINGPERFORMANCE ANDTHEARRAY SENSITIVITYTOTHESEVARIATIONSMUSTBEEVALUATED&ORSATELLITEUPLINK DESIGNS THE '4 MUST BE ESTABLISHED! COMPARATIVE MEASUREMENT FOREXAMPLE CANBEMADEBYMEASURINGTHEDIFFERENCEINTHE3.2OF THEARRAYANDTHE3.2OFASTANDARDSYSTEM ANDTHEANTENNAS'4 ISDERIVEDFROMTHE3.2DIFFERENCES4HEREFERENCESTANDARDSYSTEM TYPICALLYISCONFIGUREDFROMASTANDARDGAINHORNANDAPREAMPLIFIER 'ENERALLY MEASUREMENTSOFUPLINKARRAYANTENNASAREPERFORMEDIN INDOORFACILITIESTOPROTECTTHEFLIGHTHARDWARE)NDOORFACILITIESENVELOPE THEANTENNAINANAMBIENTNOISETEMPERATUREENVIRONMENT WHEREAS ON ORBIT THEANTENNAEXPERIENCESANAMBIENTNOISETEMPERATUREOVER THEANGULARREGIONSUBTENDEDBYTHEEARTHANDTHEREMAININGANGULAR


REGIONHASA+COSMICBACKGROUNDNOISETEMPERATURE)FCOMPARATIVE '4 MEASUREMENTS ARE MADE IN INDOOR FACILITIES THE ANTENNA NOISE TEMPERATUREMUSTBECORRECTEDTOACCOUNTFORTHEPORTIONSOFTHEON ORBIT FIELD OF VIEW HAVING THE COSMIC BACKGROUND TEMPERATURE /NE WAYTODETERMINETHEARRAYANTENNASSYSTEMNOISETEMPERATUREISBY COMPARING THE ARRAYS RECEIVER NOISE TEMPERATURE REFERENCED TO THE ARRAYS APERTURE PLANE4HE SYSTEM NOISE TEMPERATURE COMPRISED OF THE ANTENNA AND RECEIVER NOISE TEMPERATURES MUST BE ESTABLISHED 4HERECEIVERNOISETEMPERATUREISDETERMINEDBYMEASURINGTHEOUTPUT NOISEPOWERWHENTHEARRAYAPERTUREISTERMINATEDBYANABSORBER LINED FOAMCONTAINERATANAMBIENTTEMPERATUREANDWHENTHEABSORBERIS IMMERSEDINLIQUIDNITROGENATA+TEMPERATURE4HERECEIVERNOISE TEMPERATURE IS OBTAINED FROM THESE TWO NOISE MEASUREMENTS USING STANDARD9FACTORTECHNIQUES4HISMEASUREMENTINCLUDESTHEIMPACTOF ARRAYLOSSES4HERECEIVERNOISETEMPERATUREDETERMINEDINTHISWAYIS REFERENCEDTOTHEARRAYSAPERTUREPLANE7ITHINTHEMEASUREMENTFACIL ITY THE ANTENNA NOISE TEMPERATURE REFERENCED TO THE APERTURE PLANE IS THE AMBIENT TEMPERATURE4HE ARRAYS ANTENNA NOISE TEMPERATURE WHENON ORBITCANTHENBECALCULATEDUSINGTHEEMISSIONBACKGROUND TEMPERATUREANDARRAYPATTERNSFOLLOWINGTHEPROCEDURESDESCRIBEDIN #HAPTER4HEON ORBITEMISSIONBACKGROUNDINCLUDESANAMBIENTTEM PERATUREOVERTHEEARTHSFIELDOFVIEWANDA+COSMICBACKGROUNDFOR THEREMAININGFIELDOFVIEW4HISEMISSIONBACKGROUNDISPARTICULARLY IMPORTANTBECAUSEARRAYDESIGNSENDEAVORTOMINIMIZETHENUMBEROF ARRAYELEMENTSBYALLOWINGGRATINGLOBESTOEXISTBEYONDTHEEARTHS FIELDOFVIEW4HEEMISSIONCONTRIBUTIONTOTHEANTENNANOISETEMPERA TURE FOR THE FIELD OF VIEW BEYOND THE EARTH IS COUPLED BY THE ARRAY GRATINGLOBES WITHTHERESULTTHATTHEARRAYSANTENNANOISETEMPERA TUREISLOWERTHANTHEAMBIENTTEMPERATUREOFTHEEARTHSBACKGROUND 4HEON ORBIT'4ISDETERMINEDFROMTHEMEASURED'4INTHEFACILITY MULTIPLIEDBYTHERATIOOFTHESYSTEMTEMPERATUREWHENTHECALCULATED ON ORBITANTENNANOISETEMPERATUREISUSEDANDTHESYSTEMNOISETEM PERATUREWHENTHEAMBIENTANTENNANOISETEMPERATUREISUSED 4RANSMITARRAYSHAVEADDITIONALCHALLENGES4HEARRAYDEVICESMUST BEDRIVENTOTHEIRDESIGNOPERATINGPOINT GENERALLYCLOSETOSATURATION 4HUSTHEOPERATINGPOINTOFTHEARRAYMUSTBEMAINTAINED4HELOWPOWER EFFICIENCYANDGAINOFTHESEDEVICESRESULTINSIGNIFICANTTHERMALDISSIPA TION4HEEVALUATIONOFTHETHERMALDESIGNISACRITICALISSUE4HERMAL CONTROL MUST BE FURNISHED DURING EVALUATION BUT THE ON ORBIT PERFOR MANCEOFTHETHERMALCONTROLMUSTBEDETERMINED4HEPRESENCEOFINTER MODULATIONPRODUCTS SPURIOUSRESPONSES HARMONICS AND0)-SPASSIVE INTERMODULATIONPRODUCTS MUSTBEIDENTIFIEDINTHEMEASUREMENTS "ECAUSEOFTHELONGLIFETIMEREQUIREDBYSATELLITEOPERATION THESENSITIV ITYTOELEMENTFAILURESINTHEARRAYMUSTBEADDRESSEDINTHEMEASUREMENT

#HAPTER %IGHT

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#HAPTER %IGHT

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&IGURE 5NSTABLERESPONSESFORWRONGSENSEPOLARIZATION;=

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#HAPTER .INE

ALTERNATIVEDESIGNAPPROACHESFORTHEANTENNASYSTEMCANEXIST)NSUCH CASES APLANANDCRITERIAMUSTBEDEVISEDTOSELECTTHEFLIGHTDESIGN4HIS PLANREQUIRESADDRESSINGDIFFERENCESINTHEPERFORMANCECAPABILITIESOF THE DESIGN AND THE RELATIVE DEVELOPMENT RISKS OF ALTERNATIVE DESIGN APPROACHES"ASICPARAMETERS GAIN PATTERNCOVERAGE VEHICLEEFFECTS POLARIZATIONPURITY ANDSOONAREMEASUREDTOESTABLISHTHEDESIGNS2& COMPLIANCE2&TESTINGINTHISPHASETYPICALLYCAPITALIZESONGENERAL PURPOSEFACILITIESANDINSTRUMENTATIONANDISCONDUCTEDONBREADBOARD ORPROTOTYPEANTENNAHARDWARESINCETHEPRINCIPALOBJECTIVEISTOESTAB LISHTHE2&PERFORMANCE$EPENDINGONTHEDEVELOPMENTSTATUSOFTHE DESIGN THE NEED FOR ENGINEERING MODEL DESIGNS AND THEIR REQUIRED FIDELITYMUSTBEDEVISEDTODEMONSTRATE2&PERFORMANCECOMPLIANCEAND TOADDRESSISSUESFORFLIGHTSUITABILITY4HEEVOLUTIONOFPASTHERITAGE DESIGNS IS AN IMPORTANT FACTOR IN DETERMINING THE EXTENT OF REQUIRED ENGINEERINGMODELDEVELOPMENT!NYDESIGNASPECTSTHATAREUNIQUEOR FAILTOHAVEPREVIOUSFLIGHTHERITAGEARETESTEDTOREDUCEPROGRAMRISK ANDTOALLOWTIMEINTHESCHEDULETOADDRESSASPECTSWHEREDEVELOPMENT TESTINGHASIDENTIFIEDSHORTFALLSINPERFORMANCE!SSESSMENTSOFDEVEL OPMENTRISKACCOMPANYTHISSELECTIONPROCESSANDSUCHASSESSMENTSARE GENERALLYAPARTOFTHESELECTIONOFTHEFLIGHTDESIGN 4HEDEVELOPMENTTESTINGPROVIDESEXPERIENCEWITHTHETESTFACILITIES INSTRUMENTATION METHODOLOGIES DATAPROCESSING MEASUREMENTUNCER TAINTY ASSESSMENTS ADEQUACY OF TEST POINTS AND TELEMETRY DATA AND OPERATIONS TO TEST SOFTWARE!NTENNA CONTROL REQUIREMENTS AND ASSO CIATED SUPPORTING SOFTWARE MUST BE DEMONSTRATED FOR BOTH TEST AND OPERATIONS)NTERFACEREQUIREMENTSWITHOTHERPAYLOADELECTRONICSMUST ALSOBEESTABLISHEDATTHISTIME%XPERIENCEINDEVELOPMENTTESTINGALSO IDENTIFIESTHENEEDFORADDITIONALAUGMENTATIONOFTESTMETHODOLOGIES DATAPROCESSING ANDTESTCONTROLSOFTWAREREQUIREMENTSNEEDEDTOSUP PORTFUTUREQUALIFICATIONTESTING!STHECOMPLEXITYOFANTENNADESIGNS INCREASES SOFTWAREINCREASINGLYBECOMESMOREIMPORTANTINCONDUCT INGTHEREQUIREDTESTING ANDVERIFICATIONOFSOFTWAREDURINGDEVELOP MENT TESTING REDUCES RISK DURING SUBSEQUENT QUALIFICATION TESTING $EVELOPMENTTESTINGNOTONLYESTABLISHESTHEANTENNADESIGNSCOMPLI ANCEWITHSYSTEMREQUIREMENTSBUTALSOPROVIDESDATATOSUPPORTOTHER 2&ANTENNATESTINGREQUIREMENTS3UCH2&REQUIREMENTSINCLUDE%-) %-#ELECTROMAGNETICINTERFERENCEELECTROMAGNETICCOMPATIBILITY %3$ ELECTROSTATICDISCHARGE MULTIPACTION CORONA 0)-PASSIVEINTERMODU LATION ANDOTHERISSUES%NVIRONMENTALTESTINGALSOMUSTBEADDRESSED DURINGDEVELOPMENTTESTINGTOESTABLISHDESIGNSUITABILITY3UCHTESTING CANIMPOSEADDITIONALREQUIREMENTSTOMONITOR2&PERFORMANCEDURING THEENVIRONMENTALTESTING ANDTHEDEVELOPMENTANDDEMONSTRATIONOF SUITABLEMONITORINGTECHNIQUESDURINGTHEDEVELOPMENTPHASEREDUCERISK DURINGQUALIFICATIONTESTING&OREXAMPLE 2&MEASUREMENTINTHERMAL


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#HAPTER .INE

&IGURE 4HEENVIRONMENTALTESTPROCESS;=

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#HAPTER .INE

THEKEYPERFORMANCEFEATURESOFTHEANTENNADESIGNINTHEPERFORMANCE EVALUATION AND DEMONSTRATE THAT THE FLIGHT HARDWARE PERFORMANCE MATCHESTHATESTABLISHEDDURINGDEVELOPMENT 4HEQUALIFICATIONTEST ING PUTS INCREASED EMPHASIS ON SYSTEM LEVEL PARAMETERS COMPARED TO DEVELOPMENTTESTING RATHERTHANTHECOMPONENT LEVELREQUIREMENTSUSED INDEVELOPMENTTESTINGTHATDEMONSTRATEDESIGNCOMPLIANCE 2ECENT TRENDS IN SATELLITE ANTENNAS INCLUDE DESIGNS THAT INTEGRATE 2&ELECTRONICSWITHTHEANTENNAASSEMBLY7HENACTIVEELECTRONICSARE INTEGRATEDINTOTHEANTENNASYSTEM ITISESSENTIALTOIDENTIFYTHEINFANT MORTALITYINACTIVEELEMENTSASSOONASPOSSIBLETOAVOIDCOSTANDSCHED ULE PENALTIES RESULTING FROM REPLACEMENT OF AN INTEGRATED ASSEMBLY )N ADDITION TO THE NORMAL BURN IN REQUIREMENTS FOR SUCH ELECTRONICS EVALUATIONOFTHERMALCONTROLDESIGNSFORPROTECTINGSUCHELECTRONICSIS REQUIRED!DDITIONALLY THETESTPARAMETERSWHENACTIVEELECTRONICSARE INTEGRATEDINTOTHEANTENNASYSTEMARETYPICALLY'4FORRECEIVEANTEN NASAND%20FORTRANSMITANTENNASRATHERTHANGAINVALUESFORPASSIVE ANTENNA DESIGNS4HE DYNAMIC RANGE OF RECEIVING ANTENNAS AND THE LINEARITYOFTRANSMITANTENNASAREKEYPERFORMANCEREQUIREMENTSFOR SUCHDESIGNS ANDCHARACTERIZATIONSTODEMONSTRATEDESIGNCOMPLIANCE PLACEDEMANDSONTHEREQUIREDTESTINSTRUMENTATIONTOFULLYCHARACTER IZETHEDESIGNCOMPLIANCE !DDITIONALTESTINGATTENTIONDEPENDINGONTHESPECIFICIMPLEMENTA TIONISIMPOSEDTOVERIFYTHERELIABILITYOFANTENNADEPLOYMENTMECHA NISMS AND GIMBALS USED TO REPOSITION THE ANTENNAS COVERAGE AREAS 3UCHTESTINGISPERFORMEDATTHESUBSYSTEMANDINTEGRATEDSPACECRAFT LEVELS!NTENNADESIGNSTHATUSEMECHANICALPOSITIONINGINTHEIROPERA TION REQUIRE TESTING TO ENSURE THAT THE REQUIRED RANGE OF MECHANICAL TRAVELWHENINTEGRATEDWITHTHESPACECRAFTCANBEACHIEVEDANDTHATTHE ENCODERSTHATMEASURETHATPOSITIONINGACCURATELYREPORTTHEANTENNAS BORESIGHTPOSITIONING2ANGEOFMOTIONTESTINGADDITIONALLYVERIFIESNOT ONLYTHATTHEMOTIONCANBEPERFORMEDBUTALSOVERIFIESCRITICALCLEARANCE REQUIREMENTSTHATSPECIFYTHEMINIMALCLEARANCEBETWEENTHEANTENNA AND SPACECRAFT COMPONENTS #RITICAL CLEARANCE VALUES ARE SELECTED TO PROVIDEMARGINTOACCOUNTFORTHERMALCHANGESINDIMENSIONSTHATCOULD RESULT IN RESTRICTING MOTION OF THE ANTENNA4HE ANTENNA POSITIONING ON THE SPACECRAFT IS VERIFIED BY DEMONSTRATING THE COINCIDENCE OF THE MECHANICAL AND ELECTRICAL ALIGNMENTS4HE MECHANICAL AND ELECTRICAL ALIGNMENTS ARE ESTABLISHED DURING THE ANTENNAS 2& EVALUATION AND OPTICALALIGNMENTCUBESAREOFTENATTACHEDTOTHEANTENNASTRUCTURESO THEESTABLISHEDALIGNMENTCANBEUSEDDURINGSPACECRAFTASSEMBLYAND INTEGRATION %NVIRONMENTAL REQUIREMENTS ARE A MAJOR PART OF THE QUALIFICATION TESTING4HE ENVIRONMENTAL TESTING OBJECTIVES ARE TWOFOLD ASSURE THE FLIGHT HARDWARE CAN WITHSTAND THE LAUNCH AND ORBITAL ENVIRONMENTS


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#HAPTER .INE

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#HAPTER .INE

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#HAPTER .INE

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#HAPTER .INE

7HILETHEINTERNALPAYLOADELECTRONICSASSESSMENTISASIGNIFICANT ACTIVITY THE %-)%-# ISSUES FOR THE SPACECRAFT ANTENNAS PROVIDE DESIGNANDTESTCONCERNSTHATRESULTINASIGNIFICANTACTIVITYASWELL 4HE ANTENNAS ARE GENERALLY ISOLATED FROM THE INTERNAL %-)%-# SOURCESBYTHESATELLITEBUSSHIELDING4HEOPERATINGFREQUENCIESAND OTHERFREQUENCYSOURCESUSEDINFREQUENCYCONVERSIONARETHEPRINCIPAL CONCERNSINADDRESSINGANTENNASYSTEM%-)%-#ISSUES0ARTICULAR ATTENTIONSHOULDBEGIVENTOTHOSEPOTENTIALPATHSWHEREWORKMAN SHIPCANCOMPROMISETHE%-)%-#SUSCEPTIBILITY)NMANYCASES THE COUPLINGBETWEENPAYLOADANTENNASOCCURSINTHENEARFIELDOFTHESE ANTENNASBECAUSEOFTHELIMITEDPHYSICALSEPARATIONOFTHEANTENNAS MOUNTED ON THE SPACECRAFT %STIMATED VALUES OF ANTENNA NEAR FIELD COUPLINGPROVIDEAPRELIMINARYASSESSMENTOF%-)%-#SUSCEPTIBILI TIES )F POTENTIAL CONCERNS RESULT FROM THESE PRELIMINARY ESTIMATES MEASUREMENTSOFTHEACTUALANTENNAANDMOCKUPSOFTHESURROUND ING SPACECRAFT STRUCTURE CAN BE USED TO REFINE THE PRELIMINARY ESTI MATE4HESEMEASUREMENTSAREREQUIREDTODETERMINETHEOUT OF BAND RESPONSEOFTHEANTENNASASWELLASADDRESSNEARFIELDCOUPLINGATOUT OF BANDFREQUENCIES)NITIALMEASUREMENTSDURINGDEVELOPMENTCANBE PERFORMEDTOADDRESSTHEPOTENTIALOF%-)%-#SUSCEPTIBILITY 4HEINTEGRATEDFLIGHTHARDWAREISMEASUREDINSPECIALIZED%-)FACILI TIES4HEAMBIENT2&ENVIRONMENTOFTHESEFACILITIESISESTABLISHEDWITH THETESTSETSACTIVATEDTOIDENTIFYFACILITYANDEQUIPMENT2&LEVELSTHAT WOULD DEGRADE OR OBSCURE REQUIRED MEASUREMENT SENSITIVITIES 4HE SPACECRAFTHARDWAREISTHENACTIVATEDANDTESTEDFORALLOPERATIONALFUNC TIONSTOASSURE%-)%-#COMPLIANCE0ARTICULARATTENTIONISFOCUSEDON THEPREVIOUSLYIDENTIFIEDPATHSWITHPOTENTIALSHORTFALLSANDTHOSEAREAS HAVINGPOTENTIALWORKMANSHIPISSUES/FTENSUCHAREASAREEXAMINED WITHPROBESANDSPECTRUMANALYZERINSTRUMENTATIONTOIDENTIFYSOURCES OFLEAKAGE!GENERALSURVEYOF2&EMISSIONSISALSOREQUIREDTOASSURE UNANTICIPATEDEMISSIONSARENOTPRESENT 5SER3EGMENT!NTENNA4ESTING 4HE EVALUATION OF USER ANTENNAS IS GENERALLY STRAIGHTFORWARD 5SER ANTENNASARENOTSUBJECTTOTHESPACEQUALIFICATIONANDFLIGHTHARDWARE PROTECTIONREQUIREMENTSOFSPACESEGMENTANTENNATESTING5SERANTENNA EVALUATIONS CAN GENERALLY CAPITALIZE ON GENERAL PURPOSE FACILITIES AND INSTRUMENTATIONCAPABILITIES5NLIKETHESPACESEGMENTANTENNASTHAT CANNOT BE SERVICED AND MAINTAINED ON ORBIT RELIABILITY DOES NOT HAVE THESAMECRITICALIMPORTANCE.ONETHELESS USERANTENNASPROVIDESOME TESTCHALLENGESANDREQUIREMENTSPECULIARTOSPECIFICAPPLICATIONS&OR EXAMPLE SHIPBOARD INSTALLATIONS IMPOSE ENVIRONMENTAL REQUIREMENTS AND A MEANS OF PLATFORM MOTION COMPENSATION TYPICALLY SENSED BY


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#HAPTER .INE

THETRANSMITTEROFFTOAVOIDTRANSMITTERDAMAGE7HENTHETRANSMITTER ISROUTEDTOTHEANTENNATHROUGHROTARYJOINTS THE6372ATALLPOSSIBLE POSITIONSMUSTBEESTABLISHEDANDCOMPAREDTOTHE6372VALUETHAT TURNSOFFTHETRANSMITTER&INALLY THEOUT OF BANDNOISECHARACTERISTICS OF THE TRANSMITTER MUST BE ESTABLISHED AND THE RADIATED %20 LEVELS FOR THESE OUT OF BAND COMPONENTS MUST BE DETERMINED TO ASSURE THE SYSTEMDOESNOTINTERFEREWITHOTHERSYSTEMS7HENINTEGRATEDWITHTHE ANTENNA FURTHERTESTINGISREQUIREDTODEMONSTRATEPROPEROPERATION OFTHEDIPLEXER!SIMPLETESTALONGWITHAMEANSOFSPECIFICATION ISTO MEASURETHECHANGEINTHERECEIVERSNOISELEVELWHENTHETRANSMITTER ISTURNEDONANDOFF&URTHERTESTINGISNEEDEDTOINSURETHETRANSMITTER DOESNOTSATURATETHERECEIVERATOUT OF BANDFREQUENCIES ,ARGERANTENNASREQUIREEVALUATIONOFTHEANTENNAACQUISITIONAND TRACKINGPERFORMANCE!SWILLBEDISCUSSED THESEANTENNASOFTENHAVE EXCESSIVEFARFIELDREQUIREMENTS BUTMAYHAVEINSUFFICIENTPERFORMANCE TOALLOWEVALUATIONUSINGRADIOSTARSTODETERMINEANTENNAGAINCHAR ACTERISTICS-EASUREMENTSAREREQUIREDTOEVALUATEANTENNAPOINTING ACCURACY AND DYNAMIC TRACKING ACCURACY TO MAINTAIN ANTENNA ALIGN MENTWITHTHESATELLITE4HEACTUALSATELLITE IFAVAILABLE PROVIDESAN OPPORTUNITYFORSUCHTESTING&ORANTENNASYSTEMAPPLICATIONSFORRECEP TIONFROMLOW ALTITUDESATELLITES THEABILITYOFTHERECEIVERANDANTENNA TOACQUIRETHESIGNALINASPECIFIEDTIMEPERIODORBYASPECIFIEDELEVATION ANGLEREQUIRESDEMONSTRATION4HEACQUISITIONANDTRACKINGEVALUATION ALSONEEDSTOVERIFYTHATTHEANTENNAHASACQUIREDTHESATELLITEONITS MAINBEAMRATHERTHANASIDELOBE4HECOINCIDENCEOFTHERECEIVEAND TRANSMITBORESIGHTAXESALSOMUSTBEDEMONSTRATED 4WODIFFERENTCLASSESOFUSERANTENNASEXISTANDTHETESTINGMETHOD OLOGIESDIFFERINTHETWOCASES/NECLASSOFUSERANTENNASISPRODUCED IN A HIGH VOLUME AND A TEST METHODOLOGY CAPABLE OF PROVIDING HIGH CONFIDENCEINTHERESULTSWHILEBEINGCONDUCTEDINANEFFICIENTMANNER IS REQUIRED4HE SECOND CLASS OF USER ANTENNAS HAS A LIMITED PRODUC TION VOLUME 4HESE USER ANTENNAS ARE TYPICALLY LARGE FIXED DESIGNS THATHAVESPECIALIZEDREQUIREMENTSTOMEETSPECIFICAPPLICATIONS4HE ANTENNA TESTING FOR THIS CLASS OF ANTENNAS IS GENERALLY PERFORMED FOR EACHANTENNASYSTEM 4HE FIRST CLASS OF USER ANTENNAS IS PRODUCED IN LARGE VOLUMES AND TYPICALLYUSESRELATIVELYSMALLREFLECTORANTENNASFORCOSTANDPERFOR MANCE REASONS! KEY CHALLENGE FOR THIS CLASS OF TERMINAL DESIGNS IS ACCOMPLISHINGTESTINGONAPRODUCTIONBASISWITHHIGHCONFIDENCE WHILE ATTHESAMETIMECONTROLLINGCOSTS$ETAILEDTESTINGOFINDIVIDUALPRODUC TIONITEMSFORTHISCLASSOFUSERANTENNAWOULDIMPOSEIMPRACTICALTIME ANDRESOURCEREQUIREMENTS4HECOSTLIMITATIONSOFSUCHTERMINALSALSO DEPEND ON IMPLEMENTATIONS BASED ON DESIGN SIMPLICITY USING ESTAB LISHEDTECHNIQUESWITHPREVIOUSOPERATINGEXPERIENCE4ESTINGFORTHIS


CLASSOFUSERANTENNASPROCEEDSBYDEMONSTRATINGTHATAhFIRSTARTICLEv COMPLIESWITHSYSTEMREQUIREMENTS ANDTHENDEVISINGTESTTECHNIQUES TOASSUREPRODUCTIONITEMSMAINTAINTHEPERFORMANCEACHIEVEDBYTHE FIRSTARTICLEBYTESTINGALIMITEDNUMBEROFRANDOMLYSELECTEDPRODUC TIONUNITS &OREXAMPLE ANTENNASFOR63!4APPLICATIONSAREGENERALLYSIMPLE REFLECTORDESIGNSTHATCANBEMANUFACTUREDINEXPENSIVELY SATISFYESTAB LISHED MANUFACTURING TOLERANCE AND SIDELOBE ENVELOPE REQUIREMENTS ANDHAVEPREVIOUSEXPERIENCEOFOPERATIONINAVARIETYOFENVIRONMENTS )NMANYCASES THEANTENNASREFLECTORANDPOSITIONERAREAVAILABLEAS #/43 ITEMS4HE RELATIVELY BROAD BEAMWIDTHS OF THESE DESIGNS GEN ERALLY PRECLUDE ANTENNA TRACKING REQUIREMENTS AND SINCE THE USERS TYPICALLY COMMUNICATE WITH GEOSYNCHRONOUS SATELLITES FIXED ANTENNA POINTINGSUFFICES4HEFEEDSYSTEMSAREAGAINSTRAIGHTFORWARDDESIGNS FOR COMMONLY USING FREQUENCY RANGES SUCH AS # AND +U BAND4HE PRINCIPAL CHALLENGES IN TESTING FOR SUCH DESIGNS IS ASSURING THAT THE FEED MANUFACTURING MAINTAINS THE REQUIRED POLARIZATION PURITY SINCE SATELLITESCOMMONLYUSEDFOR63!4APPLICATIONSUSEORTHOGONALPOLAR IZATIONTOOBTAINTHECAPACITYBENEFITSOFPOLARIZATIONREUSE4HETESTING FORSUCHDESIGNSISPRINCIPALLYINTHEDEVELOPMENTSTAGES WITHALIM ITEDAMOUNTOFSPOTTESTINGDURINGPRODUCTIONTOASSUREQUALITYCONTROL &OREXAMPLE POLARIZATIONPURITYIMPOSESMECHANICALTOLERANCESONTHE FEED ANDDEPENDINGONTHEMANUFACTURINGMETHODSTOOLINGWEAR FOR EXAMPLETHISCANRESULTININCREASEDCROSS POLARIZATIONLEVELS SOTHAT MECHANICALMEASUREMENTSONASPOTTESTINGBASISCANBEUSEDTOASSURE COMPLIANCEATAPRODUCTIONLEVEL 4HESECONDCLASSOFUSERANTENNASINCLUDESLARGERGROUNDTERMINALS THATHAVEALIMITEDPRODUCTIONVOLUMEANDMUSTSATISFYREQUIREMENTS SPECIFICFORTHESEAPPLICATIONS3UCHDESIGNSGENERALLYREQUIRETESTING EACHANTENNA4HESEDESIGNSHAVEMORECOMPLEXTESTINGREQUIREMENTS THAN THE FIRST CLASS OF HIGH PRODUCTION ANTENNAS AS A CONSEQUENCE OF THEIRPERFORMANCEREQUIREMENTS0ROGRAMAPPLICATIONSFORTHESELARGER GROUNDTERMINALSINCLUDE44#SERVICE MISSIONCONTROL USERSEGMENTS FORCOMMUNICATIONSATELLITES GATEWAYTERMINALSFORCOMMUNICATIONSAT ELLITES VERYHIGHDATARATECOMMUNICATIONS TERMINALSTOUPLOADDATA FORDIRECTBROADCASTSERVICES ANDREADOUTRECEIVEONLY TERMINALSFOR MISSIONDATAFROMDIRECTBROADCASTSATELLITES7HILEEACHAPPLICATION HAS SPECIFIC REQUIREMENTS GENERIC TEST ELEMENTS EXIST &OR EXAMPLE MOBILEUSERSHAVEREQUIREMENTSTOMAINTAINCONNECTIVITYWITHTHESATEL LITETHATARENOTANISSUEWITHFIXEDTERMINALS,ARGEGROUNDTERMINALS SUPPORTSATELLITEPROGRAMSASTHEYEVOLVEOVERALONGLIFETIME2ELIABILITY ANDOBSOLESCENCE INADDITIONTOUPDATEDREQUIREMENTSANDCAPABILITIES DICTATECOMPONENTREPLACEMENTS WHICHINTURNREQUIREINTERFACEDEFINI TIONANDSYSTEMTESTING&URTHER TODAYSREQUIREMENTSINCLUDEREMOTE

#HAPTER .INE

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#HAPTER .INE

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#HAPTER .INE

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Satellite Antenna System Evaluation Robert Dybdal

Index A Absolute gain level, 230–232, 243 Absorber-lined tunnels, for sidelobe control, 203–207 ACG (see Automatic gain control) Acoustic tests, 289 Acquisition cost, xii Active antenna arrays, 150, 263–266 Active aperture antennas, 188–191 Active receive and transmit antennas, 242–243 ACTS (see Advanced Communication Technology Satellite) ACU (antenna control unit), 95–96 A/D (see Analog to digital converters) Adaptive antennas: on compact ranges, 237–238 evaluation of, 257–262 for user segment, 207–212 Adaptive interference cancellation, 162–165, 177, 207–209 Adaptive uplink antennas, 180–188 angular resolution of, 183–184 beam repositioning for, 184–187 minimizing location differences with, 187–188 testing of, 259 Advanced Communication Technology Satellite (ACTS), 116–117, 124 Ae (effective aperture), 4 Aerospace ground equipment (AGE) tests, 243, 281 Aft antenna, 27–28 AGE tests (see Aerospace ground equipment tests) Aliasing, 41 Alignment (of antennas with signal direction), 48–49 Amplitude errors, in monopulse combining circuitry, 61–62 Amplitude imbalance, 62–64 Amplitude ripples, 14, 15 AM/PM distortion, 78 Analog aperture distributions, 41 Analog to digital converters (A/D), 86 Anechoic chambers, 228 Angular accuracy: of antenna tracking, 50–51 for closed-loop antenna tracking, 58 for step track, 54 Angular offset: for boresight measurements, 267 for step track, 54–55 Angular resolution, 183–184 Antenna control unit (ACU), 95–96 Antenna dispersion, 210 Antenna Measurement Techniques Association, ix Antenna noise temperature (Tant), 19–20, 252 Antenna parameters, 1–23 impedance, 12–18 polarization, 8–12 spatial characteristics, 2–7 system noise temperature, 18–21 for systems, 22–23 Antenna pointing, 49–50 Antenna response, to interference, 149–151

311

Antenna size, 2, 199 Antenna technology, xiv, 25–70 for antenna tracking, 49–70 array antennas, 41–44 arrays of high-gain antennas, 44–49 development of, ix earth coverage antennas, 32–35


Antenna technology (continued) narrow coverage antennas, 35–41 wide coverage antennas, 26–32 Antenna testing, xii–xiii, 225–274 (See also Space segment antenna testing; User segment antenna testing) adaptive, 257–262 and antenna tracking, 266–272 of antennas with integrated electronics, 262–266 facilities for, 226–238 gain standards for, 243–244 instrumentation for, 241–243 near field sampling, 238–241 radio source techniques, 244–257 and system evaluations, 272–274 Antenna tracking, 49–70, 266–272 boresight measurements in, 266–268 closed-loop, 57–60, 268–272 monopulse feed designs for, 60–65 open-loop, 51–53 signal acquisition issues in, 65–70 step track, 53–57 Aperture antennas, 2 Aperture fields, 3 Aperture size (spot beam antennas), 170 Application-specific integrated circuits (ASIC), xiv, 83, 87 Architecture(s) (See also System architectures) multiple-beam antennas, 179–180 space segment architectures, 74–95 Array time delay compensation, 49 Arrays: active antenna, 150, 263–266 array antennas, 41–44 Field Programmable Gate Array (FPGA), 87, 215 of high-gain antennas, 44–49 IRIDIUM array design, 176–177 receive, 264–265 thinned, 41, 182–183 transmit, 265–266 ASIC (see Application-specific integrated circuits) Attenuators, 18 Automatic gain control (ACG), 27–28, 153, 156 Auxiliary antennas, in adaptive cancellation, 209 Average combining efficiency (Cave), 46 Axial ratio (r), 8–9, 230

B Backdoor illumination, 146 Backlobe performance (wide coverage antennas), 29, 32 Beacon alignment technique, 48–49 Beam(s): arrangement of, in multiple-beam antennas, 172–173 multiple-beam antennas, 171–180 repositioning of (adaptive uplink antennas), 184–187 spot beam antennas, 168–171 Beam scanning, 38 Beamforming: in multiple-beam antennas, 180 by networks, 150 Beamsteering (point-to-point antennas), 193 Beamwidth (hp ), 5–6 BER (see Bit error rate)

312

Bessel functions, 239 Binary-phase-shift-keying modulation (see BPSK modulation) Bit error rate (BER), 125–127, 152, 155, 243 BITE capabilities (see Built-in test equipment capabilities) Boresight measurements (antenna tracking), 266–268 Boresight towers, 308 BPSK (binary-phase-shift-keying) modulation, 127 Built-in test equipment (BITE) capabilities, 152, 300, 302, 303, 307 Burnout (LNAs), 156–157

C C (combining efficiency), 45–46 Calibration (survey equipment), 142 Cancellation, adaptive interference, 162–165, 177, 207–209 Cassegrain configuration, 37, 38, 200, 212 Cassiopeia A, 307 Cave (average combining efficiency), 46 CCIR recommendations, for sidelobe envelopes, 201–202


CDMA systems (see Code division multiple access systems) CDR (see Critical design review) Channelization: subband, 80, 81 for user segments, 180 Circular polarization, 8, 12 Closed-loop antenna tracking, 57–60, 268–272 Co-channel interference, 138–139 Code division multiple access (CDMA) systems, 129, 200 Coherent error statistics, 15–18 Combination (of off-axis antenna beams), 60–61 Combining efficiency (C), 45–46 Commercial Orbital Transportation Services (COTS) products, 301 Commercial satellite applications, xii Communication satellites, applications of, xii–xiii Compact ranges, 229, 233–238 Computer modeling (of antenna performance), 6–7 Continuous wave (CW) tones, 77, 274 Control system response, in closed-loop tracking evaluations, 270 Corona, 293–294 Corporate feed structure (array antennas), 42 COTS (Commercial Orbital Transportation Services) products, 301 Coverage: areas of, 80–81 irregular, 169–171 spot, 177–178, 181–182 of TT&C antennas, 27 Critical design review (CDR), 282, 304 Cross track sampling, 56–57 Crosslink subsystems, 91–93 Crossover (multiple-beam antennas), 175–176 Crosstalk, in closed-loop tracking evaluations, 269 CW tones (see Continuous wave tones) Cygnus, 307

D D (directivity), 4–5 DEADEN (DEterministic ADaptive Environmental Nuller) technique, 164 Delay spread, 210 Demonstration testing, 300 (See also Development testing) Deployable surfaces, for reflector antennas, 40 Design(s): of adaptive antenna, 183, 257–258 antenna, 25 critical design review, 282, 304 hat coupler, 285 IRIDIUM array design, 176–177 monopulse feed design, 60–65 multimode feed, 60 offset reflector vs. Cassegrain, 212 Preliminary Design Review, 282, 304 process of, xiii–xiv of receivers, 154 of reflector antennas, 35–36 sidelobe cancellar, 259–260 ofsystems, xiii–xiv DEterministic ADaptive Environmental Nuller (DEADEN) technique, 164 Development testing: qualification testing vs., 287–288 for space segment antennas, 279–283 for user segment antennas, 302–303 Diagnostic capabilities (on-orbit satellites), 290–291

313

Dielectric lens antennas, 40 Difference beam, in closed-loop antenna tracking, 57–58 Difference pattern null depth (ND), 62 Difference patterns, evaluations of, 269 Digital beamforming techniques, 85–87 Digital quantization, 153 Digital transponders, 75, 85–89 Diode detectors, 221 Diode limiters, 157–158 Diplexers, 32–33, 96–97 Directivity (directive gain) (D), 4–5 Dissanayake, Allnutt, and Haidara model, 117 Dual reflector antennas, 37

E Earth coverage antennas, 32–35 Earth links, 93 Eb (energy per bit), 130 Effective aperture (Ae), 4


Effective radiated power (ERP), 22, 23 of active aperture antennas, 189–191 of antenna systems, 297 of array antennas, 42 in link analysis, 158–159 Efficiency: of active aperture antennas, 189–190 EHF (extremely high frequency) systems: aperture size for, 177 and hydrometeors, 113–124 limitations of, 108–125 measurement of weather effects on, 117–119 minimizing effects of wet antennas in, 120–125 and molecular absorption, 108–113 propagation impairments of, 105, 106 8PSK (phase-shift-keying) modulation, 127 Electroforming, 207 Electromagnetic interference/electromagnetic compatibility (EMI/EMC), 137 in development testing, 284, 285, 291, 305 susceptibility standards for, 146–148 Electron density, in ionosphere, 107 Electrostatic discharge (ESD), 284, 286, 291, 294–295 EMI/EMC (see Electromagnetic interference/electromagnetic compatibility) Energy per bit (Eb), 130 Environmental requirements (space segment antennas), 285–286, 288–289 Equalization (reflector antennas), 211 ERP (see Effective radiated power) Error correction encoding, 127–128 Errors (See also Bit error rate) in amplitude, 61–62 in closed-loop antenna tracking, 58 coherent error statistics, 15–18 in gain level, 254 ESD (see Electrostatic discharge) Extremely high frequency systems (see EHF systems)

F Far field, 2 Far field ranges, 227–233 Far field separation, 3, 227–228 Faraday rotation, 107 Fast Fourier transform (FFT), 86 FDMA (see Frequency division multiple access systems) Feed blockage loss (Lb), 36 Feed systems (point-to-point antennas), 193–194 FFT (fast Fourier transform), 86 Field of view (FOV): extension of, for acquisition, 65–70 of multiple-beam antennas, 172, 176–177 subtended by the earth, 100 Field probing, 308 Field Programmable Gate Array (FPGA), 87, 215 Filtering: at IF vs. RF level, 153 Kalman filtering technique, 94, 213 to mitigate interference, 159 out-of-band, 139 First article compliance, 299 Fixed pointing techniques, 51 Flux density values (of stars), 244 Footprint values, for spot beam antennas, 168 Fore antenna, 27–28

314

Fourier transform, 3, 239 FOV (see Field of view) FPGA (see Field Programmable Gate Array) Frequency(-ies): and link performance, 130–131 operation of reflector antennas at multiple, 38–39 Frequency division multiple access (FDMA) systems, 128, 200 Frequency hopping, 128 Frequency independent antennas, 29 Frequency plan, 80, 81 Frequency reuse, 160, 178 Frequency translating transponders, 74–84 Friis transmission formula, 129–130 Front door illumination, 146

G G (antenna gain), 3–4, 158 Gain level, 5–6 absolute, 230–232, 243 of array antennas, 41–42 errors in, 254 of high-gain antennas, 44–49


of multiple-beam antennas, 171–174 of space segment antennas, 130 standards for, 243–244 Gain loss (LTol), 39–40 Gain partitioning, 154 Geosynchronous satellites, 32, 43 crosslink operation with, 92–93 limitations of, 99 step track for, 55 GPS (global positioning system): monitors for on-orbit performance of, 214–217 satellites, 43–44 user antennas, 26 Graceful degradation, 43 Grating lobes (array antennas), 28, 44, 48 Gregorian configuration, 37 Ground terminals, for on-orbit measurements, 291 Ground-based radiometer, 117–119 G/T level: of antenna systems, 297 comparative measurements of, 308 of GPS monitoring antenna, 215 of integrated antennas, 262–263 radio source measurements of, 244–247 as system figure of merit for antennas, 18–19, 22–23 for user segment, 305

H Hat coupler designs, 285, 287 Hertz, Heinrich, ix High frequency structural simulators (HFSS), 30 High-gain antennas, arrays of, 44–49 High-gain dual reflector antennas, 37–38 Horn antennas, 32, 33 rolled edge, 33–35 for sidelobe control, 202 standard gain, 243–244 Hub and spoke arrangement, 74 Hybrid antenna networks, 61–64 Hydrometeors, 113–124

I I (received inference), 159 IF (instantaneous frequency) level, filtering at, 153 Illumination errors, on far field ranges, 231–232 Illuminators: for adaptive antenna testing, 260 for closed-loop antenna tracking, 270–271 for compact ranges, 233–234 for far field ranges, 229–230 Impedance, 1–2, 12–18 Implementation loss (receivers), 152 Incident level monitors, 218–222 Installation testing, 307 Instantaneous frequency (IF) level, filtering at, 153 Instrumentation, for antenna testing, 241–243 Integrated electronics, antennas with, 262–266, 288 Integration/acceptance testing, 300, 303 INTELSAT VI, 239 INTELSAT VII/VIIA, 81–82 Intentional interference, 137–139

315

Interference, 137–165 (See also Signal to noise + interference) antenna response to, 149–151 co-channel, 138–139 environment for, 138–149 examination of sources in, 144–146 and frequency translating transponders, 76–77, 79–80 out-of-band, 151, 153 receiver response to, 149 site surveys of, 139–144 terrestrial, 138, 140 Interference mitigation, 159–165 adaptive interference cancellation, 162–165 with low sidelobe antennas, 161–162 spread spectrum modulation, 128, 160–161 Interference power, 247–249 Interference susceptibility analyses, 149–159 antenna response in, 150–151 link analyses in, 158–159 and receiver damage, 156–158 receiver response in, 151–156 Interference-to-signal ratio (I/S), 158 International Traffic in Arms Regulations (ITAR), 25 IRIDIUM array design, 176–177 Irregular coverage (spot beam antennas), 169–171


Isolation: in multiple beam antennas, 174–175 polarization, 12, 13 Isotherm height, 116 ITALSAT multiple beam transponder, 84–85, 171, 175–177 ITAR (International Traffic in Arms Regulations), 25

J Jamming, 137–138

K Kalman filtering technique, 94, 213 Key performance parameters (KPPs), 290

L L (system loss), 159 Large ground terminal antennas, 98, 299–300, 306–308 Launch phase, TT&C antennas in, 27–29 Launch processing, 218 Lb (feed blockage loss), 36 Lens antennas, 40–41 LEO (low earth orbit), 99 Light bulb testing, 282–283 Link analyses, 131, 158–159 Link impairments, for frequency translating transponders, 79 LNA (see Low noise antenna) Location, minimization of differences in, 187–188 Loss: feed blockage loss, 36 gain loss, 39–40 implementation, 152 path, 246–247 radio frequency insertion, 153 return, 14–16 system, 159 Low earth orbit (LEO), 99 Low noise antenna (LNA), 18–21, 154, 156 LTol (gain loss), 39–40

M Main beam alignment verification, 66–68 Measurement uncertainty: for compact ranges, 238 for far field ranges, 231–233 of near field sampling, 240–241 in on-orbit GPS monitoring systems, 217 of radio source techniques, 253–256 Mechanical testing, 289, 305–306 Medium earth orbit (MEO), 99 Memory technology, in transponders, 75, 86 MEO (medium earth orbit), 99 Message routers, for multiple-beam antennas, 178–179 Microstrip patch antenna elements, 219–221 Microwave systems, 137 Military applications (of satellites), xii Minimum antenna element separation, 45

316

Mission control assets, 212–222 incident level monitors, 218–222 monitors for on-orbit GPS performance, 214–217 stations, 213–214 MMIC (see Monolithic microwave integrated circuits) Modulation: BPSK, 127 8PSK, 127 Passive intermodulation, 40, 284, 286, 291, 293 QPSK, 127 Spread spectrum, 128, 160–161 and system performance, 125–129 Molecular absorption, 108–113 Monitoring antenna (GPS systems), 215 Monolithic microwave integrated circuits (MMIC), xiv, 83 Monopulse feed designs (antenna tracking), 60–65 Monopulse tracking (see closed-loop antenna tracking) Monte Carlo simulations: in adaptive antenna design, 183, 257–258 in adaptive system development, 164–165 in interference scenarios, 149 MRR (manufacturing readiness review), 282 Multimode aperture designs (monopulse antenna feeds), 64–65 Multimode feed designs, 60 Multipaction, 293–294


Multipath environments, for user segment antennas, 200 Multiple-beam antennas, 168, 171–180 architecture and applications of, 179–180 crossover and sidelobe levels of, 175–176 field of view of, 176–177 gain level of, 171–174 isolation between beam positions in, 174–175 message routers for, 178–179 within spot sizes, 177–178

N Narrow coverage antennas, 35–41 NASA, 214 ND (difference pattern null depth), 62 Near field: interference in, 144–145 sampling in, 238–241 Network analyzers, 241–242 No (noise spectral density), 130 Noise background, for UHF systems, 107–108 Noise power (Pn1), 244–247 Noise power ratio (NPR), 77–78 Noise spectral density (No), 130 Noise temperature (Tn), 20 of antennas, 19–20, 252 and molecular absorption, 110–113 radio source techniques for, 250–253 of receivers, 20, 251, 254–255 of systems (see System noise temperature) NPR (noise power ratio), 77–78

O Offset reflectors: for point-to-point antennas, 192–193 for sidelobe control, 202, 203, 206 for spot beam antennas, 170 for user segment, 212 On-orbit GPS performance, monitors for, 214–217 On-orbit testing, 274, 279–283, 290–291 Open-loop antenna tracking, 51–53 Orthogonal polarizations, 8, 120 Out-of-band filtering requirements, 139 Out-of-band interference, 151, 153

P Parameters, antenna (see Antenna parameters) Passive intermodulation (PIM), 40, 284, 286, 291, 293 Path loss, 246–247 Payload testing, 290 PDR (see Preliminary Design Review) Phase compensation tolerance, 46–47 Phase imbalance, 63–64 Phase ripples, 14, 15 PIM (see Passive intermodulation) Pn1 (noise power), 244–247 Point-to-point antennas, 192–194 Polarization, 8–12 of difference antennas, 68–69

317

on far field ranges, 228–229 orthogonal, 8, 120 of reflector antennas, 38 of user segment antennas, 199 Polarization efficiency (p), 9–12 Polarization isolation, 12, 13 Polarization reuse, 160 Power density (Pd), 2 of compact vs. far field ranges, 233 finding interference sources using, 144–146 of incident signal level monitors, 218 in link analysis, 129 Pr (see Received power) Preliminary Design Review (PDR), 282, 304 Prime focus configuration (reflector antennas), 36, 37 Program tracking techniques, 51–53 Propagation limitations, 106–125 EHF limitations, 108–125 ionospheric, 106–108 Pseudo-monopulse tracking, 58

Q QPSK (quadrature-phase-shift-keying) modulation, 127 Qualification testing: for space segment antennas, 279–283 for user segment antennas, 300, 302–303 Quasi-compact ranges, 237 Quiet zones, for antenna testing, 226


R R (see Axial ratio; Range) Radiation integral, 3 Radio frequency (RF) cycle, 1 Radio frequency (RF) digital beamforming, 87 Radio frequency (RF) insertion loss, 153 Radio frequency (RF) performance: in antenna testing, 226 development phase testing of, 284–285 for space segment antennas, 278–279 systems to measure, 213 for user segment, 304–306 Radio source techniques, 244–257 interference power, 247–249 measurement uncertainty with, 253–256 noise power measurements, 244–247 noise temperature measurements, 250–253 radio stars as basis for, 244 recommended process for, 249 and spectrum analyzer noise, 249–250 testing of large ground antennas with, 307 Radio stars, 244 Radiometer, ground-based, 117–119 Radomes, 120–122 Rain (see Hydrometeors) Rain rate, 114–116 Rake receivers, 200 Range (R) (satellites), 101 Rate-corrected step track, 55–56 Receive antennas: active, 242–243 arrays of, 264–265 Received inference (I), 159 Received power (Pr), 4, 129, 218 Receiver noise temperature (Trec), 20, 251, 254–255 Receivers, 97–98 damage to, 156–158 design of, 154 for incident signal level monitors, 219–222 response to interference by, 149, 151–156 signal detection performance for, 126 tracking, 65–66 Reference antennas (GPS systems), 215–216 Reflector antennas, 35–41 equalization requirements for, 211 high-gain dual, 37–38 for spot beam coverage, 169 testing methods for, 298–299 in user segment, 198 Regenerative repeater transponders, 75, 82–85 Rephasing (array antennas), 43 Required angle correction (), 53–54 Resolution, angular, 183–184 Return loss (RL), 14–16 Rolled edge cavity antenna, 30–31 Rolled edge horn antennas, 33–35

S Satellite beacon, for measuring weather effects, 117, 119

318

Satellite commanding, by TT&C subsystem, 94–95 Satellite transmitters (frequency translating transponders), 76 Satellites: commercial vs. military applications of, xii–xiii effect of, xi future of, xii Geosynchronous satellites (see Geosynchronous satellites) GPS, 43–44 TDRS, 214 Scalar network analyzers, 241 Sector blanking, 140–141, 159 Sensitivity, 2 Separation requirements: of adaptive uplink antennas, 183 of far field antennas, 227–228 for size diversity, 123 Shaping: of high-gain dual reflector antennas, 37–38 of reflectors for user segment, 199 Sidelobe(s): of adaptive antennas, 207–208 alignment of, 66 control of, 201–207 and interference susceptibility, 151 of multiple-beam antennas, 175–176 and terrestrial interference, 140


Sidelobe antennas, 161–162 Sidelobe cancellar design (adaptive antennas), 259–260 Signal acquisition, and antenna tracking, 65–70 Signal to noise + interference (SNIR), 149–151, 155, 158, 174, 183, 210 Site surveys (of interference), 139–144 Size diversity, 123–124 Small reflector antennas, 34 SNIR (see Signal to noise + interference) Space segment antenna(s), xi, 167–194 active aperture, 188–191 adaptive uplink, 180–188 array antennas as, 42 multiple-beam, 171–180 point-to-point, 192–194 spot beam, 168–171 user segment antennas vs., 197 Space segment antenna testing, 278–296 development phase of, 283–286 EMI/EMC issues, 295–296 ESD susceptibility measurements, 294–295 on-orbit testing, 290–291 as process, 279–283 qualification phase of, 286–290 transmitter issues, 292–294 vehicle interaction in, 291–292 Space segment architectures, 74–95 crosslinks and earth links as, 91–93 digital transponders in, 85–89 direct broadcast, 89–91 frequency translating transponders in, 75–82 regenerative repeater transponders in, 82–85 TT&C subsystems of, 93–95 Spectrum: analyzers, 141, 159, 249–250 spread spectrum modulation, 128, 160–161 Spike leakage, 157–158 Spot beam antennas, 168–171 Spot coverage areas, multiple-beam antennas for, 177–178, 181–182 Spread spectrum modulation, 128, 160–161 SRR (see System Requirements Review) Standard gain horn antennas, 243–244 Stations, as mission control asset, 213–214 Step track technique, 53–57 Sum beam, in closed-loop antenna tracking, 57–58 Sum patterns, evaluations of, 269 Sustainment testing, 301, 303 System architectures, 73–102 orbital alternatives for, 98–102 for space segment, 74–95 for user segment, 95–98 System evaluations, 225, 277–308 for space segment, 278–296 for user segment, 296–308 System loss (L), 159 System noise temperature (T), 18–21 errors in, 254–256 from radio source techniques, 250 System performance, 105–133 link analyses for projection of, 129–133 and modulation, 125–129 multiple access methods in, 128–129 propagation limitations, 106–125 System planning and development, assessment of technologies for, xiv System Requirements Review (SSR), 282, 304 System temperature (Ts), 252–253

319

Systems design, as iterative process, xiii–xiv

T Tant (see Antenna noise temperature) Tap tests, 289 Taurus, 307 TDMA systems (see Time division multiple access systems) TDRS satellites, 214 Technology (see Antenna technology) Telemetry, Tracking and Control (TT&C) antennas: function of, 73 vehicle interaction for, 291–292 wide coverage antennas in, 25–32 Temperature: noise (see Noise temperature) System temperature (Ts), 252–253 Terminal impedance, 1–2 Terrestrial interference, 138, 140 Test facilities, 226–238 for adaptive antenna testing, 258–260


Test facilities (continued) compact ranges, 233–238 far field ranges, 227–233 for space segment antennas, 281–282 Test plans: for space segment, 280–281 for user segment, 302 Testing, antenna (see Antenna testing) Thermal vacuum tests, 285, 289 hp (beamwidth), 5–6 Thinned arrays, 41, 182–183 Three-antenna method (near field sampling), 239–240 Time division multiple access (TDMA) systems, 129, 200 Tn (see Noise temperature) Tracking (see Antenna tracking) Tracking receivers, 65–66 Transmit antennas: active, 242–243 arrays of, 265–266 Transmitters: of frequency translating transponders, 76 interference from, 146 space segment testing of, 292–294 Transponders, 73 digital, 85–89 frequency translating, 75–82 regenerative repeater, 82–85 Trec (see Receiver noise temperature) Triple point, 171–172 Ts (system temperature), 252–253 TT&C antennas (see Telemetry, Tracking and Control antennas)

U UHF (ultra high frequency): factors that limit operation, 107–108 propagation impairments of, 105, 106 Uncertainty, measurement (see Measurement uncertainty) Uniform plane waves, for antenna testing, 226 User power control, 79 User segment antenna(s), xi–xii, 197–222 adaptive, 207–212 mission control assets of, 212–222 sidelobe control of, 201–207 technology used by, 198–201 User segment antenna testing, 296–308 basic parameters for, 297–298 class-dependent methodologies for, 298–300 of large ground terminal antennas, 306–308 as process, 300–304 requirements for, 304–306

V Vector network analyzers, 241–242 Vehicle interaction, in antenna testing, 291–292 Verification matrix: for development testing, 285 for space segment antennas, 279–280 for user segment antennas, 301 Very small aperture terminals (VSAT) applications, 74, 198, 299 Voltage standing wave ratio (VSWR), 14–17, 298

320

VSAT applications (see Very small aperture terminals applications) VSWR (see Voltage standing wave ratio)

W Waterfall curves, 126 Waveguide lens antennas, 40–41 Weather effects, 114, 116, 117–119 Wet antennas, minimizing effects of, 120–125 Wide coverage antennas, 26–32 World War II, ix, 114

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