Downloaded from orbit.dtu.dk on: Jan 17, 2023 Electronically Steerable Antennas for Satellite Communications Larsen, Niels Vesterdal Publication date: 2007 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Larsen, N. V. (2007). Electronically Steerable Antennas for Satellite Communications. 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E S A LECTRONICALLY TEERABLE NTENNAS S C FOR ATELLITE OMMUNICATIONS PhD Thesis Niels Vesterdal Larsen May 2007 The work presented in this thesis was carried out at Ørsted DTU and Thrane & Thrane A/S in · partial fulfillmentof therequirements forthe IndustrialPhD degreeat theTechnical Universityof Denmark. Supervisors: OlavBreinbjerg, Professor, PhD, Ørsted DTU,TechnicalUniversityofDenmark, · UlrichVesterager Gothelf,PhD, Thrane&ThraneA/S. A BSTRACT ELECTRONICALLY STEERABLE ANTENNAS FOR SATELLITE COMMUNICATIONS Astudyofphasedarrayantennasforapplicationtomobilesatellitecommunicationshas been conducted. The study is focused on small 7-element arrays but it also includes investigationsofmutual coupling,influenceof finitegroundplanes,andapplicationof sequentialrotation. Threetypesofphasedarraysaredevotedparticularattention.Theantennaelements of thesearraysare cavity-backedannularslotantennas,printeddroopingdipoleanten- nas,anddielectricresonatorantennas. Thethreearraysareanalysedwithathree-stage modelwhichincludesnumericalsimulationsofthearrays,theimpactsoffiniteground planes, and inclusionof the receiverand feed network characteristics. This allows for anassessmentof the G/T of thearray. It is concluded,that thedipolearrayoffersthe best performance among the three arrays, in particular due to its superior coverage at low elevationangles. The investigationshave led to the constructionof a prototypeof thedipolearrayonwhichmeasurementshavebeenconducted.Themeasurementsagree wellwiththenumericalsimulations. The mutual coupling between the antenna elements is investigated with emphasis on the impact of the element radiation pattern, array size, ground plane, and parasitic structures.Somemeansofreducingthemutualcouplingand,therebythearrayscanloss, areidentified.Oneofthesemeansistheuseofparasiticmonopolespositionedbetween theelementsofthearray,andsuchmonopolesareemployedinthedipolearray. The influence of finite ground planes on the array radiation is investigated in sev- eralrespects. Theinvestigationsareconductedusinga numericalMethodof Auxiliary Sourcesmodel of the ground plane. With this ground plane model, the impacts of the groundplanesize,shape,andcurvatureareanalysedaswellastheconsequencesofrais- ingthe arrayslightlyabovethesurfaceof thegroundplane. It is concluded,thatthese groundplanepropertieshavesignificantinfluenceon thearrayradiationandhencethe overallperformance. The application of sequential rotation to phased arrays is investigated using two differentmodels. An analyticalsphericalwave expansionmodel has been derivedand canbeemployedforgeneralantennaelements,planararraygeometries,andscanangles. This model is based on the assumption of identical element patterns and it does not includethemutualcoupling.Theothermodel,anumericalMethodofAuxiliarySources model,includestheentirearraywithoutmakingtheaboveassumptions.Thetwomodels demonstratethesignificantimprovementofthepolarisationpuritythatcanbeobtained withthesequentialrotationforarrayswhoseelementshavepoorpolarisationpurity.Itis furtherconcluded,thattheimprovementof thepolarisationpuritydoesnotnecessarily guaranteeanimprovementofthemain-beamcircularly-polariseddirectivity. i R ESUMÉ ELEKTRONISK STYRBARE ANTENNESYSTEMER TIL SATELLITKOMMUNIKATION Et studium af fasestyrede antennegruppertil anvendelse for mobil satellitkommunika- tion er blevet udført. Studiet er fokuseret på små 7-element antennegrupper, men det indbefatterogsåundersøgelseraf gensidigkobling,indflydelseaf endeligejordplanog anvendelseafsekventielrotation. Opmærksomheden er specielt rettet mod tre typer af fasestyrede antennegrupper. Elementernei disseantennegruppererkavitetsantennermedcirkulæreslidser,printede skrådipolantennerogdielektriskeresonatorantenner.Detreantennegrupperundersøges med en tretrins model, som inkluderer numeriske simuleringer af antennegrupperne, påvirkningernefraendeligejordplanoginklusionafkarakteristikaformodtagerogfø- denetværk. DettemuliggørenvurderingafantennegruppensG/T. Detkonkluderes,at dipolantennegruppenfungererbedstblandtdetreantennegrupper,specieltpga.enover- legen dækningsgrad ved lave elevationsvinkler. Undersøgelserne har ført til en frem- stillingafenprototypeafdipolantennegruppen,påhvilkendererblevetudførtmålinger. Målingernestemmergodtoverensmeddenumeriskesimuleringer. Dengensidigekoblingmellemantenneelementerneundersøgesmedsærligvægtpå påvirkningerfra elementernesudstrålingsmønstre,antennegruppensstørrelse, jordplan og parasitiske strukturer. Enkelte virkemidler, til at nedbringe den gensidige kobling ogdermedantennegruppensskan-tab,identificeres. Enafdisseerbrugenafparasitiske monopolerplaceretmellemantennegruppenselementer,og sådannemonopoleranven- desidipolantennegruppen. Påvirkningen fra endelige jordplan på antennegruppens udstråling undersøges i fleresammenhænge. Undersøgelserneudføresmed ennumerisk"Methodof Auxiliary Sources"-modelafjordplanet.Meddennejordplansmodelanalyserespåvirkningernefra jordplanetsstørrelse,faconog krumningsamt konsekvenserneaf at løfteantennegrup- pen en anelse over jordplanets overflade. Det konkluderes, at disse karakteristika for jordplanerharensignifikantindvirkningpåantennegruppensudstrålingogdermedden samledevirkningsgrad. Anvendelsen af sekventielrotation til fasestyredeantennegrupperundersøgesmed to forskellige modeller. En analytisk, sfærisk bølgeudviklingsmodel er blevet udledt og kan anvendes for generelle antenneelementer, plane antennegruppegeometrier og skanvinkler. I dennemodelantagesdet,atantenneelementerneharsammeudstrålings- diagram, og den gensidige kobling inkluderes ikke. Den anden model, en numerisk "Method of Auxiliary Sources"-model, inkluderer hele antennegruppen uden at gøre ovennævnte antagelser. De to modeller demonstrerer den signifikante forbedring af polarisationsrenheden, som kan opnås vha. sekventiel rotation af antennegrupper, beståendeaf elementer med dårlig polarisationsrenhed. Det konkluderesendvidere,at forbedringen af polarisationsrenheden ikke nødvendigvis garanterer en forbedring af dencirkulærtpolariserededirektivitetiantennegruppenshovedsløjfe. iii P REFACE The work presented in this thesis has been carried out at Thrane & Thrane A/S and ElectroScience,Ørsted DTU, TechnicalUniversity of Denmark (DTU). The study was · initiatedJune 2004 and ended May 2007. It has been financedprimarily by Thrane& ThraneA/S with supportfromtheIndustrialPhDinitiative. FromMay 2006,I spent6 monthsasavisitingscholarattheJetPropulsionLaboratory(JPL),Pasadena,California. TherearemanypeopletowhomIwouldliketoextendmygratitude.Especiallymy twosupervisors,fromThrane&ThraneandDTU,UlrichV.GothelfandOlavBreinbjerg. With their extensiveexperienceand knowledgeof experimentaland theoreticaltopics, theyhaveformedaninvaluableteam. ThisisindeedessentialforIndustrialPhDprojects such as this, where theory and application are equally important. I furthermore thank myfriendsandcolleaguesatThrane&ThraneandDTUformanyinterestingdiscussions and suggestions. Particularly, Tonny Rubæk and Samel Arslanagic´ are acknowledged forreadingandcommentingmanyofthechaptersofthepresentthesis. ManypeoplehavebeenhelpfulinmakingmyvisitatJPL,andCaliforniaingeneral,a greatexperience.IparticularlythankJohnHuangforacceptingmeatJPLandgenerously sharinghis immense knowledgeon antennasand phasedarrays. I alsothankthe Boyd andPoulsenfamiliesforacceptingmeintotheirhomes,providingmuchhelpandadvice, andintroducingmetotheCaliforniancultureandsocietyingeneral. Kgs. Lyngby,May,2007 NielsVesterdalLarsen The present versionof the thesis was revisedin October 2007 after the thesis defense. Thiswaswiththepurposeofcorrectingmisprintsthatoccurredintheoriginalversion. Inaddition,thestatusofthepublicationshasbeenupdated. v T C ABLE OF ONTENTS Abstract i Resumé iii Preface v Tableof Contents vii Listof Publications ix Listof Acronyms xi 1 Introduction 1 1.1 OverviewofMobileSatelliteCommunicationSystems . . . . . . . . . . . . . . . . . . . . . 1 1.2 AntennaTypesforMobileUserTerminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 ChallengesofPhasedArrayAntennaDesign. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.4 ThePresentStudy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 MathematicalModelsforPhased ArrayAnalysis 9 2.1 ElectromagneticFieldAnalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 ModelsoftheFeedNetworkandReceiverChain . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3 ModelsoftheArrayEnvironment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4 Three-StageModelofArraysonFiniteGroundPlanes . . . . . . . . . . . . . . . . . . . . . 15 2.5 GeneticAlgorithmOptimisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3 MutualCoupling 17 3.1 CrossedDipoleAntennaElementandArray . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2 InfluenceoftheElementRadiationPattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.3 InfluenceoftheArraySize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.4 InfluenceoftheGroundPlane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.5 InfluenceofParasiticStructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.6 Wide-AngleImpedanceMatching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4 ThreeArrayTypes 27 4.1 GeneralRemarksontheInvestigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4.2 Cavity-BackedAnnularSlotArray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 4.3 PrintedDroopingDipoleArray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 4.4 DielectricResonatorArray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5 InfluenceofFiniteGroundPlanes 37 5.1 MethodsforAnalysingtheInfluenceofFiniteGroundPlanes . . . . . . . . . . . . . . . . . . 37 vii