Electronically Steerable Antennas for Satellite Communications

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Electronically Steerable Antennas for Satellite Communications
Larsen, Niels Vesterdal
Publication date:
2007
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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