development and modelling of new wideband microstrip patch antennas with capacitive feed probes

239 Pages·2004·3.12 MB·English

UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
DEVELOPMENT AND MODELLING OF NEW
WIDEBAND MICROSTRIP PATCH ANTENNAS
WITH CAPACITIVE FEED PROBES
by
GordonMayhew-Ridgers
Submittedinpartialfulfillmentoftherequirementsforthedegree
PhilosophiaeDoctor
(ElectronicEngineering)
inthe
FacultyofEngineering,BuiltEnvironmentandInformationTechnology
UNIVERSITYOFPRETORIA
July2004
UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Synopsis
DEVELOPMENTANDMODELLINGOFNEWWIDEBANDMICROSTRIP
PATCHANTENNASWITHCAPACITIVEFEEDPROBES
Author: GordonMayhew-Ridgers
Promoter: Prof. J.W.Odendaal
Co-promoter: Prof. J.Joubert
Department: Electrical,ElectronicandComputerEngineering
University: UniversityofPretoria
Degree: Ph.D.(ElectronicEngineering)
Keywords: Widebandantennas,microstrippatchantennas,antennaarrays,capacitivefeed
probes,multilayeredsubstrate,full-waveanalysis,basisfunctions,attachment
modes,momentmethod,spectraldomain.
The principal contributions of this study include the development of a new capacitive feeding
mechanismforwidebandprobe-fedmicrostrippatchantennasaswellastheimplementationofa
spectral-domain moment-method formulation for the efficient analysis of large, but finite arrays
of these elements. Such antenna configurations are very useful in the wireless communications
industry,butextremelydifficulttoanalysewithcommerciallyavailablesoftware.
Probe-fedmicrostrippatchantennashavealwaysbeenapopularcandidateforavarietyofantenna
systems. Due to their many salient features, they are well suited for modern wireless communi-
cation systems. However, these systems often require antennas with wideband properties, while
aninherentlimitationofprobe-fedmicrostrippatchantennasisitsnarrowimpedancebandwidth.
Thiscanbeovercomebymanufacturingtheantennaonathicklow-losssubstrate,butatthesame
time it also complicates things by rendering the input impedance of the antenna very inductive.
In this thesis, a new capacitive feeding mechanism is introduced that can be used for probe-fed
microstrippatchantennasonthicksubstrates. Itconsistsofasmallprobe-fedcapacitorpatchthat
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UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Synopsis
issituatednexttotheresonantpatch. Thebenefitsofthisconfigurationincludethefactthatonly
onesubstratelayerisrequiredtosupporttheantenna. Itisalsoveryeasytodesignandoptimise.
The use of full-wave methods for an accurate analysis of microstrip antennas, has basically be-
come standard practice. These methods can become very demanding in terms of computational
resources,especiallywhenlargeantennaarrayshavetobeanalysed. Assuch,thisthesisincludesa
spectral-domainmoment-methodformulation,whichwasdevelopedfortheanalysisofprobe-fed
microstrip patch antennas or antenna arrays that comprise of the new capacitive feeding mecha-
nism. Here,entire-domainandsubdomainbasisfunctionsarecombinedinauniquewaysoasto
minimise the computational requirements, most notably computer memory. It is shown that, for
general antenna array configurations, memory savings of more than 2500 times can be achieved
when compared with typical commercial software packages where only subdomain basis func-
tions are used. Some of the numerical complexities that are dealt with, include various methods
to evaluate the spectral integrals as well as special algorithms to eliminate the recalculation of
duplicate interactions. The thesis also contains a quantitative comparison of various attachment
modesthatareoftenusedinthemoment-methodmodellingofprobe-to-patchtransitions.
Various numerical and experimental results are included in order to verify the spectral-domain
moment-method formulation, to characterise the new feeding mechanism and to illustrate its
use for various applications. These results show that, in terms of accuracy, the spectral-domain
moment-method formulation compares well with commercial codes, while by comparison, it de-
mands very little computer memory. The characterisation results show that the input impedance
of the antenna can be fully controlled by only adjusting the size of the capacitor patch as well as
thewidthofthegapbetweenthecapacitorpatchandtheresonantpatch. Intermsofapplications,
itisshownhowthenewantennaelementcaneffectivelybeemployedinlineararrayswithvertical
polarisation,horizontalpolarisationordualslant-polarisation. Theserepresentsomewidely-used
configurationsformodernbase-stationantennas.
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UniversityofPretoria—Electrical,ElectronicandComputerEngineering
UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Samevatting
ONTWIKKELINGENMODELLERINGVANNUWEWYEBANDMIKROSTROOK
PLAK-ANTENNESMETKAPASITIEWEVOERPENNE
Outeur: GordonMayhew-Ridgers
Promotor: Prof. J.W.Odendaal
Medepromotor: Prof. J.Joubert
Departement: Elektriese,ElektronieseenRekenaar-Ingenieurswese
Universiteit: UniversiteitvanPretoria
Graad: Ph.D.(ElektronieseIngenieurswese)
Sleutelwoorde: Wyeband antennes, mikrostrook plak-antennes, antenne-samestellings, ka-
pasitiewe voerpenne, multilaag substraat, volgolf analise, basisfunksies, heg-
modusse,momentemetode,spektraledomein.
Dievernaamstebydraesvanhierdiestudieisdieontwikkelingvan’nkapasitiewevoermeganisme
virwyebandmikrostrookplak-antenneswatdeurmiddelvanvoerpenneaangedryfword,asookdie
implementeringvan’nspektrale-domeinmomente-metodeformuleringvirdieeffektieweanalise
vangroot,maareindigesamestellingsvanhierdieantenne-elemente. Sulkeantenne-konfigurasies
isbaiebruikbaarindiedraadlosekommunikasie-industrie,maargeweldigmoeilikomteanaliseer
metkommersieel-beskikbaresagteware.
Mikrostrookplak-antenneswatdeurmiddelvanvoerpenneaangedryfword,wasnogaltydgewild
vir gebruik in ’n verskeidenheid van antenne-stelsels. Hierdie antennes het verskeie eienskappe
wathulleveralvoordeligmaakvirgebruikinmodernedraadlosekommunikasie-stelsels. Hierdie
stelselsvereisegterdikwelsantennesmetwyebandeienskappe,terwylmikrostrookplak-antennes
wat deur middel van voerpenne aangedryf word, die inherente limitasie het dat hulle nouband
is in terme van intree-impedansie. Hierdie limitasie kan oorkom word deur die antenne op ’n
dik lae-verlies substraat te vervaardig, maar kompliseer die situasie verder deurdat die intree-
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UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Samevatting
impedansie van die antenne baie induktief word. In hierdie proefskrif word ’n nuwe kapasitiewe
voermeganisme voorgestel wat geskik is vir mikrostrook plak-antennes op dik substrate en wat
deur voerpenne aangedryf word. Die nuwe voermeganisme bestaan uit ’n klein kapasitorstrokie
wat langs die resonante strook van die plak-antenne aangebring word. In plaas daarvan dat die
resonantestrookdirekmet’nvoerpenaangedryfword,worddiekapasitiewestrookmet’nvoerpen
aangedryf. Sommigevoordelevanhierdiekonfigurasieisdatneteenlaagsubstraatbenodigword
en dat die ontwerp, sowel as optimisering, van antennes met sulke voermeganismes baie maklik
is.
Die gebruik van volgolf metodes vir die akkurate analise van mikrostrook antennes het basies
standaard praktyk geword. Hierdie metodes kan baie veeleisend word in terme van rekenaar-
infrastruktuur,veralwanneerdieanalisevangrootantenne-samestellingsbenodigword. Asgevolg
hiervan, sluit hierdie proefskrif ’n spektrale-domein momente-metode formulering in wat spesi-
fiekontwikkelisvirdieanalisevanantennesenantenne-samestellingswatgebruikmaakvandie
nuwe kapasitiewe voermeganisme. In hierdie formulering word volledige-domein en subdomein
basisfunksies op ’n unieke wyse gekombineer sodat die hoeveelheid rekenaar-infrastruktuur wat
benodig word vir ’n analise geminimiseer word, veral in terme van rekenaargeheue. Dit word
byvoorbeeld gewys dat, wanneer hierdie formulering vergelyk word met kommersie¨le kodes wat
netsubdomeinbasisfunksiesgebruik,besparingsvanmeeras2500keerintermevanrekenaarge-
heuebereikkanwordwanneertipieseantenne-samestellingsgeanaliseerword. Sommigevandie
numeriese kompleksiteite wat behandel word, is die verskeie metodes wat gebruik word om in-
tegrale in die spektrale domein te evalueer, sowel as spesiale algoritmes om die herberekening
vanduplikaatinteraksiesteelimineer. Dieproefskrifbevatook’nkwantitatiewevergelykingvan
spesialebasisfunksies,oftewelhegmodusse,watbenodigwordin’nmomente-metodeformulering
omdieoorgangtussendievoerpenendiemikrostrooktebeskryf.
Die proefskrif bevat verskeie numeriese en eksperimentele resultate om die spektrale-domein
momente-metodeformuleringteverifieer,dienuwevoermeganismetekarakteriseerenteillustreer
hoe dit gebruik kan word in verskillende toepassings. In terme van akkuraatheid, vergelyk die
spektrale-domeinmomente-metodeformuleringgoedmetkommersie¨lekodes,terwylditookheel-
watminderrekenaargeheuegebruik. Diekarakteriserings-resultatewysdatdieintree-impedansie
vandieantennevolledigbeheerkanworddeurslegsdiegroottevandiekapasitorstrook,sowelas
diewydtevandiegapingtussendiekapasitorstrookendieresonantestrook,teverander. Interme
van toepassings, word dit gewys hoe die nuwe antenne-element in lineeˆre samestellings met ver-
tikalepolarisasie,horisontalepolarisasieofdubbeleskuins-polarisasiegebruikkanword. Hierdie
konfigurasiesisverteenwoordigendvantipiesebasisstasie-antennes.
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UniversityofPretoria—Electrical,ElectronicandComputerEngineering
UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Acknowledgements
I would like to start by thanking the Lord, without whom the completion of this work would not
have been possible. He has entrusted me with the abilities and provided me with the courage to
completealongjourney.
My advisors, Prof. Wimpie Odendaal and Prof. Johan Joubert, deserves a special word of appre-
ciation. They have always been there with support and guidance throughout the duration of my
graduate studies. I would like to thank Mr. Lukas Naude of the Compact Antenna Test Range at
theUniversityofPretoriaandalsoMr.DaanJansevanRensburg,formerlywiththeCompactAn-
tennaTestRange,foralltheirtimeandassistancewiththeconstructionofantennaprototypesand
manyantennameasurements. AwordofthanksgoestoDr.FransMeyerandDr.GronumSmithof
EMSoftwareandSystemsinStellenboschforprovidingmewithacopyoftheFEKOelectromag-
netic simulation software. Prof. Jim Aberle of the Arizona State University in the United States
ofAmericaandDr.MassimoSereno-Garino,formerlywiththePolitecnicodiTorinoinItaly,pro-
vided me with valuable information and advice regarding various aspects of the spectral-domain
moment-methodformulationthatwasimplemented. Iwouldliketothankthemfortheirtimeand
patience.
Myparents,familyandfriendsdefinitelydeserveaspecialwordofthanksforalwaysbeingthere
to support and encourage me. They have always showed a great deal of interest in my studies.
Finally, I must express my sincere gratitude to my wife, Francis. She knows more than anyone
elseaboutthesacrificesthathadtobemade. Iwouldliketothankherforherlove,encouragement,
patienceandunderstandingthroughoutallofmystudies. Itismuchappreciated.
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UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Preface
The purpose of this preface is to point out some notation that is used throughout this thesis as
wellassomeinformationthatisassumed,butnotclearlypointedoutelsewhere. Throughoutthis
thesis, numbers in parentheses ( ) refer to equations, whereas numbers in brackets [ ] refer to
references. In this thesis, all the fields and currents densities are assumed to be time-harmonic
with a ejωt time convention that is suppressed throughout the thesis. The variables are therefore
complex-valued, with a magnitude and phase as for any phasor analysis. Furthermore, vectors
are indicated by boldface symbols (e.g. E), vector components are indicated by italic symbols
(e.g. E ), unit vectors are indicated by italic symbols with circumflexes (e.g. xˆ), while dyadic
x
functions are indicated by boldface symbols with overbars (e.g. G¯). Spectral functions, vectors
anddyadsareindicatedwithatilde(e.g. f˜,E˜ andG˜¯). Althoughthetheoreticalformulation,which
was implemented for the purposes of this study, can handle multilayered media with magnetic
properties, itisassumedthat, foralltheexamplesinthisthesis, therelativepermeabilityisequal
toone(i.e. µ = 1)andthemagneticlosstangentisequaltozero(i.e. tanδ = 0).
r µ
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UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Contents
Synopsis ...................................................................... ii
Samevatting ................................................................... iv
Acknowledgements ............................................................ vi
Preface ....................................................................... vii
1 Introduction ............................................................... 1
1.1 BackgroundandMotivation............................................... 1
1.2 ObjectivesandScope .................................................... 7
1.3 OriginalContributions ................................................... 8
1.4 OverviewoftheThesis................................................... 10
2 WidebandProbe-FedMicrostripPatchAntennasandModellingTechniques ...... 12
2.1 IntroductoryRemarks.................................................... 12
2.2 OverviewofWidebandProbe-FedMicrostripPatchAntennas .................. 13
2.2.1 WidebandImpedance-MatchingNetworks............................ 13
2.2.2 Edge-CoupledPatches ............................................ 14
2.2.3 StackedPatches .................................................. 15
2.2.4 ShapedProbes ................................................... 16
2.2.5 CapacitiveCouplingandSlottedPatches ............................. 18
2.3 NewWidebandMicrostripPatchAntennaswithCapacitiveFeedProbes ......... 19
2.4 OverviewofModellingTechniques ........................................ 21
2.4.1 ApproximateMethods............................................. 21
2.4.2 Full-WaveMethods ............................................... 22
2.4.3 Spatial-DomainMomentMethod ................................... 26
2.4.4 Spectral-DomainMomentMethod .................................. 28
2.5 ProposedFormulation.................................................... 29
2.6 ConcludingRemarks..................................................... 32
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UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Contents
3 ImplementationoftheSpectral-DomainMoment-MethodFormulation ........... 33
3.1 IntroductoryRemarks.................................................... 33
3.2 GeneralFormulation..................................................... 35
3.3 Spectral-DomainFormulation ............................................. 39
3.4 Green’sFunction........................................................ 40
3.4.1 ReflectionCoefficients ............................................ 42
3.4.2 WaveAmplitudes................................................. 44
3.4.3 WaveFunctions .................................................. 45
3.4.4 ComponentsoftheGreen’sFunction ................................ 47
3.5 BasisFunctions ......................................................... 48
3.5.1 Piecewise-SinusoidalBasisFunctionsontheProbes.................... 51
3.5.2 RooftopBasisFunctionsontheRectangularCapacitorPatches .......... 53
3.5.3 SinusoidalBasisFunctionsontheResonantPatches.................... 54
3.6 AttachmentModes ...................................................... 56
3.6.1 RectangularAttachmentMode...................................... 57
3.6.2 CircularAttachmentMode ......................................... 61
3.6.3 Higher-OrderCircularAttachmentMode............................. 63
3.7 SystemofLinearEquations ............................................... 64
3.8 EvaluationoftheInteraction-MatrixEntries ................................. 67
3.9 IntegrationStrategies .................................................... 71
3.9.1 IntegrationStrategyforOverlappingBasisandTestingFunctions ........ 72
3.9.2 IntegrationStrategyforSeparatedBasisandTestingFunctions........... 76
3.9.3 IntegrationStrategyforSeparatedAxisymmetricBasisandTestingFunc-
tions............................................................ 85
3.10 IdentificationofDuplicateEntriesintheInteractionMatrix .................... 85
3.10.1 InteractionbetweenAxisymmetricFunctions ......................... 87
3.10.2 InteractionbetweenAxisymmetricFunctionsandFunctionswith
RectangularSupport .............................................. 88
3.10.3 InteractionbetweenFunctionswithRectangularSupport................ 90
3.11 EvaluationoftheExcitation-VectorElements ................................ 94
3.12 SolutionoftheCurrent-DensityCoefficients ................................. 95
3.13 EvaluationoftheNetworkParameters ...................................... 96
3.14 EvaluationoftheFarFields ............................................... 97
3.15 ConcludingRemarks..................................................... 101
4 NumericalandExperimentalResults ......................................... 103
4.1 IntroductoryRemarks.................................................... 103
4.2 ValidationoftheSpectral-DomainMoment-MethodImplementation ............ 104
4.2.1 SingleProbeinaGroundedSubstrate................................ 104
4.2.2 CircularVersusRectangularAttachmentModes ....................... 106
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UniversityofPretoria—Electrical,ElectronicandComputerEngineering
UUnniivveerrssiittyy ooff PPrreettoorriiaa eettdd –– MMaayyhheeww--RRiiddggeerrss,, GG ((22000044))
Contents
4.2.3 CapacitorPatches ................................................ 111
4.2.4 AntennaElementswithCapacitiveFeedProbes ....................... 117
4.3 CharacterisationofAntennaElementswithCapacitiveFeedProbes ............. 127
4.3.1 InputImpedanceoftheAntennaElement............................. 127
4.3.2 ImpedanceBandwidthoftheAntennaElement ........................ 129
4.4 Applications............................................................ 131
4.4.1 AntennaElementwithReducedCross-PolarisationLevels .............. 131
4.4.2 Dual-PolarisedAntennaElement.................................... 135
4.4.3 Two-ElementLinearly-PolarisedArray .............................. 138
4.4.4 Four-ElementVertically-PolarisedArray ............................. 142
4.4.5 Four-ElementHorizontally-PolarisedArray........................... 146
◦
4.4.6 Four-Element 45 Slant-PolarisedArray............................ 150
±
◦
4.4.7 Five-Element 45 Slant-PolarisedArray ............................ 155
±
◦
4.4.8 Nine-Element 45 Slant-PolarisedArray............................ 162
±
◦
4.4.9 ThirtySix-Element 45 Slant-PolarisedArray ....................... 167
±
◦
4.4.10 Eighty-Element 45 Slant-PolarisedArray .......................... 172
±
4.5 Alternatively-ShapedPatches ............................................. 176
4.6 ConcludingRemarks..................................................... 180
5 ConclusionsandFutureResearch ............................................ 183
5.1 GeneralConclusions..................................................... 183
5.2 FutureResearch......................................................... 185
References .................................................................... 188
A DerivationsRelatedtotheGreen’sFunction ................................... 203
A.1 Spectral-DomainGreen’s-FunctionComponents ............................. 203
A.2 ExpandedGreen’s-FunctionComponents ................................... 205
B DerivationsRelatedtotheBasisFunctions ..................................... 216
B.1 SpatialRepresentationoftheRectangularAttachmentMode ................... 216
B.2 SpectralRepresentationoftheBasisFunctions ............................... 219
B.2.1 Piecewise-SinusoidalBasisFunctionsontheProbes.................... 220
B.2.2 RooftopBasisFunctionsontheRectangularCapacitorPatches .......... 220
B.2.3 SinusoidalBasisFunctionsontheResonantPatches.................... 222
B.2.4 RectangularAttachmentMode...................................... 223
B.2.5 CircularAttachmentMode ......................................... 226
B.2.6 Higher-OrderCircularAttachmentMode............................. 228
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UniversityofPretoria—Electrical,ElectronicandComputerEngineering