Compact Adaptive Planar Antenna Arrays for Robust Satellite Navigation Systems

180 Pages·2016·8.31 MB·English

Compact Adaptive Planar Antenna
Arrays for Robust Satellite Navigation
Systems
Doctoral thesis
for attaining the academic degree of
Doctor of Engineering (Dr. -Ing.)
presented to the Faculty of Electrical Engineering and Information Technology
Technische Universität Ilmenau
by M.Sc. Safwat Irteza Butt
(30. April 1983)
1. Reviewer: Univ.-Prof. Dr. rer. nat. habil. Matthias A. Hein
2. Reviewer: Prof. Dr.-Ing. habil. Reiner S. Thomä
3. Reviewer: Dr.-Ing. Achim Dreher
Submitted on: 07.07.2015
Defended on: 13.10.2016
urn:nbn:de:gbv:ilm1-2016000659

Abstract
Over the past two decades, humankind’s reliance on global navigation satellite systems
for precise positioning, navigation and timing services has grown remarkably. Such ad-
vanced applications vary from highly accurate surveying to intelligent transport systems,
andfrommobilenetworktimingsynchronisationtoweatherandclimatemonitoring. This
envisages new and higher standards of robustness, accuracy, coverage and integrity in
modernnavigationreceivers. Recently,thishasbeenaccomplishedwiththeincorporation
of the multi-element navigation antenna receiver. However, the industrialisation of this
approach is limited due to the large antenna array size, hindered by the inter-element sep-
aration of half of the free-space wavelength, i.e. ≈ 10 cm at L band (1−2 GHz). In this
thesis, compact navigation antenna arrays with smaller inter-element separations are pro-
posed for the miniaturisation of the overall size. However, these arrays become afflicted
with the adverse effects of mutual coupling. Therefore, various figures-of-merit for the
analysis and design of a compact planar navigation antenna array, such as performance
diversity degrees-of-freedom, directional finding capabilities, and polarisation purity, in-
cluding mutual coupling effects, have been presented. This provides a general framework
for the selection and configuration of the optimum compact navigation antenna array. In
ordertomitigatethemutualcoupling,integrationofthedecouplingandmatchingnetwork
into customised compact navigation antenna array designs is performed. This is fostered
by the correlated noise characterisation of the complete receiver. Furthermore, an analyti-
calmodeloftheequivalentcarrier-to-interference-plus-noiseratioisderivedtoinvestigate
the navigation performance in interference scenarios. In the end, this is complemented by
theimplementationofthecompletenavigationreceiverforverificationandrobustnessval-
idation of the derived compact antenna array concepts in indoor and outdoor interference
scenarios.
Zusammenfassung
In den zurückliegenden zwei Jahrzehnten ist die Abhängigkeit der Industriegesellschaft
von satellitengestützten Ortungssystemen, Navigationsdiensten und Zeitsignalen drama-
tisch gewachsen. Darauf aufbauende moderne Anwendungen reichen von hochgenauen
OrtungsgerätenbiszuintelligentenTransportsystemenundvonderSynchronisationmobi-
lerNetzwerkezuWetter-undKlimabeobachtung.DiessetztneuehöhereStandardsinder
Robustheit,Genauigkeit,VerfügbarkeitundVerlässlichkeitmodernerNavigationsempfän-
ger voraus. Möglich werden diese Verbesserungen aktuell mit der Einführung von Mul-
tiantennensystemen in den Navigationsgeräten. Jedoch wird die Nutzung dieses Ansat-
zes durch die größeren Abmessungen der Antennenarrays erschwert, weil standardmäßig
der Elementabstand zu einer halben Freiraumwellenlänge gewählt wird, was im L Band
3
ca.10cmbedeutet.
In dieser Arbeit werden kompakte Antennenarrays für Navigationsempfänger mit ge-
ringeremElementabstandvorgeschlagen,dieeineMiniaturisierungderEmpfängerabmes-
sungenerlauben.DiesekompaktenArrayswerdeninihrerLeistungsfähigkeitjedochdurch
die negativen Effekte der Verkopplung zwischen den Einzelelementen beeinträchtigt. Für
die Beurteilung der Empfängerleistungsfähigkeit existieren verschiedene Qualitätspara-
meter für Analyse und Entwurf der planaren Arrays. Damit werden z. B. Diversity Frei-
heitsgrade,QualitätderRichtungsschätzung,Polarisationsreinheitunddiewechselseitigen
Kopplungen gemessen und eine Entwurfsumgebung wird vorgestellt, in der das optimale
kompakte Antennenarray für den jeweiligen Einsatzzweck ausgewählt und konfiguriert
werden kann. Dieser Prozess wird durch eine Analyse des Rauschens und seiner Korre-
lationseigenschaften für den gesamten Empfänger begleitet. Darüber hinaus wird ein ana-
lytisches Modell des effektiven carrier-to-interference-plus-noise ratio abgeleitet, um die
Leistungsfähigkeit der Navigationsempfänger in Szenarien mit Störsignalen zu untersu-
chen.SchließlichwerdendieseBetrachtungendurchdenAufbaueineskomplettenSatelli-
tennavigationsempfängers ergänzt, um mit ihm den Nachweis der Funktionsfähigkeit und
derstabilenFunktiondesentworfenenSystemsmitkompaktemArrayunterStörereinfluss
beiLaborbedingungenundimrealenAußeneinsatzzuerbringen.
Theses of the Dissertation
– Tomeetthemodernstandardsforsafety-of-lifecriticalapplicationslikeautonomous
drivingandintelligenttransportsystems,futureglobalnavigationsatellitesystems
can benefit from compact antenna arrays to achieve miniaturisation and robust-
ness.
– For any N-port antenna array, such that N > 1, the radiation process is defined by
the superposition of N orthogonal modes of radiation or the diversity degrees-of-
freedom. However,compactelectricalsizeorinter-elementseparationlessthanhalf
offree-spacewavelengthgiverisetoincreasedmutualcouplingwhichdegradesthe
efficiencyofthesedegrees-of-freedom.
– Eigen-decomposition of the antenna array spatial covariance matrix, calculated
using the scattering parameters or the far-field patterns, delivers the assessment of
thefundamentalmodesofradiationortheeigenmodes.
– The minimum eigenvalue or the eigenvector with least efficiency dominates the
overallradiationorreceptionperformanceofthecompactantennaarrays. Primarily,
this figure-of-merit can serve as a parameter for the selection and configuration of
theoptimalcompactantennaarrayinthedesignprocess.
– Compact planar antenna array configurations provide flexibility of geometrical
optimisation for efficient degrees-of-freedom and achieving improved direction-
findingcapabilities.
– The polarisation purity of the compact antenna array eigenmodes is worsened by
mutual coupling, particularly for the higher-order modes and must be taken into
accountinthedesignprocessforoptimumperformance.
– An optimum trade-off between miniaturisation and absolute radiation efficiencies
is vital for application of these arrays in robust navigation receivers because the
efficiencyenhancementprovidedbyrealisticdecouplingandmatchingislimited.
– The decoupling and matching network integration with the antenna array demands
miniaturisation of the network, and careful implementation for minimum ohmic
losses. The decoupling and matching generally comes before the low-noise ampli-
fier, and any additional losses, i.e. noise contribution, will adversely affect the
system’sperformance.
– The noise characterisation of the complete navigation antenna array receiver, in-
cluding the network losses, yields the equivalent carrier-to-interference-plus-
noise ratio by applying the conventional deterministic beamformer with null-
constraints. Thisframeworkallowsforperformancemeasurepredictionsinrespect
ofthenavigationreceiver.
– The impact of the polarisation impurity in the higher-order modes on the receiver’s
vulnerability to the arbitrary-polarised interferer is characterised in the equiv-
alent carrier-to-interference-plus-noise ratio. This is useful in analysing compact
antennaarrayrobustnessinworstinterferencescenariosbeforeitsintegrationwith
thereceiver.
– Low-cost, miniaturised, compact navigation antenna arrays, using off-the-shelf ce-
ramicpatchantennasandquadraturecouplersarepossible. Thisishelpfulformass-
production.
– The developed compact navigation antenna array receiver incorporating decoupling
and matching network integration allows for realistic measurements in real-world
scenariostoverifyitsnavigationrobustness.
– Thepracticalapplicabilityofdecouplingandmatchingforcompactantennaarrays
becomescrucialandprominentintheinterference-limitedscenarios;therefore,its
implementationisnecessaryforrobustcompactnavigationantennaarrayreceivers.
Preface
This work is a compilation of the research carried out at the RF and Microwave Research
Laboratory of the Technische Universität Ilmenau. The research has been part of the
project "Compact adaptive terminal antenna for robust satellite navigation" (KOMPAS-
SION) and the on-going project "Compact satellite receiver systems for robust navigation
applications" (KOSERNA). These projects and thus this work at the laboratory have been
funded by the German Aerospace Center (grant no. 50NA1007 and 50NA1405) on be-
halfoftheGermanFederalMinistryofEconomicsandTechnology,forwhichIamhighly
obliged.
I am grateful to the head of laboratory, Univ.-Prof. Dr. rer. nat. habil. Prof. Matthias
Hein for his valuable support and guidance. The successful completion of this work has
beenstimulatedbyhisvisionaryideasandsuggestions.
I would also like to thank Prof. Dr.-Ing. habil. Reiner S. Thomä and Dr.-Ing. Achim
Dreherforreviewingthiswork.
IamthankfultoDr.-Ing. RalfStephanforhispreciousdiscussions,andprovidingvalu-
able support into the practical aspects. I am humbly obliged to the friendly yet aspiring
environment provided by my colleagues Dipl.-Ing. Hendrik Bayer, Dipl.-Ing. Alexander
Krauss, Dipl.-Ing. Stephanie Kühn, M.Sc. Saqib Kaleem and Dipl.-Ing. Frank Wollen-
schläger. IamthankfultothetechnicalassistanceprovidedbyMr. MichaelHuhnandMr.
MatthiasZocher.
Iamthankfultothecolleaguesintheprojectconsortium. Theseinclude: M.Sc. Matteo
Sgammini, Dr.-Ing. Achim Hornbostel, and M.Sc. Lothar Kürz for their valuable support
inconductingjointresearchcollaborations. IamdeeplygratefultoM.Sc. EricSchäferfor
histechnicalinvestigationsandhissupportinwritingsofseveraljointpublications.
I am thankful to be blessed with the emotional support of my lovely wife Maryiam.
Herinsightsanddrivingforcemadethecompletionofthisworkeasierandcolourful. Iam
thankfultomybrother,AnseIrteza,forhiseverpresenceandsupport.
Finally, I am thankful to my parents for their motivational support. This work is a
tributetotheirhardshipsandefforts.
SafwatIrtezaButt
Ilmenau,7th July2015

Contents
1 Introduction 12
2 RobustnessofGlobalNavigationSatelliteSystems 15
2.1 BasicprincipleofGNSS . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.1 Characteristicsofthesatellitesignal . . . . . . . . . . . . . . . . 17
2.1.2 Positioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.3 PerformancestandardsofGNSS . . . . . . . . . . . . . . . . . . 20
2.2 Receiverarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.2.1 Front-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.2 Basebandprocessing . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.3 State-of-the-artGNSSreceivers . . . . . . . . . . . . . . . . . . 22
2.3 Typesandfeaturesofantennas . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.1 Antennagain . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.2 Polarisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3.3 Phasecentre . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3.4 CommercialGNSSantennas . . . . . . . . . . . . . . . . . . . . 31
2.4 Robustnessrequirementsandchallengingenvironments . . . . . . . . . . 32
2.4.1 Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.4.2 Multipath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.4.3 Atmosphericeffects . . . . . . . . . . . . . . . . . . . . . . . . 36
2.5 Multiple-antennabasedGNSSreceivers . . . . . . . . . . . . . . . . . . 37
2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3 EvaluationMethodologiesofCompactPlanarAntennaArrays 41
3.1 Mutualcoupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1.1 Mutualimpedance . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.1.2 Consequenceofthemutualcoupling . . . . . . . . . . . . . . . . 45
3.1.3 Surfacewavesinplanarantennas . . . . . . . . . . . . . . . . . 45
3.2 Antennaarrayspatialcovariancematrix . . . . . . . . . . . . . . . . . . 47
3.2.1 Generalisationtomulti-portantennas . . . . . . . . . . . . . . . 47
8
Contents 9
3.2.2 Influenceofthecurrentexcitationontheefficiency . . . . . . . . 49
3.2.3 Beam-patternorthogonalityandportcoupling . . . . . . . . . . . 51
3.3 Thefundamentalmodesofradiation . . . . . . . . . . . . . . . . . . . . 52
3.3.1 Theminimumeigenvalue . . . . . . . . . . . . . . . . . . . . . . 53
3.4 Diversityreception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4.1 Diversitygain . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.4.2 Diversityloss . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.5 Compactceramicpatchantennaarrayconfigurations . . . . . . . . . . . 58
3.5.1 Optimalnumberofelements . . . . . . . . . . . . . . . . . . . . 59
3.5.2 Optimalinter-elementseparation . . . . . . . . . . . . . . . . . . 60
3.5.3 Optimalgeometry . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.5.4 Examples: Fabricatedfour-elementceramicpatchantennaarrays 62
3.6 Polarisationpurity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.6.1 Tiltedceramicpatchantennaarray . . . . . . . . . . . . . . . . . 69
3.6.2 Quadrafilarhelixantennaarray . . . . . . . . . . . . . . . . . . . 69
3.7 Direction-of-Arrivalestimationcapabilities . . . . . . . . . . . . . . . . 72
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4 CompactRobustGNSSAntennaArrayReceivers 81
4.1 Techniquesforantennaarraydecoupling . . . . . . . . . . . . . . . . . . 82
4.1.1 Radiationelementleveldecoupling . . . . . . . . . . . . . . . . 83
4.1.2 Network-baseddecoupling . . . . . . . . . . . . . . . . . . . . . 84
4.2 Techniquesformodalmatching . . . . . . . . . . . . . . . . . . . . . . . 89
4.2.1 Fundamentalbandwidthlimitations . . . . . . . . . . . . . . . . 89
4.2.2 Practicalimplementationsandimplications . . . . . . . . . . . . 92
4.3 Noisecharacterisationoftherobustreceiver . . . . . . . . . . . . . . . . 93
4.3.1 Antennaarraynoise . . . . . . . . . . . . . . . . . . . . . . . . 94
4.3.2 Decouplingandmatchingnetworknoise . . . . . . . . . . . . . . 95
4.3.3 Low-noiseamplifiernoise . . . . . . . . . . . . . . . . . . . . . 97
4.4 Equivalentcarrier-to-interference-plus-noiseratio . . . . . . . . . . . . . 98
4.5 Design,implementation,andevaluationofcompactGNSSantennaarrays 100
4.5.1 Four-element λ/4 GNSS antenna arrays with integrated decou-
plingandmatchingnetworks . . . . . . . . . . . . . . . . . . . . 100
4.5.2 Co-polarisedinterferencescenarios . . . . . . . . . . . . . . . . 109
4.5.3 Arbitrarypolarisedinterferencescenarios . . . . . . . . . . . . . 114
4.6 Low-costcompactGNSSantennaarray . . . . . . . . . . . . . . . . . . 114
4.6.1 Miniaturisationofdecouplingandmatchingnetwork . . . . . . . 116
4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118