Investigation and Design of a Slotted Waveguide Antenna with Low 3D Sidelobes

121 Pages·2010·2.9 MB·Afrikaans

Investigation and Design of a Slotted
Waveguide Antenna with Low 3D
Sidelobes
by
Andries Johannes Nicolaas Maritz
Thesis presented in partial fulfilment of the
requirements for the degree of
Master of Science in Engineering
at Stellenbosch University
Supervisor:
Prof. KeithD.Palmer
DepartmentElectricalandElectronicEngineering
March 2010
Declaration
Bysubmittingthisthesiselectronically,Ideclarethattheentiretyofthework
containedthereinismyown,originalwork,thatIamtheownerofthecopy-
rightthereof(unlesstotheextentexplicitlyotherwisestated)andthatIhave
notpreviouslyinitsentiretyorinpartsubmitteditforobtaininganyquali-
fication.
March2010
Copyright©2010StellenboschUniversity
Allrightsreserved
Abstract
An investigation into the cause of undesired sidelobes in the 3D radiation
pattern of slotted waveguide arrays is conducted. It is hypothesized that
the cross-polarization of the antenna is at fault, along with the possibility
that an error is made when designing a linear array. In investigating and
findingasolutiontotheproblem,the“Z-slot”isintroducedinconjunction
withpolarizerplates. Thebasecomponentsareusedbyacustomoptimiza-
tion algorithm to design reference and solution antennas. Results of the
antennas are then compared to ascertain the cause and possible solutions
for the unwanted sidelobes. The generic nature of the process may be used
to characterize other arbitrary aperture configurations and to design larger
antennas.
iii
Opsomming
‘n Ondersoek om die oorsaak van ongewensde sylobbe in die 3D uitstraal-
patroon van golfleier-antennas vas te stel. Die hipotese is dat die probleem
ontstaanuitdiekruis-polarisasievandieantenna,tesamemet‘nverkeerde-
likke aanname dat die opstelling liniêr is. Die “Z-Gleuf” tesame met po-
lariseringsplatewordvoorgestelashulpmiddelomdiemoontlikkeoorsake
teondersoek. ‘nGespesialiseerdeoptimeerings-algoritmebenuthierdieba-
siskomponente om beide verwysings- en oplossing-antennas te ontwerp.
Resultate van die ontwerpde antennas word dan vergelyk om die oorsaak
vandieongewensdesylobbetevastestel. Diegenerieseaardvandieproses
kan toegepas word op enige gleuf-konfigurasie en om groter antennas mee
teontwerp.
iv
Acknowledgements
The author would like to thank the following people for their contribution
towardsthisproject.
• ProfK.D.Palmer
• WernerSteyn
• JonathanHoole
v
Contents
Abstract iii
Opsomming iv
Acknowledgements v
Contents vi
Abbreviations ix
ListofFigures x
ListofTables xv
1 Introduction 1
1.1 ProblemStatement . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 ProjectOverview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 ThesisOutline . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 LiteratureStudy 6
2.1 Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 ApertureAntennas . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3 TransmissionLineTheory . . . . . . . . . . . . . . . . . . . . . 19
2.4 ArraySynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.5 WaveguideSlotArrays . . . . . . . . . . . . . . . . . . . . . . . 23
3 DesignoftheWaveguideTransmissionLine 25
3.1 WaveguideSpecifications . . . . . . . . . . . . . . . . . . . . . 25
3.2 PropertiesofRectangularWaveguides . . . . . . . . . . . . . . 26
3.3 DesignofaRidgedWaveguide . . . . . . . . . . . . . . . . . . 27
4 AnalysisofApertureRadiators 32
4.1 DiscussionofSlotPropertiesofInterest . . . . . . . . . . . . . 32
4.2 Study: OffsetRectangularApertureintheBroadwall . . . . . . 34
4.3 Study: Z-slotApertureintheBroadwall . . . . . . . . . . . . . 35
vi
CONTENTS vii
4.4 Study: Z-slotApertureintheBroadwallwithPolarizerPlates . 37
4.5 Study: Z-slotApertureinaRidgedWaveguide . . . . . . . . . 38
4.6 Study: Z-slotApertureinaRidgedWaveguidewithPolarizer
Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.7 Study: Varying Polarizer Plate Lengths in a Z-slotRidged
WaveguideConfiguration . . . . . . . . . . . . . . . . . . . . . 40
4.8 EquivalentCircuitModels . . . . . . . . . . . . . . . . . . . . . 44
4.9 SimulationResults . . . . . . . . . . . . . . . . . . . . . . . . . 45
5 AlgorithmsforApertureCharacterization&AntennaOptimiza-
tion 47
5.1 DiscussionoftheParameterSweepAlgorithm . . . . . . . . . 47
5.2 ExtractionofImpedancePropertiesfromS-Parameters . . . . 49
5.3 SimulationResultsofaParameterSweep . . . . . . . . . . . . 53
5.4 OptimizationAlgorithm . . . . . . . . . . . . . . . . . . . . . . 56
5.5 ValidationofCSTModels . . . . . . . . . . . . . . . . . . . . . 65
6 AntennaDesignsandComparison 68
6.1 BenchmarkDesign . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.2 WR75Z-slotAntennaDesign . . . . . . . . . . . . . . . . . . . 73
6.3 RidgedWaveguideZ-slotAntennaDesign . . . . . . . . . . . . 78
6.4 ComparisonofBenchmarkandZ-slotAntennaProperties . . . 83
7 Conclusions 88
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.2 RecommendationsforFutureResearch . . . . . . . . . . . . . . 89
7.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Appendices 91
A BenchmarkDesign 92
A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
A.2 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
A.3 SimulatedResults . . . . . . . . . . . . . . . . . . . . . . . . . . 93
B WR75WaveguideZ-slotDesign 95
B.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
B.2 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
B.3 SimulatedResults . . . . . . . . . . . . . . . . . . . . . . . . . . 96
C RidgedWaveguideZ-slotDesign 98
C.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
C.2 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
C.3 SimulatedResults . . . . . . . . . . . . . . . . . . . . . . . . . . 100
CONTENTS viii
D WR90toRidgedWaveguideTransition 102
Bibliography 105
Abbreviations
• TE–TransverseElectric
• TM–TransverseMagnetic
• TEM–TransverseElectromagnetic
• CST–CSTMicrowaveStudio(softwaretool)
• E-Field–ElectricField
• H-Field–MagneticField
• λ –Free-SpaceWavelength
0
• f –OperatingFrequency
0
• λ –WaveguideWavelength
G
ix
List of Figures
1.1 AzimuthDepictionofRadiationPatternforanAntennaArray . . 2
1.2 3DRadiationPatternofaSlottedWaveguideAntenna . . . . . . . 2
2.1 AxisSystemforArbitraryTransmissionLinesandanExampleof
aTransmissionMode . . . . . . . . . . . . . . . . . . . . . . . . . . 7
(a) AxisSystemforGenericWaveguides . . . . . . . . . . . . . 7
(b) TE PropagationModeinaRectangularWaveguide . . . . 7
10
2.2 ParallelPlateTransmissionLine . . . . . . . . . . . . . . . . . . . . 8
2.3 AttenuationandPropagationConstantasaFunctionofFrequency 9
2.4 RectangularWaveguideDimensionsandAxisSystem . . . . . . . 10
2.5 First Modes and their Cutoff Frequencies Found for the WR90
WaveguideProfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
(a) TE : f = at6.55GHz . . . . . . . . . . . . . . . . . . . . . . 11
10 c
(b) TE : f = at13.07GHz . . . . . . . . . . . . . . . . . . . . . 11
20 c
(c) TE : f = at14.73GHz . . . . . . . . . . . . . . . . . . . . . 11
01 c
(d) TE : f = at16.12GHz . . . . . . . . . . . . . . . . . . . . . 11
11 c
(e) TM : f = at16.12GHz . . . . . . . . . . . . . . . . . . . . . 11
11 c
(f) TM : f = at19.69GHz . . . . . . . . . . . . . . . . . . . . . 11
21 c
2.6 TE ModeFieldsandCurrents . . . . . . . . . . . . . . . . . . . . 14
10
(a) E-Fieldofa TE WaveAlongtheWaveguide . . . . . . . . 14
10
(b) E-Field TE ModeinaRectangularWaveguide(atthePort) 14
10
(c) H-Fieldofa TE WaveAlongtheWaveguide . . . . . . . . 14
10
(d) SurfaceCurrent J ofa TE WaveAlongtheWaveguide . . 14
s 10
2.7 Single-RidgedWaveguide . . . . . . . . . . . . . . . . . . . . . . . 15
(a) Single-RidgedWaveguide . . . . . . . . . . . . . . . . . . . . 15
(b) ProfileandNotationofaSingle-RidgedWaveguide . . . . . 15
2.8 AnApertureCutinaScreenwithitsComplementaryComponent 16
2.9 ApertureExcitationandTransmissionLineModel . . . . . . . . . 17
2.10 Equivalent Circuit Models for Offset and Rotated Aperture An-
tennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
(a) OffsetApertureAntennaanditsEquivalentCircuitModel . 18
(b) RotatedApertureAntennaanditsEquivalentCircuitModel 18
2.11 CascadedABCDParameters . . . . . . . . . . . . . . . . . . . . . . 19
2.12 Two-PortABCDNetwork . . . . . . . . . . . . . . . . . . . . . . . 19
x