Electromagnetic Simulation, Analysis and Design with Application to Antennas and Radar Absorbers

93 Pages·2012·3.52 MB·English

Electromagnetic Simulation, Analysis and Design with
Application to Antennas and Radar Absorbers
ALIREZA MOTEVASSELIAN
Doctoral Thesis
Stockholm, Sweden 2012
KTH School of Electrical Engineering
ISSN 1653-5146 SE-100 44 Stockholm
ISBN 978-91-7501-481-4 SWEDEN
Akademisk avhandlingsommed tillståndav KunglTekniskahögskolanframlägges
tilloffentliggranskningföravläggandeavteknologiedoktorsexamenfredagenden5
oktober2012klockan13.15isalF3,KunglTekniskahögskolan,Lindstedtsvägen26,
Stockholm.
© Alireza Motevasselian, 2012
Tryck: Universitetsservice US AB
iii
Abstract
Thepresentthesisconsiders twodifferentsubjectsin theresearch area of
electromagnetics. The first part is concerned with antenna design and the
second with radar absorbers and rasorber.
Inthefirstpart,anovelexcitationtechniqueforcylindricaldielectricres-
onator antennas is introduced to produce circular polarization. The exciter
is a tape helix that is wound around the dielectric resonator and is fed by a
coaxial probe. ThehelixexcitestheHE11δ modesinphasequadratureinthe
cylindricaldielectricresonatorantenna. Theheightofthehelixisdetermined
usingtheHansen-Woodyardconditionforanend-firearraybasedonthephase
velocity of thesurface wavetravelingalong thedielectric resonator sidewall.
This phase velocity is estimated from thephase velocity in an infinitely long
dielectricrodwiththesamepermittivityandradiusasthedielectricresonator
antenna. The helical exciter is required to operate in the helix axial mode.
The height of the helix is usually taller than the height of the dielectric res-
onator core. Using this type of excitation, a 3 dB axial-ratio bandwidth of
6.4% was achieved for a sample design with dielectric constant εr ∼11. The
achieved 3 dB axial-ratio bandwidth is greater than that typical of other re-
ported single feed cylindrical dielectric resonator antennas. A prototype of
thesampledesignisfabricated andmeasuredandagoodagreement between
simulation and measurement is observed. Furthermore, two approaches for
the enhancement of the 3 dB axial ratio bandwidth are proposed: removing
the central portion of the cylindrical dielectric resonator and using stacked
cylinders. The advantages and limitations of each approach are discussed.
Another perspective on the proposed design is to consider the antenna as a
helix with a dielectric resonator core. In this perspective, the effects of the
dielectric core on thehelix antennaare discussed.
The second part of the thesis is concerned with the design of thin wide-
bandelectromagnetic planarabsorberforX-andKKu-bandwhichalsohasa
polarization sensitive transparent window at frequencies lower than L-band.
Thedesign isbased on atwo layercapacitivecircuit absorber with theback-
metal layerreplaced with apolarization sensitivefrequency selectivesurface.
Thestructureisstudiedfornormallyincidentwaveswithtwoorthogonallin-
earpolarizations. Thestructureisoptimizedtohavehightransparencyatlow
frequenciesforoneofthepolarizationsandatthesametimegoodabsorption
efficiency for both polarizations at the high-frequency band. For one of the
polarizationsa-1.9dBtransmissionwithatransmissionlossoflessthan10%
at 1 GHz as well as a 2.25:1 (75%) bandwidth of -20 dB reflection reduction
are achieved. For the other polarization we obtained more than 3:1 (100%)
bandwidth of-19 dBabsorption. Compared with ourearlier design based on
a Jaumann absorber, we succeed in significantly reducing the transmission
lossatthetransparentwindow. Furthermore,themoduleofabsorptionqual-
ity is extensively improved. The improvements are based on using periodic
arrangements of resistive patches in the structure design. The investigation
ofthestructureforobliqueanglesofincidenceandnon-idealmaterialsisalso
accomplished.

Acknowledgements
IwouldliketoexpressmydeepandsinceregratitudetomysupervisorLarsJonsson.
Iappreciateallhiscontributionsoftime,ideasandencouragementsduringmyPhD
study. It has been an honor for me to be his first PhD student. I am thankful of
his patience and support at every stage of this PhD work.
This thesis, particularly in the second part,would not havebeen possible with-
out the help of my colleague, Anders Ellgardt. I would like to record my gratitude
to him for his advice, guidance and great ideas in several aspects of my research.
It would be always a good memory in my mind, the pleasant time in our shared
office.
I am also grateful to my co-supervisor Martin Norgren for his valuable partici-
pation in part of the work as well as helpful comments and hints for the courses I
have had with him. Martin, with his great electromagnetic knowledge, is always a
worthy reference at the department.
This thesis arose in part out of years of research done since I came to the
Electromagnetic Theory Group at KTH. By that time, I have workedwith a great
number of people whose kind contributions have aided me in several aspects of
research, courses, and also in general life in Sweden. It is a pleasure to convey my
gratitude to them all in my humble acknowledgments. To mention a few, in the
first place I would like to our computer administrator, Peter Lönn, for his kind
technical support with computer hardware and software. Furthermore, I thank all
present and former colleagues at the department for good time I had with them
during lunchtime and coffee breaksandtheir contributiontothe nice atmosphere.
I am also thankful to all my friends here and in my home country who have been
my resource of encouragement.
Finally, I wish to thank my parents, my sister Mahtab, my cousins Abbas and
Nadereh, and also my dear Azadeh for their great love to me and for aiding me a
lot to accept and enjoy my new life conditions in Sweden.
Alireza Motevasselian
Stockholm, September 2012
v

Contents
Contents vii
1 Introduction 1
I GeneralIntroductiontoCircularlyPolarizedDielectricRes-
onator Antennas Using Helical Excitation 5
2 Dielectric Resonator Antennas (DRAs) 7
2.1 History and Background . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Cylindrical DRA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Coupling to DRAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3 The Helix 15
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 Analysis of the Helix . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4 Phase Velocity in Dielectric Rods and Tubes 21
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.2 Dielectric Rods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.3 Dielectric Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5 Polarization of Antennas 31
5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2 Linear, Circular, and Elliptical Polarizations. . . . . . . . . . . . . . 32
5.3 The Axial Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6 Results 35
6.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.2 Fabrication and Measurement . . . . . . . . . . . . . . . . . . . . . . 42
6.3 Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
vii
viii CONTENTS
II General Introduction to A Polarization Sensitive Rasorber
Design 49
7 Statement of the Problem 51
7.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.2 Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
8 Analysis of Stratified Periodic Structures 53
8.1 Wave Splitting Method for the Analysis of Stratified Structures . . . 53
8.2 Simulation of Periodic Structures in HFSS . . . . . . . . . . . . . . . 56
9 Jaumann-Like Rasorber 57
9.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
9.2 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
10 Capacitive Circuit Rasorber 63
10.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
10.2 The Synthesis of the Series RC Admittances . . . . . . . . . . . . . 66
10.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 67
11 Conclusion 71
IIIPapers 73
12 Paper I 77
12.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
12.2 Antenna Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 79
12.3 Design Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
12.4 Design Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
12.5 Simulation and Measured Results . . . . . . . . . . . . . . . . . . . . 85
12.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
13 Paper II 93
13.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
13.2 Antenna Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 95
13.3 Design Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
13.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 97
13.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
14 Paper III 109
14.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
14.2 Antenna Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . 110
14.3 Design and Simulation Results . . . . . . . . . . . . . . . . . . . . . 111
14.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
CONTENTS ix
15 Paper IV 117
15.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
15.2 The Antenna Design and Performance . . . . . . . . . . . . . . . . . 118
15.3 Comparison with Finite Arrays . . . . . . . . . . . . . . . . . . . . . 119
15.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
15.5 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
16 Paper V 125
16.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
16.2 Design goals and restrictions . . . . . . . . . . . . . . . . . . . . . . 127
16.3 A Gangbuster similar low-pass frequency selective surface . . . . . . 128
16.4 A FSS backed Jaumann absorber . . . . . . . . . . . . . . . . . . . . 129
16.5 Sensitivity analysis of the FSS-backed Jaumann structure . . . . . . 133
16.6 FSS Backed Jaumann Absorber for an Aircraft Wing-Front Profile . 134
16.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
17 Paper VI 141
17.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
17.2 Design goals and model . . . . . . . . . . . . . . . . . . . . . . . . . 143
17.3 The Back-LayerFSS Design . . . . . . . . . . . . . . . . . . . . . . . 145
17.4 The Optimized Design . . . . . . . . . . . . . . . . . . . . . . . . . . 147
17.5 Realization of the Optimized Circuit Model . . . . . . . . . . . . . . 149
17.6 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
17.7 Perturbation Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
17.8 Practical Considerations . . . . . . . . . . . . . . . . . . . . . . . . . 155
17.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Bibliography 161