Table Of ContentMulti-functional Chassis-based Antennas Using
Characteristic Mode Theory
by
Krishna Kumar Kishor
A thesis submitted in conformity with the requirements
for the degree of Doctor of Philosophy
Department of Electrical and Computer Engineering
University of Toronto
c Copyright 2014 by Krishna Kumar Kishor
(cid:13)
Abstract
Multi-functional Chassis-based Antennas Using Characteristic Mode Theory
Krishna Kumar Kishor
Doctor of Philosophy
Graduate Department of Electrical and Computer Engineering
University of Toronto
2014
Designing antennas for handheld devices is quite challenging primarily due to the limited
real-estate available, and the fact that internal antennas occupy a large volume. With
the need to support a variety of radio systems such as GSM, LTE and WiFi that operate
in a wide range of frequency bands, multi-band, wideband and frequency reconfigurable
antenna designs have been explored in the literature. Moreover, to support higher data
rates, the Long Term Evolution Advanced (LTE-A) standard has been introduced, which
requires supporting multiple input multiple output (MIMO) antenna technology and
carrier aggregation (CA) on a handheld device. Both of these benefit from the use of
multiple antennas or multi-port antennas, but with the limited space available, adding
more internal antennas may not be easily possible. Additionally, to realize the benefits
of these technologies the multiple antenna ports have to be well isolated from each other.
This thesis explores the utilization of the ground plane (or chassis) of a handheld
device as an antenna to meet some of these challenges. To achieve this, the theory of
characteristic modes (TCM) for conducting bodies is relied upon, to determine the eigen-
currents supported on the chassis. The orthogonality properties of these eigencurrents,
and their corresponding far-field eigenfields (electric and magnetic) makes TCM a good
tool to design multiple antennas with high isolation. This is demonstrated in this thesis
via the design of four chassis-based antennas that have different functionalities. The first
design is a two port MIMO antenna utilizing a combination of eigenmodes to achieve
ii
port isolation. The second design is a pattern reconfigurable MIMO antenna that can
operate in two states at 2.28 GHz. The third design is a four port antenna that operates
in three frequency bands, with two bands below 1 GHz for CA and the remaining two
ports for MIMO communication. The final design is a five port antenna that supports
MIMO operation in two frequency bands along with an additional port for CA in the
third band. The four designs have been experimentally verified, validating the use of
TCM as a versatile tool to design multi-functional chassis-based antennas.
iii
Dedication
To mummy and daddy,
for their love, prayers and blessings
iv
Acknowledgements
I take this opportunity to express my sincere gratitude to my supervisor, Prof. Sean
Victor Hum, for guiding and supporting me throughout this thesis. I would like to thank
him for the various opportunities he has given me, for allowing me to explore freely and
for bringing me back on track, for the discussions on several ideas, and for his critical
comments and advice. I have learnt a lot from him, and am very grateful.
I would like to thank the members of the committee Prof. Buon K. Lau, Prof. Costas
Sarris, Prof. GeorgeEleftheriades, and Prof. Ravi Adve for their questions and comments
which have helped improve the quality of this thesis. I also thank Blackberry for their
financial support in this project, and for allowing us to use their resources for performing
antenna measurements. I thank Tse Chan and Sandra Craig-Hallam for their assistance
duringthecourseofthiswork. Icannotforgetmyfellowgraduatestudents intheElectro-
magnetics group, and would like to thank them for creating a very positive environment.
I especially thank Mohammad Alam, Jonathan Lau, Hans-Dieter Lang, Tony Liang,
Hassan Mirzaei, Utkarsh Patel, Colan Ryan, Michael Selvanayagam and Alex Wong who
have been very generous with their time over the years.
My life here in Toronto wouldn’t be possible, had it not been for my friends. I would
like to thank Shruti Khanna, Chandep Lambda, Osama Hashimi, Basil Kanneth, Abdul
Latif, Kartik Narayan, Nikhil Ramesh, Suraj Ramesh, Fouzia Khan and Gerben Breimer
for the times we have shared together. I also thank the Nellikodes for being my family
here. I am deeply indebted to them. I also thank my teachers in Abu Dhabi, and would
like to remember three dear teachers who have passed away: Geetha teacher, Jeyakumar
Sir and Aranha Sir, who taught me Mathematics, Computer Science and English. They
were extremely loving and dedicated, and I am very fortunate to have been their student.
None of this would have been possible without the prayers, support and encourage-
ment of my parents, sister, brother-in-law, Dr. V. S. Gopal, my wife and in-laws. I am
very fortunate to have them in my life.
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Contents
1 Introduction 1
1.1 Mobile Phone Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Chassis Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Multiple Input Multiple Output (MIMO) and Carrier Aggregation (CA)
Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1 MIMO Communication Systems . . . . . . . . . . . . . . . . . . . 4
1.3.2 Carrier Aggregation (CA) . . . . . . . . . . . . . . . . . . . . . . 8
1.4 Motivation and Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . 11
2 Background 13
2.1 Theory of Characteristic Modes (CM) . . . . . . . . . . . . . . . . . . . . 13
2.1.1 Formulation and Computation of CMs . . . . . . . . . . . . . . . 15
2.1.2 Applying CM Theory for Antenna Design . . . . . . . . . . . . . 23
2.1.3 Modifying CMs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.2 Multiple Antenna Designs . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.2.1 Single-band Decoupled Antennas . . . . . . . . . . . . . . . . . . 45
2.2.2 Multi-band Chassis-based Antennas . . . . . . . . . . . . . . . . . 49
2.2.3 Reconfigurable MIMO Antennas . . . . . . . . . . . . . . . . . . . 51
3 A Two Port Chassis-based MIMO Antenna 54
3.1 Proposed Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
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3.2 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.2.1 Characteristic Mode Analysis . . . . . . . . . . . . . . . . . . . . 56
3.2.2 Port Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4 A Two Port Reconfigurable MIMO Antenna 67
4.1 Proposed Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.2 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.2.1 Characteristic Mode Analysis . . . . . . . . . . . . . . . . . . . . 70
4.2.2 Port Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5 Multi-port Chassis-based Antennas 92
5.1 Four port Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.1.1 Proposed Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.1.2 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . 96
5.1.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.2 Five Port Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.2.1 Proposed Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.2.2 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . 114
5.2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
6 Conclusions 135
6.1 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
A Near-fields of CMs of a Chassis 143
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B Schematics of Matching Networks 145
B.1 Two Port MIMO Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . 145
B.2 Reconfigurable MIMO Antenna . . . . . . . . . . . . . . . . . . . . . . . 146
B.3 Four Port Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
B.4 Five Port Antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
C Electromagnetic Isolation of a Two Port System 148
D Frequency Bands of some Radio Systems 150
Bibliography 151
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List Of Symbols
α modal weighting coefficient of eigenmode n
n
α modal weighting coefficient of eigenmode n normalized to real part of input power
n,norm
A magnetic vector potential
B radiation pattern in state 1 due to excitation of port i
i
B′ radiation pattern in state 2 due to excitation of port i
i
δ Kronecker delta
mn
ǫ permittivity of free space
ǫ relative permittivity
r
η waveimpedance of free space
η total efficiency of the antenna
tot
η radiation efficiency of the antenna
rad
E electric field intensity of eigenmode n
n
H channel matrix
H magnetic field intensity of eigenmode n
n
[I] discretized form of the surface current density of eigenmode n
n
J surface current density on the conducting body
J surface current density of eigenmode n
n
J surface current density on antenna due to excitation of port i
Pi
ix
k wavenumber of free space
λ real eigenvalue of mode n in the real eigenvalue equation
n
µ permeability of free space
M weighting operator in the complex eigenvalue equation
ν complex eigenvalue of mode n in the complex eigenvalue equation
n
φ electric scalar potential
e
P real part of the input power at a feed port
in
r position vector of the observation point
r′ position vector of the source point
R real part of impedance operator
ρ envelope cross-correlation coefficient
e
ρ correlation between the currents on the antenna with respect to Z
tc
ρ correlation between the currents on the antenna with respect to R
tc,MIMO
S surface of conducting body
S′ surface of integration containing S
S surface of integration at r =
∞
∞
[V] excitation vector in the Method of Moments
V volume bounded by the surface S′
X imaginary part of impedance operator
Z impedance operator
Z reactive load on the reconfigurable antenna
L
Z reactive load on the reconfigurable antenna at port 3
L3
Z reactive load on the reconfigurable antenna at port 4
L4
Z four port Z-parameters of the reconfigurable antenna
p
′
Z two port Z-parameters of the reconfigurable antenna
p
x
