ANTENNA RADIATION
CONTROL USING
ELECTROMAGNETIC
BAND GAP
Mohd Saari Mohamad Isa
A Thesis Submitted to the University of Sheffield for the Degree of
Doctor of Philosophy in Electronic and Electrical Engineering
i
ABSTRACT
The ever growing wireless technologies pose new challenges for the design of antenna
systems. The challenges can be related to the mechanical and electrical properties of the
antenna, such as dimensions, compactness and low profile with the improvement of power
directivity, gain and efficiency. The antenna design have experienced enormous advances in
the last decades and still undergoing massive developments. Many new technologies have
emerged including the development of the metamaterial structures. Electromagnetic band gap
(EBG) structure can be considered as a metamaterial that possesses some interesting
properties of high impedance and artificial magnetic conducting surface.
This work is focused on developing EBG structures to control the surface wave propagation
around the antenna. The sectorized EBG has been utilized to steer the beam around the
microstrip patch antenna. The flexible beam directive antenna with an operating frequency of
2.2GHz has been achieved by integrating a TM01 mode microstrip patch antenna with an
EBG. The circular EBG elements are arranged in six sectors with group of pin vias.
Switching pin vias in and out from each sector has steered the beam into that sector. The
flexible beam scanning antenna with a stable reflection coefficient has been achieved.
In modern wireless communication, compact systems with high gain and efficiency are
always needed. To achieve these requirements, a compact array utilizing the miniaturized
capacitive loaded EBG with a total period of λ/36 has been developed. Pin vias been used to
alter the EBG surface impedance, which controls the propagation of surface waves within the
array elements. Switching pin vias on has increased the surface impedance to be infinite,
which suppress the surface waves, whereas switching the pin vias out has reduced the surface
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isolated and propagated the signal within the array elements accordingly. The application of
EBG to control and channel the signal within the array elements has been demonstrated.
The other EBG application to control the radiation has been described for the phased array
antenna. Large array of microstrip phased array antenna with a high gain and a directive
beam has the problem of scan blindness with losses of power at a certain direction. This is
due to the surface waves, which is bound to the array surface, which stores some of the
energy. The array return loss near 0dB at the angle has demonstrated the severity of the
problem. Miniaturized EBG which is placed within the array elements has efficiently
suppressed the surface waves and improved the scan blindness problems. The simulation
results using CST software has illustrated the EBG characteristics on controlling the antenna
and array radiation. The novel finding of EBG characteristics in controlling the antenna
radiation pattern by suppressing and propagating of surface waves is the main contribution of
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ACKNOWLEDGEMENTS
First of all, thanks to Almighty Allah for all His mercy, kindness and guidance and giving me
the wisdom and strength to finish my thesis. Heartiest gratitude to my supervisors: Professor
Richard Langley and Dr. Salam Khamas for their kind advices, guidance, encouragements
and supports during my doctoral research and study. The achievements and completion of
the thesis will be very hard to be possible without their valuable, sincere and relentless
supervision. Unforgettable acknowledge to Government of Malaysia and Universiti Teknikal
Malaysia Melaka for funding my PhD. I also would like to thank Dr. Alan Tennant, Dr. Wei
Liu, Dr. Jonathan Rigelsford, Dr. Lee Ford, Dr. Greg Cook, Dr Lester Low, Steve Marsden
and all the staffs in the workshop for their helps and supports. I also would like to mention
my fellow PhD Liu, Nisar, Tarik, Ismail, Najib, Hassan and Redzuan for their helps and
supports and making my time enjoyable during my study and completing my PhD. The
discourse is incomplete without mentioning my beloved wife Mahnon Suria and daughters
Nur Ayuni Farzana and Nur Ayna Farzana for their love and patience throughout the course
of my study. Finally I would like to thanks all my families and friends in Malaysia who
iv Proceedings of the Fifth European Conference on Antennas and Propagation (EuCAP), 11-15 April 2011, Rome, Italy, pp. 216-219
M.S. Mohamad Isa, R. Langley, S.Khamas,A. Awang Md Isa, M.S.I.M. Zin, F.M. Johar, Z.Zakaria" Antenna Beam Steering using Sectorized Square EBG”, Journal of Telecommunication, Electronic and Computer Engineering (JTEC), vol. 4 no 1, pp. 39-44, June 2012
M.S. Mohamad Isa, R.Langley, S.Khamas, A. Awang Md Isa, M.S.I.M. Zin, F.M. Johar, Z.Zakaria "Microstrip Patch Antenna Array Mutual Coupling Reduction using Capacitive Loaded Miniaturized EBG”, Journal of Telecommunication, Electronic and Computer Engineering (JTEC), vol. 4 no 2, pp. 27-34 , December 2012
M.S.M.Isa, R.Langley, S.Khamas, A.A.M.Isa, M.S.I.M.Zin, Z.Zakaria, N.Z.Haron, A.Ahmad "A Novel Technique of Controlling Signal Propagation within Array Elements using Switchable Miniaturized Electromagnetic Band Gap”, 2013 IEEE Symposium on Wireless Technology & Applications (ISWTA), 22-25 September 2013, Kuching, Malaysia, pp. 178-182
M.S.M.Isa, R.Langley, S.Khamas, A.A.M.Isa, M.S.I.M.Zin, Z.Zakaria, N.Z.Haron, A.Ahmad "Microstrip Patch Antenna Array Mutual Coupling Reduction using Capacitive Loaded Miniaturized EBG”, Journal of Telecommunication, Electronic and Computer Engineering (JTEC), vol. 5 no 2, pp. 11-17 , December 2013
v
1.2 Electromagnetic Band Gap 3
1.3 Diversity Antenna 5
1.4 Leaky Wave Antenna and Surface Wave Antenna 7
1.5 Microstrip Patch Array Antenna Mutual Coupling Reduction Using
EBG. 9
2.2 Electromagnetic Band Gap 26
2.2.1 Phase Reflection for the EBG Surface 27
2.2.2 EBG Operating Frequency. 30
2.2.3 Electromagnetic Band Gap Bandwidth 34
2.2.4 EBG Performance under Incident Wave. 37
2.3 Surface wave and Leaky Wave 38
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2.4.1 Mutual Coupling between the array elements 42
2.4.2 The Effect of the Antenna Arrangement on the Mutual
Coupling within the Array Elements. 45
2.5 Phased Array Antenna 48
2.5.1 Grating Lobe for a Phased Array Antenna. 51
2.5.1 Phased Array Field Pattern. 53
2.5.2 Scan Blindness for Phased Array Antenna 56
2.6 Simulation Technique 58
2.7 Conclusion 60
Reference 61
Chapter 3 : ANTENNA BEAM STEERING USING SECTORIZED EBG
3.1 Introduction 64
3.1.1 Motivation 66
3.2 Patch Antenna Beam Steering using a Sectorized Square
Mushroom-like EBG 67
3.3 Antenna Beam Steering using a Sectorized Circular EBG 75
3.4 Fabrication and Measurement 83
3.5 Electromagnetic Band Gap Sector with a Switch Board 87
3.6 Conclusion 90
Reference 92
Chapter 4 : MICROSTRIP PATCH ARRAY ANTENNA MUTUAL COUPLING CONTROL USING MINIATURIZED EBG
4.1 Introduction 94
4.1.1 Motivation 95
4.2 Development of a Miniaturized Capacitive Loaded EBG 97
4.3 Two elements Microstrip Patch Array Antenna 105
4.3.1 Mutual Coupling Reduction using a Miniaturized
vii
4.3.2 Comparison of the Miniature capacitive EBG structure
with the mushroom-like EBG 112
4.3.3 Fabrication and Measurement 117
4.4 Mutual Coupling Control within the Array Elements using
Miniaturized EBG. 121
4.4.1 Signal Channelling within Microstrip Array Antennas
using Miniaturized EBG. 122
4.4.2 Isolation of Array Elements using Miniaturized EBG. 127
4.4.3 Switching Surface Wave Propagation within Array
Elements Using Miniaturized EBG. 132
4.5 Conclusion 138
References 140
Chapter 5 : MICROSTRIP PHASED ARRAY ANTENNA SCAN BLINDNESS ELIMINATION USING MINIATURIZED EBG
5.1 Introduction 142
5.1.1 Motivation 143
5.2 Array Scan Blindness for a Phased Array Antenna 144
5.2.1 Analysis of Scan Blindness for a Linear Phased Array
Antenna. 146
5.3. Analysis of Scan Blindness for Planar Phased Array Antenna 153
5.4 Microstrip Phased Array Scan Blindness Elimination using
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LIST OF ACRONYMS
1D One dimensional
2D Two dimensional
3D Three dimensional
AMC Artificial magnetic conductor
BAN Body area network
CAD Computer Aided Design
CPW Coplanar waveguide
CST Computer Simulation Technology
DFT Discrete Fourier transform
DNG Double negative
EBG Electromagnetic band gap
E-field Electric field
EM Electromagnetic
ETSI European Telecommunications Standards Institute
FDTD Finite difference time domain
FEM Finite elements method
FIT Finite Integration Technique
FSS Frequency selective surface
H-field Magnetic field
HIS High impedance surface
IEEE Institute of Electrical and Electronics Engineers
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LWA Leaky wave antenna
MOM Method of Moment
MPAA Microstrip patch array antenna
MWS Microwave Studio
NRI Negative reflective index
PAA Phased array antenna
PBG Photonic band gap
PCB Printed circuit board
PEC Perfect electric conductor
PMC Perfect magnetic conductor
RFIC Radio frequency integrated circuit
S Scatter
SWA Surface wave antenna
TE Transverse electric
TM Transverse magnetic
UWB Ultra wideband
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LIST OF FIGURES
Figure 1.2.1 Equivalent circuit model for the high impedance surface
Figure 2.2.1 The EBG surface with plane wave.
Figure 2.2.2 The typical EBG S11 reflection phase plot
Figure 2.2.3 Mushroom-like EBG structure (a) top view (b) side view
Figure 2.2.4 EBG current path equivalent circuit
Figure 2.2.5 EBG surface excited by incident wave
Figure 2.3.1 A radiating surface wave
Figure 2.3.2 A bound surface wave
Figure 2.4.1 Geometry of microstrip patch antenna
Figure 2.4.2 A microstrip patch antenna – E field
Figure 2.4.3 A microstrip patch antenna with coaxial probe
Figure 2.4.4 A patch antenna embedded in a high-impedance ground plane
Figure 2.4.5 Array microstrip patch antenna
Figure 2.4.6 2-ports network- representation for two antenna array.
Figure 2.4.7 T-network equivalent- for two-port network.
Figure 2.4.8 Microstrip patch antenna with (a) E-plane coupling (b) H-plane
coupling
Figure 2.4.9 Simulated result for mutual coupling comparison for a patch array in
the E-plane and H-plane configurations at 2.2GHz.
Figure 2.5.1 Linear broadside phased array antenna
Figure 2.5.2 A radiation pattern of phased arrays
xi
Figure 2.5.4 Reflection coefficient for microstrip patch array antenna
Figure 3.2.1 Microstrip transmission line to measure EBG surface transmission
coefficient.
Figure 3.2.2 Transmission coefficient, S21, within a square EBG surface using a
microstrip transmission line
Figure 3.2.3 Square EBG structure with sector A without pin via
Figure 3.2.4 Patch antenna at the centre of an EBG
Figure 3.2.5 Return losses of the Patch Antenna for A without via and
sector-F without via.
Figure 3.2.6 Normalised antenna simulated radiation pattern at 2.2GHz for
(a) sector-A without pin vias and (b) sector-F without pin via
Figure 3.3.1 Circular EBG surface with sector-A without pin via
Figure 3.3.2 Transmission coefficient, S21 within circular EBG with or without pin
vias.
Figure 3.3.3 Circular patch antenna located at 3mm above the EBG surface
Figure 3.3.4 Simulated return loss for patch antenna with EBG sector: A and F
without pin via
Figure 3.3.5 Azimuth (xy-plane) and elevation (theta) plane normalized patterns at
2.2GHz with pin vias switched out at (a) sector-A and (b) sector-F
Figure 3.3.6 Azimuth (xy-plane) for at 2.2GHz all sector with pin via switched in and out (normalised to the maximum value when the all pin vias switched out)
Figure 3.3.7 Normalized Elevation (theta) plane patterns at 2.2GHz with all pin vias
xii
Figure 3.4.1 Antenna and EBG Assembly
Figure 3.4.2 Measured and simulated return loss of the antenna with pin via
switched out at the sector/s.
Figure 3.4.3: Comparison for the antenna measured and simulated radiation patterns
at 2.2GHz for pin vias switched out
Figure 3.5.1 EBG with a switch board (a) switch board placed underneath the EBG
(b) switch “ON” and “OFF”
Figure 3.5.2 Simulated antenna return loss for sector-A and F switched off with
other sectors switched in in both cases using switch boards.
Figure 3.5.3 Antenna azimuth surface radiation pattern (theta=90º) at 2.2GHz for
switch board off in (a) sector-A and (b) sector-F
Figure 4.1.1 Top view for miniaturize EBG structure.
Figure 4.2.1 Unit cell for miniaturized EBG with capacitors
Figure 4.2.2 New equivalent circuit of capacitive loaded EBG.
Figure 4.2.3 Reflection phase for a unit cell EBG with variable cell period, p
Figure 4.2.4 Reflection phase for unit cell p=3.8mm, with variable lumped
capacitance value.
Figure 4.2.5 EBG structure with transmission line
Figure 4.2.6 Simulated transmission coefficient within EBG structure using
transmission line for the case of EBG with and without pin via
Figure 4.3.1 Patch Antenna Array arranged in the E-plane (in line)
xiii
Figure 4.3.3 Microstrip patch array antenna integrated with EBG top and side view.
Figure 4.3.4 Simulated S-parameters for a patch array antenna integrated with a
miniaturized EBG structure and for the same array without EBG
Figure 4.3.5 Array surface current at the resonance frequency 2.2GHz.
(a) Patch Array (b) Array with a miniaturized EBG.
Figure 4.3.6 Simulated E-plane elevation radiation pattern at 2.2GHz for array
antenna and array antenna with miniaturized EBG structure
(p=3.8mm).
Figure 4.3.7 Simulated elevation H-plane radiation pattern at 2.2GHz for array
antenna and array antenna with miniaturized EBG structure
Figure 4.3.8 Patch antenna array with a mushroom-like EBG
Figure 4.3.9 Simulated two elements array S-parameter using no EBG and EBG
structures of unit cell p=3.8mm (Figure 4.3.3) and 15mm (Figure
4.3.8).
Figure 4.3.10 Simulated elevation radiation pattern for array antenna at 2.2GHz,
comparing the performance of miniaturized EBG (p=3.8mm) against
the mushroom-like EBG (p=15mm) along E-plane and H-plane
Figure 4.3.11 Front and back view of the two-element microstrip path array
(a) without and (b) with miniaturized EBG (p=3.8mm).
Figure 4.3.12 Simulated and measured return loss. S11 results of two-element arrays
with and without miniaturized EBG structure (p=3.8mm)
Figure 4.3.13 Simulated and measured mutual coupling, S12 results of two-element
xiv
Figure 4.3.14 Comparison normalized E-plane radiation pattern for array antenna at
2.2GHz. (a) Array antenna without EBG (b) Array antenna with
3.8mm EBG
Figure 4.4.1 Microstrip patch array antenna integrated with miniaturized EBG.
Figure 4.4.2 Mutual coupling within the array elements against the centre element
with all the miniaturized EBG without pin via
Figure 4.4.3 Return losses for the individual array elements with all the miniaturized
EBG in EBG-A and ABG-B without pin via
Figure 4.4.4 Normalized azimuth (xy plane) radiation pattern for individual array
elements with the miniaturized EBG without pin via
Figure 4.4.5 3D view radiation pattern for individual array elements
with the miniaturized EBG without pin via
Figure 4.4.6 3D view for the combined radiation pattern for all the array elements
integrated with the miniaturized EBG-A and EBG-B without pin via
Figure 4.4.7 Normalised combined elevation radiation pattern at xz-plane (phi=0º)
for the array antenna integrated with EBG-A and EBG-B without pin
via.
Figure 4.4.8 Simulated mutual coupling between the two outer array elements and
the centre element with all EBG inserted with pin via.
Figure 4.4.9 Simulated return losses for the array elements with all the miniaturized
at EBG-A and EBG-B inserted with pin via
Figure 4.4.10 Normalized azimuth (xy plane) radiation pattern for the array elements
xv
Figure 4.4.11 3D view of the radiation pattern for the individual array elements..
Figure 4.4.12 3D view for the combined radiation pattern for all the array elements
integrated with the miniaturized EBG-A and EBG-B inserted with pin
via.
Figure 4.4.13 Normalised combined elevation pattern at xz-plane (phi=0º) for the
array antenna integrated with EBG-A and EBG-B inserted with pin via
Figure 4.4.14: Simulated mutual coupling within the array elements with EBG-A
without pin via and EBG-B inserted with pin via.
Figure 4.4.15 Simulated return losses for the array elements with pins via at EBG-A
switched out and switched in at EBG-B
Figure 4.4.16 Normalized azimuth (xy-plane) radiation pattern for the array elements
Figure 4.4.17 3D view of the radiation pattern for the individual array elements.
Figure 4.4.18 3D view for the combined radiation pattern for all the array elements
integrated with the miniaturized EBG-A without pin via and EBG-B
inserted with pin via.
Figure 4.4.19 Normalised combined elevation radiation pattern at phi=0º for the array
integrated with the miniaturized EBG-A without pin via and EBG-B
inserted with pin via.
Figure 5.2.1 Grating lobe appearance against element spacing and scan
Figure 5.2.2 Linear microstrip phased array antenna
Figure 5.2.3 E-plane radiation pattern for linear phased array separated with
0.5λ2.2GHz (68mm) period within elements (a) 3 elements (b) 5 elements
xvi
Figure 5.2.4 E-plane radiation pattern for linear phased array separated with
0.6λ2.2GHz (82mm) period within elements (a) 3 elements (b) 5 elements
(c) 7 elements (d) 15 elements
Figure 5.2.5 E-plane radiation patterns for a linear phased array centre element with
the period within elements of (a) 68mm (0.5λ2.2GHz) and (b) 82mm
(0.6λ2.2GHz) when 0º phased gradient within the elements.
Figure 5.2.6 H-plane radiation patterns for linear phased array center element with
the period within elements of (a) 68mm (0.5λ2.2GHz) and (b) 82mm
(0.6λ2.2GHz)
Figure 5.3.1 5x3 planar microstrip array antennas.
Figure 5.3.2 E-plane radiation pattern for planar phased array separated with
0.5λ2.2GHz (68mm) period within elements with the configuration of
(a) 3x3 elements (b) 5x3 elements (c) 7x3 elements
Figure 5.3.3 E-plane radiation pattern for linear phased array separated with
0.6λ2.2GHz (82mm) period within elements with the configuration of
(a) 3x3 elements (b) 5x3 elements (c) 7x3 elements
Figure 5.3.4 E-plane of active radiation patterns for planar phased array centre
element when the period within elements has been chosen as
(a) 68mm (0.5λ2.2GHz) and (b) 82mm (0.6λ2.2GHz).
Figure 5.3.5 H-plane of active radiation patterns for planar phased array centre
element with a period within elements of (a) 68mm (0.5λ2.2GHz) and (b)
xvii
Figure 5.4.1 5x3 planar phased array antenna radiation patterns against the pattern
elevation angle direction, theta (xz-plane)
Figure 5.4.1 The combined return losses characteristics for the array without EBG in
E-plane and H-plane at 2.2GHz
Figure 5.4.3 5x3 phased array antennas integrated with a miniaturized capacitive
loaded EBG.
Figure 5.4.4 Simulated E-plane radiation pattern for an array without EBG and with
EBG.
Figure 5.4.5 Simulated H-plane radiation pattern for the array centre element for the
case of array without EBG and with EBG
Figure 5.4.6 The combined return losses characteristics for the array without EBG
and with EBG in E-plane and H-plane at 2.2GHz.
Figure 5.4.7 Gain pattern of the fully excited array in E-plane (phi=0°) for the array
xviii
LIST OF TABLES
Table 5.4.1 Simulated S-parameters for the array centre element at 2.2GHz in
E-plane
Table 5.4.2: Simulated S parameters for the array centre element at 2.2GHz in
Chapter 1 Page 1
C
hapter
1
I
NTRODUCTION
1.1
Motivation
In modern communications, rapid growths of the wireless technologies have made the
antenna design more challengeable. Antenna arrays significantly improve the gain and
efficiency of the wireless application systems. Recent research has focused on the
miniaturized wireless system with low profile and light weight which mainly depends on the
compact antenna with high performance. The study on the antenna’s physical limitation can
be traced back to Chu’s work published in 1948 [1]. Chu limit has derived the trade-off
between antenna size and its performance with minimum possible quality factor (Q-factor),
maximum gain, and the maximum ratio of gain to Q-factor for an omni-directional antenna
using a spherical wave function. Considerable number of related studies have been published
Chapter 1 Page 2
Antenna design have experienced enormous advances in the last decades and still undergoing
massive developments. Many new technologies have been emerged in the modern antenna
design including the development of the metamaterial structures. The ancient Greek prefix
“meta”, which means “beyond”, describes the composite materials with unique feature not
readily available in nature. Various names have been introduced, such as, left-handed (LH)
material, double negative (DNG) material, negative reflective index (NRI) material, soft and
hard surface, artificial magnetic conductor (AMC) and high impedance surface (HIS). The
applications of metamaterial structures in the antenna design have become an exhilarating
topic among the antenna designers. Based on the metamaterial properties, novel
characteristics of antenna designs, which possibly going beyond the Chu limit, have been
reported [10-13] .
Electromagnetic band gap (EBG) structures with unique band gap features can be regarded as
metamaterials. Besides the band gap feature, EBG also possesses some other interesting
properties, such as AMC and high impedance surface. For instance, the mushroom-like EBG
structure demonstrates high surface impedance for both TE and TM mode. When the surface
is illuminated with a plane wave, the conducting surface with in-phase reflection coefficient
is obtained which resembles artificial conductor characteristics. These interesting features
have been applied to wide range of antenna designs, from linearly to circularly polarized
antennas, from wire to microstrip antenna and from conventional to novel surface wave
antennas [14-18]. The main challenge of the EBG design is to improve the antenna
performance and compactness to meet the modern wireless communication requirements.
The antenna compactness can be realized with closer and miniaturized techniques which
might cause some degradation in performance due to the surface wave. The control on
Chapter 1 Page 3
1.2
Electromagnetic Band Gap
Recently, there has been a growing interest in utilizing the electromagnetic band gap (EBG)
structures in the antenna design. The EBG structure can be classified as an artificial material
that operates in a specified frequency range and manipulates the propagation of
electromagnetic waves. The research on the EBG can be traced back to the earlier
development of the photonic band gap (PBG) materials in the optical spectrum. The typical
PBG structures proposed in [19, 20] have been realised by drilling holes in the dielectric
structure, which prevent the propagation of the electromagnetic waves within a certain
frequency range. The terminology of the suppressing surface wave has been suggested in
[21], which is based on the photonic band-gap (PBG) phenomena in optics and realised by a
periodical structure that has been found to be effective in improving the performance of an
antenna placed on top of that structure. The front-to-backward ratio of the antenna has been
enhanced by introducing PBG under or around the antenna. However, due to the
manufacturing difficulties and bulky size, the development of periodic band gap materials
based on the PBG concept was limited.
A planar EBG structure , which is also known as the unipolar compact photonic band gap
(UC-PCB), has been proposed by Fei-Ran on 1999 [22]. It has been constructed using a two
dimensional square lattice cells that consist of a metal pad with four connecting lines and
etched on the grounded dielectric substrate. The UC-PBG structure has demonstrated a 180°
phase difference compared to a PEC at the stop band frequency which demonstrates its’
characteristic as an artificial magnetic conductor of EBG. The main advantage of this type of
structure is the simpler fabrication process whereas the main drawback is introduced by the
Chapter 1 Page 4
The pioneer planar based mushroom-like EBG has been invented in 1999 by D. Sievenpiper
[23, 24]. The EBG structure is composed of a metallic EBG patch with a grounded dielectric
substrate and a metallic pin via connecting both metals. In several publications [25-27], it
has been demonstrated that the mutual coupling within the array antennas can be reduced by
integrating the EBG structure into the design.
(a) (b)
Figure 1.2.1 : Equivalent circuit model for the high impedance surface [24]
The two-dimensional array of the EBG elements can be illustrated as an electrical band stop
filter and could be modelled using a basic LC circuit as shown on Figure 1.2.1. The
capacitance, C, is distributed by the coupling effect of the top metal patches, while the
inductance, L, is produced by the current loop within the structure through the pin via as
shown on Figure 1.2.1 (a). The values of capacitance and inductance in the equivalent circuit
depend on the EBG cell dimensions and the thickness of the substrate, respectively.
For wireless communication applications, compactness and low profile is always a challenge
to the antenna engineers. To meet the required demands, compact convoluted geometries of
the EBG have been designed which has increased the equivalent capacitance with a reduction
Chapter 1 Page 5
Miniaturized EBG structures that utilize the lumped elements have also been realised, for
instance a miniaturized EBG has been developed using a parallel capacitance and inductance
[32]. Alternative design that uses loaded of capacitor elements within adjacent patch with
series of loaded inductors and vias has been proposed [33]. In both of those studies, the size
of EBG structure has been greatly reduced by up to λ/20. The miniaturized EBG utilizing
only capacitive lumped elements is one of the focuses in this research.
1.3
Diversity Antenna
Antennas are key components of any wireless communication system since they allow the
transfer of a signal (in a wired system) to waves that propagate through space and can be
received by another antenna. The receiving antenna is responsible for the reciprocal process,
which is turning an electromagnetic wave into a signal or voltage at its terminals so that it can
subsequently be processed by the receiver.
Antenna diversity is among the popular technique used to improve the wireless link
performance especially when the line-of-sight between transmitter and receiver is unclear.
Signal might be reflected and bounced back, which can introduce phase shift, attenuation,
distortion, interference, signal fading, and sometimes a total loss of the signal. The diversity
system with multiple antennas at the receiver makes several observations for the similar
signal. Each antenna will receive a different quality of signal. Thus, in some cases, one of the
antennas receives a weak signal, while other antennas might receive a stronger signal.
Collectively, the whole system would be able to provide a better quality of the received signal
![Figure 1.2.1 : Equivalent circuit model for the high impedance surface [24]](https://thumb-ap.123doks.com/thumbv2/123dok/542165.63234/23.612.111.515.227.397/figure-equivalent-circuit-model-high-impedance-surface.webp)
