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DEVELOPMENT OF WIDEBAND PHASED
ARRAY ANTENNA
ABDINASIR MOHAMED ABDI
UNIVERSITI TUN HUSSEIN ONN MALAYSIA
i
DEVELOPMENT OF WIDEBAND PHASED ARRAY ANTENNA
ABDINASIR MOHEMED ABDI
A Project Report submitted in partial
Fulfillment of the requirement for the award of the
Degree of Master of Electrical Engineering
Faculty of Electrical and Electronic Engineering
Universiti Tun Hussein Onn Malaysia
JANUARY 2018
iii
DEDICATION
Special dedicated to my caring and loving mother, Sado Ali Farah and to my beloved
father Mohamed Abdi Yuosuf, as well as my siblings for their support,
encouragement and constant love throughout my life. Thank you so much to all of
you for tireless and continued support.
iv
ACKNOWLEDGEMENT
In the name of Allah, the Most Gracious, and Most Merciful
Alhamdulillah Praise be to Almighty Allah the only owner (Subhanahu Wa
Ta‟ala) who gave me the courage and patience to carry out this project required for
the conferment of the Master Degree. Peace and blessing of Allah be upon his last
prophet Mohammed (Sallulahu-Alayhi Wassalam) and all his companions (Sahaba),
(Razi-Allaho-Anhum) who devoted their lives towards the prosperity and spread of
Islam.
I would like to express my sincere appreciation and heartfelt gratitude goes to
my supervisor, Dr. Noorsaliza Binti Abdullah for her kindness, constant endeavor,
and guidance, and the numerous moments of attention she devoted through out of
this project. This thesis would not have been possible finished without her
encouragement and support.
My greatest thanks to my family, especially both my parents whose has given
a lot of love, courage, sacrifice and support. Thanks also to all my friends and
colleagues who give me ideas and support to me in order to complete this report.
Thank you all for you kindness and generosity may Allah bless you all
rewarding paradise Insha Allah
v
ABSTRACT
Wideband communication system covering the range from 4 to 8 GHz requires
compact antenna to provide desirable characteristic over whole operating band. This
project consists of two designs; first design is presented with optimum geometry of
an ultra wideband circular patch antenna. To achieve an UWB characteristic, a patch
antenna is designed before proceeding to the bandwidth optimization techniques for
the proposed antenna which generates (3.1 – 10.6 GHz). While the second design
wideband phased array antenna was realized by adding one element and meander
line T-divider, partial ground plane and two slots at ground plane. The antenna was
designed and optimized using CST Microwave studio (CSTMWS). The proposed
antenna‟s parameters were optimized with various options such as differing the
ground plane length, different slot position, and the distance between the elements,
and found to operate satisfactorily. An optimized bandwidth has been noticed in this
design. Moreover, the antennas structure offers great advantages due to its simple
designs and small dimensions working with c-band application. The antenna has
been fabricated using FR-4 substrate and tested using network analyzer which has
range between 3GHz to 9GHz at the radio frequency (RF) laboratory. Simulation
result for wideband 4-8 GHz while the measurement result drops at 7.8 - 4.2 GHz,
and the gain is 3.65 dB, and directivity 5.35 dBi. As well as the phase difference
between the port 1 to port 2 is -154° and the phase from port 1 to port 3 is 66.8°.The
antenna performance showed good agreement between both simulation and
measurement results with only some small deviation and this observed deviation is
due to the different numerical modeling and meshing techniques.
vi
ABSTRAK
Sistem komunikasi wideband meliputi rangkaian dari empat (4) hingga lapan (8)
GHz yang memerlukan antena padat untuk membekalkan ciri yang wajar ke atas
semua operasi jejalur. Projek ini merangkumi dua reka bentuk: Reka bentuk pertama
adalah dikemukakan dengan geometri optimum dari antena tampalan pusingan
wideband ultra. Untuk memenuhi ciri-ciri UWB, antena tampalan direka sebelum
memulakan teknik pengoptimuman jalur lebar bagi antena yang dicadangkan yang di
mana ia menjana (3.1-10.6GHz). Sementara itu, reka bentuk kedua fasa pelbagai
antena wideband disiapkan dengan menambah satu elemen dan garis berliku-liku
pembahagi-T, satah tanah separa dan dua slot pada satah tanah. Antena direka dan
dioptimumkan menggunakan studio CST gelombang mikro (CSTMWS). Parameter
antena yang dicadangkan dioptimumkan dengan pelbagai pilihan,contohnya
perbezaan panjang satah tanah, kedudukan slot yang berlainan, dan jarak antara
elemen-elemen, dan ia didapati berfungsi dengan baik. Jalur lebar yang
dioptimumkan telah diperhatikan dalam reka bentuk ini. Selain itu, struktur antena
menawarkan kelebihan yang besar disebabkan oleh reka bentuknya mudah dan
dimensinya kecil yang berfungsi dengan aplikasi c-penjalur. Antena telah direka
dengan menggunakan substrat FR-4 dan diuji menggunakan penganalisis rangkaian
yang mempunyai jarak antara 3GHz hingga 9GHz di makmal frekuensi radio (RF).
Hasil simulasi untuk wideband bagi 4-8 GHz semasa hasil pengukuran telah turun
pada 7.8-4.2 GHz, dan faedahnya ialah 3.65 dB, dan berarah 5.35 dBi. Begitu
jugadengan perbezaan fasa antara port 1 hingga port 2 ialah -154° dan fasa dari port 1
hingga port 3 ialah 66.8°. Prestasi antena menunjukkan persetujuan yang baik di
antara kedua-dua simulasi dan hasil pengukuran dengan hanya beberapa sisihan kecil
dan sisihan yang diperhatikan adalah kerana model pemodelan dan teknik berangka
yang berlainan.
vii
CONTENTS
TITLE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF SYMBOLS AND ABBREVIATIONS xiii
CHAPTER 1 INTRODUCTION 1
1.1 Project background 1
1.2 Motivation 2
1.3 Problem Statement 3
1.4 Objectives 4
1.5 Scope of Project 4
1.6 Thesis Organization 5
CHAPTER 2 LITERATURE REVIEW 6
2.1 Introduction 6
viii
2.2 Antenna History for UWB And Array Antenna 6
2.3 Requirements for wideband Antennas 7
2.4 Advantages of wideband 8
2.5 Application Of wideband 9
2.5.1 Communication System 9
2.5.2 Radar Systems 10
2.5.3 Positioning Systems 11
2.6 Wideband Fractal Antennas 12
2.7 Previous Work 13
CHAPTER 3 METHODOLOGY 23
3.1 Introduction 23
3.2 Flowchart 24
3.3 Patch Antenna Design Process 25
3.4 Basic Antenna Design Equations of the patch 25
3.5 Simulation Procedure 27
3.6 The proposed wideband phased array antenna 28
3.7 Modifying of the ground plane 30
3.8 Fabrication 31
3.8.1 Lamination and UV light process 32
3.8.2 Developing process 33
3.8.3 Etching process 34
3.8.4 Stripping process 34
3.8.5 Soldering process 35
3.9 Summary 35
ix
CHAPTER 4 RESULTS AND DISCUSSION 36
4.1 Introduction 36
4.2 Result of the Ultra Wideband phase array antenna 37
4.2.1 UWB Antenna‟s Design 37
4.2.2 UWB Return Loss S11 38
4.3 Parametric Studies 39
4.3.1 Effects of the Ground Plane for UWB
Antenna
39
4.4 Wideband phase array Antenna‟s Design 40
4.4.1 Return Loss S11 41
4.4.2 VSWR 42
4.4.3 Radiation Pattern 43
4.4.4 Gain 46
4.4.5 Directivity 46
4.4.6 The Gain and Directivity 47
4.5 Phased Array Antenna 48
4.6 Parametric Studies 50
4.6.1 Size of the Partial Ground Plane 50
4.7 Conclusion 52
CHAPTER 5 CONCLUSION AND RECOMMENDATION
53
5.1 Conclusion 53
5.2 Recommendations 55
REFERENCES 56
APPENDIX 61
x
LIST OF TABLES
3.1 Parameter values of one element 28
3.2 Optimized values of wideband 1x2 element parameters 29
4.1 Data result of ground plane size variation 40
4.2 Data result of ground plane size variation 1x2 element 51
xi
LIST OF FIGURE
2.1 Fractal Line Antenna 12
3.1
Project Flow Chart 24
3.2 Antenna Design Patch And Ground View
27
3.3 Assessment Of Proposed Antennas Show
dimensions of mender T-divider
29
3.4 Partial Ground Plane For Wideband
30
3.5 Flow Chart Of Fabrication Process
31
3.6 Laminating Process
32
3.7 Lamination Machine
32
3.8 UV Exposure Units
33
3.9 Developing Machine
33
3.10 Etching Machine 34
3.11 Stripping Machine
34
3.12 Development Of The Antenna Fabricated View 35
4.1 UWB Design In Simulation 37
4.2 UWB Antenna Result For simulation and
measurement
38
4.3 Effects Of Partial Ground Plane
39
xii
4.4 Development Of Wideband Phase Array
Antenna Design View
41
4.5 Wideband Antenna Result
42
4.6 VSWR For Wideband Antenna Result
43
4.7a Radiation Pattern of The Antenna (dB) for
wideband.
44
4.7b Radiation Pattern of The Antenna (dB) for single
element
45
4.8 Gain for Wideband Phased Array Antenna
46
4.9 Directivity for Wideband Phased Array Antenna
47
4.10a Gain Vs Directivity for Wideband
47
4.10b Gain Vs Directivity for Single Element
48
4.11a Phase Difference for Two Ports In CST
49
4.11b Phase Difference for Port 1 To Port 2
49
4.11c Phase Difference for Port 1 To Port 3
49
4.12 Effects Of Partial Ground Plane 51
xiii
LIST OF SYMBOLS AND ABBREVIATIONS
GPR - Ground Penetration Radar
UWB - Ultra-wideband
RF - Radio frequency
RFID - Radio Frequency Indentified
SLL - Side Lobe Level
CPW - Coplanar Wave Guide
DS - Direct Sequence
MB - Multi-band
OFDM - Orthogonal frequency-division multiplexing
FCC - Federal Communication Commission
WPAN - Wireless Personal Area Network
TMDA - Time Division Multiple Access
GPS - Global Positioning System
EPLRS - Enhanced Position Location and Reporting System
FPR - Fabry–Perot Resonator
RCS - Radar Cross-Section
RVSM - Remote Vital Sign Monitoring
EMC - Electromagnetic Compatibility
IR - Impulse Radio
1CST - Computer Simulation Technology
2MWS - Microwave Studio
3dB - Decibels
4dBi - Decibels Isotropic
5BW - Bandwidth
6SMA - Sub-miniature A
UV - Ultraviolet
GP - Ground plane
xiv
PCB - Printed Circuit Board
VSWR - Voltage Standing Wave Ratio
GHz - Giga Hertz
Mm - Millimeter
FR-4 - Flame Retardant 4
εr - Dielectric Constant Of The Substrate
h - Height of dielectric substrate
- Free space wavelength
Fc - Center Frequency
c - Speed Of Light
h - Changing Of Height of the Partial Ground Plane
Leff - Effective length
SWR - Standing Wave Ratio
RL - Return Loss
S11 - Return loss or Reflection Coefficient (dB)
- Reflection Coefficient
FH - Upper Frequency
FL - Lower Frequency
1
CHAPTER 1
INTRODUCTION
1.1 Project background
Wideband communication system covering the range from 4 to 8 GHz requires a
compact antenna to provide desirable characteristic over the whole operating band.
Due to the of the simple structures of the wideband antennas, and their offering of
attractive features such as wide band, and Omni-directional radiation patterns, they
have been studied for wideband communication systems. Wideband technology has
been regarded as one of the most promising wireless technologies, which promises to
revolutionize high data rate transmission. It is also used in medical imaging, ground-
penetrating radar (GPR), position location and tracking. Since an antenna acts like a
filter for the generated ultra short pulse, one of the key issues is the design of a
compact antenna with an wideband characteristic wideband communication systems.
There are a huge number of wideband single antenna constructions [1].
The existing wideband antennas lack high gains and usually satisfy omni-
directional radiation patterns. However, applications such as target detections, 3D
microwave imaging, sensor networks and RFID readers need high gains and narrow
beam widths [2]. Wideband arrays can be good choices for the purpose of achieving
directional radiation patterns. Much research has been investigated on this topic a
wideband array of 2-5 antennas is investigated by simulation. Each antenna is
designed for 6-8.5 GHz European wideband band with an elliptical-shaped radiator
and is excited through a two-step stripline.
2
Employed four identical compact planar circular slot microstrip antennas to
compose 1x2 array with uniform amplitude distribution. Actually, the single element
used in an Ultra-wideband array, plays a crucial role to meet the requirements of an
approximately constant directive radiation pattern [3].Another important parameter
in an antenna array is the mutual coupling between the elements, which influences
the performance of an antenna array. In addition, it may lead to the changes in array
gain, side lobe level, array polarization, and its size [4]. Initially, it addresses linear
dipoles (narrow band) to approximate the coupling effects for wideband linear
antenna array [5]. Investigating on the mutual coupling effect for 2-element and 4-
element wideband linear arrays. It is assumed that both antenna arrays are fed
independently by uniform amplitude distributions.
In this project, we propose a novel wideband phased array antenna (2 elements)
with a semi-elliptical radiating patch. Indeed, it is a combination of two semi-circular
patches and a rectangular patch. As mentioned above, the single element of an
antenna array is of paramount importance. There would be many microstrip antennas
designed for wideband applications. However, the lack of suffice effective designs
for satisfying array demands while keeping wideband characteristics directed us
toward the design of this novel single element. This structure has been utilized to
construct a 1×2 linear antenna array in order to achieve a better result and a more
directive pattern than the previous designs as confirmed by the simulation results
presented and discussed in detail in the project.
1.2 Motivation
The wideband technology has undergone remarkable achievements during the past
few years. In spite of all the promising prospects featured by wideband, there are still
challenges in making this technology fulfill its full potential. One particular
challenge is the wideband antenna. In recent years, many varieties of wideband
antennas have been proposed and investigated.
They present a simple structure and wideband characteristics with nearly
omni-directional radiation patterns. However, for some space-limited applications,
wideband antennas need to feature a compact size while maintaining wideband
3
characteristics. Therefore, miniaturization of wideband antennas becomes an
interesting research topic and deserves a comprehensive investigation and analysis.
In this thesis, three different miniaturisation approaches are applied to wideband
antennas and all the miniaturised wideband antennas are investigated in detail in
order to understand their operations. In addition, a competent wideband antenna
should also have good time domain characteristics. Unlike traditional narrow band
systems, wideband systems usually employ short pulses to convey information. In
other words, a huge bandwidth is occupied. In this case the antenna parameters will
have to be treated as functions of frequency and will impose more significant impacts
on the input signal. Moreover, successful transmission and reception of wideband
signals entails minimization of ringing, spreading and distortion of the pulses in the
time domain. Therefore, it is indispensable and important to study antenna
characteristics in the time domain. In this thesis, a Coplanar Waveguide (CPW)-Fed
disc monopole antenna is exemplified to evaluate its time domain behavior.
1.3 Problem Statement
One of the critical issues in this wideband antenna design is the size of the antenna
for portable devices, because the size affects the gain and bandwidth greatly [6].
Therefore, to miniaturize the antennas capable of providing wideband bandwidth for
impedance matching and acceptable gain will be a challenging task. Planar monopole
is used to reduce the size of the proposed antennas. Some novelty wideband planar
monopole antennas are investigated in detail in order to understand their operations;
find out the mechanism that leads to wideband characteristics and to obtain some
quantitative guidelines for designing of this type of antennas. In order to obtain the
wideband bandwidth and Omni-directional radiation pattern, four matching
techniques are applied to the proposed wideband antennas, such as the use of slots,
the use of bevels and notches at the bottom of patch, the truncation ground plane, and
the slotted ground plane[7].
4
All these techniques are applied to the small wideband antenna without
degrading the required wideband antenna‟s performance. The size of slots, bevels
and notches are critically affect to the impedance bandwidth. The distance between
truncation ground plane to the bottom of the patch is as matching point, where it
determines the resonance frequency.
To ensure the broad bandwidth can be obtained, the proper designs on those
parameters are required. The theory characteristic modes are used to design and
optimize the proposed wideband antennas as well as some new designs are studied.
From the study of the behavior of characteristic modes, important information about
the resonant frequency and the bandwidth of an antenna can be obtained. The current
behaviors of the antenna are investigated in order to obtain several new slotted
wideband antennas. High radiation efficiency and linear phase are also required.
1.4 Objectives
The objectives of this project are:
i. To design a wideband phased array antenna for C band application.
ii. To design a wideband T-divider for the wideband antenna.
iii. To validate the simulation results by fabrication and measurement.
1.5 Scope of Project
i. Design the antenna and t-divider for frequency 4-8 GHz using CST
Microwave software.
ii. Fabricate the designed antenna.
iii. Conduct a measurement using Vector Network Analyzer for S-parameter and
Phase.
5
1.6 Thesis Organization
This thesis is composed of five chapters. That will explain in details all the work
carried out during my research project progress is given below:
Chapter one is summarized the introduction to the project background,
objectives, problem statement, scope of project and issues related wideband
application system.
Chapter two introduces the history of wideband and antenna description. It
also discusses structure of a wideband antenna miniaturized techniques, like meander
line, fractal and more including the antenna basic parameters, feeding methods,
methods of analysis, advantage and disadvantage of wideband antennas.
Chapter three is mainly consists of project methodology and explanation
about the design and fabrication process for wideband phased array antenna as well
as flow chart that shows the process of the design.
Chapter four will explain in detail all the results such as simulations results,
parameter studies, fabrication method, compared the results of simulation and
fabrication.
Chapter five consists of conclusion and recommendation of the project.
6
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter discusses about the theoretical of wideband antenna that is related to the
project such as the basics of wideband antenna and the general phased array antenna,
and we talk about others that can use a very low energy level for short-range, high-
bandwidth communications over a large portion of the radio spectrum. These
sections of the thesis also review a number of papers, which have formed the basis
for the research component of this paper. This thesis provides an approaching into
the background of wideband phased array antenna. Many papers have been studied in
order to gain required knowledge that is needed in the design process. There are also
many references from source such as books, publications and articles and so on.
2.2 Antenna History for UWB and Array Antenna
Array antennas and printed antennas have become important after the World War 2.
For the last 40 to 50 years, the focus has been on the development of printed
antennas. Microstrip printed antennas received an extensive attention due to
advantages such as low profile, light weight, low cost and small size. However,
conventional microstrip antennas are narrowband and measures for substantially
increasing their operational bandwidth were needed; examples of antennas with
increased bandwidth are the stacked structures and those with parasitic patches [8].
7
After the adoption of the First Report and Order by the Federal
Communication Commission, that permitted the commercial operation of UWB
technology, UWB research and development has evolved very fast from theoretical
study to engineering design as well as from general concepts to specific prototypes
[9]. Looking through the history of UWB antennas, it can be noticed that before
1990‟s all proposed UWB antennas were based on general volumetric structures,
such as Schelkunoff‟s spheroidal antenna (1941), Lodge‟s & Carter‟s biconical
antenna (1898, 1939), Lindenblad‟s coaxial horn element (1941), Brillouin‟s
omnidirectional and directional coaxial horn antenna (1948), King‟s conical horn
antenna (1942), Katzin‟s rectangular horn antenna (1946), Stohr‟s ellipsoidal
monopole and dipole antenna (1968) and Harmuth‟s large current radiator (1985). As
explained previously, from 1992 onwards, several microstrip, slot and planar
monopole antennas with simple structures such as circular, elliptical or trapezoidal
shapes have been proposed. Today the state of the art of UWB antennas focuses on
these microstrip, slot and planar monopole antennas with different matching
techniques [10]. In this dissertation, the research is directed towards planar UWB
antennas that are also suitable for array environments. In the following section the
basic concepts concerning the antenna elements will be reviewed.
2.3 Requirements for Wideband Antennas
According to the FCC definition [11], a wideband antenna has a fractional bandwidth
of 20%, while it has 25% fractional bandwidth in radar domain [12]. Hence, first of
all an antenna should have more than a certain value of fractional bandwidth to be
called an wideband antenna. Secondly the performance, both the reflection and
radiation characteristic of the antenna, should be stable over the entire operational
bandwidth of the antenna. Another requirement of the wideband antenna comes from
the size of its which should be small enough to be compatible with the wideband
unit.
Mechanically, they should be low-profile, embeddable and easily integrated
for portable devices. For example, the antennas that are required to have omni-
directional radiation patterns and to be used in mobile devices should be small
8
enough to fit in the mobile terminal. Finally the robustness and the low cost are also
key requirements. After these general requirements, some antenna design parameters
are strongly dependent on the modulation schemes that are used by the wideband
systems. The multi-band orthogonal frequency division multiplexing (MBOFDM)
based wireless communication systems require antenna systems with extremely wide
band width covering all operating sub-bands. Similarly pulse based systems, referred
to as direct sequence UWB (DS-UWB), require wide impedance bandwidth covering
that part of the spectrum where the major pulse energy falls in. A linear phase
response of the antenna is also an important parameter in the pulsed-based systems
[13].
2.4 Advantages of Wideband
Due to its wideband nature, wideband communication systems present unique
benefits that are attractive for radar and wireless communication applications. The
primary advantages of UWB can be summarized as follows [14].
i. Potential for high data rate
ii. Multipath immunity
iii. Potential small size and low equipment cost
iv. High-precision ranging and localization at the centimeter level
The extremely large bandwidth occupancy of wideband provides the potential
of very high theoretical capacity, yielding very high data rates. This can be
demonstrated by considering Shannon‟s capacity equation [15].
)N
S(1 log BC 2 (2.1)
Where
C Is the Maximum Channel Capacity,
B The Signal Bandwidth,
S The Signal Power
N The Noise Power.
9
2.5 Application of Wideband
Wideband is the leading technology for freeing people from wires, enabling wireless
connection of multiple devices for transmission of video, audio and other high
bandwidth data. Designed for short range, WPAN, it is used to relay data from a host
device to other devices in the immediate area (up to 10 m or 30 feet).
Recent years, rapid developments have been experimented on the technology
using wideband signals. Wideband technology offer major enhancements in three
wireless application areas: communications, radar and positioning or ranging.
2.5.1 Communication System
Using wideband techniques and the available large RF bandwidths, ultra wideband
communication links has become feasible. The exceptionally large available
bandwidth is used as the basis for a short-range wireless local area network with data
rates approaching gigabits per second.
This bandwidth is available at relatively low frequencies thus the attenuation
due to building materials is significantly lower for wideband transmissions than for
millimeter wave high bandwidth solutions. By operating at lower frequencies, path
losses are minimized and the required emitted power is also reduced to achieve better
performance [16].
Wideband radios operate in the presence of high levels of interference by
trading data rate for processing gain. The attributes of low emitted power and wide
signal bandwidth result in a very low spectral power density of the wideband signal.
This means that wideband radios operate in the same spectrum space as narrowband
radios on a non-interfering basis. Computer peripherals offer another fitting use of
wideband, especially when mobility is important and numerous wireless devices are
utilized in a shared space. A mouse, keyboard, printer, monitor, audio speakers,
microphone, joystick, and PDA are in wireless, all sending messages to the same
computer from anywhere in the given range [17].
10
Wideband also is used as the communication link in a sensor network. A
wideband sensor network frees the patient from the tangle of wired sensors. Sensors
are being used in medical situation to determine pulse rate, temperature, and other
critical life signs. Wideband is used to transport the sensor information without
wires, but also function as a sensor of respiration, heartbeat, and in some instance for
medical imaging.
Wideband pulses are used to provide extremely high data rate performance in
multi-user network applications. These short duration waveforms are relatively
immune to multipath cancellation effects as observed in mobile and in-building
environments. Multipath cancellation occurs when a strong reflected wave arrives
partially or totally out of phase with the direct path signal, causing a reduced
amplitude response in the receiver. With very short pulses, the direct path has come
and gone before the reflected path arrives and no cancellation occurs. As a
consequence, wideband systems are particularly well suited for high-speed
multimedia, mobile wireless applications. In addition, because of the extremely
short duration waveforms, packet burst and time division multiple access (TDMA)
protocols for multi-user communications are readily implemented [18].
2.5.2 Radar Systems
For radar applications, these short pulses provide very fine range resolution and
precision distance and positioning measurement capabilities. The very large
bandwidth translates into superb radar resolution, which has the ability to
differentiate between closely spaced targets. This high resolution is obtained even
through lossy media such as foliage, soil and wall and floor of the buildings. Other
advantages of wideband short pulses are immunity to passive interference (rain, fog,
clutter, aerosols, etc) and ability to detect very slowly moving or stationary targets
[19].wideband antennas arrays are especially important, to have both fine range and
angular resolution in radars.
11
In radar cross-section (RCS) range, a single wideband antenna replaces a
large set of narrow band antennas that are normally used to cover the whole
frequency band of interest. Wideband signals enable inexpensive high definition
radar. Radar will be used in areas currently unthinkable such as, automotive sensors,
smart airbags, intelligent highway initiatives, personal security sensors, precision
surveying, and through-the wall public safety application.
Operation of vehicular radar in the 22 to 29 GHz band is permitted under the
wideband rules using directional antennas on automobiles. These devices are able to
detect the location and movement of the objects near a vehicle, enabling features
such as near collision avoidance, improved air bag activation, and suspension
systems that better respond to road conditions.
2.5.3 Positioning Systems
For global positioning system (GPS), location and positioning require the use of time
to resolve signals that allow position determination to within ten of meters. Greater
accuracy is enhanced with special techniques used. Since there is a direct relationship
between bandwidth and precision, therefore increasing bandwidth will also increase
positional measurement precision, with wideband techniques extremely fine
positioning becomes feasible, e.g. sub-centimeter and even sub-millimeter. In
satellite communications where wide band feeds save space and weight by
supporting many communication channels with just one antenna.
The architectures for UWB position-determination systems would resemble
traditional systems, e.g. multi-alterations like GPS or radio ranging like the military‟s
enhanced position location and reporting system (EPLRS). Having relatively low
frequency of operation, this type of system has the potential to work within buildings
with minimal attenuation of the signal.
12
2.6 Wideband Fractal Antennas
Multi functionality with miniaturized characteristics is the need of today‟s wireless
communication. The concept of fractal geometry was first introduced in 1975 by
Benoit Mandelbrot. Since then, considerable research has been carried out in the
application of fractals to achieve wide bandwidth, thereby opposing the use of
antenna arrays, which take a lot of space and are bulky as compared to fractal
microstrip antennas [20]. The fractal antennas are based on self-similarity and space
filling properties and the original geometry is scaled down by the desired factors.
These unique features of fractal geometry are used for multiband and wideband
applications. Sierpinski gasket is a deterministic fractal based on self-similar
property. The construction algorithm for the Sierpinski gasket using an equilateral
triangle base geometry was given in [21] step wise. The space filling property led to
curves that were electrically very long, but fit into a compact physical space. This
second property of fractals is also known as „Infinite Perimeter‟. The fractals bring
probability of multiplying self similar shapes infinitesimal times and thereby stretch
the perimeter infinitely. However, in practice there is a physical limit to the increase
in the number of iterations. Because of its strength, this characteristic is called as the
Infinite Perimeter [22]. „Space Filling Curves‟ is a method of achieving infinite
perimeter. One of the examples of space filling curves is Koch Curve, which
multiplies the perimeter many times. Steven Best studied and tested multiband
behaviour of the Sierpinski Gasket Antenna. He presented a comparison of the
multiband behaviour of Sierpinski Gasket and several modified gaskets. The major
portions of the Sierpinski Gasket‟s self similar fractal gap structure were eliminated
completely without affecting the multiband behavior characteristics.
Figure 2.1: Fractal Line Antenna
13
Fractal design has been chosen in RFID. Fractal methods mean broken or
irregular fragments fractals describe a complex set of geometries ranging from self-
similar. As shown in Figure 2.1, fractal design has been found advantage from its
fractal geometries. It is compact in size, produced wideband and multiband
frequency operations. Nevertheless, it has another disadvantage, including low gain,
low power handling capability, and poor power polarization [23].
2.7 Previous Work
Wideband aperture-coupled antenna array based on Fabry–Perot resonator for C-
band applications is proposed by (Reza Khajeh Mohammad Lou1 2017)[24]. Novel
Fabry–Perot resonator (FPR) antenna array in a C-band, which produces broader
gain bandwidth, flatter radiation efficiency and wider circular polarisation in
comparison with conventional antenna arrays, is introduced. These improved
characteristics are obtained using a super strate constituting two complementary
frequency selective surfaces placed above a 2 × 2 antenna array and fed by a 4 × 4
modified Butler matrix. The performance of the FPR antenna was verified by
simulated and experimental outcomes. The experimental results indicated that the
FPR antenna array possesses an impedance bandwidth between 3.7 and 8.55 GHz for
S11 ≤ −10 dB, which covers the C-band fully (4–8 GHz). Moreover, the impedance
bandwidth is approximately covered by the 3 dB gain bandwidth between 4.4 and 7.5
GHz with a peak value of 18.1 dBi. Finally, the FPR antenna array has a 3 dB axial-
ratio bandwidth of 3.5 GHz between 4.35 and 7.85 GHz that includes major wireless
standards.
14
A Design of C-Band Wideband Conformal Omni directional Antenna. The
technique of short-circuiting posts, loaded disk and ground plane transformation is
adopted in the antenna design. The effects of key parameters on impedance matching
are analysed in detail. The simulated and measured results show that the proposed
antenna can work in a wideband. The relative bandwidth with S11 ≤ 10dB reaches
47.1%, covering from4.7 GHz to 7.6 GHz. The radiation pattern is similar to a
monopole antenna within the bandwidth. The proposed antenna can be flush-
mounted on a planar surface and therefore is a candidate of a conformal omni
directional antenna. A low-profile wideband antenna is presented in this paper. The
antenna is built on a mono polar cone antenna which is flattened with the addition of
metal cavity, short-circuiting posts and loaded disk .These additional structures
widen the bandwidth of the proposed antenna and make the antenna more reliable by.
(Qihong He 2016)[25].
Dual-polarized wideband high-efficiency phased array antenna was proposed
by (kai zhou, 2015) A dual-polarized planar phased array antenna for K band is
presented in this paper. To realize dual-polarization operation, dielectric loaded dual-
polarized radiator is proposed. The antenna has low-profile architecture, measuring
only 10.4mm×10.4mm. A X-band prototype is measured for experimental
verification. The measured result shows good agreement with the simulation. A
16×16 element array for the dual polarization is analyzed by simulation. A maximum
of ±40° beam scan capability is achieved for the dual-polarized planar array. And the
proposed array maintains good radiation pattern sand low-profile electrical
dimensions. Circular polarization, compared to linear polarization, allows for greater
flexibility in orientation angle between receiver and transmitter, weather reflections
and other kinds of interferences. Different types of phased array antenna have been
discussed. Most studies on dual- polarization array antennas use dielectric substrates
because of the easy realization of the radiating elements and feeding networks, good
performance of isolation and cross-polarization. However, the antennas in suffer
from large losses and are not suitable for high gains because the loss increases with
the array size and in their discussion unit-cell radiation efficiency is very low.
Therefore, an effective integration design of dual-polarized antenna is highly
required to enhance the efficiency of dual polarized array [26].
15
Aperture-coupled dual-polarized wideband microstrip antenna with high port-
to-port isolation in C-Band is presented in this paper. The proposed antenna contains
reflector, substrate, patch and director. By means of four shorting pins the bandwidth
increases noticeably. It has 50% bandwidth of -10 dB return loss at the 5.25 GHz
canter frequency, and minimum 31.5dB isolation across the band. The reflector helps
to improve Front to Back (F/B) ratio of better than 20dB. Moreover, it has a peak
gain of 9.2 dBi. The structure of the antenna is compact and easy to fabricate.
Therefore, it‟s a suitable candidate for arrays, and could be used in base stations for
Wi-Fi applications. In this paper, a wideband aperture-coupled dual-polarized
antenna with high isolation at C-Band has presented. By using four shorting pins the
-10 dB bandwidth of the antenna has increased from 24% to 50%. The isolation and
cross polarization have become better than 31.5 dB and 28 dB respectively. The
proposed antenna has a peak gain of 9.2 dBi.by (A. Vaziri 2013) [27].
Design of a one-dimensional wideband and wide scanning phased array
antenna is proposed by (By Z.N.Jiang, 2016).This paper presents an improved
phased array antenna which is based on the Vivaldi antenna. This phased array
antenna has good wideband bandwidth characteristics. Meanwhile, its scanning angle
has reached to 60 degrees. The length of each radiation unit has been optimized
under the application of the low side lobe algorithm, for the purpose of weakening
the side lobe. By the one-dimensional arrangement of radiation units, the gain of this
antenna is highly improved. A sort of exponential tapered microstrip line is applied
in the antenna design while several metal boards are used to reduce mutual coupling
among these radiating units. This paper describes a phased-array antenna system
which is based on the Vivaldi antenna. The simulation results show that the coherent
bandwidth of this antenna reaches up to 130% with scanning angle up to 60 degrees,
undoubtedly meet the wideband requirements. As can be seen, this antenna system
has a very broad application prospect, and it's worthy of being researched and
explored further [28].
16
Wideband dual-polarization, low-profile cavity backed four-arm Archimedean spiral
antenna is first presented. This is further extended to a linear array of spiral antennas.
Beam forming capability of the linear array for both polarizations is measured and
presented for a 4:1 Wideband dual-circular polarized phased arrays are advantageous
in multi-function and multi-band applications. Circular polarization is also of interest
for the rejection of rain clutter and for satellite communications. Spiral antennas are
known to exhibit good circular polarization over a wide bandwidth. However, it is
limited to a single polarization that is dependent on the direction of the winding
sense of the spiral. Obtaining dual-circular polarization in a spiral antenna has been
mentioned in multiple sources but there are very few published results. In addition, it
requires a cavity-backing to prevent bi-directional radiation. Previously, it was
established that a ground plane placed a distance of λ/4 away from the antenna limits
the bandwidth of the spiral antenna. Proposed by, Hongzhao Ray Fang, 2015[29].
A Very Low-Profile UWB Phased Array Antenna Design for Supporting
Wide Angle Beam Steering is proposed by Henry H. Vo (2016). This paper presents
a design example of a low-profile UWB dual-polarization array antenna design based
on tightly coupled dipole elements. This supports array can support beam steering for
more than 60° beam steering in both E- and H-plane with more than 2.5:1 impedance
bandwidth, from 0.55fc to 1.45fc where fc is the center frequency. An 18x18 array
prototype was fabricated and measured to validate the performance of the design.
Also it presents an improved low-profile UWB phased array antenna design which
minimizes mutual coupling between array elements, and thus allowing steering
pattern beam to wide angles. This is accomplished by properly designing the antenna
element, feed geometry, and array configurations. Some key design parameters
include the tightly coupled dipoles, extremely simple feed structures, and array
height above ground plane, dielectric superstrate, and parasitic ring [30].
Accurate remote vital sign monitoring with 10 GHz ultra-wide patch antenna
array is proposed by Muhammad Saqib Rabbani,(2017).Patch antenna array has been
presented at 10 GHz frequency with improved gain (14dBi) and far-field radiation
capabilities for accurate detection of human respiration and heart beat rate with
Doppler radar technique.
17
The measured and simulation antennas‟ results showed good agreement.
Feasibility of 10 GHz channel has been studied for remote vital sign monitoring
(RVSM) under Doppler radar theory. Both the breathing rate (BR) and heart rate
(HR) of a man have been accurately detected from various distances ranging from 5
cm to 4 m with as small transmitted power as -10 dBm. Microstrip patch antenna
array has been presented for RVSM at 10 GHz frequency with UWB Doppler radar.
The tested antennas showed good performance in terms of bandwidth, gain and side
lob levels for RVSM measurements. Theoretical analysis of RVSM with 10 GHz
Doppler radar has been presented. The antennas bandwidth (9.4–10.6 GHz) gives an
extra flexibility to adjust the transmitter‟s tone frequency to avoid the null detection
of HR signal caused by various combinations of the BR and HR amplitudes [31].
A novel Microstrip-fed wideband LPM monopole planar antenna with a very
compact size is presented and investigated. Using different geometry parameters of
the ladder number N, the rectangular patches geometry for ladder elements, the
ladder step length and the length of ground plane, the optimizing antenna parameters
with proper values, a very good impedance matching and improvement bandwidth
can be obtained within a compact size of 12 mm×12 mm. This can be the result of
the ladder‟s space-filling character and its special layout properties. The operating
bandwidth of the proposed LPM antennas covers the frequency band between 3.1
GHz and 10.6 GHz for VSWR less than 2. The measured return loss (S11) and
radiation patterns are in excellent agreement with the simulation. The results suggest
that the proposed LPM antenna is suitable for UWB communication applications,
since then, planar microstrip antennas with different shapes and feeding structures
(microstrip, coaxial, and coplanar waveguide) have been found as suitable design and
implementation to fulfill UWB system requirement. By Han Yu‟nan1 (2015)[32].
Mario Leib (2010) was proposed In-Phase and Anti-Phase Power Dividers for
UWB Differentially Fed Antenna Arrays. This letter presents two novel power
dividers operating in the FCC frequency range from 3.1 to 10.6 GHz. The two
outputs of each power divider are coplanar striplines, while the input is a microstrip
line [33]. Hence, the power dividers act as baluns and are suited for differentially fed
antennas. The in-phase version shows a return loss of better than 15 dB from 1 to
12.3 GHz, whereas for the anti-phase version the return loss is better than 10 dB
from 1 to 12.3 GHz.
18
Besides the characterization of the dividers, a linear antenna array fed by one of the
dividers is shown, and measurement results in the time domain and frequency
domain are presented. The mean gain of the realized four-element array is 9.7 dBi.
A Wideband Vivaldi Antenna Array in L and S bands (2016).This paper
designed and fabricated a 1×4 ultra wideband (UWB) Vivaldi antenna array for a
phased-array radar system. Vivaldi antenna array is a common solution in
applications which require broad bandwidth over several octaves and wide scan
volume. The measured impedance bandwidth of the four antenna elements are over
2.25:1 with voltage standing wave ratio (VSWR), by Yin Yue [34].
Wideband optically addressed transmitting phased array (Shouyuan Shi,
2013). In this paper was presented an ultra-wideband optically addressed transmitting
phased array antenna, consisting of ultra-wideband and tunable RF synthesizer,
optically addressed phase feeding network, and high-speed photo detector integrated
wideband antenna array. RF source generation and optical feed network are capable
of cover the frequency range up to 50 GHz. A set of 4x4 antenna arrays, such as horn
and patch antennas in Ka band are designed, fabricated and characterized, ready for
the further integration to the 1x4 ultra-wideband transmitting array system. Ultra-
wideband (UWB) phased arrays are receiving increased attention due to their ability
to realize multifunctional systems that span several frequency bands for applications,
such as radar, ultra-fast communication, RF sensing, and imaging system. However,
the development and integration of the corresponding RF components within the
arrays become extremely challenging at such high frequencies. Accordingly,
optically fed phased array is a good substitution with advantages over conventional
electronically addressed phased arrays, such as SWaP (size, weight, and power),
immunity to EMC, and extreme frequency agility. We have demonstrated a system
concept that is capable of generating widely tunable carrier signals with excellent
spectral purity and line width.
19
This system is based on the use of electro-optic phase modulation to frequency-shift
a portion of the output from a Master semiconductor laser by a selectable multiple of
a low-frequency reference, then using that shifted portion to phase lock a second
semiconductor laser, such that, when the two lasers are mixed on a fast photo
detector, the resulting RF beat tone exhibits extraordinary spectral purity. The
success in the development of the high quality and ultra-wideband RF source inspires
us to explore its applications, such as, ultra-wideband phased antenna arrays. The
laser outputs are fed into an optical interleaving and feeding network, consisting of
two 1-to-N beam splitters, N electro-optic phase modulators, N 2-to-1 beam
combiners and fiber couplers. The beam splitting, phasing, and recombining can be
achieved through typical fiber-based components. The proposed approach, however,
imposes some technical difficulties in the practical implementation. Due to thermal
and mechanical stresses in each channel, the relative phase between channels will
drift over time, thereby resulting into significant distortion in the RF beams forming
[35].
An Ultra wideband (UWB) Switched-Antenna-Array Radar Imaging System
is presented by Gregory L. Charvat, (2010) [36]. A low-cost ultra wideband (UWB),
1.926-4.069 GHz, phased array radar system is developed that requires only one
exciter and digital receiver that is time-division-multiplexed (TDM) across 8 receive
elements and 13 transmit elements, synthesizing a fully populated 2.24 m long (λ/2
element-to element spacing) linear phased array. A 2.24 m linear phased array with a
3 GHz center frequency would require 44 antenna elements but this system requires
only 21 elements and time to acquire bi-static pulses across a subset of element
combinations. This radar system beam forms in the near field, where the target scene
of interest is located 3-70 m down range. It utilizes digital beam forming, computed
using the range migration synthetic aperture radar (SAR) algorithm. The phased
array antenna is fed by transmit and receive fan-out switch matrices that are
connected to a UWB LFM pulse compressed radar operating in stretch mode. The
peak transmit power is 1 mW and the transmitted LFM pulses are long in time
duration (2.5-10 ms), requiring the radar to transmit and receive simultaneously. It
will be shown through simulation and measurement that the bi-static antenna pairs
are nearly equivalent to 44 elements spaced λ/2 across a linear array.
20
This result is due to the fact that the phase center position errors relative to uniform
λ/2 element spacing are negligible. This radar is capable of imaging free-space target
scenes made up of objects as small as 15.24 cm tall rods and 3.2 cm tall metal nails
at a 0.5 Hz rate. Applications for this radar system include short-range near-real-time
imaging of unknown targets through a lossy dielectric slab and radar cross section
(RCS) measurements.
Wideband multi-beam antenna array is presented by Alexia Moreno
Penarrubia (2016) [37]. This array consists of three wideband monopoles, which
have been designed to work at frequencies from 4.5 GHz to 10 GHz. The monopoles
present compact size and are mounted parallel to a reflector ground plane, thus, it is
achieved a directive pattern of radiation. The bandwidth of the array is 2 GHz and
includes frequencies from 5 GHz to 7 GHz. Furthermore, it is proposed a 3-way own
design feeding network and a 4-way network based on Butler matrix. The first one
will be used to feed the array. Every output port of the 3-way network is connected to
the input of each monopole that is included in the array. These networks have been
designed to provide similar phase shifts between adjacent input ports of the array
with different values depending on which network input port is used. Using all
network input ports simultaneously, it is possible to achieve the multi-beam effect on
the antenna.
High performance novel UWB array antenna for brain tumor detection via
scattering parameters in microwave imaging simulation system (M.A.Jamlos,
2015).this paper presents microwave imaging system simulation for brain tumor
detection of human head model developed using computer simulation technology
software. The detection method applied by analyzing processed scattering parameter
(s-parameter) signals difference in the absence and presence of tumor in head model.
The simulation system covered novel design of UWB array antenna as scanning
probe and human head model with tumor inside. The antenna operated from 2.6 GHz
until 13.1 GHz, dimensions of 80 × 45 (mm) and maximum gain of 12.12 dB used to
scan 9 different points at the head model. Matrix laboratory software is utilized to
analyze s-parameter in frequency and time domain.
21
The generated s-parameters of frequency domain transformed into time domain
through inverse fast Fourier transform for easier analysis. Smoothing „mslowess‟
procedure is applied in filtering out the noise for accurate results. Brain tumor
presence indicated by lower reflection coefficient values compared to higher values
recorded by brain tumor absence [38]
Triple band notched UWB antenna array was proposed by Nikitha Prem E.K
in (2016).To reduce the interference problems from nearby communication systems
within an ultra wideband, the requirement for an efficient band notched design is
increased. The proposed triple band notch antenna array is a coplanar waveguide fed
radiator with inbuilt notching resonators, etched to achieve desired band rejection.
Three different notch antennas, each corresponds to a specific band rejection are used
in a single structure. C shape & inverted u shape slots in the patch and CSRR in the
ground plane, each corresponds to a specific band of frequency rejection such as
Wimax [3.5 GHz], WLAN [5.2GHz], and Satellite Service Bands [8.2GHz]. The
introduction of the EBG structures in between the two antennas shows the significant
reduction in the mutual coupling effects and improves the antenna parameters (peak
realized gain, radiation pattern)[39].
An ultra-wideband (UWB) E-plane mono pulse antenna working in the
frequency range from 3.1 to 10.6 GHz is proposed. The UWB -plane two-element
array is constructed using Vivaldi antennas. By shortening the adjacent tapered lines
of the two Vivaldi antennas and using corrugated edges, sum and difference
characteristics of the array are improved. The UWB mono pulse comparator is a
multilayer planar magic T consisting of an UWB 90° directional coupler and two
UWB 45° phase shifters in series. By integrating the array and the comparator, the
UWB -plane mono pulse antenna is designed and fabricated with the low-cost PCB
process. In the frequency range from 3.1 to 10.6 GHz, the sum gain is measured as
more than 10.1 dBi, the side lobe level less than 13.1 dB, and the null depth greater
than 22.5 dB. The good sum and difference characteristics obtained make the
proposed UWB -plane mono pulse antenna desirable for target detecting and
tracking.
22
The Vivaldi antennas are spaced close enough less than one wavelength apart at the
shortest wavelength in the receiving band to eliminate grating lobes when they are
used as elements to design UWB arrays. In such a case, the array needs large number
of elements to form tight coupling for UWB operation. In this two methods are
proposed to make the UWB array obtain small grating lobes with only two elements
when their distance is about 1.77 wavelengths at the highest working frequency. The
first method is to shorten the length of the adjacent tapered lines of the Vivaldi
antennas for available coupling and grating lobes reduction. The second method is to
apply corrugated edges for adjusting the coupling and improving the radiation
characteristics. (Ya-Wei Wang, 2014) [40].
A Miniaturized Wideband Vivaldi Antenna and Phased Array by (Zhou
Changfei,(2014)) [41]. A novel miniaturized Vivaldi antenna is presented in this
paper. Two kinds of regular slot edge (RSE) structures are employed in this antenna.
The transversal slot edges help to extend the low-end operating frequency and
improve the radiation characteristics, while the longitudinal ones have the potential
to inhibit the back lobe, contributing to the enhancement of antenna gain. Based on
the antenna element, a wideband 1×5 E-plane Vivaldi antenna array is designed with
a total gain of 10.9-13.7dBi. This array is able to work from 8 to 12GHz and scan
angle up to 22°. As the modern communication has an increasing demand of ultra
wideband antennas in both military and civil applications, compact wideband
antennas attract more and more attention. Since Gibson proposed the tapered slot
antenna (TSA), Vivaldi antenna has been widely developed. Its potential of
moderately high directivity, low profile and ease of fabrication makes Vivaldi
antenna a key role for wideband phased array, high-speed wireless communication,
remote sensing and radar.
23
CHAPTER 3
METHODOLOGY
3.1 Introduction
This chapter explains the methods used in order to obtain the optimum result of the
project, starting from the designing process until the testing process. This project
consists of two parts software and hardware, the software part consists. The design
and simulation processes are done by using CST Microwave Studio. The simulation
result is optimized to achieve the best performance of the antenna. While, the
hardware part is fabricated on the FR4 substrate with dielectric constant of ɛr 4.3 in
UTHM laboratory (EMC) and the |S11| measurement will be measured using the
network analyzer.
Initially, this project starts with the project background research and the
definition problem statement. Literature review about previous research and theories
have been the basic references in order to define the logic specification to accomplish
for the wideband phased array antenna. The define specification will also be
considered at the application, especially for the UWB and wideband. Figure 3.1
shows as the flowing of steps required in designing the UWB and wideband antenna.
Generally, this chapter focuses on three major processes, which are: designing
process, simulation process and fabrication process.
24
3.2 Flow chart
Start
Antenna Design using
CST
Performance Analyze
&characterization
Satisfied
Specification
Fabrication and
Measurements
Result and discussion
Report
END
Research and Literature Review
Study of the Project
Figure 3.1: Project flow chart
No
Yes
Design One
Element for UWB
Developing the Design
Two elements for
wideband phase array
Element for Wideband
56
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