DEBRETABOR UNIVERSITY
FACULTY OF TECHNOLOGY
DEPARTMENTS OF ELECTRICAL AND COMPUTER ENGINEERING
DESIGN AND PERFORMANCE ANALYSIS OF MICROSTRIP PATCH
ARRAY ANTENNA AT ISM BAND
By
Name
ID No
Henok Chernet
0679/07
Gabzachew Ayele
1263/07
Berihun Ashagrie
0208/07
Advisor
Mr. Juhar Muhammed
A Thesis Submitted to the Department of Electrical and Computer Engineering
(communication engineering)
In partial fulfillment for award of the Degree of Bachelor of Science in Electrical & Computer
Engineering (communication engineering)
June 2019
Debre Tabor University
Debre Tabor, Ethiopia
1
DEBRETABOR UNIVERSITY
FACULTY OF TECHNOLOGY
DEPARTMENTS OF ELECTRICAL AND COMPUTER ENGINEERING
DESIGN AND PERFORMANCE ANALYSIS OF MICROSTRIP
PATCH ARRAY ANTENNA AT ISM BAND
Henok Chernet
Gabzachew Ayele
Berihun Ashagrie
A thesis submitted to Debre Tabor University in partial fulfillment of the requirements for the
degree of Bachelor of Science in the Electrical & Computer Engineering in the technology
faculty.
June 2019
Debre Tabor University
Debre Tabor, Ethiopia
i
DECLARATION
We, students of electrical and computer engineering stream of communication engineering at
Debre Tabor University faculty of Technology with a final year project on the title “DESIGN AND
PERFORMANCE ANALYSIS OF MICROSTRIP PATCH ARRAY ANTENNA AT ISM
BAND” have declare that this thesis is our original work. And all sources of materials that could
be used to accomplish this project is fully acknowledged.
Name of Students
Signature
Date
Henok Chernet
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----------------
Gabzachew Ayele
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----------------
Berihun Ashagrie
----------------
----------------
Approved by:
Name
Mr. Juhar Muhammed
signature
date
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APPROVAL
This project has been submitted for examination with our approval as a university advisor.
Advisor
Mr. Juhar Muhammed (MSc)
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Signature
Date
Head of Department:
Mr. Juhar Muhammed (MSc)
...…………..
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Signature
Date
..………….
……………
Signature
Date
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Signature
Date
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Signature
Date
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Signature
Date
Department Chair Holder
Mr. Mola Belete (MSc)
Examiners
1
Name
2
Name
3
Name
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ACKNOWLEDGMENT
Above all we would like to thank great fully for God, the almighty, and the merciful. Without
his blessing and endorsement this final year project would not have been accomplished and then
we would like to thank our family for supporting us through all the years economically as well as
ideally. Next to this we would also like to express sincere gratitude to our academic advisor Mr.
Juhar Muhammed for his ceaseless supporting, motivation, supervision and various advices on how
to complete this Project.
We express my sincere gratitude and indebtedness to the thesis guide Prof. Jawahar, for his
initiative in this field of research, for his valuable guidance, encouragement and affection for the
successful completion of this work. His sincere sympathies and kind attitude always encouraged
us to carry out the present work firmly.
We would also be very grateful to announce thanks to all electrical and computer engineering staff
members and teachers for their polit help for all questions that we have asked them.
Last but not least, we would like to thank all my friends and well-wishers who were involved
directly or indirectly in successful completion of the present work.
iv
ABSTRACT
The performance and advantages of microstrip patch antennas such as low weight, low profile, and
low cost made them the perfect choice for communication systems engineers. They have the
capability to integrate with microwave circuits and therefore they are very well suited for
applications such as cell devices, WLAN applications, navigation systems and many others.
In this study, a Microstrip Line fed patch antenna array for application in the 2.4GHz ISM band
was implemented using the Ansoft HFSS software. The design issues include micro strip antenna
dimensions, feeding techniques and various polarization mechanisms whereas the performance
issues include return loss, bandwidth issues directivity and radiation pattern of micro strip
patch array antennas. Standard formulas were used to calculate different parameters of the antenna.
These were just used as a basis of design as some parameters varied considerably during simulation.
A way of improving the bandwidth, radiation pattern and minimize the return loss would have been
expected for effective communication. To achieve this requirement, we are designed micro strip
patch array antennas with micro strip line feeding based on impedance matching technique using
HFSS software. The performance of the designed antenna is then compared with the single patch
antenna in term of return loss, Voltage Standing Wave Ratio (VSWR), bandwidth, directivity,
radiation pattern. A good extent of the antenna design was hence done through trial and error. The
proposed antenna was designed to work at 2.4 GHz frequency band. We are observed the effect of
increasing the substrate height and dielectric constant on the size of antenna and its bandwidth, the
comparison of circular versus rectangular single element patch antenna, the effect of impedance
matching on the different parameters of antenna ,effect of varying the number of elements and
spacing between elements are going to discuss.
Keywords: Microstrip Patch Array antenna, ISM Band, HFSS Software, Impedance Matching,
return loss, VSWR.
v
TABLE OF CONTENTS
ACKNOWLEDGMENT ............................................................................................................ iv
ABSTRACT ............................................................................................................................... v
LIST OF FIGURES ................................................................................................................... ix
LIST OF TABLES ..................................................................................................................... xi
LIST OF SYMBOLS ................................................................................................................ xii
LIST OF ABBREVIATIONS .................................................................................................. xiii
CHAPTER ONE ......................................................................................................................... 1
INTRODUCTION ...................................................................................................................... 1
1.1 Background ....................................................................................................................... 1
1.4 Statement of the Problem ................................................................................................... 1
1.3 Objectives of The Project ................................................................................................... 2
1.3.1 General Objective ....................................................................................................... 2
1.3.2 Specific Objectives...................................................................................................... 2
1.7 Methodology of The Thesis ............................................................................................... 3
1.4 Scope of the study ............................................................................................................. 4
1.5 Limitation of The Thesis .................................................................................................... 4
1.6 Motivation of The Thesis ................................................................................................... 4
1.8 Significance of The Study .................................................................................................. 5
1.9 Organization of the Thesis ................................................................................................. 6
CHAPTER TWO ........................................................................................................................ 7
LITERATURE SERVE AND REVIEW ..................................................................................... 7
2.1 LITERATURE SERVE ..................................................................................................... 7
2.2.1 Lobes .......................................................................................................................... 8
2.2.2 Radiation Pattern ......................................................................................................... 9
vi
2.2.3 Azimuth and Elevation Plane (E and H plane) ............................................................. 9
2.2.4 Return Loss ............................................................................................................... 10
2.2.5 Bandwidth ................................................................................................................. 10
2.2.6 3-dB Beam width ...................................................................................................... 11
2.2.7 VSWR ...................................................................................................................... 11
2.2.8 Directivity ................................................................................................................. 11
2.2.9 Antenna Gain ............................................................................................................ 11
2.2.10 Polarization ............................................................................................................. 11
2.2.11 Front-to-back ratio................................................................................................... 12
2.2.12 Microstrip Antenna ................................................................................................. 12
2.2.12.1 Basic Characteristics ............................................................................................ 12
2.2.13 Arrays and Feed Networks ...................................................................................... 16
CHAPTER THREE .................................................................................................................. 22
SYSTEM DESIGN AND ANALYSIS ...................................................................................... 22
3.1 INTRODUCTION ........................................................................................................... 22
3.2 Design procedure ............................................................................................................. 22
3.2.1 Design equation of single element rectangular patch antenna ..................................... 22
3.2.2 Design equations of single element circular patch antenna ......................................... 24
3.4 Impedance ....................................................................................................................... 26
3.5 Feeding Methods ............................................................................................................. 27
3.6 Microstrip Discontinuities................................................................................................ 28
3.7 Main Beam Direction ...................................................................................................... 30
3.8 Matching of Microstrip Lines to the Source ..................................................................... 30
3.8.1 Quarter Wave Transformer ........................................................................................ 31
3.9 Micro strip Patches Array Antenna Design ...................................................................... 32
vii
3.9.1 Calculation of the Impedance for Quarter-Wave Transformer .................................... 33
3.9.2 Simulation ................................................................................................................. 34
CHAPTER FOUR..................................................................................................................... 35
SIMULATION RESULT AND DISCUSSION ......................................................................... 35
4.1 INTRODUCTION ........................................................................................................... 35
4.2 RESULT AND DISCUSSION......................................................................................... 35
4.2.1 Effect of increasing the dielectric constant and thickness of substrate ........................ 35
4.2.2 The effect of changing dielectric constant(substrate) on the antenna parameter .......... 36
4.2.3 Comparison of rectangular and circular single element patch antenna ........................ 39
4.2.4 The Effect of Impedance Matching on Circular ......................................................... 42
4.2.5 The effect of increasing number of elements in micro strip patch antenna.................. 46
4.2.6 Effect of spacing between antenna elements .............................................................. 52
CHAPTER FIVE ...................................................................................................................... 59
CONCLUSION AND RECOMMENDATION ......................................................................... 59
5.1 INTRODUCTION ........................................................................................................... 59
5.2 CONCLUSION ............................................................................................................... 59
5.3 RECOMMENDATION ................................................................................................... 61
APPENDIX .............................................................................................................................. 62
Appendix A ........................................................................................................................... 62
Appendix B ........................................................................................................................... 63
viii
LIST OF FIGURES
Figure 1. 1 Flow Chart Of Methodology ..................................................................................... 3
Figure 2. 1 Antenna Measurement Co-Ordinate System ............................................................. 9
Figure 2. 2 Microstrip antenna and coordinate system .............................................................. 13
Figure 2. 3 Microstrip Line and Its Electric Field Lines, And Effective Dielectric Constant ..... 15
Figure 2. 4 Physical and effective lengths of rectangular microstrip patch ................................ 16
Figure 2. 5 Microstrip patch antenna with feed from side .......................................................... 18
Figure 2. 6 Rectangular microstrip patch antenna ...................................................................... 19
Figure 2. 7 Coaxial line feed .................................................................................................... 20
Figure 2. 8 Proximity coupling feed method ............................................................................. 20
Figure 2. 9 Aperture coupling feed method ............................................................................... 21
Figure 3. 1 Design of single element rectangular patch antenna ................................................. 24
Figure 3. 2 Design of single element rectangular patch antenna ................................................. 26
Figure 3. 3 Feed arrangements for microstrip patch arrays......................................................... 27
Figure 3. 4 Configuration for compensated right-angled bends ................................................. 29
Figure 3. 5 Characteristics of the step width junction discontinuity .......................................... 29
Figure 3. 6 T-junction discontinuity compensation and minimization of the effect ................... 30
Figure 3. 7 Two element patch antenna ..................................................................................... 32
Figure 3. 8 Four element patch antenna ..................................................................................... 33
Figure 3. 9 element patch antenna HFSS model ........................................................................ 34
Figure 4. 1 Return loss Polyamide quartz .................................................................................. 37
Figure 4. 2 Return loss Arlon AD410 ........................................................................................ 37
Figure 4. 3 Return loss Polyamide ............................................................................................. 38
Figure 4. 4 Return loss for fr4 epoxy ......................................................................................... 38
Figure 4. 5 Single element design of circular and rectangular patch antenna 40Figure 4.6. 1 Return
loss of single element Rectangular patch antenna ...................................................................... 40
Figure 4.6. 2 Return loss of single element Circular patch antenna ............................................ 40
Figure 4.7 1 Radiation pattern of single element rectangular and circular patches respectively .. 41
Figure 4.8. 1 gain of single element rectangular patch ............................................................... 41
ix
Figure 4.8. 2 Gain of single element circular patch .................................................................... 41
Figure 4.9 1 Return loss of less matched antenna ...................................................................... 42
Figure 4.9 2 Gain of less matched antenna ................................................................................ 43
Figure 4.9 3 Directivity of less matched antenna………………………………………………...43
Figure 4.10 1 retuen loss of better impedance matching ............................................................ 44
Figure 4.10 2 gain of better impedance matching ...................................................................... 44
Figure 4.10 3 directivity of better impedance matching ............................................................. 45
FIgure 4.11. 1 design of patch antenna for 2 elements ............................................................... 47
FIgure 4.11. 2 return loss of patch antenna for 2 elements ......................................................... 47
FIgure 4.11. 3 gain of patch antenna for 2 elements .................................................................. 47
FIgure 4.11. 4 directivity of patch antenna for 2 elements ......................................................... 48
FIgure 4.11. 5 radiation pattern of patch antenna for 2 elements ................................................ 48
Figure 4.12. 1 design of 4×1 microstrip array patch antenna ...................................................... 49
Figure 4.12. 2 return loss of 4×1 microstrip array patch antenna ................................................ 49
Figure 4.12. 3 gain of 4×1 microstrip array patch antenna ......................................................... 50
Figure 4.12. 4 directivity of 4×1 microstrip array patch antenna ................................................ 50
Figure 4.12. 5 radiation pattern of 4×1 microstrip array patch antenna...................................... 51
Figure 4.13. 1 terurn loss of antenna for element spacing 52,5. .................................................. 52
Figure 4.13. 2 gain of antenna for element spacing 52,5. ........................................................... 53
Figure 4.13. 3 directivity of antenna for element spacing 52,5. .................................................. 53
Figure 4.14. 1 gain of antenna for element spacing 52,5. ........................................................... 54
Figure 4.14. 2 directivity of antenna for element spacing 72,5. ................................................. 55
Figure4.15. 1 return loss of 4×1 array antenna for Wi-fi application .......................................... 57
Figure4.15. 2 VSWR of 4×1 array antenna for Wi-fi application ............................................... 57
Figure4.15. 3 gain of 4×1 array antenna for Wi-fi application ................................................... 57
Figure4.15. 4 directivity of 4×1 array antenna for Wi-fi application ......................................... 58
x
LIST OF TABLES
Table 4. 1 Effect of Increasing Versus Width and Length of The Patch………………………..36
Table 4. 2 Effect of substrate thickness on width and length of the patch ................................... 36
Table 4. 3 Return loss of different substrate at a given resonant frequency ................................ 38
Table 4. 4 Band width of the different substrates ...................................................................... 39
Table 4. 5 comparison of less impedance matched antenna and more impedance matched....... 45
Table 4. 6 parameter dimension of 2×1 array microstrip patch antenna..................................... 46
Table 4. 7 dimensions of design parameter for 4×1.................................................................. 49
Table 4. 8 comparison result of 1,2and 4 element antennas ....................................................... 51
Table 4. 9 designing parameters of different element spacing antenna ...................................... 52
Table 4. 10 results of different element spacing array antenna .................................................. 55
Table 4. 11 designing parameter for 2.45GHz frequency obtained by calculation ...................... 56
Table 4. 12 designing parameter for 2.45GHz frequency obtained by inspection method .......... 56
Table 4. 13 the comparison result for Wi-Fi application antenna .............................................. 58
Table 5. 1 parameter comparison of different element microstrip patch antenna ....................... 60
xi
LIST OF SYMBOLS
𝑊𝑔
ground width
𝑓𝑈
upper cut-off frequency
f2
frequency high
f1
frequency low
fc
frequency center
AF
planar antenna array factor
h
dielectric thickness
σ
conductivity of the conductor
𝜆𝑜
Free space wavelength
c
free space velocity of light, which is 3x108 m/s
h
height of dielectric substrate
W
width of the patch
L
length of the patch
𝜆
Effective wavelength
dBi
decibels relative to an isotropic radiator
Le f f
effective length of the patch

radiation efficiency
D
directivity of the patch antenna
AF
array factor
N
number of elements
BW
bandwidth
ℇr
dielectric constant of the substrate
ZL
load impedance
Z0
characteristic impedance
G
gain
xii
LIST OF ABBREVIATIONS
CST
Computer Simulation Technology
DGS
Defected Ground Structure
EMBMS
Enhanced Multimedia Broadcast/Multicast Services
FDTD
Finite Difference Time Domain- analysis
GPS
Global positioning systems
GSM
Geographical positioning system for Mobile communication
HFSS
High Frequency Simulation Software
HPBW
Half Power Beam Width
HSDPA
High Speed Downlink Packet Access
IEEE
International Electrical and Electronics Engineers
ISM
Industrial Scientific And Medical
MIMO
Multiple Input Multiple Out put
MSA
Microstrip Antenna
OFDM
Orthogonal Frequency Division Multiplexing
RF
Radio Frequency
RFID
Radio frequency identification
RL
Return Loss
RMS
Root mean square
SINR
Interference plus Noise Ratio
UMTS
Universal Mobile Telecommunications System
UTRAN
Universal Terrestrial Radio Access Network
VSWR
Voltage Standing Wave Ratio
WCDMAFDD
wideband code division multiple access Frequency Division
Duplex
Wi-Fi
wireless fidelity
WiMAX
Worldwide Interoperability for Microwave Access
WLAN
Wireless local Area Networks
xiii
CHAPTER ONE
INTRODUCTION
1.1 Background
An antenna is a transducer between a guided wave and a radiated wave, or vice versa. The structure
that "guides" the energy to the antenna is most evident as a coaxial cable attached to the antenna.
A patch antenna is a type of radio antenna with a low profile, which can be mounted on a flat
surface. It consists of a flat sheet of metal, usually copper, mounted on a larger sheet of metal called
a ground plane. A patch array antenna is, in general, some arrangement of multiple patch antennas
that are all driven by the same source. Frequently, this arrangement consists of patches arranged in
orderly rows and columns (a rectangular array). The reason for these types of arrangements is
higher gain. Higher gain commonly implies a narrower beam width and that is, indeed, the case
with patch arrays. This report presents the design and analysis of patch network antenna array for
the 2.4GHz ISM band which is largely license exempt and can be accessed freely for example
Bluetooth. The antenna will be designed with an aim of achieving high directivity and at least a
10% fractional bandwidth. The antenna will have a center frequency of 2.44 which is almost the
same as the given ISM band center frequency. It was so chosen so as to have a bandwidth whose
range is falls within the 2.4 GHz band. The work presented here is the continuation or enhancement
of the 2013 final year patch antenna array project where a basic 4 element patch antenna array was
designed without much emphasis on the gain, directivity or bandwidth.
The report consists of five chapters. After the introduction, the necessary theoretical background
is presented in the second chapter. Then a chapter describing the design and all the steps and
choices made for the patch antenna array follows. An Analysis of the simulated results together
with discussions is done in chapter four. The conclusion, which includes a short summary of the
design achievements, is presented in chapter five.
1.4 Statement of the Problem
With the ever-increasing need for mobile communication and the emergence of many systems, it
is important to design broadband antennas to cover a wide frequency range. The design of an
efficient wide band small size antenna, for recent wireless applications, is a major challenge.
1
Microstrip patch antennas have found extensive application in wireless communication system
owing to their advantages such as low profile, conformability, low-cost fabrication and ease of
integration with feed networks. [1]
However, microstrip antenna have some drawbacks
➢ including narrow bandwidth
This band width problem can be improved by increasing width of patch or selecting appropriate
substrate
➢ low power handling capability
High power in antenna can cause voltage breakdown and excessive heat (due to conductor and
dielectric antenna losses), which would result in an antenna failure. Usually the maximum power
for a single microstrip antenna for frequencies <5GHz shall be less than 50W.Greater power
handling can be achieved by combining multiple elements into arrays.
➢ low gain
To improve gain of patch antenna, (1) antenna VSWR should be near to unity (2) Substrate material must
have lowest loss.
➢ low impedance matching
Impedance matching can also be done by calculating the input impedance then applying quarter
wave impedance matching technique.
1.3 Objectives of The Project
1.3.1 General Objective
The main objective of this project is to design and simulate microstrip patch antenna for ISM band
applications using 2.45 GHz.
1.3.2 Specific Objectives
➢ To study the reduction methods of mutual coupling and return loss in microstrip
array antennas
➢ To increase the efficiency of the microstrip patch antenna by decrease the loss of
the reflection, it's executed by using FR4 eproxi changing technique as a substrate
in microstrip patch antenna.
2
➢ To improve the bandwidth by increasing the thickness of dielectric substrate and
dielectric constant with lower value. By increasing the Bandwidth more data can
be carried out, on the other side high Q-factor gives better directivity hence more
gain for that here a tradeoff is required between Bandwidth and Q-factor (quality
factor). Reduce the microstrip bandwidth limitation due to the narrow band of
microstrip patches in order to increase the bandwidth.
➢ To reduce the energy loss that happening from surface wave, the surface waves
consume apart of energy of the signal thus decreasing the desired signal amplitude
and contributing to deterioration in the antenna efficiency that weaken the
microstrip antenna’s performance.
➢ To study different parameters of microstrip patch array antenna.
1.7 Methodology of The Thesis
This thesis project involves seven main procedures to achieve its objectives. The procedures
involved simulations of the substrate parameter using HFSS software. The following flow chart
summarizes the procedures.
Literature Survey
Determine Antenna Parameter (Including Feeding Techniques)
Selecting of substrate types
Design of single element rectangular patch for different substrate
Design of single element circular patch antenna
Design of array patch antenna
Result And Discussion Based On Optimization
Figure 1. 1 Flow Chart of Methodology
3
1.4 Scope of the study
The scopes of this project have various strategies can be used for this purpose such as:
➢ Use the resonant frequency 2.45 GHz for Wi-Fi application; the resonant frequency is
chosen from IEEE 802.11-2004 span of 2.4-2.5GHz.
➢ Choose the ER4 epoxy as dielectric substrates that have the value of dielectric constant 4.4
in order to reduce the surface wave excisions.
➢ Utilize the transmission Line model for calculation of patch dimension. It’s simplest of all
and gives good physical insight.
➢ Simulate and Verify antenna design performance by apply HFSS and MATLAB code to
design patch antenna.
1.5 Limitation of The Thesis
In this thesis the final band width efficiency in 4.06% but as [26] the maximum efficiency of patch
antenna for Wi-Fi application is 5.26% because of this we can note get this maximum band width
efficiency .and it also have limitation of describing power handling capacity of the antenna .this is
because of that we uses a student version of HFSS software.
1.6 Motivation of The Thesis
Currently the most commonly used WLAN system is the IEEE 802.11b system, with a maximum
throughput of 11 Mbps using a narrowband system. Keeping on par with the growth of broadband
connectivity in the landline sector, the new generation of WLAN systems are designed with a
maximum throughput of at least 54 Mbps. Broadband refers to transmission of information using
a system that uses a comparatively larger frequency band, resulting in increases data transfer rate
or throughput. If the broadband WLAN is to make an entry into the market and have an impact, it
is important that the systems are versatile and performs extremely well. The broadband 802.11a
system requires them to have a good coverage without failing signal strength. The range of
coverage is dependent directly on the antenna performance hence the significance of the broadband
antenna. A key requirement of a WLAN system is that it should be low profile, where it is almost
invisible to the user. For this reason, the microstrip patch antennas are the antennas of choice for
4
WLAN use due to their small real estate area and the ability to be designed to blend into the
surroundings.
Many antenna designs are already present in the market that will successfully meet the broadband
requirement. For example, an omni-directional discone antenna can transmit in all direction and
perform extremely well over a very large bandwidth. These antennas are usually large metallic
cumbersome objects and extremely indiscreet. Aside from the appearance, directivity and security
are important features of WLAN systems.
The system coverage often needs to be limited to designated areas, and since the 802.11x systems
use the ISM bands, there are transmitted power limitations to reduce interference. It is important
for the system to be highly directive in order to reduce coverage in unwanted areas. Primarily, it is
due to possible LAN security breaches in case the LAN’s coverage extends outside the property
and received by unwanted parties. The outside parties may then gain access to documents and other
resources. Besides the security issue, there is also possible interference from neighboring WLAN
systems. There have been documented incidents in congested downtown business districts, where
earlier WLAN systems perform very poorly due to interference from neighboring systems.
As a
result, the demand has increased for broadband WLAN antennas that meet all the desired
requirements. The Broadband antennas are required to be compact, low-profile, directive with high
transmission efficiency and designed to be discreet. Due to these well met requirements coupled
with the ease of manufacture and repeatability makes the Microstrip patch antennas very well suited
for Broadband wireless applications.
1.8 Significance of The Study
The important doing this thesis paper is to show the advantages of using microstrip patch antenna
for wireless LAN and wireless fidelity (Wi-Fi) applications. This is done by improving the
performance of microstrip patch antenna by using of different techniques and parameters of
antenna.
The evolution of modern wireless communications systems has increased dramatically the demand
for antennas, capable to be embedded in portable, or not, devices which serve a wireless land
mobile or terrestrial-satellite network. With time and requirements, these devices become smaller
in size and hence the antennas required for transmit and receive signals have also to be smaller and
lightweight. As a matter of fact, microstrip antennas can meet these requirements. As they are
5
lightweight and have low profile it is feasible them to be structured conformally to the mounting
hosts. Moreover, they are easy fabricated, have low cost and are easy integrated into arrays or in to
microwave printed circuits. So, they are attractive choices for the above-mentioned type of
applications.
1.9 Organization of the Thesis
This thesis is organized into five chapters. Chapter 1 presents the introductory part of the thesis by
describing an overview of antenna, the motivation of the work, the methodology of the thesis and
the limitations included in this introductory chapter. Chapter 2 provides literature serve and
fundamental review of antenna. In This Chapter Array Antennas are explain especially microstrip
patch array antennas. Chapter 3 covers the System Design and Analysis. In this chapter we
discussed the procedures, parameter selection and techniques that used we used to design our
antenna. The result and discussion of thesis is discuses in chapter4.
Finally, conclusion and recommendation for future work is discussed in chapter 5.
6
CHAPTER TWO
LITERATURE SERVE AND REVIEW
2.1 LITERATURE SERVE
According to [1] the substrate material plays significant role determining the size and bandwidth
of an antenna. Increasing the dielectric constant decreases the size but lowers the bandwidth and
efficiency of the antenna while decreasing the dielectric constant increases the bandwidth but with
an increase in size. Some research papers reviews are mentioned below.
In [3] antenna is feed using microstrip feeding technique and simulated using IE3D software The
antenna shows single band bandwidth of 2 GHz for the working band of 4-6 GHz. The proposed
antenna is useful for IEEE 802.11 WLAN standards in the 5.2/5.8 GHz band and WiMAX
standards in the 5.5 GHz band.
In [4] defected ground plane is in the form of L shaped slot and the rectangular parasitic patches
and diagonal cuts at top corners can increase the bandwidth. For the first and second resonant
frequencies Return losses of −17dB and −30 dB respectively, can be achieved when the diagonal
cut is at optimum value.
In [5] a rectangular microstrip patch antenna with DGS has been simulated using High Frequency
Simulation Software (HFSS) at 2.45 GHz frequency, antenna is fed by Quarter Transformer
feeding. The rectangular patch antenna designed with swastika shaped DGS structure, shows gain
of 7dB. Patch antenna with Defected Ground Structure (DGS) demonstrate properties like
improved returning loss, VSWR, bandwidth, gain of the antenna as compared to the conventional
antenna.
In [6] a single frequency microstrip patch antenna feed using microstrip line fed and simulated
using CST Microwave Studio software. Antenna operates at the frequency 5.2 GHz WLAN
standard. Resultant impedance bandwidth is around 190 MHz with the having value of return loss
as -47 dB has been obtained. The antenna also shows impedance of 50.89 ohm.
In [10] antenna operating at 2.4 GHz frequency band for WLAN applications uses rectangular slot
in the ground plane is located at different locations in the bottom of the substrate are considered
and results of optimized patch antenna were obtained. Return loss improvement is from -17.72dB
to -26.92dB. Gain improvement is from-5.1dB to -5.9dB.
7
In [11] antenna Simulated At 4.30 GHz frequency and it is proved that when defect is introduced
in ground plane of the single band antenna then the resulting antenna has its resonant frequency at
lower side that is at 2.5GHz , which shows that the antenna has compact in size and showing
improvement in gain and bandwidth. Here multiband operation of antenna is also obtained.
In [12] very compact antenna was designed, the antenna for WLAN operating in band of 2.4 and
5GHz. Various results are obtained by varying different dimensions of patch. Antenna is feed using
microstrip feed. Different defected ground structures (DGS) have been developed analyzed.
In [13] and it is concluded that although the DGS has applications in the field of the, microwave
oscillators, microwave filter design, microwave couplers to increase the coupling, microwave
amplifiers, etc., it can be used in the microstrip antenna design for various advantages such as
antenna size reduction mutual coupling reduction, harmonic suppression, cross polarization
reduction, in antenna arrays etc.
An antenna is generally a bidirectional device, that is, the power through the antenna can flow in
both directions, coupling electromagnetic energy from the transmitter to free space and from free
space to the receiver, and hence it works as a transmitting as well as a receiving device.
Transmission lines are used to transfer electromagnetic energy from one point to another within a
circuit and this mode of energy transfer is generally known as guided wave propagation. An
antenna can be thought of as a mode transformer which transforms a guided-wave field distribution
into a radiated-wave field distribution. It can also be thought of as a mode transformer which
transforms a radiated-wave field distribution into a guided-wave field distribution (since the two
waves may have different impedances, it may also be thought of as an impedance transformer) [8].
2.2 Review on Fundamental Specification of Antenna
2.2.1 Lobes
Any given antenna pattern has portions of the pattern that are called lobes. A lobe can be a main
lobe, a side lobe or a back lobe and these descriptions refer to that portion of the antenna pattern in
which the lobe appears. In general, a lobe is any part of the pattern that is surrounded by regions
of weaker radiation. So, a lobe is any part of the pattern that sticks out [15].
8
2.2.2 Radiation Pattern
Radiation pattern is graphical representation of the relative field strength transmitted from or
received by the antenna. It is measurement of radiation around the antenna. Antenna radiation
patterns are taken at one frequency, one polarization and one plane cut. The patterns are usually
presented in polar or rectilinear form with a dB strength scale. It is important to state that an antenna
radiates energy in all directions, at least to some extent, so the antenna pattern is three-dimensional.
It is common, however, to describe this 3D pattern with two planar patterns, called the principal
plane patterns. These principal plane patterns can be obtained by making two slices through the 3D
pattern through the maximum value of the pattern or by direct measurement. It is these principal
plane patterns that are commonly referred to as the antenna patterns [14, 15].
2.2.3 Azimuth and Elevation Plane (E and H plane)
Characterizing an antenna's radiation properties with two principal plane patterns works quite
well for antennas that have well-behaved patterns, that is, not much information is lost when only
two planes are shown. Figure 2.1 shows a possible coordinate system used for making such antenna
measurements [15].
Figure 2. 1 Antenna Measurement Co-Ordinate System [15]
The term azimuth is commonly found in reference to "the horizon" or "the horizontal" whereas the
term elevation commonly refers to "the vertical". When used to describe antenna patterns, these
terms assume that the antenna is mounted (or measured) in the orientation in which it will be used.
9
In Figure 2.1, the 𝑥𝑦-plane (𝜃 = 90°) is the azimuth plane (E-plane). The azimuth plane pattern is
measured when the measurement is made traversing the entire 𝑥𝑦-plane around the antenna under
test. The elevation plane (H-plane) is then a plane orthogonal to the 𝑥𝑦-plane, say the 𝑦𝑧-plane
(Φ = 90°). The elevation plane pattern is made traversing the entire 𝑦𝑧-plane around the antenna
under test [15].
The Poynting vector describes both the direction of propagation and the power density of the
electromagnetic wave. It is found from the vector cross product of the electric and magnetic fields
and is denoted S:
𝑆 = 𝐸 × 𝐻∗
𝑤/𝑚2
(2 − 1)
Root mean square (RMS) values are used to express the magnitude of the fields. 𝐻 ∗ is the complex
conjugate of the magnetic field phasor. The magnetic field is proportional to the electric field in the
far field. The constant of proportion is η, the impedance of free space (η =376.73):
|𝑆 | = 𝑆 =
|𝐸|2
𝜂
𝑤/𝑚2
(2 − 2)
Because the Poynting vector is the vector product of the two fields, it is orthogonal to both fields
and the triplet defines a right-handed coordinate system: (E, H, S) [6].
2.2.4 Return Loss
Return loss is a measure of the reflected energy from a transmitted signal. It is a logarithmic ratio
measured in dB (decibel) that compares the power reflected by the antenna to the power that is fed
into the antenna from the transmission line. The larger the value of return loss the less is the energy
reflected. For good impedance matching resonant frequency must lie below −10 𝑑𝐵. [14].
2.2.5 Bandwidth
Bandwidth is defined as the range between upper cut-off frequency (𝑓𝑈 ) at -10 dB and lower cutoff (𝑓𝐿 ) frequency at -10 dB. Bandwidth indicates range of frequency for which an antenna provides
satisfactory operation [14].
10
2.2.6 3-dB Beam width
Also known as the Half Power Beam width (HPBW) is typically defined for each of the principle
planes. The 3-dB beam width in each plane is defined as the angle between the points in the main
lobe that are down from the maximum gain by 3dB. This is the point where the magnitude of the
radiation pattern decreases by 50% (or -3 dB) from the peak of the main beam [14, 15].
2.2.7 VSWR
VSWR stands for Voltage Standing Wave Ratio. The parameter VSWR is a measure that
numerically describes how well the antenna is impedance matched to the radio or transmission line
it is connected to. The smaller the VSWR the better the antenna matched to the transmission line
and the more the power delivered to the antenna. For the perfect matching VSWR = 1, there is no
reflection and return loss. In the real system it is very hard to achieve a perfect match, so it is
defined that having VSWR < 2 is still good matching system [14].
2.2.8 Directivity
Directivity of an antenna is a measure of the concentration of the radiated power in a particular
direction [14]. If the antenna had 100% radiation efficiency, all directivity would be converted to
gain. Typical half wave patches have efficiencies well above 90% [13].
2.2.9 Antenna Gain
Gain is a measure of the ability of the antenna to direct the input power into radiation in a particular
direction and is measured at the peak radiation intensity [6]. It is standard practice to use an
isotropic radiator as the reference antenna in this definition. An isotropic radiator is a hypothetical
lossless antenna that radiates its energy equally in all directions. This means that the gain of an
isotropic radiator is G=1 (or 0 dB). It is customary to use the unit dBi(decibels relative to an
isotropic radiator) for gain with respect to an isotropic radiator [15].
2.2.10 Polarization
The Polarization of an antenna is the polarization of the wave radiated by the antenna in the far
field [8]. Polarization is a property of waves that can oscillate with more than one direction [16].
11
The plane in which the electric field varies is also known as the polarization plane. For optimum
system performance, transmit and receive antennas must have the same polarization [13].
2.2.11 Front-to-back ratio
The front-to-back (F/B) ratio is used a figure of merit that attempts to describe the level of radiation
from the back of a directional antenna. Basically, it is the ratio of the peak gain in the forward
direction to the gain 180-degrees behind the peak. On a dB scale, it is just the difference between
the peak gain in the forward direction and the gain 180-degrees behind the peak [15].
2.2.12 Microstrip Antenna
Microstrip antennas are also referred to as patch antennas. They are low profile, conformable to
planar and non-planar surfaces, simple and inexpensive to manufacture using modern printedcircuit technology, mechanically robust when mounted on rigid surfaces, compatible with MMIC
designs and when the particular patch shape and mode are selected, they are very versatile in terms
of resonant frequency, polarization, pattern and impedance [1].
Major operational disadvantages of microstrip antennas are their low efficiency, low power, high
Q (sometimes in excess of 100), poor polarization purity, poor scan performance, spurious feed
radiation and very narrow frequency bandwidth, which is typically only a fraction of a percent or
at most a few percent. There are methods, however, such as increasing the height of the substrate
that can be used to extend the efficiency (to as large as 90 percent if surface waves are not included)
and bandwidth (up to about 35 percent). However, as the height increases, surface waves are
introduced which usually are not desirable because they extract power from the total available for
direct radiation (space waves). The surface waves travel within the substrate and they are scattered
at bends and surface discontinuities, such as the truncation of the dielectric and ground plane and
degrade the antenna pattern and polarization characteristics [1].
2.2.12.1 Basic Characteristics
Microstrip antennas, as shown in Figure 2.2, consist of a very thin (t ≪ λ0 , where λ0 is the freespace wavelength) metallic strip (patch) placed a small fraction of a wavelength (h≪ λ0 , usually
0.003λ0 ≤ h≤0.05λ0 ) above a ground plane. The microstrip patch is designed so its pattern
maximum is normal to the patch (broadside radiator). This is accomplished by properly choosing
12
the mode (field configuration) of excitation beneath the patch. End-fire radiation can also be
accomplished by judicious mode selection. For a rectangular patch, the length L of the element is
usually λ0 /3 <L<λ0 /2. The strip (patch) and the ground plane are separated by a dielectric sheet
(referred to as the substrate). There are numerous substrates that can be used for the design of
microstrip antennas, and their dielectric constants are usually in the range of 2.2≤𝜀𝑟 ≤12. The ones
that are most desirable for good antenna performance are thick substrates whose dielectric constant
is in the lower end of the range because they provide better efficiency, larger bandwidth, loosely
bound fields for radiation into space, but at the expense of larger element size [1].
The radiating elements and the feed lines are usually photo-etched on the dielectric substrate. The
radiating patch may be square, rectangular, thin strip (dipole), circular, elliptical, triangular, or any
other configuration. Square, rectangular, dipole (strip), and circular are the most common because
of ease of analysis and fabrication, and their attractive radiation characteristics, especially low
cross-polarization radiation [1].
Figure 2. 2 Microstrip antenna and coordinate system [1]
There are many configurations that can be used to feed microstrip antennas. The four most popular
methods are the microstrip line, coaxial probe, aperture coupling, and proximity coupling. The
microstrip-line feed is easy to fabricate, simple to match by controlling the inset position and rather
13
simple to model. However, as the substrate thickness increases, surface waves and spurious feed
radiation increase, which for practical designs limit the bandwidth [1].
There are various methods of analysis for microstrip antennas with the most popular models being
the transmission-line, cavity, and full wave models (which include primarily integral
equations/Moment Method). The transmission-line model is the easiest of all, it gives good
physical insight, but is less accurate and it is more difficult to model coupling [1].
2.2.12.2 Transmission line analysis for a rectangular patch
2.2.12.2.1 Fringing Effects
Because the dimensions of the patch are finite along the length and width, the fields at the edges of
the patch undergo fringing. This is illustrated along the length in Figures 2.2(a, b) for the two
radiating slots of the microstrip antenna. The same applies along the width. The amount of fringing
is a function of the dimensions of the patch and the height of the substrate. For the principal Eplane (𝑥𝑦-plane) fringing is a function of the ratio of the length of the patch L to the height h of the
substrate (L/h) and the dielectric constant 𝜀𝑟 of the substrate. Since for microstrip antennas L/h≫1,
fringing is reduced; however, it must be considered because it influences the resonant frequency of
the antenna. The same applies for the width. For a microstrip line shown in Figure 2.3(a), typical
electric field lines are shown in Figure 2.3(b). This is a nonhomogeneous line of two dielectrics;
typically, the substrate and air. As can be seen, most of the electric field lines reside in the substrate
and parts of some lines exist in air. As W/h≫1 and 𝜀𝑟 ≫ 1, the electric field lines concentrate
mostly in the substrate. Fringing in this case makes the microstrip line look wider electrically
compared to its physical dimensions. Since some of the waves travel in the substrate and some in
air, an effective dielectric constant 𝜀𝑟𝑒𝑓𝑓 is introduced to account for fringing and the wave
propagation in the line [1].
14
Figure 2. 3 Microstrip Line and Its Electric Field Lines, And Effective Dielectric Constant [1]
The effective dielectric constant is defined as the dielectric constant of the uniform dielectric
material so that the line of Figure 2.3(c) has identical electrical characteristics, particularly
propagation constant, as the actual line of Figure 2.2(a).
2.2.12.2.2 Effective Length, Resonant Frequency, and Effective Width
Because of the fringing effects, electrically the patch of the microstrip antenna looks greater than
its physical dimensions. For the principal E-plane (𝑥𝑦 plane), this is demonstrated in Figure 2.4(a)
where the dimensions of the patch along its length have been extended on each end by a distance
∆𝐿, which is a function of the effective dielectric constant 𝜀𝑟𝑒𝑓𝑓 and the width-to height ratio (w/h)
[1].
Since the length of the patch has been extended by ∆𝐿 on each side, the effective length of the patch
is now (L=𝜆/2 for for dominant 𝑇𝑀010 mode with no fringing)
𝐿𝑒𝑓𝑓 = 𝐿 + 2∆𝐿
(2 − 3)
For the dominant 𝑇𝑀010 mode, the resonant frequency of the microstrip antenna is a function of
its length. Usually given by
(𝑓𝑟 )010 =
1
2𝐿√𝜀𝑟 √𝜇0 𝜀0
=
15
𝑣0
2𝐿√𝜀𝑟
(2 − 4)
Figure 2. 4 Physical and effective lengths of rectangular microstrip patch [1]
where 𝑣0 is the speed of light in free space. Since (2-4) does not account for fringing, it must be
modified to include edge effects and should be computed using
(𝑓𝑟𝑐 )010 =
=𝑞
1
2𝐿𝑒𝑓𝑓 √𝜀𝑟𝑒𝑓𝑓 √𝜇0 𝜀0
=
1
2(𝐿 + 2∆𝐿)√𝜀𝑟𝐸𝐹𝐹 √𝜇0 𝜀0
𝑣0
2𝐿√𝜀𝑟
=𝑞
1
2𝐿√𝜀𝑟 √𝜇0 𝜀0
(2 − 5)
where
𝑞=
(𝑓𝑟𝑐 )010
(𝑓𝑟 )010
(2 − 6)
The 𝑞 factor is referred to as the fringe factor (length reduction factor). As the substrate height
increases, fringing also increases and leads to larger separation between the radiating edges and
lower resonant frequencies [1].
2.2.13 Arrays and Feed Networks
Usually the radiation pattern of a single element is relatively wide, and each element provides low
values of directivity (gain). In many applications it is necessary to design antennas with very
directive characteristics (very high gains) to meet the demands of long-distance communication.
This can only be accomplished by increasing the electrical size of the antenna. Enlarging the
16
dimensions of single elements often leads to more directive characteristics. Another way to enlarge
the dimensions of the antenna, without necessarily increasing the size of the individual elements,
is to form an assembly of radiating elements in an electrical and geometrical configuration. This
new antenna, formed by multielement which are driven by the same source, is referred to as an
array. In most cases, the elements of an array are identical. This is not necessary, but it is often
convenient, simpler, and more practical [1].
The total field of the array is determined by the vector addition of the fields radiated by the
individual elements. This assumes that the current in each element is the same as that of the isolated
element (neglecting coupling). This is usually not the case and depends on the separation between
the elements. To provide very directive patterns, it is necessary that the fields from the elements of
the array interfere constructively (add) in the desired directions and interfere destructively (cancel
each other) in the remaining space. Ideally this can be accomplished, but practically it is only
approached. In an array of identical elements, there are at least five controls that can be used to
shape the overall pattern of the antenna [1]. These are:
1. The geometrical configuration of the overall array (linear, circular, rectangular, spherical,
etc.)
2. The relative displacement between the elements
3. The excitation amplitude of the individual elements
4. The excitation phase of the individual elements
5. The relative pattern of the individual elements
Arrays are very versatile and are used, among other things, to synthesize a required pattern that
cannot be achieved with a single element. In addition, they are used to scan the beam of an antenna
system, increase the directivity, and perform various other functions which would be difficult with
any one single element. The elements can be fed by a single line or by multiple lines in a feed
network arrangement.
2.2.13.1 Feeding Methods
There are many methods of feeding a microstrip antenna. The most popular methods are:
1. Microstrip Line.
2. Coaxial Probe (coplanar feed).
3. Proximity Coupling.
17
4. Aperture Coupling.
Because of the antenna is radiating from one side of the substrate, so it is easy to feed it from
the other side (the ground plane), or from the side of the element.
The most important thing to be considered is the maximum transfer of power (matching of the
feed line with the input impedance of the antenna), this will be discussed later in the section
of Impedance Matching.
Many good designs have been discarded because of their bad feeding. The designer can build
an antenna with good characteristics and good radiation parameter and high efficiency but
when feeding is bad, the total efficiency could be reduced to a low level which makes the
whole system to be rejected.
1. Microstrip Line Feed
This method of line feeding is very widely used because it is very simple to design and analyze,
and very easy to manufacture. Figure (2.2) shows a patch with microstrip line feed from the
side of the patch.
Figure 2. 5 Microstrip patch antenna with feed from side [1]
The position of the feed point (𝑦0 ) of the patch in figure (2.2b) has been discussed in detail
in the section of Impedance Matching.
Feeding technique of the patch in figure (2.2a) and figure (2.3) is discussed in [7]. It is widely
used in both one patch antenna and multi-patches (array) antennas.
The impedance of the patch is given by [7]:
r
 L
Za = 90
 r − 1  W 
2
2
The characteristic impedance of the transition section should be:
18
(2.7)
ZT = 50* Z a
(2.8)
The width of the transition line is calculated from [7]:
ZT =
60
r
ln(
8d WT
+ )
WT 4d
(2.9)
The width of the 50Ω microstrip feed can be found using the equation (2.4) below:
Zo =
120
W 2 W
 reff (1.393 + + ln( + 1.444))
h 3
h
(2.10)
Where Z o = 50Ω
The length of the strip can be found from (4.24)
Rin ( x =0) = cos2 (

L
Xo )
(2.11)
The length of the transition line is quarter the wavelength:
l=

4
=
o
4  reff
Figure 2. 6 Rectangular microstrip patch antenna [1]
2. Coaxial Feed (Coplanar Feed)
Coupling of power to the patch antenna through a probe is very simple, cheap, and effective
19
(2.12)
way. If the designer adjusts the feed point to50Ω, so he just needs to use a 50Ω coaxial
cable with N-type coaxial connector.
The N-coaxial connector is coupled to the back side of the microstrip antenna (the ground
plane) and the center connector of the coaxial will be passed through the substrate and
soldered to the patch, as shown in the figure (2.4).
Figure 2. 7 Coaxial line feed [4]
Figure 2. 8 Proximity coupling feed method [3]
3. Proximity Coupling
Proximity coupling is use two substrates  r1 and  r 2 . The patch will be on the top, the ground
plane in the bottom and a microstrip line is connected to the power source and lying between
the two substrates as shown in the figure (2.5). This type is known also as “electromagnetically
coupled microstrip feed”.
20
The principle of this mechanism is that the behavior between the patch and the feed strip line
is capacitive. Analysis and design of such an antenna is little more complicated than the other ones
discussed in the previous sections because the designer must take into account the effect
of the coupling capacitor between the strip feed line and the patch as well as the equivalent RLC resonant circuit representing the patch and the calculating of two substrates (  r1 and  r 2 ). The
coupling capacitor of this antenna can be designed for impedance matching of the antenna.
4.
Aperture Coupling
Figure 2. 9 Aperture coupling feed method [6]
Figure (2.6) shows the layers of the microstrip patch antenna using the aperture mechanism.
The ground plane has an aperture in a shape of a circle or rectangular, and separates two
substrates: the upper substrate  r1 with the patch on it, and the lower substrate  r 2 with the
microstrip feed line under it. This type of coupling gives wider bandwidth. Another property
of this type is the radiating of the feeding strip line is reduced by the shielding effect of the
ground plane. This feature improves the polarization purity [8].
21
CHAPTER THREE
SYSTEM DESIGN AND ANALYSIS
3.1 INTRODUCTION
The rectangular patch antenna is approximately a one-half wavelength long section of rectangular
Micro strip transmission line. When air is the antenna substrate, the length of the rectangular Micro
strip antenna is approximately one-half of a free-space wavelength [1, 2]. The length of the antenna
decreases as the relative dielectric constant of the substrate increases. The antenna has become a
necessity for many applications in recent wireless communication such as radar, microwave and
space communication. The specifications for the design purpose of the structure are as follows:
➢ Type of antenna: Rectangular Micro strip and circular microstrip Patch antenna
➢ Resonance frequency: 2.45GHz.
➢ Input impedance: 50 
➢ Feeding method: Micro strip Line Feed
A rectangular and circular patch was chosen as the basis of the design because of its ease of
fabrication and analysis. The microstrip line was used as the feeding method as it is easy to
fabricate, simple to match by controlling the inset feed position and rather simple to model. The
antenna was designed to work in the 2.4GHz ISM band which has a frequency range of 2.4-2.5GHz,
a center frequency of 2.450GHz, a bandwidth of 100MHz and is freely available worldwide. Some
applications in the 2.4GHz ISM band include the home microwave oven, Sulphur lamps,
communication applications such as wireless LANs, Bluetooth and radio control equipment such
as low power remote control of toys [3].
3.2 Design procedure
3.2.1 Design equation of single element rectangular patch antenna
The FR4 Epoxy, whose loss tangent is 0.02, was chosen as the dielectric material substrate. To
commence the design procedure assumes, specific information had to be included: dielectric
constant of the substrate (𝜀𝑟 ), the resonant frequency (𝑓𝑟 ) and the height of the substrate, ℎ.
𝜀𝑟 = 4.4 , 𝑓𝑟 = 2.4𝐺𝐻𝑧, ℎ = 1.6𝑚𝑚
For an efficient radiator, the practical width that leads to good radiation efficiencies is
22
𝑊=
1
2
𝑣𝑜
2
√
=
√
2𝑓𝑟 √𝜇𝑜 𝜀𝑜 𝜀𝑟 + 1 2𝑓𝑟 𝜀𝑟 + 1
(3 − 1)
= 37.58𝑚𝑚
where 𝑣𝑜 is the free-space velocity of light.
The initial values (at low frequencies) of the effective dielectric constant are referred to as the static
values, and they were calculated as
𝑊/ℎ > 1
𝜀𝑟𝑒𝑓𝑓=
𝜖𝑟 + 1 𝜀𝑟 − 1
ℎ 1
+
[1 + 12 ]−2
2
2
𝑊
(3 − 2)
= 3.99
A very popular and practical approximate relation was then used to find the normalized extension
of the length as
𝑊
(𝜀𝑟𝑒𝑓𝑓 + 0.3)( ℎ + 0.264)
∆𝐿
= 0.412
𝑊
ℎ
(𝜀𝑟𝑒𝑓𝑓 − 0.258)( ℎ + 0.8)
(3 − 3)
∆𝐿 = 0.741𝑚𝑚
The actual length of the patch was determined by solving 𝐿 as,
𝐿=
1
2𝑓𝑟 √𝜀𝑟𝑒𝑓𝑓 √𝜇𝑜 𝜀𝑜
− 2∆𝐿
= 29.15𝑚𝑚
23
(3 − 4)
Table 3.1: Dimension value of single rectangular patch antenna
No
substrate name
r
W
L
h
1
Polyamide
4
39.53
30.86
1.6
quartz
2
Arlon AD410
4.1
39.14
30.49
1.6
3
Polyamide
4.3
38.39
29.78
1.6
4
FR4 epoxy
4.4
38.04
29.44
1.6
GW
W
L
GL
Figure 3. 1 Design of single element rectangular patch antenna
3.2.2 Design equations of single element circular patch antenna
Based on the cavity model formulation, a design procedure is outlined which leads to practical
designs of circular microstrip patch antennas for the dominant‫ ܯ‬mode. The procedure assumes that
24
the specified information includes the dielectric constant of the substrate (ℇ𝑟 ), the resonant
frequency (𝑓𝑟 ) and height of the substrate h.
Since the dimension of the patch is treated a circular loop, the actual radius of the patch is given
by [18]
𝑎=
F
2ℎ
𝜋𝐹
(1 +
[ln ( ) + 1.7726])1/2
𝜋ℇ𝑟 𝐹
2ℎ
Where 𝐹 =
3−5
8.791∗109
𝑓𝑟√𝐸𝑟
Equation (9) does not take into considerations the fringing effect. Since fringing makes the patch
electrically larger, the effective radius of patch is used and is given by [18]
𝑎𝑒 = a(1 +
2ℎ
𝜋𝐹
𝜋ℇ𝑟 𝐹
1
[ln ( ) + 1.7726])2
2ℎ
(3 − 6)
2
Hence, the resonant frequency for the dominant 𝑇𝑀110
is given by [18]
(𝑓𝑟)110 =
1.8412𝑉𝑜
2𝜋𝑎𝑒 √𝐸𝑟
(3 − 7)
Where Vo is the velocity of light.
3.3 Ground plane of single element microstrip patch antenna
As part of the antenna, the ground plane should be infinite in size as for a monopole antenna but in
reality, this is not easy to apply besides a small size of ground plane is desired. In practice, it has
been found that the microstrip impedance with finite ground plane width (𝑍𝑜 ) is practically equal
to the impedance value with infinite width ground plane (𝑍𝑖 ) , if the ground width 𝑊𝑔 is at least
greater than 3*W. The radiation of a microstrip antenna is generated by the fringing field between
the patch and the ground plane, the minimum size of the ground plane is therefore related to the
thickness of the dielectric substrate. [9, 11].
25
GW
a
GL
Figure 3. 2 Design of single element rectangular patch antenna
The size of the ground plane was chosen as:
𝐺𝑊 = 6 ∗ ℎ + 𝑤
(3 − 8𝑎)
𝐺𝐿 = 6 ∗ ℎ + 𝑙
(3 − 8𝑏)
3.4 Impedance
For efficient transfer of power from a transmission line to the patch antenna, the input impedance
of the patch antenna needed to be matched to the characteristic impedance of the transmission line.
It was observed that impedance seen by a transmission line attached to the radiating edge was very
high, and also the impedance (ratio of voltage to current) decreased as one moved towards the
center of the patch. Therefore, depending on the characteristic impedance of the transmission line,
an appropriate point on the patch was chosen through calculation as the feed point [8].
In order to access the appropriate impedance, point on the patch, a recess was created in the patch.
The recess or inset feed was used to improve the impedance matching between the patch and the
feed line. The inset feed position, where the input impedance was 50 ohms and the lengths and
widths for the microstrip feeds were calculated using the MATLAB code in appendix B. A FDTDFinite Difference Time Domain- analysis shows that the inset disturbs the transmission line or
26
cavity model and increases the impedance variation with distance compared to a coaxial probe feed
given a patch resonant length L and feed position 𝑦𝑜 from the center. Transmission line analysis
method was applied as it gives a good insight. However, it is more difficult to model coupling as
well as less accurate [1, 6, 8].
3.5 Feeding Methods
The first is referred to as a series-feed network while the second is referred to as a corporate-feed
network. The corporate-feed network is used to provide power splits of 2𝑛 (i.e., n=2, 4, 8, 16, 32,
etc.). This is accomplished by using either tapered lines or using quarter-wavelength impedance
transformers [1].
Figure 3. 3 Feed arrangements for microstrip patch arrays [1]
Corporate-fed arrays are general and versatile. With this method the designer has more control of
the feed of each element (amplitude and phase) and it is ideal for scanning phased arrays, multibeam arrays, or shaped-beam arrays. The phase of each element can be controlled using phase
shifters while the amplitude can be adjusted using either amplifiers or attenuators [1].
Those who have been designing and testing microstrip arrays indicate that radiation from the feed
line, using either a series or corporate-feed network, is a serious problem that limits the crosspolarization and side lobe level of the arrays [38]. Both cross-polarization and side lobe levels can
be improved by isolating the feed network from the radiating face of the array. This can be
accomplished using either probe feeds or aperture coupling [1].
In microstrip arrays, as in any other array, mutual coupling between elements can introduce scanblindness which limits, for a certain maximum reflection coefficient, the angular volume over
which the arrays can be scanned. For microstrip antennas, this scan limitation is strongly influenced
27
by surface waves within the substrate. This scan angular volume can be extended by eliminating
surface waves. One way to do this is to use cavities in conjunction with microstrip elements. It has
been shown that the presence of cavities, either circular or rectangular, can have a pronounced
enhancement in the E-plane scan volume, especially for thicker substrates. The H-plane scan
volume is not strongly enhanced. However, the shape of the cavity, circular or rectangular, does
not strongly influence the results [1].
3.6 Microstrip Discontinuities
Surface waves are electromagnetic waves that propagate on the dielectric interface layer of the
microstrip. The propagation modes of surface waves are practically TE and TM. Surface waves are
generally at any discontinuity of the microstrip. Once generated, they travel and radiate, coupling
with other microstrip of the circuit, decreasing isolation between different networks and signal
attenuation. Surface waves are a cause of crosstalk, coupling, and attenuation in a multi-microstrip
circuit. For this reason, surface waves are always an undesired phenomenon [9].
A discontinuity in a microstrip is caused by an abrupt change in geometry of the strip conductor,
and electric and magnetic field distributions are modified near the discontinuity. The altered
electric field distribution gives rise to a change in capacitance, and the changed magnetic field
distribution to a change in inductance.
1. Bends
Four 90° bends were encountered in the design. This brought about excess capacitance at the square
corners making the characteristic impedance value to be lower than that of the uniform connecting
lines. A bend of this angle doesn’t work well above a few GHz due to a high VSWR. The same
holds true for bends with angles greater than 90°
Compensation for the microstrip corner bend was made by the use of decreased capacitance
technique. Since experiments on various bends have proven that a decrease in the input reflection
coefficients can be achieved if the corner is chamfered (mitered), the following configuration was
applied
28
Figure 3. 4 Configuration for compensated right-angled bends [13]
W is the width of the line Therefore,
1.8 × 2.62 = 4.716𝑚𝑚
2. Step Width Junction
This discontinuity was found at the 𝜆⁄4 𝑇𝑟𝑎𝑛𝑠𝑓𝑜𝑟𝑚𝑒𝑟𝑠. The effect of the fringing capacitance
associated with the wider line of the step discontinuity is similar to an increase in the length of that
line.
Figure 3. 5 Characteristics of the step width junction discontinuity [13]
In terms of distributed elements, the discontinuity capacitance C has the effect of an increase in
length of the wide line w1, and an equal decrease in length of the narrow line w2. To compensate
for the excess capacitance, the wider line w1 was made to be electrically longer by a length of
9.26mm.
3. T-Junction
These discontinuities were found in the patch antenna array as branch –lines. The T-Junctions were
easily compensated for by simply adjusting the lengths of the different lines. The offset in the main
line is usually very small, and the main effect is on the length of the stub
29
Figure 3. 6 T-junction discontinuity compensation and minimization of the effect [13]
𝑤1 = 12 = 2.62𝑚𝑚 ;
0.7𝑤1 = 0.7 × 2.62 = 1.834𝑚𝑚
3.7 Main Beam Direction
For the 4-element array of figure 3.4, the main beam was directed broadside to the array by ensuring
there was no input phase difference from element to element. To implement an even number of inphase patch elements, the feed network needed to be carefully designed. The distance from the 50ohm SMA source to each patch element needed to be identical or multiples of λ. Unequal line
lengths would have produced phase shifts, which would yield fixed beams that would be scanned
away from the broadside. A quarter-wave transformer was used to match the 100-ohm line to a 50ohm line. The 100-ohm microstrip line was fed using a 50-ohm SMA. In the design of an effective
in-phase radiator, the distance between the patch elements needed to be optimized to yield a peak
gain. The antenna-array chapter in Antenna Theory by Balanis provided insight on the optimum
antenna separation distance. The author identified a separation distance of 𝜆/2 as providing the
optimal gain. In the design, this separation was used as 31.33mm [2, 4].
3.8 Matching of Microstrip Lines to the Source
The characteristic impedance of a transmission line of the microstrip feed patch was designed with
respect to the source impedance. The characteristic impedance 𝑍𝑜 of the transmission line from the
source with respect to the source impedance 𝑍𝑠 was
𝑍𝑜 = 𝑛. 𝑍𝑠
𝑍𝑜 = 2 × 50 = 100 𝑂ℎ𝑚𝑠
30
(3 − 8)
Where the factor 𝑛 was the number of twigs emanating from the node connected to the source. The
inner conductor of the coax was soldered to the 100-ohm microstrip line, and the outer conductor
connected to the ground plane. Since the coax fed two 100-ohm microstrip lines in parallel, no
mismatch occurred at this input as the parallel combination of the two microstrip lines was equal
to 50-ohm [4, 10].
3.8.1 Quarter Wave Transformer
For the input impedance of a transmission line of length L with a characteristic impedance 𝑍𝑜 and
connected to a load with impedance 𝑍𝐴 :
 z + jzo tan(  L) 
zin (− L) = z0  A

 zo + jz A tan(  L) 
(3-9)
When the length of the transformer is a quarter wavelength;
𝜆
𝑍𝑜2
𝑍𝑖𝑛 (𝐿 = ) =
4
𝑍𝐴
(3 − 10)
The above states that by using a quarter-wavelength of a transmission line, the impedance of the
load 𝑍𝐴 can be transformed by the above equation.
Hence by using a transmission line with a characteristic impedance of 50-ohms, the 50-ohm inset
feed line was matched to
𝑍𝑜 = √50 ∗ 50
(3 − 11)
= 50 𝑜ℎ𝑚𝑠
Where 𝑍𝑜 = Characteristic impedance of the quarter-wavelength transformer
This ensured that no power would be reflected back to the SMA feed point as it tried to deliver
power to the antenna [5]. The length of the quarter wavelength transformer was calculated as:
𝐿=
𝜆
𝜆0
=
4 4√𝜀𝑟𝑒𝑓𝑓
= 15.39𝑚𝑚
Where 𝜆 = Effective wavelength and 𝜆𝑜 = Free space wavelength
31
(3 − 12)
3.9 Micro strip Patches Array Antenna Design
In order to increase main beam gain, reduce side lobe radiation, and increase directivity, the patch
antenna design was expanded to a four-element array. The design layout is shown in Figure 5. Two
and Four elements are used, separated by λ/2. The patch radius for each element is the same as the
single patch antenna described above. The probe position was optimized in HFSS to ensure a 50
Ohm match including adjacent patch coupling. A rectangular distribution of antenna elements was
chosen to obtain identical E-plane and H-plane array factor patterns. Four identical antenna
elements were used to allow array factor application to the measured patch radiation pattern for
array predictions. The xyz coordinates are defined to the left of the figure. The array substrate is in
the xy-plane. The z-direction is perpendicular to the substrate.
100 

2
100 
50 
Figure 3. 7 Two element patch antenna
The design values shown in Figure 3.7 and Figure 3.8 are outlined in Table 3.2. Note that the
element spacing refers to the distance between probe feed locations or between corresponding
edges of adjacent patch edges, not to the separation distance. Separation distance refers to the
distance between adjacent patch edges.
32



2
2
2
 /8
100 
100 
100 
70 
100 
70 
 /8
50 
Figure 3. 8 Four element patch antenna
Table 3.2: Parameter dimension for 2*1 array and 4*1 array patch antenna
Parameter
Dimension
Radius
17mm
Element spacing
62.5mm
Width of 70  transmission line
1.6mm
Width of 50  transmission line
3mm
Width of 100  transmission line
0.7mm
3.9.1 Calculation of the Impedance for Quarter-Wave Transformer
Using the following equation whereby replacing Z0 = 50  and Rin =100  The transformer
Characteristic impedance is illustrated as:
ZT = 50* Z a
ZT = 50*100 =70 
50  ,70  and 100  Transmission Line Calculation As a single patch, the different impedance
dimensions are obtained by using the same TX line Calculator.
33
3.9.2 Simulation
The antenna array was designed using the Ansoft HFSS 15.0 software. HFSS is a 3D full wave
electromagnetic field simulator. It uses the finite element method together with adaptive meshing
to solve the wave equations. If a 3D model has been made, HFSS sets up the mesh automatically.
HFSS computes S-parameters, can calculate and plot both the near and far field radiation and
compute important antenna parameters such as gain and radiation efficiency. This software was
used to vary the sizes of the patches, microstrip feed lines and ground plane in order to come up
with the desired results [12]. Figure 3.8 illustrates the HFSS antenna model.
Figure 3. 9 element patch antenna HFSS model
34
CHAPTER FOUR
SIMULATION RESULT AND DISCUSSION
4.1 INTRODUCTION
In this chapter, the effect of different essential parameters such as spacing of elements and
increasing number of elements, substrate height and dielectric constant on gain, band width, VSWR
and mutual coupling for performance analysis and design of rectangular and circular microstrip
patch antenna at ISM band is introduced. After the formation of the sets of the initial conditions, the
results of the performed computer simulations are presented in the form of tables and figures. And finally,
the results will be discussed in term of the selected parameters for comparison.
We use a MATLAB software to calculate the dimensions of patch antenna and transmission line
width, and in addition to this we use HFSS Ansys software to analysis the performance of
microstrip antenna and evaluate the various parameter of antenna like return loss, bandwidth and
radiation pattern etc.
4.2 RESULT AND DISCUSSION
4.2.1 Effect of increasing the dielectric constant and thickness of substrate
With changing the substrate material, the dielectric constant of the substrate changes i.e. changing
the substrate material means the changing the dielectric constant (εr). Although, wide variety of
substrate materials have been found to exist suitable for microstrip patch antenna design with
mechanical, thermal, and electrical properties which are attractive for use in both planar and
conformal antenna configurations. However, tolerance control of the dielectric constant remains a
problem for accurate designs, particularly at higher microwave and millimeter frequencies [10].
Here, we used four different substrate materials Polyamide quartz, Arlon AD410, as shown in the
table 4.1.
As shown in the table 4.1 when increasing the dielectric constant of the material the size of patch
antenna (width and length) will decrease, this helps us to design an antenna with smaller size that
can be compatible with modern technology’s like Wi-Fi, Bluetooth and remotes.
35
Table 4. 1 Effect of Increasing εr Versus Width and Length of The Patch
No
substrate name
 r (substrate)
W
L
H
1
Polyamide quartz
4
39.53
30.86
1.6
2
Arlon AD410
4.1
39.14
30.49
1.6
3
Polyamide
4.3
38.39
29.78
1.6
4
FR4 epoxy
4.4
38.04
29.44
1.6
Table 4. 2 Effect of substrate thickness on width and length of the patch
No
substrate name
r
W
L
h
1
FR4 epoxy
4.4
38.04
29.63
1
2
FR4 epoxy
4.4
38.04
29.47
1.5
3
FR4 epoxy
4.4
38.04
29.29
2
4
FR4 epoxy
4.4
38.04
29.07
2.5
As shown in table 4.2 when we increase the thickness of the substrate by keeping constant of
operating frequency and substrate type, the width of patch also became constant but inversely to
the height; the length of the patch antenna will decrease. But increasing the size of the height of
the substrate cannot be a proper solution for antenna design because the size of antenna is needed
to be smaller as much as possible to full file current demand of technology.
4.2.2 The effect of changing dielectric constant(substrate) on the antenna parameter
In our thesis we have consider different type of dielectric material whose relative dielectric constant
i.e. ɛr are lie between ranges 4 to 4.4 as listed on the table 4.1 and we set the resonance frequency
2.4GHZ.
36
4.2.2.1 Return Loss
This is important to calculate the input and output of signal source, because if load is mismatched
the whole power is not delivered to load and there is a return of power that is called loss, since this
loss is returned hence is called return loss. The response of S11 versus frequency curve clearly
explain return loss.
Figure 4. 1 Return loss Polyamide quartz
Figure 4. 2 Return loss Arlon AD410
37
Figure 4. 3 Return loss Polyamide
Figure 4. 4 Return loss for fr4 epoxy
Table 4. 3 Return loss of different substrate at a given resonant frequency
substrate name
r
Return loss(dB)
Freq (GHz)
Polyamide quartz
4
-11.3669
2.3
Arlon AD410
4.1
-11.0796
2.3
Polyamide
4.3
-6.2463
2.3
FR4 epoxy
4.4
-5.6781
2.3
By observation of table 4.3, we can conclude that as we increase the relative dielectric permittivity
of the substrate of antenna then return loss is increasing hence very les amount of power is
forwarded to radiating element hence radiating characteristics can be degraded. It is also observed
38
that if substrate materials are different but have same relative dielectric constant then return loss is
remain same for both materials.
4.2.2.2 Bandwidth
In microstrip patch antenna the bandwidth is inversely proportional to the square root of the
dielectric constant of the substrate. S11 response of patch antenna is used for calculation of
bandwidth.
Table 4. 4 Band width of the different substrates
substrate name
r
Frequ1(GHz)
Frequ2(GHz)
Band width (%)
f2 − f 1
*100%
fc
Polyamide quartz
4
2.232
2.3695
5.9783
Arlon AD410
4.1
2.232
2.3689
5.9522
Polyamide
4.3
2.2554
2.3397
3.66522
FR4 epoxy
4.4
2.2646
2.3395
3.25652
By observation of table 4.4 we can conclude that as we increase the relative dielectric permittivity of
the substrate of antenna the bandwidth of antenna is decreases.
4.2.3 Comparison of rectangular and circular single element patch antenna
Figure 4.5 shows the design of both rectangular and circular patch antennas and its dimension. As
shown in the Figure, both patches are fed by microstrip line inset feed. A Substrate with  r =4.4
and thickness h=1.6 mm is used in both designs, as well. Figure 4.6 shows the return loss for both
designs in Figure 4.5. It can be seen that the radiation pattern in both designs is in broadside
direction. Both designs are resonating at 2.4 GHz as shown in Figure 4.7.
39
Figure 4. 5 Single element design of circular and rectangular patch antenna
Figure 4.6. 1 Return loss of single element Rectangular patch antenna
Figure 4.6. 2 Return loss of single element Circular patch antenna
40
Figure 4.7 1 Radiation pattern of single element rectangular and circular patches respectively
Figure 4.8. 1 gain of single element rectangular patch
Figure 4.8. 2 Gain of single element circular patch
41
As shown in the figure 4.8.1 and 4.8.2 the gain of rectangular patch is 3.25 and the gain of circular
patch antenna is 3.365. For the same return loss and the same parameter, the circular patch antenna
has better gain performance of 3.65 and as shown in the 3D polar plot the coverage of circular
patch is approaches to aspherical pattern.
4.2.4 The Effect of Impedance Matching on Circular
As impedance mismatch in RF network causes power to be reflected back to the source from the
impedance mismatch boundary. This reflection creates a standing wave, which leads storage of
power instead of transmitting it to the load3. Hence, there will be less power delivered from the
input to the load or other parts of the system. Along with this, standing waves may damage and
overheat the RF device because of increased peak power level. Other advantages of proper
termination of load are reduction in amplitude and phase error, reduction in power loss and
improvement in the signal to noise ratio.
Mostly, impedance of antenna is matched by 50Ω feed line because of the fact that almost all the
microwave sources and lines are manufactured with 50Ω characteristic impedance. This can be
observed by its return loss and VSWR.
Figure 4.9 1 Return loss of less matched antenna
42
Figure 4.9 2 Gain of less matched antenna
Figure 4.9 3 Directivity of less matched antenna
From the figure 4.9.1 we can observe
Return loss =-15.62
Maximum gain =3.36
Directivity= 6.39 and the band width of
43
Figure 4.10 1 return loss of better impedance matching
Figure 4.10. 2 gain of better impedance matching
44
Figure 4.10. 3 directivity of better impedance matching
From the figure 4.10 we can observe
Return loss =-21.95
Maximum gain =3.37
Directivity= 6.38
Table 4. 5 comparison of less impedance matched antenna and more impedance matched
Parameters
Less impedance matched
More impedance matched
Return loss
-15.62
-21.95
VSWR
2.9
1.39
Maximum gain
3.36
3.37
Directivity
6.39
6.38
Band width (%)
3.75
5.416
However, Impedance matching is a challenging step in the antenna design to achieve optimum
performance parameters like return loss, efficiency, gain etc. as shown in the table 4.5 Impedance
matching also helps in tuning the antenna frequency with a much easier and faster way than
modifying the antenna geometry. Proper impedance matching also helps in improving the
bandwidth of antenna because impedance matching circuits add some additional resonances.
45
Impedance matching circuits also allow incorporating last minute design change by allowing
freedom in choosing the values of discrete components, independently. Generally, impedance
matching is used to increase the performance of a patch antenna.
4.2.5 The effect of increasing number of elements in micro strip patch antenna
An antenna array is a set of N spatially separated antennas. The number of antennas in an array can
be as small as 2, or as large as several thousand (as in the AN/FPS-85 Phased Array Radar Facility
operated by U. S. Air Force). In general, the performance of an antenna array (for whatever
application it is being used) increases with the number of antennas (elements) in the array; the
drawback of course is the increased cost, size, and complexity.[10]In addition to this High power
in antenna can cause voltage breakdown and excessive heat (due to conductor and dielectric
antenna losses), which would results in an antenna failure. Usually the maximum power for a single
microstrip antenna for frequencies <5GHz shall be less than 50W. And Greater power handling
can be achieved by combining multiple elements into arrays.[18] The effect of increasing antenna
elements for patch antenna are discussed below.
4.2.5.1 2×1 Element Array Patch Antenna
Based on the dimensions that are given in to the table 4.6 the 2×1 patch antenna is designed on the
HFSS as shown in the figure 4.11 a and the results also discussed on the figures below.
Table 4. 6 parameter dimension of 2×1 array microstrip patch antenna
Parameter
Dimension
Radius
17mm
Element spacing
62.5mm
Width of 50  Tx line
3mm
Width of 100  Tx line
0.7mm
46
Figure 4.11. 1 design of patch antenna for 2 elements
Figure 4.11. 2 return loss of patch antenna for 2 elements
Figure 4.11. 3 gain of patch antenna for 2 elements
47
Figure 4.11. 4 directivity of patch antenna for 2 elements
Figure 4.11. 5 radiation pattern of patch antenna for 2 elements
48
4.2.5.2 4×1 Element Array Patch Antenna
Table 4. 7 dimensions of design parameter for 4×1
Parameter
Dimension
Radius
17mm
Element spacing
62.5mm
Width of 70  Tx line
1.6mm
Width of 50  Tx line
3mm
Width of 100  Tx line
0.7mm
Figure 4.12. 1 design of 4×1 microstrip array patch antenna
Figure 4.12. 2 return loss of 4×1 microstrip array patch antenna
49
Figure 4.12. 3 gain of 4×1 microstrip array patch antenna
Figure 4.12. 4 directivity of 4×1 microstrip array patch antenna
50
Figure 4.12. 5 radiation pattern of 4×1 microstrip array patch antenna
From the figure 4.10, figure 4.11 and figure 4.12 we can construct a table
Table 4. 8 comparison result of 1,2and 4 element antennas
Parameter
Single element
2 element Array
4 element Array
Return loss (dB)
16
16
16
Max Gain (dB)
3.36
5.63
8.264
Max directivity(dB) 6,39
8.46
9.08
As shown in the table 4.8 when increase the number of elements of an antenna, the gain and
directivity of antenna also increase respectively. this enables the antenna to get more performance
than a smaller number of elements. But when we increase the number of elements in an array
antenna the impedance matching will decrease this is because the radiation that is generated by
one’s element will affect the other neighboring element that can cause of impedance mismatch.
And in addition to this, occurrence of interference between element is increase (mutual
interference).to handle this problem the proper element spacing is important.
51
4.2.6 Effect of spacing between antenna elements
Mutual coupling and return loss are important factors which must be considered in the design of
array antennas. When one array element radiates, a portion of its radiated power is absorbed by
other elements and induces current on them. The mutual coupling effect leads to problems such as
beam forming error, scanning error, and input power wastage [7–9]. Therefore, the effect of mutual
coupling must be reduced in array antenna design. To do this, several methods such as changing
feed position, feed structure, or patch shape have been reported [10–14].
Based on the standard formulas that are shown in chapter 3 for antenna design we calculate the
dimensions of our design by using MATLAB code that shown in the appendix B and the results
are presented on table 4.9.
Table 4. 9 designing parameters of different element spacing antenna
Design No Spacing(mm) Radius (mm)
Width of 50(mm)
Width of
Width of
70(mm)
100(mm)
1
52.5
17
3
1.6
0.7
2
62.5
17
3
1.6
0.7
3
82.5
17
3
1.6
0.7
We are design an antenna base on the data that are shown in the table 4.9 and the results are shown
in figure13, figure 14.
Figure 4.13. 1 return loss of antenna for element spacing 52,5.
52
Figure 4.13. 2 gain of antenna for element spacing 52,5.
Figure 4.13. 3 directivity of antenna for element spacing 52,5.
53
Figure 14a return loss of antenna for element spacing 72,5.
Figure 4.14. 1 gain of antenna for element spacing 52,5.
54
Figure 4.14. 2 directivity of antenna for element spacing 72,5mm.
From the Figure 4.14 we make a table that describe the different parameter of 4*1 element patch
array antenna.
Table 4. 10 results of different element spacing array antenna
No
Element
Return
Directivity(dB) Gain
Bandwidth
spacing(mm)
loss(dB)
(dB)
efficiency (%)
1
52.5
-0.13
8.67
7.48
0
2
62.5
-16
9.26
8.26
3.75
3
72.5
-12
9.44
8.48
2.43
As shown in table 4.10 from the three designed antennas the return loss is better for the element
spacing of 62.5(  / 2 )and within increasing of antenna spacing the gain and the directivity will also
increase within the range of  / 2 to  where lambda is the wave length of the operating frequency.
with the same as return loss band width efficiency from the designed array antenna for the spacing
 / 2 is highest. From this we can say because of the element spacing the occurrence of interference
between the antenna element is high the return loss became increase and band width became
decrease on the other side with in increasing of antenna spacing more than specified length the
return loss became increase and band width efficiency will decrease.
Based on the results that are discussed above we are designed an antenna that is can work for WiFi application. This Wi-Fi antenna design to work at ISM band range of frequency that is 2.4GHz
55
to 2.5GHz. The operating frequency is desired to be the center of its grange of operation that is
2.45GHz.
To make our design we use 4*1 phased line array antenna that can have a better performance than
a single element and 2*1 phased line array antenna. To overcome mutual coupling effect, we use
 / 2 spacing between the element that can gives a better band width efficiency. In addition to this
to get a better impedance matching we use inspection method. Due to this inspection method the
dimensions(width) of impedance matching lines are changed.
Table 4. 11 designing parameter for 2.45GHz frequency obtained by calculation
Parameter
Dimension
Radius
17.12mm
Element Spacing
62.5mm
Operating frequency
2.45GHz
Width of 50 
3mm
Width of 70 
1.6mm
Width of 100 
0.7mm
Table 4. 12 Designing parameter for 2.45GHz frequency obtained by inspection method
Radius
16.82mm
Element Spacing
62.5mm
Operating frequency
2.45GHz
Width of 50  Tx line
3mm
Width of 70  Tx line
1.6mm
Width of 100  Tx line
0.8mm
56
Figure 4.15. 1 return loss of 4×1 array antenna for Wi-fi application
Figure 4.15. 2 VSWR of 4×1 array antenna for Wi-fi application
Figure 4.15. 3 gain of 4×1 array antenna for Wi-fi application
57
Figure 4.15. 4 directivity of 4×1 array antenna for Wi-fi application
As shown in the figure 4.15 we improved the return loss of the antenna to get a better impedance
matching between the transmission line and antenna elements. This helps to transfer power that
come source or (transmission line) and radiated by the antenna. This also prevents our circuit
element damage from that caused by reflected power.
As we can see in figure 10, figure 11 and figure 12 the antenna gain, and directivity are better than
a single element and 2*1 phased line array patch antenna. And the results of the above figures are
summarized in the table below.
Table 4. 13 the comparison result for Wi-Fi application antenna
Parameter
Single element
two element
four element
Wi-Fi
antenna
antenna
antenna
application
antenna
Return loss(dB)
-21,95
-16
VSWR (dB)
1.39
2.76
Gain(dB)
3.37
5.63
8.26
8.037
Directivity(dB)
6.38
8.46
9.08
9.31
efficiency 2.46
2.92
3.45
4.06
BW
-16
-18
2.16
(%)
58
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 INTRODUCTION
This chapter concludes with a summary for this thesis and the future prospects of rectangular and
circular micro strip antenna. In this thesis paper we used different techniques and antenna
parameters to design a micro strip patch antenna at ISM band of frequency(2.4GHz-2.5GHz) that
can be applicable for Wi-Fi. For simulation purpose we use HFSS Ansys student version software
and MATLAB code for calculating dimensions of the desired antenna. HFSS is a 3D full wave
electromagnetic field simulator. It uses the finite element method together with adaptive meshing
to solve the wave equations. If a 3D model has been made, HFSS sets up the mesh automatically.
HFSS computes S-parameters, can calculate and plot both the near and far field radiation and
compute important antenna parameters such as gain and radiation efficiency.
5.2 CONCLUSION
Different parameters are affecting the design of patch antenna, those are operating frequency,
substrate material, thickness of substrate and for array antenna element spacing is also important.
With changing the substrate material, the dielectric constant of the substrate changes i.e. changing
the substrate material means the changing the dielectric constant (εr). When the dielectric constant
of the substrate increases the dimensions of patch antenna is decrease and when the height of the
substrate increases the width if the patch is constant, but length will decrease.
we can conclude that as we increase the relative dielectric permittivity of the substrate of antenna
then return loss is increasing hence very les amount of power is forwarded to radiating element
hence radiating characteristics can be degraded. As shown in the comparison of rectangular and
circular patch antenna. For the same return loss and the same parameter, the circular patch antenna
have better gain performance of 3.65 and as shown in the 3D polar plot the coverage of circular
patch is approaches to aspherical pattern. It can be seen that the radiation patterns in both designs
are in broadside direction. Small side lobes appear in rectangular. Side lobes approximately
disappear in circular design.
59
Impedance matching is also the important thing in the design of antenna. As impedance mismatch
in RF network causes power to be reflected back to the source from the impedance mismatch
boundary. This reflection creates a standing wave, which leads storage of power instead of
transmitting it to the load. Hence, there will be less power delivered from the input to the load or
other parts of the system. Along with this, standing waves may damage and overheat the RF device
because of increased peak power level. In addition to this impedance making is also used to increase
the efficiency of band width.
An antenna array is a set of N spatially separated antennas. The number of antennas in an array can
be as small as 2, or as large as several thousand. This will used to increase the different parameters
antenna that are discussed in chapter 4.
Table 5. 1 parameter comparison of different element microstrip patch antenna
Parameter
Single element ()
2 element array
4 element array
Return loss
16Db
16 dB
16 dB
Max Gain
3.36dB
5.63dB
8.264dB
Max directivity
6,39dB
8.46 dB
9.08 dB
Mutual coupling and return loss are important factors which must be considered in the design of
array antennas. When one array element radiates, a portion of its radiated power is absorbed by
other elements and induces current on them. Therefore, the effect of mutual coupling must be
reduced in array antenna design.
A 4 element, microstrip fed patch antenna array of circular shaped radiating elements was
successfully designed using the FR4 Epoxy substrate. Through analysis with the Ansoft HFSS
simulation software, it was observed that the antenna worked in the 2.4GHz ISM band by having
a resonance frequency of 2.66 GHz and had a fractional bandwidth of 4.06% and a directivity of
9.31dB. The patch antenna array was coaxially fed through a 50- ohm cable with a 50 -ohm smaconnector. Impedance matching was done well though not accurately. The maximum achievable
gain by the antenna was 5.2235 dB.
60
5.3 RECOMMENDATION
Antenna design is a vast field for researchers and engineers. Further improvement of the 1x4 micro
strip patch array antenna can be made in the following areas. A Micro strip Line fed Rectangular
Micro strip Patch Antenna with the dimension parametersh-1.6mm, L-24.256mm, W-34.2mm with
a dielectric constant of 4.4 at an operating frequency of 2.6GHz from this project can be said as the
optimized design. It is very important to take the feed technique the impedance and the substrate
is the main parameters into consideration.
The proper position to terminate the Feed line also affects the performance of the antenna. As said
different type of feed technique affects the performance of the antenna. Micro strip Feed line is
shown in this thesis and the results implies the performance of the antenna is good.
In future other different type of feed techniques can be used to evaluate the overall performance of
the antenna without missing the optimized parameters in the action. Extensively and exclusively
focusing on the area of different design methods especially in minimizing the mutual coupling
between the elements. Besides, can also use different shapes of micro strip patches such as square
and hexagonal shape to carry out the research. Finally we want to recommend; can carry out the
research by increase the array element in order to enhance the performance of the patch antenna.
61
APPENDIX
Appendix A
Conductance
Each radiating slot is represented by a parallel equivalent admittance Y (with conductance G and
susceptance B). This is shown in FigureA1. 4.
Figure A1.4 Rectangular microstrip patch and its equivalent circuit transmission-line model
The slots are labeled as #1 and #2. The equivalent admittance of slot #1, based on an
infinitely wide, infinite slot, is given by
𝑌1 = 𝐺1 + 𝑗𝐵1
(𝐴1)
Where for a slot of finite width W
𝐺1 =
𝐵1 =
𝑊
1
[1 − (𝑘𝑜 ℎ)2 ]
120𝜆𝑜
24
𝑊
[1 − 0.636𝑙𝑛(𝑘𝑜 ℎ)]
120𝜆𝑜
ℎ
1
<
𝜆𝑜 10
ℎ
1
<
𝜆𝑜 10
(𝐴2)
(𝐴3)
Since slot #2 is identical to slot #1, its equivalent admittance is
𝑌2 = 𝑌1 , 𝐺2 = 𝐺1 ,
𝐵2 = 𝐵1
(𝐴4)
In general, the conductance is defined as
𝐺1 =
2𝑃𝑟𝑎𝑑
|𝑣𝑜 |2
(𝐴5)
The radiated power is written as
62
𝑘𝑜 𝑊
|𝑣𝑜 |2 𝜋 sin( 2 𝑐𝑜𝑠𝜃) 2
∫ [
𝑃𝑟𝑎𝑑 =
] 𝑠𝑖𝑛3 𝜃𝑑𝜃
2𝜋𝜂𝑜 0
𝑐𝑜𝑠𝜃
(𝐴6)
Therefore, the conductance of (1-10) can be expressed as
𝐺1 =
𝐼1
120𝜋 2
(𝐴7)
Where
2
𝑘 𝑊
sin( 𝑜2 𝑐𝑜𝑠𝜃
𝐼1 = ∫ [
]
𝑐𝑜𝑠𝜃
0
𝜋
= −2 + cos(𝑋) + 𝑋𝑆𝑖 (𝑋) +
𝑋 = 𝑘𝑜 𝑊
sin(𝑋)
𝑋
(𝐴8)
(𝐴9)
Asymptotic values of (1-12) and (1-12a) are
𝐺1 =
1 𝑊 2
( )
90 𝜆0
1 𝑊
( )
{ 120 𝜆𝑜
𝑊 ≪ 𝜆𝑜
(𝐴10)
𝑊 ≫ 𝜆𝑜
Appendix B
%Program to calculate the parameters to design a rectangular patch antenna
%the user have to feed the values of frequency, dielectric constant, and
%height of the dielectric.
%program will calculate automatically the width and length of the patch
%and the width and length of the transition and transmission feed line.
f = input( 'input frequency f in Ghz: ');
Er = input ( 'input dielectric constant of the substrate ');
h = input( 'input height of substrate h in mm: ');
h=h/1000;
f=f*1e9; % turn frequency to HZ
c = 3e8; % speed of light
% calculating Width and Length of the Patch
W = ( c / ( 2 * f ) ) * ( ( 2 / ( Er + 1 ) )^0.5);
Er_eff = (Er+1)/2 + (( Er -1 )/2)*(1/(sqrt(1+(12*(h/W)))));
L_eff = c/(2*f*sqrt(Er_eff));
a1 = ( Er_eff + 0.3 ) * ( ( W / h ) + 0.264 );
a2 = ( Er_eff - 0.258 ) * ( ( W / h ) + 0.8 );
delta_L = (0.412 * ( a1 / a2 )) * h;
L = L_eff - 2*delta_L;
63
str=['width of the patch = ', num2str(W*1000), ' mm']
str=['length of the patch = ', num2str(L*1000), ' mm']
% Calculating the input impedance of the patch
Zo = 90 * Er^2*(L/W)^2/(Er-1);
% Calculating the strip transition line
Zt=sqrt(50*Zo);
a3=exp(Zt*sqrt(Er)/60); p=-4*h*a3; q=32*h^2;
Wt1=-(p/2) + sqrt((p/2)^2-q);
Wt2=-(p/2) - sqrt((p/2)^2-q); %width of the transition line
Er_t= (Er+1)/2 + (( Er -1 )/2)*(1/(sqrt(1+(12*(h/Wt2)))));
L_t=(c/f)/(4*sqrt(Er_t)); %length of transition line
str=['width of the transition line = ', num2str(Wt2*1000), ' mm']
str=['length of transition line = ', num2str(L_t*1000), ' mm']
% Calculating the 50 ohm transmission line
syms x;
Z0=50;
d=h*1000;
a = 1.393-(120*pi/(Z0*sqrt(Er)));
RR1=inline('x/d+0.667*log(x/d+1.44)+a');
64
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