Rectangular patch Antenna

CHAPTER 1

INTRODUCTION

This chapter consists of a brief introduction to my project including problem
statement, objectives, scope of work and outline of my thesis. This chapter highlighted
the important of the project and the arrangement of this thesis.

1.1 INTRODUCTION

Antenna is one of the important elements in the RF system for receiving or
transmitting signals from and into the air as medium. Without proper design of the
antenna, the signal generated by the RF system will not be transmitted and no signal can
be detected at the receiver. Antenna design is an active field in communication for future
development. Many types of antenna have been designed to suit with most devices. One
of the types of antenna is the microstrip patch antenna (MPA). The microstrip antenna
has been said to be the most innovative area in the antenna engineering with its low
material cost and easy to fabricate which the process can be made inside universities or
research institute. The idea of microstrip antenna was first presented in year 1950‟s but it
only got serious attention in the 1970‟s [1].

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Due to MPA advantages such as low profile and the capability to be fabricated using
lithographic technology, antenna developers and researchers can come out with a novel
design of antenna which will reduce the cost of its development. Through printed circuit
technology, the antenna can be fabricated in mass volume which contributes to cost
reduction.

MPA are planar antennas used in wireless links and other microwave applications. It uses
conductive strips and patches formed on the top surface of a thin dielectric substrate
separating them from a conductive layer on the bottom surface which is the ground for
the antenna. A patch is typically wider than a strip and its shape and dimension are
important features of the antenna. MPA are probably the most widely used antennas
today due to their advantages such as light weight, low volume, low cost, compatibilit y
with integrated circuits and easy installation on the rigid surface. Furthermore, they can
be easily designed to operate in dual-band, multi-band application, dual or circular
polarization. They are important in many commercial applications [7]. They are
extremely compatible for embedded antennas in handheld wireless devices such as
cellular phones, pagers etc. These low profile antennas are also useful in aircraft,
satellites and missile applications, where size, weight, cost, ease of installation, and
aerodynamic profile are strict constraints [8].

MPA with inset feed has been studied extensively over the past two decades because of
its advantages. However, length of MPA is comparable to half wavelength with single
resonant frequency with bandwidth around 2%. Moreover, some applications of the MPA
in communication systems required smaller antenna size in order to meet the
miniaturization requirements. So, significant advances in the design of compact MPA
have been presented over the last years.

Many methods are used to reduce the size of MPA like using planar inverted F antenna
structure (PIFA) or using substrate with high dielectric constant [9]. Defected Ground
Structure (DGS) is one of the methods to reduce the antenna size.

DGS is relatively a new area of research and application associated with printed circuit
and antennas. The evolution of DGS is from the electron band gap (EBG) structure [10].

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The substrate with DGS must be designed so that it becoming metamaterial. The substrate
with DGS is considered as metamaterial substrate when both relative permittivity, εr and
permeability, µr are negative.

The invented metamaterial antenna will have comparable performance and smaller size
to conventional one. The substrate that I used was RO3003. The metamaterial antenna
behaves as if it were much larger than it really is.

By designing the antenna with the DGS makes possible to reduce the size for a particular
frequency as compared to the antenna without the DGS. MPA inherently has narrow
bandwidth and bandwidth enhancement is usually demanded for practical applications, so
for extending the bandwidth, DGS approaches can also be utilized.

1.2 PROBLEM STATEMENT

In the microstrip antenna application, one of the problem is to reduce its size while
having considerable performance. Moreover, the propagating of surface wave will reduce
the efficiency of the antenna. This is due to the increment of the side and back radiation.
When this happen, the front lobe or main lobe will decrease which lead to reduction in
gain.

1.3 OBJECTIVES OF THE PROJECT

Conventional antenna follows the right-hand rule which determine how
electromagnetic wave behaves. This antenna radiates at frequency of half wavelength of
the patch length while metamaterial antenna able to omit this rule. Metamaterial antenna
able to radiates while having smaller size of antenna. Moreover, metamaterial offers an
alternative solution to widen the antenna applications using the left-hand rule. The
unique properties of metamaterial enable the enhancement of the conventional antenna,
thus open more opportunities for better antenna design. This project will emphasize on
obtaining the metamaterial using DGS with optimized parameters of negative index
behaviour in which both permittivity and permeability co-exist simultaneously in the
required frequency region.

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The main objectives of this project are:

i) To prove the concept of metamaterial.

ii) To reduce the size of rectangular patch antenna by implementing
metamaterial as substrate.

iii) To compare the performance of DGS and conventional antenna.

1.4 SCOPE OF WORK

This project focuses on the development of two miniaturized rectangular patch
antenna using DGSs that functions at 4.7 GHz and 2.4GHz. The scope of the project will
includes the study of metamaterial having both negative permittivity and permeability.
Then, produce the metamaterial substrate by using DGS. The work includes the designing
of DGS that will change RO3003 substrate into metamaterial. These substrates are then
tested through simulation using NRW method to find the metamaterial functional
frequency. Then, both conventional and DGS antennas are designed to resonate at the
obtained frequency. The parameter of conventional rectangular patch antenna is based on
formula [11] and [12] while DGS patch antennas size are tuned to work at the desire
frequency. All simulation for conventional and DGS antennas had been done in CST
MWS. Thus, the size and performance of conventional and DGS antenna are compared.
Fabrication was made to verify the simulation results.

1.5 ORGANIZATION OF THE THESIS

This thesis consists of six chapters and the overview of all the chapters are as follows:

Chapter 1: This chapter provides a brief introduction on the background, the objectives of
the project and scope of work involved in accomplishing the project.

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Chapter 2: Literature review of fundamental of antenna properties, equation of
conventional rectangular patch antenna, metamaterial and defected ground structure
(DGS) are described in this chapter. This chapter focuses on fundamentals and theories of
metamaterial and how it‟s able to reduce antenna size.

Chapter 3: This chapter gives an overview of the antenna design methodology,
simulation, fabrication and testing (measurement) procedures.

Chapter 4: This chapter describes the simulation and measurement results obtained from
this project, including description and discussion.

Chapter 5: A final conclusion is made in chapter 5 based on the outcome of the project,
followed by the recommendations for the future work.

1.6 SUMMARY

Understanding of metamaterial is the most important topic in this project to develop
miniaturized antenna. By obtaining metamaterial substrate will introduce „left handed‟
region. The size reduction is due to the antenna radiates or resonates at lower frequency.
Moreover, conventional antenna radiates at frequency of half wavelength of patch length
while metamaterial antenna omit this rule. The metamaterial substrates are realized using
DGS. DGS is used to alter the electrical properties of RO3003 so that both permittivity
and permeability becoming negative.

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CHAPTER 2

LITERATURE REVIEW

This chapter consists of explanation to antenna fundamentals, microstrip patch
antenna (MPA), metamaterial, negative refractive index and defected ground structure
(DGS).

2.1 INTRODUCTION

Antenna is a device used for radiating and receiving an electromagnetic wave in
free space [13]. The antenna works as an interface between transmission lines and free
space. Antenna is designed for certain frequency band. Beyond the operating band, the
antenna rejects the signal. Therefore, we might look at the antenna as a band pass filter
and a transducer. There are many different types of antennas.

The isotropic point source radiator is one of the basic theoretical antenna which is
considered as a radiation reference for other antennas. In reality such antenna cannot
exist. The isotropic point source radiator radiates equally in all direction in free space.
Antennas‟ gains are measured with reference to an isotropic radiator and are rated in
decibels with respect to an isotropic radiator (dBi). Antennas can be categorized into 9
types which are [7]:

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i. Active integrated antennas

ii. Antenna arrays (including smart antennas)

iii. Dielectric antennas (such as dielectric resonant antennas)

iv. Microstrip antennas (such as patches)

v. Lens antennas (sphere)

vi. Wire antennas (such as dipoles and loops)

vii. Aperture antennas (such as pyramidal horns)

viii. Reflector antennas (such as parabolic dish antennas)

ix. Leaky wave antennas

2.2 ANTENNA PROPERTIES

This part describes the performance of antenna, definitions of its various parameters.
Some of the parameters are interrelated and not at all of them need to be specified for
complete description of the antenna performance.

2.2.1 Polarization

Polarization is the direction of wave transmitted (radiated) by the antenna. It is a
property of an electromagnetic wave describing the time varying direction and relative
magnitude of the electric field vector. Polarization may be classified as linear, circular, or
elliptical as shown in Figure 2.1. Polarization shows the orientation of the electric field
vector component of the electromagnetic field. In line-of-sight communications it is
important that transmitting and receiving antennas have the same polarization (horizontal,
vertical or circular). In non-line-of-sight the received signal undergoes multiple
reflections which change the wave polarization randomly.

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Linear Elliptical Circular

E = electrical field vector

Figure 2.1: Types of antenna polarization [2]

2.2.2 Radiation pattern

An antenna radiation pattern is defined as a mathematical function or a graphical
representation of the radiation properties of the antenna as a function of space
coordinates. In most cases, the radiation pattern is determined in the far-field region and
is represented as a function of the directional coordinates. Radiation properties include
power flux density, radiation intensity, field strength, directivity phase or polarization.
Radiation pattern provides information which describes how an antenna directs the
energy it radiates and it is determined in the far field region. The information can be
presented in the form of a polar plot for both horizontal (azimuth) and vertical as figure
2.2.

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Figure 2.2: Polar radiation pattern [3]

Figure 2.3 shows radiation pattern in 3D. The radiation pattern could be divided into:

i. Main lobes

This is the radiation lobe containing the direction of maximum radiation.

ii. Side lobes

These are the minor lobes adjacent to the main lobe and are separated by various
nulls. Side lobes are generally the largest among the minor lobes.

iii. Back Lobes

This is the minor lobe diametrically opposite the main lobe.

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First null beamwidth Major lobe

Half power beamwidth
(HPBW)

Minor lobes Side lobe

Back lobe
Minor lobes

Figure: 2.3 Radiation pattern [3].

2.2.3 Half Power Beam width (HPBW)

The half power beam width is defined as the angle between the two directions in which
the radiation intensity is one half the maximum value of the beam. The term beam width
describe the 3dB beam width as shown in Figure 2.4.

The beam width of the antenna is a very important figure-of-merit, and it often used to as
a trade off between it and the side lobe level. By controlling the width of the beam, the
gain of antenna can be increased or decreased. By narrowing the beam width, the gain
will increase and it is also creating sectors at the same time [14].

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Figure 2.4: Rectangular plot of radiation pattern [2].

2.2.4 Antenna Gain

Antenna gain is a measure of directivity properties and the efficiency of the antenna.
It is defined as the ratio of the radiation intensity in the peak intensity direction to the
intensity that would be obtained if the power accepted by the antenna were radiated
isotropically. The gain is similar to directivity except the efficiency is taken into account.
Antenna gain is measured in dBi. The gain of the antenna can be described as how far the
signal can travel through the distance. When the antenna has a higher gain it does not
increase the power but the shape of the radiation field will lengthen the distance of the
propagated wave. The higher the gain, the farther the wave will travel concentrating its
output wave more tightly [15]. The gain of an antenna will equal to its directivity if the
antenna is 100% efficient. Normally there are two types of reference antenna can be used
to determine the antenna gain. Firstly is the isotropic antenna where the gain is given in
dBi and secondly is the half wave dipole antenna given in dBd. I will be using only dBi
as a reference.

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2.2.5 Voltage Standing Wave Ratio (VSWR)

Voltage Standing Wave Ratio is the ratio of the maximum to minimum voltage on the
antenna feeding line. Standing wave happen when the matching is not perfect which the
power put into antenna is reflected back and not radiated. For perfectly impedance
matched antenna the VSWR is 1:1. VWSR causes return loss or loss of forward energy
through a system.

2.2.6 Bandwidth

The bandwidth of an antenna means the range of frequencies that the antenna can
operate. The bandwidth of an antenna is defined as the range of frequencies within which
the performance of the antenna, with respect to some characteristics, conforms to a
specified standard [16]. In other words, there is no unique characterization of the
bandwidth and the specifications are set to meet the needs of each particular application.
There are different definitions for antenna bandwidth standard. I considered the
bandwidth at -10 dB at the lower and upper centre frequency from the return loss versus
frequency graph as shown in figure 2.5.

Figure 2.5: Graph return loss versus frequency [4]

Return loss is a measure of reflection from an antenna. 0 dB means that all the power is
reflected; hence the matching is not good. -10dB means that 10% of incident power is
reflected; meaning 90% of the power is accepted by the antenna. So, having -10dB as a
bandwidth reference is an assumption that 10% of the energy loss.

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Referring to figure 2.5, the value of bandwidth can be calculated in the form of
percentage as formula (1) below:

𝑓2 −𝑓1
𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡𝑕 = 𝑥 100% (1)
𝑓2 +𝑓1

2.3 MICROSTRIP ANTENNA

2.3.1 Overview of Microstrip Antenna

A microstrip antenna consists of conducting patch and a ground plane separated by
dielectric substrate. This concept was undeveloped until the revolution in electronic
circuit miniaturization and large-scale integration in 1970. The early work of Munson on
microstrip antennas for use as a low profile flush mounted antennas on rockets and
missiles showed that this was a practical concept for use in many antenna system
problems. Various mathematical models were developed for this antenna and its
applications were extended to many other fields. The number of papers, articles published
in the journals for the last ten years. The microstrip antennas are the present day antenna
designer‟s choice. Low dielectric constant substrates are generally preferred for
maximum radiation. The conducting patch can take any shape but rectangular and
circular configurations are the most commonly used configuration. A microstrip antenna
is characterized by its length, width, input impedance, gain and radiation patterns.
Various parameters, related calculation and feeding technique will be discussed further
through this chapter. The length of the antenna is about half wavelength of its operational
frequency. The length of the patch is very critical and important that result to the
frequency radiated.

2.3.2 Surface wave effect

The surface wave gives effect of reduction to the amplitude of the input signal
before propagate through the air. Additionally, surface waves also introduce spurious
coupling between different circuit or antenna elements. This effect severely degrades the
performance of microstrip filters because the parasitic interaction reduces the isolation in
the stop bands. Surface waves reaching the outer boundaries of an open microstrip
structure are reflected and diffracted by the edges. The diffracted waves provide an

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additional contribution to radiation which degrading the antenna pattern by raising the
side lobe and the cross polarization levels. Surface wave effects are mostly negative, for
circuits and for antennas, so their excitation should be suppressed if possible.

2.3.3 Microstrip line

Microstrip line is a conductor of width W printed on a thin grounded dielectric substrate
of thickness h and relative permittivity, 𝜀 𝑟 . Microstrip line is used as a feeding technique
for inset feed. Moreover, the electrical properties which are the permittivity and
permeability can also be achieve using this method. The diagram of the microstrip line is
shown in figure 2.6.

Figure 2.6: Microstrip line with width W and thickness h.

The effective dielectric constant of a microstrip line is given by [9] as equation (2):

𝜀 𝑟 +1 𝜀 𝑟 −1 12𝑕 −1
𝜀 𝑒𝑓𝑓 = + (1 + )2 (2)
2 2 𝑊

The value of characteristic impedance used mostly 50Ω and 75 Ω. The value that I am
using is 50 Ω transmission line.

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The characteristic impedance, Zo can be calculated as:

60 8𝑕 𝑤 𝑤
ln + 𝑓𝑜𝑟 ≤1
𝜀 𝑒𝑓𝑓 𝑤 4𝑕 𝑕

𝑍𝑜 = (3)
120 𝜋 𝑤 𝑤 𝑤
[ + 1.393 + 0.667 ln + 1.444 ] 𝑓𝑜𝑟 ≥1
𝜀 𝑒𝑓𝑓 𝑕 𝑕 𝑕

2.3.4 Rectangular patch antenna design

The figure 2.7 shows the microstrip diagram of rectangular shape of microstrip patch
antenna and the equivalent circuit. The arrows show how the wave flows through the
patch and the ground plane [11].

Figure 2.7: Microstrip diagram and equivalent circuit [4].

The conventional patch antenna equations were taken from [11] and [12]. The equation
to realize the conventional rectangular patch antennas are shown as below:

−1
𝑐 𝜀 𝑟 +1 2
𝑊= (4)
2𝑓 𝑟 2

Where W is the patch antenna width, 𝑓𝑟 is the operational frequency and εr is the substrate
permittivity.

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Another point to note is that the EM fields are not contained entirely within the
microstrip patch but propagate outside of the patch as well. This phenomena result to
fringing effect. Two parallel plates of microstrip and ground will form a capacitor; the
electric field does not end abruptly at the edge of the plates. There is some field outside
that plates that curves from one to the other. This causes the real capacitance to be larger
than what I calculate using the ideal formula. Thus I will have larger capacitance
compare to ideal equation. While considering the fringing effect the effective length and
the effective permittivity will change. Figure 2.8 shows that EM field are not contained
entirely within the microstrip patch.

Figure 2.8: EM fields around the microstrip line [5].

c
L= − 2∆l (5)
2f r εeff

Where L is the patch antenna length and c is speed of EM wave in vacuum which equal to
3x108m/s.

𝑤
𝜀 𝑒𝑓𝑓 +0.3 𝑕
+0.264
∆𝑙 = 0.412𝑕 𝑤 (6)
𝜀 𝑒𝑓𝑓 −0.258 +0.8
𝑕

The substrate length and width dimensions are calculated as equation (7) and (8):

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𝑊𝑠 = 𝑊 + 6𝑕 (7)
𝐿 𝑠 = 𝐿 + 6𝑕 (8)

Where Ws is the substrate width and Ls is the substrate length

2.3.5 Feeding Techniques

Antenna feeding technique can generally divide into two categories which are
contacting and non-contacting. The four most popular feed techniques used in patch
antenna are the microstrip line, coaxial probe (both contacting schemes), aperture
coupling and proximity coupling (both non-contacting).

2.3.5.1 Microstrip Line Feed

Microstrip line feed is a feeding method where a conducting strip is connected to
the patch directly from the edge as shown in figure 2.9. The microstrip line is etched on
the same substrate surface which gives advantage of having planar structure. The method
is easy to fabricate because it only need a single layer substrate and no hole.

Microstrip feed
Patch

Substrate

Ground plane

Figure 2.9: Microstrip line feed [5].

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Another point to note is that microstrip line feed need an inset cut in the patch. The
purpose of the inset cut in the patch is to match the impedance of the feed line to the
patch without the need for any additional matching element. This is achieved by properly
controlling the inset position. Hence this is an easy feeding scheme, since it provides ease
of fabrication and simplicity in modelling as well as impedance matching.

This feeding method will be used in my antenna design. The simplified calculation for
the length of the inset cut shown by equation (9):

(9)

where:

l = the inset cut length

εr = Permittivity of the dielectric

L = Length of the microstrip patch

2.3.5.2 Coaxial feed

The Coaxial feed is a very common technique used for feeding Microstrip patch
antennas. As seen from Figure 2.10, the inner conductor of the coaxial connector extends
through the dielectric and is soldered to the radiating patch, while the outer conductor is
connected to the ground plane.

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Substrate

Patch

(a)

Substrate

Coaxial
Ground plane
connector

(b)

Figure 2.10 Rectangular patch antenna structure with coaxial feed: (a) Top view (b) side
view [5].

The benefit of this feeding method is that the connector can be put at any location within
the patch to match the impedance. Moreover, this feed method is easy to fabricate and
has low spurious radiation. However, there is some disadvantage. When dealing with
thicker substrate the inductance increase could effect to the matching problem.

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2.3.5.3 Aperture Coupled Feed

Patch Aperture slot
Microstrip line

Substrate 1
Ground plane
Substrate 2

Figure 2.11: Diagram of aperture coupled feed [5].

The coupling aperture is usually centred under the patch, leading to lower cross-
polarization due to symmetry of the configuration. The amount of coupling from the
feed line to the patch is determined by the shape, size and location of the aperture. Since
the ground plane separates the patch and the feed line, spurious radiation is minimized.
Generally, a high dielectric material is used for bottom substrate and a thick, low
dielectric constant material is used for the top substrate to optimize radiation from the
patch [18]. The major disadvantage of this feeding technique is that it is difficult to
fabricate due to multiple layers, which also increases the antenna thickness. This feeding
scheme also provides narrow bandwidth.

2.3.4.3 Proximity Coupled Feed

This type of feed technique is more less the same as aperture couple feed except that the
microstrip line is optimized to get the best matching. The main advantage of this feed
technique is that it eliminates spurious feed radiation and provides high bandwidth [18].

Matching can be achieved by controlling the length of the feed line and the width-to-line
ratio of the patch. The main disadvantage of this method is using double layer substrate
and needs proper alignment which is tedious in fabrication process.

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Patch

Microstrip line

Substrate 1

Substrate 2

Figure 2.12: Proximity Coupled feed [5]

2.4 METAMATERIAL

2.4.1 Metamaterial theory

Metamaterial define as artificial effective electromagnetic structures with unusual
properties not readily found in nature. However, „unusual‟ is generally meant to imply
material properties which have been hardly explored before the turn of 20 th century, in
particular negative refractive index [19].

Metamaterial is a material having negative relative permittivity and permeability. These
two properties determine how a material will interact with electromagnetic radiation.
When both permittivity and permeability are simultaneously negative, it‟s then having a
negative refractive index (NRI) or left-handed material (LHM). This relationship is
shown by the following Maxwell‟s equation for refractive index:

𝑛 = ± 𝜇𝜀 (8)

Maxwell‟s equation tells us how the electromagnetic wave behaves which contain both
electric and magnetic field. Figure 2.13 shows the electric and magnetic field which
propagates in perpendicular to each other. The field directions in a plane wave also form

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right angles with respect to their direction of travel (the propagation direction). When an
electromagnetic wave enters in a material, the fields of the wave interact with the
electrons and other charges of the atoms and molecules that compose the material,
causing them to move about. For example, this interaction alters the motion of the wave-
changing its speed or wavelength.

Electric field
Electric field

Propagation direction

Magnetic field

Figure 2.13: Electromagnetic wave [6]

Knowing that the permittivity and permeability are the only material properties that
relevant in changing the wave behaviour, thus changing or tuning this value gives higher
degree of freedom in designing an antenna.

Another point to notes is that only when both permittivity and permeability are positive
and negative is useful in antenna design as shown is figure 2.14. Single negative region
which is region II and IV impede the signal. Region I is where the permittivity and
permeability are both positive. This region is most explored. This is where most of
material behaves. However, region III is less explored. This is where the matamaterial
exist. Materials that exist and behave in this region are not readily available in nature. At
the intersection (point A) it is the zero refractive index (n) diagrams.

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Figure 2.14: Permittivity-permeability(ε-μ) diagram which shows the material classifications
[14].

2.4.2 Behaviour of wave

An electromagnetic wave can be depicted as a sinusoidal varying function that travels
to the right or to the left as a function of time. Figure 2.15 shows that the wave travels
into the material having positive refractive index from n1 to n2. The speed of the wave
decreases as the refractive index of the mataterial increase.

S
O
U
R
C
E
n1 n2>n1

Figure 2.15: Wave incidents on a positive index material [6].

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When the refractive index is negative, the speed of the wave, given by c/n is negative and
the wave travels backwards toward the source as shown in Figure 2.16. Therefore, in
left-handed metamaterial, wave propagates in the opposite direction to the energy flows.

S
O
U
R
C
E
n1 n2>-n1

Figure 2.16: Wave incidents on a negative index material [6].

2.4.3 Refraction and Snell's Law

One of the most important fundamental theories that govern the optical effect or
bending of light between two material is the refraction. Refraction is a basic theory
behind lenses and other optical element that focus, changing direction and manipulates
light. The principle and theory applicable for other wave as well such as RF signal.
Highly sophisticated and complex optical devices are developed by carefully shaping
materials so that light is refracted in desired ways. Every material, including air, has an
index-of-refraction (or refractive index). When an electromagnetic wave travels from a
material with refractive index n1 to another material with refractive index n2 the change in
its trajectory can be determined from the ratio of refractive indices n2/n1 by the use of
Snell's Law shown in equation (9).

𝑛1 sin 𝜃1 = 𝑛2 𝑠𝑖𝑛𝜃2 (9)

The Snell‟s law is also applicable for left-handed material with the same refraction angle
with respect to normal line except in different direction as shown in figure 2.17. These

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figures show how travelling waves from free space entering right-handed (having
positive-index of refraction) and left-handed (having negative-index of refraction)
material.

Positive-index material Negative-index material

Figure 2.17: Incident wave travelling through positive-index and negative-index material.

In addition, figure 2.18 and 2.19 show how the spreading patterns of the waves on
entering and exiting the conventional and LHM material respectively. For conventional
material, the refracted waves are spreading away after entering and exiting the medium.
For LHM, the waves are refracted in such a way as to produce a focus inside the material
and then another just outside. The radiation pattern is more a beamlike, which leads to
the creation of highly directional antennas and also may allow more antennas to be placed
in closely packed space.

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Vacuum Conventional
material

Figure 2.18: Refracted rays in conventional material [6].

Vacuum
Conventional
material

Figure 2.19: Refracted rays in Left-handed material [6].

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2.4.4 Metamaterial structures

There are four basic structures that had been discussed in literatures to realize
metamaterial substrates as in figure 2.20. Combining the electric dipole and magnetic
dipole structure can result to metamaterial substrate.

The summary of the different elements used for metamaterial synthesis shows in
figure 2.20. Each one of the element can be considered as either electric or magnetic
dipole. Split-ring resonators (SRRs) and slot lines can be considered as magnetic dipole
while metal wire lines and complementary split-ring resonator (CSRRs) are regarded as
electric dipole.

(a) (b)

(c) (d)

Figure 2.20: Structure used for metamaterial synthesis (a) SRRs , (b) metal wire lines, (c) CSRRs,
(d) slot lines

Metamaterial substrates are synthesized by combining electric and magnetic dipole
elements. These structures are able to realize metamaterial if properly aligned.
Specifically, there are four combination methods as listed below [19]:

• SRR and Wire dipole: This is the widely used combination structure.

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• SRR and CSRR: This structure does no gain much popularity because the
arrangement is difficult.

• Slot dipole and wire dipole: The mushroom as figure 2.21a structures falls in this
category.

• Slot dipole and CSRR: The structure as shown in figure 2.21b. This structure had been
used for wideband filter applications

(a)

(b)

Figure 2.21: Metamaterial structure (a) Mushroom structure, (b) Planar CRLH structure

2.4.5 Nicholson Ross Weir (NRW)

NRW is a tool or method converting scattering parameter from the simulation or
measurement into electrical properties which are permittivity, εr and permeability, µr.

In the NRW algorithm, the reflection coefficient is

Γ = 𝜒 ± χ2 − 1 (10)

Where,

2 2
𝑠11 −𝑠21 +1
𝜒= (11)
2𝑠11

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As a step to acquire the correct root, X is must be in the form of S-parameter, the
magnitude of the reflection coefficient, must be less than one. The following stage is to
calculate the transmission coefficient of the metamaterial.

S 11 +S 21 −Γ
Τ= (12)
1−(S 11 +S 21 )Γ

1 1
ln = ln + 𝑗(𝜃 𝑇 + 2𝜋𝑛) (13)
𝑇 𝑇

Where

𝐿
𝑛= (14)
𝜆𝑔

Where

𝑛 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑜𝑜𝑡

𝐿 = 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑙𝑒𝑛𝑔𝑡𝑕 𝑖𝑛 𝑐𝑚

𝜆 𝑔 = 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡𝑕 𝑖𝑛 𝑐𝑚

𝜃 𝑇 = 𝑝𝑕𝑎𝑠𝑒 𝑜𝑓 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑖𝑛 𝑟𝑎𝑑𝑖𝑎𝑛

we define:

1 1 1
2 =- [ ln⁡ )]2
( (15)
Λ 2𝜋𝐿 Τ

Then we can solve for the permeability using

1+Γ
𝜇𝑟 = 1 1
(16)
(1−Γ)Λ −
𝜆2 𝜆2
0 𝑐

Where 𝜆0 is the free space wavelength and 𝜆 𝑐 is the cutoff wavelength.

The permittivity is given by

𝜆2 1 1 1
𝜀𝑟 = 0
[ 𝜆 2 − [2𝜋𝐿 ln ]2 ] (17)
𝜇𝑟 𝑐 Τ

29

2.5 RELATION BETWEEN DGS, EBG AND METAMATERIAL

The concept of DGS arises from the studies of Photonic Band Gap (PBG) structure which
dealing with manipulating light wave. PBG is known as Electron Band Gap (EBG) in
electromagnetic application. They are actually artificial periodic structures that can give
metamaterial behavior. These structures would have periodic arrangement of metallic,
𝑛𝜆 𝑔
dielectric or metalodielectric bodies with a lattice period 𝑝 = , λ being the guide
2

wavelength. In 1999, a group of researchers further simplified the geometry and
discarded the periodic nature of pattern. They simply use a unit cell of dumbbell shape to
the same response as EBG which known as „Defected Ground Structure‟ (DGS).
Therefore, a DGS is regarded as a simplified variant of EBG on a ground plane [23].
Thus DGS can be described as a unit cell EBG or an EBG with limited number of cells.
The DGS slots are resonant in nature. The presence of DGS can realize metamaterial
substrate.

Figure 2.23 shows different geometries that have been explored with the aim of achieving
improved performance in term of stopband and passbands, compactness, and ease of
design [23].

30

(a) (b) (c) (d) (e)

(f) (g) (h) (i) (j)

(k) (l) (n) (o)

(p) (q) (r) (s) (t)

Figure 2.23 : Different DGS geometries : (a) dumbbell-shape (b) Spiral-shaped (c) H-shaped (d)
U-shaped (e) arrow head dumbbell (f) concentric ring shaped (g) split-ring resonators (h)
interdigital (i) cross-shaped (j) circular head dumbbell (k) square heads connected with U slots (l)
open loop dumbbell (m) fractal (n)half-circle (o) V-shaped (q) meander lines (r) U-head dumbbell
(s) double equilateral U (t) square slots connected with narrow slot at edge.

DGS has been widely used in the development of miniaturized antennas. In, our design,
DGS is a defect etched in the ground plane that can give metamaterial behavior in
reducing the antenna size. DGS is basically used in microstrip antenna design for
different applications such as antenna size reduction, cross polarization reduction, mutual
coupling reduction in antenna arrays, harmonic suppression etc. DGS are widely used in
microwave devices to make the system compact and effective [21].

31

CHAPTER 3

METHODOLOGY

3.1 METHODOLOGY OVERVIEW

This chapter consists of the design methodology used for this project which
includes the description on the selected DGS structures, conventional and DGS antenna
simulation and fabrication process. The methodology of this project starts by
understanding of the microstrip antenna technology. This includes the properties study of
the antenna such as operating frequency, radiation pattern, and antenna gain. The related
literature reviews are carried out from reference books and IEEE publish paper. The
simulation has been done by using Computer Simulation Technology Microwave Studio
(CST MWS). To meet the theoretical expectation, the design is being optimized
accordingly. The methodology described here is illustrated in Figure 3.1. The simulations
performed also have limitation. The fabrication process is started after the optimization
result from the simulation.

32

3.2 FLOW CHART OF DESIGN METHODOLOGY

The implementation of this project includes two main parts which are software
design and hardware design. The approaches of the project design are represented in the
flow chart in figure 1. The software simulation includes the designing of conventional
antennas and DGS metamaterial antennas. CST Microwave Studio software is used for
antenna simulation. The designing of DGS antennas are implemented by finding the
metamaterial response of the substrate having both permittivity, εr and permeability, µr
negative. The bottom copper of Rogers3003 must critically shape for these purposes.

Start

Design possible metamaterial
structure

NO
CST simulation

Metamaterial structure used

Optimize antennas design

Antenna fabricate

Measurement

Data analysis

End

Figure 3.1: Flow chart of antenna design.

33

3.3 DGS STRUCTURES

Before designing the antenna with DGS substrate, two DGS structures were
designed first. The target parameter is for the substrate to behave as metamaterial at 4.75
GHz and 2.45 GHz. The characteristics parameters of the substrate are described in the
Table 3.1. RO3003 has good permittivity accuracy with deviations of only 0.04 mm. The
substrate thickness is 0.5 mm. The loss tangent is a parameter of a dielectric material that
quantifies its inherent dissipation of electromagnetic energy. This substrate has low
tangent loss which is 0.0013. Lower tangent loss means lower signal loss. Thus the
substrate is suitable for antenna design.
Table 3.1: Characteristic parameter of substrate (RO3003)
Characteristics Values
Permittivity, εr 3.00 ± 0.04
Permeability, µr 1.00
Loss tangen, tan 𝛿 0.0013
Thickness, h 0.5 mm
Copper cladding, t 0.035 mm

The DGSs are designed to resonate at 2.4 GHz and 4.7 GHz. These structures are designed
based on [4]. Two DGS structures have been designed. The first design (a) is the circular
rings and the second design (b) is the split rings. Structure (b) is a modification made from
(a) so that the substrate behaves as metamaterial at 2.45 GHz.

34

DGS

Copper

(a) (b)
Figure 3.2: Bottom view of DGS structures: (a) circular rings behave as metamaterial at 4.75
GHz, (b) split rings behave as metamaterial at 2.45 GHz.

3.4 INVESTIGATION OF METAMATERIAL SUBSTRATE

The designing of DGS antennas are implemented by finding the metamaterial
response of the substrate having both permittivity, εr and permeability, µr negative at
desired frequency. The bottom copper of Rogers 3003 must be critically shaped for this
purpose.

The transmission line method is selected for analysis purposes as shown in figure 3.3.
The substrate two-port S-parameter was extracted using this technique in simulation. The
NRW method act as a converter to obtain the permittivity, εr and permeability,µr of the
material. The transmission line technique has been introduced by Zijie lu [19].

50 Ω line

DGS structure

Figure 3.3.Transmission line method [17].

35

As mention before the value of permittivity and permeability of the substrate can be
changed, influenced by introducing DGS. The location of negative permittivity, εr and
permeability, µr were observed base on NRW calculation. Microsoft Excel was used to
make calculation faster. Optimization was done so that the substrate becomes
metamaterial at desired frequency.

In figure 3.4 the blue line represents the permittivity, εr value and the red line
represents permeability, µr value. Figure shows that for circular rings structure having
both permittivity and permeability becoming negative at 4.7 GHz frequency band.
Therefore, we can realize that this substrate operate as metamaterial at 4.7 GHz.
Moreover, this substrate also operates as metamaterial at higher frequency. As we can see
at 9.6 GHz, both electrical properties are negative.

4.75 GHz
εr= -154
µr= -0.000818

Figure 3.4: Relative permittivity, εr and permeability, µr value versus frequencies for substrate
with circular rings DGS

36

In figure 3.5 the blue line represents the permittivity, εr value and the red line
represents permeability, µr value. Figure shows that for circular rings structure having
both permittivity, εr and permeability, µr becoming negative at 2.4 GHz frequency band.
Therefore, we can realize that this substrate operate as metamaterial at 2.4 GHz.
Moreover, this substrate also operates as metamaterial at higher frequency. As we can see
at 9.6 GHz, both electrical properties are negative.

2.45 GHz
εr= -132
µr= -0.000461

Figure 3.5: Permittivity, εr and permeability, µr value versus frequencies for substrate with slip
rings DGS.

Final physical parameters of both substrates are shown as in figure 3.6. These
substrate structures had been tuned to get the metamaterial functional at desired
frequencies. Figure 3.6 shows two rings with inner radii of 5 mm and 6 mm. Both of
rings have 0.5mm width operate with (a) 4.7 GHz and (b) 2.45 GHz. The rings have 1.29
mm gap.
The slip rings structure is a modification made from double rings so that the
substrate behaves as metamaterial at 2.45 GHz. The 1.29 mm gap increase the copper
area thus increases the total capacitance value.

37

17.9 17.5
1.29

20.0 20.0
(a) (b)
Figure 3.6: Designed metamaterial substrates dimension (mm) (a) double rings and (b) slip ring
physical parameter.

3.5 ANTENNA DESIGN

This part discusses the process of designing the rectangular patch and DGS
antenna. Antenna design process also includes optimization, fabrication and measurement
process.

3.5.1 Designing rectangular patch antenna

The simulation of conventional antenna is designed for the purpose of comparison to
DGS one. Two conventional MPA antennas were designed at 4.75 GHz and 2.4 GHz
respectively. The conventional patch antenna equations were taken from [10] and [11] as
mention previously in chapter 2.

The objectives of the antenna design are described in the Table 3.2. The antenna
design should have the value of return loss less than negative 10dB at the operational
frequency. The antenna considered to radiate as return loss is less than negative 10dB.
Specifically, the return loss should be as low as possible to reduce the matching
impedance. Moreover, the design antenna should have linear polarization.

38

Table 3.2: Characteristics goals of conventional rectangular patch antenna
Frequency of operation 4.7 GHz and 2.4
GHz
Return loss (dB) <-10dB
Feeding method Microstrip line
Polarization Linear

Base on simulation each of conventional rectangular patch antennas are able to
operate at 4.75 GHz and 2.4 GHz respectively. The dimension is as shown in figure 3.7a
and 3.7b. The simulation template used was „Antenna (mobile phone)‟ which have the
following default settings as table 3.3. The setting units of mm and GHz in simulation are
due the ease of simulation. The boundaries of simulation are set to free space for all
direction. These settings are used to calculate the farfield radiation pattern so that the
antenna surrounding set as open space.
Table 3.3 Settings for CST MWS
Measurement unit length mm
Measurement unit frequency GHz
Boundaries Free space

25.6

21.3

3.9
21.3 17.9

6.1

(a)

39

47.2

43.5

39.0 4.3
35.0
11.0

(b)
Figure 3.7 Top view dimensions (mm) of conventional rectangular patch antenna : (a) 4.7 GHz
antenna (b) 2.4 GHz antenna

The simulation was done from 1GHz to 10 GHz. All the calculation of EM field
was done using „transient solver‟ with default settings. The optimization was done so that
the antennas having lowest reflection coefficient at the desired frequency. The length of
the inset cut were tune to get the result.
Figure 3.8a shows return loss of 4.7 GHz conventional patch antenna having
different inset cut length. Changing the length of inset cut will change the impedance
value. Different values of inset cut length are observed for the purpose of optimization.
Having short inset length such 3.0 mm the return loss is negative 5.1 dB and with deeper
inset length of 6.5 mm the return loss become negative 16.1 dB. The best inset length is
6.1 mm with return loss of negative 28.0 dB.
Figure 3.8b shows return loss of 2.4 GHz conventional patch antenna having
different inset cut length. Having inset length of 11.4 mm the return loss become negative
18.3 dB. The best inset length is 11 mm with return loss of negative 21.7 dB. Thus it can
be understood that if the inset cut is far from the matching impedance the return loss will
increase.

40

: -5.1
: -5.5
: -0.8
-17.0
: -5.5
: : -5.5
-23.4
: : -5.5
-28.0
: -16.1

(a)

: -21.7
: -21.6
: -21.0
: -19.7
: -
: -18.3
5.5

(b)
Figure 3.8: Result of return loss simulation on variations inset cut length for conventional
rectangular patch antenna: (a) 4.7 GHz antenna (b) 2.4 GHz antenna

41

Table 3.4 summarized the physical parameters that change the antenna
performance. By increasing or decreasing the inset cut, patch width or length the design
antenna is able to achieve the desired frequency and performance.
The correct length of inset feed will have the lowest reflection coefficient. Shorter
or longer inset cut will increase the reflection coefficient.
Reducing the antenna width will increase the antenna resonance frequency.
Increasing the length will reduce the resonance frequency. Excessive reduction or
increment will increase reflection coefficient.
Reducing the length will increase the antenna resonance frequency. Increasing the
length will reduce the resonance frequency. Antenna resonates mainly due to antenna
length which is half wave length of the operational frequency. Thus the length of patch
length affects the resonance frequency more than the patch width.

Table 3.4 Antenna Design Optimization
Design Parameters Comment
Inset cut length Need specific length. Longer or shorter
increase the reflection coefficient.

Antenna Width Reduce width = increase resonance
frequency.
Increase width = reduce the resonance
frequency.
Antenna Length Reduce length = increase the antenna
resonance frequency.
Increase length = reduce the resonance
frequency.

42

3.5.2 Designing rectangular patch antenna with DGS

The metamaterial antennas were designed using two DGS substrates that were
discussed before. The two rings structure used to implement metamaterial antenna that
operates at 4.75 GHz and the slip rings at 2.45 GHz. Figure 3.9 shows diagram of DGS
antenna.

Rectangular patch

RO3003 Substrate

Defected ground structure

Figure 3.9: 3D view structure DGS antenna.

Then, the patch size including the length, width was tuned so that the antenna operates at
the desired frequency. Moreover, the inset cut was also tuned to obtain the best matching
impedance.

3.6 FABRICATION PROCESS

The fabrication process involves 5 steps which are:

 Generate mask on transparency film
 Photo exposure process
 Etching in developer solution
 Etching in Ferric Chloride
 Soldering the probe.

Each of the listed process will be explained further below.

43

3.6.1 Generate mask on transparency film

First step is to transfer the antennas top and bottom layer structure into .DXF format
that is compatible with Auto-Computer Added Drawing (AutoCAD) and print it onto the
transparency film.

3.6.2 Photo exposure process

Second step is the Ultraviolet exposure process. It is done to transfer the image of the
circuit pattern with a film in a UV exposure machine onto to the photo resist laminated
board.

3.6.3 Etching in developer solution

The third step is to ensure the pattern will be fully developed, during the developing
process. The photo resist developer solution was used to wash away the exposed resist.
Then the solution was removed by spray wash. In this process, water was added with
Sodium Hydroxide (NaOH).

3.6.4 Etching in Ferric Chloride

Fourth step is the etching in ferric chloride. It will remove the unwanted copper area
and this process was followed by the removal of the solution by water.

3.6.5 Soldering the probe

The second process in the fabrication is the soldering process. This process only
can be done after the etching process has finish. In this process, a port and a solder will
be used. The soldering process actually is to connect the port to the antenna. After that,
the feeder will be soldered together with the antenna. 1mm SMA connector was soldered
to the microstrip antenna.

44

3.7 MEASUREMENTS

The measurement is done to investigate the performance of the fabricated antenna.
The return loss and the radiation pattern are analyzed and investigated. From the return
loss, we also can observe the transmission loss and bandwidth. Then, the measurement
will be compared to the simulation. The return loss was measured using Vector Network
Analyzer (VNA). The equipment was calibrated before taking any measurements. One-
port scattering parameter for both conventional and DGS antenna were measured. Then,
all the measurement data was stored.

The radiation patterns were measured in anechoic chamber room. Anechoic chamber
are guarded with absorbers located around the walls. The absorbers are used to absorb the
unwanted signal to reduce the reflected signal. It can increase the efficiency of the
measurement process. The equipments were divided into two sections. The first section
consist of the horn antenna and VNA, the second section consist of a spectrum analyzer,
a positioner and a rotator.

The first section is the transmitter part and the second section is the receiving part.
The antenna under test (AUT) will be placed at the rotator. The positioner will control the
rotator to rotate the tested antenna from 0 degrees to 360 degrees. The received signal of
the antenna will be measured by the spectrum analyzer at different angle in the term of
signal to noise ratio. This measurement is done to see the radiation pattern of the antenna.
To use these device, the experience user is needed to guide inexperience user to use these
device because it can make hazardous effect by higher frequency and quite expensive.

Figure 3.10 shows all the connection of the devices for anechoic chamber. The VNA
is connected to reference antenna (horn antenna). The rotator are connected to the
antenna under test (AUT). From that the measurement value decision can be made
whether the value is same from the expected requirement.

45

Antenna
under test
(AUT)
Horn antenna

Rotator

VNA Spectrum
analyzer

Figure 3.10: Anechoic chamber

46

CHAPTER 4

RESULT AND DISCUSSION

4.1 INTRODUCTION

In Chapter 3, metamaterial substrate and microstrip patch antenna had been
designed. The method and procedures in designing metamaterial structure and microstrip
patch antenna had been elaborated extensively in chapter 3. This chapter presents the
results and findings of both 4.75 GHz and 2.45 GHz antennas.

4.2 4.75 GHZ ANTENNAS
This part presents the simulation and measurement of 4.75 GHz antenna. Both
conventional and DGS antenna had been build. This part also consists of comparison
between conventional and DGS antenna performance in term of return loss, bandwidth
and radiation pattern.

4.2.1 Antenna parameters

The simulation result shows that metamaterial antenna can reduce the of rectangular
patch antenna. The antenna with circular rings DGS can reduce the size up to 34.3% as
shown in figure 4.1. This antenna operates at 4.75 GHz.

47

25.6

21.3
19.0
2.9
21.3 3.9 17.9
17.5
13.6
7.1
6.1

20.0
(a) (b)

Figure 4.1: Top view dimension of the of 4.7 GHz antennas (a) conventional (b) metamaterial antenna
with circular rings DGS.

4.2.2 Simulation: Return loss comparison between conventional and DGS

Figure 4.2: Comparison of return loss simulation data of conventional antenna and DGS
metamaterial antenna.

48

Figure 4.2 describes the return loss 𝑆11 response of metamaterial microstrip
antenna compared to return loss 𝑆11 response of conventional antenna. Noticed that the
rectangular patch antenna with DGS gives better return loss which is -35.6dB compared
to the simulated result of patch antenna without DGS which is just -25.7dB. The
operating frequency of the DGS antenna is between 4.65 GHz to 4.74 GHz. The
bandwidth of DGS antenna is 96 MHz which is greater than conventional antenna which
is just 50.8 MHz. Notice that DGS antenna increase the bandwidth by 89%.

4.2.3 Simulation: Radiation pattern of 4.75 GHz antennas

Figure 4.3 (a) and 4.3 (b) shows the 3D radiation pattern for the conventional antenna and
DGS metamaterial antenna at 4.7 GHz. The simulated gain for the DGS metamaterial
antenna is 3.5 dBi as for the conventional antenna the simulated gain is 4.41 dBi. This
shows that DGS antenna have considerable gain as compared to conventional one.
Figure 4.3 (c) and (d) show the polar plot for the conventional antenna and DGS
metamaterial antenna. The beam main lobe direction for conventional antenna is 4 degree
with beam width 102.5 degree. The beam main lobe direction for DGS antenna is 5
degree with beam width 95.4 degree.

(a) (b)

49

Figure 4.3 : 4.7 GHz radiation pattern (a) 3D conventional antenna (b) 3D Antenna with DGS (c)
Polar plot Conventional Antenna (d) Polar plot of DGS Antenna.

Table 4.1 describes all data obtained from simulation in CST Microwave Studio. The
directivity of DGS metamaterial antenna is 4.28 dBi slightly less than directivity of
conventional antenna that has 6.3 dBi of directivity change is due to the introduction of
DGS. Based on the data analyzed, it can be concluded that the performance of both the
antenna through simulation more less the same.

Table 4.1: Comparison Between 4.7GHz Conventional and DGS Antenna

Parameter 4.7GHz 4.7GHz
conventional DGS
antenna antenna
Return loss,dB -25.7 -35.6
Bandwidth, 50.7 97.2
MHz
Gain, dBi 4.41 3.5
Directivity, 6.3 4.28
dBi
Size, mm2 545.28 358
Total 64.4 83.6
Efficiency, %

50

4.2.4 Comparison between simulation and measurement

Figure 4.4 shows the size comparison between conventional, DGS antenna and 50
cent Malaysian coin. These antennas operate at 4.7 GHz. These antennas are connected
with SMA connector. The smaller antenna is the 4.7 GHz metamaterial antenna. The
metamaterial antenna has a DGS structure at the ground.

(a) (b)
Figure 4.4:Size comparison of fabricated 4.7 GHz antenna(a) front view (b) bottom view

The simulation results indicate that the metamaterial structure has an effect to the
conventional patch antenna by shifting the frequency regions to different value as well as
affecting the S11 parameters. As far as current simulations performed, it is shown that
the metamaterial structure will be able to reduce the size of the patch antenna.

Figure 4.5 shows comparison between measurement and simulation result of 4.7
GHz conventional antenna. The measurement shows negative 15.5 dB return loss which
is higher compared to the simulation with negative 25.7 dB. The fabricated antenna
operates at 4.7 GHz which is in good agreement with simulation.

Figure 4.6 shows comparison between measurement and simulation result of 4.7
GHz DGS antenna. The measurement result shows negative 15.6 dB return loss which is
higher compared to the simulation with negative 25.7 dB. The fabricated antenna
operates at 4.7 GHz which is in good agreement with simulation. It can be concluded that
the build antenna has a lower performance compared to simulation.

51

Figure 4.5: Graph simulation and measurement of 4.7 GHz conventional antenna versus
frequency.

Figure 4.6: Graph simulation and measurement of 4.7 GHz DGS antenna versus frequency.

52

4.2.5 Comparison of conventional and DGS antenna

Figure 4.7 shows the comparison of 4.7 GHz DGS and conventional antenna that
I have fabricated and measured. Figure 4.2 describes the return loss 𝑆11 response of
metamaterial microstrip antenna compared to return loss 𝑆11 response of conventional
antenna. Notice that the rectangular patch antenna with DGS having comparable return
loss which is -15.6dB.

Figure 4.7: Graph comparing between 4.7 GHz conventional and DGS antennas.

It can be concluded from the S11 comparison graphs that the resonant frequency
has shifted in the magnitude from the designed frequency for most of the designs. The
root cause of the shift is could be due to the patch and substrate dimension that varies in
fabrication process.

53

4.2.6 Radiation pattern measurements

The antenna radiation patter was measured inside the anechoic chamber. The setup
of the experiment in measuring the radiation pattern is described chapter 3. Figure 4.8
shows the measured radiation pattern, of the DGS metamaterial antenna and conventional
antenna resonating at 4.7GHz. For the conventional antenna radiation pattern the
maximum power received is –45.18 dBm as for the DGS metamaterial antenna decrease
to -44.16 dBm .

0
350 360 2 10 20
340 30
330 0 40
320 -2 50
310 -4 60
300 -6 70
-8
290 80
-10
280 90 dBm conventional
-12
270 100
260 110
250 120
240 130
230 140
220 150
210 160
200 190 180 170

(a)

54

0
350 360 2 10 20
340 30
330 0 40
320 -2 50
310 -4 60
300 -6 70
-8
290 80
-10
280 90 dBm DGS
-12
270 100
260 110
250 120
240 130
230 140
220 150
210 160
200 190 180 170

(b)

Figure 4.8: Measurement radiation pattern (a) conventional antenna.(b) Antenna with DGS

4.3 2.4 GHZ ANTENNAS

This part presents the simulation and measurement of 2.4 GHz antenna. Both
conventional and DGS antenna had been build. This part also consists of comparison
between conventional and DGS antenna performance in term of return loss, bandwidth
and radiation pattern.
4.3.1 Antenna parameters

The simulation result shows that metamaterial antenna can reduce the of rectangular
patch antenna. The antenna with slip rings DGS can reduce the size up to 80% as shown
in figure 4.9. This antenna operates at 2.4 GHz.

55

47.2

43.5

39.0 16.0
4.3
35.0 17.5 14.8
11.0

20.0
(a) (b)
Figure 4.9: Top view dimension (mm) of the of 2.4 GHz antennas (a) conventional (b)
metamaterial antenna with slips rings DGS

4.3.2 Simulation: return loss comparison between conventional and DGS

Figure 4.10: Comparison of return loss simulation data of conventional antenna and DGS
metamaterial antenna

Figure 4.10 describes the return loss 𝑆11 response of metamaterial microstrip
antenna compared to return loss 𝑆11 response of conventional antenna. Noticed that the
DGS antenna return loss is -24 dB compared to the simulated result of patch antenna
without DGS which is just -22 dB. The operating frequency of the DGS antenna is

56

between 2.452 GHz to 2.468 GHz. The bandwidth of DGS antenna is 15 MHz which is
smaller than conventional antenna which is 21.6 MHz Notice that 2.4GHz DGS antenna
have to compensate bandwidth by 30.56%.

4.3.3 Simulation: Radiation pattern of 2.4 GHz antenna

Figure 4.11 (a) and 4.11 (b) show the 3D radiation pattern for the conventional
antenna and DGS metamaterial antenna at 2.4 GHz. The simulated gain for the DGS
metamaterial antenna is 4.48 dBi as for the conventional antenna the simulated
directivity is 5.96 dBi .
Figure 4.11 (c) and (d) show the polar plot for the conventional antenna and DGS
metamaterial antenna. The beam main lobe direction for conventional antenna is 2 degree
with beam width 100.2 degree. The beam main lobe direction for DGS antenna is 5
degree with beam width 102.3 degree.

(a) (b)

57

(c) (d)
Figure 4.11: 2.4 GHz antenna radiation pattern (a) 3D Conventional antenna (b) Antenna with
DGS (c) Polar plot Conventional Antenna (d) Polar plot of DGS Antenna.

Table 4.2 describes all data obtained from simulation in CST Microwave Studio. The
directivity of DGS metamaterial antenna is 4.48 dBi slightly less than directivity of
conventional antenna that has 5.96 dBi of directivity due to the introduction of DGS.
Based on the data analyzed, it can be concluded that the performance of both the antenna
through simulation more less the same.

Table 4.2: Comparison Between 2.4GHz Conventional and DGS Antenna

Parameter 2.4GHz 2.4GHz
conventional DGS
antenna antenna
Return loss -22.2 -24.1
Bandwidth, MHz 22.7 15.2
Gain, dBi 1.88 -10.9
Directivity, dBi 5.96 4.48
Size, mm2 1840.8 350
Total efficiency,% 38.8 2.9

58

4.2.4 Comparison between simulation and measurement

Figure 4.12 shows the size comparison between conventional, DGS antenna and 50
cent Malaysian coin. The smaller antenna is the metamaterial antenna. These antennas
operate at 2.4 GHz. These antennas are connected with SMA connector.

Figure 4.12: Size comparison of fabricated 2.4 GHz antenna

The simulation results indicate that the metamaterial structure has an effect to the
conventional patch antenna by shifting the frequency regions to different value as well as
affecting the S11 parameters. As far as current simulations performed, it is shown that
the metamaterial structure will be able to reduce the size of the patch antenna.

Figure 4.13 shows comparison between measurement and simulation result of
2.4 GHz conventional antenna. The measurement shows negative 15.0 dB return loss
which is higher compared to the simulation with negative 22.2 dB. The fabricated
antenna operates at 2.6 GHz. Noticed that the fabricated antenna operates at higher
frequency.

Figure 4.14 shows comparison between measurement and simulation result of
2.4 GHz DGS antenna. The measurement result shows negative 16.2 dB return loss
which is higher compared to the simulation with negative 24.4 dB. The fabricated
antenna operates at 2.4 GHz which is in good agreement with simulation. It can be
concluded that the build antenna has a lower performance compared to simulation.

59

Figure 4.13: Graph simulation and measurement of 2.4 GHz conventional antenna versus
frequency.

Figure 4.14: Graph simulation and measurement of 2.4 GHz DGS antenna versus frequency.

60

4.2.5 Comparison of conventional and DGS antenna

Figure 4.15 shows the comparison of 2.4 GHz DGS and conventional antenna that
I have fabricated and measured. Figure 4.15 describes the return loss 𝑆11 response of
metamaterial microstrip antenna compared to return loss 𝑆11 response of conventional
antenna. Notice that the rectangular patch antenna with DGS having comparable return
loss which is -15.6dB. The DGS antenna operates at lower frequency compared to
conventional one.

Figure 4.15: Graph comparing between 2.4 GHz conventional and DGS antenna.

4.2.6 Radiation pattern measurements

The antenna radiation patter was measured inside the anechoic chamber. The setup
of the experiment in measuring the radiation pattern is described chapter 3
Figure 4.16 shows the measured radiation pattern, of the DGS metamaterial
antenna and conventional antenna resonating at 4.7GHz. For the conventional antenna
radiation pattern the power received is –35.38 dBm as for the DGS metamaterial antenna
decrease to -45.43 dBm .

61

0
350 360 2 10 20
340 30
330 0 40
320 -2 50
310 -4 60
300 -6 70
-8
290 80
-10
280 90 dBm conventional
-12
270 100
260 110
250 120
240 130
230 140
220 150
210 160
200 190 180 170

(a)

0
350 360 0 10 20
340 -2 30
330 -4 40
320 -6 50
310 -8 60
-10
300 70
-12
290 -14 80
-16
280 90 dBm DGS
-18
270 100
260 110
250 120
240 130
230 140
220 150
210 160
200 190 180 170

(b)

Figure 4.16: Measurement of radiation pattern (a) 2.4 GHz conventional antenna (b) 2.4GHz
antenna with DGS.

62

2.4 CONCLUSION
Based on the data, the dimension of a microstrip patch antenna operating at 4.7
GHz had been successfully reduced up to 34 % of the original dimension while having
larger bandwidth. Moreover, 2.4 GHz metamaterial antenna is able to reduce the size up
to 80% but having poor performance. I noticed that the reflection coefficient reduced and
shift in all measurements. This is due to the poor matching which related to the
introduction of SMA connector, soldering and accuracy of etching process. However,
overall the measurements values are comparable to the simulation result.

63

CHAPTER 5

CONCLUSION AND FUTURE IMPROVEMENTS

5.1 CONCLUSIONS

The goals of this project is to design two miniaturized rectangular patch antenna that
operate at 4.75 GHz and 2.4GHz frequencies using metamaterial substrate. The antennas
fabricated expected of having comparable or better performance to the conventional one.
The conventional microstrip antenna was designed as a reference with a microstrip line as
a feed.

The S11 (input return loss) plot for microstrip antennas have a magnitude of much less
that –10dB at the operating frequency which means that the matching impedance is
achieve.

It is proved that the microstrip antenna with metamaterial substrate can improves the size
of the antenna. Moreover, this project proves that DGS can be implemented to alter the
electrical properties.

As an overall conclusion, all the planned works and the objectives of this project have
been successfully implemented and achieved, even though the performance of the

64

antenna designed do not shows a big different after integrated with DGS structures. But,
the improvement of the antenna size and bandwidth still can be noticed.

5.2 SUGGESTION FOR FUTURE WORKS

In term of DGS structure, the design can be further improve in terms of basic parameters
such as type of substrate, dielectric constant, the thickness of the substrate. From this
project , we can design the DGS structure for different frequency of operation. Moreover,
investigation into designing the microstrip antenna with different patch shapes and sizes
are vital. In term of DGS structure, the design can be further improve

The DGS structure also can be applied in the array antenna. This array antenna can be
further classified according to the different thickness of the substrate and the various
value of dielectric constant.

In addition the slip rings structure DGS should be further study for filter application. In
the future different structure of DGS should be design in order to improve the
performance of the microwave devices.

65

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66

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67

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68

APPENDICES

 Roogers 3000 datasheet Series High Frequency Laminated
 GPR antenna Bandwidth

69

Rectangular patch Antenna

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