1

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, compatibility

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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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.

E = electrical field vector

Linear Elliptical Circular

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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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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].

First null beamwidth

Half power beamwidth

(HPBW)

Minor lobes

Major lobe

Side lobe

Back lobe

Minor lobes

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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:

𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡𝑕 = 𝑓2−𝑓1

𝑓2+𝑓1𝑥 100% (1)

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, 휀𝑟 . 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):

휀𝑒𝑓𝑓 = 휀𝑟+1

2+

휀𝑟−1

2(1 +

12𝑕

𝑊)−1

2 (2)

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:

𝑍𝑜 =

60

휀𝑒𝑓𝑓ln

8𝑕

𝑤+

𝑤

4𝑕 𝑓𝑜𝑟

𝑤

𝑕≤ 1

120 𝜋

휀𝑒𝑓𝑓[𝑤

𝑕+ 1.393 + 0.667 ln

𝑤

𝑕+ 1.444 ]

𝑓𝑜𝑟

𝑤

𝑕≥ 1

(3)

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:

𝑊 =𝑐

2𝑓𝑟 휀𝑟+1

2

−1

2 (4)

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].

L = c

2fr εeff− 2∆l (5)

Where L is the patch antenna length and c is speed of EM wave in vacuum which equal to

3x108m/s.

∆𝑙 = 0.412𝑕 휀𝑒𝑓𝑓 +0.3

휀𝑒𝑓𝑓 −0.258

𝑤

𝑕+0.264𝑤

𝑕+0.8

(6)

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

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𝑊𝑠 = 𝑊 + 6𝑕 (7)

𝐿𝑠 = 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.

Figure 2.9: Microstrip line feed [5].

Patch

Substrate

Ground plane

Microstrip feed

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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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(a)

(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.

Substrate

Patch

Ground plane Coaxial

connector

Substrate

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2.3.5.3 Aperture Coupled Feed

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.

Aperture slot Patch

Microstrip line

Substrate 1

Substrate 2 Ground plane

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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 20th

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 = ± 𝜇휀 (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

Patch

Substrate 1

Substrate 2

Microstrip line

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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.

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.

Electric field

Propagation direction

Electric field

Magnetic field

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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.

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

n2>n1 n1

S

O

U

R

C

E

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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.

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 = 𝑛2𝑠𝑖𝑛𝜃2 (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

S

O

U

R

C

E n2>-n1 n1

25

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.

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.

Positive-index material Negative-index material

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

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

Vacuum Conventional

material

Conventional

material

Vacuum

27

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.

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.

(a) (b)

(c) (d)

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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

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,

𝜒 =𝑠11

2 −𝑠212 +1

2𝑠11 (11)

(a)

(b)

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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.

Τ =S11 +S21 −Γ

1−(S11 +S21 )Γ (12)

ln 1

𝑇 = ln

1

𝑇 + 𝑗(𝜃𝑇 + 2𝜋𝑛) (13)

Where

𝑛 =𝐿

𝜆𝑔 (14)

Where

𝑛 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑜𝑜𝑡

𝐿 = 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑙𝑒𝑛𝑔𝑡𝑕 𝑖𝑛 𝑐𝑚

𝜆𝑔 = 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡𝑕 𝑖𝑛 𝑐𝑚

𝜃𝑇 = 𝑝𝑕𝑎𝑠𝑒 𝑜𝑓 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑖𝑛 𝑟𝑎𝑑𝑖𝑎𝑛

we define:

1

Λ2 =- [

1

2𝜋𝐿ln(

1

Τ)]2 (15)

Then we can solve for the permeability using

𝜇𝑟 =1+Γ

(1−Γ)Λ 1

𝜆02−

1

𝜆𝑐2

(16)

Where 𝜆0 is the free space wavelength and 𝜆𝑐 is the cutoff wavelength.

The permittivity is given by

휀𝑟 =𝜆0

2

𝜇𝑟[

1

𝜆𝑐2 − [

1

2𝜋𝐿ln

1

Τ ]2] (17)

30

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,

dielectric or metalodielectric bodies with a lattice period 𝑝 =𝑛𝜆𝑔

2, λ being the guide

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].

31

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].

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

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

(k) (l)

(t)

(n) (o)

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

32

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.

33

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.

Figure 3.1: Flow chart of antenna design.

End

Data analysis

Measurement

Antenna fabricate

Optimize antennas design

Metamaterial structure used

CST simulation

Design possible metamaterial

structure

Start

NO

34

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.

35

(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].

Figure 3.3.Transmission line method [17].

50 Ω line

DGS structure

DGS

Copper

36

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.

Figure 3.4: Relative permittivity, εr and permeability, µr value versus frequencies for substrate

with circular rings DGS

4.75 GHz

εr= -154

µr= -0.000818

37

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.

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.

2.45 GHz

εr= -132

µr= -0.000461

38

(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.

17.9

20.0

17.5

20.0

1.29

39

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

(a)

3.9 21.3

25.6

21.3

6.1

17.9

40

(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.

47.2

43.5

11.0

39.0 4.3 35.0

41

(a)

(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

: -28.0

: -16.1

: -5.1

: -5.5

: -0.8

: -5.5 : -17.0

: -5.5 : -23.4

: -5.5

: -19.7

: -18.3

: -21.7

: -21.0

: -

5.5

: -21.6

42

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.

43

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.

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.

Rectangular patch

RO3003 Substrate

Defected ground structure

44

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.

45

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.

46

Figure 3.10: Anechoic chamber

VNA Spectrum

analyzer

Horn antenna

Antenna

under test

(AUT)

Rotator

47

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.

48

(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.

3.9 21.3

21.3

6.1

17.9

25.6

20.0

2.9

19.0

17.5 13.6

7.1

49

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)

50

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 conventional antenna

4.7GHz DGS antenna

Return loss,dB -25.7 -35.6

Bandwidth, MHz

50.7 97.2

Gain, dBi 4.41 3.5

Directivity, dBi

6.3 4.28

Size, mm2 545.28 358

Total Efficiency, %

64.4 83.6

51

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.

52

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.

53

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.

54

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 .

(a)

-12

-10

-8

-6

-4

-2

0

20

10 2030

40

50

60

70

80

90

100

110

120

130

140150

160170180190200

210220

230

240

250

260

270

280

290

300

310

320

330340

350 360

dBm conventional

55

(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.

-12

-10

-8

-6

-4

-2

0

20

10 2030

4050

60

70

80

90

100

110

120

130

140150

160170180190200

210220

230

240

250

260

270

280

290

300

310

320

330340

350 360

dBm DGS

56

(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

43.5

11.0

39.0 4.3 35.0

47.2

16.0

14.8 17.5

20.0

57

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)

58

(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 conventional antenna

2.4GHz DGS 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

59

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.

60

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.

61

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 .

62

(a)

(b)

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

antenna with DGS.

-12

-10

-8

-6

-4

-2

0

20

10 2030

40

50

60

70

80

90

100

110

120

130

140150

160170180190200

210220

230

240

250

260

270

280

290

300

310

320

330340

350 360

dBm conventional

-18-16-14-12-10

-8-6-4-20

010 20

3040

50

60

70

80

90

100

110

120

130

140150

160170180190200

210220

230

240

250

260

270

280

290

300

310

320

330340

350 360

dBm DGS

63

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.

64

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

65

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.

66

REFERENCE

[1] Pozar, D.M. Microstrip antennas. Proceedings of the IEEE. Volume 80, Issue 1,

Jan. 1992 Page(s):79 – 91.

[2] M.I.A. Khaliah, “ Electromagnetic Band Gap (EBG) for Microstrip Antenna

Design”, Master of Engineering (Electrical –Electronic Telecommunication),

Faculty of Electrical Engineering, Universiti Teknologi Malaysia 2007.

[3] Ahmed A. Kishk, “Fundamentals of Antennas”, Center of Electromagnetic

System Research (CEDAR), Department of Electrical Engineering, University of

Mississippi.

[4] R, M. Kamal, “ Electromagnetic Band Gap (EBG) Structure in Microwave Device

Design”, Jabatan Kejuruteraan Radio, Fakulti Kejuruteraan Elektrik, Universiti

Teknologi Malaysia 2008.

[5] C.V.V. Reddy, “Design of Linear Polarized Rectanglar Microstrip Patch Antenna

Using IEED/PSO”, Department of Electronics and Communication Engineering,

National Institute of Technology Rourkela 2009.

[6] H, Suria, “ Antenna with Metamaterial Design”,Faculty of Electrical Engineering,

Universiti Teknologi Malaysia 2007.

[7] J. Q. Howell, “Microstrip Antennas,” in Dig. Int. Symp. Antennas Propogat.

Soc., Williamsburg, VA, Dec. 1972, pp. 177-180

[8] Nashaat, D.; Elsadek, H.A.; Abdallah, E.; Elhenawy, H.; Iskander, M.F.; ,

"Multiband and miniaturized inset feed microstrip patch antenna using multiple

spiral-shaped defect ground structure (DGS)," Antennas and Propagation Society

International Symposium, 2009. APSURSI '09. IEEE , vol., no., pp.1-4, 1-5 June

2009

[9] Debatosh Guha, “Microstrip and printed antennas, new trends technique and

application,” John Wiley & Sons, New York, 2010

[10] Matin, M.A. “A Design Rule for Inset-fed Rectangular Microstrip Patch

Antenna,”.

67

[11] David M. Pozar, "Input impedance and mutual coupling of rectangular microstrip

antennas," IEEE Transactions on Antennas & Propagation, Vol. AP-30,

November 1982, pp. 1191-1196.

[12] IEEE standard definitions of terms for antennas. IEEE Std 145-1993 21 June 1993

[13] Balanis, C.A. Antenna Theory: Analysis and Design. 2nd Ed. New York: John

Wiley and Sons. 1997.

[14] J. Q. Howell, “Microstrip Antennas,” in Dig. Int. Symp. Antennas Propogat.

Soc., Williamsburg, VA, Dec. 1972, pp. 177-180

[15] C. A. Balanis, “Antenna Theory, Analysis and Design,” John Wiley & Sons, New

York, 2008

[16] James, J. R., and P. S. Hall (Eds), Handbook of Microstrip Antennas, Peter

Pereginus, London, UK, 1989.

[17] S K Behera, “Novel Tuned Rectangular Patch Antenna As a Load for Phase

Power Combining” Ph.D Thesis, Jadavpur University, Kolkata.

[18] Microstrip and printed antennas, new trends technique and application

[19] Zijie Lu, “Two-Port Transmission Line Technique for Dielectric Property

Characterization of PolymerElectrolyte Membranes,” J. Phys. Chem. B , 2009

[20] J. Garcia, J. Bonache, I. Gil, F. Martin, M. Castillo, and J. Martel, “Miniaturized

microstrip and CPW filters using coupled metamaterial resonators,” IEEE Trans.

Microwave Theory Tech., vol. 54, no. 6, pp. 2628–2635, June 2006.

[21] H. S. Rajeshwar Lal Dua, Neha Gambhir, "2.45 GHz Microstrip Patch Antenna

with Defected Ground Structure for Bluetooth," International Journal of Soft

Computing and Wang, Weijen, “ Directive antenna using metamaterial

substrates,” Open Educational Resources (OER).

[22] K.A. Carver and J.A. Mink, "Microstrip antenna technology," IEEE Transactions

on Antennas & Propagation, Vol. 29, January 1981, pp. 2-24.

[23] N. F. Salam, "Metamaterial Antenna with Dual Concentric Square Defected

Ground " Bachelor of Engineering (Hons). in Electrical, Fakulti Kejuruteraan

Elektrik, Universiti Teknologi MARA 2012.

68

[24] H. Pues and A. Van De Capelle, "Accurate transmission line model for the

rectangular microstrip antenna," IEEE Proceedings on Microwaves, Optics &

Antennas, Vol. 134, 1984, pp. 334−340.

[25] David M. Pozar, "Input impedance and mutual coupling of rectangular microstrip

antennas," IEEE Transactions on Antennas & Propagation, Vol. AP-30,

November 1982, pp. 1191-1196.

[26] Lorena I. Basilio, Michael A.Khayat, Jeffery Williams, and Stuart A. Long, "The

Dependence of the Input Impedance on Feed Position of Probe and Microstrip

Line − Fed patch Antennas," IEEE Transactions on Antennas & Propagation,

Vol. 49, January 2001, pp. 45-47.

[27] Rahmat-Samii, Y.; , "Metamaterials in Antenna Applications: Classifications,

Designs and Applications," Antenna Technology Small Antennas and Novel

Metamaterials, 2006 IEEE International Workshop on , vol., no., pp. 1- 4, March

6-8, 2006

69

APPENDICES

Roogers 3000 datasheet Series High Frequency Laminated

GPR antenna Bandwidth