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Title: -“Enhanced Antenna with reduced VSWR”
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ABSTRACT
We present an old method%%%%quotes detected%%%% of antenna design to solve for the
current distribution in a Different -shaped antenna excited by an electric field with arbitrary
polarization. The scattered far-field amplitude, phase, and polarization of the antennas are
extracted. The antenna design technique presented here is an efficient method for probing
the large design parameter space of such antennas, which have been proposed as basic
building blocks for the design of ultrathin and %%%%quotes detected%%%% TBFS scale
surfaces. Our calculation is based on and is validated by comparison to the results of design -
difference simulations. The computation time is approximately five orders of magnitude less
than for TBFS scale simulations. This speed-up relies mainly on the use of the thin-wire
approximation, whose domain of validity is discussed. This method can be generalized to
more complex geometries such as zigzag antennas structure.

This work presents the design of a CNT based cylindrical Dielectric Resonator Antenna (DRA)
coupled to narrow slot aperture that is fed by coaxial line. The fundamental TE11 mode and
higher-order TE13%%%%quotes detected%%%% mode are excited with their resonant
frequencies respectively. These frequencies can be controlled by changing the DRA
dimensions. A dielectric resonator with high permittivity is used to miniaturize the global
structure. The proposed antenna is designed to have dual band operation suitable for both
DCS (1710 - 1880 MHz) %%%%quotes detected%%%% and WLAN (2400 - 2484 MHz)
applications. The return loss, radiation pattern and gain of the proposed antenna are
evaluated. Reasonable agreement between simulation and experimental results is obtained.
CHAPTER 1
INTRODUCTION
1.1 Introduction
Wireless Communications are%%%%quotes detected%%%% becoming as a part of day-to-
day life of human beings. So, to achieve efficient and affordable wireless communications,
compact and efficient radiators required. Indeed, one of the efficient radiators is dielectric
resonator antenna (DRA). The dielectric resonator antenna efficiently radiates at microwave
frequencies. DRA is economically affordable and it is having desirable features like - easy
%%%%quotes detected%%%% design, simple fabrication methods and gives flexibility in
design and to analyse the results in order to achieve required resonant frequencies
depending upon our coverage requirements. In general DRA having high-radiation efficiency,
bandwidth and polarization flexibility make them by far superior and better replacement to
conventional microstrip patch antennas (MPA). DRAs are intrinsically immune to those
surface wave power leakage and conductor loss problems, which plagues the MPA and
reduces their efficiency. DRA consists of high dielectric constant materials, high quality
factors and mounted on a grounded dielectric substrate of lower permittivity [1]. DRA is
fabricated from low-loss and high relative dielectric constant material of various shapes
whose resonant frequencies are functions of the shape, dimensions of the shape and
permittivity of the material. The DRAs have properties such as very less phase noise, small
size, stability in frequency and temperature, ease of integration with existing technologies
and other hybrid MIC circuitries, flexible construction and the ability to withstand harsh
environments. The DRA has some interesting characteristics, like small size, ease of
fabrication, high radiation efficiency, increased bandwidth and low production cost. DRAs are
very promising for applications in wireless communications like Wireless Local Area Network
sand millimetre wave applications.
The resonating frequencies of a DRA are nothing but the function of size, shape and dielectric
constants only. Due to this flexibility in DRAs, they can be designed with different shapes as
per coverage requirements depending upon the applications in the wireless communication
industries. For many years, the dielectric resonator %%%%quotes detected%%%% (DR) has
primarily been used in microwave circuits, such as oscillators and filters, where the DR is
normally made of high permittivity material, with dielectric constant εr> 20. The unloaded Q-
factor is usually between 50 and 500 but can be as high as 10,000. Because of these
traditional applications, the DR was usually treated as an energy storage device rather than
as a radiator [2]. DRAs can also be excited with different feeding methods, such as microstrip
lines, dielectric image waveguide feeding, aperture coupling, probes, slots, and co-planar
lines. The DRAs are good replacement for the Microstrip antenna, because the DRA has a
much wider impedance bandwidth and higher power handling capability due to their many
advantageous and attractive features. As such, these include their flexibility in design, light
weight, compact size, the versatility in their shape and feeding mechanism, simple structures,
easy fabrication and wide impedance bandwidth.
Wireless communications are, by any measure, the promptest growing segment of the
communications industry in wireless field. As such, it has captured the attention of the media
and the imagination of the public, end users and consumers. Cellular systems have
experienced exponential growth over the last decade and there are currently around two
billion users %%%%quotes detected%%%% worldwide. Indeed, the cellular phones have
become a critical business tool and part of everyday life in most developed countries and are
rapidly supplanting antiquated wire line systems in many developing countries. In addition,
wireless local area networks (WLAN) currently supplement or replace wired networks in
many homes, businesses, and campuses. Many new applications, including wireless sensor
networks, automated highways and factories, smart homes and appliances, and remote
telemedicine, are emerging from research ideas to concrete systems. The explosive growth
of wireless systems coupled with the proliferation of laptop and palmtop computers indicate
a bright future for %%%%quotes detected%%%% wireless networks, both as stand-alone
systems and as part of the larger networking infrastructure. However, many technical
challenges remain in designing robust wireless networks that deliver the performance
necessary to support emerging applications [3].

1.2 Background

For the past decade, DRAs have been considered as an important antenna research area by
most antenna designers and researchers as they may offer several advantages compared to
many other antennas. Activity has been encouraged by the availability of ceramic materials
with very high relative permittivity and very low loss.
This section will review the work carried out by a number of people in this area of antenna
design.

In 1939, R. D. Richter [4] %%%%quotes detected%%%% showed that non - metalized

dielectric objects can function as electrical resonators which he called dielectric resonators.
In 1965, a technical report by H.Y. Yee [5] [6] discuss of and presented both theoretical and
experimental work on dielectric resonators, including resonant frequencies and modes of the
natural resonant frequency of a DR. Further experimental data on circuit implementations of
DR was discussed by Karp [7]. The work carried out by Yee represents the basic foundation of
the work established by other researchers in more recent times.

Significant theoretical work on the modal and resonant behaviour of a low-loss, very high
permittivity resonator was performed by Van BIadel [4, 5]. Further work on analytic models,
based on variations of the dielectric waveguide mode1 developed through the work of
Okaya, Barash and Marcatili [6], yielded more accurate determinations of DR circuit
properties [7-9]. With computers, the applications of numerical methods to electromagnetic
problems in the 1980's led to the solution of the resonant frequency and Q-factor for many
shapes of dielectric resonators, summarized in [10].
For the last 3 decades, DR|As have been one of the classes of novel antennas that have been
investigated and extensively reported on. Since the1970s, DRs have been used to achieve the
reduction of passive and active microwave components, such as oscillators and filters [10,
11]. The idea of using a DR as an antenna had not been widely accepted until the original
paper on the 1cylindrical DRA [12] was published in 1983. Long and McAllister extended the
dielectric resonator antenna investigation to rectangular [13] and hemispherical [14] DRAs.
Other shapes were also studied, including the triangular [15], spherical-cap [16], and
cylindrical-ring [17, 18] DRA.

DRAs have a limited bandwidth of operation due to their resonant nature, but this can be
improved by reducing the inherent Q-factor of the resonant antenna or by introducing
additional resonances. Emphasis has been on compact designs for portable wireless
applications, and on new DRA shapes or hybrid antennas for enhanced bandwidth
performance to meet the requirements for emerging broadband or ultra-wideband systems.
DRAs can achieve larger impedance bandwidths by adopting various enhancement
techniques. During1990s, emphasis was placed on applying analytical or numerical
techniques to determine the input impedance, the fields inside the resonator and the Q-
factor [19]. DRs made of low permittivity materials (8 ≤ εr ≤ 20) and placed in open
environments show small radiation Q-factors if excited in their lower-order modes as
demonstrated in [12]. The effects of an air gap in a lower effective dielectric constant were
reported in [20, 21], which entails both a decrease in shift of the resonance frequencies and
the Q-factor results, was reported. A design for a millimetre-wave high Q-factor parallel
feeding scheme for DRA arrays was modelled demonstrated in [22].

In 1989 Kishket. al. [23] were the first to investigate stack in two different DRAs on top of one
another. Since the two coupled DRAs exhibit two different resonant frequencies, even if they
have the same resonant frequency in isolation, the configuration has a dual-resonance
operation, thus broadening the antenna bandwidth. There are many models of developed
bandwidths using multiple DRAs in multiple stacked, coplanar embedded used of an air gap,
used of collinear parasitic elements, and used of a DR coating with impedance bandwidths
ranging from 25% to nearly 80% [23-33]. Similar bandwidth results can be achieved by
modifying the shape of the DRA or by adopting new feeding structures [30, 34-48]. [40]
Discusses measuring radiation efficiency of a DRA.
The efficiency was measured by directly placing the DR on a metal plane; the results report
that the conductor loss was small compared to the radiated power. This measurement
illustrates that dielectric resonators, fabricated with low loss dielectric materials, have high
radiation efficiency. The measured efficiency was found to be 98% for a hybrid operating
mode of the DR.
1.3 Thesis Motivation

Dielectric resonator antennas (DRA) possess some attractive characteristics which are making
them as very promising and affordable at microwave frequencies for wireless applications
especially for WLAN applications. Wireless Communications are becoming part in day-to-day
life of public. So, to achieve efficient wireless communications, efficient radiators required.
Definitely, one of the promising radiators is nothing but dielectric resonator antenna (DRA).
The dielectric resonator antenna efficiently radiates at millimetre-wave frequencies. DRA is
economically affordable. DRA has desirable features like - easy design, simple fabrication
methods and gives flexibility in design and to analyse the results in order to achieve required
resonant frequencies depending upon our coverage requirements. In this thesis we will find
the design of dielectric resonator antenna and analysing for optimizing the antenna
parameters through parametrical studies.

1.4 Scope of this Project

The scope of this project work is to design and fabrication of a Dielectric Resonator Antenna
which can be used for narrow band specific wireless applications according to the Federal
communication commission specifications. That is used the operating frequencies like
WiMAX, WLAN, Wi-Fi etc. and the antenna should be small in size and easy-to-manufacture
with available laboratory equipment. The return loss must be less than -10 dBi at wireless
frequencies, which means only 10% of power will be reflected back while 90% of power is
transmitted. Other aspects, such as beam width, side lobes, VSWR, Polarization, Impedance
measurements were not considered during the design stage. Special attention had paid in
design stage to get the double bands at a time by optimizing the feeding techniques and
structures of the dielectric resonators.
1.5 Thesis Outline
The following topics are the outline of this thesis,
Chapter 1: In this chapter the introduction of DRA is given along with wireless technology.
Also, the background of DRA is mentioned. The thesis objective, motivation, scope and
outline are described in this chapter.

Chapter 2: In this chapter the basics of antenna parameters which were used in antenna
measurements such as return loss, directivity, radiation pattern, bandwidth, VSWR, gain etc.
are presented.

Chapter 3: This chapter%%%%quotes detected%%%% presents the Literature survey carried

out on DRA.
Chapter 4: This chapter gives the basic theory behind DRA and basic shapes used in DRAs are
discussed. Some of the Bandwidth Enhancement techniques in DRAs are also discussed. The
advantage of stacked Dielectric method in Bandwidth Enhancement, when compared to
other methods is also presented This Chapter also presents the basic theory behind the
various feeding or excitation techniques for DRA including the basic geometries and their
characteristics. The advantages and disadvantages of different feeding methods also
discussed in brief.
Chapter 5: This chapter shows the design and result of DRA including all parametric studies of
the return loss, radiation patterns of proposed DRA, gain and directivity graphical views for
specific wireless applications.

Chapter 6: This chapter presents a conclusion and the scope of future work about DRAs for
specific wireless applications%%%%quotes detected%%%%.
CHAPTER 2
Microstrip Patch Antenna%%%%quotes detected%%%%
Microstrip antennas are attractive due to their light weight, conformability and low cost.
These antennas can be integrated with printed strip-line feed networks and active devices.
This is a relatively new area of antenna engineering. The radiation properties of micro strip
structures have been known since the mid 1950’s%%%%quotes detected%%%%.
The application of this type of antennas started in early 1970’s when conformal antennas
were required for missiles. Rectangular and circular micro strip resonant patches have been
used extensively in a variety of array configurations. A major contributing factor for recent
%%%%quotes detected%%%% advancement of microstrip antennas is the current revolution
in electronic circuit miniaturization brought about by developments in large scale integration.
As conventional antennas are often bulky and costly part of an electronic system, micro strip
antennas based on photolithographic Ztechnology are seen as an engineering breakthrough.
[5] %%%%quotes detected%%%%

2.1. Introduction
In its most fundamental form, a Microstrip Patch antenna consists of a radiating patch on
one side of a dielectric substrate which has a ground plane on the other side as shown in
Figure 2.1. The patch is generally made of conducting material such as copper or gold and
can take any possible shape. The radiating patch is usually photo etched on the dielectric
substrate.
In order to simplify analysis and performance prediction, the patch is generally square,
rectangular, circular, triangular, and elliptical or some other common shape as shown in
Figure 2.1. For a rectangular patch, the length L of the patch is usually 0.3333λo<L< 0.5λo,
where is the free-space wavelength. The patch is selected to be very thin such that t <<λo
(where t is the patch thickness). The height h of the dielectric substrate is usually
0.003λo<h<0.05λo %%%%quotes detected%%%% the dielectric constant of the substrate (ε)
typically in the range 2.2 ≤ εr≤ 12.
Microstrip patch antenna radiates primarily because of the fringing fields between the patch
edge and the ground plane. For good antenna performance, a thick dielectric substrate
having a low dielectric constant is desirable since this provides better efficiency, larger
bandwidth and better radiation. However, such a configuration leads to a larger antenna size.
In order to design a compact Microstrip patch antenna, substrates with higher dielectric
constants must be used which are less efficient and results in narrower bandwidth. Hence a
trade-off must be realized between the antenna dimensions and antenna performance.

2.2 Microstrip or Printed Dipole Antennas

Microstrip or printed dipoles differ geometrically from rectangular patch antenna in their
length to width ratio. The width of a dipole is typically less than 0. 05λo.The radiation
patterns of the dipole & patch are similar owing to similar to longitudinal current
distribution. However, radiation resistance, bandwidth, and cross- polar radiation differ
widely. Microstrip dipole 2.4(a) & (b) are attractive elements owing to their desirable
properties such as small size and linear polarization. The dipoles are well suited for higher
frequencies for which substrate can be electrically thick. Therefore, attain significant choice
of feed mechanism which is very important in microstrip%%%%quotes detected%%%%
dipoles & should be included in analysis. The symmetrical folded printed dipole, consists of a
folded dipole combined with another similar dipole (mirror image) to yield a symmetrical
structure. Alternatively, this structure can be considered to be rectangular patch with an h
shaped slot. The VSWR =2 B.W of this dipole can be 15%.

2.3 Printed Slot Antennas

Printed slot antennas comprise a slot in the ground plane of grounded substrate. The slot can
have virtually any shape. Theoretically, most of the microstrip patch shapes shown in fig 2.2
can be realized in the form of printed slot. However, only a few basic slot shapes have been
studied. These include a rectangular annular slot, rectangular ring slot, tapered slot. These
are shown in fig 2.4. Like microstrip antennas, the slot antennas can be feed either by
microstrip line or co-planar waveguide. Slot antennas are generally bidirectional radiator i.e.,
they radiate on both side of slot. Unidirectional radiation is obtained by using a reflector
plate on one side of the slot.
2.4 Microstrip Travelling Wave Antennas

A Microstrip travelling wave antennas (MTA) may consist of chain shaped periodic conductor
or a long microstrip line of sufficient width to support TE mode. Other end of travelling wave
antennas is terminated in matched resistive load to avoid the standing wave on the antenna.
Travelling wave microstrip%%%%quotes detected%%%% antennas can be designed so that
the main beam lies in any direction from broadside to end fire. Various configurations for
MTAs are shown in fig 2.5. The tapered slot antenna is a surface wave antenna. It radiates in
the end-fire direction. Travelling wave antennas such as rampart-line antenna, chain
antenna, square-loop antenna and crank-type antenna is used for circular polarization.
The characteristics of microstrip patch antennas, microstrip slot antennas, and printed dipole
antennas are compared in table 2.1
2.5 Advantages and Disadvantages

Microstrip %%%%quotes detected%%%% patch antennas are increasing in popularity for use
in wireless applications due to their low-profile structure. Therefore, they are extremely
compatible for embedded antennas in handheld wireless devices such as cellular phones,
pagers etc. The telemetry and communication antennas on missiles need to be thin and
conformal and are often in the form of Microstrip patch antennas. Another area where they
have been used successfully is in Satellite communication. Some of their principal advantages
discussed [9] are given below:

• Light weight and low volume.

• Low profile planar configuration which can be easily made conformal to host surface.
• Low fabrication cost, hence can be manufactured in large quantities.
• Supports both, linear as well as circular polarization.
• Can be easily integrated with microwave integrated circuits (MICs).
• Capable of dual and triple frequency operations.
• Mechanically robust when mounted on rigid surfaces.
Microstrip%%%%quotes detected%%%% patch antennas suffer from more drawbacks as
compared to conventional antennas. Some of their major disadvantages [9] are given below:
Narrow bandwidth.
• Low efficiency.
• Low Gain.
• Extraneous radiation from feeds and junctions.
• Poor end fire radiator except tapered slot antennas.
• Low power handling capacity.
• Surface wave excitation.

Microstrip%%%%quotes detected%%%% patch antennas have a very high antenna quality

factor (Q). It represents the losses associated with the antenna where a large Q leads to
narrow bandwidth and low efficiency. Q can be reduced by increasing the thickness of the
dielectric substrate. But as the thickness increases, an increasing fraction of the total power
delivered by the source goes into a surface wave. This surface wave contribution can be
counted as an unwanted power loss. Since, it is ultimately scattered at the dielectric bends
and causes degradation of the antenna characteristics. Other problems such as lower gain
and lower power handling capacity can be overcome by using an array configuration for the
elements.

2.6 Feeding

Microstrip%%%%quotes detected%%%% antennas have radiating elements on one side of a

dielectric substrate, and thus early microstrip antennas were fed either by a microstrip line or
a coaxial probe through the ground plane. Since then a number of new feeding techniques
have been developed. Prominent among these are coaxial feed, microstrip (coplanar) feed,
proximity-coupled microstrip%%%%quotes detected%%%% feed, aperture-coupled
microstrip feed, and coplanar waveguide feed.
Selection of the feeding technique is governed by a number of factors. The most important
consideration is the efficient transfer of power between the radiating structure and feed
structure, that is, impedance matching between the two. Associated with impedance
matching are stepped impedance transformers, bends, stubs, junctions, transitions and so
on, which introduce discontinuities leading to spurious radiation and surface wave loss. The
undesired radiation may increase the side lobe level and the cross-polar amplitude of the
radiation pattern. Minimization of spurious radiation and its effect on the feed is one of the
important factors for the evaluation of the feed. Another consideration is the suitability of
the feed for array applications. Some feed structures are amenable to better performance
because of the larger number of parameters available.
The most four popular feeding techniques for microstrip patch antenna are: (coaxial feeding,
microstrip%%%%quotes detected%%%% feeding, proximity feeding and aperture feeding).

2.6.1 Coaxial feeding

It is one of the basic techniques used in feeding microwave power. The coaxial cable is
connected to the antenna such that its outer conductor is attached to the ground plane while
the inner conductor is soldered to the metal patch [4]

Coaxial feeding is simple to design, easy to fabricate, easy to match and have low spurious
radiation [5]. However coaxial feeding has the disadvantages of requiring high soldering
precision. There is difficulty in using coaxial feeding with an array since a large number of
solder joints will be needed. Coaxial feeding usually gives narrow bandwidth and when a
thick substrate is used a longer probe will be needed which increases the surface power and
feed inductance [6].

2.6.2 Microstrip%%%%quotes detected%%%% feeding

In microstrip%%%%quotes detected%%%% feed, the patch is fed by a microstrip line that is

located on the same plane as the patch. In this case, both the feeding and the patch form
one structure. Microstrip feeding is simple to model, easy to match and easy to fabricate. It is
also a good choice for use in antenna-array feeding networks. However, microstrip feed has
the disadvantage of narrow bandwidth and the introduction of coupling between the feeding
line and the patch which leads to spurious radiation and the required matching between the
microstrip patch and the 50 Ω feeding line. Microstrip feed can be classified into 3 categories:

Direct feed:
Direct feed where the feeding point is on one edge of the patch as shown in Figure 2.11
Direct feed needs a matching network between the feed line and the patch (such as quarter
wavelength transformer). The Quarter wave length transformer compensates the impedance
differences between the patch and the 50 Ω feed line. The quarter wave length transformer
is calculated according to formulas found in [9].

Inset feed:
In Inset feed, where the feeding point is inside the patch. The location of the feed is the same
that will be used for coaxial feed. The 50 Ω feed line is surrounded with an air gap till the
feeding point as shown in Figure 2.11 The inset microstrip feeding technique is more suitable
for arrays feeding networks [6, 7].

Gap-coupled:
In Gap-couple, the feeding line does not contact the patch. There is an air gap between the
50 Ω line and the patch as shown in Figure 2.12. The antenna is fed by coupling between the
50 Ω feed line and the patch.
2.6.3 Proximity coupled feeding
Proximity coupled feeding consists of two dielectric substrate layers. The microstrip patch
antenna is located on the top of the upper substrate & the microstrip feeding line is located
on the top of the lower substrate as shown in Figure 2.14. It is a non-contacting feed where
the feeding is conducted through electromagnetic coupling that takes place between the
patch and the microstrip%%%%quotes detected%%%% line. The two substrates parameters
can be chosen different than each other to enhance antenna performance [6, 8]. The
proximity coupled feeding reduces spurious radiation and increase bandwidth. However, it
needs precise alignment between the 2 layers in multilayer fabrication.

2.6.4 Aperture coupled feeding

Aperture coupled feeding consists of two substrate layers with common ground plane in-
between the two substrates, the microstrip patch antenna is on the top of the upper
substrate & the microstrip feeding line on the bottom of the lower substrate and there is a
slot cut in the ground plane as shown in Figure 2.15. The slot can be of any size or shape and
is used to enhance the antenna parameters. It is a non-contacting feed; the feeding is done
through electromagnetic coupling between the patch and the microstrip%%%%quotes
detected%%%% line through the slot in the ground plane. The two substrates parameters can
be chosen different than each other to enhance antenna performance [4, 8]. The aperture
feeding reduces spurious radiation. It also increases the antenna bandwidth, improves
polarization purity and reduces cross-polarization. But it has the same difficulty of the
aperture feeding which is the multilayer fabrication.

2.7 Analytical Evaluation of a Rectangular Patch Antenna

The objective of antenna analysis is to predict the radiation characteristics such as radiation
patterns, gain, and polarization as well as input impedance, bandwidth, mutual coupling, and
antenna efficiency. The analysis of microstrip antennas is complicated by the presence of in
homogeneity of dielectric & boundary conditions, narrow frequency band characteristics, a
wide variety of feed, patch shape, and substrate configurations. The good model has the
following basic characteristics:
It can be used to calculate all impedance and radiation characteristics of the antenna
Its results are accurate enough for the intended purpose
It is simple for providing the proposed accuracy for the impedance and radiation properties.
It lends itself to interpretation in terms of known physical phenomena.

In common practice, microstrip antennas are evaluated using one of three analysis methods:
the transmission line model, the cavity model, and the full-wave model. The transmission line
model is the easiest of all, it gives good physical insight. But it is less accurate and more
difficult to model with coupling effect of antenna. Compared to the transmission line model,
the cavity model is more accurate but at the same time, it is more complex and difficult to
model coupling effect. In general, when applied properly, the full wave model is very
accurate, and very versatile. It can analyze single element, finite array, layered elements and
an arbitrary shaped element of microstrip antenna and also coupling effect of the antenna.

2.7.1 Methods of analysis

The preferred models for the analysis of Microstrip patch antennas are the transmission line
model, cavity model, and full wave model (which include primarily integral
equations/Moment Method). The transmission line model is the simplest of all and it gives
good physical insight but it is less accurate. The cavity model is more accurate and gives good
physical insight but is complex in nature. The full wave models are extremely accurate,
versatile and can treat single elements, finite and infinite arrays, stacked elements, arbitrary
shaped elements and coupling. These give less insight as compared to the two models
mentioned above and are far more complex in nature.
Due to the attention given to the microstrip antenna and the importance to understand its
physical insight, there are many methods to analyze microstrip antennas. Among these
methods: -

Transmission-line model:
It is the simplest and easiest model. It gives good physical insight. However, it is not versatile,
less accurate and difficult in modeling coupling [8].
The transmission line model, as shown in the Figure 2.16, represents the microstrip antenna
by two slots, separated by saucepans B and conductance G of length L patch. Due to the
dimensions of the patch are finite (or shorter than the base plate) along in length and width,
the fields at the edges of the patch undergo fringing. The fringing fields act to extend the
effective length of the patch. Thus, the length of a half-wave patch is slightly less than a half
wavelength in the dielectric material.

Cavity model:
It is more complex than the transmission-line model and also difficult in modeling coupling.
However, it is more accurate and gives more physical insight [4, 6].

Full wave:
It is the most accurate and versatile model, it can be applied to any microstrip antenna
structure. However, it is very complex and gives less physical insight [4, 6].
Microstrip antennas drawbacks are sometimes beneficial. There are some applications that
require narrow frequency bandwidth such as government security systems. There are many
modifications techniques that can be done to overcome some of the microstrip antenna
disadvantages. Stacking, choosing thick substrate, coplanar parasitic elements can increase
the antenna bandwidth up to 60% or more. Array configuration can be used to overcome low
gain and low power. Photonic band gap structures can be used to overcome poor efficiency,
mutual coupling, reduced gain and radiation pattern degradation [4].
Due to the advantages and ease of fabrication of microstrip antenna, it is the most commonly
used an antenna element that has a variety in its designs [6]. There are a lot of antenna
combinations based on: patch shape, feeding technique, substrate parameters, perturbations
technique if used and array arrangements, the combination of these parameters can be
optimized to meet a wide array of antenna requirements.
2.7.2 Fringing Effect: -
The amount of fringing of the antenna is a function of the dimensions of the patch and the
height of the substrate. Due to fringing electric field lines travels in non-homogeneous
material, typically substrate and air, an effective dielectric constant is introduced. For electric
line with air above the substrate, the effective dielectric constant has values in the range of
1 <Ɛreff<Ɛr. The dielectric constant for most applications is much greater than unity. The
effective dielectric constant is expressed by the function of frequency. As the frequency of
operation increases, most of the electric field concentrates in the substrate, and therefore,
the microstrip behaves more like a homogeneous electric line of one dielectric, and the
effective dielectric constant approaches the value of one dielectric constant of the substrate.
Experimental results of the effective dielectric constant for microstrip with three different
substrates are shown in Fig 2.18

This model represents the microstrip antenna by two slots of width W and height h,
separated by a transmission line of length L. The microstrip is essentially a non-homogeneous
line of two dielectrics, typically the substrate and air.
Hence, as seen from Figure 2.19, most of the electric field lines reside in the substrate and
parts of some lines in air. As a result, this transmission line cannot support pure transverse-
electric-magnetic (TEM) mode of transmission, since the phase velocities would be different
in the air and the substrate. Instead, the dominant mode of propagation would be the quasi-
TEM mode. Hence, an effective dielectric constant (εreff) must be obtained in order to
account for the fringing and the wave propagation in the line. The value of εreff is slightly
less than εr because the fringing fields around the periphery of the patch are not confined in
the dielectric substrate but are also spread in the air as shown in Figure 2.18 above. The
expression for εreff is given as:

Where εreff = Effective dielectric constant

εr= Dielectric constant of substrate
h = Height of dielectric substrate
W = Width of the patch

Consider Figure 2.20 below, which shows a rectangular microstrip patch antenna of length L,
width W resting on a substrate of height h. The co-ordinate axis is selected such that the
length is along the x direction, width is along the y direction and the height is along the z
direction.

In order to operate in the fundamental TM10 mode, the length of the patch must be slightly
less than λ/2 where λ is the wavelength in the dielectric medium and is equal to λo/√εreff
where λo is the free space wavelength. The TM10mode implies that the field varies one λ/2
cycle along the length, there is no variation along the width of the patch. In the Figure 2.16
shown below, the microstrip patch antenna is represented by two slots, separated by a
transmission line of length L and open circuited at both the ends. Along the width of the
patch, the voltage is maximum and current is minimum due to the open ends. The fields at
the edges can be resolved into normal and tangential components with respect to the
ground plane.

It is seen from Figure 2.21 that the normal components of the electric field at the two edges
along the width are in opposite directions and thus out of phase. Since, the patch is λ/2 long.
Hence, they cancel each other in the broadside direction. The tangential components (seen
in Figure 2.22), which are in phase, means that the resulting fields combine to give maximum
radiated field normal to the surface of the structure. Hence the edges along the width can be
represented as two radiating slots, which are λ/2 apart and excited in phase and radiating in
the half space above the ground plane. The fringing fields along the width can be modeled as
radiating slots and electrically the patch of the microstrip antenna looks greater than its
physical dimensions. The dimensions of the patch along its length have now been extended
on each end by a distance ∆L, which is given as:

The effective length of patch Leff is given as;

Leff = L + 2∆L
For given resonant frequency, effective length is given as:

For a rectangular microstrip patch antenna, the resonant frequency for any
Mode is given by [1] as:

Where m and n are modes along L and M respectively.

2.7.3 Cavity Model

Microstrip antenna resembles dielectric loaded cavities exhibit higher order resonances. The
normalized fields within the dielectric substrate can be found more accurately by treating
that region as a cavity bounded by electric conductors (above and below) and by magnetic
wall along the perimeter of the patch. The bases for this assumption are the following points
(for height of substrate h << wave length of the field).

The fields in the interior region do not vary with z-axis because the substrate is very thin, h<<
λ.
The electric field is z-axis directed only; the magnetic field has only the transverse
components in the region bounded by the patch metallization and the ground plane. This
observation provides for the electric walls at the top and bottom
The electric current in the patch has no component normal to the edge of the patch
metallization, which implies that the tangential component of magnetic field along the edge
is negligible; a magnetic wall can be placed along the periphery.
This approximation model leads to reactive input impedance; it does not radiate any power.
However, the actual fields can be approximated to the generated field of the model and is
possible to analyze radiation pattern, input admittance, and resonant frequency.

2.7.4 Current Densities

When the Microstrip antenna (cavity modeled) is energized, charge distribution is

established on upper and lower surfaces of the patch, as well as on the surface of the ground
plane. The charge distribution is controlled by two mechanisms; attractive and a repulsive
mechanism. The attraction is between the corresponding opposite charges on the bottom
side of the patch and ground plane, which tends to maintain the charge concentration on the
bottom of the patch. The repulsive is between like charges from the bottom of the patch,
around its edges, to its top surface as shown in Fig 2.23. The movement of these charges
creates corresponding current densities Jband Jt, at the bottom and top surfaces of the
patch.
Since for the most practical microstrip the height to width ratio is very small, and due to
attractive and a repulsive mechanism of charges, only small amount of current flows at the
top surface of the patch and large amount of charges are concentrated underneath the
patch. The concentration of charges produces current density Jb and Jt at the patch.
However, this flow of current decrease as the height to width ratio increases. It implies that
there is no tangential magnetic field component at the edges of the patch. This condition
allows a Microstrip antenna to be modeled by a four-sided magnetic wall model as shown in
Figure 2.19.

As shown in figure, equivalent current density and magnetic field density are shown:

Js = nxHa and Ms = -nxEa

Where Ea and Ha represent the electric and the magnetic field at the slots.
Considering the presence of the ground plane, the only nonzero current density is the
Equivalent magnetic current density Ms. Applying image theory of the magnetic current in
the electric ground plane, equivalent magnetic current density Ms is given as: -
Ms = -2nxEa
Typical E and H plane of Microstrip antenna of two slots with the source of the same
magnitude and phase is presented in Figure 2.25.

Treating the cavity model as Microstrip antenna is not sufficient to find the absolute
amplitude of the electric and magnetic fields. Naturally, the cavity is lossless and requires
introductory losses by considering effective loss tangent to behave as an antenna. Because,
the thickness of the microstrip antenna is usually very small, the waves generated within the
dielectric substrate undergoes considerable reflections when the fields arrive at the edge of
the patch. The electric field is nearly normal to the surface of the patch. Therefore, only TM
field configuration is considered within the cavity.

2.7.5 Field Configuration

It is common practice in the analysis of electromagnetic boundary value problems to use

auxiliary vector potentials as aids in obtaining solution for electric (E) and magnetic (H) fields.
The most common vector potential functions are the A, Magnetic vector potential, and E,
electric vector potential. These field configurations must be satisfying Maxwell’s equations or
the wave equation or the appropriate boundary conditions.
A transverse magnetic mode, (TM) is a field configuration whose magnetic field component
lies in a plane that is transverse to the direction of wave propagation. Consider that the wave
propagation of the microstrip antenna is to x-axis. Hence, magnetic vector potential of cavity
model is generally obtained from the homogeneous wave equation: -
……… (2.1) Where k2 = ω2με
Since the field expression of TM to a given direction is independent of the other coordinate
system. It is sufficient to let the vector potential A have only a component in the direction in
which the fields are propagated. The remaining components of A as well as all of F are set
equal to zero.
The solution for equation 2.1 is expressed as follow [4]:

Ax=*AXcos(kxx)+BXsin(kxx)+ *AYcos(kyy)+BYsin(kyy)+ *Axcos(kzz)+Bxsin(kzz)+ …. (2.2)

Where, Kx, Ky and Kz and are the wave numbers along x, y, z directions, respectively. Its
value is determined subject to the boundary conditions.
Considering the boundary condition of the cavity model, Hz (0<x<h, y=0, 0<z<W)= 0 and
Hz(0<x<h, y=L,0<z<W)=0, the vector potential is described as

Ax = Amnpcos(kxx)cos(kyy)cos(kzz) ………………………………………..(2.3)

Where Amnprepresents the amplitude coefficients of each mnp mode resonant frequency
determines the dominant mode of cavity operation and it is obtained using the following
equations. %%%%quotes detected%%%%
1. If L>W>h, the mode with lowest frequency (dominant mode) is TM010 and it’s resonant
Frequency is:
2. If L>W>L/2, the mode is TM001 and its resonant frequency is:

3. If L>L/2>W>h, the order of the mode is TM020 and its resonant frequency is:

2.8 Antenna Parameters

2.8.1 Radiation pattern

The basic term “radiation” means that, the distribution of power through respective fields of
antenna. An antenna radiation pattern or antenna pattern is defined as “A mathematical
function or a graphical representation of radiation properties of the antenna as a function of
space coordinates”. However, in most cases the radiation pattern is determined in the far
field region and is represented as function of directional coordinates. The properties of
Radiation are power flux density, radiation intensity, field strength, directivity phase or
polarization. The radiation properties of most concern are the two or three-dimensional
spatial distribution of radiated energy as function of the observer’s position along a path or
surface of constant radius. A trace of received power at constant radius is called power
pattern. On the other hand, a graph of spatial variation of the electric (or magnetic) field
along constant radius is called amplitude field pattern. In practice the dimensional pattern is
measured and recorded in series of two dimensional patterns [4].
2.8.2 Radiation Intensity

Radiation intensity in given direction is defined as “the power radiated from an antenna per
unit solid angle”. The radiation intensity is far field parameter and it can be obtained by
simply multiplying the radiation density by the square of the distance [4]. In the
mathematical from it can
be expressed as
U=r2Wrad (2.1)
U = Radiation intensity (W/Unit solid angle)
Wrad = Radiation intensity (W/m2)
The radiation intensity is also related to far-zone electric field of an antenna by

2.8.3 Directivity

In the 1983, version of the IEEE standard Definition of terms for antennas, there has been a
substantive change in definition of directivity, compared to definition of 1973 version.
Basically the term directivity in the new 1983 version has been used to replace the term
directive gain of the old 1973 version. In the 1983 version the term directive gain has been
deprecated. According to authors of the new standard this change brings this standard in line
with common usage among antenna engineers and with other international standard notably
those of the international electrochemical commission (IEC) therefore directivity of an
antenna defined as the ratio of radiation intensity in given direction from the antenna to the
radiation intensity averaged over all directions. The average radiation intensity is equal to the
total power radiated by the antenna divided by 4 . if direction is not specified the direction
of maximum radiation intensity is implied. Stated more simply the directivity of non-isotropic
source is equal to the ratio of it radiation intensity in given direction over that of isotropic
source [3]. In mathematical form it can be written as:
2.8.4 Gain
Another useful measure describing the performance of antenna is the gain. Although the gain
of antenna is closely related to the directivity, remember that directivity is measure that
describes only the directional properties of the antenna, and it is therefore controlled only by
pattern. Absolute gain of an antenna is defined as the ratio of intensity, in a given direction
to
the radiation intensity that would be obtained if power accepted by antenna were radiated
isotropically. The radiation intensity corresponding to isotropically radiated power is equal to
the power accepted by the antenna divided by 4. In equation form this can be expressed as
G=
When the direction is not stated the power, gain is usually taken in direction of maximum
radiation [4].
2.8.5 Antenna efficiency
The total antenna efficiency egois used to take into account losses at the input terminals and
within the structure of the antenna [3]. Such losses may be due, to two factors given below
Reflection because of the mismatch between the transmission line and the antenna
I2R losses (conduction and dielectric)
2.8.6 Half power beam width

The half power beam width%%%%quotes detected%%%% is defined as in a plane containing

the direction of maximum of a beam the angle between two directions in which the radiation
intensity is one half the maximum value of the beam often the term beam width is used to
describe the angle between any two points on the pattern such as the angle between 10-dB
points. In this case the specific point on the pattern must be described the 3- dB beam width.
The beam width of the antenna is very important figure of merit and is often used to as
trade-off between it and side lobe level; that is as the beam width decreases the side lobe
increases and vice versa. In addition, the beam width of antenna is also used to describe the
resolution capabilities of the antenna to distinguish between two adjacent radiating sources
or radar targets. The most common resolution criterion states that the resolution capabilities
of antenna to distinguish between two sources is equal to half the first null beam width
(FNBW/2) which is usually used to approximate the half power beam width (HPBW). That is
two sources separated by angular distance equal or greater than FNBW/2 = HPBW of an
antenna with uniform distribution can be resolved. If the separation is smaller ten antennas
will be tending to smooth the angular separation distance [4].
2.7 Bandwidth

The bandwidth of an antenna is defined as the range of frequency with in which the
performance of antenna with respect to some charters tics conform to specified standard.
The bandwidth can be considered to be a range of frequency on either side of centre
frequency where the antenna characteristics are within acceptable value of those at centre
frequency. For broad band antenna%%%%quotes detected%%%% the bandwidth is usually
expressed as the ratio of upper to lower frequency of acceptable operation. Because the
characteristics of an antenna do not necessarily vary in the same manner or are even
critically affected by the frequency there is no unique characterization of the bandwidth [4].

2.7.1 Frequency Bandwidth

Narrowband - These antennas cover a small range of the order of few percent around the
designed operating frequency.

Impedance Bandwidth- The impedance variation with frequency of the antenna element
results in a limitation of the frequency range over which the element can be matched to its
feed line.
Impedance Bandwidth is usually specified in terms of a return loss or maximum SWR
(typically less than 2.0 or 1.5) over a frequency range conversion of bandwidth from one SWR
level to another can be accomplished by using the relation between Bandwidth B and Q
(2.13)
% Impedance Bandwidth = (2.14)

2.8. Voltage Standing Wave Ratio (VSWR) %%%%quotes detected%%%%

The standing wave ratio (SWR), also known as the voltage standing wave ratio (VSWR), is not
strictly an antenna characteristic, but is used to describe the performance of an antenna
when attached to a transmission line. It is a measure of how well the antenna terminal
impedance is matched to the characteristic impedance of the transmission line. Specifically,
the VSWR is the ratio of the maximum to the minimum RF voltage along the transmission
line. The maxima and minima along the lines are caused by partial reinforcement and
cancellation of a forward moving RF signal on the transmission line%%%%quotes
detected%%%% and its reflection from the antenna terminals. If the antenna terminal
impedance exhibits no reactive (imaginary) part and the resistive (real) part is equal to the
characteristic impedance of the transmission line, then the antenna and transmission line
perfectly obeys impedance matching condition [4]. In general, (2.15)
2.9 Polarization
In general polarization of an antenna is referred as, the orientation of radiation of that
antenna. Polarization of an antenna in given direction is defined as the polarization of the
wave transmitted by the antenna. When the direction is not stated the polarization is taken
to be polarization in direction of maximum gain%%%%quotes detected%%%% . In practice
polarization of the radiated energy varies with direction from the centre of the antenna so
that different part of the pattern may have different polarization. Polarization of radiated
wave is defined as that properties of electromagnetic wave describing the time varying
direction and relative magnitude of electric field vector specifically the figure traced as a
function of time by the extremity of vector at fixed location at in space and sense in which it
is traced as observed along the direction of propagation [4].
Linear
Circular
Elliptical

2.10 Input impedance%%%%quotes detected%%%%

Input impedance is defined as “the impedance presented by an antenna at it terminals or the
ratio of voltage to current at pair of terminals or the ratio of the appropriate component of
the electric to magnetic fields at a point”. In this section we are primarily interested in the
input impedance at pair of terminals which are input terminals of the antenna [5].

2.10 Feeding Methods

There are several techniques available to feed or transmit electromagnetic energy to a

dielectric resonator antenna. The five most popular feeding methods are the coaxial probe,
slot aperture, microstrip line, co-planar coupling and dielectric image guide [1].

2.10.1 Coaxial Feed

The Coaxial feed or probe feed is a very common technique used for feeding dielectric
resonator antennas as shown in figure 4.1. In this method, the probe can either be placed
adjacent to the DRA or can be embedded within it. The amount of coupling can be enhanced
by adjusting the probe height and the DRA location. In DRA, various modes can be excited
depending on the location of the probe, For the probe located adjacent to the DRA, the
magnetic fields of the TE11δ mode of the rectangular DRA are excited and radiate like a
horizontal magnetic dipole. For a probe located in the centre of a cylindrical DRA, the TE011
mode is excited and radiating like a vertical dipole. Another benefit of using probe coupling is
that one can couple directly into a 50Ω system, without the requirement for a matching
network. Probes are suitable at lower frequencies where aperture coupling may not be
applied due to the large size of the slot required [2].
2.10.2 Slot Aperture

In slot aperture method%%%%quotes detected%%%% , a DRA is exciting through an

aperture in the ground plane upon which it is placed. Aperture coupling is applicable to DRAs
of any shapes such as rectangular, cylindrical or hemispherical. The aperture works like a
magnetic current running parallel to the size of the slot, which excites the magnetic fields
inside the DRA. The aperture type of feeding consists of a slot cut in a ground plane and fed
by a microstrip line below the ground plane. For avoiding spurious radiation, feed network is
located below the ground plane. Moreover, slot coupling is an attractive technique for
integrating DRAs with printed feed structures. The coupling level can be changed by
moving%%%%quotes detected%%%% the DRA with respect to the slot. Generally, a high
dielectric material is used for the substrate and a thick, low dielectric constant material is
used for the top dielectric resonator patch to optimize radiation from the antenna. The main
drawback of this feed technique is that it is problematic to fabricate due to multiple layers,
which also increases the antenna thickness. This feeding method also provides narrow
bandwidth (up to 21%) [2].
2.10.3 Microstrip Line Feed
In this type of feed technique, a conducting strip is connected directly to the edge of the
patch as shown in figure 4.3. A common method for coupling to dielectric resonators in
microwave circuits is by proximity coupling to microstrip lines. Microstrip coupling will excite
the magnetic fields in the DRA to create the short horizontal magnetic dipole mode. The level
of coupling can be changed by the lateral location of the DRA with respect to the microstrip
line and on the relative permittivity of the DRA [2].

In DRAs, the amount of coupling is generally quite small for requiring wide bandwidth.
Microstrip lines can be used as a series feed for a linear array of DRAs. This is an easy feeding
technique since it offers ease of fabrication and simplicity in modelling along with impedance
matching. However, as the thickness of the dielectric substrate being used, rises, surface
waves and spurious feed radiation also rises, which hampers the bandwidth of the antenna
[1]. One drawback of this method is that the polarization of the array is analysed by the
orientation of the microstrip line such as the direction of the magnetic fields in the DRA will
be parallel to the microstrip line [6], [8].

2.10.4 Analytical Evaluation of Dielectric Resonator Antenna%%%%quotes detected%%%%

In designing, input impedance is the important parameter which is a feed to excite the DRA.
Input impedance as a function of frequency is to determine the bandwidth of operation and
for matching the antenna to the circuit. Unfortunately, there are no simple closed-form
expressions for predicting the input impedance of the DRA when excited by a particular feed
and rigorous analytical. Here, some of the techniques that have been used to predict the
input impedance for DRAs excited by the various feed [10].

2.10.4.1 Green’s function analysis

For a probe-fed DRA, the input impedance (Zin) can be determined using the following
equation:
E= Electric fields of the DRA
Js = Applied source current density on the probe
IO = Magnitude of the current on the probe
The electric fields of the DRA depend on the source excitation and determined by using:

Here, G represents Green ‘s function for the DRA. By using some simple assumptions about a
single-mode operation and the currents on the probe, the Green‘s function for a
hemispherical DRA was first derived and was then used to predict the input impedance of the
probe-fed DRA operating in the TE111 mode%%%%quotes detected%%%% . This technique
was also applied to a probe–fed hemispherical DRA operating in the TM101 mode. The input
impedance of conformal strip feeds and aperture feeds can also be analysed using Green‘s
function. The advantage to this technique is the relatively fast computation time required to
obtain the input impedance. It is useful method for analysing the effects of altering probe
dimensions and probe location and can be used for optimizing the input impedance. The
main drawback is its limitation only to hemispherical DRA geometries. For other DRA shapes,
different analytical techniques are required [2].
2.10.5 Co-Planar Waveguide Feed %%%%quotes detected%%%%
The Co- planar feed is a very common technique used for coupling in dielectric resonator
antennas. Here, figure 4.5 shows a cylindrical DRA coupled to a co-planar loop. The coupling
level can be adjusted by locating the DRA over the loop [1], [5].

The coupling behaviour of the co-planar loop is similar to coaxial probe, but the loop offers
the advantage of being non-obtrusive. By moving the feed loop from the edge of the DRA to
the centre, one can couple into either the HE11δ mode or the TE011 mode of the cylindrical
DRA [1], [2].
Co-planar waveguide (CPW) feeding technique is also referred as planar strip line feeding.
CPW feeding technique more advantageous compared to other feeding techniques, because
it having the fallowing attractive features.
They are
Lower radiation leakage
Less dispersion than microstrip lines

Active devices can be mounted%%%%quotes detected%%%% on top of the circuit like on

microstrip.
It can provide extremely high frequency response (100 GHz or more). Since connecting to
CPW does not involve or require any parasitic discontinuities in the ground plane [2].

The coplanar waveguide (CPW) is such a transmission line that can achieve high radiation
efficiency demands. In addition, the CPW has lower loss than the microstrip line. One
promising application with the coplanar waveguide fed antenna techniques is that a fibre
optics system can be integrated with the slot antenna. Recently, different types of CPW-fed
slot antennas have been designed for wideband applications, achieving 50% bandwidth in a
multi-slot design and 60% and width by optimizing a tuning stub as with microstrip line
excitation, slot antennas excited by coplanar waveguides also have bidirectional radiation
characteristics [11].
Planar printed antennas fed by coplanar waveguides (CPW) have various benefits, because it
is constructed on one-layer design, low cost, low profile and uncomplicated to integrate to
the transceiver circuit board [13].

2.10.5.1 Finite Ground CPW Feeding Method (FG-CPW):

The above figure represents the clear view of finite ground coplanar waveguide method. It
has feeding slots like same as coplanar waveguide feeding and it also having ground plane in
bottom side of the substrate [15].
Chapter 3
Literature survey

%%%%skip contents%%%%
Gaurav Varshney, Shailza Gotra, V.S. Pandey, R.S. Yaduvanshi “Inverted sigmoid shaped
multiband DRA with dual band circular polarization.” IEEE transactions 2018 *1+.
In this paper, a multiband DRA has been designed with inverted-sigmoid shaped DR
providing the dual band CP response. A metallic strip is applied at DR to achieve the dual
band CP response. The fundamental and higher order hybrid modes have been excited in the
antenna structure due to its specific geometry. The 3-dB AR bandwidth of 19.98% in the
lower band and 3.07% in the upper band has been achieved. The upper 3-dB AR pass band
has been tuned in different 10-dB impedance pass bands by changing the location and size of
the metallic strip. The proposed antenna provides the peak gain of 4.85 and 6.38 dBi in the
lower and upper CP bands, respectively. In addition, the antenna response has been tuned to
find the triple band CP characteristics.
CHAPTER 4
Dielectric Resonator Antenna
4.1 Introduction of Dielectric Resonator Antenna (DRA) %%%%quotes detected%%%%
The structure of DRA mainly consists of three basic components; they are first one Substrate,
secondly ground (Perfect Electric Conductor) material etched on substrate and some
dielectric resonating material placed above the ground, generally referred as “Dielectric
Resonator (DR)”. The designing of DRs and using them in structures of DRAs, discussed in
chapters 5-8.Basically DR is an electronic component that exhibits ‘resonance’ for a wide
range of frequencies, generally in the microwave band.
If the DR placed in an open environment, Power will be lost in the radiated fields only. This
fact makes dielectric resonators useful as antenna elements instead of elements in
microwave circuits as energy storage devices [1].
Wi-MAX and WLAN are the standard-based technologies enabling the delivery of last mile
wireless broadband access [2]. WiMAX refers to interoperable implementations of the IEEE
802.16 wireless-networks standard which can operate at higher bit rates or over longer
distances. It is capable of operating in 3.4-3.6 GHz frequency range as well as at 5.5 GHz band
[5]. While WLAN standards in the 2.4-GHz range have recently emerged in the market, the
data rates supported by such systems are limited to a few megabits per second. By contrast,
a number of standards have been defined in the 5-6 GHz range that allow data rates greater
than 20 Mb/s, offering attractive solutions for real-time imaging, multimedia, and high-speed
video applications. To achieve the necessary applications a high performance wide band
antenna with high radiation efficiency are required [3]. Over the past few years, the dielectric
resonator antenna (DRA) has received extensive attention due to its several advantages such
as low profile, light weight, low dissipation loss, high dielectric strength and higher power
handling capacity [5]. DRA can be in a few geometries including cylindrical, rectangular,
spherical, half-split cylindrical, disk, hemispherical and triangular shaped.
The main purpose of design any antenna is to obtain a wide range of bandwidth. Several
bandwidth enhancement techniques have been reported on modified feed geometries and
changing the shape of the%%%%quotes detected%%%% DRA. By using different bandwidth
enhancement techniques in this thesis different shape of dielectric resonator antennas are
designed and simulated. There is few software’s available which allow the optimization of
the antenna. Here, Simulation process was done by using Computer Simulation Technology
(CST). In this thesis, have been design different shapes of single and multiple dielectric
resonator antennas for wireless applications. Bandwidth enhancement techniques are used
to obtain a large bandwidth for particular resonant frequencies.

4.2 Basic Characteristics of DRA

DRA offers several attractive features including the fallowing characteristics:
In DRAs, we can use a wide range of dielectric constants ( = 2.1 – 100), that allowing the
designer to have control over the physical size of the DRA and its bandwidth.
The Size of DRA is proportional to λ0/√ , where λ0 is the free space wavelength at the
resonant frequency, and is the dielectric constant of the material.
DRAs can be designed to operate over a wide range of frequencies from 1.3 GHz to 40 GHz
[2].
High radiation efficiency (95%) due to the absence of conductor or surface wave losses.
Several feeding mechanisms can be used (including slots, probes, microstrip lines, dielectric
image guide, and coplanar %%%%quotes detected%%%% waveguide lines) to efficiently
excite DRAs.
DRA can be excited by several modes, many of which radiate pattern similar to short electric
or magnetic dipoles, producing either broadside or Omni-directional radiation patterns for
different coverage requirements [4].
By choosing a dielectric material with low-loss characteristics, high-radiation efficiency can
be maintained, even at millimetre-wave frequencies, due to an absence of surface waves and
minimal conductor losses associated with the DRA [1], [4].
A Tolerance ± 0.5; ±1.0; ±2.0 ppm/ oC.
Figure 4.1 DRAs of various shapes (cylindrical, rectangular, hemispherical, low-profile
circular-disk, low-profile triangular)
4.3 Advantages
In the past few years, extensive studies on the DRA have been focused on resonators of
various shapes, the feeding techniques, and bandwidth enhancement methods. Specific
features of DRAs has made them suitable for a variety of applications specially millimetre
wave (MMW) applications. DRAs can be easily coupled to almost all types of transmission
lines. They can be integrated easily with MMIC circuits. In MMW applications conductor loss
of metallic antennas become severe and the antenna efficiency decreases considerably,
conversely the only loss for a DRA is that due to the imperfect material of the DRA which can
be very small in practice.
Therefore DRAs have high radiation efficiency. In comparison to microstrip patch antennas,
Dielectric resonator antennas have wider impedance bandwidths. For a typical DRA with
dielectric constant of 10 the impedance bandwidth of 10% can be achieved. Avoidance of
surface waves is another attractive advantage of DRAs over microstrip antennas. Single DRAs
of different shapes has been possible, including rectangular, cylindrical, triangular, conical,
hemispherical, etc. However, among these different shapes cylindrical and rectangular are
the most common and the rectangular has the advantage of having one more degree of
freedom for design purposes. Here, a variety of feed structures, which electromagnetic fields
can be coupled to DRAs [6]. Usually common feed arrangements are coplanar waveguide
feeding, microstrip aperture coupling, direct microstrip coupling, probe coupling and
conformal strip coupling. Among these feed configurations, aperture coupling is more
suitable for MMW applications. In aperture coupling configuration, since the DRA is placed
on the ground plane of the microstrip feed, Figure 3.1 DRAs of various shapes (cylindrical,
rectangular, hemispherical, low-profile circular-disk, low-profile triangular) parasitic radiation
from the microstrip line is avoided. Isolation of the feed network from the radiating element
is another advantage of the aperture coupling method [5].
DRAs have been extensively used for numerous applications since they have many attractive
characteristics such as low profile, light weight, low cost, and inherently wide bandwidth.
They could be used for numerous applications as both individual elements and in an array
environment. In addition, wide bandwidth, low cost, low dissipation loss at high frequency,
and high radiation efficiency are the inherent advantages of DRAs over conventional patch
antennas. Compared with Microstrip antennas, which suffer from higher conduction loss and
surface waves in antenna array applications, DRAs have high radiation efficiency and high-
power handling capability due to lack of metallic loss. Unlike the microstrip antenna, DRA
does not support surface waves if placed on a ground plane directly. In recent years, DRAs
have been considered as potential antennas for mobile phone applications. A general
problem in the miniaturization of RF resonators used in filters and small antennas is decrease
of efficiency, due to conductor losses. In DRAs, lower conductor losses, compared to those in
typical metal antennas such as microstrip patches can be expected because DRAs have fewer
metal parts. Thus, DRAs are good potential alternatives, especially when very small antenna
elements are needed. In addition, they can be easily incorporated into microwave integrated
circuits because they can be fabricated directly on the printed circuit board (PCB) of the
phone. Specific features of DRAs have made them suitable for a variety of applications
specially MMW applications. DRAs have small size and low cost. They can be easily coupled
to almost all types of transmission lines [1], [5].
DRA have several advantages compared to conventional microwave antennas, and therefore
many applications cover the broad frequency range. Some of the principal advantages of
dielectric resonator antennas compared to conventional microstrip antennas are:
DRA has a much wide impendence bandwidth than microstrip antenna because it radiates
through the whole antenna surface except ground port while microstrip antenna radiate only
through two narrow radiation slots.
Higher efficiency.
Avoidance of surface waves is another attractive advantage of DRAs over microstrip antennas
However, dielectric resonator antennas have some advantages:
Light weight, low volume, and low-profile configuration, which can be made conformal;
DRA has high degree of flexibility and versatility, allowing for designs to suit a wide range of
physical or electrical requirements of varied communication applications.
Easy of fabrication
High radiation efficiency
High dielectric strength and higher power handling capacity
In DRA, various shapes of resonators can be used (rectangular, cylindrical, hemispherical,
etc.) that allow flexibility in design.
Low production cost
Several feeding mechanisms can be used (probes, slots, microstrip lines, dielectric image
guides, and coplanar waveguide lines) to efficiently excite DRAs, making them amenable to
integration with various existing technologies [1], [3], [6] - [8].
4.4 Problems with Microstrip patch antenna
Narrow Bandwidth for Electrically thin substrates
High frequencies Results in,
More ohmic losses
Electrically thicker substrates which support surface waves and decrease radiation efficiency.
Low gain
Poor polarization purity
Spurious feed radiation
MPA having low dielectric strength, hence they cannot handle as much output power as
other antennas
4.5 Advantages of DRA over Microstrip Antenna
In general, Dielectric Resonator antennas having more attractive features compared to
general microstrip patch antennas. The list of key advantages of DRAs over Microstrip patch
antennas listed as fallows [2].
Much wider Bandwidth
More over operating Bandwidth of a DRA can be varied by the permittivity ( ) of the
resonator material and its dimensions.
Radiation efficiency is more
Because DRA radiates through the whole antenna surface but in case of microstrip patch
antenna radiates only through patch.
Avoidance of surface wave and metal losses.
DRA’s have high dielectric strength
Hence DRA’s having higher power handling capacity.
DRA’s can operate in a wide temperature range
More over the temperature stable ceramics enables the antenna to operate in a wide
temperature range.
4.6 Bandwidth Enhancement by Using DRA’s
The key attractive feature in Dielectric Resonator antennas is Bandwidth Enhancement. By
choosing proper structure for DRAs we can easily increase the bandwidth. The important
techniques used in Bandwidth Enhancement by using DRA’s as listed below *16+. Optimizing
the feeding mechanisms and the DRA parameters.
Use of modified feed geometries (stub matching).
Changing the shape of DRAs.
Using Stacked Dielectric Resonators in DRA designs.
Introduction of air gap between the ground and Dielectric Resonator.
Changing the dielectric constant of Dielectric Resonator.
Use of parasitic coupling with different resonators.
In present DRA structures the stacked method used to enhance the Bandwidth.
4.7 Basic-shaped Dielectric Resonator Antenna
Three basic shapes of the DRA as Cylindrical, rectangular and hemispherical are the most
commonly used. Here, we studied about different shapes of DRAs and their various field
mode configurations. These analyses can be used to predict the resonant frequency,
radiation Q-factor, and radiation pattern of DRA [17].
4.7.1 Cylindrical DRA
Cylindrical DRA has advantages over hemispherical and rectangular shape DRA. It offers
greater design flexibility, where the ration of radius/height controls the resonant frequency
and the quality (Q) factor. By varying the DRA‘s dimensions different Q-factor can be
obtained. In cylindrical DRA fabrication is much easier than hemispherical DRA and various
modes can be easily excited which results in either broadside or Omni-directional radiation
patters. It offers one degree of freedom more than the hemispherical shape; it has aspect
ratio a/h which determines the Q factor for a given dielectric constant [18].

Different subclasses of DRAs can be derived from cylindrical shape such as split-cylindrical
DRA, cylindrical-ring DRA, electric monopole DRA, disk-loaded cylindrical DRA, sectored
cylindrical and ring DRAs, elliptical DRA, conical DRAs. Ring DRA which is a subclass of the
cylindrical DRA that offers increased impedance bandwidth performance. Cylindrical
dielectric resonators are used in circuit applications, filters, and oscillators and especially in
microstrip technology, where resonant waveguide cavities are not very practical. The
geometry of the cylindrical DRA is shown in figure 3.2. It consists of a material with a height
h, radius a, and dielectric constant ( ). This shape offers one degree of freedom more than
hemispherical shape because it has aspect ratio a/h, which determines k0a and the Q-factor
for a given dielectric constant [19].

4.7.2 Hemispherical DRA

Hemispherical shape DRA offers an advantage over the rectangular and cylindrical shapes as
the interface between the dielectric and air is simpler. By that, a closed form expression cab
obtained for the Green‘s function%%%%quotes detected%%%% .
The hemispherical DRA is characterized by a radius a, a dielectric constant as shown in figure
3.3. Here, we assumed that the hemispherical DRA which is mounted on ground plane has
infinite conductivity and infinite extent. Image theory is useful to equate the hemispherical
DRA of radius =a ‘to an isolated dielectric sphere having the same radius. Transverse electric
(TE) and transverse magnetic (TM) are different modes in dielectric sphere. Transverse
electric (TE) modes having a zero value for the radial component of the Electric field (Er=0),
while transverse magnetic(TM) modes have a zero-radial component of the magnetic field
(Hr=0). The two fundamental modes for hemispherical DRA are TE111, whose radiation
pattern is similar to a short horizontal magnetic dipole and TM101, whose radiation pattern
is similar to a short electric monopole [21].

4.7.3 Rectangular DRA

The rectangular shape DRA has more advantages over cylindrical and hemispherical shape
DRA. It offers a second degree of freedom which is one more than cylindrical shape and two
more than hemispherical shape. It provides designer to have a greater design flexibility to
achieve the desired profile and bandwidth characteristics for a given resonant frequency and
dielectric constant. In an isolated rectangular dielectric guide, the various modes can be
divided into TE and TM, but with the DRA mounted on the ground plane only TE mode can
typically excited. The rectangular DRA can maintenance TE modes (TEx, TEy and TEz) which
would radiate like short magnetic dipole. The resonant frequency of each of these modes will
be a function of the DRA dimensions. By properly choosing the DRA dimensions, the designer
can avoid the unwanted modes to appear over the frequency band during operation.
Resonant frequency of TE modes can be calculated by solving the transcendental equation
[1].
4.8 Compact DRAs

Compact DRAs%%%%quotes detected%%%% has always been a challenging issue among

antenna design researchers. By using a small volume of DR, a high dielectric constant
material can resonate at a lower resonant frequency. But the Q-factor and hence a lower
bandwidth with the resonant frequency becoming highly temperature dependent will
increase [33].
The existence of specific DR shapes which isolated one or more planes of symmetry has been
noted. This plane of symmetry serves as an electric wall for certain modes; it works as a
magnetic wall for the other modes. Half-split cylindrical DR was paced over a metallic ground
plane, which was at the plane of symmetry (ɸ = 0ᵒ) were the motivation for the work in *8+.
The particular antenna configuration was excited in TE01δ mode with a low Qr by this means
facilitating more than 8% bandwidth. Numerical analysis of a half split cylindrical DRA on a
ground plane excited in the low Q, modes TE01δ and HEM12δ using a method of moment
approach for the coupling between a body of revolution (BOR) geometry and a non-BOR
geometry is reported [34]. %%%%quotes detected%%%%
Half-volume design for the broadside modes of a cylindrical (HEM11δ) and rectangular
(TE11δ) DRAs based on the aforesaid approach is presented in *1+. However, they used an
additional metallic plate attached to the plane of symmetry of the DR which was oriented in
the orthogonal plane to that in [8]. In the same paper, the authors put forward the concept
for further size reduction of the DRA of using a metallic post in its place of the metallic plate.
The above design was analysed by FDTD and additionally representative a higher directivity
for the half-volume DRA was carried out by [36]. Revolutionizing low-volume design by using
circular and annular sector DRAs was reported where a 75 % reduction in volume is
established [37]. The design used different inner to outer radius ratios, sector angles and
boundary conditions (metallic, open or mixed) for the sector DRA. The structure modification
in [35] was used to create circular polarisation [38]. The bandwidth enhancement of split-
cylinder DRAs numerically and experimentally exhaustively studied in [39]. Rectangular DRA
has been using of partial vertical and horizontal metallization on proposed to reduce the
overall dimensions of the DRA to be used at WLAN applications [40]A compact, stacked,
rectangular dielectric resonator antenna was designed for UWB applications. Shorting plate is
attached to one narrow wall of the DRA to reduce its size volume up to 67%, has been
achieved [21]. A thorough rectangular DRA analysis of a reduced volume based on the above
principle using FDTD and measurements has been presented in [31].

4.9 Multi-band DRAs

A dual-band antenna%%%%quotes detected%%%% can replace two single band antennas of
suitable operating bands. The work in [23] on stacked wideband DRA shows the design of
dual-band DRAs by choosing two DRAs of different dimensions, excited by a single feed. A
wideband antenna unless it is operating over a useful application band, is useless. This paper
[26] recommends the design of independent application bands where the antenna radiates
only over those bands introduced a slot excited double element rectangular DRA for dual or
wideband application. Stacking of two cylindrical DRAs excited by an annular ring excited by a
probe has shown three-band behaviour [27]. Dual frequency operation was achieved by
incorporating additional DRA in a parent DRA, both cylindrical in shape, so that the volume of
the structure remains unchanged is presented in [28]. A cylindrical ring DRA is fed with two
orthogonal microstrip feeds for dual resonance is reported [29]. This also has the effect of
producing orthogonally polarised bands but with similar broadside radiation patterns. Special
eye shaped DRA is also shown to be effective in producing dual radiating modes
[30]. Compact multiband antenna system using a dielectric resonator antenna (DRA) was
presented in [31]. The antenna designed to cover three frequency bands operating for
different wireless applications (DVB-H, WIFI and WiMAX).
Dual-frequency operation can be achieved by adding an additional radiator to the DRA. This
principle is implemented in [18] where a cylindrical DRA and a ring-slot are fed together by a
circular slot thereby allowing radiation from the two at respective resonances. It will be
advantageous in this context if the feed to the DRA is also radiating at a particular frequency.
The rectangular slot-feed to the DRA is made radiating by adjusting its dimensions where this
technique is explained in [19]. Furthermore, design introduced another by using a Shaped
microstrip feed that radiates in addition to exciting the DRA [20]. A ceramic loaded annular
ring monopole antenna is found to resonate in the dual W/LAN bands [21].
4.10 Wideband DRAs%%%%quotes detected%%%%

In the early 90s, studies on stacked DRA designs were carried out both experimentally and
numerically [22-24]. Two rectangular DRAs separated by a metallic plate yielded a much
broader bandwidth of 76.8% [29]. Keeping the separate DR elements as a single entity in the
above cases was tiresome and was avoided by fabricating single stacked DRA structures in
the form of flipped pyramid [40], T and L shaped equilateral triangular [25, 26] which offered
a maximum bandwidth in excess of 60%. Furthermore, an air gap between a cylindrical DRA
and the ground plane, a kind of fabrication imperfection can cause increase of the resonant
curve of the DRA [21, 37]. This was the effect of reduced unloaded or radiation Q-factor of
the DRA due to an increased effective radiating area. Later, an aperture fed rectangular DRA
was proposed, with its centre portion removed. This DRA and its image formed a rectangular
ring DRA to obtain a 28 % bandwidth [30]. This was motivated by the work of [38] which
reported that the Qr of certain modes of a cylindrical ring DR is lower than those of the
corresponding cylindrical DR.

Special DRA %%%%quotes detected%%%% shapes similar to conical [39] and split-cylinder
[29] were also reported to have wide bandwidths. Such geometries however suffered from
an increased antenna dimension, specifically the DRA height, compared to an individual
element. Embedding one DRA within another, in the form of an annular ring solved the
above problem where the antenna dimensions are the same as that of the parent DRA [25,
40]. A detailed comparative study of the stacked and embedded wideband DRAs with the
homogeneous DRA was also carried out [17] [31]. Later, a stacked-embedded DRA design
improved the bandwidth to 68 % [22]. %%%%quotes detected%%%% Designs using a simple
DRA is also presented for bandwidth enhancement [23, 24], where an aspect ratio greater
that unity led to acceptable excitation and merging of dual modes of similar radiation
properties. Feeding techniques like T shaped [25] and L shaped [26] microstrip also improved
the impedance bandwidth. To be suitable with low-Qr, DRA shapes like cylindrical cup, novel
feeds like L, hook and J shaped probes [27, 28] were also found suitable in addition to the
probe or slot feed. Modification of the feed geometry proved to be a successful method for
improving the impedance matching and bandwidth used a vertical metallic stub extended
from a coaxial probe [29] or a microstrip line [30] enhanced the bandwidth to 43% and 19%
respectively for cylindrical and rectangular DRAs. In addition, this was also shown to improve
the impedance matching. A fork-like tuning stub [31] coupling energy from a microstrip
through a circular aperture to the DRA also improved the bandwidth. %%%%quotes
detected%%%% An aperture feed which excites the DRA in addition to radiating itself [32,
33] was capable of producing two merged resonances causing wide bandwidth operation. A
hybrid dielectric resonator antenna for ultra wideband was presented in [34]. The dielectric
structure enhanced the impedance bandwidth of the antenna to 148.4% with frequency
range (6.2 - 42 GHz). As square ring di-electric resonator (SRDR) was presented with ‘U’
shaped microstrip feed [95]. The proposed DRA achieves an impedance bandwidth of 46.7%
for 3.9 to 6.20 GHz. A simple dielectric resonator antenna with a notch band for ultra-
wideband was reported in [36]. The design gives band width from 3.71 GHz to 13.01 GHz. a
notch was created at 5.725 GHz which reduces the interference due to local Wi-MAX
communication system.
Nevertheless, more literature on the DRA has appeared in recent decades. This literature
showed many investigators were active, and the number of publications has significantly
increased. These works have continued in the areas of compact designs, multi-band and
wideband designs, miniaturization techniques, and low-profile designs; in 1994, Mongiaet al.
demonstrated the radiation properties of a low-profile rectangular DRA with a very high
permittivity (r =100) [37], and Esselle studied a low-profile DRA of low-permittivity (r = 10.8)
[38]. For a long time, DRAs have concentrated on linear polarisation (LP), but systems using
circular polarisation (CP) are sometimes preferred because they are insensitive to the
transmitter and receiver orientations. In 1985, Haneishi & Takazawa presented the first CP
DRA [39]. Consequently, %%%%quotes detected%%%% more effort has been devoted to
the CP DRA in recent years.

A large part of this research includes the revision of new dielectric resonator antenna shapes,
including hexagonal, conical, elliptical, tetrahedral, and stairstepped shapes. Alternatives are
hybrid antenna designs, using dielectric resonator antennas in combination with microstrip
patches, slots, or monopoles. Many of the recent publications were concerned with
designing dielectric resonator antennas for specific applications, including integration into
mobile handsets for PCS, IMT-2000%%%%quotes detected%%%% , and WLAN applications;
use in UWB applications; radar applications; breast-cancer imaging; cellular base-station
antennas; RFID; spatial power combining; direction finding; and all-dielectric wireless
receivers. The literature has also investigated linear and planar array techniques for dielectric
resonator antennas, and ways of improving their manufacture and integration in systems.
CHAPTER 5
RESULTS AND SIMULATION

An antenna prototype%%%%quotes detected%%%% was fabricated using FR4 substrate as

shown in Figures. Illustrate the measured and simulated return loss of the Microwave range
antenna, which is plotted together with the simulated results for comparison purpose and
reasonable agreement between them is observed. The measured resonant frequencies of the
lower and upper bands are 1.80 GHz and 2.43 GHz respectively, which agree very well with
the HFSS simulated frequencies of f1 = 1.82 GHz (0.025 % error) and f2 = 2.4 GHz (1.25 %
error) . The measured bandwidths of the lower and upper bands%%%%quotes
detected%%%% are 8.3 % (1.72 - 1.87 GHz) and 3.7 % (2.39 - 2.48 GHz), respectively,
covering the entire DCS and (C, K, KU) bands. Figure 7 shows the maximum measured gain
versus frequency for the proposed antenna. The curve exhibits two peak VSWR of -59dBi and
-50dBi at 1.8 GHz and 2.4 GHz respectively. Figures. Shows the measured radiation patterns
of the proposed DRA at the two TE111 and TE113 mode frequencies. The figure, reveals that
the two resonant modes exhibit broadside radiation patterns and are very similar to each
other, which is desirable. For each resonant mode, the co-polarization field are stronger than
the cross-polarized counterparts by more than 20 dB in the broadside direction (° = 0). A
good asymmetry radiation pattern in the two plans E and H is observed. However, an
asymmetry in the H plane TE111 mode pattern is remarked at 70°. This shows that the effect
of the matching slot on radiation field is not significant

IX.CONCLUSIONS
The research work%%%%quotes detected%%%% in this thesis includes two major aspects
related to the dielectric resonator antennas (DRAs): The first part of the thesis describes
multifunction and diversity DRA implemented using a single dielectric resonator (DR), while
the second part of the thesis extends DRA research from microwave to the visible spectrum.
These two aspects are respectively based on two attractive features of DRAs,
•Various resonant modes can exist in a DR volume and each mode is related to different
radiation characteristics. The orthogonality of field distribution for the fundamental modes
builds the basis for realization of low coupling multi-mode design. The resonance frequency
and bandwidth of selected orthogonal modes can be designed to satisfy the desired
requirements by optimizing the DR geometry and the configuration of the feeding network.
•The high radiation efficiency of DRA has been experimentally proved in the millimetre wave
(MMW) frequency region due to the absence of the inherent conductor losses in DR. This
motivates further scaling towards optical frequencies, and suggests favourable performance
when compared%%%%quotes detected%%%% to metallic optical antennas.

Apart from these two features, other advantages of DRAs, including small size, light weight,
low cost, coupling to most transmission lines and design flexibility, allow for a wide range of
designs to satisfy specified requirements.
In light of these features, various DRAs have been proposed in the literature with enhanced
performance in terms of bandwidth, gain, radiation efficiency and functionality. It is noted
that a deep and thoughtful understanding of resonance frequency, ex- cited modes, and
impedance bandwidth and radiation characteristics is generally required to create novel
advanced designs. As basis for this understanding, the canonical DRA geometries, including
hemisphere, rectangle and cylinder, are the fundamental building blocks for all other
advanced DRA%%%%quotes detected%%%% geometries.
A compact CNT based cylindrical dielectric resonator antenna fed by a coaxial line has been
proposed and measured. The designed prototype has a dual-band operation suitable for both
DCS (1710 - 1880MHz) and Microwave (2400 - 2484MHz) applications. The compact CNT
based cylindrical directional antenna achieves a desirable directional radiation pattern with a
vswr of -59 dBi for the 1.8 GHz band and -50dBi for the 2.4 GHz band. It has a small size
which satisfies the new communication system requirements.
CHAPTER 6
CONCLUSION AND FUTURE WORK

6.1 Conclusions
Different shapes %%%%quotes detected%%%% of Dielectric resonator antennas have been
studied in this thesis. In the first part of the thesis an introduction of DRA about its
characteristics, advantages, applications and several bandwidth enhancement techniques
have been studied. Optimizations on the antenna parameters are also explained. The
following conclusions made as designed structures of DRAs, the same as follows.

A new %%%%quotes detected%%%% double back cylindrical dielectric resonator antenna is

realized by using Teflon and FR4 materials. The resonance of a CPW inductive feeding slot is
merged with that of a double back cylindrical DR so as to achieve required band for Wi-Fi
operation. The simulated results show that the designed antenna offered desired resonant
frequency at 2.4GHz, which covers the Wi-Fi application bands. This antenna provides
maximum Gain of 9.1557dBi. The proposed very compact Cylindrical DRA design is overall
suitable for wireless local area networks (WLAN).

Different shapes of DRAs like cylindrical DRA designed for different wireless applications with
unique CPW feeding. The Compact CPW Fed Dielectric Resonator Antenna having Peak Gain
is 1.097dBi at 2.4 GHz.

Also, the DRA is compared with circular patch antenna. The circular patch antenna offers gain
of 1.0067dBi at 2.4 GHz frequency. So, it can be concluded that the DRA offers high gain at
2.4GHz frequency%%%%quotes detected%%%% .

6.2 Future work

Based on observations, the following topics were identified which would helpful for further
investigation.
As operating frequencies continue to rise, DRAs becomes much more useful.

Need to develop integration techniques for fabrications.

DRA gain and directivities will be increased by using DRA Arrays.
Fabrications will be carried out of the remaining DRA designs.
Fabrication and measurements of stacked DRAs and other designed DRAs will be carried out
in future.
Since the impedance bandwidth of Dielectric resonator antenna can be enhanced by using
multiple DRAs (stacked, embedded and DRA array), design of dielectric resonator antenna
using DRA array, embedded technique will be carried out in future.

Designing the DRAs by utilizing stack shaped DRAs for getting multiple resonant frequencies
for different wireless applications.

Especially for getting wide bandwidths and UWB bands, designing of DRAs introducing with
air gap between ground and dielectric resonator will be carried out in future.

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