STUDY ON IMPROVED RADIATION PERFORMANCE CHARACTERISTICS OF FRACTAL ANTENNA FOR WIRELESS APPLICATIONS

STUDY ON IMPROVED RADIATION PERFORMANCE CHARACTERISTICS OF FRACTAL ANTENNA FOR WIRELESS APPLICATIONS

DEPT. OF ECE, SDMIT UJIRE

CHAPTER 1

Introduction

The term “wireless” is commonly used in the telecommunications industry to refer

to telecommunications systems (e.g., radio transmitters and receivers, remote controls,

computer networks, network terminals, etc.) which use some form of energy (e.g. Radio

frequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to transfer

information without the use of wires. Information is transferred in this manner over both

short and long distances. Applications may involve point-to-point communication, point-

to-multipoint communication, broadcasting, cellular networks and other wireless

networks.

Antenna is a very important component for the wireless communication systems

using radio frequency and microwaves. By definition, an antenna is a device used to

transform an RF signal, traveling on a conductor, into an electromagnetic wave in free

space. The IEEE Standard Definitions of Terms for Antennas (IEEE Standard 145-1983)

defines the antenna or aerial as “a means for radiating or receiving radio waves”. In other

words it is a transitional structure between free space and a guiding device that is made to

efficiently radiate and receive radiated electromagnetic waves. Antennas are commonly

used in radio, television broadcasting, cell phones, radar and other systems involving the

use of electromagnetic waves. Antennas demonstrate a property known as reciprocity,

which means that an antenna will maintain the same characteristics regardless if it is

transmitting or receiving.

With Advance of wireless communication systems and increasing importance of

other wireless applications, wide band and low profile antennas are in great demand for

both commercial and military applications. For antenna design that possess the following

highly desirable attributes: i) Compact size ii) Low profile iii) Conformal iv) Multiband

and broadband, there are a variety of approaches that have been developed over years,

which can be utilized to achieve one or more of these design objectives. The use of fractal

geometry is a solution to the design of multiband antennas. In recent years several fractal

geometries have been introduced for antenna applications with varying degrees of success

in improving antenna characteristics. Fractal represents a class of geometry with very

unique properties that are useful to antenna designers. The efficient packing of this

electrically large element constitutes a miniaturization technique to produce small-size

elements suitable for installation in portable telecommunication devices. The space filling



property, when applied to an antenna element, leads to an increase of electrical length.

The more convoluted and longer surface currents results in lowering the antenna resonant

frequency for a given overall extension of resonator. Therefore given a desired resonance

frequency, the physical size of the whole structure can be reduced. Method to improve the

antenna performance is by using the electromagnetic band gap (EBG) structure on

microstrip antenna. EBG structure are periodic lattices, which can provide effective and

flexible control over the propagation of the EM waves within a particular band. It has

been shown that this structure can lower input return loss and widen the impedance

bandwidth of microstrip antenna by suppressing the unwanted surface waves. The

inclusion of EBG in microstrip antenna design allows gain enhancement, enhanced

directivity, improved bandwidth and size miniaturization. Similarly, since microstrip

antennas are very versatile and are used, among other things, to synthesize a required

pattern that cannot be achieved with a single element. In addition, they are used to scan

the beam of an antenna system, increase the directivity, and perform various other

functions which would be difficult with any one single element. The elements can be fed

by a single line or by multiple lines in a feed network arrangement, so in this paper we

also used an array to develop the performance of this antenna.

1.1 Aim and Objectives

The aim of this project is to make a detailed study on the design and to study how

will the performance of Microstrip fractal antenna is improved with the introduction of

the two elemental array and EBG structure in the fractal antenna design using IE3D

software. In addition to this we also analyze the matching of practical and simulated

results.

1.2 Organization of the report

Antenna Basics

Microstrip Patch Antenna

Fractals

Design Specifications

Simulation and Results

Conclusion and Future Scope



CHAPTER 2

Antenna theory

2.1 Introduction

Communications has become the key to momentous changes in the organization

of businesses and industries as they themselves adjust to the shift to an information

economy. Information is indeed the lifeblood of modern economies and antennas provide

mother earth a solution to a wireless communication system.

The radio antenna is an essential component in any radio system. An antenna is a

device that provides a means for radiating or receiving radio waves. In other words, it

provides a transition from guided waves on a transmission line to a “free space” wave

(and vice versa in the receiving case). Thus information can be transferred between

different locations without any intervening structure. Furthermore, antennas are required

in situations where it is impossible, impractical or uneconomical to provide guiding

structures between the transmitter and the receiver.

A guided wave traveling along a transmission line, which opens out as in figure

2.1, will radiate as free space wave. The guided wave is a plane wave while the free space

wave is a spherically expanding wave. Along the uniform part of the line, energy is

guided, as a plane wave with little loss, provided the spacing between the wires is a small

fraction of a wavelength. At the right, as the transmission line separation approaches a

wavelength or more, the wave tends to be radiated so that the opened-out line acts like an

antenna, which launched the free space wave. The currents on the transmission line flow

out on the transmission line and end there, but the fields associated with them keep on

going. To be more explicit, the region of transition between the guided wave and the free

space wave may be defined as an antenna.

In this vast and dynamic field, the antenna technology has been an indispensable

partner of the communication revolution. Many major advances that took place over the

years are now in common use. Despite numerous challenges, the antenna technology has

grown with a fast pace to harass the electromagnetic spectrum, which is one of the

greatest gifts of nature.



Figure 2.1 Antenna as a Transition Device

2.2 Antenna Properties

An antenna is an electrical conductor or system of conductors

Transmitter – Radiates electromagnetic energy into space

Receiver – Collects electromagnetic energy from space

The IEEE definition of an antenna as given by Stutzman and Thiele is, “That part of a

transmitting or receiving system that is designed to radiate or receive electromagnetic

waves”.

The performance of the antenna is determined by several factors called antenna

properties are defined in following sections.

2.2.1 Antenna Gain

Gain is a measure of the ability of the antenna to direct the input power into

radiation in a particular direction and is measured at the peak radiation intensity. Consider

the power density radiated by an isotropic antenna with input power P0 at a distance R

which is given by S = P0/4πR2. An isotropic antenna radiates equally in all directions, and

it’s radiated power density S is found by dividing the radiated power by the area of the



sphere 4πR2. An isotropic radiator is considered to be 100% efficient. The gain of an

actual antenna increases the power density in the direction of the peak radiation:

Equation-2.1

Gain is achieved by directing the radiation away from other parts of the radiation sphere.

In general, gain is defined as the gain-biased pattern of the antenna.

Equation-2.2

2.2.2 Antenna directivity

Directivity is a measure of the concentration of radiation in the direction of the

maximum.

Equation-2.3

Directivity and gain differ only by the efficiency, but directivity is easily estimated from

patterns. Gain—directivity times efficiency—must be measured. The average radiation

intensity can be found from a surface integral over theradiation sphere of the radiation

intensity divided by 4π, the area of the sphere in steradians:

Equation-2.4

This is the radiated power divided by the area of a unit sphere. The radiation intensity

U(θ,φ) separates into a sum of co- and cross-polarization components:

Equation-2.5

Both co- and cross-polarization directivities can be defined:

Equation-2.6



Directivity can also be defined for an arbitrarydirection D(θ,φ) as radiation

intensitydivided by the average radiation intensity, butwhen the coordinate angles are

notspecified, we calculate directivity at Umax.

2.2.3 Antenna Efficiency

The surface integral of the radiation intensity over the radiation sphere divided by

the input power P0 is a measure of the relative power radiated by the antenna, or the

antenna efficiency.

Equation-2.7

where Pr is the radiated power. Material losses in the antenna or reflected power due to

poor impedance match reduce the radiated power.

2.2.4 Input Impedance

The input impedance of an antenna is defined as “the impedance presented by an

antenna at its terminals or the ratio of the voltage to the current at the pair of terminals or

the ratio of the appropriate components of the electric to magnetic fields at a point”.

Hence the impedance of the antenna can be written as given below.

Equation-2.8

Where,Zin is the antenna impedance at the terminals

Rin is the antenna resistance at the terminals

Xin is the antenna reactance at the terminals

The imaginary part, Xin of the input impedance represents the power stored in the

near field of the antenna. The resistive part, Rin of the input impedance consists of two

components, the radiation resistance Rr and the loss resistance RL. The power associated

with the radiation resistance is the power actually radiated by the antenna, while the

power dissipated in the loss resistance is lost as heat in the antenna itself due to dielectric

or conducting losses.

2.2.5 Polarization

The polarization of an antenna is the polarization of the wave radiated from the

antenna. Areceiving antenna has to be in the same polarization as the transmitting antenna

otherwise it will not resonate. Polarization is a property of the electromagnetic wave; it



describes the magnitude and direction of the electric field vector as a function of time,

with other words “the orientation of the electric field for a given position in space”. A

simple strait wire has one polarization when mounted vertically, and different polarization

when mounted horizontally figure (2.2). Polarization can be classified as linear, circular,

and elliptical.

In linear polarization the antenna radiates power in the plane of propagation, only

one plane, the antenna is vertically linear polarized when the electric field is

perpendicular to the earth’s surface, and horizontally linear polarized when the electric

field is parallel to the earth’s surface. Circular polarization antenna radiates power in all

planes in the direction of propagation(vertical, horizontal, and between them). The plane

of propagation rotates in circle making one complete cycle in one period of wave.

Figure 2.2 - Polarization of electromagnetic wave

2.2.6 Return Loss

It is a parameter which indicates the amount of power that is “lost” to the load and

does not return as a reflection. Hence the RL is a parameter to indicate how well the

matching between the transmitter and antenna has taken place. Simply put it is the S11 of

an antenna. A graph of S11 of an antenna vs frequency is called its return loss curve. For

optimum working such a graph must show a dip at the operating frequency and have a

minimum dB value at this frequency. This parameter was found to be of crucial

importance to our project as we sought to adjust the antenna dimensions for a fixed

operating frequency (say 1.9 GHz). A simple RL curve is shown in figure 2.1.

Figure 2.3 – RL curve of an antenna



2.2.7 Radiation Pattern

The radiation pattern of an antenna is a plot of the far-field radiation properties of

an antenna as a function of the spatial co-ordinates which are specified by the elevation

angle (θ) and the azimuth angle (φ) . More specifically it is a plot of the power radiated

from an antenna per unit solid angle which is nothing but the radiation intensity. It can be

plotted as a 3D graph or as a 2D polar or Cartesian slice of this 3D graph. It is an

extremely parameter as it shows the antenna’s directivity as well as gain at various points

in space. It serves as the signature of an antenna and one look at it is often enough to

realize the antenna that produced it.Because this parameter was so important to our

software simulations we needed to understand it completely. A general 3D radiation

pattern is also shown in figure 2.5.

Figure 2.4 – 2D Polar Plot Figure 2.5 – 3D Radiation Pattern

(Yagi antenna) (Rectangular Patch)

2.2.8 Beamwidth

Beamwidth of an antenna is easily determined from its 2D radiation pattern and is

also a very important parameter. Beamwidth is the angular separation of the half-power

points of the radiated pattern. The way in which beamwidth is determined is shown in

figure 2.6.

Figure 2.6 – Determination of HPBW from radiation pattern



2.3 Types of Antennas

Antennas can be classified in several ways. One way is the frequency band of

operation. Others include physical structure and electrical/electromagnetic design. Most

simple, non-directional antennas are basic dipoles or monopoles. More complex,

directional antennas consist of arrays of elements, such as dipoles, or use one active and

several passive elements, as in the Yagi antenna. New antenna technologies are being

developed that allow an antenna to rapidly change its pattern in response to changes in

direction of arrival of the received signal. These antennas and the supporting technology

are called adaptive or “smart” antennas and may be used for the higher frequency bands

in the future. A few commonly used antennas are described in the following sections.

2.3.1 Dipoles and Monopoles

The vertical dipole or its electromagnetic equivalent, the monopole could be

considered one of the best antennas for LMR applications. It is omni directional (in

azimuth) and, if it is a half-wavelength long, has a gain of 1.64 (or G = 2.15 dBi) in the

horizontal plane. A center- fed, vertical dipole is illustrated in figure 2.7 (a). Although

this is a simple antenna, it can be difficult to mount on a mast or vehicle. The ideal

vertical monopole is illustrated in figure 2.7 (b). It is half a dipole placed in half space,

with a perfectly conducting, infinite surface at the boundary.

Figure 2.7 - The vertical dipole and its electromagnetic equivalent, the vertical

monopole

2.3.2 Corner Reflector

An antenna comprised of one or more dipole elements in front of a corner

reflector, called the corner-reflector antenna, is illustrated in figure 2.8.



Figure 2.8 - Corner-reflector antennas

2.3.3 Yagi Antenna

Another antenna design that uses passive elements is the Yagi antenna. This

antenna, illustrated in figure 2.9, is inexpensive and effective. It can be constructed with

one or more (usually one or two) reflector elements and one or more (usually two or

more) director elements. Figure 2.10 shows a Yagi antenna with one reflector, a folded-

dipole active element, and seven directors, mounted for horizontal polarization.

Figure 2.9 - The Yagi antenna — (a) three elements and (b) multiple elements

Figure 2.10 - A Typical Yagi antenna



CHAPTER 3

Microstrip patch antennas

A microstrip antenna consists of conducting patch on a ground plane separated by

dielectric substrate. This concept was undeveloped until the revolution in electronic

circuit miniaturization and large-scale integration in 1970. After that many authors have

described the radiation from the ground plane by a dielectric substrate for different

configurations. The early work of Munson on micro strip antennas for use as a low profile

flush mounted antennas on rockets and missiles showed that this was a practical concept

for use in many antenna system problems. Various mathematical models were developed

for this antenna and its applications were extended to many other fields. The number of

papers, articles published in the journals for the last ten years, on these antennas shows

the importance gained by them. The micro strip antennas are the present day antenna

designer’s choice.

Low dielectric constant substrates are generally preferred for maximum radiation.

The conducting patch can take any shape but rectangular and circular configurations are

the most commonly used configuration. Other configurations are complex to analyze and

require heavy numerical computations. A microstrip antenna is characterized by its

Length, Width, Input impedance, and Gain and radiation patterns. Various parameters of

the microstrip antenna and its design considerations were discussed in the subsequent

chapters. The length of the antenna is nearly half wavelength in the dielectric; it is a very

critical parameter, which governs the resonant frequency of the antenna. There are no

hard and fast rules to find the width of the patch.

3.1 Waves on Microstrip

The mechanisms of transmission and radiation in a microstrip can be understood

by considering a point current source (Hertz dipole) located on top of the grounded

dielectric substrate (fig. 3.1) This source radiates electromagnetic waves. Depending on

the direction toward which waves are transmitted, they fall within three distinct

categories, each of which exhibits different behaviors.

Figure 3.1- Hertz dipole on a microstrip substrate



3.1.1 Surface Waves

The waves transmitted slightly downward, having elevation angles θ between

π/2and π -arcsin (1/√εr), meet the ground plane, which reflects them, and then meet the

dielectric-to-air boundary, which also reflects them (total reflection condition). The

magnitude of the field amplitudes builds up for some particular incidence angles that

leads to the excitation of a discrete set of surface wave modes; which are similar to the

modes in metallic waveguide.

The fields remain mostly trapped within the dielectric, decaying exponentially

above the interface (fig 3.2). The vector α, pointing upward, indicates the direction of

largest attenuation. The wave propagates horizontally along β, with little absorption in

good quality dielectric. With two directions of α and β orthogonal to each other, the wave

is a non-uniform plane wave. Surface waves spread out in cylindrical fashion around the

excitation point, with field amplitudes decreasing with distance (r), say1/r, more slowly

than space waves. The same guiding mechanism provides propagation within optical

fibers.

Surface waves take up some part of the signal’s energy, which does not reach the

intended user. The signal’s amplitude is thus reduced, contributing to an apparent

attenuation or a decrease in antenna efficiency. Additionally, surface waves also

introduce spurious coupling between different circuit or antenna elements. This effect

severely degrades the performance of microstrip filters because the parasitic interaction

reduces the isolation in the stop bands.

In large periodic phased arrays, the effect of surface wave coupling becomes

particularly obnoxious, and the array can neither transmit nor receive when it is pointed at

some particular directions (blind spots). This is due to a resonance phenomenon, when the

surface waves excite in synchronism the Floquet modes of the periodic structure. Surface

waves reaching the outer boundaries of an open microstrip structure are reflected and

diffracted by the edges. The diffracted waves provide an additional contribution to

radiation, degrading the antenna pattern by raising the side lobe and the cross polarization

levels. Surface wave effects are mostly negative, for circuits and for antennas, so their

excitation should be suppressed if possible.

Figure 3.2 – Surface waves



3.1.2 Leaky Waves

Waves directed more sharply downward, with θ angles between π - arcsin (1/√εr)

and π, are also reflected by the ground plane but only partially by the dielectric-to-air

boundary. They progressively leak from the substrate into the air (Fig 3.3), hence their

name laky waves, and eventually contribute to radiation. The leaky waves are also non-

uniform plane waves for which the attenuation direction α points downward, which may

appear to be rather odd; the amplitude of the waves increases as one moves away from the

dielectric surface. This apparent paradox is easily understood by looking at the figure 3.3;

actually, the field amplitude increases as one move away from the substrate because the

wave radiates from a point where the signal amplitude is larger. Since the structure is

finite, this apparent divergent behavior can only exist locally, and the wave vanishes

abruptly as one crosses the trajectory of the first ray in the figure.

In more complex structures made with several layers of different dielectrics, leaky

waves can be used to increase the apparent antenna size and thus provide a larger gain.

This occurs for favorable stacking arrangements and at a particular frequency.

Conversely, leaky waves are not excited in some other multilayer structures.

Figure 3.3 – Leaky waves

3.1.3 Guided Waves

When realizing printed circuits, one locally adds a metal layer on top of the

substrate, which modifies the geometry, introducing an additional reflecting boundary.

Waves directed into the dielectric located under the upper conductor bounce back and

forth on the metal boundaries, which form a parallel plate waveguide. The waves in the

metallic guide can only exist for some particular values of the angle of incidence, forming

a discrete set of waveguide modes. The guided waves provide the normal operation of all

transmission lines and circuits, in which the electromagnetic fields are mostly

concentrated in the volume below the upper conductor. On the other hand, this buildup of

electromagnetic energy is not favorable for patch antennas, which behave like resonators

with a limited frequency bandwidth.



3.2 Patch antennas

Microstrip patch antennas are the most common form of printed antennas. They

are popular for their low profile, geometry and low cost.A microstrip device in its

simplest form is a layered structure with two parallel conductors separated by a thin

dielectric substrate. The lower conductor acts as a ground plane. The device becomes a

radiating microstrip antenna when the upper conductor is a patch with a length that is an

appreciable fraction of a wavelength (λ), approximately half a wavelength (λ / 2). In other

words, 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 Fig. 3.4.

Figure 3.4 - Typical microstrip patch antenna

The patch is generally made of conducting material such as copper or gold and can take

any possible shape. Some of the typical patch shapes are shown in Fig. 3.5.

Figure 3.5 - Different shapes and sizes of patch

The radiating patch and the feed lines are usually photo etched on the dielectric

substrate. Microstrip patch antennas radiate primarily because of the fringing fields

between the patch edge and the ground plane. Microstrip patch antennas have many

advantages when compared to conventional antennas. As such, they have found usage in

a wide variety of applications ranging from embedded antennas such as in a cellular



phone, pagers etc. to telemetry and communication antennas on missiles and in satellite

communications.

Some of their principal advantages are,

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

In spite of the many advantages, these antennas also suffer from a number of

disadvantages.

Some of these disadvantages are,

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.

3.3 Feed Techniques for Patch Antennas

Microstrip antennas are fed by a variety of methods that are broadly classified into

two main categories, namely, contacting and non-contacting. In the contacting method,

the RF power is fed directly to the radiating patch using a connecting element such as a

microstrip line. In the non-contacting method, electromagnetic field coupling is done to

transfer power between the microstrip line and the radiating patch.

The four most popular feed techniques used are the microstrip line, coaxial probe

(both contacting schemes), aperture coupling and proximity coupling (both non-

contacting schemes). These are discussed in subsequent sections.



3.3.1 Microstrip Line Feed

This type of feed technique excitation of the antenna would be by the Microstrip

line of the same substrate as the patch that is here can be considered as an extension to the

Microstrip line, and these both can be fabricated simultaneously. This conducting strip is

directly connected to the edge of the Micro strip patch. , as known the conducting strip is

smaller than that of the patch in width. This type of structure has actually an advantage of

feeding the directly done to the same substrate to yield a planar structure as said above.

The coupling between the Microstrip line and the patch is in the form of the edge or butt-

in coupling as shown in the figure. Or it is through a gap between them.

Figure 3.6 - A Type of Microstrip feed and the corresponding equivalent circuits,

Microstrip feed at a radiating edge

Figure 3.7 - Rectangular microstrip patch antenna

3.3.2 Coaxial Feed

The coaxial feed or probe feed is a very common contacting scheme of feeding

patch antennas. The configuration of a coaxial feed is shown in Fig.3.8. As seen from Fig.

3.8, the inner conductor of the coaxial connector extends through the dielectric and is



soldered to the radiating patch, while the outer conductor is connected to the ground

plane.

Figure 3.8 – coaxial feed

The main advantage of this type of feeding scheme is that the feed can be placed

at any desired location inside the patch in order to match with its input impedance. This

feed method is easy to fabricate and has low spurious radiation

As we are using only probe feed and linefeed techniques in our design, we do not

discuss further about other remaining methods of feeding here.

3.4 Methods of Analysis for Patch Antennas

The most popular models for 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.

3.4.1 Transmission Line Model –Radiation mechanism

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. A typical microstrip



line is shown in Fig. 3.9 while the electric field lines associated with it are shown in Fig.

3.10.

Figure 3.9 - Physical and effective length of a microstrip patch

Figure 3.10 - Electric field lines

As seen from Fig. 3.10, most of the electric field lines reside in the substrate while

some electric field lines exist in the 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 Fig. 3.10 above. The expression for εreff is given as:

Equation - 3.1

Where εreff denotes effective dielectric constant, εr stands for dielectric constant of

substrate, h represents height of dielectric substrate, and W identifies width of the patch.



Figure 3.11 shows the transmission line model for patch antenna, where Fig.

3.11(a) is the patch antenna, Fig. 3.11(b) is the top view and Fig. 3.11(c) is the side view

of the antenna.

(a) Microstrip patch antenna

(b) Top view of antenna (c) Side view of antenna

Figure 3.11 - Transmission line model for patch antenna

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 λ0 / εreff, where λ0is the free space wavelength. The TM10 model implies that the field

varies one λ / 2 cycle along the length and there is no variation along the width of the

patch. In Fig. 3.11(b) shown above, 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 Fig 3.11(c) 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 and hence they cancel each other in the broadside direction. The tangential

components (seen in Fig 3.11(c)), 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 areλ / 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.

3.5 Microstrip antenna arrays

An antenna array is a system of similar antennas oriented similarly to get greater

directivity in described direction. In other words, it is a radiating system consisting of

several spaced and properly phased radiators. In many microstrip antenna applications,

system requirements can be met with a single patch element. In other cases, however

systems require higher antenna gains while maintaining low profile structures, which calls

for the development of microstrip arrays. Microstrip arrays due to their extremely thin

profiles offers 3 outstanding advantages relative to other type of antennas, low weight,

low profile, with conformability and low manufacturing cost.

A microstrip array is the integration of microstrip element with a coaxial feed. It

may be classified in many ways. The spectral distribution of elements is common

classification: array may be linear planar or volume. The advantages of microstrip

antennas appear when all the elements of the array along with the feed network are

monolithically etched from one side of the printed circuit board they are,

The process of photo etching hundred’s as even thousands of microwave

components in one process result in a low cost antenna array.

The resulting printed circuit board is very thin. Since the array is designed to

operate from the ground place on the back of the printed board, its performance is

unaffected by mounting to a metallic surface such as an aircraft or a missile. The

resulting design is doubly conformal. It is conformal to underlying structure to



which it can be bolted or laminated and it is extremely conformal aerodynamically

because of minimum protrusion.

Microstrip arrays have high performance because an infinite variety and quantity

of antenna elements power dividers, matching sections, phasing sections etc. can

be added to printed circuit board without any cost impact. This gives the design

engineer many components that are not commercially available in separate

packages.

The microstrip array is very reliable since the entire array is one continuous piece

of copper.

However, microstrip antennas arrays also have some disadvantages as,

Narrow bandwidth (by using optimization, the bandwidth can be increase).

Poor isolation between feed and radiating elements.

Possibility of excitation of surface waves.

Low efficiency due to high loss mainly in feeding network

Larger size

Higher cost

To minimize these effects, accurate analysis techniques optimum design methods

and innovative array concepts are imperative to the successful of microstrip array

antennas.

There are various types of antenna can be design by using array technique such as

dual band microstrip antenna, multiband microstrip antenna and ultra-wide band antenna.

Below are the figures of some application of array structure:

Figure 3.12 - Dual band microstrip antenna



Figure 3.13 - Ultra wideband antenna

For the previous figures, inset feed technique is used as a feeding technique for all

elements in array. To minimize the losses at the transmission lines, quarter wave length

transformer matching technique is used together with power divider. By using power

divider, the supply current can be divided equally to each patch means that each patch can

radiates power equally. Referring to the above figures, the usage of power divider is not

needed.

3.6 Electromagnetic Band Gap (EBG) structure

In recent years, there has been growing interest in utilizing electromagnetic band-

gap (EBG) structures in the electromagnetic and antenna community. The EBG

terminology has been suggested based on the photonic band-gap (PBG) phenomena in

optics that are realized by periodical structures. There are diverse forms of EBG

structures design such as EBG structures integrated with active device and multilayer

EBG structures.

Electromagnetic Band Gap (EBG) always referred as photonic band gap (PBG)

surface or high impedance surface. This structure is compact which has good potential to

build low profile and high efficiency antenna surface. The main advantage of EBG

structure is their ability to suppress the surface wave current. The generation of surface

waves decreases the antenna efficiency and degrades the antenna pattern. Furthermore, it

increases the mutual coupling of the antenna array which causes the blind angle of a

scanning array. The feature of surface-wave suppression helps to improve antenna’s

performance such as increasing the antenna gain and less power wasted when reducing

backward direction. There are two types of EBG structure to be discussed. Firstly is

Perforated dielectric and the second one is Metallodielectric structures. Perforated

dielectric is defined as effectively suppress unwanted substrate mode commonly exist in



microstrip antenna. This structure designed by drill periodic holes on dielectric subtracts

to introduce another dielectric but in practical, this structure is difficult to implement.

Metallodielectric structure is exhibits an attractive reflection phase future where the

reflected field change continuously from 180 degrees to -180 degrees versus frequency. It

was allow a low profile wire antenna to radiate efficiently with enhance bandwidth,

radiation pattern, gain, reduce back radiation and reduce size lobe.

EBG structure can be design by various shapes and every shape will have

different frequency band gap. Something special of the EBG structure is it can be

designed which has a characteristic whether it is inductive or more capacitive.

3.6.1 Suppression of surface waves by EBG structure

Surface wave propagation is a serious problem in microstrip antennas. Surface

waves reduce antenna efficiency and gain, limit bandwidth, increase end-fire radiation,

increase cross-polarization levels, and limit the applicable frequency range of microstrip

antennas.Two solutions to the surface wave problem are available now. One of the

approaches is based on the micromachining technology in which part of the substrate

beneath the radiating element is removed to realize a low efficiency dielectric constant

environment for the antenna. In this case the power loss through surface wave excitation

is reduced and coupling of power to the space wave enhanced. The second technique

relies on photonics band gap (PBG) engineering. In this case, the substrate is periodically

loaded so that the surface wave dispersion diagram presents a forbidden frequency range

(stop band or band gap) about the antenna operating frequency. Because the surface

waves cannot propagate along the substrate, an increase amount of radiating power

couples to the space waves. Also, other surface wave coupling effects like mutual

coupling between array elements and interference with onboard systems are now absent.

The figure below shows the blocking of propagation surface wave on waveguide by using

EBG (PBG) structure.

Figure 3.14 - The blocking of propagation surface wave by EBG structure



Photonics band gap materials are new class of periodic dielectrics, which arethe

photonics analogs of semiconductors. Electromagnetic waves behave in photonics

substrates as electrons behave in semiconductors. Various type of periodic loading of

substrates has been studied to realize the PBG nature of the substrate. Early attempts

involved drilling a periodic pattern of holes in the substrate or etching a periodic pattern

of circle in the ground plane. Next, a periodic pattern of the metallic pads was shorted to

the ground plane with vias. Recently, a new loading pattern has been studied. This type of

planar or 2-D loading is simple to realize (no via are necessary) and is compatible with

standard monolithic microwaves integrated circuit fabrication technology.

The transmission coefficient of a PBG substrate is characterized by a band gap or

stop band region. The transmission and reflection coefficient of a microstrip line in PBG

substrate with circles etched in the ground plane are shown like figure 3.16.

Figure 3.15 - Square lattice of etched circles Figure 3.16 – Square lattice of small

in the ground plane metal pads with grounding vias in the

center

3.6.2 Principle of Electromagnetic Band Gap (EBG) structure

The basic design of EBG structure is shown in figure 3.17 known as mushroom

like EBG structure. This structure has frequency range where the surface impedance is

very high. The equivalent LC circuit acts as a two-dimensional electric filter in this range

of frequency to block the flow of the surface waves. The central frequency of the band

gap is shown in equation 3.2. The inductor L results from the current flowing through the

vias, and the capacitor C due to the gap effect between the adjacent patches. Thus, the

approach to increase the inductance or capacitance will naturally result in the decrease of

band-gap position.



Figure 3.17 - 2D EBG structure

Central frequency of the band gap is given by;

Equation – 3.2

Where;

Equation – 3.3

Equation – 3.4

The bandwidth of the electromagnetic band gap is given by;

Equation – 3.5

Therefore, the antenna with EBG structure operates at a lower frequency compared to the

antenna without EBG structure. Normally, when design the microstrip antenna operates at

lower frequency, the larger size of substrate needed. So, the EBG structure can reduce the

size of the antenna and the fabrication cost. Next, the EBG structure can enhance the

bandwidth of the original antenna structure.



CHAPTER 4

Fractals

“A fractal is a shape made of parts similar to the whole in some way”

4.1 Fractal’s Definition

According to Webster’s Dictionary a fractal is defined as being “derived from the

Latin fractus meaning broken, uneven: any of various extremely irregular curves or shape

that repeat themselves at any scale on which they are examined.”

4.2 Why Fractal Antennas?

The relationship of the physical size of the antenna to its operating wavelength is a

fundamental parameter in antenna design. The physical size of an antenna is generally

half or quarter of its operating free space wavelength, and the range of frequencies over

which the antenna operate satisfactorily is normally 10-40% of this center wavelength.

This range of frequencies is generally called the bandwidth of the antenna. Making the

dimensions of the antenna much smaller than its operating wavelength will reduce its

radiation resistance, efficiency and bandwidth.

Fractal geometry due to its self-similarity property can overcome this limitation of

antenna size and its operating wavelength, that is, fractal antennas can be much smaller

size than the operating wavelength without seriously affecting the other antenna

parameters. Also antennas based on fractal geometry display multiband behavior, not

easily available in conventional antenna design.

In summary, the compact size of the fractal antenna (relative to its operating

wavelength) and its multiband behavior makes it’s very useful in current

telecommunication industry.

4.3 Basics of Fractals

In the study of antennas, fractal antenna theory is a relatively new area. The term

“fractal” means broken or irregular fragments. It was originally coined by Mandelbrot

(1983) to describe a family of complex shapes that possess an inherent self-similarity or

self-affinity in their geometrical structure. Jiggered (1990) defined fractal

electrodynamics as an area in which fractal geometry was combined with electromagnetic



theory for the purpose of investigating a new class of radiation, propagation and

scattering problems. One of the most promising area fractal electrodynamics re-searches

is in its application to antenna theory and design. There are varieties of approaches that

have been developed over the years, which can be utilized to archive one or more of these

design objectives. The development of fractal geometry came largely from an in depth

study of the pattern nature, with the advance of wireless communication system and their

increasing importance wide band and low profile antennas are in great demand for both

commercial and military applications. A fractal is a rough or fragmented geometric shape

that can be split into parts, each of which is a reduced-size copy of the whole and this

property is called self -similarity. Fractal geometries are composite designs that repeat

themselves or their statistical characteristics and are thus “self-similar” fractal geometry

finds a variety of applications in engineering. Fractal geometry is space filling contours of

regular or irregular shapes, and is super imposed of too much iteration and they describe

the self-similar property of fractal geometry. Fractals are a class of shapes which have not

characteristic size. Each fractal is composed of multiple iterations of a single elementary

shape the iteration can continue infinitely, thus forming a shape within a finite boundary

but of infinite length or area.

4.4 Main features of fractals

It has a finite structure at arbitrarily small scales

It is too irregular to be easily described in traditional Euclidean geometric

It is self-similar

Simple and recursive.

Modern telecommunication systems require the antenna with wider bandwidth

and smaller dimension than conventionally possible. This has initiated antenna research in

various directions, are of which is by using fractal shaped antenna elements. In recent

years several fractal geometries have been introduced for antenna application with

varying degree of success in improving antenna characteristics. Some of these geometries

have been particularly useful in reducing the size of the antenna, while other designs aim

at incorporating multiband characteristics. These are low profile antennas with moderate

gain and can be made operative at multiple frequency bands and hence are

multifunctional. In our present work we focus on generation of multi frequency which

yields increases the bandwidth and size reduction of antenna. A plus shape patch is taken



as a base shape and in first iteration four other plus shape patches of the order of 1/3 of

base shape are placed touching the base shape. Similarly second iterations are taken by

further placing plus shaped patches at even reduced scales. It is found that as the iteration

number and iteration factor increases, the resonance frequencies become lower than those

of the zero iteration, which represents a conventional plus shape patch.

4.5 Self-similar fractals

The explosive growth of wireless systems and booming demand for a variety of

new wireless applications have renewed interest in multiband antennas. The most recent

multi-band antenna development is based upon the exploitation of the self-similarity

property of fractal shapes. A self-similar set is one that consists of scaled down copies of

itself, i.e., a contraction which reduces an image by same factors horizontally and

vertically.

(a) (b) (c)

(d)

Figure 4.1 - Self- similar Fractal structures (a) initiator (b) 1st iteration (c) 2nd

iteration (d) 3rd iteration

In mathematics, a self- similar object is exactly or approximately similar to a part of itself

(i.e. the whole has the same shape as one or more of the parts).



4.6 Self-affine fractals

This fractal is self- affine instead of self-similar because the pieces are scaled by

different amounts in the x- and y-directions. A rescaling procedure used in fractal

geometry and performed on a two variable system. For example, in a system utilizing an

x-axis and y- axis representing time and price, the x-axis could be rescaled by one ratio

and/or procedure while the y-axis is rescaled by a different ratio and/or procedure.

(a) (b)

(c) (d)

Figure 4.2 - Self- affine Fractal structures (a) initiator (b) 1st iteration (c) 2nd

iteration (d) 3rd iteration

A Self-affine set, on the other hand, is a contraction which reduces an image by

different factors, horizontally and vertically. Thus, it can provide additional flexibility in

the antenna design, since by selecting the scale factors appropriately, resonances can be

spaced by different factors.

4.7 Type of fractal antennas

4.7.1 Koch curve

The Koch fractal curve is one of the most well-known fractal shapes. It consists of

repeated application of the IFS. The Koch curve is shown in Figure 4.3. Each iteration

adds length to the total curve which results in a total length that is 4/3 the length of Koch

curve and is given by



L = (4

3)k

Equation – 4.1

Here k is the iteration stage.

Figure 4.3: Koch Curve

4.7.2 Sierpinski gasket

The Sierpinski gasket or triangle is generated by using triangle as the basic

function shape. The Sierpinski Gasket fractal is generated by the IFS method and Figure

4.4 shows the step generation of Sierpinski gasket

Figure 4.4: Sierpinski gasket

4.7.3 Sierpinski carpet

The Sierpinski carpet is shown in Figure 4.5, it uses a square instead of the

triangle as the basic function shape.

Figure 4.5: Sierpinski carpet iterative constriction



4.8 Advantages and applications

4.8.1 Advantages

Very broadband and multiband frequency response that derives from the inherent

properties of the fractal geometry of the antenna.

Compact size compared to antennas of conventional designs, while maintaining

good to excellent efficiencies and gains.

Mechanical simplicity and robustness.

Design to particular multi frequency characteristics containing specified stop

bands as well as specific multiple pass bands.

The wideband capability of fractal antennas allows smaller antennas that have

from 10:1 to 200:1 bandwidths that can handle moderate to high power.

4.8.2 Applications

Fractal antennas provide optimal design solutions for commercial applications

like-wireless network, telematics, RFID, portable devices, automated meter

reading.

It is used in defense applications such as electronic warfare, signal intelligence,

tactical communications.

4.8.3 Some of the Disadvantages of fractals

Complexity in modeling the antenna

The benefit begin to diminish after first few iterations



CHAPTER 5

Antenna design

5.1 Design Specifications

The three essential parameters for the design of a rectangular Microstrip Patch Antenna

are:

Frequency of operation (fₒ): The resonant frequency of the antenna must be selected

according to our applications. We use the resonating frequency as 2 GHz for our

design. This frequency range is used for wireless applications.

Dielectric constant of the substrate (εr): Glass Epoxy is used in our design with

dielectric constant of 4.4.

Height of dielectric substrate (h): Height of dielectric substrate controls the

bandwidth. The value of h used in our design is 1.6mm.

Hence the essential parameter values for our design are:

fₒ=2GHz

εr=4.4

h=1.6mm

Figure 5.1 – Microstrip Antenna

Step 1: Calculation of the Width (W):

The width of the Microstrip patch antenna is given by equation (5.1) as

Equation – 5.1

Substituting c = 3e8 m/s, εr= 4.4 and fₒ = 2GHz, we get

W=45.6mm.



Step 2: Calculation of Effective Dielectric constant (εreff):

Equation (5.2) gives the effective Dielectric constant as

Equation – 5.2

Substituting εr = 4.4, W = 45.6mm and h = 1.6mm we get

εreff = 4.126.

Step 3: Calculation of Effective length (Leff):

Equation (5.3) gives the effective length as:

Equation – 5.3

Substituting c = 3e8 m/s, εreff = 4.126 and fₒ = 2GHz, we get

Leff = 36.92mm.

Step 4: Calculation of length extension (ΔL):

Equation (5.4) gives the length extension as:

Equation – 5.4

Substituting εreff = 4.126, W= 45.6mm and h = 1.6mm we get:

ΔL = 0.0740mm.

Step 5: Calculation of actual length of patch (L):

The actual length is obtained by re-writing equation (5.5) as:

L = Leff-2ΔL Equation - 5.5

Substituting Leff = 36.92mm and ΔL = 0.0740mm we get:

L=35.44mm.

Step 6: Calculation of actual length of patch (L):

The actual length is obtained by re-writing equation (5.5) as:

L = Leff - 2ΔL Equation - 5.6

Substituting Leff = 36.92mm and ΔL = 0.0740mm we get:



L=35.44mm.

Step 7: Design of 50Ω micro strip feed line:

For Zo=50Ω, εr=4.4

W/d= 8eA/e2A-2; for w/d>2 Equation- 5.7

2/π [B-1-ln (2B-1) +εr-1/2 εr ln (B-1)+0.39-(0.61/ εr); for w/d<2

Where, A= Zo (εr+1)1/2/120 + (εr-1)/ (εr+1)[0.23+0.11/ εr] and B=377π/2Zoεr1/2

Let us assume w/d<2, &after calculation B=5.643

Therefore w/d=1.9133;

Width of feed line Wf 50=W=1.6×10-3×1.9133=0.3061cm

Step 8: Design of length of feed line:

λg = λ0/εeff1/2; where εeff = εr-[ εr - εe/1+G(f/fp)];G=( Zo-5/60)1/2 +0.004Zo Equation-5.8

fp= Zo/2µ0h

Therefore G=1.066025 and fp=12.434GHz and εeff =4.1336 hence λg=7.37cm

Therefore Lf50= λg/4=1.8445cm

Step 9: Length of quarter wave transformer:

In this case select Zo= (Zin×Zt) 1/2=112.6131Ω where Zin=243.550Ω and Zt=50 Ω

Now G = (Zo-5/60)1/2+0.004, Zo=1.78968

For 2GHzεe=4.126, therefore using above formulas fp=2.0045GHz, εeff=4.1247,

λg=7.3823cm.Therefore Lt= λg/4=1.456cm

Step 10: Width of quarter wave transformer:

A=Zo (εr+1)1/2/120+ εr-1/ εr+1[0.23+0.11/ εr] and W/d= 8eA/e2A-2;

Substituting Zo and εr we get A= 2.3413 therefore W/d= .078413

Therefore width of quarter wave transformer Wt =W=1.6×10-3×0.78413=1.2546mm

Step 11: Calculation of the ground plane dimensions (Lg, Wg):

The transmission line model is applicable to infinite ground planes only. However, for

practical considerations, it is essential to have a finite ground plane. It has been shown in

many open literatures that similar results for finite and infinite ground planes can be

obtained if the size of the ground plane is greater than the patch dimensions by



approximately six times the substrate thickness all around the periphery. Hence, for this

design, the ground plane dimensions would be given as:

Lg = 6h + L=6 (1.6) + 72.33=81.93mm Equation – 5.9

Wg = 6h + W=6 (1.6) + 45.6=55.2mm Equation – 5.10

5.2 Software Tool Used: ZEALAND IE3D

The electromagnetic simulation software adopted is Zealand’s IE3D. IE3D is an

integrated full wave electromagnetic simulation and optimization package for the analysis

and design of 3-D Microstrip antennas, microwave and millimeter-wave integrated

circuits and high speed printed circuit board.

5.3Applications of IE3D

It is used for the design of

Microwave circuits and MMICs.

RF circuits and RFIDs.

Microwave, RF and wireless antennas.

PCB, electronic packaging and signal integrity.



5.4 Project Flow

Figure 5.1 – Flow Diagram of the Project

START

LITERATURE

Review

Dimension Calculation

Design in Zealand IE3D Software

Simulation

Analysis

Expected

Results?

Fabricate

Measurement using

Network Analyzer

Comparing simulation

And practical result

Analysis and report

Writing

END



5.5 Hardware Tool Used: Network Analyzer E5062A

The testing of antenna is done using E5062A which is a Two Port Vector Network

Analyzer from Agilent technologies. The ENA series vector network analyzer provides

the best combination of speed and accuracy for measuring multiport and balanced

components such as fibers, duplexers and RF modules up to 3GHz. A vector analyzer

provides a simple and complete vector network measurement in a compact, fully

integrated RF network. E5062A vector network analyzer offers built-in source, receiver

and s-parameter test set covering frequencies from 300 KHz to 3GHZ.

Figure 5.2 Network Analyzer



CHAPTER 6

Simulated and practical results

We have designed two antennas with 2 iterations on each antenna along with base

reference antenna. Here are our antennas with their nomenclature.

Antenna 1 (Fig 6.1 to 6.12)

Here we have taken rectangular patch as the reference antenna and carried out

2 further iterations on it with a scale factor of 1/4 to form self – affine fractal geometry on

reference antenna along with EBG structure.

Antenna 2 (Fig 6.13 to 6.32)

Here we have taken 2 rectangular patches as a 2-elemental reference antenna

array and carried out three further iterations on it with scaling factor of 1/3 to form plus

shaped self - similar fractal geometry from reference array. Here microstrip feed method

is used.



Reference Antenna with EBG structure

Figure 6.1 – Software design Figure 6.2 – Hardware Design

S- Parameter display of Reference antenna with EBG

Figure 6.3–Simulated Result Figure 6.4 – Practical Result

Base Antenna with EBG structure (Self-Affine Geometry)

Figure 6.5 - Software design Figure 6.6 – Hardware Design



S- Parameter Display of Base Antenna with EBG structure

(Self-Affine Geometry)

Figure 6.7 - Simulated Result Figure 6.8 -Practical Result

Antenna 1st Iteration with EBG structure (Self-Affine Geometry)

Figure 6.9–Software design Figure 6.10 – Hardware Design

S- Parameter Display of 1st iteration with EBG structure

(Self-Affine Geometry)

Figure 6.11 - Simulated Result Figure 6.12 - Practical Result



Reference array antenna

Figure 6.13 – Software Design

Figure 6.14 – Hardware Design

S- Parameter Display of Reference Antenna array

Figure 6.15 – Simulated Result

Figure 6.16 - Practical Result



Base array antenna without slot (Self-Similar Geometry)



S- Parameter Display of Base Antenna array without slot

(Self-Similar Geometry)


Figure 6.20–Practical Result



Base array antenna with slot (1mm, 21.82mm)

(Self-similar Geometry)

Figure 6.21–Software Design


S- Parameter Display of Base Antenna array with slot (1mm, 21.82mm)






1st iteration of Antenna array with slot (1mm, 21.82mm)




S- Parameter Display of 1st iteration with slot (1mm, 21.82mm)


Figure 6.27 - Simulated Result




2nd iteration of Antenna array with slot (1mm, 21.82mm)




S- Parameter Display of 2nd iteration with slot (1mm, 21.82mm)






Comparison of gain in single element antenna and 2 - element array

Antenna

Figure 6.33 – Gain of Single Element Figure 6.34 – Gain of Antenna Array

Comparison of gain in Antenna Reference with and without EBG

Figure 6.35 – Gain without EBG Figure 6.36 - Gain with EBG

Here we can see that by the use of 2 – Elemental array for antenna design, the gain

of the antenna has been improved by a factor of 3 compared to single element antenna

reference. Similarly, we got gain improvement with other iterations of design. Hence, we

can conclude that performance of single element antenna will improve with the increase

in the number of antenna elements used in the antenna design.

In a similar way, when we compared the gains of antenna with EBG structure and

antenna without EBG structure, gain of the antenna is been improved with the EBG

structure by a factor of around 2. Therefore we can conclude that, the use of EBG

structure in the antenna design will improve its performance in a good manner.



COMPARISION OF SIMULATED AND PRACTICAL

RESULTS

ANTENNA

NAME

SIMULATED RESULT

PRACTICAL RESULT

FREQUENCY

(GHz)

RETURN

LOSS

(dB)

FREQUENCY

(GHz)

RETURN

LOSS

(dB)

ANTENNA ARRAY

Reference

1.99 -15.48 1.98 -21.79

Base antenna

without slot

2.25 -13 2.31 -13.91

Base antenna

with slot

1.26 -33.24 1.36 -12.96

1st Iteration

1.03 -23.84 1.09 -16.10

2nd Iteration

0.97 -17.60 1.03 -18.39

ANTENNA WITH EBG

Base antenna

1.98 -17.57 1.98 -15.26

1st Iteration

1.17 -17.96 1.19 -12.90

2nd Iteration

1.14 -12.14 1.17 -17.50



CONCLUSION

Rectangular microstrip antenna array and rectangular microstrip antenna with

square EBG structure are designed using the appropriate design formulae and is

fabricated using quick fabrication procedure, then it is tested using the vector network

analyzer E5062A. The antenna design is worked out at frequency 2GHz frequency. When

tested practically it was properly matching with designed frequency.

In this report, a novel electromagnetic band gap structure (EBGs) is proposed. A

fractal microstrip antenna is implemented using the EBGs as a ground plane, and the

measured results show that the reduction in the surface wave level is remarkable.

Compared with the reference antenna at improvement of the return loss is achieved, and

the back lobe is reduced. Thus considerable size reduction& a total bandwidth are

achieved. In addition to this, use of array in our design resulted in improved radiation

with enhance bandwidth and good return loss. Simulation is carried out using IE3D

software and it is found that simulated results are in good agreement with the

experimental results.

The dielectric constant plays a major role in the overall performance of a patch

antenna. It affects both the width, in turn the characteristic impedance and the length

resulting in an altered resonant frequency. We have used the fiber glass substrate (glass

epoxy) but the permittivity (εr) alters from batch to batch sometimes even between

different sheets of substrates.

As we have implemented antenna arrays using fractal geometry to improve the

performance of single element antenna, traditional wideband antennas (spiral and log –

periodic) can be analyzed with fractal geometry to shed new light on their operating

principles. In addition to this, EBG structure of different shapes (like plus shape, spiral

shape etc.) can analyzed with antenna elements with good multiband and improved

characteristics.



FUTURE SCOPE

In our project, aim of improving the performance (Ex: gain, directivity, return loss) of the

antenna is achieved.

Future challenges of a Microstrip antenna are:

Bandwidth Extension Techniques

Control of Radiation Patterns

Reducing Losses/increasing efficiency

Improving feed networks

Size reduction techniques:

The bandwidth can be increased as follows

By increasing the thickness of the substrate

By use of high dielectric constant of the substrate so that physical dimensions of

the parallel plate transmission line decreases.

By increasing the inductance of the micro strip by cutting holes or slots in it.

By adding reactive components to reduce the VSWR

In order to increase the directivity of the micro strip antennas multiple Microstrip

radiators are used to cascade to form an array.

There are several methods to implement the antenna design with the use of

different fractal geometries like Koch curves, Hilbert structures etc., different number of

antenna elements in the design and also different types of EBG structures (Ex: plus

shaped EBG, hexagonal EBGs, circular shapes etc.).Therefore we can further improve

our design by using different implementations in our design and by using metallic vias in

our design in the future.



REFERENCES

[1] IE3D User’s Manual, Release 9, Zealand software, Inc.

[2] “Bandwidth enhancement of dual patch microstrip antenna array using dummy EBG

patterns on feedline” by MANIK GUJRAL B.Eng. (Hons.), NUS in 2007.

[3] “Design and Analysis of Microstrip Patch Antenna Arrays” – Ahmed Fatthi Alsager.

[4] “Design and Simulation of Multiband Microstrip Patch Antenna for Mobile

Communications” by Daniel Mammo.

[5] “Design of linearly polarized rectangular microstrip patch antenna using ie3d/pso” -

C. Vishnu vardhana reddy and Rahul rana.

[6] Pattern Analysis of “The Rectangular Microstrip Patch Antenna” - Vivekananda

Lanka Subrahmanya.

[7] “Development of a Self-Affine Fractal Multiband Antenna for Wireless Applications”

- Jagadeesha S., Vani R. M. & P. V. Hunagund.

[8] “A Self-Similar Fractal Antenna with Square EBG Structure” - Jagadeesha.S,

Vani.R.M, P.V. Hunagund.

[9] “Fractal geometry: what is it? And what does it do?” by B.B. Mandelbrot.

[10] “A Self-Affine Fractal Multiband Antenna” - Sachendra N. Sinha, Senior Member,

IEEE, and Manish Jain.

[11] “A Self-Similar Fractal Cantor Antenna for MICS Band Wireless Applications” by

Gopalakrishnan Srivatsun, Sundaresan Subha Rani, Gangadaran Saisundara Krishnan.

[12] “Electromagnetic band gap (EBG) structure in microwave device design” by

Mohamad Kamal A. Rahim.

STUDY ON IMPROVED RADIATION PERFORMANCE CHARACTERISTICS OF FRACTAL ANTENNA FOR WIRELESS APPLICATIONS

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