1

CHAPTER 1

INTRODUCTION

This chapter discusses the latest trends in wireless systems, history

of wireless communications, primitive antennas and fractal antennas desirable

for communication. The chapter concludes with an outline of the dissertation.

1.1 LATEST TRENDS IN WIRELESS SYSTEMS

The vision of the Wireless World Research Forum (WWRF)

estimated that 7 trillion wireless devices will serve 7 billion people by 2017

(Jefferies 2008). Wireless technology has helped to simplify network which

enables multiple users to share common resources available. Currently,

Wireless Local Area Networks (WLAN) are incorporated widely in areas

such as residence, educational institutions, and business centers. It focuses on

many applications including wireless sensor networks, automated highways,

palmtops, electronic gadgets, factories, and navigation aids. Wireless

networking means the connectivity to have data transmission between

multiple users. Wireless networking is used to access the common

databases/resources concurrently without additional or interfering wiring in a

host. The resources include a broadband internet connection, data transfer

from one host to another network printing, streaming of audio and video files

through wireless connectivity with directional antennas (Sedat Atmaca et al

2006). The demand for broadband grows across the globe. There is an urgent

need to improve the capacity of these networks.

2

In last decades, there is an explosive growth in cellular system and

there is no chance that this growth will never slow down (Berridge et al

1998). Presently, three billion users in world utilize systems/devices to

establish wireless connectivity. The progressive increase in wireless

systems/devices which are connected, indicates a shining future for wireless

networks. The stand-alone systems with larger networking infrastructure

results in crammed wireless band.

Research in this area is driven by the need for larger capacity

networks with dual band, multiband, wideband, low cost, and compact

device/terminals which provide better mobility and interoperability. The

antenna plays a major role and it is considered as the heart for any

communication/wireless system. It serves in establishing a successful

wireless communication link between systems. It is crucial to consider the

size and the cost, which should deliver the need of wireless systems, markets

and the customers (Pozar 1996 and Rahmat-Samii et al 1998).

Patch antenna is a solution which has a tendency to occupy less

space on wireless boards. The antenna has many advantages. Inspite of this,

the antennas have a major disability. The disability is that the antenna exhibits

very narrow bandwidth for any design frequency. The antenna surmounts

various wireless applications with better bandwidth and return loss, which

allows prototype model to distribute a variety of wireless applications. A

competent design with the aid of fractal geometry on the antenna essentially

miniaturizes the size of antenna and can be made to resonate for multiband.

As a result, there is a progress in the overall performance of antennas.

A special attention towards the enhancement in modern antenna

technology is discussed in this chapter with the ancient times of history of

wireless communication. In general, this it includes a brief classification of

antennas, current developments in printed antenna technology and the

3

advantage of fractal geometry. This chapter concludes with the motivation of

the work along with the dissertation organization.

1.2 WIRELESS COMMUNICATION CHRONICLE -A CONCISE

THUMBNAIL

In 1873, James clerk discovered the objective reality of

electromagnetic waves, which resulted in wireless communication (Maxwell

1873). He claimed that electromagnetic radiation of other wavelengths

should be achieved when the light is electromagnetic in character. The

objective reality of these electromagnetic waves was logically proved by

Heinrich Hertz with the aid of first spark-gap generator in 1888. In 1896,

Guglielmo Marconi logically proved wireless telegraph by transmitting

message to English telegraph office (Beynon 1975). During the year 1894-

1900 processed research on electromagnetic waves with the first horn antenna

was investigated (Krauss 1985).

Guglielmo Marconi discovered the transmission of three dot morse

code for the letter �S� over a distance of three kilometer in modern wireless

communication (Garratt 1994). The first part of antenna era was expatiated

with an experiment on a transmitting antenna. This antenna has 50 vertical

wires. It resembles a fan. It is connected to the ground with a spark

transmitter. The receiving antenna was a 200m wire pulled and supported by

a kite. The radio transmission through wire antenna was made possible to the

other side of the world (1992).

In 1982, Global System for Mobile communication (GSM) group

was organized which laid as a backbone for the modern wireless mobile

networks. The release of first GSM specification and the experimentation of

�L� band digital radio were the key proceedings in wireless communication

history. In 1983, Edwin Armstrong marked the Frequency Modulation (FM)

4

to David Sarnoff. In 1940, Daniel Noble, a professor of electrical engineering

at the university of Connecticut designed FM mobile radio for the state police

(George 1992). FM is a means of access to the transmission of digital

information carried over RF. The development in wireless technologies

creates an appeal for refined and non voice services such as Wireless Fidility

(WiFi), 3G, in addition to GSM, Code Division Multiple Access (CDMA),

and Universal Mobile Telecommunication System (UMTS) (Simon Haykin et

al 2005).

The first GSM call was made in Finland in 1991. Six years later

the IEEE 802.11 standard also known as WiFi was formed (Blake 1928).

Uninterrupted Bluetooth special interest group was formed. The first

Bluetooth product was introduced by Ericcson in the year 2000 (Bowers

1978). Wireless headset, and phone adapter was meant for cell phones. The

research in wireless communication is now rapidly increasing which enables

the communication easy. An overview of WiFi, GSM, CDMA, and UMTS

frequency band allocations for modern wireless communication standards are

summarized in Table 1.1.

1.3 ROLE OF ANTENNAS IN WIRELESS COMMUNICATION

SYSTEMS

Antenna is one of the deciding factors of components in wireless

communication systems. An antenna is regarded as an aerial according to

IEEE standard which is meant for radiating or receiving radio waves

(IEEE 1983). All antennas operate in accordance with electromagnetic

theory. The word antenna is derived from a Latin word antemna which

became, in Latin language antennae. Marconi was the first person to use the

term antenna. He used the term in a lecture in 1909 (Garratt 1994).

5

Table 1.1 Frequency band allocations

System Description Frequency Band (MHz)

GSM-900 Global System for Mobile communication

880-960

GPS Global Positioning systems 1208-1248 and1556-1595

DCS-1800 Digital Communications Service 1710-1795

PCS -1900 Personal Communication System 1850-1990

PHS Personal Handy-Phone 1905-1920

UMTS Universal Mobile Telecommunications Systems

1920-2170

Wi-Bro Wireless Broadband 2300-2390

ISM Industrial, Scientific and Medical 2400-2484 , 5150-5350 and 5275-5825

DVB-H Digital Video Broadcasting 470-890

RFID Radio Frequency Identification systems

30-2400

UWB Ultra Wide Band 3100-10600

The theories of James Clerk Maxwell in electricity and magnetism

paved way for the gradual development of antennas. In 1940, antenna

technology was generally related to a wire type of radiating elements. These

antennas operate in Ultra High Frequency (UHF) range frequencies. Modern

antenna technology with its associated elements namely waveguides,

apertures horn antenna, and reflectors, set forth a new era during the Second

World War (Sterling et al 2000). This new era of microwave communication

began by the discovery of microwave sources such as klystron and

magnetron.

6

Antenna technology was witnessed during the period of Second

World War. Ensuingly, there was a development in computer architecture,

and technology which plays a major role in the advancement of modern

antenna technology. The introduction of examining complex antenna were

dealt with numerical methods. It is burdensome to analyze the design of

antenna (Branko et al 2002).

A drastic change in the improvement of antenna technology was

witnessed in the middle years of nineteenth century. The improvement

technology of antennas impedance bandwidth is as great as 40:1 or more.

Instead of linear dimensions, these wideband antennas had the geometries

specified by angles. Therefore, antennas are stated as frequency independent.

Television reception, point to point communication and feed for

reflects, and lenses are considered as the major applications of these wideband

antennas. A new radiating element was introduced. Comparing to earlier

design patch antenna, many applications with much ease of fabrication was

found. These antennas provide coordination with active components. A

range of antenna characteristics namely gain, radiation pattern, and dimension

of main element can be controlled electronically.

In recent years, major advancement in millimeter wave antennas

has been made successful. In one compact unit, active and passive circuits

were combined with the radiating elements. Smart antennas which is other

wise called as adaptive arrays were also introduced. It incorporates signal

processing algorithms. The above said antennas pave way for easy integration

with the advanced digital systems (Tapan Sakar 2006).

In outline, antennas are the important components of any electric

system. They are the connecting links between a transmitter and free space,

then free space to a receiver. Between a guided wave and free space,

7

antennas acts as a transducer. To set up a successful communication between

any device, antenna serves as a stepping stone.

Courtesy: Antenna theory and design by Balanis.

1.3.1 Classification of Antennas

Antennas are broadly classified as:

i) Wire Antenna

ii) Aperture Antenna

iii) Corner Antenna

iv) Dipole Antenna

v) Printed Antenna

Antennas are commonly employed in automobiles, buildings, radio

receiver units warships, and aircrafts. This family covers classical antenna

types such as dipole, loop, helix, etc. In wire antennas, loop antennas are a

category. It can be realized in different shapes such as square, triangle,

rectangle and circular loops. Circular loop antenna is most commonly

employed in loop antenna. It has a simple construction. Aperture antennas

are the most appropriate candidate for aircraft and space applications, where

the antenna has to be mounted on the surface of large crafts.

To obtain improvement in radiation characteristics in the desired

direction, antenna arrays shall be incorporated by replacing single antenna

element. A few antennas are depicted in Figure 1.1. A recent development in

array antennas which includes adaptive array is capable of beam forming

(Kin-Lu Wong et al 2004, Chen et al 2007 and Keizer et al 2007).

8

As the name implies, printed antennas are simple and inexpensive

to fabricate using modern printed circuit technology. They are low profile and

conformable to planar and non planar surfaces. Planar antennas are

compatible with Monolithic Microwave Integrated Circuit (MMIC) designs.

One among the most popular printed antenna is Microstrip patch antenna.

Figure 1.1 Classification of antennas

Square Loop Antenna Log Periodic Array Antenna

Spiral Antenna Pyramidal Horn Antenna Helical Antenna

9

1.4 PLANAR ANTENNAS �AN OVERVIEW

The prenominal development in wireless communication systems

resulted in tremendous growth of compact handheld devices such as phones

and Personal Digital Assistants (PDA) (Row 2005 and Frigon et al 2007).

The antenna employed has to occupy less space on wireless boards. It helps

the antenna to be miniaturized in size and to meet the requirements. Planar

antennas are widely used in communication devices; especially in WLAN. It

is because they can be easily included on a board which reduces the

packaging cost.

Earlier, these antennas found application in microwave such as

microstrip, slot lines, coplanar lines, etc. Multiple resonances in the antenna

are obtained by introducing slots or various resonating patches that are

compact to bring down the lateral dimension (Pozar 1992 and James et al

2003).

Planar antennas with printed circuit technology on Printed Circuit

Board (PCB), tends to exhibit miniaturization. The various types of printed

antennas are presented in the following sessions.

The key features of printed antennas are:

Light weight and small volume (overall dimensional)

Easy to fabricate using printed circuit technology

Easy to integrate with electronic components

Easy to convert into array systems

These antennas suffer a major drawback of serving low efficiency

due to substrate dielectric loss.

10

1.4.1 Microstrip Antenna

Figure 1.2 depicts a simple microstrip patch antenna. These

antennas consists of a radiating element on one side and dielectric substrate

on the otherside, which is known as a ground plane. The signal is coupled

with the main radiating element through any one feeding techniques.

Figure 1.2 2D View of microstrip patch antenna

The patch is designed around 2

in wavelength to radiate effectively

and permits fringing of electromagnetic fields between the edge and the

ground plane.

Modern wireless systems widely employ microstrip patch antennas.

It is compact compared to conventional microwave antennas. Advances of

wireless communication system, and other wireless applications, antenna

design has become more significant in the recent years. The microstrip patch

antenna has attracted wide interest due to its fundamental characteristics.

Ground plane

Substrate

Radiating element

11

General Characteristics of microstrip antennas are:

Light weight and low volume

Low profile planar configuration, hence it can be easily

mounted on wireless boards

Fabrication cost is low, so bulk production becomes easy

Easily integrated with microwave integrated circuits

Operates for dual and triple bands with two orientations

Exhibits linear and circular polarizations with lucid feed

techniques

Microstrip patch antenna suffers major drawbacks when compared

to primitive antennas. The reasons are as follows.

Narrow bandwidth and its associated problems

Power handling capacity, efficiency and gain is low

Ohmic loss due to feed structure of arrays is more

Excitation of surface waves

Complex feed structures are required for high- performance

arrays

Inappropriate radiation from feed lines and junctions

12

Triangle Circle Ellipse

Square Rectangle Dipole Arc

Annular ring

Figure 1.3 Different geometries employed for microstrip antennas

Increase in quality factor (Q) of antenna, tends to exhibit narrow

bandwidth and low efficiency. If Q is reduced by increasing the substrate

thickness, power delivered by the source goes into a surface waves.

Therefore, it results in wastage of power loss. The surface waves

degrades the antenna characteristics due to scattering (Kin-Lu Wong et al

2002). Figure 1.3 displays a few commonly employed shapes. These patches

are not restricted to the shapes.

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14

of the resonators in a suitable form (Bhatti et al 2007). A planar monopole

antenna can be treated as a cylindrical monopole antenna with large effective

diameter.

In microstrip line feed technique, the feed line is directly connected

to the edge of the monopole radiator as shown in Figure 1.5. Here the patch

and the feed line are etched on the same substrate to provide a planar

structure. It provides easy integration with RF circuit boards but creates

spurious feed radiation. Various interesting designs involving PIFA, stacked

antennas and Electronic Band Gap (EBG) antennas are reported in the

literature of multiband and wideband applications (Virga and Rahmat-samii

1997, Mclean et al 1999, Skrivervik et al 2001, Raj Mittra 2005 and Sim et al

2006). The PIFA marches towards multiband characteristics with capacitive

loading which increases the overall size of the antenna (Rowell and Murch

1997, Garg et al 2001 and Park et al 2006).

1.4.3 Commonly Adapted Techniques for Exciting Printed Antennas

There are many configurations that can be used to feed microstrip/

printed antennas.

A few popular methods are listed below:

i) Coaxial probe feed (Probe feed)

ii) Microstrip line feed

iii) Aperture coupled feed

iv) Proximity coupled feed

v) Coplanar feed line.

15

In the case of a coaxial probe feed, the inner conductor of the

coaxial connector is soldered to the radiating monopole/ main radiating

element, while the outer conductor is grounded. In this folder, the entire

system is not planar because the radiating structure is perpendicular to the

ground plane. The coaxial probe feed is easy to fabricate, and match. It has

low spurious radiation. Nevertheless, coaxial feed has narrow bandwidth.

Microstrip feed is easy to model and fabricate. It is effortless to match the

impedance of antenna in inset position.

Figure 1.5 Feeding techniques of patch antennas

Transmission Line Feed Coplanar Wave Guide Feed

Coaxial Feed

16

(a) (b)

(d) (c)

Figure 1.6 Equivalent circuit of Microstrip feed line (a) Coaxial feed (b) Aperture coupling (c) Proximity coupling of patch antenna and (d) Transmission line feed

On the other hand, the substrate width, surface waves, and spurious

feed radiation increases, for practical designs which is frontier of the

bandwidth. The equivalent circuits for these feed techniques are given in

Figure 1.6 and the Table 1.2 illustrates the performance comparison between

the different feed techniques (Bahl and Bhartia 1980, Rainee Simons 2001,

Ramesh Garg 2001 and Balanis 2011).

17

Table 1.2 Comparison in different feed techniques of printed antennas

Uniqueness Coaxial probeInset feed

Proximity coupled

Aperture

Coupled CPW Feed

Spurious Feed radiation

More Less

Polarization Poor Excellent Good

Fabrication Soldering and

drilling Easy Alignment needed

Reliability Poor Better Good

Impedance matching

Easy

Bandwidth 2-5% 13% 21% 3%

1.4.4 Coplanar Waveguide and its Application in Antennas

Figure 1.7 shows a 2D View of Coplanar Waveguide. The Coplanar

Waveguide (CPW) was invented by Wen (1969). The main difference

between a CPW and a microstrip is that, if two microstrips are placed on a

same plane with spacing between them becomes CPW. This is the main

difference between a CPW and microstrip. The further improvements have

reached to Elevated CPW (ECPW).

A prevalent CPW consists of a centre strip conductor at the centre

and partial ground planes at both the sides of a dielectric substrate. CPW is

more advantageous when compared to a microstrip line.

18

Figure 1.7 2D View of Coplanar Waveguide

The features of CPW are easy to fabricate. In CPW, hosting of

active and passive devices is easy. In CPW, shunt as well as series surface

mounting of active and passive devices are possible. These techniques,

eliminate the need for wraparound through holes due to which the size reduction and radiation loss are achieved (Browne 1989 and Browne 1990). In

addition, the ground planes exist between any two adjacent lines. The effect

of cross talk is minimized between the line significantly (Browne 1987). Besides, ratio of distances between the line determines the characteristic

impedance. Hence, size reduction is possible. CPW circuits can be made

denser than conventional microstrip circuits. These, as well as several other

advantages, make CPW ideally suited for Microwave Integrated Circuits (MIC) and MMIC applications.

1.4.4.1 Categories of coplanar waveguides

Generally, CPW can be classified as:

Conventional CPW

Conductor backed CPW

Elevated CPW

Micro-machined CPW

Ground

Ground

Strip

19

In a conventional CPW, the ground planes are of semi-infinite

extent on either side. However, in a practical circuit the ground planes are

made of finite extent.

The micro machined CPWs are of two types namely:

The micro shield line

The CPW suspended by a silicon dioxide membrane above a

micro machined groove (Browne 1987, Browne 1992, Weller

et al 1995 and milanovic et al 1997).

1.4.4.2 Coplanar waveguide antennas

Nowadays, CPW fed monopoles are increasingly popular for dual

band and wideband applications due to the following features.

i) Low radiation loss

ii) Less dispersion

iii) Wide bandwidth

iv) Simple uni-planar structure

v) Easy integration with active devices without via holes

Behaviour of CPW fed antenna with self-affine fractal which has

anisotropic symmetric scaling factor is projected. The advantages of

uniplanar antennas are said above. CPW fed antennas have been widely used

in integrating MMICs, and packaging active components with low loss

transmission line. It is a renowned candidate for larger input impedance

bandwidth (Wang et al 2003). Currently, monopole antennas are fed with

20

asymmetric coplanar strip line and slot line feed structures. CPW along with

feed can be mounted to host directly without via holes is an advantage.

Broadly CPW antennas are classified into three types. They are:

i) Grounded CPW patch antenna

ii) Electromagnetically coupled coplanar fed antenna

iii) Aperture coupled patch antenna.

In grounded CPW patch antenna, the patch is formed by widening

the center strip conductor of the CPW. The outer conductor of the connector

is integrated to the grounded CPW lower ground plane. These results in

effective transition from co-axial to grounded CPW (Greiser 1976). In

electromagnetically coupled CPW feed, CPW and patch antenna are located

on opposite sides of a dielectric substrate. Electromagnetic energy from the

CPW is coupled to the patch antenna element (Menzel 1991 and Giauffret

et al 1999). The aperture coupled CPW patch antenna consists of main patch

and grounded CPW feed structure with a gap in the conductor. These are

fabricated on substrates independently and aperture is etched in the common

ground plane (Lee 1992).

1.4.5 Design Methodology of Printed Monopole Antennas

Presently, enormous variety of printed monopole antenna designs

for single band, dual band, multiband and ultra wideband are used for wireless

applications. The proposed structure varies from one application to other.

Basically, printed monopole antenna is a conductor which is designed to

match the impedance of main radiating element. It forms a straight line.

Specifically, it is a transmission line operated at /4 in wavelengths. The

21

major drawback in this antenna design is its outsized height. Practically,

integration is impossible to a compact communication gadget such as mobile

phone.

Figure 1.8 Different geometries of printed monopole antennas

The height of monopole structure can be reduced by techniques

such as bending and folding by maintaining the length and width of a

transmission line. These methods tend to reduce the total antenna height to

some extent (I-Fong Chen et al 2003 Seong-Youp Suh et al 2004 and Hanhua

Yang et al 2009). Excitation of monopole antenna in different modes tend to

exhibit multiband resonance due to different current flow path. These

include, meandered line and inverted �L� geometry (Shun-Yun Lin et al 2006

and Wen-Shan Chen et al 2008). Figure 1.8 represents various printed

monopole structures.

1.5 DESIGN CHALLENGES IN ANTENNA

Modern wireless communication industry eagerly looks forward for

a hand held device capable of accommodating a variety of applications such

as WLAN, Industrial, Scientific and Medicine (ISM), Digital Communication

Circular Element Rectangular Element Hexagonal Element

22

Service (DCS), and Bluetooth. These applications are advancing swiftly. In

Multiple-Input Multiple-Output (MIMO) systems, antenna isolation is an

issue. An antenna element in proximity is a herculean task to solve the needs

(Gesbert et al 2003).

Another challenge is the prototype which has to occupy small space

available on most of the wireless devices. The model has to overcome tuning

issues to meet the requirements. Yet another challenge is that the costs of the

substrate has to be very low and spectrum has to be effectively utilized. In

order to overcome these challenges, the need in designing multiband antennas

with consistent return loss, Voltage Standing Wave Ratio (VSWR), radiation

pattern, bandwidth and polarization over the wide frequency band are

required.

Generally, most of the multiband antennas meet the requirements of

minimum return loss and on the other hand, the cost of the substrate is another

prime parameter which has to be considered. The miniaturization of the

handheld communication devices demand for small antennas with convincing

specifications such as bandwidth, pattern characteristics which includes

polarization, less sensitivity, etc.

1.6 FRACTAL ANTENNA - AN OVERVIEW

The wireless technologies are the most practical solution to meet

the great demand for broadband all over the world. WLANs are incorporated

widely in areas such as residence, educational institutions, business centers,

LAN to Local Area Network (LAN) bridging, urban access etc. They are

used in many applications including wireless sensor networks, automated

highways, palmtops, electronic gadgets, factories, and navigation aids.

Wireless networking means the connectivity for data transmission between

23

multiple users to access the common databases/resources concurrently

without additional or interfering wiring in a host. The subscribers eagerly

seem to look forward for a technology which could support high data

transmission, seamless connectivity, and functions for more than one

operating frequency which leads to WLAN with multistandard transceivers

(Elwan et al 2001).

Mandelbrot coined the name �fractals� where dimensions were not

whole numbers. Later, John Gianvittoria and many others have contributed to

this geometry in particular. It deals with regular and irregular cantors seen in

nature and day to day life. Fractal geometries have found a place in science

and engineering. Fractal geometry is alarmed with the properties of fractal

objects which are typically known as fractals. A snow structure, fern leaves,

bark of trees and pebbles are a few examples considered for these geometries.

The classification of fractal geometries are displayed in Figure 1.9. A few

geometries are depicted in Figure 1.10.

24

Figure 1.9 Classification of fractal geometries

Mandelbrot sets

Strange Attractors

Birfurcation Diagram

Julia Set

Fractal Classes

Deterministic Non Deterministic

Linear Non-Linear

Iterative Function Systems (IFS)

Cantor Set

Koch Curve

Minkowski Curve

Hilbert Curve

Sierpinski Gasket

Fractal Brownian motion Diffusion Limited aggregation

25

Fern leaves Bark of tree Broccoli

Butterfly Flower

Figure 1.10 Examples of fractal geometries

Fractal geometry finds a variety of application in engineering.

The basic properties of fractals are as follows:

i) They have definite cantor even at small scales.

ii) They are self-similar and space filling cantors.

iii) They have fractal dimension and are recursive in nature.

iv) They are irregular to describe in mathematical geometry.

(Mandelbrot 1983, Gianvittoria and Rahmat Samii 2002).

F

Figure 1.11

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27

Iterated Function System (IFS) fractals are shaped at the beginning

of simple plane transformations namely scaling, dislocation, and the plane

axes rotation.

Following steps are involved in the creation of an IFS fractal:

Defining a set of plane transformations

Drawing an initial pattern on the plane (any pattern)

Transforming the initial pattern using the transformations

defined in first step

Transforming the new portrait (grouping of initial, and

transformed patterns) using the same set of transformations

Repeating the fourth step as many times as possible (in theory,

this procedure can be repeated an infinite number of times)

The most famous IFS fractals are the Sierpinski Triangle and the

Koch Snowflake which is depicted in Figure 1.11 (Courtesy:Fractals.org)

Presently, self- similarity property of fractal geometry is a

promising candidate to realize miniaturized multiband antennas, dual band,

compact size, low profile and conformal (Peitgen and Rixter 1986, Cohen

1997, Puente et al 2000, Gianvittoria and Rahmat Samii 2002, Werner and

Suman Ganguly 2003). Cohen conducted numerical based analysis on fractal

geometries and concluded that these antennas might have a feature of

reducing the resonant frequency (Cohen 1995 and Cohen and Hohlfeld 1996).

An antenna is capable of switching/operating for various

frequencies, modifying the structure and self-affinity. Antennas are feasible

means of facing the urgent requirements of multistandard transceivers

(Bernhard 2003, Yang and Rahmat Samii 2005, Norouzzadeha and Jafaria

28

2005 and Pan et al 2008). Reconfigurability is achieved by varying the basic

configuration of the geometry which has already undergone resonating. This

paves way for compactness through modifying the resonating structures,

self-similar and space-filling fractal geometry which finds application in

designing multiband and miniaturized antennas (Bernhard 2003).

Recently, fractal antennas have been renowned as patch antennas.

Fractal tree is generated at random by deposition technique to attain

multiband property and is reported (Punete et al 1996). Later in 2000,

iterative model for Sierpinski gasket fractals was introduced. He developed

wire antenna anticipating its response as a task of its angle (Puneta et al 1996,

Walker et al 1998, Hara Prasad et al 2000 and Punete et al 2000). The various

dipole and planar fractal antennas using computer aided design was proposed.

The fractal cantor exhibits triadic and multiband resonances for Koch,

Minkowski curves, Sierpinski carpet, and gasket antennas (Chavka 2007).

Multiple layers of fractal geometries with different dielectric

substrates which are stacked one above the other has been considered (Song

et al 1999 and Carrier et al 2003). These antennas also find application in

Lower Frequency (LF) band, Very High Frequency (VHF) and UHF.

Similarly, Sierpinski carpets also exhibits multi resonance frequency (Du et al

2001). Design of a multiband antenna for mobile handset operations

proposed to cover GSM/Global Positioning Systems (GPS) / DCS / Personal

Communication Systems (PCS) / UMTS / Bluetooth/WLAN / WiFi /

Worldwide Interoperability for Microwave Access (WiMAX) applications.

The antenna comprises of a loop and a monopole antenna. The antenna

exhibits a wide multi-operation band with good radiation patterns. The

designed antenna measures 35 mm in width and 80 mm in length. The

proposed structure exhibits a VSWR of 3:1 ratio (Hsuan-Wei Hsieh et al

2009).

29

Modern mobile handsets are frequently essential to function at

multiple frequency bands to assist the applications for various communication

needs. In outlook of these budding trends in mobile communication, novel

antenna designs are needed. Several techniques have been exploited in the

design to satisfy multiband requirements (Ang et al 2003, Yu et al 2003 and

Guo et al 2004b). Furthermore, the necessities for the mobile stations are to

be compressed and the light weight are also demanded (Guo et al 2003).

Fractal antenna has been rewarded more and more due to the multiband

response and reduction of the size of the antenna. A promising fractal

geometry ensures a successful design of a multiband antenna which is a

square fractal antenna (Dehkhoda and Tavakoli 2005).

Today�s aggressive market needs a multimode capabilities for

every wireless device because of the intensifying stipulate for new, higher

speed mobile broadband, and multifunction applications. However, mobile

handsets are characterized by miniaturized size. It reduces weight. There is a

progress in modern integrating circuit technology which satisfies the users

need. The design of suitable RF frontend, plays a very important and critical

role to reach this conclusion. Pertaining to dimension constraint, the use of

predictable monopole-like antennas are generally avoided because of their

relatively large sizes, when compared to that of the device itself (Guo 200c).

This study has led to the invention of novel fractal geometry which

is applied in designing fractal antennas for wireless communication

applications. It includes Koch curve, tree antenna Sierpinski and Minkowski

fractal antennas. The self-affinity property of fractal antenna with multilayer

aperture coupling provides multiband operation. It has been investigated

(Sinha and Jain 2007). Design and development of antennas incorporating

fractal concept for multifunctional application is still an open issue.

30

1.7 ANALYSIS OF ANTENNA

Numerical analysis of antennas and its characterization are essential

to refrain after fabrication. A number of numerical analysis methods have

been proposed for analysis planar antennas. Each method has its own

beneficial and detrimental effects.

A few analysis methods are as follows:

i) Methods of Moments

ii) Finite Element Method

iii) Finite Difference Time Domain Method

1.7.1 Methods of Moments

Harrington (1968) found computational electromagnetics during the

year 1967 to compute Method of Moments (MoM). The MoM technique is

used for analyzing electrically small antenna, and its structures. Numerical

analysis solution is based on integral equations for the currents induced in the

structure by sources or incident fields. The process concerned in computation

of MoM, is the structure which is divided into a number of parts governed to

symbolize current on the parts with some functions. The boundary conditions

with an appropriate set of testing functions are generated by a set of

equations. The number of parts on which current distribution is represented,

is proportional to the order of matrix.

1.7.2 Finite Element Method

Courant (1943) first proposed Finite Element Method (FEM) which

deals with a wide range of geometries are complex in nature, and

distributions. In this method, subdivisions are preceded by triangular

31

elements to divide the surface or volume elements to solve three dimensional

or two dimensional structure boundary value problems with less significant

complexity. The method is used to solve heterogeneous and anisotropic

electromagnetic wave effectively.

1.7.3 Finite Difference Time Domain Method

Finite Difference Time Domain Method (FDTD) was formulated in

time domain Yee (1966). The route cause for development of FDTD

method is onset high speed computers with very huge memory size. It

computes Maxwell�s equation in time domain. FDTD method of analyzing

complex problem was made simple by transforming differential equation into

algebraic equations. Empire software which is used to solve the design issues

is related to multiband integrated mobile phones (Manteuffel et al 2001).

1.8 CAD SIMULATION

The abnormal increase in wireless market and need for wireless

devices/connecting devices is enabled with additional features to unite all in a

single system. The technology changes progressively, and so accurate

electromagnetic computer aided design simulation is required to meet the

design challenges for an RF design engineer. Initially, Computer Aided

Design (CAD) is focused on small design of linear circuits. Later, this lead to

analysis, optimization of discrete, and hybrid microwave integrated circuits.

In 1980, low cost personal computers were invented. This enabled

more nonlinear circuits, communication systems and electromagnetic

simulation to incorporate in systems (Besser and Glimore 2003). Function

description of CAD simulation software is listed in Table 1.3.

32

Table 1.3 Functional description of CAD simulation software

S.No Software/ Development/Year

Description/Capabilities References

1. MICAP Two port microwave simulator Tymshare (1969)

2 SPEEDY- Fairchild Semiconductors

Microwave Scattering parameter database

Besser (1970)

3 SPICE program- University of California, Berkeley and 1970

Low frequency analog integrated Circuit Design

Besser et al 1973 4 Compact � Commercial

software Analyzing microwave circuits

5 Super Compact �Advanced version of Compact software

Transmission line model and its discontinuities, matching network synthesis.

Besser et al (1981)

6 Smithtool SmithChart- interactive tool 7 Touchstone -1984 Microwave design-program

based active tool 8 Microwave Harmonica Nonlinear circuit simulation to

perform harmonic balance Besser et al (1981)

9 MDS software- Hewlett Packard and Eagleware

Single electronic automation design simulator.

10 GENESYS- Eagleware-Elanix

Supports variety of amplifiers, mixers, splitters couplers, and filters

Besser and Gilmore (2003)

11 EEs- Hewlett Packard-1990

RF simulation

12 Microwave office-2000 Electromagnetic simulation 13 APLAC-Finland 14 Sonnet, Ansoft and 3D

HFSS -1990 Electromagnetic simulation

15 Zeland MoM-EM and circuit simulation

16 ADS- Advanced design system software-Agilent

RF designs, complex RF/microwave modules, integrated MMICs for communication systems etc

33

1.9 EXPERIMENTAL FACILITIES

The proposed antennas in this thesis are fabricated in PCB and

tested. The testing here involves two modules:

i) The return loss is measured using Agilent vector network

analyzer of series E5062A. This measures from 300 KHz

upto 3 GHz. The facility available in Agilent Multipurpose

Lab Station, and PSG - Agilent Centre of Excellence,

Department of Electronics and Communication Engineering,

PSG College of Technology, Coimbatore has been utilized.

ii) Radiation characteristics are measured in anechoic chamber in

Thiagarajar Advanced Research Centre (TARC), Thiagarajar

College of Engineering, Madurai. The anechoic chamber

measures 8 m × 4 m × 4 m which is of rectangle in shape and

constructed to maximize the volume of silent zone. The

radiation pattern of the antenna was measured using Agilent

Vector Network Analyzer N5230A.

The performance of prototype has also been evaluated using rabbit

processor by transmitting data�s through GSM network. The return loss (S11)

is measured using single port calibration. Figure 1.12 depicts a measurement

in an anechoic chamber, and Figure 1.13 illustrates a pictorial representation

of a typical anechoic chamber. The chamber operates at a bandwidth

800 MHz to 20 GHz. If a standard antenna is used as the transmitter and

device under test as receiver, S21 is measured using Network analyzer.

Tradition software is incorporated to control the positioner as well as to

retrieve the data from the network analyzer.

The software is also capable of generating radiation pattern graphs

for individual frequencies, or S21 verses frequency at various angles of test

34

antenna. Here, the position control in increment employed to standard gain

antenna, through a television receiver, the functioning and positioning is

monitored periodically throughout the measurements. The radiation patterns

of antenna are calculated in E plane and H planes using Vector network

analyzer. By gain comparison method, the fabricated antennas was tested.

So, the absolute gain of the Device Under Test (DUT) can be obtained.

Primarily, the relative gains are evaluated, when compared with that of

standard gain of the antenna. It results in absolute value.

`

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Positioner

Reference antenna

Network analyzer Amplifier

Control Unit Personal Computer

Device under test

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36

1.11 SCOPE OF THE DISSERTATION

Nowadays, wireless applications of antennas are being designed

using a meander line and the substrates cost is very high. Loading of active

element and multilayer and fractal geometries are common. Among these,

fractal antennas which are compact, multiband and wideband radiator stays as

a good candidate. Many attempts have also been made in modeling and

optimization of fractal antenna.

The dissertation aims in proposing two novel fractal antennas such

as �L� (step) model and �Y� Minkowski fractal cantor antennas for multiband

wireless applications. A modified self-similar fractal antennas for multiband

wireless applications and telemedicine applications are also proposed.

The proposed fractal cantor antennas address the issues in

manufacturing cost and earlier designs in this thesis. The developed cantors

exhibit self-similar property of fractal geometry.

1.12 DISSERTATION ORGANIZATION

Chapter 1 projects an outline research in antennas. The primitive

antennas such as printed monopoles and other planar antennas and their

feeding techniques are discussed in this chapter. It concludes by explaining

the motivation of the research.

Chapter 2 provides the necessary methods of design and their

implementation of self affine fractal cantor antenna on a low cost substrate for

Medical Implants Communication Service band wireless application. A few

physiological parameters are transmitted through Rabbit processor to test the

performance of antenna.

37

Chapter 3 presents a compact antenna for wideband wireless

applications, such as WLAN and Long Term Evolution (LTE) standards. The

significance of slots on fractal geometry based on the performance has been

experimentally studied. This includes the effect of port positions at various

iterations on the geometry. Later, simulation treatments for WLAN MIMO

antenna systems are considered.

Chapter 4 introduces a novel self-similar fractal antenna for

multiband wireless applications, and iterative function coefficient formulation

of the geometry. The contacts for size reduction on these geometries were

studied. The significance of geometry for each port positions exhibiting

variations, appreciably change the characteristics diverging to multiband

characteristics. The fractal geometry has been experimentally verified. The

developed antenna on a metamaterial platform is simulated to depict that the

fractal antenna performs better on different material too.

Chapter 5 describes another novel self-similar fractal antenna,

intended for multistandard wireless transceiver. The novel antenna is

miniaturized and presented with mathematical generation of iterative

function coefficient formulation. The miniaturizations of these geometries

were studied. The consequence of geometry for each port positions, and feed

location exhibits variations substantially and transform the characteristics of

multiband. The fractal geometry has been experimentally verified, and

compared with previously developed antenna. The corollary of various

dielectric substrates is compared. The effect of fractal monopole is also

studied.

Chapter gives the conclusions of the research carried out.