FRACTAL ANTENNA FOR AEROSPACE NAVIGATION

DISSERTATION

ON

DESIGN OF FRACTAL MICROSTRIP PATCH

ANTENNA FOR AEROSPACE NAVIGATION

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE

AWARD OF THE DEGREE OF

MASTER OF TECHNOLOGY

ELECTRONICS AND COMMUNICATION ENGINEERING

(SPECIALIZATION IN COMMUNICATION SYSTEMS)

SUBMITTED BY

Rupleen Kaur (2013ECB1235)

(Reg. No. 2013 RG/A-277)

UNDER THE SUPERVISION OF

Er. Satbir Singh (Assistant Professor)

DEPARTMENT OF ELECTRONICS AND COMMUNICATION

ENGINEERING

GURU NANAK DEV UNIVERSITY, RC GURDASPUR

JULY, 2015

Dept.of ECE, GNDU, Regional Campus Gurdaspur i

Guru Nanak Dev University, Regional Campus, Gurdaspur Department of Electronics & Communication Engineering

(Established by State Legislature Act No 21 of 1969) Accredited at “A” grade level by NAAC and awarded

“University with Potential for Excellence” status by UGC Phone: 01874-240517, Fax: 01874-242678

CERTIFICATE

Certified that the thesis entitled “Design of Fractal Microstrip Patch Antenna for

Aerospace Navigation” submitted by Rupleen Kaur (Regd. No. 2013 RG/A-277) in the

partial fulfillment of the requirements for the award of the degree of Master of

Technology (Electronics and Communication Engineering) of Guru Nanak Dev

University, is a record of student’s own work carried under my supervision and guidance.

To the best of our knowledge, this thesis has not been submitted to any University or

institute for award of any degree. It is further understood that by this certificate the

undersigned do not endorse or approve any statement made, opinion expressed or

conclusion drawn herein, but approve the thesis only for the purpose for which it is

submitted.

Supervisor

Er. Satbir Singh

Assistant Professor,

Department of Electronics and Communication

Engineering,

Guru Nanak Dev University

Regional Campus,

Gurdaspur-143521,

Punjab, India

Dated:

Co-Supervisor

Er. Naveen Kumar

(IEEE Member)

Executive Director

Elixir Publication

Chandigarh, India

Dept.of ECE, GNDU, Regional Campus Gurdaspur ii

DECLARATION

I, Rupleen Kaur, bearing University Registration Number 2013 RG/A-277, a student of

M.Tech (Regular) of Electronics & Communication Engineering Department; hereby

declare that I own the full responsibility for the information, results etc. provided in this

thesis titled “Design of Fractal Microstrip Patch Antenna for Aerospace Navigation”

submitted to Guru Nanak Dev University for the award of M.Tech (ECE) degree. I

hereby declare that this thesis is my own work and effort and that it has not been

submitted anywhere for any award. Where other sources of information have been used,

they have been acknowledged. I have taken care in all respect to honor the intellectual

property right and have acknowledged the contribution of others for using them in

academic purpose. I further declare that in case of violation of intellectual property right

or copyright, I as the candidate will be fully responsible for the same, my honorable

supervisors and Institute will not be responsible for the violation of any intellectual

property right.

Rupleen Kaur

Roll no. 2013 ECB 1235

Date:

Place: Guru Nanak Dev University, Regional Campus, Gurdaspur

Dept.of ECE, GNDU, Regional Campus Gurdaspur iii

ACKNOWLEDGEMENT

The completion of any project brings with it a sense of satisfaction, but it won’t be

complete without thanking the people who made it possible and whose constant support

crowned my efforts with success. I wish to express my deepest gratitude to Er. Satbir

Singh, Assistant Professor, Dept. of ECE, GNDU, Regional Campus Gurdaspur for his

sincere and invaluable guidance, suggestions and constant encouragement, and belief in

me, which inspired me to submit my thesis.

I am thankful to Dr. Anu Sheetal, Professor and Incharge of Dept. of ECE, GNDU,

Regional Campus Gurdaspur for providing full facilities for the execution of this thesis

work.

My sincere thanks to Er. Naveen Kumar, Director, Elixir Publications, Chandigarh for his

consistent guidance, encouragement and help in learning HFSS software. I also attribute

my sincere gratitude to NITTTR, Chandigarh for providing necessary lab facilities and

equipments.

I am grateful to all of my friends for helping me and would also like to thank all those

who have directly or indirectly contributed to the success of this work. Their intelligence

and innovation have helped me go through my every query and ended up in a huge

success.

Big thanks to my Institution and all of my faculty members for helping me in completing

my thesis and providing me with immense knowledge related to the subject.

I am extremely happy to acknowledge and express my sincere gratitude to my parents for

their constant support and encouragement.

Rupleen Kaur

Roll no. 2013 ECB 1235

Dept.of ECE, GNDU, Regional Campus Gurdaspur iv

ABSTRACT

In navigational applications antenna plays an important role in determining the location,

tracking and mapping of vehicles. In the recent years navigational antennas have

progressed rapidly and are required to perform various services like surveying, mapping

and providing geographical information without compromising size, weight and

performance. There has been a great demand for antenna designs that have multiband and

wideband properties. Hence the antenna required should be small in size, light in weight,

operates at multiband frequencies, consumes low power and provides high reliability.

Earlier Navigation was based on observations and not on scientific methods but modern

navigation determines the position by collecting the information from satellites through

the receivers. Navigational tools were initially developed for military users but with the

advent of wireless communication systems it has been adopted in civil as well. In military

applications navigational antennas are required for many applications such as

surveillance, beam steering, beam forming, tracking etc. These antennas are positioned

on aircrafts, ships or other vehicles. In aerospace navigation, antennas use radio

frequencies to communicate with air traffic control and find its destination. Therefore

different antennas are required for different purposes and hence they need a large space.

In order to overcome this problem i.e., instead of using number of antennas, a multiband

antenna that can be operated at many frequencies is the need of today.

During this thesis work a compact, mechanically robust antenna that has the capability of

operating at multiple frequencies has been designed. The antenna is a single feed fractal

microstrip patch antenna. It has two circular and two rectangular slots on the ground in

order to improve the resonance of the antenna. Moreover the antenna has conventional

Koch fractal design on the top of the patch to get multiple frequency bands. High

Frequency Structure Simulator (HFSS) software will be used for designing and obtaining

the results for the antenna. High Frequency Structure Simulator (HFSS) is an industry

standard simulation tool. It has powerful drawing capabilities to simply the antenna

design. It is seen that after simulation the antenna provides desired resonant frequencies

that have good operating bandwidth.

Dept.of ECE, GNDU, Regional Campus Gurdaspur v

TABLE OF CONTENTS

Page no.

Certificate i

Declaration ii

Acknowledgement iii

Abstract iv

Table of Contents v-ix

List of Abbreviations x

List of Figures xi-xiii

List of Tables xiv

CHAPTER 1

INTRODUCTION 1-20

1.1 Overview 1

1.2 Antenna design issues in aerospace navigation 3

1.2.1 Coverage 3

1.2.2 Space Available 3

1.3 Antenna Fundamentals 3

1.4 How an Antenna Radiates 4

1.5 Near and Far Field Regions 5

1.6 Antenna Performance Parameters 6

1.6.1 Radiation Pattern 6

1.6.2 Directivity 7

1.6.3 Input Impedance 8

1.6.4 VSWR 9

1.6.5 Return Loss 10

1.6.6 Antenna Efficiency 10

1.6.7 Antenna Gain 11

1.6.8 Polarization 11

Dept.of ECE, GNDU, Regional Campus Gurdaspur vi

1.6.9 Bandwidth 12

1.7 Types of Antennas 13

1.7.1 Half Wave Dipole 13

1.7.2 Monopole Antenna 14

1.7.3 Loop Antenna 15

1.7.4 Helical Antenna 17

1.7.5 Horn Antenna 18

1.8 Organization of Thesis 19

CHAPTER 2

FRACTAL MICROSTRIP PATCH ANTENNA 21-33

2.1 Introduction 21

2.2 Advantages and Disadvantages of Microstrip Patch

Antenna

21

2.3 Basic Principle of Operation 22

2.4 Feeding Techniques 23

2.4.1 Coaxial Probe Feed 23

2.4.2 Microstrip Line Feed 24

2.5 Parameters Determining the Performance of Microstrip

Patch Antenna

25

2.5.1 Effect of Substrate 25

2.5.2 Effect of Parasitic Patches 25

2.5.3 Effect of Multilayer Configuration 25

2.6. Fractals 26

2.6.1 Introduction 26

2.7 Dimensions of Fractal Geometry 27

2.8 Fractal Geometries 28

2.8.1 Sierpinski Gasket 28

2.8.2 Sierpinski Carpet 29

2.8.3 Koch Curve 29

Dept.of ECE, GNDU, Regional Campus Gurdaspur vii

2.8.4 Hilbert Curve 30

2.8.5 Minkowski Curve 30

2.8.6 Pythagorean Tree Fractal 31

2.9 Advantages and Disadvantages of Fractal Geometries 31

2.9.1 Advantages of Fractal Geometries 31

2.9.2 Disadvantages of Fractal Geometries 31

2.10 Applications of Fractal Geometries 32

2.10.1 Astronomy 32

2.10.2 Nature 32

2.10.3 Computer Science 32

2.10.4 Telecommunication and Medicine 33

CHAPTER 3

LITERATURE SURVEY 34-42

3.1 Literature Review 34

3.2 Inferences Drawn 41

CHAPTER 4

PROPOSED RESEARCH WORK 43-50

4.1 Problem Definition 43

4.2 Objective 43

4.3 Scope of Work 44

4.4 Methodology of Proposed Research work 44

4.4.1 Design Methodology 44

4.4.2 Selection of Design Parameters 45

4.4.3 Selected Geometry 45

4.5 Design of Fractal Microstrip Patch Antennas 45

4.5.1 A Simple Microstrip Patch Antenna 45

4.5.2 A Multiband Microstrip Patch Antenna with Koch

Fractal Geometry

47

Dept.of ECE, GNDU, Regional Campus Gurdaspur viii

4.5.3 A Multiband Fractal Antenna with Four Slots on the

Ground Plane

49

CHAPTER 5

SIMULATED AND MEASURED RESULTS

VALIDATION

51-67

5.1 Introduction 51

5.2 Simulated Results of Microstrip Patch Antenna 51-53

5.2.1 Return Loss Characteristics 51


5.2.3 Gain 52

5.2.4 Voltage Standing Wave Ratio 53

5.3 Simulated Results of Fractal Patch Antenna 54-56



5.3.3 Gain 55


5.4 Simulated Results of Multiband Fractal Patch Antenna

with Slots on the Ground Plane

57-60



5.4.3 Gain 59


5.5 Validation of Simulated Results 60

5.6 Hardware Implementation 62

5.6.1 Introduction 62

5.7 Fabrication Techniques 62

5.8 Hardware Testing 64

5.9 Performance Assessment of Fabricated Antenna 65


Dept.of ECE, GNDU, Regional Campus Gurdaspur ix

5.9.2 Comparison between Simulated and Measured

Results

66

CHAPTER 6

CONCLUSION AND FUTURE WORK

68-69

6.1 Conclusion 68

6.2 Future Work 69

LIST OF PUBLICATIONS xv

REFERENCES xiv-xviii

Dept.of ECE, GNDU, Regional Campus Gurdaspur x

LIST OF ABBREVIATIONS

HF High Frequency

NAVAID Navigational Aid

RMM Remote Monitoring and Management

LLWAS Low Level Wind shear Alert System

TACAN Tactical Air Navigation

DME Distance Measuring Equipment

GPS Global Positioning System

GLONASS Global Orbiting Navigational Satellite

System

RADAR Radio Detection and Ranging

ASDE Airport Service Detection Equipment

HFSS High Frequency Structure Simulator

Dept.of ECE, GNDU, Regional Campus Gurdaspur xi

LIST OF FIGURES

Figure No. Description Page No.

Figure 1.1 Radiation Pattern from an antenna 4

Figure 1.2 Field regions nearby an antenna 6

Figure 1.3 Radiation Pattern of Directional Antenna 7

Figure 1.4 Equivalent circuit of transmitting antenna 9

Figure 1.5 Various polarization schemes 11

Figure 1.6 Bandwidth from the plot of reflection coefficient 12

Figure 1.7 Half wave dipole 13

Figure 1.8 Radiation Pattern of Half wave dipole 14

Figure 1.9 Monopole Antenna 14

Figure 1.10 Radiation Pattern of Monopole Antenna 15

Figure 1.11 Loop Antennas 16

Figure 1.12 Radiation Pattern of Loop Antenna 16

Figure 1.13 Helix Antenna 17

Figure 1.14 Radiation Pattern of Helical Antenna 18

Figure 1.15 Types of Horn Antennas 18

Figure 2.1 Microstrip Antenna Structure 21

Figure 2.2 Side view of Microstrip Patch Antenna 23

Figure 2.3 Coaxial Probe Feed for Microstrip Patch Antenna 24

Figure 2.4 Microstrip Line Feed for Microstrip Patch Antenna 24

Figure 2.5 Multilayer Configuration 26

Figure 2.6 Sierpinski Gasket 29

Figure 2.7 Sierpinski Carpet 29

Figure 2.8 Koch Curve 30

Figure 2.9 Hilbert Curve 30

Figure 2.10 Minkowski Curve 31

Figure 2.11 Pythagorean Tree Fractal 31

Dept.of ECE, GNDU, Regional Campus Gurdaspur xii

Figure 4.1 Flow graph of Design Methodology of Proposed

Research Work

44

Figure 4.2 Microstrip Patch Antenna (a) Top View (b) 3D View in

HFSS

46

Figure 4.3 3D View in HFSS (a) First iteration (b) Second iteration

(c) Third iteration

48

Figure 4.4 3D View of fractal microstrip patch antenna in HFSS 48

Figure 4.5 Multiband Fractal Patch Antenna with Slotted Ground

Plane (a) Bottom View (b) 3D view

49

Figure 4.6 Detailed Dimensions of Proposed Antenna in HFSS 50

Figure 5.1 Simulated Return Loss of basic Microstrip Patch

Antenna

51

Figure 5.2 3D Radiation Pattern of Microstrip Patch Antenna 52

Figure 5.3 Simulated 3-D Gain Plot of Microstrip Patch Antenna 53

Figure 5.4 Simulated VSWR plot of microstrip patch antenna 53

Figure 5.5 Simulated Return Loss of Fractal Patch Antenna 54

Figure 5.6 Simulated 3D radiation pattern of Fractal Patch Antenna 55

Figure 5.7 Simulated 3D Gain plot of Fractal Patch Antenna 56

Figure 5.8 Simulated VSWR plot of fractal patch antenna 56

Figure 5.9 Simulated Return Loss of Multiband Fractal Antenna 57

Figure 5.10 Simulated 3D radiation pattern of Multiband Fractal

Antenna

58

Figure 5.11 Simulated 3-D Gain Plot of Multiband Fractal Antenna 59

Figure 5.12 Simulated VSWR plot of Multiband Fractal Antenna 60

Figure 5.13 Mask generated using Coral Draw (a) Fractal geometry

(b) Ground slots

63

Figure 5.14 Screens Generated in Screen Printing technique (a)

Antenna Ground Plane (b) T-shaped Top Patch

63

Figure 5.15 Final Fabricated antenna layout (a) Top View (b)

Bottom View (c) Side view

64

Dept.of ECE, GNDU, Regional Campus Gurdaspur xiii

Figure 5.16 Fractal Patch Antenna mounted on Network Analyzer 65

Figure 5.17 Measured Return Loss of Multiband Fractal Antenna 66

Figure 5.18 Measured v/s Simulated Return Loss of Multiband

Fractal Antenna

67

Dept.of ECE, GNDU, Regional Campus Gurdaspur xiv

LIST OF TABLES

Table No. Description Page No.

Table 1.1 Various Frequency Bands for Aerospace Navigation 2

Table 4.1 Detailed Dimensions of Proposed Microstrip Patch

Antenna

46

Table 4.2 Detailed Dimensions of Proposed Multiband Fractal

Antenna

50

Table 5.1 Comparison between Proposed Multiband Fractal

Antenna with the Design Proposed in [30]

60

Dept. of ECE, GNDU, Regional Campus Gurdaspur 1

CHAPTER 1

INTRODUCTION

1.1 Overview

In 1886, Henry Hertz developed a wireless communication system in which an electric

spark occurred in dipole and loop antenna. Since then antennas are being used for

television, mobile and satellite communication. In the year 1880, Nicola Tesla suggested

a radio to transmit information and described first radio communication systems in his

papers in the year 1891. At the same time, Guglielmo Marconi was the first to patent the

telegraph and signified the importance of wireless communication. In 1940, the first

standard for communication technology was introduced [1]. A large growth in wireless

technologies was seen during 1980’s and 1990’s, due to which cheap wireless services

were introduced all over the world. In 21st century a great progress can be seen in

wireless technologies in which the devices are becoming smaller to integrate various

services.

In wireless applications antenna plays an important role as it converts electrical power

into radio waves. An antenna acts as an interface between space and transmission line.

Earlier each antenna operates at a single frequency therefore different antennas were

required for different purposes. Today’s communication requires an antenna that provides

high gain, wide bandwidth, supports multiple frequencies, is compact in size and satisfies

various requirements of the system.

Earlier Navigation was based on observations and not on scientific methods but modern

navigation determines the position by collecting the information from satellites through

the receivers. Navigational tools were initially developed for military users but with the

advent of wireless communication systems it has been adopted in civil as well. Mobile

phones, computers, laptops have GPS functionality. The GPS is a space based satellite

system that provides location information anytime and anywhere. In military applications

navigational antennas are required for many applications such as surveillance, beam

steering, beam forming, radar, tracking etc. These antennas are positioned on aircrafts,

ships or other vehicles. In aerospace navigation, antennas use radio frequencies to


communicate with air traffic control and find its destination. Various frequency bands

allocated for aerospace navigational applications are listed below in Table 1.1.

Table 1.1 Various Frequency Bands for Aerospace Navigation

Frequency

Band Name

2100 - 28,000 kHz HF Communications

750 MHz NAVAID (Marker Beacons)

8-12 GHz X-band

932 – 935 & 941 – 944

MHz

RMM, LLWAS, etc.

960 – 1215 MHz NAVAID (TACAN / DME, etc.)

1215 – 1390 MHz Air Route Surveillance Radar; GPS and GLONASS L1

1545 – 1559 MHz Satellite-Based Comm (To Aircraft)

1559 – 1610 MHz Satellite Navigation; GPS and GLONASS L1

1646.5 – 1660.5 MHz Satellite-Based Comm (From Aircraft)

9000 – 9200 MHz Military Precision Approach Radar

14.4 – 15.35 GHz Microwave Link

15.7 – 16.2 GHz Radar (ASDE-3)

18-19 GHz Point to Point Radio Communication


A great improvement can be seen in aerospace navigation and various new standards are

being used throughout the world. In order to implement the new standards it is essential

to have an antenna that is low profile, supports various frequencies and provides good

transmission and reception signals. However designing such an antenna is a difficult task

because various parameters such as space, volume and presence of other objects play an

important role. Various design issues are discussed below.

1.2 Antenna Design Issues in Aerospace Navigation

Aerospace navigation requires an antenna that supports wideband/multiband frequencies

and is small in size. The major challenge in designing an antenna for aerospace

navigation is that it covers maximum frequencies while consuming less volume.

Therefore an antenna that has light weight, low cost, robust, flexible and can support

multiple frequencies is the need of today [2].

Various design issues are briefly explained below:

1.2.1 Coverage

Wireless devices should be designed in such a way that it covers maximum frequencies

that are allocated to a particular application. Earlier different antennas were used for

different purposes. The latest trend in designing an antenna for navigation purpose is that

it covers maximum frequencies. This affects in designing a complex patch antenna with

fractal shapes on its patch.

1.2.2 Space Available

Now-a-days the inclination in wireless communication is to design a compact antenna so

that it can be easily positioned even in places where volume is a major issue. While

designing a low profile antenna, complexity increases as patch is designed using fractal

geometries. Moreover bandwidth and radiation efficiency are directly proportional to the

size of the antenna. Therefore as size increases performance also increases and hence

more volume is required.


1.3 Antenna Fundamentals

Antennas are very essential part of communication systems. An antenna converts RF

signal that is travelling on a conductor into an electromagnetic wave. Antennas exhibits

reciprocity property i.e., antenna has same characteristics while transmitting or receiving.

In order to pair transmission and reception, antenna must be tuned to similar frequency

band of the radio to which it is linked.

1.4 How an Antenna Radiates

Firstly, let us consider how radiation takes place. Radiation in conducting wire takes

place mainly due to deceleration or acceleration of charge. No current flows, if there is no

motion of charge and hence no radiation occurs. However, when a charge moves along

bent or curved wire with uniform velocity, radiation is produced [3].

Figure 1.1 Radiation pattern from an antenna


To understand the concept of radiation from an antenna, let us consider a voltage source

connected to a transmission line. When a voltage is applied across the conductor, a

sinusoidal electric field is produced and thus electric lines of force are also formed. The

free electrons in the conductor are dislocated by electric lines of force which in turn

produce charge by the movement of these charge carriers and hence magnetic field is

created.

Electromagnetic waves that travel between the conductors are created due to time varying

magnetic and electric fields. When these waves come close to the open space, they form

free space waves by simply joining the open ends of electric field lines. Since electrical

disturbances are created continuously by the sinusoidal source, therefore electromagnetic

waves are also radiated continuously into the free space. The electromagnetic waves are

preserved inside the antenna and transmission lines due to the presence of charged

particles, but the moment they penetrate into the free space closed loops are formed and

are radiated.

1.5 Near and Far Field Regions

The antenna field patterns are associated with two types of energy: reactive energy and

radiating energy. Therefore space around the antenna is divided into three regions as

shown in figure 1.3.

Reactive near field region: This region is influenced by reactive field. The energy in

reactive field appears as reactance by oscillating towards and away from the antenna.

Therefore the energy appears as reactance. In this no energy is dissipated, in fact it is

stored in the given region. The exterior most boundary is at a distance of R1=

0.62√D3/λ where λ is the wavelength, D is the highest dimension of antenna and R1 is

the distance from the antenna.

Radiating near field region (Fresnel region): This region resides between the far field

region and the near field region. In this field radiation fields dominate while reactive

fields are smaller. The exterior most boundary is at a distance of R2= 2D2/λ where λ is

the wavelength and R2 is the distance from the antenna [3].

Far-field region (Fraunhofer region): The region beyond radiating near field region is

the far field region. Here only the radiation fields are present and the reactive field


does not exist. In this region, field distribution is independent from the distance of the

antenna.

Figure 1.2 Field regions nearby an antenna

1.6 Antenna Performance Parameters

The performance of the antenna can be measured from various parameters. Some

important parameters are discussed below.

1.6.1 Radiation Pattern

Radiation Pattern or Antenna Pattern is the total strength of the radiated field in different

directions from the antenna, at a given distance. The radiation pattern also describes

receiving properties of an antenna. The radiation pattern is measured in two dimensions

i.e., the vertical or horizontal planes, although it is a three dimensional pattern [3]. The

measurements of the pattern are either presented in a polar or rectangular format. The

points in the polar coordinate graph are positioned alongside a rotating radius and they

intersect with several concentric circles. In rectangular plot it is difficult to conceptualize

the behavior of antenna at different directions.

To understand the concept if radiation pattern, let us consider a directional antenna. A

directional antenna radiates more in a particular direction while less in other directions.

An omnidirectional antenna is an exceptional case of directional antenna having constant


radiation pattern in E-plane and varies in orthogonal or H-plane. Figure 1.3 shows the

radiation pattern of a directional antenna.

Figure 1.3 Radiation Pattern of Directional Antenna

HPBW: The angle linked by half power points of the main lobe is known as Half

Power Beam width (HPBW).

Major Lobe: This lobe contains the maximum intensity of radiation in a particular

direction.

Minor Lobes: These lobes contain the radiation in undesired directions. Therefore all

the lobes other than major lobe are the minor lobes.

Back Lobe: The lobe exactly in the opposite direction of the main lobe is called back

lobe.

Side Lobe: The lobes adjacent to main lobe are called side lobes. These lobes are

unrelated by various nulls.

1.6.2 Directivity

Directivity can be defined as an ability of an antenna to transmit more power in a specific

direction while transmitting or receive more power from a specific direction while

receiving [3]. Or we can say, the directivity of an object whose physical properties vary

in different directions, is defined as the ratio of its radiation intensity in a specific


direction, over that of an isotropic source, whose physical properties remain same

throughout all the directions. Therefore

D= U/Ui = 4πU/P (1.1)

where D = directivity of the antenna

U = the radiation strength of the antenna

Ui = the radiation strength of an isotropic source

P = the total power emitted

Directivity is the ratio of two radiation strengths; therefore it is a dimensionless quantity.

It is expressed in dBi. For the antenna to be more directive, it will have a narrow main

lobe rather than a broad one.

1.6.3 Input Impedance

The input impedance of an antenna can be defined as the ratio of the voltage to the

current at the antenna and the transmission cable connecting them [3]. The impedance of

the pair should be same for an efficient transfer of energy. The impedance of an antenna

should not be different from 50Ω. Mathematically input impedance can be represented as:

Zin = Rin + jXin (1.2)

where Zin = antenna impedance at the terminals

Rin = antenna resistance at the terminals

Xin = antenna reactance at the terminals

The imaginary part of the input impedance, Xin shows the radiation strength stored in the

near field of the antenna. Rin called the resistive part of the input impedance is composed

of two parts, loss resistance RL and radiation resistance Rr. Radiation reactance represents

the actual power transmitted by an antenna while loss resistance is the heat dissipated

from the antenna.


1.6.4 Voltage Standing Wave Ratio

For an antenna to function effectively, transfer of maximum power between the

transmitter and the antenna should take place. This can happen only when the impedance

of the transmitter (Zs) is matched to the impedance of the antenna (Zin). Maximum Power

Transfer theorem says that maximum power can be transmitted only if the impedance of

the antenna is a complex conjugate of the impedance of the transmitter and vice-versa.

Therefore, condition for impedance matching is:

Zin = Zs* (1.3)

If the above condition is not fulfilled, then some of the radiations are reflected back,

leading to formation of standing waves, which can be distinguished by a parameter

known as Voltage Standing Wave Ratio (VSWR). Mathematically:

VSWR =1 + |Γ| /1 − |Γ| (1.4)

ᴦ = Vr / Vi = Zin – Zs/ Zin+ Zs (1.5)

ᴦ = reflection coefficient

Vi = amplitude of incident wave

Vr = amplitude of reflected wave

Figure 1.4 Equivalent circuit of transmitting antenna


The value of VSWR should be less because higher the value, the greater is the mismatch

between the antenna and the transmitter. Ideally the value of VSWR should be unity.

1.6.5 Return Loss (RL)

Return loss can be defined as the power that is wasted to the load and is not returning as a

reflection. Return loss also indicates the mismatching between the transmitter and the

antenna. Mathematically it is represented as:

RL = -20 log |Γ| (1.6)

If impedance matching is perfect then Γ= 0 and RL = infinity, i.e., no reflected power.

Similarly when Γ= 1 and RL = 0dB, this means that all the incident power is reflected

back. The value of VSWR should not exceed 3, since this value gives RL of -10 dB.

1.6.6 Antenna Efficiency

Antenna efficiency can be defined as the amount of losses occurring within the antenna

and at various terminals of the antenna. Various losses can be defined as:

Reflection Losses: These losses occur mainly due to impedance mismatching between

the terminals and the antenna.

I2R losses: These are the conduction and dielectric losses.

Hence mathematically efficiency of the antenna can be defined as:

et= er ec ed (1.7)

where et = total antenna efficiency

er = mismatch efficiency

ec = conduction efficiency

ed = dielectric efficiency


1.6.7 Antenna Gain

Antenna gain is closely associated with the directivity of the antenna. Directivity can be

defined as an ability of an antenna to transmit more power in a specific direction while

transmitting or receive more power from a specific direction while receiving. Therefore,

if the efficiency of the antenna is 100% then the antenna can act as an isotropic radiator

whose directivity is equal to the gain of the antenna. More precisely, we can define

antenna gain as an ability of an antenna to achieve more power in one direction at the

expense of lost power in other directions.

1.6.8 Polarization

Polarization is defined as the direction of electric field of an electromagnetic wave. It

describes the direction and position of electric field with respect to ground [3].

Polarization is of two types i.e., linear and circular polarization.

Linear polarization: In linear polarization electric field path is back and forth along a

line. Figure 1.5 represents linear polarization.

Figure 1.5 Various polarization schemes


Circular polarization: In circular polarization, electric field vector rotates in circular

path while remaining constant in height. Circular polarization is further of two types:

Right hand circular polarized wave and Left hand circular polarized wave. In Right

hand circular polarized wave, the electric field vector rotates in clockwise motion. In

Left hand circular polarized wave; the electric field vector rotates in anticlockwise

motion. Figure 1.6 represents circular polarization.

1.6.9 Bandwidth

Bandwidth can be defined as range of accessible frequencies on the sides of center

frequency where the various parameters of antenna such as input impedance,

polarization, radiation pattern, gain lie near to the values that are obtained at the center

frequency [3]. For a broad band antenna, bandwidth can be described as the ratio of the

upper frequency and the lower frequency, whereas for narrowband antenna bandwidth is

the percentage of difference between the upper and the lower frequency from the center

frequency.

Figure 1.6 Bandwidth from the plot of reflection coefficient


Therefore mathematically bandwidth can be defined as:

BW broadband = 𝑓𝐻

𝑓𝐿 (1.8)

BW narrowband (%) = [ 𝑓𝐻 − 𝑓𝐿/ 𝑓𝐶] × 100 (1.9)

Where 𝑓𝐻 is the upper frequency.

𝑓𝐿 is the lower frequency.

𝑓𝐶 is the center frequency.

1.7 Types of Antennas

Antennas are of different sizes and shapes according to different wireless applications.

The size and shape and the material used to make an antenna determines various

characteristics of the antenna. Following are the different types of antennas used in

wireless communication.

1.7.1 Half Wave Dipole

As the name implies the length of the antenna is half of its wavelength. In order to

maintain the balance of the performance, dipoles can be longer or shorter than half the

wavelength.

Figure 1.7 Half wave dipole


Wire transmission line is used to feed the dipole antenna. In this the two sinusoidal

currents are equal in amplitude but opposite in direction [4]. Hence, no radiation occurs

from the transmission line due to cancellation effect. The gain of 2 dB can be achieved

from dipole antenna having bandwidth of 10%. The half power beamwidth of dipole

antenna is about 78degrees with directivity equals to 1.64. Figure 1.8 shows radiation

pattern of half wave dipole antenna.

Figure 1.8 Radiation Pattern of Half wave dipole

1.7.2 Monopole Antenna

The monopole antenna has been derived by applying the image theory to the dipole

antenna. According to the theory, if a conducting plate is positioned beneath a single

element of length L/2 and this length is carrying the current, then integration of the

element and its image functions in a similar manner as a dipole of length L except that

the radiations exist only in the area the plane.

Figure 1.9 Monopole Antenna


In this type of antenna, the radiation resistance is halved and the directivity is doubled to

that of a dipole antenna. This type of antennas finds its applications in mobiles where the

handset case or the car body acts as a conducting plane. It is a quarter wavelength

monopole and the gain varies from 2-6 dB. The directivity is 3.28 and the radiation

resistance is 36.5 Ω. The radiation pattern is shown in figure 1.10.

Figure 1.10 Radiation Pattern of Monopole Antenna

1.7.3 Loop Antennas

A conductor bent into the closed curve shape forming a square or a circle with a gap to

form terminals is called as loop antenna. There are basically two types of loop antennas:

electrically large loop antenna and electrically small loop antenna. If the total

circumference is approximately equal to the wavelength then it called as electrically large

loop antenna. An electrically small loop antenna has small total loop circumference as

compared to the wavelength.

As shown in figure 1.12, the radiation pattern of the dipole antennas is identical to

small circular loop antenna, regardless of the fact that the dipole is vertically polarized

and loop antennas are horizontally polarized [4].

If the core of the loop antenna is filled with ferrite, the performance can be increased

because ferrite increases the radiation resistance.


Figure 1.11 Loop Antennas

The radiation pattern of small loop antenna is different from that of large loop antenna. It

is seen that the radiation pattern of large loop antenna is maximum along the z axis. In the

loop, a null is along the z axis and a lobe along the y axis. A gain of -2dB to 3dB can be

seen in loop antennas. These antennas have bandwidth around 10% and can be used in

pagers and AM broadcast receivers.

Figure 1.12 Radiation Pattern of Loop Antenna


1.7.4 Helical Antennas

In helical antenna a wounded helical shaped conductor is connected to the ground plane.

Figure 1.13 shows a helix antenna. The antenna basically has two principal modes called

normal mode (broadside radiation) and axial mode (endfire radiation). For the helical

antenna to operate in the normal mode, the diameter of the helix should be very small as

compared to the wavelength. However, when the circumference of the helix is same as

that of the order of the wavelength, then the antenna is operating in axial mode.

Figure 1.13 Helix Antenna

In normal mode of operation, the field is minimum along the helix axis and maximum in

a plane normal to the axis. In this mode low bandwidth is obtained and can be used for

handheld devices [4]

In the axial mode of operation, the antenna radiates single beam along the axis of the

helical antenna. This mode gives high bandwidth and better gain when compared to

normal mode of operation. In this mode, as the turns on the helix increases, the beam

becomes narrower. In this mode antenna is widely used in satellite communication

because of its broadband nature. Figure 1.14 shows the different radiation patterns of

helix antenna.


Figure 1.14 Radiation Pattern of Helical Antenna

1.7.5 Horn Antenna

Horn antennas are widely used in microwave regions where waveguides are used as feed

forming a megaphone like structures.

Figure 1.15 Types of Horn Antenna


Horn antennas have many advantages such as low VSWR, low weight, wide bandwidth,

high gain and are easy to manufacture [4]. Rectangular, elliptical and circular are various

apertures of horn antennas. Various geometries of horn antennas are shown in figure

1.15. Rectangular waveguide feed having broad horizontal wall is used as feed in these

horn antennas.

H-plane Horn Antenna: If a narrow wall of waveguide is used as feed for broad wall

dimension of horn antenna, then it is known as H-plane horn antenna.

E-plane Horn Antenna: If the broad wall dimensions of horn antenna have a

waveguide feed in E-plane, and then it is called as E-plane horn antenna.

Pyramidal Horn Antenna: If the broad wall dimensions of horn antenna have a

waveguide feed in E as well as H-plane then it is called as pyramidal horn antenna.

The horn antenna reduces reflected waves and increases travelling waves which results in

wide bandwidth and low VSWR [5]. The antenna is widely used in satellite tracking,

communication dishes as a feed element.

In the above section various antennas and their properties have been discussed.

Microstrip Patch antenna is another commonly used antenna. The aim of the thesis work

is to design a compact patch antenna using various fractal geometries for aerospace

navigation and is explained in the next chapters.

1.8 Organization of Thesis

A low profile antenna covering multiple frequencies of aerospace navigation is presented

in this thesis. The design of the antenna is compact, robust and simple. Organization of

thesis is explained below.

Chapter 2 covers fundamental and theory of Microstrip Patch Antenna. Various design

parameters are also discussed. Furthermore various fractal geometries and their

characteristics are also analyzed.

Chapter 3 covers literature review. Articles covering various fractal designs on

microstrip patch antenna are reviewed and inference is also drawn after studying these

articles.


Chapter 4 covers proposed work and methodology adopted to obtain results from

simulation of proposed antenna.

Chapter 5 provides the results. Simulations are performed to obtain the results. Various

parameters such as gain plot, return loss characteristics, far field patterns and Voltage

Standing Wave Ratio (VSWR) plot are discussed in this chapter. It also includes the

hardware implementation. Various steps for the fabrication of the antenna are explained

and the measured results are compared with the simulated results.

Chapter 6 includes the conclusion of the thesis work and suggestions are also presented

for future development of the antenna.


CHAPTER 2

FRACTAL MICROSTRIP PATCH ANTENNA

2.1 Microstrip Patch Antenna

Microstrip patch antenna was developed by Bob Munson in 1972. It consists of radiating

patches that are placed on the top of the dielectric substrate and a conductive layer is

present on the bottom surface of the substrate, forming a ground for the antenna. The

shape and dimensions of the patch are the important features of the antenna [6].

Microstrip patch antennas are light in weight because of absence of machined parts and

are simpler, compact and easy to manufacture with printed circuit technology.

Figure 2.1 Microstrip Patch Antenna Structure

2.2 Advantages and Disadvantages of Microstrip Patch Antenna

Microstrip antennas are widely used in wireless applications due to their compact

structure. They are used as navigational antennas in aerospace and space communication.

These antennas are thin and compact and hence are extremely suited for handheld devices

such as pagers, phones etc [7]. Some of the major pros of Microstrip Antennas are:

Compact and light in weight.

Low manufacturing cost.

Supports circular as well as linear polarization.

Supports multiple frequencies.


Robust and can be placed on rigid surfaces.

Can be merged with microwave integrated circuits (MICs).

Some of the major disadvantages of Microstrip Antenna when compared with

conventional antennas are:

Limited bandwidth.

Nearly 6dB gain.

High ohmic losses.

Limited power handling capacity.

Little efficiency due to conductor and dielectric losses.

Low impedance bandwidth.

Artificial feed radiation from strips, surface waves, etc.

Microstrip patch antennas have high quality factor (Q). Quality Factor shows losses in the

antenna. Moreover high value of Q tends to have narrow bandwidth and low efficiency.

In order to reduce the value of Q, thick dielectric substrates should be used. But thickness

leads to unwanted power as power forwarded by the source goes into surface wave. By

array configuration, lower power handling capacity and lower gain can be overcome.

2.3 Basic Principle of Operation

Figure 2.2 shows a patch antenna in which ground is usually made of PC board. The

middle conductor of the coax represents probe feed to pair electromagnetic energy in and

out of patch.

The electric field is maximum (positive) at one side of the patch and minimum (negative)

at the other and zero at the core of the patch. The positive and negative sides changes

continuously with the phase of applied signal [8].

In a patch, the flow of electric field does not stop unexpectedly as in a cavity; rather it

expands towards the periphery. The expanding of field towards periphery is known as

fringing field and this causes the patch to radiate. This is the basic principle of a patch

antenna.


Figure 2.2 Side view of Patch Antenna

The electric field is maximum (positive) at one side of the patch and minimum (negative)

at the other and zero at the core of the patch. The positive and negative sides changes

continuously with the phase of applied signal [8].

In a patch, the flow of electric field does not stop unexpectedly as in a cavity; rather it

expands towards the periphery. The expanding of field towards periphery is known as

fringing field and this causes the patch to radiate. This is the basic principle of a patch

antenna.

2.4 Feeding Techniques

The feeding methods in Microstrip Patch antennas can be categorized as contacting and

non-contacting. In non-contacting electromagnetic field coupling is executed for the

transmission of power within the radiating patch and the microstrip line. On the other

hand in contacting, power is fed directly to the patch using bridging element. In

Microstrip Patch Antennas following are the feeding techniques:

Coaxial probe feed

Microstrip transmission line feed

2.4.1 Coaxial Probe Feed

Coaxial Probe Feed is the most common feeding technique used in Microstrip Patch

antennas. In this technique inner most conductor of coaxial connector expands from the


dielectric to the patch whereas, the outer conductor of the cable is joined to the ground

plane. Figure 2.3 shows a microstrip patch antenna with coaxial probe feed [7].

Figure 2.3 Coaxial Probe Feed for Microstrip Patch Antenna

The main advantage of such feeding technique is that it can be placed anywhere inside

the patch according to its input impedance. This method is easy to manufacture and

produces low artificial radiations. Nevertheless the main disadvantage is that it produces

narrow bandwidth and drilling of hole inside the substrate is somewhat difficult [9].

2.4.2 Microstrip Line Feed

In this type of technique, a strip of conductor is joined directly to the edge of microstrip

patch antenna as depicted in figure 2.4. The strip is shorter in width when compared to

the patch. The main advantage of this is that the feed can be engraved on the same

substrate and with the same material.

Figure 2.4 Microstrip Line Feed for Microstrip Patch Antenna


In this we do not need any additional matching element to match the impedance of the

patch to the feed line. This technique is easy to fabricate. However the disadvantage of

such technique as the thickness of the substrate increases, spurious waves and surface

waves also increases which in turn holds back the bandwidth of antenna.

2.5 Parameters Determining the Performance of Microstrip Patch

Antenna

A microstrip patch antenna consists of a ground plane, substrate and a patch. Various

parameters determine the performance of the antenna, some of which are explained

below:

2.5.1 Effect of Substrate

It is seen that the bandwidth of the antenna depends upon various parameters of the

substrate. The quality factor Q varies inversely with the impedance bandwidth of the

patch antenna. Therefore various parameters of substrate such as thickness and dielectric

constant can be changed to obtain different values of Q. Here Q is:

Q = Energy stored/Power lost

The bandwidth also depends upon the thickness of the substrate. As the thickness of the

substrate increases the bandwidth also increases. On the contrary when εr decreases,

bandwidth increases. However a thick substrate results in poor radiation efficiency. Also

thick substrates give rise to fictions radiation and radiation from the probe feed also

increases. Therefore this can be counted as a limitation in obtaining an octave bandwidth.

2.5.2 Effect of Parasitic Patches

A parasitic patch can be defined as a patch that is placed close to the feed patch. The

presence of parasitic patch excites the feed patch through coupling between the two

patches. If the resonance frequencies of the two patches are in close proximity to each

other, then a wide bandwidth can be obtained because the VSWR is of responses that

results in broad bandwidth.


2.5.3 Effect of Multilayer Configuration

When two or more patches of the dielectric substrate are placed together on different

layers, they form multilayer configurations. A multilayer configuration shows a decline

in radiation pattern when compared to single layer. One major drawback is the increase in

height which is not advantageous in the applications where space is a major issue. This

configuration also increases back radiation. Multilayer configuration yields broad

bandwidth [10, 11].

Figure 2.5 Multilayer Configuration

2.6 FRACTALS

2.6.1 Introduction

The word fractal was first devised by Benoit Mandelbort in the year 1975. It has been

derived from a Latin word “fractus” meaning fractured or broken. The fractal geometries

are generated from the complex structures occurring in nature. In the year 1988, Nathan

Cohen built the first fractal antenna. These antennas are designed using simple fractal

geometries which have self similar and space filling properties. Self similar property

associated with fractal geometry enables to design different parts of antenna that look

similar to each other when viewed at different scale. Space filling property reduces the

size of antenna when compared to other traditional antennas. Therefore by using fractal


geometries a compact antenna that can be operated at different frequencies can be

obtained.

Antennas with fractal geometries are quiet attractive due to their low weight, compact

size, multiband nature and easy manufacturing. The geometries of fractal antenna are

difficult to define using Euclidean geometries. The fractal antennas undergo number of

iteration forming a copy of the parent. Hence these antennas are also known as “Natural

Antennas” because their geometry resembles natural occurring phenomena such as

branches of trees, rivers, galaxies etc.

The antenna that undergoes number of iterations is called deterministic fractal antenna.

These antennas are designed using broken lines known as generators. The segments

forming broken line are substituted by the generator forming first iteration according to

the algorithm. The step is repeated infinitely resulting in fractal geometries. The iteration

function system decides the number of iterations [12].

A. Properties of Fractal Geometries

Space Filling Properties: Fractal Geometries have space filling curves.

Self Similarity: An object is approximately similar to a part of itself.

B. Fractal Geometry Types

Geometries are based on shapes that are self similar. There are two geometry types:

Random: These geometries are not exactly familiar to a part of itself but are quiet

familiar.

Deterministic: A generator is taken and is applied on successive size scales.

2.7 Dimensions of Fractal Geometry

Dimensions can be defined as the number of parameters or co-ordinates of an object.

There are different parameters for dimensions of fractal geometries such as self

similarity, topological dimension, and box counting dimension. Here self similarity

dimension is considered to define fractal geometries [14]. The self similarity dimension is

defined as:

𝐷s = log 𝑁/ log(1

𝑠) (2.1)


N is the number of self similar copies.

s is the scale factor.

Fractal Antennas have repeating patterns, therefore despite of using the word “repeat” we

use “iterate” and the process of repeating pattern is called iteration. The iterative function

is given by:

𝑊(𝑥) = 𝐴𝑥 + 𝑡 = [𝑎 𝑏𝑐 𝑑

] [𝑥1 𝑥2

] + [𝑒 𝑓] (2.2)

Where 𝐴 = [(

1

𝑠) 𝑐𝑜𝑠𝜃 − (

1

𝑠) 𝑠𝑖𝑛𝜃

(1

𝑠) 𝑠𝑖𝑛𝜃 (

1

𝑠) 𝑐𝑜𝑠𝜃

] (2.3)

Here a, b, c, d is defined by rotation and scaling of initial geometry and e and f denote the

translation.

Fractal geometries have two main components:

1. Initiator: The basic geometry of fractal antenna.

2. Generator: Shape that we get after different iterations.

Fractal antennas provide better input impedance and can be used in devices where space

is a major issue because of space filling property. These antennas can show multiband

properties due to self similar design. By using self similar property a number of copies

can be found within the whole geometry. Hence fractal geometries do not have any

characteristic size and shape. Despite of having so many advantages fractal antennas are

difficult to fabricate and sometimes provide lower gain.

2.8 Fractal Geometries

2.8.1 Sierpinski Gasket

In 1915, Waclaw Sierpinski designed Sierpinski triangle. In this the equilateral triangle is

subdivided into smaller equilateral triangles. This pattern can be generated using

mathematical equations.


In order to create this geometry an equilateral triangle is cut out from the center of main

triangle and thus resulting in three smaller triangles of equal dimensions, called first

iteration as shown in figure 2.6. This process is carried out infinitely. This geometry is

most commonly used for antenna applications. This is used for monopole and dipole

antenna configurations [6].

Figure 2.6 Sierpinski Gasket

2.8.2 Sierpinski Carpet

This geometry is similar to sierpinski gasket, but it uses squares in place of triangles. In

first order iteration a square having dimensions one third of the main square is subtracted

from the center of the square. This process is repeated infinite times in order to get next

order iterations. The pattern is repeated in a symmetrical manner such that each etched

square is one third in dimension of the sharing square. Figure 2.7 represents geometry of

Sierpinski Carpet [14].

Figure 2.7 Sierpinski Carpet


2.8.3 Koch Curve

In the year 1998, von Koch monopole antenna improved various features such as

radiation resistance, bandwidth and resonance frequency when compared to conventional

antennas.

Figure 2.8 Koch Curve

This geometry is quiet simple. It starts with a straight line as an initiator. The line is

divided into three equal parts; the segment in the middle is replaced with two other of

same length. This is the first iteration version and is called the generator. Monopole and

dipole antennas can be constructed with Koch Curve geometry. Figure 2.8 shows the

geometry of Koch Curve [15].

2.8.4 Hilbert Curve

This geometry is also known as Space Filling Curve since it fills the area it occupies.

In this geometry each consecutive iteration consists of previous four copies of iteration.

The geometry is simple as the curves can be drawn easily and the lines of the geometry

do not intersect with each other. The fractal geometry of Hilbert Curve is shown in figure

2.9 [16].

Figure 2.9 Hilbert Curve


2.8.5 Minkowski Curve

In 1907, a German mathematician, Hermann Minkowski devised a new fractal shape

called Minkowski Sausage and later known as Minkowski Curve.

Figure 2.10 Minkowski Curve

This fractal geometry reduces the size of antenna and also increases the efficiency by

occupying the volume with electrical length. The fractal geometry of the fractal design is

shown in figure 2.10 [17].

2.8.6 Pythagorean Tree Fractal

In Pythagorean Tree Fractal the geometry starts with square, called zeroth iteration.

When two other squares are placed upon the first square such that the corners coincides

with the main square then this is known as second order iteration. The process is followed

by infinite iterations accordingly. The fractal geometry of Pythagorean Tree Fractal is

shown in figure 2.11 [18].

Figure 2.11 Pythagorean Tree Fractal


2.9 Advantages and Disadvantages of Fractal Geometries

2.9.1 Advantages of Fractal Geometries

Small in size

Better input impedance

Wideband/multiband support

2.9.2 Disadvantages of Fractal Geometries

Fabrication and Design is complicated

Numerical limitations

Lower Gain in some cases

2.10 APPLICATIONS OF FRACTAL GEOMETRIES:

Fractals can be described as anything that appears irregular. Fractal geometries are

unique and random. Common fractal shapes found are:

leaves of the trees

a DNA molecule

various veins in our hands

irregular patterns of clouds

an oxygen molecule

Various applications of fractal geometries are discussed below:

2.10.1 Astronomy

Fractal geometries can be seen in space as well. According to cosmologists, the matter is

spread uniformly across space. But the above assumption is not true. Astronomers

assume that the universe is not smooth at large scales but the assumptions can be true at

small scales. But various scientists claims that the structure of universe is fractal at all

scales.


2.10.2 Nature

Tree is a good example to show fractal geometry in nature. Study various branches,

leaves and structures of tree. It is seen that they all possess similarity in their fields.

Another example to show similarity in nature is weather. Weather forecasts are not

generally accurate because of minor disturbances in heating, solar etc. More examples of

fractal geometries in nature can be mountains, coastlines etc.

2.10.3 Computer Science

Fractal image compression is the most useful technique used in computer science. Using

this technique, images can be compressed much more than their usual ways. Another

advantage of fractals in computer science is image enlargement without pixelisation.

2.10.4 Telecommunication and Medicines

Fractals can be used for biosensor interactions in medical field. Fractals have found their

way in sector of telecommunications because of its small size and light in weight.

Fractals provide multiband behavior by transmitting the currents in different arms.


CHAPTER 3

LITERATURE SURVEY

In the world of wireless communication, there has been an ever increasing demand of

compact, small and low power consumption antenna designs. Therefore compromise has

to be made among bandwidth, volume or radiation pattern of an antenna while designing

a compact antenna that is capable of covering maximum frequency bands required for a

given application.

3.1 Literature Review

Tu Zhen et al. in [19] designed a Minkowski Fractal Loop yagi Antenna based on Rao-

Wilton-Glisson (RWG) and delta-feed gap model. The Minkowski loop yagi antenna is

iterated up to 1st level. The proposed antenna operates at 880-960 MHz frequency band.

Minkowski loop reduces the size of the antenna up to 34.5% as compared to square loop

yagi antenna working on same frequency band. The size of the Minkowski loop yagi

antenna is 8.5 × 8.5 cm2. The gain of the antenna is between 10dBi-11.2dBi. The antenna

provides good return loss over targeted frequencies.

J.B. Pereira et al. in [20] designed a simple printed fractal monopole antenna for WLAN

USB dongle applications. In this antenna a combination of fractal geometry and

meandered line is used to achieve multiband characteristics. The proposed antenna covers

a bandwidth of 2.22 to 2.52GHz and 5.03 to 5.84 GHz that covers entire band required

for various WLAN standards such as 802.11 a/b/g standards. The size of the antenna is

50 × 20 mm2 which is perfect for a USB dongle. Moreover the antenna provides good

return loss and maximum gain of 2.4dBi and 1.8 dBi over 5.2/5.8GHz and 2.4GHz band

respectively.

Joan Gemio et al. in [21] designed a triangular monopole on a fractal ground plane to

obtain a dual band antenna for WLAN applications. The design of the ground plane is

based on Sierpinski gasket. The antenna covers 2.45 and 5.4 GHz frequency bands of


WLAN. It is seen that directivity and efficiency changes significantly by using fractal

based ground plane as compared to solid ground plane of same dimensions. The

directivity of the antenna is 3.4 dB and 4.6 dB for 2.45 GHz and 5.4 GHz respectively.

This antenna can be used for indoor environments.

Y.B. Thakare et al. in [22] designed a novel star shaped fractal patch antenna for the

reduction of backscattering of radar cross section (RCS). The size of the antenna was

reduced to 50% when compared with a conventional circular microstrip patch (CCMP)

antenna. The proposed antenna operates at 0.85-4GHz frequency band. It is seen that as

the number of iterations increases, a reduction in backscattering RCS can be observed at

multiband because of frequency selective nature, when compared to other conventional

patch antennas. In addition by varying the size and thickness of the substrate

backscattering can be reduced. The size of the antenna is 110mm ×110mm. The proposed

antenna design can be used for many defense and civilian applications.

S.R. Anoop et al. in [23] designed fractal microstrip patch antenna for multiband

operation. The square patch of the antenna is iterated upto three iteration. The dimensions

of the patch are 27mm × 27mm. The proposed antenna design resonates at 2.6 GHz, 3.3

GHz, 4.5 GHz and 6.9 GHz. Due to self similarity between different parts of patch, the

antenna shows multiple frequency bands. The proposed antenna has compact structure

and is designed on FR4 substrate. It is observed that after each iteration, the antenna

resonates at more number of frequency bands. The average percentage of bandwidth is

10.92. The antenna provides good gain and radiation properties.

Atif Jamil et al. in [24] designed a compact multiband hybrid meandered Koch fractal

antenna for USB dongle. The proposed antenna is designed using Koch-meandered

fractal geometry and covers a bandwidth of 5.1406- 5.8737 GHz and 2.2909-2.553 GHz.

The minimum return loss is achieved at the lower band of 2.41GHz of -28.9dB and the

upper band shows a return loss of -20.8dB at 5.36GHz. The dimensions of the antenna

are 14.2mm × 10mm and it covers a complete band of WLAN IEEE 802.11 a/b/g

standard. The antenna provides good symmetric radiation patterns and high gain. The


antenna is compact and provides good performance and can be used in USB dongle for

WLAN applications.

A. Ismahayati et al. in [25] presents the design of Koch fractal antenna and monopole

antenna. By using fractal geometry a compact size and multiband behavior can be

obtained. Various parameters such as gain, bandwidth, reflection coefficient and radiation

pattern of monopole antenna and Koch fractal antenna are discussed. The size and

dimensions of the two antennas are kept same. The results show that Koch fractal antenna

is better than planar monopole as it covers more number of resonant frequencies,

provides larger bandwidth and is compact in size. The Koch fractal antenna operates at

three frequencies i.e., 7 GHz, 2.4GHz and 5.8GHz while planar monopole antenna

resonates at a single frequency, covering a bandwidth of 360-368 MHz. Therefore it is

seen that as the number of iterations increases in fractal design, more frequencies are

covered. Moreover size of the Koch fractal antenna reduces up to 20% when compared to

planar monopole antenna.

Yogesh Kumar Choukiker et al. in [26] designed a wideband fractal antenna with

combination of two fractal geometries. The wideband mechanism is achieved by studying

the behavior of current on the patch. The antenna is realized using cantor and Koch

fractal geometries and covers a bandwidth of 1.64GHz- 3.5 GHz. The dimension of the

antenna is 66mm × 25mm and is fed using microstrip line with a matching of 50Ω. A

gain of 2.5 dBi- 6 dBi can be observed at a wideband frequency range with

omnidirectional radiation patterns. The antenna can be used for many wireless

applications.

Hitesh Dholakiya et al. in [27] presented a single slot on the patch of the microstrip patch

antenna to enhance the bandwidth of the antenna. The antenna provides 3.5 times higher

bandwidth than conventional microstrip patch antenna. The proposed antenna covers a

frequency range of 2 to 6 GHz and obtains gain of 4dB. The size of the antenna is 75mm

× 75mm.The dimensions of the slot on the patch of the antenna is 30mm × 30mm. The


slot on the patch is iterated three times and each consecutive iteration increases the

bandwidth of the antenna. The antenna can be used for many applications.

D. Kumar et al. in [28] designed miniature fractal antenna for wireless applications. In

this design copper is used as an antenna material while FR4 is used as a substrate. The

dimension of the antenna is 36mm × 20mm × 1.6mm.The proposed antenna operates at

two frequencies i.e., 180MHz and 200MHz. It is seen that the radiation pattern of the

antenna is mainly directional radiating large amount of energy in upward direction. The

VSWR values of 1.19, 1.2, 1.26 and 1.84 are well matched with impedance values of

55Ω, 57 Ω, 36 Ω and 43 Ω respectively. Also backward radiation is low because of the

presence of separate ground plane. Radiations can be achieved in C, J and X band

regions.

Dilara Khatun et al. in [29] designed a multiband fractal square Koch antenna for

UHF/SHF application. The antenna operates 496MHz and 1430MHz after first iteration

and 460MHZ, 1248MHz, 1926MHz and 4390MHz after second iteration. The feed of the

antenna is located at the origin. The proposed antenna provides a gain of 4.9dB after first

iteration and 8dB after second iteration. It is seen that as the number of iterations

increases, operating bands also increases since the first iteration provided two frequency

bands while second iteration provided four frequency bands. Therefore the antenna can

be operated for UHF/SHF applications because of its multiband behavior.

Trushit Upadhyaya et al. in [30] designed a square patch fractal antenna to obtain

multiband behavior of patch resonator antenna. The proposed antenna operates at 2.7-

2.9GHz for aeronautical navigation and 9.0-9.3GHz for Maritime radio navigation. In

this modified conventional Koch geometry is used to design the antenna. The square

patch is iterated consecutively three times. The dimension of the antenna is 70mm ×

70mm × 3.2mm. A gain of about 8.53dB with good radiation pattern can be observed.

The antenna provides good return loss over targeted frequencies. The proposed antenna

can be used for various military and commercial applications.


Dr. S. Arivazhagan et al. in [31] designed a triangular fractal patch antenna with slit for

Indian Regional Navigational Satellite System (IRNSS) and GPS Aided and Geo

Augmented Navigation (GAGAN) applications. These systems are based on satellites and

are designed to provide support over Asian- Pacific regions. The proposed antenna

operates at 1175 MHz, 1575.2 MHz and 2492.08 MHz. Sierpinski Gasket fractal

geometry is used to design this antenna. The directivity of the antenna is 6.29723dB

while the gain is equal to 5.052dB. The antenna shows good radiation properties and

supports multiple bands. The designed antenna can be used for military applications.

S. Banu et al. in [32] designed a fractal microstrip patch antenna for Wireless Power

Transmission (WPT) systems. The patch of the microstrip antenna is iterated up to 3rd

level. The proposed antenna operates at frequency range of 1 to 5 GHz covering

1.86/2.29/3.02/4.50 GHz. The dimensions of the antenna are 54.36mm × 46.72mm. The

directivity of the antenna is 7.48 dB while gain oscillates from 2.98 to 3.01 dB. The

antenna operates at multiple frequencies and hence can be used in Wireless Power

Transmission (WPT) systems in Solar Power Satellites. The antenna operates at S-band

and C- band and has small size and light weight. Therefore authors concluded that fractal

antennas can be used to replace conventional patch antennas due to their size reduction

property.

Raj Kumar et al. in [33] designed a compact fractal monopole antenna for Ultra

Wideband (UWB) applications. The dimension of the proposed antenna is 40mm ×

40mm. The antenna operates at a bandwidth of 8.54 GHz covering frequencies from

2.8GHz to 11.4 GHz. The antenna is designed on FR4 substrate. It is observed that the

antenna is Omni-directional in H-plane and bidirectional in E-plane. The antenna

provides good return loss over targeted frequencies with peak gain of around 5dB. The

proposed antenna can be easily integrated with MMIC devices and can be useful for

navigational applications such as radar and fourth generation wireless communication

applications.


N.H.M. Sukaimi et al. in [34] designed a multilayer fractal patch antenna using Low

Temperature Co-Fired Ceramic (LTCC) Technology. In this design a Minkowski fractal

design has been used. The proposed antenna design eight layers of substrate are used.

The Ferro A6S with dielectric constant 5.9 is used as a substrate with thickness 0.096mm.

The proposed antenna covers a bandwidth from 2.33 MHz to 16.1 MHz. The dimension

of the ground plane of the proposed antenna is 35 × 25 mm2 while total thickness is

0.8mm. A gain of 10.02 dB is provided by the proposed antenna. It is observed that the

better simulation results are obtained using fractal patch antennas when compared with

convention patch antennas.

Sundaravel Elumalai Muthumani et al. in [35] designed a compact slot loaded fractal

patch antenna that provides bidirectional radiation properties. In this design Koch fractal

design has been used. Slots are introduced in the middle and corner edges of the radiating

patch to reduce the size of the antenna. The antenna resonates at 1.53 GHz and 1.27 GHz.

The antenna shows bidirectional and good radiation properties in co-polarized H-plane

and E-plane. The size of the antenna is reduced 60 % of the conventional patch antennas.

The proposed antenna can be used in handheld devices such as mobile phones.

Yuming Nie et al. in [36] designed a compact triband fractal Planar Inverted F Antenna

(PIFA) for mobile handset applications. The proposed antenna resonates at GSM (0.89-

0.96GHz), DCS (1.71 GHz- 1.88GHz) and WLAN (2.445 GHz- 2.455GHz) frequency

bands. The dimensions of the antenna are 41mm × 21mm × 1.55mm and consuming a

volume of nearly 1.51 cm3. Because of very compact size, the antenna can be used inside

commercial mobile handsets. The reflection co-efficient of the proposed antenna is – 6dB

in GSM and DCS bands and -10dB in WLAN. It has been observed that the antenna

provides good radiation properties and return loss for all the operating bands.

T. Rama Rao et al. in [37] designed a fractal patch antenna for UWB wireless

communications. A new fractal design is proposed by the authors to design the antenna.

In this two circles are removed with center on the main patch. After this, an arc is

removed from the main patch. The same process is repeated four times. The dimensions


of the proposed antenna are 34mm ×32mm× 1.6mm. The radiation pattern of the antenna

is nearly omnidirectional with gain of 4.83dB. The antenna operates at a bandwidth of

7.90 GHz covering range of frequencies from 3.24GHz to 11.14GHz with an efficiency

of 93.55%. The antenna is quiet suitable for Ultra Wideband wireless communication

systems. Moreover the proposed antenna is small in size, low cost and is easy to

fabricate.

Sayantan Dhar et al. in [38] designed a dielectric resonator antenna that operates at

multiple frequencies. The antenna is designed using Minkowski fractal geometry to

reduce the size of the antenna and to generate multiple frequency bands. The dielectric

load improves the impedance bandwidth as well as gain of the antenna. The proposed

antenna operates at GSM (890-960 MHz), PCS (1850-1990 MHz), IEEE 802.11 b/g/n

(2.4-2.485 GHz), WiMAX (3.4-3.6 GHz) and IEEE 802.11 a/h/j/n (5.15- 5.85 GHz). The

dimension of the antenna is 100mm × 100mm × 1.6mm. The antenna provides a gain of

1.1-3.1dBi over various frequency bands. The antenna provides good return loss over

targeted frequencies.

Malathi Kanagasabai et al. in [39] designed a circularly polarized broadband antenna

using fractal geometry to achieve broad VSWR bandwidth and Axial Ratio bandwidth

(ARBW). The proposed antenna operates at 1.47 GHz- 1.83 GHz and 1.47GHz – 1.83

GHz. The dimension of the antenna is 65mm × 65mm × 1.6mm. The antenna provides a

gain of 6.6dB at 1.775GHz. A reflector at half wave distance from the radiator has been

installed to make the antenna bidirectional. The antenna provides good return loss over

targeted frequencies and an efficiency of 76% to 94% in the operating band.

V. Dinesh et al. in [40] designed a rectangular carpet fractal antenna for various wireless

applications. The dimension of the patch of the proposed antenna is 100mm × 100mm

and resonates at two frequencies i.e., 3.6GHz and 7GHz. The antenna is designed using

Sierpinski gasket carpet fractal geometry and is iterated up to 3 iterations. The antenna is

designed on FR-4 substrate with thickness of 1.6mm. The proposed antenna provides a

gain of 3.9711 dB. The antenna provides good return loss over targeted frequencies.


V. Dhana Raj et al. in [41] designed microstrip apollonian gasket fractal antenna for

multiband wireless applications. The proposed antenna operates in L-band and C-band to

X-band. The antenna has various advantages in terms of size, volume and design when

compared to other conventional antennas. The maximum gain of the antenna is 3.61dB.

The proposed antenna shows a maximum return loss of -28.97dB and VSWR of 1.09 at

8.16 GHz. The antenna can be used for vehicular Radar, PCS, imaging systems and GPS.

Shrivishal Tripathi et al. in [42] designed a compact octagonal shaped fractal antenna for

Ultra Wideband (UWB) Multiple Input Multiple Output (MIMO) applications. The

antenna is designed using Koch fractal geometry. For good isolation fractal monopoles

are placed orthogonal to each other. The dimension of the antenna is 45mm × 45mm and

shows quasi omnidirectional radiation pattern. The proposed antenna shows bandwidth

from 2- 10.6 GHz and isolation better than 17dB can be seen over entire UWB range. The

antenna shows good pulse preserving capability and hence can be used for various

wireless applications.

Tanmoy Sarkar et al. in [43] designed a microstrip patch antenna using different fractal

slot structures for bandwidth enhancement. The proposed antenna operates at 3.20 GHz,

3.37 GHz and 4.26 GHz. A gain of 4.5 dB to 5.3 dB can be achieved for the impedance

bandwidth from 3.20 GHz to 4.26 GHz. It is observed that the bandwidth of the antenna

improves by introducing fractal geometry when compared to conventional antennas.

Apollonian shaped fractal slot achieves maximum percentage of bandwidth. Moreover

gain of the antenna also improves with the introduction of fractal geometries.

3.2 Inferences Drawn

As it is clear from the literature survey of Microstrip Patch antenna and various Fractal

geometries that an antenna is required that is small in size, light in weight, operates at

multiple frequencies, consumes low power and provides high reliability. Fractal

geometries used with microstrip patch antenna reduces the size of antenna and also

enhances multiband properties by increasing the number of fractal iterations.


Today’s communication requires an antenna that provides higher gain, wider bandwidth,

supports multiple frequencies and is compact in size so that it consumes less space.

Therefore variety of approaches need to developed in order to get the desirable features

of antenna. The new approaches should be able to corporate with the existing technology.

A smaller antenna that supports multiple frequencies is the need for the aerospace

navigation applications.

Microstrip Patch Antenna with Fractal designs is used for aerospace navigation

applications. Microstrip patch antenna alone cannot provide multiband properties and in

order to get multiband properties patch antenna is coupled with fractal geometries. In

fractal antennas coupling between sharp angles produce different current paths achieving

multiband operations. Also by increasing the number of fractal iterations, perimeter of

patch increases and effective area decreases and hence size of the antenna can be

reduced. Antennas used in aerospace navigation should also exhibit Omni directional

characteristics in order to communicate with the air traffic. A microstrip patch antenna

with fractal geometries provide multiband and omni directional properties and hence can

be used for aerospace navigation.

Fractal Microstrip Patch Antenna is preferred over other conventional antennas because it

provides low profile planar configuration, has small size, supports multiband and

wideband operations and provides better input impedance. These features make fractal

antennas unique from other antennas and make them suitable for using with navigation

applications.


CHAPTER 4

PROPOSED RESEARCH WORK

4.1 Problem Definition

The latest development in aerospace navigation is to design a mechanically robust

antenna that has the capability of operating at multiple frequencies. The problem of

covering maximum navigational frequencies is the need of today and can be achieved by

using fractal designs [44]. A fractal design not only covers maximum frequencies but also

reduces the size of the antenna and can be used in places where space is a major issue.

Therefore the aim of the thesis is to design a fractal microstrip patch antenna that has

desired multiband resonance, compact profile and exhibits omni directional

characteristics.

4.2 Objectives

In this thesis, a mechanically robust and low profile antenna is designed to operate at

various frequency bands. The main objectives of the thesis work are:

• To study the recent progress and trends towards fractal microstrip patch antenna.

• To design a small microstrip patch antenna using fractal geometries.

• To design an antenna that it covers maximum navigation frequencies.

• To reduce the size of the antenna.

• To improve the gain of the antenna.

• To design an Omni directional antenna to obtain good radiation pattern.

Therefore microstrip patch antenna using various fractal geometries is designed and

optimized that has compact structure and supports multiple frequency bands mainly

7.5GHz, 9.60GHz, 12.15GHz, 13.90 GHz, 15.30 GHz and16.30 GHz.


4.3 Scope of Work

In this work, a conventional Koch fractal antenna with slots on the ground plane is

designed. The fractal designs covers maximum number of frequency bands and also

reduces the size of the antenna. The slots are well positioned and are used to cover the

desire frequency bands.

4.4 Methodology of Proposed Research Work

4.4.1 Design Methodology

The simulation of the antenna is carried out using High Frequency Structure Simulator

(HFSS) software. High Frequency Structure Simulator (HFSS) is an industry standard

simulation tool. It has powerful drawing capabilities to simply the antenna design. It is

seen that after simulation the antenna provides desired resonant frequencies that have

good operating bandwidth. Designing a multiband antenna using fractal geometries is a

complicated task because slight changes in different parameters can affect resonant

frequencies or return loss. The main design methodology is shown in figure 4.1.

Figure 4.1 Flow graph of Design Methodology of Proposed Research Work

Selection of Design

parameters

Modeling of

Multiband Antenna structure.

Optimizing Design

Parameters

Comparison & Result Validation


4.4.2 Selection of Design Parameters

The aim of this thesis work is to design an antenna that is compact in size and supports

multiple frequency bands. Moreover this antenna must be able to operate in various

frequency bands such as 7.5GHz, 9.60GHz, 12.15GHz, 13.90 GHz, 15.30 GHz and16.30

GHz. As a result various antennas were studied and their behavior and characteristics

were observed. Among these antennas Microstrip Patch Antenna (MSA) with fractal

geometry is considered as the most promising candidate. Therefore various fractal

geometries are studied and basics are learned to develop a multi-band structure.

There are many fractal geometries to design multi-band antenna. These geometries result

in dual band and tri-band operations. It is also observed that the overall sizes of the

antenna also reduces by using these designs and hence are suitable for device where less

space is required. From all the above characteristics of fractal patch antenna it is

observed that it is highly suitable for small and compact devices where space is a major

issue.

4.4.3 Selected Geometry

The geometry of the antenna is simple and robust that is commonly used in various

navigation applications. In this design FR4 is used as dielectric material with dielectric

constant, ɛr = 4.4; loss tangent, δ = 0.02 and height of substrate, h = 1.6mm. To feed the

antenna co-axial cable is used from the backside of the PCB where the ground plane lies.

4.5 Design of Fractal Microstrip Patch Antenna

In this section various levels of iterations of fractal designs will be discussed along with

proposed multiband fractal antenna with slots on the ground plane. To understand the

concept of microstrip patch antenna with conventional Koch fractal geometry, a basic

design is analyzed first.

4.5.1 A Simple Microstrip Patch Antenna

Before designing a multi-band fractal patch antenna, various designing process of simple

microstrip patch antenna and its characteristics will be discussed. By designing simple

patch antenna, various characteristics, concepts and other factors that determine the


performance of patch antenna are studied in detailed manner. The basic dimensions of

Microstrip Patch Antenna are derived using following equation.

Lp + Wp = λ/2 (4.1)

The resultant dimensions of Microstrip Patch Antenna are:

Lp = 45mm

Wp = 45mm

Figure 4.2 Microstrip Patch Antenna (a) Top View (b) 3D View in HFSS

Table 4.1 Detailed Dimensions of Proposed Microstrip Patch Antenna

Parameter

Value (mm)

Lg 45

Wg 45

Lp 40

Wp 40

Ls 45

Ws 45

h 1.6


The proposed antenna consists of a ground plane, substrate and a radiating patch as

shown in figure 4.2 (a) and (b). The total volume occupied by the antenna is

approximately 3240mm3. In this geometry the antenna structure resonates at 3.4 GHz, 7

GHz and 9 GHz. Although the antenna shows multiband behavior but these frequencies

are not desirable for aerospace navigation. In order to get desired frequencies, Koch

fractal design is deployed on patch antenna and its various effects are discussed in the

next section.

4.5.2 A Multiband Microstrip Patch Antenna with Koch Fractal Geometry

The structure of the proposed microstrip patch antenna with conventional Koch fractal

geometry and its three iteration levels is shown in figure 4.3 (a), (b), (c). The proposed

fractal antenna consists of a radiating patch, ground plane and co-axial feed. By using

fractal geometries the size of the antenna can be reduced while it still maintains its

multiband behavior.

The fractal geometry can be changed mainly by two factors: the iteration number and

iteration factor. The construction law of geometry is depicted by the iteration factor and

the number of iteration processes is represented by the iteration number. Here ¼ factors

are taken. Let us assume that the dimensions of the patch are equal to parameter A, where

A = 40. Various design steps of fractal antenna are explained below.

Step 0: In 0th iteration, the shape of the patch is square with an area A2 and perimeter

4A.

Step 1: In 1st iteration four squares with dimensions of A/4 are cut out from the

middle of the sides of the main square as shown in figure 4.3 (a). Hence Area =

0.75A2 and Perimeter = 6A.

Step 2: In 2nd iteration, the so formed four edges are taken as individual squares and

again four squares with dimensions 3A/32 are cut out of them as shown in figure 4.3

(b). Hence Area = 0.60 A2 and Perimeter = 9A.

Step 3: In 3rd iteration, the three small edges are taken as individual squares and again

the above steps are repeated and squares of dimensions 9A/256 are cut out from these

edges as shown in figure 4.3 (c). Hence Area = 0.36 A2 and Perimeter = 15.75 A.


Figure 4.3 3D View in HFSS (a) First iteration (b) Second iteration (c) Third iteration

The dimensions of the ground plane of the antenna are 45×45×1.6 mm3 and that of a

radiating patch are 40×40 mm2. The 3D view in HFSS of the proposed antenna is shown

in figure 4.4. All the iterations are the modification of conventional Koch geometry.

Figure 4.4 3D View of fractal microstrip patch antenna in HFSS

The main objective of the thesis work is to design a compact, robust and multiband

antenna that covers maximum number of navigation frequencies and can be used in

devices where less space is available. Therefore the dimension of the antenna is 45mm ×

45mm × 1.6mm. With these dimensions the antenna resonates at 7.50 GHz, 11.5 GHz,


13.5 GHz, 15.5 GHz and 16.5 GHz with good bandwidth to serve for various navigation

applications

4.5.3 A Multiband Fractal Patch Antenna with Four Slots on the Ground Plane

The structure of the proposed fractal antenna with different slots on the ground plane is

shown in figure 4.5. Modifying the ground plane results in enhancement of operational

bandwidth and coverage of other navigation frequencies. The dimensions of the ground

plane of the proposed antenna are 45mm × 45mm × 1.6mm and that of radiating patch are

40mm × 40mm. The slots placed on the ground plane results in obtaining certain

navigational frequencies that a simple fractal patch antenna was not able to cover.

Moreover these slots also results in the improvement of operation bandwidth and

simplified the design of PCB.

Figure 4.5 Multiband Fractal Patch Antenna with Slotted Ground Plane (a) Bottom View (b) 3D view

Figure 4.6 shows the detailed dimensions of proposed antenna with two rectangular and

two circular slots on the ground plane. All the four slots are placed close to the edges of

the ground plane of the antenna. The location of feed is selected after observations and

optimization so that the antenna resonates at 2.6 GHz and 9.4 GHz.

The dimensions and the position of the four slots are so selected so as to achieve

maximum operating bandwidth at each resonating frequencies. Also a wideband of 7

GHz is obtained after introduction of slots on the ground plane. Values of dimensions are

given in table 4.3. The proposed antenna supports several frequency bands. The main

objective of the research work is to design a small, low profile multiband antenna for


aerospace navigation. The size of the antenna is very compact and can be used in places

where space is a major issue. The navigational bands covered by proposed antenna are

HF communication ( 2.6 GHz), NAVAID ( 7.5 GHz), LLWAS, RMM, LDRCL ( 9.4

GHz), Surveillance RADAR, GPS, GLONASS L1, Satellite Based Navigation, fixed

links, Military RADAR (12.6 GHz – 18.6 GHz).

Figure 4.6 Detailed Dimensions of Proposed Antenna in HFSS

Table 4.2 Detailed Dimensions of Proposed Multiband Fractal Antenna

Parameter Value (mm)

Lg 45

Wg 45

Lp 40

Wp 40

Ls 45

Ws 45

R1 03

L1 10

L2 10

h 1.6


CHAPTER 5

SIMULATED AND MEASURED RESULTS VALIDATION

5.1 Introduction

All the results presented in this chapter are produced by the simulation software called

High Frequency Structural Simulator (HFSS). High Frequency Structure Simulator

(HFSS) is an industry standard simulation tool. It has powerful drawing capabilities to

simply the antenna design. In this chapter, the various results such as radiation patterns,

3-D Gain plots, return loss and VSWR plots are discussed.

5.2 Simulated Results of Microstrip Patch Antenna

The first step is designing and simulation of microstrip patch antenna using HFSS

software. The basic microstrip patch antenna resonates at only two frequencies and a gain

of 3dBi is observed.

5.2.1 Return Loss Characteristics

The following plot in figure 5.1 shows the return loss of basic microstrip patch antenna

design.

Return Coefficient v/s Frequency

Figure 5.1 Simulated Return of basic Microstrip Patch Antenna


From the plot shown in figure 5.1, it can be observed that the antenna resonates at 3.4

GHz, 7GHz, 9 GHz, 12.6 GHz and 14.6 GHz. The return loss obtained is -11.91, -18.66, -

11.33, -11.51, and -14.24 respectively.


The simulated 3D radiation pattern at 2.5 GHz can be obtained from the simulation

results using High Frequency Structural Simulator (HFSS) software as shown in figure

5.2. It can be seen from the plot that antenna provides almost omni directional radiation

and can be used for navigation applications.

Figure 5.2 3D Radiation Pattern of Microstrip Patch Antenna

5.2.3 Gain

The gain describes the efficiency of the efficiency of the antenna. The net gain of the

antenna obtained after simulating microstrip patch antenna is shown in figure 5.3. A gain

of 2.69 dB is observed at 7GHz. The gain obtained has a moderate value and is observed

to be good according to the performance of the antenna.


Figure 5.3 Simulated 3-D Gain Plot of Microstrip Patch Antenna

5.2.4 Voltage Standing Wave Ratio (VSWR)

The value of Voltage Standing Wave Ratio (VSWR) should be 3:1 or less than 3dB at

resonate frequency. This value is advantageous for most of the applications of wireless

communication. Figure 5.4 shows the simulated results of VSWR for the frequency range

from 1 GHz to 20 GHz.

VSWR v/s Frequency

Figure 5.4 Simulated VSWR plot of microstrip patch antenna


5.3 Simulated Results of Fractal Patch Antenna

After designing and analyzing basic microstrip patch antenna, the following step is to

design fractal microstrip patch antenna using modified conventional Koch geometry.

Proposed antenna covers multiple frequencies and covers a wideband of 7 GHz.

5.3.1 Return Loss Characteristics

The following plot in figure 5.5 shows the return loss for fractal patch antenna.

Return Coefficient v/s Frequency

Figure 5.5 Simulated Return Loss of Fractal Patch Antenna

From the plot shown in figure 7.5, it can be observed that the proposed antenna resonates

at 2.6 GHz, 4.6 GHz, 7 GHz, 8.6 GHz, 11 GHz, 13.4 GHz , 14.2 GHz, 15.4GHz, 16.6

GHz and 18.2 GHz with return loss -8.27, -6.95, -10.59, -5.87, -13.59, -23.93, -13.86, -


28.69, -20.78 and -9.92 respectively. The navigational bands covered by the antenna are

HF Communication (2.1-2.8 GHz), NAVAID (7.5 GHz), Air Router Surveillance Radar,

GPS, GLONASS L1 (12.15- 13.9 GHz), Sattelite Based Communication (15.45- 15.59

GHz), Satellite Navigation (15.59- 16.10 GHz) and Fixed Links and LDRCL (17.10 –

18.50GHz).


The simulated 3 D radiation pattern is obtained from the simulated results and is shown

in figure 5.6. It can be observed from the results that the antenna is almost omni

directional and hence can be used for aerospace navigation supporting multiple standards.

Figure 5.6 Simulated 3D radiation pattern of Fractal Patch Antenna

5.3.3 Gain

The gain determines the efficiency of the antenna and is important figure of merit of

antenna. The overall gain of the proposed antenna after simulation is shown in figure 5.7.

A peak gain of 7.36 dB is obtained at frequency 13.4 GHz.


Figure 5.7 Simulated 3D Gain plot of Fractal Patch Antenna




communication. Figure 5.8 shows the simulated results of VSWR for the frequency

sweep from 1 GHz to 20 GHz. The value of VSWR is less than 3 at all the resonating

frequencies.

VSWR v/s Frequency

Figure 5.8 Simulated VSWR plot of fractal patch antenna


5.4 Simulated Results of Multiband Fractal Patch Antenna with Slots on

the Ground Plane

The antenna designed in the previous section was a wideband antenna with Koch fractal

geometry on its patch. It can be observed that the fractal geometries not only reduces the

size of the patch and allows the other components to integrate on the same substrate but

also provide multiple frequencies with good return loss peaks. It can be seen that various

navigational frequencies were not covered by the fractal patch antenna. Therefore, in

order to cover those frequencies we extend the designing of the antenna by introducing

various slots on the ground plane. These slots provided good resonance along with good

gain and impedance bandwidth. Thus, introduction of slots on the ground plane further

improves the performance of the antenna.

5.4.1 Return loss characteristics

The plot shown in figure 5.9 shows the return loss of the proposed antenna. The proposed

antenna covers multiple frequencies with wideband of 7 GHz.

Return Coefficient vs. Frequency

Figure 5.9 Simulated Return Loss of Multiband Fractal Antenna


From the plot shown in above figure, it can be observed that the proposed antenna

resonates at 2.6 GHz, 7GHz, 9.4 GHz, 11.4 GHz, 13.4 GHz, 17 GHz, 18.2 GHz

and19.4GHz with return loss of -9.15, -10.49, -22.60, -23.32, -43.76, -13.13, -11.38 and -

12.11 respectively. The navigational bands covered by the proposed antenna are HF

communication (2.1- 2.8 GHz), NAVAID (7.50 GHz), RMM, LLWAS, LDRCL (9.32-

9.4GHz), Military RADAR (9-9.2 GHz), Air route Surveillance RADAR; GPS (12.15-

13.9 GHz), Microwave Link (14.4-15.35 GHz), Satellite Based Communication to

aircraft ( 15.45- 15.59 GHz), GPS, RADAR (15.7-16.2 GHz) GLONASS L1 (15.59-

16.10GHz), Satellite based communication from aircraft (16.45-16.60 GHz) and LDRCL

(17.10-18.50 GHz).


The simulated 3 D radiation pattern is obtained from the simulated results and is shown

in figure 5.10. It can be observed from the results that the antenna is almost omni

directional and hence can be used for aerospace navigation supporting multiple standards.

Figure 5.10 Simulated 3D radiation pattern of Multiband Fractal Antenna


5.4.3 Gain

The gain determines the efficiency of the antenna and is important figure of merit of

antenna. The overall gain of the proposed antenna after simulation is shown in figure

5.11. A peak gain of 7.95 dB is obtained at frequency 11.4 GHz.

Figure 5.11 Simulated 3-D Gain Plot of Multiband Fractal Antenna




communication. Figure 5.12 shows the simulated results of VSWR for the frequency

sweep from 1 GHz to 20 GHz. The value of VSWR is less than 3 at all the resonating

frequencies. As seen VSWR at 7GHz, 9.4 GHz, 11.4 GHz, 13.4 GHz, 17 GHz, 18.2 GHz

and19.4GHz is 2.9dB, 1.25dB, 1.9dB, 0.14dB, 3dB and 3dB respectively.


VSWR vs. Frequency

Figure 5.12 Simulated VSWR plot of Multiband Fractal Antenna

5.5 VALIDATION OF SIMULATED RESULTS

Table 5.1 Comparison between Proposed Multiband Fractal Antenna with the Design

Proposed in [30]

Antenna Design/

Parameters

Volume (mm3) Return Loss(dB) Frequency Bands

Covered

Design in [33] 15,680 3GHz: -22.20

7.49GHz: -18.70

9.68GHz: -30.96

11.2GHz: -15.82

HF Communication

(2.1- 2.8 GHz),

NAVAID(7.50

GHz), & Military

RADAR (9-9.2

GHz).

Proposed Design 3,240 2.6 GHz: -9.15 HF communication


7GHz: -10.49

9.4 GHz: -22.60

11.4 GHz: -23.32

13.4 GHz: -43.76

17 GHz: -13.13

18.2 GHz: -11.38

19.4GHz: -12.11

(2.1- 2.8 GHz),

NAVAID (7.50

GHz), RMM,

LLWAS, LDRCL

(9.32- 9.4GHz),

Military RADAR (9-

9.2 GHz), Air route

Surveillance

RADAR; GPS

(12.15- 13.9 GHz),

Microwave Link

(14.4-15.35 GHz),

Satellite Based

Communication to

aircraft ( 15.45-

15.59 GHz), GPS,

RADAR (15.7-16.2

GHz) GLONASS L1

(15.59- 16.10GHz),

Satellite based

communication from

aircraft (16.45-16.60

GHz) and LDRCL

(17.10-18.50 GHz).

It is clear from the data given in table 7.1 that the proposed multiband fractal antenna

covers more frequencies and there is an overall size reduction of 79.33% as compared to

proposed design in [30].

% Size Reduction = 100 –3240

15680× 100 = 79.33%


5.6 HARDWARE IMPLEMENTATION

5.6.1 Introduction

Hardware implementation can be defined as designing an electronic circuit or a physical

device as modeled by a computer program. In the previous section we have designed a

fractal patch antenna using High Frequency Structure Simulator (HFSS) software. High

Frequency Structure Simulator (HFSS) is an industry standard simulation tool. It has

powerful drawing capabilities to simply the antenna design. It is seen that after simulation

the antenna provides desired resonant frequencies that have good operating bandwidth,

radiation patterns and gain.

Hardware is an essential part of wireless communication systems. Therefore in this

section various techniques adopted to design a hardware prototype of simulated antenna

and its various results will be discussed.

5.7 Fabrication Techniques

Various techniques are available to fabricate a fractal microstrip patch antenna.

Fabrication is a very complex and time consuming task where problems are faced and

dealt constantly. Therefore a simple and low cost method that has been used to design

this fractal patch antenna is discussed. Following are the various design steps adopted to

fabricate fractal microstrip patch antenna.

Step 1: The first step to fabricate an antenna is to cut out various shapes (such as ground

plane, substrate and patch) required in antenna fabrication of exact dimensions using

Vernier Caliper. The Vernier Caliper is an instrument that can be used to calculate

internal and external distances accurately.

Step 2: According to the design, mask of fractal geometry and slots on the ground plane

are designed using Coral Draw for the fabrication of fractal patch antenna. Coral Draw is

graphic designing software that is used for producing blueprints for fractal designs, slots,

computer chips etc. The mask layout so obtained is shown in figure 5.13.


Figure 5.13 Mask generated using Coral Draw (a) Fractal geometry (b) Ground slots

Step 3: In order to transfer the mask image on copper plated PCB board screen printing

lithography technique is used. In screen printing lithography an ink is forced on the metal

surface through an allready prepared screen to create a pattern.

Before coating the positive photo resist (PPR) , PCB sheets are cleaned using organic

solvent and dried with hot air gun. The PCB is pre-heated in an oven at 90 degree celcius

in order to remove impurities. Now the masks that was prepared earlier is now built onto

both the sides of the PCB .

After the mask is transferred onto the PCB, it is again placed in oven at a temperature of

130 degree celcius so that it becomes hard and rigid.

Figure 5.14 Screens Generated in Screen Printing technique (a) Antenna Ground Plane (b) Fractal

Geometry


Step 4: In order to remove unwanted parts, chemical etching is done. The exposed parts

are etched out using solution of ferric chloride (FeCl3). Then these parts are rinsed in

water and dried in air [45].

Step 5: The fabricated patch antenna is mounted accurately on predesigned mask of

copper sheet called the ground plane. The female connector is soldered at the predecided

feed location of PCB from the backside of the fabricated antenna. Hence the final

fabricated antenna is obtained through various steps. The final antenna so obtained is

shown in figure 5.15.

Figure 5.15 Final Fabricated antenna layout (a) Top View (b) Bottom View (c) Side view

5.8 Hardware Testing

The next and final step in hardware implementation is the testing of fabricated antenna

hardware. Network Analyzer measures the return loss of the fractal patch antenna. In this


the final antenna is mounted onto the network analyzer and results are observed. The

antenna structure was tested using Anritsu Vector Network Analyzer MS46322A. The

fabricated fractal antenna and the network analyzer is shown in figure 8.3.

Figure 5.16 Fractal Patch Antenna mounted on Network Analyzer

5.9 Performance Assessment of Fabricated Antenna

In this section we will assess the performance of the fabricated fractal patch antenna in

terms of frequency vs. return loss as compared to the results of simulated fractal patch

antenna.

5.9.1 Return Loss Characterstics

The plot shown in figure 5.17 shows the return loss of the fabricated antenna.


Figure 5.17 Measured Return Loss of Multiband Fractal Antenna

From the plot shown in above figure 5.17, it can be observed that the fabricated antenna

resonates at 2.235 GHz, 7.36GHz, 10.88GHz, 12.30GHz, 14.77 GHz and 17.625 GHz

with return loss of -13.628, -15.755, -47.51, -29.022, -11.79 and -13.57 respectively.

The navigational bands covered by the fabricated antenna are HF communication (2.1-

2.8 GHz), NAVAID (7.50 GHz), Air route Surveillance RADAR; GPS (12.15- 13.9

GHz), Microwave Link (14.4-15.35 GHz), and LDRCL (17.10-18.50 GHz).

5.9.2 Comparison between Simulated and Measured Results

Figure 5.18 Measured v/s Simulated Return Loss of Multiband Fractal Antenna


Figure 5.18 shows measured vs. simulated return loss graph. It is concluded that the

results are in excellent agreement with each other. Therefore it is clearly depicted that the

fabricated Fractal Antenna covers all the described operating bands for the aerospace

navigation. The measured and simulated results show that the antenna is well suited for

aerospace navigation covering 7.5GHz, 9.32-9.35GHz, 9.41-9.44 GHz, 8-12GHz, 12.15-

13.90 GHz, 15.45-15.59 GHz, 15.59-16.10 GHz, 14.4-15.35 GHz, 15.7-16.2 GHz, 16.46-

16.60 GHz and 18-19 GHz frequency bands.


CHAPTER 6

CONCLUSION AND FUTURE WORK

6.1 Conclusion

In this dissertation, fractal antenna used for aerospace navigation has been proposed. The

project incorporates simulation of modified conventional Koch fractal antenna. The

results in chapter-7 shows the multiband performance of fractal patch antenna at various

resonant frequencies, improved VSWR (Voltage Standing Wave Ratio), gain, radiation

pattern and performance on a reduced size when compared to non fractal geometries. The

fractal geometries provide various advantages such as broadband characteristics,

compressed resonant behavior, improved reliability, space filling and size reducing

capability. Even though the size is reduced, the fractal antennas show surprisingly good

performance and number of resonant frequency bands increases with each iteration. The

results show that Koch fractal antenna is an excellent alternative to conventional antenna

systems in aerospace navigation. The Koch fractal antenna exhibits excellent

performance at 9.4 GHz, 11.4 GHz and 13.4 GHz with a wideband of 7GHz from

12.55GHz to 19.5GHz. The radiation pattern shown by fractal antennas is uniform in all

directions. The radiation pattern is consistent with doughnut shaped characteristics of λ/2

dipole. The appreciable advantage of fractal antenna is its compactness. A size reduction

of nearly 50% can be achieved when compared to traditional microstrip patch antennas.

This is highly remarkable for aerospace navigation applications. Since the size is reduced

to half the size of traditional antenna, hence, it could be easily integrated in the objects

where space is a major issue. The Koch fractal geometry has notable impedance

bandwidth, allowing flexibility in the application where it is used. Another advantage of

fractal antennas is that these can be easily integrated on PCB. Hence Koch fractal antenna

shows an excellent solution as compared to traditional monopole antennas.

The aim of the thesis was to design a low profile antenna for aerospace navigation. The

dimensions of the ground plane of the proposed antenna are 45mm × 45mm while the

patch dimensions are 40mm × 40mm. Hence the design is compact enough to be

positioned in small places. The simulated antenna shows a gain of 7.95dB, nearly omni


directional radiation pattern and wideband of 7GHz which is highly useful for navigation

applications.

6.2 Future Scope

Since the designed fractal antenna is still in its early stage, therefore there are many

possibilities for future work on this topic. The Koch fractal geometry was chosen for this

thesis work because this the best documented fractal antenna types in current research.

However, many possible fractal geometries exists that may show desirable results. Thus,

a possible approach for future work is to investigate other types of fractals for antenna

applications. Further this thesis work includes return loss graphs of fabricated antenna;

therefore various studies can be done on the fabricated antenna that may include graphs

of gain, radiation pattern, Voltage Standing Wave Ratio, etc.

Fractal antenna can be studied in several fields. One such field is to implement fractal

antennas into current technologies for expanding wireless market. Another area can be

that they can be used in loop antennas so as to design antennas with lower cross sections.

The design proposed in the thesis work can be extended to design fractal patterns for

antenna arrays.

Dept.of ECE, GNDU, Regional Campus Gurdaspur xv

LIST OF PUBLICATIONS

[1] Rupleen Kaur, Satbir Singh and Naveen Kumar, “A Review of Various Fractal

Geometries for Wireless Application”, International Conference on Electronic

Design Innovations and Technologies, April 2015.

[2] Rupleen Kaur, Sahil Saini and Satbir Singh, “An Overview of Fractal Antenna

Geometries”, National Conference on Latest Initiatives and Innovations in

Communication and Electronics, April 2015.

[3] Sahil Saini, Rupleen Kaur and Satbir Singh, “A Review of Planar Inverted F

Antenna (PIFA) for Wireless Applications”, National Conference on Latest

Initiatives and Innovations in Communication and Electronics, April 2015.

[4] Rupleen Kaur, Satbir Singh, Sahil Saini and Naveen Kumar, “A Multiband Fractal

Square Patch Antenna for Aerospace Navigation”, IEEE 12th

India International

Conference, December 2015. [Accepted]

[5] Sahil Saini, Satbir Singh, Rupleen Kaur and Naveen Kumar, “A Compact T-Slot

Multiband Planar Inverted-F Antenna for Handheld Devices”, IEEE 12th

India

International Conference, December 2015. [Accepted]

Dept.of ECE, GNDU, Regional Campus Gurdaspur xvi

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FRACTAL ANTENNA FOR AEROSPACE NAVIGATION

Engineering

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