design of fractal patch antenna for size and radar cross-section reduction

PROJECT REPORT

Design of a Fractal Patch Antenna for size and

radar cross-section reduction.

Submitted by:

SAAD SHAHID KHOKHAR 09-TE-01

MUHAMMAD JUNAID ASHFAQ 09-TE-25

NAVEED AHMED CHUGHTAI 09-TE-40

TAIMOOR SALEEM 09-TE-50

DEPARTMENT OF TELECOMMUNICATION ENGINEERING

UNIVERSITY OF ENGINEERING AND TECHNOLOGY,

TAXILA

June, 2012

Design of a Fractal Patch Antenna for size and radar cross-section reduction.

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CONTENTS

CHAPTER NO TITLE PAGE #

ABSTRACT ..........3

LIST OF TABLES4

LIST OF FIGURES .4

LIST OF ABBREVIATIONS......4

01 INTRODUCTION

1.1 OVERVIEW....5

02 LITERATURE REVIEW

2.1 DETAILED INTRODUCTION .....6 2.2 OBJECTIVES ............7 2.2.1 PROJECT OBJECTIVES .......7 2.2.2 ACADEMIC OBJECTIVES...7 2.3 PROJECT OVERVIEW.................................................7

2.3.1 MONOPOLE ......7 2.3.2 PIFA ....7 2.3.3 USB CONNECTOR ...7

03 IMPLEMENTATION IN HFSS

3.1 ANALYSIS REQUIREMENTS.9 3.1.1 SYSTEM SOFTWARE REQUIREMENTS ..9 3.1.2 SYSTEM HARDWARE REQUIREMENTS.........9

3.2 DESIGN AND ANALYSIS OF PROPOSED

ANTENNA 9 3.3 STRUCTURE OF PROPOSED ANTENNA ......11

3.4 IMLEMENTATION ON HFSS...............15 3.4.1 DESIGNING MODEL........15

3.4.2 ANALYSIS PROCEDURES....15

3.5 TESTING AND RESULTS ..14 3.5.1 RESULTS OF SWEEPING THE PROPOSED

ANTENNA14

CONCLUSION ...16 REFERENCES ... 17


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ABSTRACT

This research study presents a novel design of star-shaped fractal patch antenna for

miniaturisation and backscattering radar cross-section (RCS) reduction. The

proposed fractal antenna gives 50% size reduction compared with a conventional

circular microstrip patch (CCMP) antenna. The antenna is studied experimentally

for return loss behaviour using Ansoft HFSS. It can be useful for wireless

application in 0.85-5 GHz frequency band. Further, the study focuses on

backscattering RCS (both monostatic and bistatic) reduction by the proposed

antenna compared with the CCMP antenna. It is found that increase in number of

fractal iterations included in the conventional patch to design fractal antenna

geometry reduces backscattering RCS at multiband compared to the conventional

patch antenna. This reduction in backscattering RCS by the antenna is observed at

multiband. The antenna can be tuned for low backscattering by variation in the

substrate dielectric constant and thickness and the supersaturate dielectric constant

and thickness. For maximum RCS reduction by the antenna, optimisation of

substrate thickness becomes necessary. The study also deals with effect of

frequency and aspect angle variation on backscattering RCS reduction.


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LIST OF TABLES

TABLE 1: OPTIMIZED PARAMETERS FOR THE PROPOSED ANTENNA

LIST OF FIGURES

FIG 1 : PHOTOS OF FABRICATED ANTENNA IN ITS FRONT, BACK AND

SIDE VIEWS .

FIG. 3(a): GEOMETRY OF PROPOSED ANTENNA INTEGARTED WITH USB

CONNECTOR ....

FIG. 3(b): DETAILED DIMENSIONS OF ANTENNA ..

FIG. 3(c): SHOWING EXCITATION

FIG. 3(d): SIMULATED RESULTS OF THE PROPOSED ANTENNA..

FIG. 3(e): SIMULATED RETURN LOSS FOR PROPOSED ANTENNA

FIG. 3(f): RETURN LOSS

FIG. 3(g): RADIATION PATTERN.

FIG. 3(h): 3D POLAR PLOT

LIST OF ABBREVIATIONS

CCMPA: Conventional Circular Microstrip Patch Antenna

RCS: Radar Cross-section


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CHAPTER 1

INTRODUCTION

1.1 OVERVIEW

Microstrip antennas are used in a broad range of applications such as airborne,

navigation and mobile etc. This is primarily due to their simplicity of fabrication,

ease of production, low manufacturing cost, light in weight, conformal and easy

to integrate with RF devices. The antenna size with respect to the wavelength is

the parameter that will have influence on the radiation characteristics. For

efficient radiation, the size should be of the order of half a wavelength or larger.

Studies proved, for size reduction and multi-frequency performance, fractal

geometry antenna is better than conventional antenna. Therefore fractal

geometries are used in the design of microstrip antennas for miniaturization and

backscattering radar cross-section. These self-similar or self-affine and space

filling fractal microstrip antenna increases the effective electrical length of the

antenna to reduce the size of the antenna and make them frequency independent.

Our project focuses on the designing of a rectangular fractal patch antenna in

Ansoft HFSS; that will make a significant size reduction as compared to the

conventional patch antenna. Whereas maximum radar cross-section by the

antenna will be achieved by making variations in the substrate dielectric constant

and thickness.


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CHAPTER 2

LITERATURE REVIEW

2.1 DETAILED INTRODUCTION

Fractal geometries are used in design of microstrip antennas for miniaturization

and multiband [1] applications. These self-similar or self-affine and space filling

fractal microstrip antenna increases the effective electrical length of the antenna to

reduce the size of the antenna and make them frequency independent. Also, self-

similar or self-affine property gives multiband resonance in the antenna. Most

practical planar antennas give rise to a very large backscattered field at normal

incidence [2, 3]. Geometrical shaping and ferrite substrate use are reported for

radar cross section (RCS) reduction. Elimination of specular reflection over a wide

range of aspect angles by using strip grating surface is also reported in [4, 5]. Other

RCS reduction techniques reported are resistive loading [6], varactor tuning [7]

and substratesupersaturate layer structure [810]. The antenna can be responsible

for the larger part of the total RCS of the aircraft designed to have low

observability. Therefore scattering behavior of antennas is important for defense

applications [11]. In fact, antenna scattering can be source of electromagnetic

compatibility problems and causes interference with other systems on the same

platform [12]. Wide usages of fractal antennas make sense in the RCS study and its

reduction for antenna designer [1315]. Fractal geometries show multiband [16]

Backscattering reduction. The study can be used to design antenna for low

backscattering in the applicable frequency band.


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2.2 OBJECTIVES

2.2.1 Project Objectives

i. Design a square shaped fractal antenna for size reduction.

ii. Achieve maximum radar cross-section by the antenna

2.2 .2 Academic Objectives

1. Study HFSS (High Frequency Structure Simulator).

2. Detailed observation of the Fractal Geometries antennas applied in Patch

Criterion.

2.3 PROJECT OVERVIEW

2.4 .1 Fractal Geometries in Antenna:

A fractal antenna is an antenna that uses a fractal, self-similar design to maximize

the length, or increase the perimeter (on inside sections or the outer structure), of

material that can receive or transmit electromagnetic radiation within a given total

surface area or volume.

2.3.2 Patch Antenna:

A patch antenna (also known as a rectangular microstrip antenna) is a type of radio

antenna with a low profile, which can be mounted on a flat surface. It consists of a

flat rectangular sheet or "patch" of metal, mounted over a larger sheet of metal

called a ground plane. The assembly is usually contained inside a plastic radome,

which protects the antenna structure from damage. Patch antennas are simple to


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fabricate and easy to modify and customize. They are the original type of

microstrip antenna; the two metal sheets together form a resonant piece of

microstrip transmission line with a length of approximately one-half wavelength of

the radio waves. The radiation mechanism arises from discontinuities at each

truncated edge of the microstrip transmission line. The radiation at the edges

causes the antenna to act slightly larger electrically than its physical dimensions, so

in order for the antenna to be resonant, a length of microstrip transmission line

slightly shorter than one-half a wavelength at the frequency is used. A patch

antenna is usually constructed on a dielectric substrate, using the same materials

and lithography processes used to make printed circuit boards.

2.3.3 Microstrip Antenna:

In telecommunication, there are several types of microstrip antennas (also known

as printed antennas) the most common of which is the microstrip patch antenna or

patch antenna.


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CHAPTER 3

IMPLEMENTATION IN HFSS

3.1 ANALYSIS REQUIREMENTS

3.1.1 System Software Requirements

HFSS

3.1.2System Hardware Requirements

Not Implemented

3.2 DESIGN AND ANALYSIS OF PROPOSED ANTENNA

First, a circular metallic patch of dimension 80 mm is designed. Then a 12 point

star shaped fractal geometry with dimension 79.3 mm is subtracted from solid

nearly circular patch to expose substrate material to create first fractal iteration.

Proper care has been taken to maintain electrical connectivity throughout the

circular boundary. Such four electrically interactive iterations are included in the

antenna geometry to design the final fractal geometry for the proposed antenna as

shown in Fig. 1g. The axis dimensions in mm for subsequent nearly circular

patches are 57, 41.766, 29.7, whereas axis dimensions in mm for subsequent star

fractal geometry are 57.86, 41.18, and 29.42. The design is fabricated on the

substrate with dielectric constant r 4.3, thickness 1.53 mm and dimensions 110

mm*110 mm backed by metallic ground of the same dimensions. The coaxial feed

is located at -24.85 mm (X-axis), 24.32 mm (Y-axis) at nearly 458 radially.


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Table 1: Optimized Parameters for the Proposed Antenna

Parameters Values

Size of Substrate 100x100mm2

Size of Ground 100x100mm2

Thickness 0.05 mm

Width 100 mm

Gap between

iterations

0.2 mm

Gap ground and

Patch

0.05 mm


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3.3 STRUCTURE OF PROPOSED ANTENNA

Fig.3 (a) Step wise procedure for Fractal Geometry

(a) Conventional circular microstrip patch antenna (CCMPA)

(b) First fractal iteration in CCMPA

(c) Second fractal iteration in CCMPA

(d) Third fractal iteration in CCMPA

(e) Fourth fractal iteration in CCMPA

(f) Previously studied fractal CMPA


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3.4 IMPLEMENTATION ON HFSS

3.4.1 Designing Model

First task is to make iteration of peculiar pattern. In HFSS, there is no option

for drawing star; therefore we followed the indirect approach. First we create

a cylinder of desired dimension, than form 3 polyhedral of 3 sides with equal

spacing then combining all 3 polyhedral using UNITE option we have

created a star shaped pattern of 12 corners sharing space with cylinder. The

star shaped pattern then subtracted from the cylinder using SUBTRACT

option in HFSS. By doing this we have achieved the desired shape of the

iteration. Similarly we draw 4 iterations of different dimensions.

Then we created the substrate and air with box. Feed is subtracted from the

first iteration.

Fig.3 (b) Design of proposed antenna for size and backscattering RCS

reduction

Note: Black color indicates substrate. White color indicates metallic patch

on substrate.


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Fig.3 (c) Design of Fractal Antenna Geometry in HFSS

3.4.2 Analysis Procedures in HFSS

Excitation is performed through the coaxial feed. This is done by drawing a

circle in the bottom, and using Lumped port excitation option in HFSS.

Then the air box is radiated by RADIATION option. The GROUND is

implemented by infinite ground plane on the bottom face of the air 0.05 mm

beneath the patch.

In the solution setup, frequency of 4.8 GHz is given. The sweep is done by

discrete method in the range of 2 to 10 GHz with 100 counts.


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3.5 TESTING AND RESULTS

3.5.1 Results of Sweeping the Proposed Antenna

Analyzing the Model, following are the results.

Fig. 3(d) Return Loss


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Fig. 3(e) Radiation pattern

Fig. 3(f) Directivity


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CONCLUSION

The research study is mainly focused on the miniaturisation of antenna and

backscattering RCS reduction in various aspects. Fractal-based antenna geometry

helps to reduce size of antenna as well as backscattering RCS compared to

conventional antenna geometry. Fractal antenna geometry gives multiband RCS

reduction because of frequency selective nature. Backscattered RCS reduction is a

function of the dielectric thickness and the dielectric constant for all types of RCS

calculations. Backscattering reduction can be achieved for wide beamwidth and

bandwidth by optimising the thickness of the substrate. The superstrate loading on

The metallic patch can be used for frequency tuning, bandwidth enhancement and

RCS reduction. This study is useful to model the target of low backscattering. The

study helps antenna designer to tune the antenna for minimum RCS since RCS

reduction is important for many defence and civilian applications.


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REFERENCES

[1] PUENTE-BALIARDA C., ROMEU J., POUS R., CARDAMA A.: On the behaviour of the Sierpinski multiband fractal antenna, IEEE Trans. Antenna Propog., 1998, AP-46, pp. 517524

[2] BACH ANDERSEN J.: Transmitting, receiving, and scattering properties of antennas. Proc. Antenna 03, Kalmar, Sweden, May 2003

[3] PAQUAY M., IRIARTE J.C., EDERRA I., GONZALO R., DE MAAGT P.:

Thin AMC structure for radar cross-section reduction, IEEE Trans. Antennas Propag., 2007, 55, (12), pp. 5567

[4] STEPHEN D.S., MATHEW T., MOHANAN P., NAIR K.G.: A modified strip grating with dual periodicity for RCS reduction, Microw. Opt. Technol. Lett., 1994, 7, (7), pp. 315317

[5] MATHEW T., STEPHEN D.S., ANANDAN C.K., MOHANAN P., NAIR .G.:

Wideband trapezoidal strip grating for elimination of specular reflection, IEEE Electron. Lett., 1994, 30, (13), pp. 10371039

[6] POZAR D.M.: Radiation and scattering from a microstrip patch on a uniaxial substrate, IEEE Trans. Antennas Propag., 1987, 35, pp. 613621

[7] SAED M.A.: Broadband CPW-FEW planar slot antennas with various tunning stubs, Progress Electromagn. Res., 2006, PIER 66, pp. 199212

[8] WU B.I., WANG W., PACHECO J., ET AL.: A study of using metamaterial as antenna substrate to enhance gain, Progress Electromagn. Res., 2005, PIER 51, pp. 295328

[9] JACKSON D.R.: RCS of a rectangular microstrip patch in a substratesuperstrate geometry, IEEE Trans. Antennas Propag., 1990, 38, pp. 28

[10] WANG S., GUAN X., WANG D., MA X., SU Y.: Electromagnetic scattering by mixed conducting/dielectric objects using higher order MOM, Progress Electromagn. Res., 2006, PIER 66, pp. 5163


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[11] LI Y.L.: Scattering cross section for airborne and its application, J. Electromagn. Waves Appl., 2007, 21, (15), pp. 23412349

[12] JOSEFSSON L., PERSSON P.: Conformal array antenna theory and design, Inst. Electr. Electron. Eng., Inc., 2006, p. 421

[13] CUI G., LIU Y., GONG S.: A novel fractal patch antenna with low RCS, J. Electromagn. Waves Appl., 2007, 21, (15), pp. 24032411 [14] JACKSON D.R.: RCS of a rectangular microstrip patch in a substrateSuperstrate geometry, IEEE Trans. Antennas Propag., 1990, 38, pp. 28

[15] ARVAS E., SARKAR T.K.: RCS of two dimensional structures consisting of both dielectric and conductors dielectric and conductors of arbitrary cross section, IEEE Tans. Antenna Propag.-37, 1989, 5, pp. 546554

[16] MUNK B.A.: Frequency selective surfaces, theory and design (Wiley Publication, New York, 2000)

design of fractal patch antenna for size and radar cross-section reduction

Documents

proposed fractal antenna

analysis of proposed

conventional patch antenna

fractal antenna geometry

structure of proposed

shaped fractal patch

detailed dimensions

photos of fabricated