Design of Fractal Patch Antenna for Size and Radar Cross-Section Reduction
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Transcript of Design of Fractal Patch Antenna for Size and Radar Cross-Section Reduction
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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
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section 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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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Fig. 3(e) Radiation pattern
Fig. 3(f) Directivity
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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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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Design of a Fractal Patch Antenna for size and radar cross-section reduction.
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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)