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A Project Report

On

DESIGN OF PROBE FEED RECTANGULAR PATCH ANTENNA WITH

CURVATURE TO IMPROVE BEAMWIDTH

In partial fufillment for the award of the degree of

BACHELOR OF TECHNOLOGY

In

ELECTRONICS & COMMUNICATION ENGINEERING

Submitted by

Akash Pandey

Under the Guidance of

Prof. S. D. Dixit

J. K. INSTITUTE OF APPLIED PHYSICS AND TECHNOLOGY (DEPT OF

ELECTRONICS & COMM ENGG.), UNIVERSITY OF ALLAHABAD,

ALLAHABAD-211002

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J. K. INSTITUTE OF APPLIED PHYSICS AND TECHNOLOGY

(DEPT OF ELECTRONICS & COMM ENGG.), UNIVERSITY OF

ALLAHABAD, ALLAHABAD-211002

Certificate

This is to certify that the thesis entitles Design of Probe Feed

Rectangular Patch Antenna with Curvature to improve Beamwidth

is submitted in partial fufillment for the award of the degree of

Bachelor of Technology in Electronics & Communication Engineering

at J. K. Institute of Applied Physics & Technology, University of

Allahabad.

It is faithful record of bonafide project work carried by Mr. Vineet

Mishra (Enrl No: 09AU/429) under my supervision and guidance.

Prof. S. D. Dixit

Department of Electronics & Communication Engg.

J. K. Institute of Applied Physics & Technology

University of Allahabad

Allahabad-211002

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ACKNOWLEDGEMENT

I would like to express my gratitude to my project guide Prof. S. D. Dixit

for his constant support, guidance and valuable advice for the completion of

this work. I am very grateful to him for his valuable ideas and expertise.

I am very thankful to Prof. R. R. Tewari (Head of Department) for his

prestigious, support and infinite supervision. It was his cheerful and sincere

cooperation, regular encouragement and assistance of every kind which made

my dissertation a fruitful, pleasant and lifetime expertise.

I express my sincere thanks to my parents & batchmates who provided

me the congenial help and atmosphere during my dissertation.

Project Team :

Akash Pandey (Roll No :- 05)

Vineet Mishra (Roll No :- 35)

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INDEX S.No Topic Page

No 1. Abstract 5 2. Introduction 6 3. Chapter 1- Antenna Terminologies 8 4. Chapter 2- Microstrip Patch Antenna 21 5. Chapter 3- Designing of Antenna 36 6. Chapter 4- Modelling, Simulation &

Optimisation 42

7. Chapter 5- Result & Conclusion 50 8. Applications 52 9 Bibliography 54

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ABSTRACT

A new design of a broad-band probe-fed patch antenna with a CURVED patch

is presented. The curved patch is obtained by bending the conventional patch

into an U-shape, seen in the resonant direction of the patch antenna. The

proposed design is applicable to the patch antenna with a planar ground plane

with a thin-air substrate. With the use of the proposed curved patch, the

required probe-pin length in the substrate remains to be small, although the

effective substrate thickness is significantly increased, resulting in a much

wider operating bandwidth. Also, by choosing proper dimensions of the curved

patch, the antenna gain for frequencies over the obtained wide bandwidth is

enhanced, compared to the conventional patch antenna with a planar plane

patch.

MICROSTRIP antennas are usually with a narrow-bandwidth operation, which

greatly limits their possible applications. To enhance the antennas operating

bandwidth, the use of a thick and low-permittivity substrate, such as a thick

air or foam substrate, has been known to be very effective. Further more

parasitic element is used to increase the beamwidth of microstrip patch

antenna.

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INTRODUCTION

A patch antenna is a narrowband, wide-beam antenna fabricated by etching the

antenna element pattern in metal trace bonded to an insulating dielectric

substrate with a continuous metal layer bonded to the opposite side of the

substrate which forms a groundplane. Common microstrip antenna radiator

shapes are square, rectangular, circular and elliptical, but any continuous shape

is possible. Some patch antennas eschew a dielectric substrate and suspend a

metal patch in air above a ground plane using dielectric spacers; the resulting

structure is less robust but provides better bandwidth. Because such antennas

have a very low profile, are mechanically rugged and can be conformable, they

are often mounted on the exterior of aircraft and spacecraft, or are incorporated

into mobile radio communications devices.

OBJECTIVE

The objective of this project is to design a microstrip patch antenna which is

required to operate in the L- band (1-1.12 GHz). The microstrip patch antenna

has a number of characteristics favorable for this application. The microstrip

patch antenna is a antenna which consist of metallic patch of rectangular or

circular shape on a grounded substrate.

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CHAPTER 1

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ANTENNA TERMINOLOGIES

An antenna is a transducer designed to transmit or receive electromagnetic waves. In

other words, antennas convert electromagnetic waves into electrical currents and vice versa.

Antennas are used in systems such as radio and television broadcasting, point-to-point radio

communication, wireless LAN, radar, and space exploration. Antennas usually work in air or

outer space, but can also be operated under water or even through soil and rock at certain

frequencies for short distances.

Physically, an antenna is an arrangement of conductors that generate a radiating

electromagnetic field in response to an applied alternating voltage and the associated

alternating electric current, or can be placed in an electromagnetic field so that the field will

induce an alternating current in the antenna and a voltage between its terminals. Some

antenna devices (parabolic antenna, Horn Antenna) just adapt the free space to another type

of antenna.

ANTENNA ARRAY:- An antenna array is two or more antennas coupled to a common

source or load to produce a specific directional radiation pattern. The spatial relationship

between individual antennas contributes to the directivity of an antenna.

RADIATION PATTERN: - The radiation pattern of an antenna is a plot of the far-field radiation

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

elevation angle and the azimuth angle . More specifically it is a plot of the power radiated from

an antenna per unit solid angle, which is nothing but the radiation intensity.

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HALF POWER BEAM WIDTH: -The half power beam width (HPBW) can be defined as

the angle subtended by the half power points of the main lobe.

MAIN LOBE: - This is the radiation lobe containing the direction of maximum radiation.

MINOR LOBE: - All the lobes other than the main lobe are called the minor lobes. These

lobes represent the radiation in undesired directions. The level of minor lobes is HPBW usually

expressed as a ratio of the power density in the lobe in question to that of the major lobe. This ratio is

called as the side lobe level (expressed in decibels).

BACK LOBE: - This is the minor lobe diametrically opposite the main lobe.

SIDE LOBE: - These are the minor lobes adjacent to the main lobe and are separated by various

nulls. Side lobes are generally the largest among the minor lobes.

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GRATING LOBES: - For discrete aperture antennas (such as phased arrays) in which

the element spacing is much greater than a half wavelength, the aliasing effect causes some

sidelobes to become substantially larger in amplitude, and approaching the level of the main

lobe; these are called grating lobes, and they are identical, or nearly identical in the example

shown, copies of the main beams. Grating lobes are a special case of a sidelobe. In such a

case, the sidelobes should be considered all the lobes lying between the main lobe and the

first grating lobe, or between grating lobes. It is conceptually useful to distinguish between

sidelobes and grating lobes because grating lobes have larger amplitudes than most, if not all,

of the other side lobes.

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DIRECTIVITY: - The directivity of an antenna has been defined by as the ratio of the

radiation intensity in a given direction from the antenna to the radiation intensity averaged

over all directions. In other words, the directivity of a nonisotropic source is equal to the

ratio of its radiation intensity in a given direction, over that of an isotropic source. The

directivity of a nonisotropic source is equal to the ratio of its radiation intensity in a given

direction, over that of an isotropic source.

Where D is the directivity of the antenna.

U is the radiation intensity of the antenna.

Ui is the radiation intensity of an isotropic source.

Dmax is the maximum directivity.

P is the total power radiated.

INPUT IMPEDANCE: -The input impedance of an antenna is defined by as the

impedance presented by an antenna at its terminals or the ratio of the voltage to the current at the

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pair of terminals or the ratio of the appropriate components of the electric to magnetic fields at a

point.

RETURN LOSS (RL): - The Return Loss (RL) is a parameter, which indicates the

amount of power that is lost to the load and does not return as a reflection. The RL is given

by,

(db)

ANTENNA EFFICIENCY: - The antenna efficiency is a parameter, which takes into account the

amount of losses at the terminals of the antenna and within the structure of the antenna. These losses

are given by

Reflections because of mismatch between the transmitter and the antenna

R / 2 losses (conduction and dielectric).

BANDWIDTH: -The bandwidth of an antenna is defined by as the range of usable frequencies

within which the performance of the antenna, with respect to some characteristic, conforms to a

specified standard. The bandwidth can be the range of frequencies on either side of the center

frequency where the antenna characteristics like input impedance, radiation pattern, beam width,

polarization, side lobe level or gain, are close to those values which have been obtained at the center

frequency. The bandwidth of a broadband antenna can be defined as the ratio of the upper to lower

frequencies of acceptable operation. The bandwidth of a narrowband antenna can be defined as the

percentage of the frequency difference over the center frequency.

Where fH = upper frequency.

fL = lower frequency.

fc = center frequency.

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Fig: Measuring bandwidth from the plot of the reflection

co efficient

POLARISATION: -Polarization of a radiated wave is defined by as that property of an

electromagnetic wave describing the time varying direction and relative magnitude of the electric

field vector. The polarization of an antenna refers to the polarization of the electric field vector of

the radiated wave. In other words, the position and direction of the electric field with reference to

the earths surface or ground determines the wave polarization. The most common types of

polarization include the linear (horizontal or vertical) and circular (right hand polarization or the left

hand polarization).

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FIG: A LINEARLY (VERTICALLY) POLARIZED WAVE

CIRCULAR POLARISATION: -In a circularly polarized wave, the electric field vector

remains constant in length but rotates around in a circular path. A left hand circular polarized wave is

one in which the wave rotates counterclockwise whereas right hand circular polarized wave exhibits

clockwise motion as shown in Figure.

LINEAR POLARISATION: -If the path of the electric field vector is back and forth along a

line, it is said to be linearly polarized. Figure shows a linearly polarized wave.

VOLTAGE STANDING WAVE RATIO (VSWR): -The VSWR is basically a measure of the

impedance mismatch between the transmitter and the antenna. The higher the VSWR, the greater is

the mismatch. The minimum VSWR which corresponds to a perfect match is unity. The VSWR is

given by Makarov as,

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Where is the reflection coefficient

Vs is the amplitude of the reflected wave.

Vi is the amplitude of the incident wave.

REACTIVE NEAR-FIELD REGION: - In this region, the reactive field dominates. The

reactive energy oscillates towards and away from the antenna, thus appearing as reactance. In this

region, energy is only stored and no energy is dissipated. The outermost boundary for this region is at

a distance,

Where R1 is the distance from the antenna surface.

D is the largest dimension of the antenna and is the wavelength.

RADIATING NEAR-FIELD REGION (FRESNEL REGION): - Radiating near-field region

(also called Fresnel region) is the region, which lies between the reactive near-field region and the

far field region. Reactive fields are smaller in this field as compared to the reactive near-field region

and the radiation fields dominate. In this region, the angular field distribution is a function of the

distance from the antenna. The outermost boundary for this region is at a distance,

Where R2 is the distance from the antenna surface.

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FAR-FIELD REGION (FRAUNHOFER REGION): - Far-field region (also

called Fraunhofer region): The region beyond is the far field region. In this

region, the reactive fields are absent and only the radiation fields exist. The angular field

distribution is not dependent on the distance from the antenna in this region and the power

density varies as the inverse square of the radial distance in this region.

DECIBELS: - Decibels (dB) is commonly used to describe gain or loss in circuits. The

number of decibels is found from:

Gain in dB = 10log(gain factor)

ARRAY ELEMENT: - In an array antenna, a single radiating element or a convenient grouping of

radiating elements that have fixed relative excitations.

ARRAY FACTOR: - The radiation pattern of an array antenna when each array element is

considered to radiate isotropically.

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AVERAGE SIDE LOBE LEVEL: - The average value of the relative power pattern of an antenna

taken over a specified angular region, which excludes the main beam, the power pattern being

relative to the peak of the main beam.

BEAM OF AN ANTENNA: - The major lobe of the radiation pattern of an antenna.

BEAMWIDTH: - In a radiation pattern containing the direction of the maximum of a lobe, the

solid angle subtended between the half-power power points of the main lobe.

POWER GAIN OR SIMPLY GAIN: - The power gain or simply gain Gp, of an antenna referred

to an isotropic source is the ratio of its maximum radiation intensity to the radiation intensity of a

loss less isotropic source with the same power input.

Gp = (4Pi Umax) / (P input)

LINEAR ARRAY ANTENNA: - A one-dimensional array of elements whose corresponding

points lie along a straight line.

RECTANGULAR ARRAY: - A regular arrangement of array elements, in a plane,

such that lines connecting corresponding points of adjacent elements form rectangles

RADIATION EFFICIENCY: - The ratio of the gain to the directivity of an antenna is called the

radiation efficiency, n.

n = Gp / D

NULLS: - In an antenna radiation pattern, a null is a zone in which the effective radiated power is at

a minimum. A null often has a narrow directivity angle compared to that of the main beam. Thus,

the null is useful for several purposes, such as suppression of interfering signals in a given direction.

RADIATION RESISTANCE: - The resistance that, if inserted in place of an antenna, would

consume the same amount of power that is radiated by the antenna.

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BEAM DIVERGENCE: - The beam divergence of an electromagnetic beam is the increase in

beam diameter with distance from the aperture from which the beam emerges in any plane that

intersects the beam axis.

BEAM DIAMETER: - Of an electromagnetic beam, along any specified line that (a) intersects the

beam axis and (b) lies in any specified plane normal to the beam axis, the distance between the two

diametrically opposite points at which the irradiance is a specified fraction.

BORESIGHT: - 1. The physical axis of a directional antenna.

2. To align a directional antenna, using either an optical procedure or a fixed

target at a known location.

DEPARTURE ANGLE: - The angle between the axis of the main lobe of an antenna pattern and

the horizontal plane at the transmitting antenna.

EFFECTIVE ANTENNA GAIN CONTOUR: - An envelope of antenna gain contours resulting

from moving the bore sight of a steerable satellite beam along the limits of the effective bore sight

area.

EFFECTIVE BORESIGHT AREA: - An area on the surface of the Earth within which the bore

sight of a steerable satellite beam is pointed. There may be more than one unconnected effective

bore sight area to which a single steerable satellite beam can be pointed.

EFFECTIVE HEIGHT: - The height of the center of radiation of an antenna above the effective

ground level.

PHASED ARRAY: - A group of antennas in which the relative phases of the respective signals

feeding the antennas are varied in such a way that the effective radiation pattern of the array is

reinforced in a desired direction and suppressed in undesired directions. The relative amplitudes of--

and constructive and destructive interference effects among-- the signals radiated by the individual

antennas determine the effective radiation pattern of the array.

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ANGULAR WIDTH: - The angular width (or beamwidth) is defined as the angle between two

directions where the radiation is dropped by 3 dB regarding the radiation in main lobe direction. This

angle is located in a plane containing the main lobe direction.

RADIATION POWER DENSITY: - The quantity used to describe the power associated with an

electromagnetic wave is the instantaneous Poynting vector defined as,

W = E x H

OMNIDIRECTIONAL PATTERN: - An omni directional pattern is the special type

of directional pattern. It is non-directional in azimuth plane and directional in elevation plane.

ISOTROPIC PATTERN: - Isotropic radiator is defined as the hypothetical loss less

antenna having equal radiation in all directions.

Q FACTOR: - The Q-factor of an antenna is proportional to the ratio of energy stored to the

energy lost per cycle.

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CHAPTER-2

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MICROSTRIP PATCH ANTENNA

2.1 INTRODUCTION

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

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

antenna. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the

antenna element pattern in metal trace bonded to an insulating dielectric substrate with a

continuous metal layer bonded to the opposite side of the substrate which forms a

groundplane. Common microstrip antenna radiator shapes are square, rectangular, circular

and elliptical, but any continuous shape is possible. Some patch antennas eschew a dielectric

substrate and suspend a metal patch in air above a ground plane using dielectric spacers; the

resulting structure is less robust but provides better bandwidth. Because such antennas have a

very low profile, are mechanically rugged and can be conformable, they are often mounted on

the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications

devices.

Microstrip antennas are also relatively inexpensive to manufacture and design because of

the simple 2-dimensional physical geometry. They are usually employed at UHF and higher

frequencies because the size of the antenna is directly tied to the wavelength at the resonance

frequency. A single patch antenna provides a maximum directive gain of around 6-9 dBi. It is

relatively easy to print an array of patches on a single (large) substrate using lithographic

techniques. Patch arrays can provide much higher gains than a single patch at little additional

cost; matching and phase adjustment can be performed with printed microstrip feed

structures, again in the same operations that form the radiating patches. The ability to create

high gain arrays in a low-profile antenna is one reason that patch arrays are common on

airplanes and in other military applications.

In its most basic form, a Microstrip patch antenna consists of a radiating patch on one side of a

dielectric substrate which has a ground plane on the other side as shown in Figure 3.1.The patch is

generally made of conducting material such as copper or gold and can take any possible shape. The

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

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FIGURE 2.1 STRUCTURE OF A MICROSTRIP PATCH ANTENNA

In order to simplify analysis and performance prediction, the patch is generally square,

rectangular, circular, triangular, and elliptical or some other common shape as shown in Figure 3.2.

For a rectangular patch, the length L of the patch is usually , where is

the free-space wavelength. The patch is selected to be very thin such that (where t is the

patch thickness). The height h of the dielectric substrate is usually . The

dielectric constant of the substrate ( ) is typically in the range

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FIGURE 2.2 COMMON SHAPES OF MICROSTRIP PATCH ELEMENTS

Microstrip patch antennas radiate primarily because of the fringing fields between the patch edge

and the ground plane. For good antenna performance, a thick dielectric substrate having a low

dielectric constant is desirable since this provides better efficiency, larger bandwidth and better

radiation Gibson P.J. However, such a configuration leads to a larger antenna size.

In order to design a compact Microstrip patch antenna, higher dielectric constants must be used

which are less efficient and result in narrower bandwidth. Hence a compromise must be reached

between antenna dimensions and antenna performance.

Microstrip patch antennas have a very high antenna quality factor (Q). Q represents the losses

associated with the antenna and a large Q leads to narrow bandwidth and low efficiency. Q can be

reduced by increasing the thickness of the dielectric substrate. But as the thickness increases, an

increasing fraction of the total power delivered by the source goes into a surface wave. This surface

wave contribution can be counted as an unwanted power loss since it is ultimately scattered at the

dielectric bends and causes degradation of the antenna characteristics.

However, surface waves can be minimized by use of photonic band gap structures. Other

problems such as lower gain and lower power handling capacity can be overcome by using an array

configuration for the elements.

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2.2 RADIATION MECHANISM

The most popular models for the analysis of Microstrip patch antennas are the transmission

line model, cavity model, and full wave model (which include primarily integral

equations/Moment Method). The transmission line model is the simplest of all and it gives

good physical insight but it is less accurate. The cavity model is more accurate and gives

good physical insight but is complex in nature. The full wave models are extremely accurate,

versatile and can treat single elements, finite and infinite arrays, stacked elements, arbitrary

shape elements and coupling. These give less insight as compared to the two models

mentioned above and are far more complex in nature.

Transmission Line Model: -

This model represents the microstrip antenna by two slots of width W and height h , separated by a

transmission line of length L. The microstrip is essentially a nonhomogeneous line of two dielectrics,

typically the substrate and air.

FIG 2.3: MICROSTRIP LINE FIG 2.4: ELECTRIC FIELD LINES

Hence, as seen from Figure 3.4, most of the electric field lines reside in the substrate and parts of

some lines in air. As a result, this transmission line cannot support pure transverse electric- magnetic

(TEM) mode of transmission, since the phase velocities would be different in the air and the

substrate. Instead, the dominant mode of propagation would be the quasi-TEM mode. Hence, an

effective dielectric constant must be obtained in order to account for the fringing and the

wave propagation in the line. The value of is slightly less then because the fringing fields

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around the periphery of the patch are not confined in the dielectric substrate but are also spread in

the air as shown in Figure 3.4 above. The expression for is given by:

h = Height of dielectric substrate

W = Width of the patch

Consider Figure 3.5 below, which shows a rectangular microstrip patch antenna of length L, width W

resting on a substrate of height h. The co-ordinate axis is selected such that the length is along the x

direction, width is along the y direction and the height is along the z direction.

FIGURE 3.5: MICROSTRIP PATCH ANTENNA

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In order to operate in the fundamental mode, the length of the patch must be slightly less

than 2 / where is the wavelength in the dielectric medium and is equal to where

is the free space wavelength. The mode implies that the field varies one 2 / cycle along

the length, and there is no variation along the width of the patch. In the Figure 3.6 shown below, the

microstrip patch antenna is represented by two slots, separated by a transmission line of length L

and open circuited at both the ends. Along the width of the patch, the voltage is maximum and

current is minimum due to the open ends. The fields at the edges can be resolved into normal and

tangential components with respect to the ground plane.

FIGURE 2.6: TOP VIEW OF ANTENNA AND SIDE VIEW OF ANTENNA

It is seen from Figure 3.6 that the normal components of the electric field at the two edges along

the width are in opposite directions and thus out of phase since the patch is /2 long and hence they

cancel each other in the broadside direction. The tangential components, which are in phase, means

that the resulting fields combine to give maximum radiated field normal to the surface of the

structure. Hence the edges along the width can be represented as two radiating slots, which are /2

apart and excited in phase and radiating in the half space above the ground plane. The fringing fields

along the width can be modeled as radiating slots and electrically the patch of the microstrip

antenna looks greater than its physical dimensions. The dimensions of the patch along its length

have now been extended on each end by a distance L., Which is given empirically by Hammers tad

as:

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The effective length of the patch now becomes:

For a given resonance frequency , the effective length is given by as:

For a rectangular Microstrip patch antenna, the resonance frequency for any mode is given

by James and Hall as:

Where m and n are modes along L and W respectively.

For efficient radiation, Bahl and Bhartia as give the width W:

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2.3 FEED TECHNIQUES

Microstrip patch antennas can be fed by a variety of methods. These methods can be classified into

two categories- contacting and non-contacting

In the contacting method, the RF power is fed directly to the radiating patch using a connecting

element such as a microstrip line.

The two popular feed methods of this type are:

a. Microstrip line feed

b. Coaxial probe feed

In the non-contacting scheme, electromagnetic field coupling is done to transfer power between

the microstrip line and the radiating patch.

The two popular feed methods of this type are:

a. Aperture coupled feed

b. Proximity coupled feed

Microstrip Line Feed: -

In this type of feed technique, a conducting strip is connected directly to the edge of the microstrip

patch as shown in the figure below. The conducting strip is smaller in width as compared to the

patch and this kind of feed arrangement has the advantage that the feed can be etched on the same

substrate to provide a planar structure.

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FIG 3.7 MICROSTRIP LINE FEED

The purpose of the inset cut in the patch is to match the impedance of the feed line to the patch

without the need for any additional matching element. This is achieved by properly controlling the

inset position. Hence this is an easy feeding scheme, since it provides ease of fabrication and

simplicity in modeling as well as impedance matching. However as the thickness of the dielectric

substrate being used, increases, surface waves and spurious feed radiation also increases, which

hampers the bandwidth of the antenna. The feed radiation also leads to undesired cross polarized

radiation.

Coaxial Feed: -

The Coaxial feed or probe feed is a very common technique used for feeding Microstrip patch

antennas. As seen from the figure below, the inner conductor of the coaxial connector extends

through the dielectric and is soldered to the radiating patch, while the outer conductor is connected

to the ground plane.

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FIG 2.8: PROBE FED RECTANGULAR MICROSTRIP PATCH ANTENNA

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

location inside the patch in order to match with its input impedance. This feed method is easy to

fabricate and has low spurious radiation. However, its major disadvantage is that it provides narrow

bandwidth and is difficult to model since a hole has to be drilled in the substrate and the connector

protrudes outside the ground plane, thus not making it completely planar for thick substrates ( h >

0.02o ). Also, for thicker substrates, the increased probe length makes the input impedance more

inductive, leading to matching problems. It is seen above that for a thick dielectric substrate, which

provides broad bandwidth, the microstrip line feed and the coaxial feed suffer from numerous

disadvantages. The non-contacting feed techniques which have been discussed below, solve these

problems.

Aperture Coupled Feed: -

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In this type of feed technique, the ground plane as shown in Figure below separates the radiating

patch and the microstrip feed line. Coupling between the patch and the feed line is made through a

slot or an aperture in the ground plane.

FIG 2.9: APERTURE-COUPLED FEED

The coupling aperture is usually centered under the patch, leading to lower cross polarization due to

symmetry of the configuration. The amount of coupling from the feed line to the patch is

determined by the shape, size and location of the aperture. Since the ground plane separates the

patch and the feed line, spurious radiation is minimized. Generally, a high dielectric material is used

for the bottom substrate and a thick, low dielectric constant material is used for the top substrate to

optimize radiation from the patch. The major disadvantage of this feed technique is that it is difficult

to fabricate due to multiple layers, which also increases the antenna thickness. This feeding scheme

also provides narrow bandwidth.

Proximity Coupled Feed:

This type of feed technique is also called as the electromagnetic coupling scheme. As shown in the

figure below, two dielectric substrates are used such that the feed line is between the two

substrates and the radiating patch is on top of the upper substrate. This scheme also provides

choices between two different dielectric media, one for the patch and one for the feed line to

optimize the individual performances.

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FIG 2.10: PROXIMITY COUPLED FEED

Matching can be achieved by controlling the length of the feed line and the width-to-line ratio of the

patch. The major disadvantage of this feed scheme is that it is difficult to fabricate because of the

two dielectric layers, which need proper alignment. Also, there is an increase in the overall thickness

of the antenna.

Table below summarizes the characteristics of the different feed techniques

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2.4 Advantages and Disadvantages

Microstrip patch antennas are increasing in popularity for use in wireless applications due to

their low-profile structure. Therefore they are extremely compatible for embedded antennas

in handheld wireless devices such as cellular phones, pagers etc... The telemetry and

communication antennas on missiles need to be thin and conformal and are often Microstrip

patch antennas. Another area where they have been used successfully is in Satellite

communication. Some of their principal advantages are given below:

Light weight and low volume.

Low profile planar configuration which can be easily made conformal to host surface.

Low fabrication cost, hence can be manufactured in large quantities.

Supports both, linear as well as circular polarization.

Can be easily integrated with microwave integrated circuits (MICs).

Capable of dual and triple frequency operations.

Mechanically robust when mounted on rigid surfaces.

Microstrip patch antennas suffer from a number of disadvantages as compared to

conventional antennas.

Some of their major disadvantages are given below:

Narrow bandwidth

Low efficiency

Low Gain

Extraneous radiation from feeds and junctions

Poor end fire radiator except tapered slot antennas

Low power handling capacity.

2.5 APPLICATIONS

Notable system applications for which microstrip antennas have been developed include:

Satellite communications

Doppler and other radar

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Radio altimeters

Missile telemetry

Weapon fusing

Man pack equipment

Feed elements in complex antennas

Satellite navigation receiver

Biomedical radiator

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CHAPTER-3

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DESIGNING OF ANTENNA

The procedure for designing a rectangular microstrip patch antenna is explained below. Few

microstrip antennas with different patch are designed. Finally, the results obtained from the

simulations are demonstrated .All design are performed using HFSS (High Frequency

Simulation Structure)

3.1 HFSS:-

HFSS is an interactive software package for calculating the electromagnetic behavior of a structure.

The software includes post-processing commands for analyzing this behavior in detail. Using HFSS,

you can compute:

Basic electromagnetic field quantities and, for open boundary problems, radiated near and far

fields.

Characteristic port impedances and propagation constants.

Generalized S-parameters and S-parameters renormalized to specific port impedances.

The Eigen modes, or resonances, of a structure.

You are expected to draw the structure, specify material characteristics for each object, and identify

ports and special surface characteristics. HFSS then generates the necessary field solutions and

associated port characteristics and S-parameters. As you set up the problem, HFSS allows you to

specify whether to solve the problem at one specific frequency or at several frequencies within a

range.

The HFSS Antenna Design Kit is a stand-alone GUI-based utility which automates the geometry

creation, solution setup, and post-processing reports for over 25 antenna elements. This tool allows

antenna designers to efficiently analyze common antenna types using HFSS and also assists new

users in learning to use HFSS for antenna design. The design kit can be integrated into the HFSS user

interface or launched from the standard Windows menu. All antenna models created by the design

kit are ready to simulate in HFSS.

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3.2DESIGN SPECIFICATIONS: -

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

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

appropriately. The microstrip antenna is designed in L Band.The L band is part of the microwave

region of the electromagnetic spectrum. Its frequency range is from 0.390 to 1.55 GHz. Hence the

antenna designed must be able to operate in this frequency range. The resonant frequency selected

for my design is 1.06GHz.This is because my frequency range is 1GHz to 1.12GHz.

Dielectric constant of the substrate (r): The dielectric material selected for my

design is air which has a dielectric constant of 1.0004.For designing of antennas dielectric constant

should be in the range of A substrate in the lower range of dielectric constant

should be selected since it provides better efficiency, larger bandwidth. My project consist of two

design one with air as substrate and other one has RT/DUROID along with rohacel.Combined

dielectric constant of both substrate is almost similar to air.

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Height of dielectric substrate (h): In many applications it is essential that the

antenna is not bulky. The height of the substrate should lie in the range

.Hence; the height of the dielectric substrate is selected as 14 mm.

Height is calculated as h = 0.05*283 = 14mm (approx.).

Hence, the essential parameters for the design are:

= 1.06 GHz

r= 1

h = 14mm

Calculation of the Length (L): The length of the Microstrip patch antenna is calculated

as:

f=1.06 GHz

=c/f

= (3*10^8)/(1.06*10^9)

= 283mm

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where c is the wavelength of light and f is the operating frequency.

g = /(r)^0.5

= 283/(1)^0.5

g = 283mm

Length of patch, L= g/2

L=141.5mm

Calculation of the width(W):-The width of the Microstrip patch antenna is calculated

as:

W=(c/2fr)*(2/(r+1))^0.5

= (3*10^8/2*1.06*10^9)*(2/(1+1))^0.5

= 141.5mm

Calculation of L:-It is calculated as follow:

L= 0.412*h*(r+0.3)*(w/h+0.264)/ ((r-0.258)*(w/h+0.813))

= 78.03477/8.1292

= 10(approx)

Leff = L-L

= 141.5- 2*10

= 122(approx)

The following Microstrip antennas are also designed in a similar fashion.

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FIGURE 3.1: Antenna showing probe feeding

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CHAPTER-4

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MODELLING, SIMULATION AND OPTIMIZATION

4.1 MODELLING IN HFSS

1. First ground plane is drawn in any plane(say XY)of particular dimension (340mm*340mm)

and boundary is assigned as perfectly electric.

2. Rectangular patch of dimension 142mm*122mm(as calculated mathematically)is drawn at

height 14mm above the ground plane and is assigned perfectly electric.

3. Substrate is kept as air.

4. Probe of material 'pec' is drawn along length with height 16.5mm whose position is

calculated mathematically as 22mm from centre.

5. Portcap of material 'pec' is placed below the ground plane covering the probe.

6. Subtractions are carried out with probe and ground ,probe and patch and Teflon and

ground.

7. Assign excitation by defining the wave port around the probe.

8. Draw radiation box around complete antenna and assign radiation boundary.

9. Set the solution frequency as 1.06GHz and define the desired range of frequency(1GHz-

1.12GHz).

10. Analyze the design and check for return loss and amount of beamwidth.

11. Antenna is optimized by changing the parameters to obtain desired centre frequency and

bandwidth.

On optimizing the antenna to obtain frequency 1.06GHz values of parameters are as follows :-

Length of the patch = 126mm

Width of the patch = 126mm

position of the probe = 46mm

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4.2 SIMULATION

Antenna designs, however efficient they might be, could be understood a lot better when their

performance is simulated. Generally in antenna problems, the actual practical result might not be

the same as the one predicted by theory and a better understanding of the Functionality of the

structure in terms of the reflection and radiation characteristics is warranted. In this project, the

High Frequency Structure Simulator (HFSS) of Ansoft has been used extensively to perform antenna

simulations.

The task at hand for the antenna designer is to first draw the structure, specify material

characteristics for each object and identify ports and special surface characteristics. The system then

generates the necessary field solutions and associated port characteristics and S-parameters. As we

sets up the problem, Ansoft HFSS allows us to specify whether to solve the problem at one specific

frequency or at several frequencies within a range. Results along with figures and graphs are as

follows:

4.3 OPTIMIZATION

After comparing and optimizing following results and cases are obtained. They are as follows:

CASE 1: First we had studied simple probe fed patch antenna with air as a

substrate. Parameters of this antenna are same as discussed above.

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Figure4.1: Return loss of patch antenna with air as substrate of height 14mm

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Figure4.2: Graphs showing Realized Gain for the above antenna

along with the Beamwidth obtained in different

planes

CASE 2:- Design of antenna having a small curvature in its patch is shown below. Two views of the antenna is shown below. For height,

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h=28 mm of the edge from the ground plane this antenna possesses

characteristic of increased beamwidth and also increased bandwidth.

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Figure4.3: Return loss of patch antenna with air as substrate and with curvature of height 28mm

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00Theta [deg]

-70.00

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

dB

(Re

alize

dG

ain

L3

X)

HFSSDesign1XY Plot 2 ANSOFTCurve Info xdb10Beamw idth(3)

dB(RealizedGainL3X)Setup1 : LastAdaptiveFreq='1.06GHz' Phi='0deg'

51.6960

dB(RealizedGainL3X)Setup1 : LastAdaptiveFreq='1.06GHz' Phi='90deg'

110.6138

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Figure4.4: Graphs showing Realized Gain for the above antenna

along with the Beamwidth obtained in different

planes.

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00Theta [deg]

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

-0.00

5.00

10.00d

B(R

ea

lize

dG

ain

L3

Y)

HFSSDesign1XY Plot 3 ANSOFTCurve Info xdb10Beamw idth(3)

dB(RealizedGainL3Y)Setup1 : LastAdaptiveFreq='1.06GHz' Phi='0deg'

94.3446

dB(RealizedGainL3Y)Setup1 : LastAdaptiveFreq='1.06GHz' Phi='90deg'

46.0283

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CHAPTER-5

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RESULT AND CONCLUSION

RESULT:

The table 7.1 shows the return losses obtained from simulation for CASE 1 for

resonant frequency 1.06GHz

FREQUENCY(GHz) RETURN LOSS(dB)

1.03 -10.4

1.06 -43.0 1.09 -10.8

1.12 -5.5

TABLE 5.1: RETURN LOSS (SIMULATED RESULT)

The table 5.2 shows the return losses obtained from simulation for CASE 2 for

resonant frequency 1.06GHz.

FREQUENCY(GHz) RETURN LOSS(dB)

1.03 -10.9

1.06 -30.0 1.09 -9.97

1.12 -6.0

TABLE 5.2: RETURN LOSS (SIMULATED RESULT)

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CONCLUSION

A new broad-band design of a probe-fed rectangular patch antenna with a U-

shaped patch has been proposed and experimentally studied. For constructed

prototypes of the proposed design, the impedance bandwidth (1:1.5 VSWR)

greater than 12% can easily be obtained. Moreover, the antenna gain of the

proposed design can be greater than that of a conventional probe-fed patch

antenna and peak antenna gain can reach 8 dB or larger. The XPLs in the E-

plane pattern for the constructed prototypes are all well above 10 dB and the

XPLs in the H-plane pattern can be improved to be about 14 dB, which is even

better than that of a corresponding conventional probe-fed patch antenna with a

thin air substrate.

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APPLICATIONS

A cross Vivaldi antenna is designed and investigated for a radar based breast tumor

detection. The antenna performance is examined over the frequency range of 2.2-

5.4GHz. results obtained through simulations and experiments demonstrate the ability

of the antenna to detect tumors in 3D breast models.

The pattern of EM field is known as lobes or beams. By proper control of the

interacting transmitters, the beams may be shaped or formed, a process known as

beam forming. Vivaldi antenna are used to achieve this.

Vivaldi antenna elements are installed behind a radome on aircraft systems.

FIGURE 11.1: VIVALDI ANTENNA ELEMENTS IN AIRCRAFT SYSTEMS.

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The Broadband Dual Polarized Vivaldi Antenna Arrays as shown below are widely

used in Mobile Communication Applications.

FIGURE11.2: TWO HORIZONTAL AND TWO VERTICAL VIVALDI ELEMENTS

IN TYPICAL ARRAY CONFIGURATION

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BIBLIOGRAPHY

Schaubert & Shin, A parameter study of stripline-fed Vivaldi notch-antenna arrays,

IEEE Trans. on Antennas and Propagation, Vol. 47, No. 5, May 1999, pp. 879-886.

Noronha et al, Designing antennas for UWB systems, Microwaves & RF Journal,

June 2003, pp. 53-61.

Langley et al, Novel ultrawide-bandwidth Vivaldi antenna with low

crosspolarization, Electronic Letters, Vol. 29, No. 23, 1993, pp. 2004-2005.

Schuppert, Microstrip/slotline transitions: Modeling and experimental

investigations, IEEE Trans., Vol. MTT-36, 1988, pp. 1272-1282.

H. Atwater, The Design of the Radial Line Stub: A Useful Microstrip Circuit

Element, Microwave Journal, Vol. 28, 1985, pp.149-156.

http://www.ansoft.com

H.Y. Wang et al, Rigorous analysis of Tapered Slot Antennas on dielectric

substrates, 10th International Conference on Antennas and Propagation, 1997.

R. Janaswamy and D.H. Schaubert, Analysis of a Tapered Slot Antenna, IEEE

Transactions on Antennas and Propagation, Vol. AP-35, No. 9, September 1987, pp.

1058-1065.

Yngvesson et al, The tapered slot antenna A new integrated element for millimeter-

wave applications, IEEE Transactions on Microwave Theory and Techniques, Vol.

37, No. 2, February 1989, pp. 365-374.