final report rahul

8/6/2019 Final Report Rahul

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1.INTRODUCTION

Deschamps first proposed the concept of the MSA in 1953. The numerous

advantages of MSA, such as its low weight, small volume, and ease of fabrication

using printed-circuit technology, led to the design of several configurations forvarious applications. With increasing requirements for personal and mobile

communications, the demand for smaller and low-profile antennas has brought

the MSA to the forefront. An MSA in its simplest form consists of a radiating patch

on one side of a dielectric substrate and a ground plane on the other side.

However, other shapes, such as the square, circular, triangular, semicircular,

sectoral, and annular ring shapes are also used.

Figure.1

Antenna is a very important component of communication systems. By definition,

an Antenna is a device used to transform an RF signal, traveling on conductor,into an electromagnetic wave in free space. The Antenna must be able to radiate

efficiently so the power supplied by the transmitter is not wasted. An efficient

transmitter must have exact dimensions. The dimensions are determined by the

frequencies and gets critical at higher frequencies. Microstrip antennas can be

made to emulate many of the different styles of antennas explained above.


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Microstrip antennas offer several tradeoffs that need to be considered. Because

they are manufactured with PCB traces on actual PCB (Printed Circuit Boards)

boards, they can be very small and lightweight. This comes at the cost of not

being able to handle as much output power as other antennas, and they are made

for very specific frequency ranges.

To provide a quality service for the recent increased demand in mobile

communication, the development of antenna, which is a core instrument in

communication devices, has become an important issue. As all devices are

becoming small and the antenna also must become smaller, lighter, and mass

production. One of the antennas satisfying the characteristics is the micro strip

antenna. The micro strip antenna is very easily manufactured and can be produce.

In this project, a broadband micro strip patch antenna which has a resonancearound 2.4 GHz and 3.23GHz has been designed. Basically a wideband micro strip

patch antenna has been designed for high-speed wireless local area networks. Togain access to a local WLAN network in different parts of the world micro strip

antenna is the ideal choice for such an application due to its low-profile,

lightweight, low-cost and ease of integration with microwave circuits. However,

standard rectangular micro strip patch antenna has the drawback of narrow

bandwidth.


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2.Advantages

MSAs have several advantages compared to the conventional microwave

antennas. The main advantages of MSAs are listed as follows:

y They are lightweight and have a small volume and a low-profilePlanar configuration.

y They can be made conformal to the host surface.y Their ease of mass production using printed-circuit technology leads

to a low fabrication cost.

y They are easier to integrate with other MICs on the same substrate.y They allow both linear polarization and CP.y They can be made compact for use in personal mobile communication.y They allow for dual- and triple-frequency operations.

DISADVANTAGES:-

1. Low efficiency.

2. Low power handling capability.

3. High Q (sometimes in excess of 100).

4. Poor polarization purity.

5. Poor scan performance.


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6. Spurious feed radiation and very narrow frequency bandwidth.

7. Practical limitations on gain.

8. Poor isolation between the feed and radiating elements.

9. High performance arrays require complex feed systems.

APPLICATIONS:-1. Vehicle based satellite link antennas and switched beam array. [2]

2. Global positioning systems (GPS).

3. In Radar for missiles and telemetry.

4. Mobile handheld radios, pagers, intruder alarms , personal communication.

5. Radio altimeter.

6. Telemetry.

7. Feed element in complex antennas and large light weight apertures.

8. Air craft antennas.

9. Application in microwave cancer therapy.

10. Adaptive arrays in multitarget acquisition.


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OBJECTIVES

Future wireless communication networks will need to support extremely high

data rates in order to meet the rapidly growing demand for broadbandapplications such as high quality audio and video. Existing wireless

communications technologies such as third generation cellular telephony and

wireless local area networks cannot support broadband data rates (of the order of

hundreds of millions of bits per second) due to their sensitivity to severe wireless

channel impairments such as the time-varying attenuation caused by user

mobility. To make things even more difficult, there are limited resources such as

the available frequency bandwidth, allowable transmission power and

computational ability of portable devices. Furthermore, in order to accommodatethe increasing number of subscribers, future mobile communication systems will

require more capacity, flexibility and easy deployment. These difficulties may be

overcome by designing clever networks and data transmission schemes specially

suited for the wireless channel.

During the last decade, new cooperative networking approaches and very

promising technologies emerged to respond to these demands. On the one hand,

a new networking paradigm for wireless systems is offered by ad hoc networks. Itpromises broadband access, easy deployment, flexibility, and large capacity. On

the other hand, the use of multiple antennas at both transmitter and receiver

ends can enormously increase the data rate and performance robustness without

increasing neither the transmit power nor the bandwidth.

The research will provide means for improving user data rates, reducing spectrum

requirements, and lowering emitted electromagnetic radiation, thus prolonging

battery life time.


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The objectives for this project are as follows:-

1. Bandwidth extension techniques.

2. Control of radiation patterns involving side lobes, beam shaping, cross-

polarization, circular polarization, surface wave and ground plane effects.

3. Reducing loss and increasing radiation efficiency.

4. Optimal feeder systems (array architecture).

5. Improved lower cost sub rates.

6. Tolerance control and operational factors.

Some generic types of bandwidth extension techniques are:-

1. Increasing antenna volume by incorporating parasitic elements, stacked

substrates, use of foam dielectrics.

2. Creation of multiple resonances in input response by addition of external

passive networks and or internal resonant structures.

3. Incorporation of dissipative loading by adding lossy material or resistors.

4. Wider effective bandwidth by introducing varactor and pin diode.


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3. Waves on Microstrip

The mechanisms of transmission and radiation in a microstrip can be understood

by considering a point current source (Hertz dipole) located on top of thegrounded dielectric substrate (fig. 1.1) This source radiates electromagnetic

waves. Depending on the direction toward which waves are transmitted, they fall

within three distinct categories, each of which exhibits different behaviors.

3.1 Surface Waves

The waves transmitted slightly downward, having elevation angles between

/2and - arcsin (1/r), meet the ground plane, which reflects them, and then

meet the dielectric-to-air boundary, which also reflects them (total reflection

condition). The magnitude of the field amplitudes builds up for some particular

incidence angles that leads to the excitation of a discrete set of surface wave

modes; which are similar to the modes in metallic waveguide. The fields remain

mostly trapped within the dielectric, decaying exponentially above the interface

(fig1.2). The vector , pointing upward, indicates the direction of largestAttenuation. The wave propagates horizontally along , with little absorption in

good quality dielectric. With two directions of and orthogonal to each other,

the wave is a non-uniform plane wave. Surface waves spread out in cylindrical

fashion around the excitation point, with field amplitudes decreasing with

distance (r), say1/r, more slowly than space waves. The same guiding mechanism


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provides propagation within optical fibers. Surface waves take up some part of

the signals energy, which does not reach the intended user. The signals

amplitude is thus reduced, contributing to an apparent attenuation or a decrease

in antenna efficiency. Additionally, surface waves also introduce spurious for

coupling between different circuit and antenna elements. This effect severelydegrades the performance of microstrip filters because the parasitic interaction

reduces the isolation in the stop bands. In large periodic phased arrays, the effect

of surface wave coupling becomes particularly obnoxious, and the array can

neither transmit nor receive when it is pointed at some particular directions (blind

spots). This is due to a resonance phenomenon, when the surface waves excite in

synchronism the Floquet modes of the periodic structure. Surface waves reaching

the outer boundaries of an open microstrip structure are reflected and diffracted

by the edges. The diffracted waves provide an additional contribution to

radiation, degrading the antenna pattern by raising the side lobe and the crosspolarization levels. Surface wave effects are mostly negative, for circuits and for

antennas, so their excitation should be suppressed if possible.


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3.2 Leaky Waves

Waves directed more sharply downward, with angles between - arcsin (1/r)

and , are also reflected by the ground plane but only partially by the dielectric-

to-air boundary. They progressively leak from the substrate into the air (Fig 1.3),

hence their name laky waves, and eventually contribute to radiation. The leaky

waves are also nonuniform plane waves for which the attenuation direction

points downward, which may appear to be rather odd; the amplitude of the

waves increases as one moves away from the dielectric surface. This apparentparadox is easily understood by looking at the figure 1.3; actually, the field

amplitude increases as one move away from the substrate because the wave

radiates from a point where the signal amplitude is larger. Since the structure is

finite, this apparent divergent behavior can only exist locally, and the wave

vanishes abruptly as one crosses the trajectory of the first ray in the figure. In

more complex structures made with several layers of different dielectrics, leaky

waves can be used to increase the apparent antenna size and thus provide a

larger gain. This occurs for favorable stacking arrangements and at a particular

frequency. Conversely, leaky waves are not excited in some other multilayerstructures.


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3.3 Guided Waves

When realizing printed circuits, one locally adds a metal layer on top of the

substrate, which modifies the geometry, introducing an additional reflectingboundary. Waves directed into the dielectric located under the upper conductor

bounce back and forth on the metal boundaries, which form a parallel plate

waveguide. The waves in the metallic guide can only exist for some Particular

values of the angle of incidence, forming a discrete set of waveguide modes. The

guided waves provide the normal operation of all transmission lines and circuits,

in which the electromagnetic fields are mostly concentrated in the volume below

the upper conductor. On the other hand, this buildup of electromagnetic energy is

not favorable for patch antennas, which behave like resonators with a limited

frequency bandwidth.


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4.Feeding Methods

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 connectingelement such as a microstrip line. In the non-contacting scheme, electromagnetic

field coupling is done to transfer power between the microstrip line and the

radiating patch. The four most popular feed techniques used are the microstrip

line, coaxial probe (both contacting schemes), aperture coupling and proximity

coupling (both non-contacting schemes).

4 (a) Microstrip Line Feed

Figure 2.3


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

of the Microstrip patch as shown in Figure 2.3. 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. The purpose of the inset cut in the patch is to match the impedance ofthe 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.

Advantages:

(1) Easy to fabricate.

(2) Simple to match by controlling the inset position.

(3) Simple to model.

Disadvantages:

(1) As the substrate thickness increases, surface waves and spurious feed

radiation increases, which limits the bandwidth (2 5%).

(2) Possess inherent asymmetries which generate higher order modes which

produce cross-polarised radiation.


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4 (b) Coaxial Feed

Figure 2.4

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

Microstrips patch antennas. As seen from Figure 2.4, 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. The main

advantage of this type of feeding scheme is that the feed can be placed at anydesired 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, a

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 >


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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 issues.

Advantages:

(1) Easy to fabricate and match.

(2) Low spurious radiation.

Disadvantages:

(1) More difficult to model for thickness of substrates (h > 0.02P).

(2) It has narrow bandwidth.(3) Possess inherent asymmetries which generate higher order modeswhich

produce cross-polarised radiation.

4 (c) Aperture Coupled Feed

Figure. 2.5


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In this type of feed technique, the radiating patch and the microstrip feed lines

are separated by the ground plane as shown in Figure 2.5. Coupling between the

patch and the feed line is made through a slot or an aperture in the ground plane.

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

crosspolarization due to symmetry of the configuration. The amount of couplingfrom 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

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.

Disadvantages:

(1) Most difficult of all to fabricate.

(2) Narrow bandwidth.

Advantages:

(1) Easier to model.

(2) Moderate spurious radiation.

4 (d) Proximity Coupled Feed


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Figure 2.6

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

As shown in Figure 2.6, 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. The main advantage of this feed technique is that it eliminates spurious

feed radiation and provides very high bandwidth (as high as 13%), due to overall

increase in the thickness of the microstrip patch antenna. 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. Matching can beachieved 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.

Advantages:

(1) Largest bandwidth (high as 13%).

(2) Easy to model.

(3) Low spurious radiation.

Disadvantages:

(1) Fabrication is difficult.


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5. Methods of Analysis

The preferred models for the analysis of Microstrip patch antennas are theTransmission 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 shaped elements

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

above and are far more complex in nature.

5.1 Transmission Line ModelThis model represents the microstrip antenna by two slots of width Wand 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.

Hence, as seen from above Figure, 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 (reff) must be obtained in order to account for the


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fringing and the wave propagation in the line. The value of reff is slightly less

then r because the fringing fields around the periphery of the patch are not

confined in the dielectric substrate but are also spread in the air as shown in

Figure above. The expression for reffis given by Balanis as:

Where reff= Effective dielectric constantr= Dielectric constant of substrate

h = Height of dielectric substrate

W= Width of the patch

Consider Figure 2.7 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. In order to operate in the

fundamental TM10 mode, the length of the patch must be slightly less than /2

where is the wavelength in the dielectric medium and is equal to o/reffwhere o is the free space wavelength. The TM10 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 2.10 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.


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It is seen from Figure 2.8 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 (seen in Figure 2.8), 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 Hammerstad as:


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7.Software used for simulation

I have used IE3D trail version for the design and simulation of antennas. Initially i

have practiced Microstrip patch antenna with inset feed and the results were very

accurate.IE3D software is based on MOM(method of moments).

In the MoM, the surface currents are used to model the microstrip patch, and

volume polarization currents in the dielectric slab are used to model the fields in

the dielectric slab. An integral equation is formulated for the unknown currents

on the microstrip patches and the feed lines and their images in the ground plane

the integral equations are transformed into algebraic equations that can be easily

solved using a computer. This method takes into account the fringing fields

outside the physical boundary of the two-dimensional patch, thus providing a

more exact solution.

The use of high speed digital computers not only allows more computations to be

made than before, it makes practical methods of solution too repetitious for hand

calculation. It is now more convenient to use computer time to reduce the

analytical effort. Approximation techniques, once considered a last resort, can be

carried to such high orders on computers that they are for most purposes as good

as exact solutions. They also permit treatment of problems not solvable by exactmethods. METHOD OF MOMENTS gives most specific solution used in IE3Dfor

antenna analysis and simulation.

Consider the inhomogeneous equation

L(f) = g

where L is a linear operator,

g is known(source of excitation)

and f is to be determined(field of response, unknown function to be

determined).


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Let f be expanded in a series of functions f1, f2, f3... in the domain of L, as

F= .(1)where the n are constants. We shall call the fn expansion functions or

basis functions. For exact solutions, (1) is usually an Infinite summation and the'

fn form a complete set of basis functions. For approximate solutions, (1) is usually

a finite summation. Substituting (2) in (1), and using the linearity of L, we have

..(2)

It is assumed that a suitable inner product (f, g) has been determined forthe problem. Now define a set of weighting functions, or testing functions, w1 w2

w3,.. in the range of Lt and take the inner product of (1-22) with each wm. The

result is

m = 1, 2, 3,.. This set of equations can be written in the matrix form as

[Imn ][xn]=[gm]..(4)

Where

[Imn]=

.(5)


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=

[gm]=

(6)

If the matrix [f] is nonsingular its inverse exists. The n are then given by

[ [gm] .(7)

and the solution for f is given by (1). For concise expression of this result,define the matrix, of functions

[fn]=[f1 f2 f3](8)

And write f=[fn][xn]=[fn][gm]

This solution may be exact or approximate, depending upon the choice of

the fn and wn The particular choice wn = fn is known as Galerkin's method [6,7 ],

If the matrix [f] is of infinite order, it can be inverted only in special cases,

for example, if it is diagonal. The classical eigenfunction method leads to a

diagonal matrix, and can be thought of as a special case of the method of

moments, If the sets fn and wn are finite, the matrix is of finite order, and can be

inverted by known methods .

One of the main tasks in any particular problem is the choice of the fn and

wn. The fn should be linearly independent and chosen so that some superposition

(1-21) can approximate f reasonably well. The wn should also be linearly

independent and chosen so that the products (wm g) depend on relatively

independent properties of g. Some additional factors which affect the choice of fn

and wn are


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(1) The accuracy of solution desired,

(2) The ease of evaluation of the matrix elements,

(3) The size of the matrix that can be inverted, and

(4) The realization of a well-conditioned matrix [l],


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A Comparison of Commercial Software

Packages for Microstrip Antenna Analysis

Introduction:

Both computer power and software capabilities have increased substantially in

recent years, and there are now a variety of general purpose software packages

commercially available for the analysis and design of antennas and microwave

components. Before the advent of such software, a common practice in industry

and universities was to write custom computer codes for the solution of specific

antenna geometry. Although this situation led to steady progress in the

development of improved numerical electromagnetic methods, as well as the

nurturing of a generation of electromagnetic practitioners and a continuous flow

of journal articles, it was a costly, slow, and inflexible approach. Today it is usually

much more cost effective to acquire and use general purpose CAD packages

capable of modeling a wide range of antenna geometries that may be of

interest. Nevertheless, not all antenna CAD packages have the same capabilities

or performance, and each may be best suited for a particular type of problem. In

this paper we compare five commercial software packages for the analysis ofseveral types of commonly used microstrip antennas. Factors including accuracy,

speed of execution, setup time, and cost are presented. Measured impedance

data is used as a standard for comparison, and results are also compared with

custom full-wave moment method codes.


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Software Packages Used in this Comparison;

Five commercial CAD packages were used in this comparative study:

Ensemble

PCAAD Antenna Design

Momentu

Hewlett-Packard

HFSS Hewlett-Packard

IE3D Zeland Software,

Ensemble, Momentum, and IE3D all employ full-wave moment method solutions

to treat general 2.5D planar antenna and circuit geometries, making them well-

suited for printed antennas. These packages can model multilayer microstrip

antennas with probe, aperture, and proximity feeds. PCAAD is a general-purpose

antenna CAD package, using cavity and transmission line models for several

standard microstrip geometries, but is not capable of treating general multilayer

antenna geometries. HFSS is a finite element solution that is general enough to

model full 3D geometries, including planar antenna structures, but often the fine

detail needed to model thin dielectric features requires a very large number of

cells. The price of these packages range from about $400 to $50,000.

Discussion:

Generally an accuracy figure of 0.2 or less implies a numerical solution that isproviding a fairly rigorous model of the antenna impedance over a relatively wide

frequency range, and this model should provide results that are more than

adequate for design purposes. (Smith chart plots of the impedance loci for these

cases will be shown during the presentation.) Run times generally increase in

proportion to the number of expansion modes or discretization cells used in the


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solution. Run times less than 10-20 seconds per frequency point are probably low

enough that most users will look to other evaluation criteria for these cases.

Setup times obviously depend heavily on the experience of the user, so the above

figures should only be used as a rough indication of what might be expected for

geometries of this type.

We feel the above results are representative of what can be expected when

modeling microstrip antennas with the CAD packages studied here, but it is

important to realize that this has not been an exhaustive test, and that results

may vary considerably for different geometries, dimensions, or material

parameters. For example, it is known that the simple cavity and transmission line

models in PCAAD will fail for electrically thick substrates, or with substrates

having a high dielectric constant. It is suspected that some of the other packageswill give poorer results for these cases, as well.

As might be expected, the above comparisons show that the best accuracy and

speed are obtained with custom-written full-wave moment method codes. Of

course, codes of this type are very limited in versatility, and even small changes in

geometry may require modifications to the code itself. Next in rank of

performance are the 2.5D planar moment method codes (Ensemble, IE3D,

Momentum), which give comparable accuracies and run times. It appears thatMomentum usually gives slightly more accurate results, with slightly longer run

times, but it is likely that the accuracy of Ensemble and IE3D would improve if

more expansion modes were used (at the cost of longer run times). We did not

pursue this line of inquiry, using essentially the default, or suggested

discretizations for each package. The finite element method used in HFSS works

reasonably well for the simpler antenna geometries, but does not seem to be well

suited for the more complicated multilayer cases.

We are presently evaluating a commercial FDTD package, and results for the

above test cases will be presented at the conference if available.


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Final Comment:

Finally, we would like to emphasize that although commercial CAD products

provide analysis tools of unparalleled power and flexibility, no computer package

is a substitute for a fundamental conceptual understanding of electromagneticsand the art of antenna design. The old adage that "garbage in equals garbage out"

applies more than ever before.


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8. ANTENNA LAYOUT

Figure. a

The figure shows the micro strip patch antenna with two parallel slits

incorporated to attain a dual band of frequencies. A comprehensive parametricstudy has been carried out to understand the effects of various dimensional

parameters and to optimize the performance of the final design.


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9.ANTENNA DESIGN METHOD

The antenna geometry is shown in Fig. 1. First, a rectangular micro strip patch

antenna is designed based on the standard design procedure to determine the

length (L) and width (W) for resonant frequencies. It is fed by a strip line. Twoparallel slots are incorporated to perturb the surface current path, introducing

local inductive effect that is responsible for the excitation of a second resonant

mode. The slot length (Ls), slot width (Ws), and the center arm dimensions (Wt

and Lt) of the patch control the frequency of the second resonant mode and the

achievable bandwidth. A common rectangular patch antenna can be represented

by means of the equivalent circuit. The BW is approximately 15% for r=2.2 and

h=.010. The r can be chosen close to unity to obtain broader bandwidth. The

expression for approximately calculating the % age bandwidth of the RMSA in terms

of patch dimension and substrate parameter is given by

% .0 *

WB W A h

r LP I!

Where W and L are the width and length of RMSA. However W should be taken less

than to avoid excitation of higher order modes .Another simplified relation for quick

calculation of BW for VSWR=2 of MSA operating at frequency f in GHz, with h

expressed in cms is given by

. 5 0 ( ^ 2 )B W h f!

The BW can also be defined in terms of antenna radiation parameters. It is defined as

the frequency range over which radiation parameters such as the gain, half power

beam width (HPBW) and side lobe levels are within the specified minimum and

maximum limits. This definition is more complete as it also takes care of the input

impedance mismatch, which also contributes to change in gain. The expression for

calculating the directivity D of the RMSA is given by

0 . 2 6 . 6 1 0 l o g (1 . 6 / )D W rI!


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10. PARAMETRIC STUDY

A substrate with dielectric permittivity of2.4 and thickness of 1.58 mm is selected

to obtain compact radiation structure. The antenna parameters are listed below

in millimeters

Parameters Design Values

Length of patch 39.6mm

Width of patch 46.9mm

Length of slot 14.2mm

Width of slot 1.4mm

Inset depth 13.2mm

Achieving impedance matching at both frequencies:- It is achieved by varying the

slot width when we increase slot width ,the input impedance change. It is also

found that increasing the inset feed length simultaneously reduce the input

impedance at both frequency to 50 .The inset feed has slight effect on both

resonant frequencies and thus slight tuning is required.

In order for the antenna to operate efficiently, maximum transfer of power must

take place between the transmitter and antenna. Maximum power transfer can

take place only when the impedance of the antenna matched to that of

transmitter. The VSWR expresses the degree of match .When VSWR=1 the match

is perfect. A minimum VSWR


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Figure .b Smith chart


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11. SIMULATION RESULTS

The results of the simulated antenna using IE3D are tabulated below.

Parameters Resonantfrequency

(2.40 GHz)

Resonantfrequency

(3.23 GHz)

Return loss (db) -22.5 -18.5

VSWR 1.8 1.8

Antenna

efficiency (%)

85 42.3

Axial ratio 117.5 38

Gain (dbi) 6.7 -3.32

Figure c. Return loss


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Figure d. Voltage standing ratio (VSRW)

In telecommunications, standing wave ratio (SWR) is the ratio of the amplitude of

a partial standing wave at an antinodes (maximum) to the amplitude at an

adjacent node (minimum), in an electrical transmission line. SWR is used as aefficiency measure for transmission lines, electrical cables that conduct radio

frequency signals, used for purposes such as connecting radio transmitters and

receivers with their antennas. It is give by formula show below


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Figure e. Antenna efficiency and radiation efficiency

The efficiency of an antenna relates the power delivered to the antenna and the

power radiated or dissipated within the antenna. A high efficiency antenna has

most of the power present at the antenna's input radiated away. A low efficiencyantenna has most of the power absorbed as losses within the antenna, or

reflected away due to impedance mismatch.


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Figure. f Axial ratio

The antenna presented in this is basically linear polarized, so for that the axial

ratio should be high, ideally infinity.

The axial ratio is the ratio of orthogonal components of an E-field.


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Figure. g Gain

It is the ratio of the power required at the input of a loss-free reference

antenna to the power supplied to the input of the given antenna to produce, in a

given direction, the same field strength at the same distance. Note

1: Antenna gain is usually expressed in dB. Note 2: Unless otherwise specified, the

gain refers to the direction of maximum radiation. The gain may be considered for

a specified polarization.


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Figure h. Radiation pattern

In the field ofantenna design the term radiation pattern most commonly refers to

the directional(angular) dependence of the strength of the radio from the

antenna. It is a fundamental property of antennas that the receivingpattern (sensitivity as a function of direction) of an antenna when used

for receiving is identical to the far-field radiation pattern of the antenna when

used for transmitting. This is a consequence of the reciprocity theorem of

electromagnetic and is proved below.


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12. APPLICATIONS

For many applications, the advantages of micro strip antennas far outweigh their

limitations. Initially, micro strip antennas found widespread applications in

military systems such as missiles, rockets and satellites .Currently, these antennas

are being increasingly used in commercial sector, due to the reduced cost of

substrate material and mature fabrication technology. With continued research

and development and increased usage, micro strip antennas are ultimately

accepted to replace conventional antennas for most applications. The present

design has an efficiency of 85% and can be used in wireless routers.

Figure i. Router


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13. CONCLUSION

A wide band parallel slot micro strip patch antenna has been designed for

wireless communication system. The reflection coefficient is 8.94db for both the

resonant frequencies. The performance is satisfactory and at the same time the

antenna is thin and compact with low dielectric constant substrate material.

These features are very important for the portability of wireless communication

equipment. It should be noted that the performance of the proposed antenna is

not optimized. By varying slot length and width the second resonant frequency

can be changed without affecting the resonant frequency of fundamental mode .


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14. Reference

1. Ayoub, A. F. A., Analysis of rectangular micro strip antennas with air

substrates,Journal of Electromagnetic Waves and Applications, Vol. 17, No. 12,

1755-1766, 2003.

2. Vetharatnam, G., B. K. Chung, and H. T. Chuah, Design of a micro strip patch

antenna array for airborne SAR applications, Journal of Electromagnetic Waves

and Applications, Vol 19, No. 12, 1687-1701, 2005.

3. Yang, F., X. X. Zhang, X. Ye, and Y. Rahmat-Samii, Wide-band E-shaped patch

antennas for wireless communications, IEEE Trans. Antennas Propagat., Vol. 49,

No. 7, 1094-1100, July 2001

4. Wong, K. L. and W. H. Hsu, Abroad-band rectangular patch antenna with a

pair of wide slits, IEEE Trans. Antennas Propagat., Vol. 49, No. 9, 1345-1347,

September 2001.

5. Ge, Y., K. P. Esselle, and T. S. Bird, E-shaped patch antennas for high-speed

wireless networks, IEEE Trans. Antennas Propagat., Vol. 52, No. 12, 3213-3219, Dec.

2004.

6. Ge, Y., K. P. Esselle, and T. S. Bird, Acompact E-shaped patch antenna

with corrugated wings, IEEE Trans. Antennas Propagat., Vol. 54, No. 8, 2411-

2413, Aug. 2006.

7. Yu, A. and X. X. Zhang, A method to enhance the bandwidth of microstrip

antennas using a modified E-shaped patch, Proceedings of Radio and Wireless

Conference, 261-264, Aug. 10-13,2003.

8. Lee, K. F., et al., Experimental and simulation studies of the coaxially fed

U-slots rectangular patch antenna, IEE Proc. Microw. Antenna Propag., Vol. 144,

No. 5, 354-358, October 1997.

9. Rafi, G. and L. Shafai, Broadband microstrip patch antenna with V-slot, IEE

Proc. Microw. Antenna Propag., Vol. 151, No. 5, 435-440, October 2004.


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INDEX

1.Introduction


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2.Antenna layout

3. Antenna design method

4.Parametric study

5.Simulation Results

6. Applications

7.Conclusion

8.References

final report rahul

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