ABSTRACT

With the modern Electronic wireless communication and Radar development, an antenna is a critical item. Every electronic equipment either transmits or receivers or both, an antenna is indispensible.

Hence we propose to design an aero space Micro strip Antenna in s-band for telemetry or commanding application by using conventional and classical method for the design of dimension for rectangular type. This will be fabricated by using printed circuit technique. A micro strip structure is structured by using a dielectric material at the top and bottom. Bottom is used as ground plane and top is etched by standard techniques. We will fabricating this by taking the mask ant he screen printing will done. We propose to feed the antenna by using the available coaxial RF connector for input/output of SMA type.

This will be tested after connecting the connector for its electrical characteristics like VSWR, input impedance, Return losses on a smith chart. After satisfying and iterating for correct frequency, we will finalize the feed point location.

We propose to design a VSWR of 2:1 ratio and return loss of more than or equal to 15db at a particular frequency in s-band and hence we get the antenna band width from this measurement. We propose to carry out the antenna radiation to find E & H plane beam width of antenna pattern coverage and gain.

Since the above design is only for a particular frequency, for a band of frequencies or at any frequency a software program with mat lab is complied for various thickness and various dielectric.

Finally results will be compared with expected, measured and simulate one and their variations and analyzed.

INDEX

ABSTRACT Page no:

LIST OF SYMBOLS

LIST OF FIGURES

LIST OF TABLES

CHAPTER–1 INTRODUCTION

1.1 Introduction 1

1.2 Definition Of Antena 1

1.3 Origin of Antenna 2

1.4 History of Antenna Technology 3

1.5 Basic Antenna Characteristics 4

1.5.1 Radiation pattern 4

1.5.2 Gain 4

1.5.3 Directivity 5

1.5.4 Polarization 5

1.5.5 VSWR 5

1.5.6 Reflection Coefficient and Return Loss 6

1.5.7 Bandwidth 6

1.5.8 Beam width 6

1.6 Types of Antenna 7

1.7 Aim and Objective of the Project 7

CHAPTER– 2 OVERVIEW OF THE MICROSTRIP ANTENNA

2.1 History Of Micro Strip Antenna 9

2.2 Definition Of Micro Strip Antenna 9

2.3 Advantages And Disadvantages 10

2.4 Radiation Mehcanism 11

2.5 Various Micro Strip Antenna Configurations 13

2.5.1 Micro strip patch antenna 13

2.5.2 Micro strip or Printed Dipole Antenna 15

CHAPTER–3 HARDWARE IMPLIMENTATION OF PROJECT

3.1 Introduction 16

3.2 Basic Principles of Operation 17

3.3 Resonant Frequency 18

3.4 Radiation Patterns 18

3.5 Radiation Efficiency 20

3.6 Bandwidth 22

3.7 Input Impedance 23

3.8 Feed Techniques 24

3.8.1 Micro strip Line Feed 24

3.8.2 Coaxial Feed 25

3.8.3 Aperture Coupled Feed 26

3.8.4 Proximity Coupled Feed 27

3.9 Methods of Analysis 29

3.9.1 Analytical Models 29

3.9.2 Transmission Line Model 31

CHAPTER – 4 IMPLEMENTATION & FABRICATION

4.1 Selection of Substrate 35

4.2 Design procedure for Rectangular Micro strip Antenna 38

4.2.1 Considered Values 38

4.2.2 Initial Design Values 38

4.3 Microwave Co-axial Connector 44

4.4 Fabrication Procedure 47

4.5 Step By Step Design Procedure 49

CHAPTER-5 MEASUREMENTS, TESTING & RESULT ANALYSIS

5.1 MESUREMENTS 53

5.2 TESTING 53

5.2.1 Network Analyzer 53

5.2.2 Elements of Network Analyzer 54

5.2.3 Reflection Measurement 58

5.2.4 RADIATION PATTERN MEASUREMENTS 63

5.2.5 Gain Measurement 67

5.3 ANALYSIS 69

CHAPTER-6 CONCLUSIONS 71

CHAPTER-7 FUTURE SCOPE 72

CHAPTER-8 BIBLOGRAPHY 73

CHAPTER-9 MAT LAB PROGRAM 75

LIST OF SYMBOLS

B Band Width of the Micro Strip Antenna

C Velocity of Antenna

E Electric Field Vector

I Feed Current

K Magnetic Current Line Source

L Length of Rectangular Patch

S Voltage Standing Wave Ratio

V Feed Voltage

W Width of Rectangular Patch

Z Input Impedance

εr Relative Di-electric Constant

εeff Effective Di-electric Constant

Vp Phase Velocity

Rr Radiation Resistance

Fr Resonant Frequency

Λo Free Space Wavelength

∆ Skin Depth

δ Loss Tangent

Λ Wavelength in Di-electric Substrate

η Free Space Impedance

σ Conductivity of Metal

µo Permeability of Free Space

εo Permittivity of Free Space

R, θ, Ф Spherical Co-ordinates

Rin Input Resistance

Q, Qt Total Q Factor

Qs Associated Q Factor of the Surface Wave Loss

Qr Associated Q Factor of the Radiation Loss

Qd Associated Q Factor of the Di-electric Loss

Qc Associated Q Factor of the Conductor Loss

Psw Power Lost in Surface Wave Generation

Prad, P Power Radiated

Ko Wave Number

Js Electric Current Vector

h Thickness of Substrate

LIST OF FIGURES

Figure 1.1 Schematic of an Antenna System

Figure 1.2 Electromagnetic spectrum

Figure 2.1 Structure of a Microstrip Patch Antenna

Figure 2.2 Electric field distributions in microstrip cavity

Figure 2.3 Charge distribution and current density on a microstrip antenna

Figure 2.4 Microstrip patch antenna shapes commonly used in practice

Figure 2.5 Other possible geometries of Microstrip patches

Figure 3.1 Rectangular Patch Antennas

Figure 3.2 Circular Patch Antennas

Figure 3.3 Electric & Magnetic Current Distributions

Figure 3.4 Simulated Radiation Pattern (E & H plane) polar plot

Figure 3.5 Radiation Efficiency for a rectangular patch Antenna

Figure 3.6 Calculated & Measured Bandwidth

Figure 3.7 Equivalent Circuit of Patch Antenna

Figure 3.8 Microstrip Line Feed

Figure 3.9 Probe fed Rectangular Microstrip Patch Antenna

Figure 3.10 Aperture-coupled feed

Figure 3.11 Proximity-coupled Feed

Figure 3.12 Microstrip Line

Figure 3.13 Electric Field Lines

Figure 3.14 Microstrip Patch Antenna proximity feed

Figure 3.15 Top View of Antenna

Figure 3.16 Side View of Antenna

Figure 4.1 Variation of Width with Frequency

Figure 4.2 Variation of Length with the Frequency

Figure 4.3 Variation of Gain with the Frequency

Figure 4.4 Variation of Bandwidth with Frequency for different dielectric substrate antennas

Figure 4.5 APC-7 Connector

Figure 4.6 BNC Connector

Figure 4.7 SMA Connector

Figure 4.8 SMC Connector

Figure 4.9 TNC Connector

Figure 4.10 Type N Connector

Figure 4.11 Flow chart showing the fabrication process

Figure 4.12 Photographic Negative of ground plane Used for Fabrication

Figure 4.13 Photographic Negative of patch Used for Fabrication

Figure 5.1 Major elements of Network Analyzer

Figure 5.2 Vector Network Analyzer used for testing of our antenna

Figure 5.3 Plot of our antenna Return Loss measurement for resonant frequency

Figure 5.4 Plot of our antenna SWR for resonant frequency

Figure 5.5 Plot of our antenna Impedance on a Smith Chart

Figure 5.6 Experimental Set Up For Plotting Radiation Pattern

Figure 5.7 Anechoic Chambers with Free Space Environment

Figure 5.8 Anechoic Chamber when Our Antenna is being Tested

Figure 5.9 Plot of Our antenna Radiation pattern in E and H plane

Figure 5.10 Bottom (ground plane) view of Our Antenna

Figure 5.11 Top view (patch) of Our Antenna

LIST OF TABLES

Table 3.1 Characteristics of the Different Feed Techniques

Table 4.1 Thickness of Cladding for Different Materials

Table 4.2 Dielectric and Loss Tangent for Different Materials

Table 4.3 Basic Features of the Most Common Connector Series

Table 5.1 Specifications of Network Analyzer

Table 5.2 Gain Measurement

Table 5.3 Comparison of calculated and measured values

CHAPTER 1

INTRODUCTION

1.1 Introduction

In high performance aircrafts, spacecrafts, satellites, missiles and other aerospace

applications where size, weight, performance, ease of installation and aerodynamics

profile are the constraints, a low or flat/conformal profile antenna may be required. In

recent years various types of flat profile printed antennas have been developed such as

Microstrip antenna (MSA), strip line, slot antenna, cavity backed printed antenna and

printed dipole antenna. When the characteristics of these antenna types are compared, the

micro strip antenna is found to be more advantageous.

Microstrip antenna are conformable to planar or non planar surface, simple and

inexpensive to manufacture, cost effective compatible with Monolithic Microwave

Integrated Circuits (MMIC) designs and when a particular patch shape like rectangular,

circular, triangular etc., And excitation modes like TM01, TM10 are selected; they are very

versatile in terms of resonant frequency, polarization, radiation patterns and impedance.

In this Project work Design, Fabrication and Testing of linear polarized co-axial

fed microstrip rectangular patch antenna in S-band at 2250 for aerospace applications is

presented. Microstrip antennas have several advantages compared to conventional

microwave antennas and therefore have many applications over the broad frequency

range from 100MHz to 50GHz.

1.2 Definition of Antenna

An antenna (or aerial) is a transducer designed to transmit or receive

electromagnetic waves. In other words, antennas convert electromagnetic waves into

electrical currents and vice-versa. They are used with waves in the radio part of the

electromagnetic spectrum, that is, radio waves, and are a necessary part of all radio

equipment. Antenna has many uses: communication, radar, telemetry, navigation etc.

Figure 1.1 shows the output from a coherent source (e.g. an oscillator) is directed

out into free space using an antenna. The signal source is linked to the antenna by some

kind of transmission line (like open wire), co-axial cable, waveguide, strip lines and

microstrip lines.

The antenna acts as a sort of impedance (50ohm of transmitter impedance to free

space impedance of 377ohm vice-versa) transformer. It takes the electromagnetic field

pattern, moving along the guide and transforms it into some other pattern, which is

radiated out into free space.

Figure 1.1 Schematic of an antenna system

Using this simple picture one can establish two basic properties of any antenna:

Firstly, the antenna doesn't itself generate any power. So, unless the antenna is

imperfect and dissipates some power, the total powers carried by the guide and

free space fields must be the same. (In reality, all practical antennas tend to be

slightly resistive so some power is normally lost, but for now one can assume any

loss is small enough to ignore.)

Secondly, the antenna is a reciprocal device — i.e. it behaves in the same way

irrespective of which way it pass signal power through it. This reciprocal behavior

is a useful feature of a coherent antenna. It means that, in principle, the only real

difference between a ‘transmitting’ and a ‘receiving’ antenna is the direction one

has chosen to pass signals through it.

1.3 Origin of Antennas

Communication is the process of transferring information from one entity to

another. Communication has existed since the beginning of human beings, but it was not

until the 20th century that people began to study the process. At first this was achieved by

sound through voice. As the distance of communicating increased, various devices were

introduced, such as drums, horns and so forth and for even greater distances visual

methods were introduced such as signal flags and smoke signals in the daytime and

fireworks at night. These optical communication devices, of course, utilize the light

portion of electromagnetic spectrum. It has only been recently in human history that the

electromagnetic spectrum outside the visible region has been employed for

communication, through the use of radio.

Figure 1.2 Electromagnetic spectrum

The antenna is an essential component in any radio system which provides a

means for radiating or receiving radio waves that is it provides a transition from a guided

wave on a transmission line to a free-space wave.

1.4 History of Antenna Technology

The theoretical foundations for antennas rest on Maxwell’s equations. James

Clark Maxwell in 1864 presented his results before Royal Society, which showed that

light and electromagnetics were one in physical phenomenon and also predicted that light

and electromagnetic disturbances both can be explained by waves travelling at the same

speed. And in 1886 Heinrich Hertz verified the above and discovered that the electrical

disturbances could detected with a secondary circuit of proper dimensions for resonance

and containing an air gap for sparks to occur.

Guglielmo Marconi built a microwave parabolic cylinder at a wavelength of 25

cm for his original code transmission and worked at longer wavelengths for improved

communication range. Marconi is considered as the father of amateur radio. Antenna

developments in the early years were limited by the availability signal generators. About

1920 resonant length antennas were possible after the De Forest triode tube was used to

produce continuous wave signals up to 1MHz.

At these higher frequencies antennas could be built with a physical size in

resonant region. Just before World War II microwave (about 1 GHz) klystron and

magnetron signal generators were developed along with hollow pipe waveguides. These

lead to the development of horn antennas, although Jagadish Chandra Bose in India

produced the first electromagnetic horn antenna many years earlier. The first commercial

microwave radiotelephone system in 1934 was between England and France and operated

at 1.8G Hz. During the war an intensive development effort primarily detected toward

radar, spawned many modern antenna types, such as large reflectors, lenses and

waveguide slot arrays.

1.5 Basic Antenna Characteristics

An antenna is a structure that is made to efficiently radiate and receive radiated

electromagnetic waves. There are several important antenna characteristics that should be

considered when choosing an antenna for application such as Gain, radiation pattern,

bandwidth, beam width etc., are as follows:

1.5.1 Radiation pattern

Practically any antenna cannot radiate energy with same strength uniformly in all

directions. The radiation from antenna in any direction is measured in terms of field

strength at a point located at a particular distance from antenna. Radiation pattern of an

antenna indicates the distribution of energy radiated by the antenna in the free space. In

general radiation pattern is a graph which shows the variation of actual field strength of

electromagnetic field of all the points equidistant from antenna. The two basic radiation

patterns are field strength radiation pattern which is expressed in terms of field strength

E (in V/m) and power radiation pattern expressed in terms of power per unit solid angle.

Field radiation pattern is a 3-dimensional pattern. To achieve this it requires

representing the radiation for all angles of Φ and θ which give E-plane (vertical plane)

and H-plane (horizontal plane) pattern respectively.

1.5.2 Gain

Antenna gain relates the intensity of an antenna in a given direction to the

intensity that would be produced by a hypothetical ideal antenna that radiates equally in

all directions (isotropically) and has no losses. Since the radiation intensity from a

lossless isotropic antenna equals the power into the antenna divided by a solid angle of 4π

steridians, we can write the following equation:

Gain = 4π * Radiation Intensity/Antenna Input Power

1.5.3 Directivity

The directive gain of the antenna is the measure of the concentration of radiated

power in a particular direction. It may be regarded as the ability of the antenna to direct

radiated power in a given direction. It is usually a ratio of radiation intensity in a given

direction to the average radiation intensity. Generally D > 1, except in the case of an

isotropic antenna for which D = 1. An antenna with directivity D >> 1 is directive

antenna.

1.5.4 Polarization

Polarization is the orientation of the electromagnetic waves far from the source.

There are several types of polarization that apply to antennas. They are Linear (which

comprises vertical and horizontal), oblique, Elliptical (left hand and right hand

polarizations), circular (left hand and right hand) polarizations.

1.5.5 VSWR

VSWR is the ratio of the maximum to minimum values of the “voltage standing

wave" pattern that is created when signals are reflected on a transmission line. This

measurement can be taken using a "slotted line" apparatus that allows the user to measure

the field strength in a transmission line at different distances along the line.

The voltage standing wave ratio is a measure of how well a load is impedance-

matched to a source. The value of VSWR is always expressed as a ratio with 1 in the

denominator (2:1, 3:1, etc.) It is a scalar measurement only (no angle), so although they

reflect waves oppositely, a short circuit and an open circuit have the same VSWR value

(infinity:1). A perfect impedance match corresponds to a VSWR 1:1, but in practice you

will never achieve it. Impedance matching means you will get maximum power transfer

from source to load.

1.5.6 Reflection Coefficient and Return Loss

Reflection coefficient shows what fraction of an incident signal is reflected when

a source drives a load. A reflection coefficient magnitude of zero is a perfect match, a

value of one is perfect reflection. The symbol for reflection coefficient is uppercase

Greek letter gamma (Γ). Note that the reflection coefficient is a vector, so it includes an

angle. Unlike VSWR, the reflection coefficient can distinguish between short and open

circuits. A short circuit has a value of -1 (1 at an angle of 180 degrees), while an open

circuit is one at an angle of 0 degrees. Quite often we refer to only the magnitude of the

reflection coefficient.

Return Loss shows the level of the reflected signal with respect to the incident

signal in dB. The negative sign is dropped from the return loss value, so a large value for

return loss indicates a small reflected signal. The return loss of a load is merely the

magnitude of the reflection coefficient expressed in decibels. The correct equation for

return loss is:

Return loss = -20 x log [mag (Γ)]

1.5.7 Bandwidth

The bandwidth of an antenna is defined as the range of frequencies within which

the performance of the antenna with respect to some characteristics conforms to a

specific standard.

The reason for this qualitative definition is that all the antenna parameters are

changed with frequency and the importance of the different parameters as gain, return

loss, beam width, side-lobe level etc., much depends on the frequency band.

The bandwidth of an antenna for gain (-3dB from the maximum) is defined as

Bandwidth (%) = (fv-fl)*100 fc

Where fv is the upper frequency, fl is the lower frequency, and fc is the centre

frequency.

1.5.8 Beam width

Antenna beam width is defined as the angle between half power point on the main

beam. In case that we have a logarithm radiation power pattern in [dB] units, it means

that we measure the angle between two 3dB points.

1.6 Types of Antennas

There are two fundamental types of antenna directional patterns, which, with

reference to a specific two dimensional plane (usually horizontal [parallel to the ground]

or [vertical perpendicular to the ground]), are either:

1. Omni-directional (radiates equally in all directions), such as a vertical rod (in the

horizontal plane) or

2. Directional (radiates more in one direction than in the other).

In colloquial usage "omni directional" usually refers to all horizontal directions

with reception above and below the antenna being reduced in favor of better reception

near the horizon. A directional antenna usually refers to one focusing a narrow beam in a

single specific direction such as a telescope or satellite dish, or, at least, focusing in a

sector such as a 120° horizontal fan pattern in the case of a panel antenna at a cell site.

The present antenna in this project i.e., Microstrip antenna is an antenna which

radiates normal to the patch surface into the hemisphere (180° in elevation plane).

1.7 Aim and Objective of the Project:

1. The main aim of the project is to design an aerospace wide beam width

rectangular micro strip antenna for an aerospace vehicle such as a missile,

satellite, aircraft etc., by using available Microstrip substrate (printed circuit board

of type FR4 with dielectric constant of 4.4 and loss tangent of 0.02 and thickness

of 1.6mmof double clad copper), calculated the dimensions of the patch W

(width) and L (length) and also theoretically calculated the antenna bandwidth for

VSWR of ≤2:1 at a frequency of 2250MHz in s-band (2-4 GHz) frequency. And

then we calculated the 3-dB beam width in principle E-plane and H-plane.

2. The Micro strip antenna is carried out for fabrication by using the AutoCAD

software on a PC of size 13.5cm × 13.5cm and h=1.6mm (thickness). The

fabrication process has been done with help of M/s Sravanthi Electronic Industry

by using the standard PCB techniques. After the fabrication, the feed point at 1/3

of half distance is drilled with 1.3mm hole and then connected sub miniature type-

A (SMA) female RF connector of type radial R12540300 with the centre

conductor of diameter 1.28mm. This has been soldered on the Microstrip patch at

a point where 50Ω’s impedance is achieved at 2250MHz. The ground plane is

also soldered with the outer conductor of coaxial connector.

3. Then the centre conductor is checked, to not have short circuit with the ground

plane by an ohm meter and it is found that there was no short circuit. The antenna

has been tested by using an automatic vector network analyzer of type R&S ZVL

at M/s Advanced Communication Division, Charlapally, Hyderabad, a sister

concern of Advanced Radio Mast (ARM). The test has been conducted for the

following:

1. VSWR

2. Return Loss

3. Impedance by smith chart

4. Radiation pattern in E-plan and H-plane

5. Gain

CHAPTER 2

OVERVIEW OF MICROSTRIP ANTENNA

2.1 History of Microstrip Antenna

The concept of microstrip radiators was first proposed by Deschamps as early as

1953. The first practical antennas were developed in the early 1970’s by Howell and

Munson. Since then, extensive research and development of microstrip antennas and

arrays, exploiting the new advantages such as light weight, low volume, low cost, low

cost, compatible with integrated circuits, etc., have led to the diversified applications and

to the establishment of the topic as a separate entity within the broad field of microwave

antennas.

2.2 Definition of Microstrip Antenna

A microstrip antenna in its simplest configuration consists of a radiating patch on

one side of a dielectric substrate (εr ≤ 10), which has a ground plane on the other side.

The patch conductors, normally of copper and gold, can assume virtually any shape, but

conventional shapes are generally used to simplify analysis and performance prediction.

A patch antenna is a narrowband, wide-beam antenna. Feeding in microstrip is achieved

through use of coaxial line with an inner conductor that terminates on the patch. The

placement of the feed is important for proper operation of the antenna.

Figure 2.1 Structure of a Microstrip Patch Antenna

2.3 Advantages and Disadvantages of Microstrip Antenna

Microstrip antennas have several advantages compared to conventional

microwave antennas and therefore many applications over the broad frequency range

from 100MHz to 50GHz. Some of the principle advantages are:

Light weight, low volume, low profile planar configurations which can be made

conformal:

Low fabrication cost ; readily amenable to mass production;

Can be made thin ; hence, they do not perturb the aerodynamics of host aerospace

vehicles;

The antennas can be easily mounted on missiles, rockets and satellites without

major alterations;

These antennas have low scattering cross section;

Linear, circular (left hand or right hand) polarizations are possible with simple

changes in the feed positions;

Dual frequency and dual polarization antennas can be easily made;

No cavity backing required;

Can be easily integrated with microwave integrated circuits;

Microstrip antennas are compatible with modular designs (solid state devices such

as oscillators, amplifiers, variable attenuators, switches, modulators, mixers etc.

can be added directly to the antenna substrate board);

Feed lines and matching networks are fabricated simultaneously with the antenna

structure;

However, Microstrip antennas also have some disadvantages compared to

conventional microwave antennas are:

Narrow bandwidth and associated tolerance problems;

Loss, hence somewhat lower gain(~ 6dB);

Large ohmic loss in the feed structure of arrays;

Complex feed structure required for high performance arrays;

Polarization purity is difficult to achieve;

Extraneous radiation from feeds and junctions;

Low power handling capability

Excitation of surface waves

Reduced gain and efficiency as well as unacceptably high levels of cross-

polarization and mutual coupling within an array element at high frequencies

There are ways to minimize the effect of some of the limitations. For example,

bandwidth can be increased to more than 60%by usage of special techniques;

lower gain and lower power handling limitations can be overcome through an

array configuration;

surface wave associated limitations poor efficiency, increased mutual coupling,

reduced gain and radiation pattern degradation can be overcome by the use of

photonic band gap structures;

2.4 Radiation Mechanism of Microstrip Antenna

The radiation from a Microstrip line, a structure similar to Microstrip antenna,

can be reduced considerably if the substrate employed is thin and has a higher relative

dielectric constant. Radiation from Microstrip antenna, on the other hand, is encouraged

for better radiation efficiency. Therefore, thick substrates with low permittivity are used

in Microstrip antennas. Radiation from Microstrip antenna can be determined from the

field distribution between patch metallization and the ground plane.

Alternatively, radiation pattern can be described in terms of surface current

distribution on the patch metallization. An accurate calculation of the field or current

distribution of the patch is very complicated. However, crude approximations and simple

arguments can be used to develop a workable model for a Microstrip antenna. Consider a

Microstrip antenna that has been connected to a microwave source. The energization of

the patch will establish a charge distribution on upper and lower surfaces of the patch, as

well as on the surface of the ground plane as shown in figure below:

Figure 2.2 Electric field distributions in microstrip cavity

The –ve and +ve nature of the charge distribution arises because the patch is about a half-

wave long at the dominant mode. The repulsive forces between like charges on the

bottom surface, around its edges, to its top surface.

This movement of charge creates corresponding current densities and at the

bottom and top surface of the patch as shown in figure below:

Figure 2.3 Charge distribution and current density on a microstrip antenna

For most microstrip antennas, the ratio h/W is very small. Therefore, the attractive

force between the charges dominates and most of the charge concentration and the

current flow remain underneath the patch. A small amount of current flows around the

edges the edges of the patch to its top surface and are responsible for weak magnetic field

tangential to the edges. Hence, we can make a simple approximation that the magnetic

field is zero and one can place magnetic walls all around the periphery of the patch. This

assumption has the greater validity for thin substrates with high εr. Also, since the

substrate used is very thin compared to the wavelength (h<<λ) in the dielectric, the field

variations along the height can be considered to be constant and electric field nearly

normal to the surface of the patch.

Consequently, the patch can be modeled as a cavity with electric walls (because

the electric field is near normal to the patch surface) at the top and below and four

magnetic walls along the edges of the patch (because the tangential magnetic field is very

weak). Only TM modes are possible in this cavity.

2.5 Various Micro strip Antenna Configurations:

Microstrip antennas are characterized by large number of physical parameters

than are conventional microstrip antennas. They can be designed to have many

geometrical shapes and dimensions. All Microstrip antennas can be divided into four

basic categories:

1. Microstrip patch antennas

2. Microstrip dipoles

3. Printed slot antennas

4. Microstrip travelling-wave antennas.

2.5.1 Microstrip patch antenna

A Microstrip patch antenna (MPA) consists of a conducting patch of any planar

geometry on one side of dielectric substrate backed by a ground plane on the other side.

There are virtually an unlimited number of patch patterns for which radiation

characteristics may be calculated. The basic configurations used in practice are:

Figure 2.4 Microstrip patch antenna shapes commonly used in practice

Figure 2.5 Other possible geometries of Microstrip patches

2.5.2 Microstrip or Printed Dipole Antennas

Microstrip or printed dipole differs geometrically from rectangular patch antennas

in their length-to-width ratio. The width of a dipole is typically less than 0.05λo. The

radiation patterns of the dipole and patch are similar owing to similar longitudinal current

distributions. However, the radiation resistance, bandwidth, and cross-polar radiation

differ widely. These are well suited for higher frequencies for which the substrate can be

electrically thick and therefore can attain significant bandwidth.

CHAPTER 3

RECTANGULAR PATCH ANTENNA

3.1 Introduction

Microstrip antennas are among the most widely used types of antennas in the

microwave frequency range, and they are often used in the millimeter-wave frequency

range as well (Below approximately 1 GHz, the size of a microstrip antenna is usually too

large to be practical, and other types of antennas such as wire antennas dominate) also

called patch antennas. Microstrip patch antennas consist of a metallic patch of metal that

is on top of a grounded dielectric substrate of thickness h, with relative permittivity and

permeability εr and μr as shown in Figure 3.1 (usually μr = 1). The metallic patch may be

of various shapes, with rectangular and circular being the most common, as shown in

Figure 3.1& 3.2.

Figure 3.1 Rectangular Patch Antennas

Figure 3.2 Circular Patch Antennas

Most of the discussion in this section will be limited to the rectangular patch,

although the basic principles are the same for the circular patch. (Many of the CAD

formulas presented will apply approximately for the circular patch if the circular patch is

modeled as a square patch of the same area). Various methods may be used to feed the

patch, as discussed below. One advantage of the microstrip antenna is that it is usually

low profile, in the sense that the substrate is fairly thin.

If the substrate is thin enough, the antenna actually becomes “conformal,”

meaning that the substrate can be bent to conform to a curved surface (e.g., a cylindrical

structure). A typical substrate thickness is about 0.02 λ0. The metallic patch is usually

fabricated by a photolithographic etching process or a mechanical milling process,

making the construction relatively easy and inexpensive (the cost is mainly that of the

substrate material).

Other advantages include the fact that the microstrip antenna is usually

lightweight (for thin substrates) and durable. Disadvantages of the microstrip antenna

include the fact that it is usually narrowband, with bandwidths of a few percent being

typical. Some methods for enhancing bandwidth are discussed later. Also, the radiation

efficiency of the patch antenna tends to be lower than some other types of antennas, with

efficiencies between 70% and 90% being typical.

3.2 Basic Principles of Operation

The metallic patch essentially creates a resonant cavity, where the patch is the top

of the cavity, the ground plane is the bottom of the cavity, and the edges of the patch

form the sides of the cavity. The edges of the patch act approximately as an open-circuit

boundary condition. Hence, the patch acts approximately as a cavity with perfect electric

conductor on the top and bottom surfaces, and a perfect “magnetic conductor” on the

sides. This point of view is very useful in analyzing the patch antenna, as well as in

understanding its behavior. Inside the patch cavity the electric field is essentially z

directed and independent of the z coordinate. Hence, the patch cavity modes are

described by a double index (m, n). For the (m, n) cavity mode of the rectangular patch

the electric field has the form

…………………..(3.1)

Where L is the patch length and W is the patch width. The patch is usually

operated in the(1,0) mode, so that L is the resonant dimension, and the field is essentially

constant in the y direction.

3.3 Resonant Frequency

The resonance frequency for the (1, 0) mode is given by

…………………………..……………….(3.2)

Where c is the speed of light in vacuum. To account for the fringing of the cavity

fields at the edges of the patch, the length, the effective length Le is chosen as

Le= L + 2ΔL

The Hammerstad formula for the fringing extension is [1]

………………………..(3.3)

Where,

………………………(3.4

3.4 Radiation Patterns

The radiation field of the microstrip antenna may be determined using either an

“electric current model” or a “magnetic current model”. In the electric current model, the

current is used directly to find the far-field radiation pattern. The electric current for the

(1, 0) patch mode. If the substrate is neglected (replaced by air) for the calculation of the

radiation pattern, the pattern may be found directly from image theory. If the substrate is

accounted for, and is assumed infinite, the reciprocity method may be used to determine

the far-field pattern.

(a)Electric Current for (1, 0) patch

(b) Magnetic Current for (1, 0) patch

Figure 3.3 Electric & Magnetic Current Distributions

In the magnetic current model, the equivalence principle is used to replace the

patch by a magnetic surface current that flows on the perimeter of the patch. The

magnetic surface current is given by:

……………………………..(3.5)

Where E is the electric field of the cavity mode at the edge of the patch and n is

the outward pointing unit-normal vector at the patch boundary. The far-field pattern may

once again be determined by image theory or reciprocity, depending on whether the

substrate is neglected or not [4]. The dominant part of the radiation field comes from the

“radiating edges” at x = 0 and x = L. The two non-radiating edges do not affect the pattern

in the principle planes (the E plane at φ = 0 and the H plane at φ = π/2), and have a small

effect for other planes.

It can be shown that the electric and magnetic current models yield exactly the

same result for the far-field pattern, provided the pattern of each current is calculated in

the presence of the substrate at the resonant frequency of the patch cavity mode [5]. If the

substrate is neglected, the agreement is only approximate, with the largest difference

being near the horizon.

The patch is resonant with W/ L = 1.5. Note that the E-plane pattern is broader

than the H-plane pattern.

Figure 3.4 Simulated Radiation Pattern (E & H plane) polar plot

3.5 Radiation Efficiency

The radiation efficiency of the patch antenna is affected not only by conductor

and dielectric losses, but also by surface-wave excitation - since the dominant TM mode

of the grounded substrate will be excited by the patch. As the substrate thickness

decreases, the effect of the conductor and dielectric losses becomes more severe, limiting

the efficiency. On the other hand, as the substrate thickness increases, the surface-wave

power increases, thus limiting the efficiency. Surface-wave excitation is undesirable for

other reasons as well, since surface waves contribute to mutual coupling between

elements in an array, and also cause undesirable edge diffraction at the edges of the

ground plane or substrate, which often contributes to distortions in the pattern and to back

radiation.

For an air (or foam) substrate there is no surface-wave excitation. In this case,

higher efficiency is obtained by making the substrate thicker, to minimize conductor and

dielectric losses (making the substrate too thick may lead to difficulty in matching,

however, as discussed above). For a substrate with a moderate relative permittivity such

as εr = 2.2, the efficiency will be maximum when the substrate thickness is approximately

λ0 = 0.02. The radiation efficiency is defined as

Where Psp is the power radiated into space, and the total input power Ptotal is given

as the sum of Pc - the power dissipated by conductor loss, Pd- the power dissipated by

dielectric loss, and Psw - the surface-wave power. The efficiency may also be expressed in

terms of the corresponding Q factors as

A plot of radiation efficiency for a resonant rectangular patch antenna with W / L

= 1.5 on a substrate of relative permittivity εr = 2.2 or εr = 10.8 is shown in Figure 3.4.

The result is plotted efficiency versus normalized (electrical) thickness of the substrate,

which does not involve frequency.

The conductivity of the copper patch and ground plane is assumed to be ζ =

3.0×107 [S/m] and the dielectric loss tangent is taken as tanδd = 0.001. The resonance

frequency is 5 GHz. However, a specified frequency is necessary to determine conductor

loss. For h / λ0 < 0.02, the conductor and dielectric losses dominate, while for h /λ0 >

0.02, the surface-wave losses dominate. (If there were no conductor or dielectric losses,

the efficiency would approach 100% as the substrate thickness approaches zero.

Figure 3.5 Radiation Efficiency for a rectangular patch Antenna

3.6 Bandwidth

The bandwidth increases as the substrate thickness increases (the bandwidth is

directly proportional to h if conductor, dielectric, and surface-wave losses are ignored).

However, increasing the substrate thickness lowers the Q of the cavity, which increases

spurious radiation from the feed, as well as from higher-order modes in the patch cavity.

Also, the patch typically becomes difficult to match as the substrate thickness increases

beyond a certain point (typically about 0.05 λ0). This is especially true when feeding with

a coaxial probe, since a thicker substrate results in a larger probe inductance appearing in

series with the patch impedance. However, in recent years considerable effort has been

spent to improve the bandwidth of the microstrip antenna, in part by using alternative

feeding schemes. The aperture-coupled feed of is one scheme that overcomes the

problem of probe inductance, at the cost of increased complexity.

Lowering the substrate permittivity also increases the bandwidth of the patch

antenna. However, this has the disadvantage of making the patch larger. Also, because of

the patch cavity is lowered, there will usually be increased radiation from higher-order

modes, degrading the polarization purity of the radiation.

By using a combination of aperture-coupled feeding and a low-permittivity foam

substrate, bandwidths exceeding 25% have been obtained. The use of stacked patches (a

parasitic patch located above the primary driven patch) can also be used to increase

bandwidth even further, by increasing the effective height of the structure and by creating

a double-tuned resonance effect.

Figure 3.6 Calculated & Measured Bandwidth

Figure 3.6 shows calculated and measured bandwidth for the same patch. It is

seen that bandwidth is improved by using a lower substrate permittivity, and by making

the substrate thicker.

3.7 Input Impedance

A variety of approximate models have been proposed for the calculation of input

impedance for a probe-fed patch. These include the transmission line method, the cavity

model, and the spectral-domain method. These models usually work well for thin

substrates, typically giving reliable results for h / λ0 < 0.02.

The cavity model has the advantage of allowing for a simple physical CAD model

of the patch to be developed, as shown in Figure 3.7

In this model the patch cavity is modeled as a parallel RLC circuit, while the

probe inductance is modeled as a series inductor. The input impedance of this circuit is

approximately described by

Figure 3.7 Equivalent Circuit of Patch Antenna

3.8 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. 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).

3.8.1 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 Figure 3.8. 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.

Figure 3.8 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.

3.8.2 Coaxial Feed

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

Microstrip patch antennas. As seen from Figure 3.8, 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 any desired location inside the patch in

order to match with its input impedance.

Figure 3.9 Probe fed Rectangular Microstrip Patch Antenna

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 > 0.02λo). 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.

3.8.3 Aperture Coupled Feed

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

separated by the ground plane as shown in Figure 3.9. 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 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

Figure 3.10 Aperture-coupled feed

. 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.

3.8.4 Proximity Coupled Feed

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

As shown in Figure 3.11, 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.

Figure 3.11 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 3.1 Characteristics of the different feed techniques.

3.9 Methods of Analysis

The preferred 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 shaped elements and coupling. These give less insight as

compared to the two models mentioned above and are far more complex in nature.

3.9.1 Analytical Models

There are many methods of analysis and are divided into two types-

1. Model – Based Analysis Technique

2. Full – Wave Analysis Technique

The various model – based and full – wave analysis techniques that have been used for the analysis of the Microstrip Antenna are:

Wire Grid Model Cavity Model

Modal Dispersion Model

Transmission Line Model

Integral Equation Method

Vector Potential Approach

Dyadic Green’s Function Technique

Radiating Aperture Method

In Wire Grid Model the antenna is modeled as a fine grid of wire segments. The

currents on the wire segments are solved using the Richmond’s reaction theorem to get

all the antenna characteristics of interest.

The Cavity Model offers both simplicity and physical insight. In this model the

antenna is treated as a cavity whose fields are computed using the full model expansions.

The importance of this model is that it includes the effects of non resonant modes.

The Modal Expansion Method is similar to cavity model but differs in

impedance boundary conditions that are imposed at the four radiating walls to obtain a

solution. Though the method does not lead to an exact solution, it provides a good insight

into the physics of antenna.

The Transmission Line Model considers the antenna as two radiating slots

perpendicular to the feed line of length L. This model is easy to analyze due to its

simplicity but suffers from some disadvantages. This model is limited to square and

rectangular geometries.

The Integral equation method is general method and can treat patches of

arbitrary shapes including those with thick substrate. The method requires considerable

analytical and computational efforts and provides little physical insight.

In Vector Potential Approach, the field produced by a horizontal electric dipole

is determined and the antenna characteristics are then evaluated by numerical techniques.

Though the solution obtained is rigorous, it is less attractive due to lack of closed form

expressions.

In Dyadic Green’s Function Method the characteristics of the micro strip

antenna are evaluated and the field from an arbitrary source distribution may be found by

means of a super position integral.

In Radiating aperture method the Vector Kirchoff relation is used. This method

is mathematically precise if the aperture fields are known exactly.

Transmission model is adapted in this work for the analysis of the rectangular

microstrip antennas and is explained in detail below.

3.9.2 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 non-

homogeneous line of two dielectrics, typically the substrate and air. Hence, as seen from

Figure 3.12, most of the electric field lines reside in the substrate and parts of some lines

in air.

Figure 3.12 Microstrip Line Figure 3.13 Electric Field

Lines

As a result, this transmission line cannot support pure transverse-electromagnetic

(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 (εreff) must be obtained in order to account for the

fringing and the wave propagation in the line. The value of εreff is slightly less then εr

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 3.13 above. The

expression for εreff is given by Balanis:

Where εreff = Effective dielectric constant

εr = Dielectric constant of substrate

h = Height of dielectric substrate

W = Width of the patch

Consider Figure 3.14below, 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 3.14 Microstrip Patch Antenna proximity feed

In order to operate in the fundamental TM10 mode, the length of the patch must be

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

λo/√εreff where λo is the free space wavelength. The TM10 mode implies that the field

varies one λ/2 cycle along the length, and there is no variation along the width of the

patch. In the Figure 3.14 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 3.15 Top View of Antenna Figure 3.16 Side View of

Antenna

It is seen from Figure 3.15 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 λ/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 λ/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 ΔL, which is given empirically

by Hammerstad:

The effective length of the patch is given by:

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

For a rectangular Microstrip antenna, the resonant frequency for any TMmn is given by

James and Hall:

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

For efficient radiation, the width is given by:

CHAPTER 4

IMPLEMENTATION & FABRICATION

This chapter deals with the procedure for practically designing a rectangular

microstrip antenna. The overall goal of a design is to achieve specific performance

characteristics at a stipulated operating frequency. The design of a rectangular microstrip

antenna involves the following process:

1. Selection of substrate and

2. Calculating length, width and feed point of the patch

3. Selection of connector

4.1 Selection of Substrate

The selection of a substrate material is a balance between the required electrical,

mechanical and environmental performance required by a design versus economic

constraints. Generally, if one has the available design volume to use air as a substrate for

a Microstrip antenna, this is a good choice. The antenna efficiency is high, the gain is

maximized as is the impedance bandwidth of a conventional Microstrip antenna. The

surface wave loss when air is used as a substrate is minimal.

When a dielectric substrate is selected, one is interested in a material with the

lowest tangent (tan δ) available. The loss tangent is a metric of the quantity of electrical

energy which is converted to heat by a dielectric. The lowest possible loss tangent

maximizes the antenna efficiency (decreases the losses).

The relative dielectric constant εr of the substrate determines the physical size of a

patch antenna. The larger the dielectric constant the smaller the element size, but also the

smaller the impedance, bandwidth and directivity and the surface wave loss increases.

The use of the substrates with higher dielectric constants also tightens fabrication

tolerances. The tolerance of the dielectric value is also of significant importance in

manufacturing yield.

A Monte-Carlo type analysis using the cavity model is a good method of

estimating antenna manufacturing yield for a rectangular Microstrip antenna when an

etching tolerance, substrate thickness tolerance, feed point location tolerance and

dielectric tolerances are known.

Substrate electrical and physical parameters also vary with temperature. Recent

work by Kabacik and Bialkowski indicates that Teflon/Fiberglass substrates can have a

significant variation of dielectric constant for many airborne and space borne

applications. The dielectric constant and loss tangent of Teflon fiberglass often differed

from what was quoted by manufacturers in their datasheets compared with measurements

and were valid over a much narrower temperature range that encountered in many

aerospace applications. The performance variations are due to changes in the material

dielectric properties–thermal expansion had a minor effect on Microstrip antenna

performance.

Generally the metal cladding to the dielectric substrate material is copper. Two

types of copper foil are used as cladding, rolled foil and electrodeposited foil. Rolled foil

is passed through a rolling mill a number of times until the desired physical dimensions

are obtained and bonded the substrate. Rolled copper has a polished mirror-like

appearance. Electrodeposited foil is created by electrodeposition of copper onto an inert

form. A thin layer of copper is continuously removed from the form then bonded to the

substrate.

The computation of characteristic impedance and losses of a Microstrip

transmission line depend on the copper foil thickness. The copper cladding is described in

terms of weight per square yard.

The thickness of the cladding may then be derived and is listed in the table below:

Foil weight Foil thickness

½ oz (14gms) 0.0007 in (0.01778mm)

1 oz (28gms) 0.0014 in (0.03556mm)

2 oz (57gms) 0.0028 in (0.07112mm)

4 oz (142gms) 0.0056 in (0.14224mm)

Table 4.1 Thickness of cladding for different materials

Material Εr Tan δ

Teflon (PTFE) 2.1 0.0005

Rexolite 1422 2.55 0.0007

Noryl 2.6 0.0011

FR4 4.4 0.02

Alumina 9.8 0.0003

Table 4.2 Dielectric and Loss tangent for different materials

Generally, dielectric constant εr and loss tangent tanδ increase with temperature.

In space applications moisture outgassing produces a lower dielectric constant and loss

tangent.

Teflon (Polytetrafluoroethylene) has very desirable electrical qualities but is not

recommended for many space applications. An extensive discussion of PTFE substrates

and their fabrication may be found in the literature.

Rexolite is a very good material for space applications and has many desirable

mechanical properties. Rexolite is easily machined and its dielectric constant remains

stable up to 100 GHz.

Noryl is suitable for many commercial microwave applications. It has a much

lower loss than FR4 and is relatively cost effective, but it is soft and melts at a relatively

low temperature which can create soldering complications, and sometimes has unsuitable

mechanical properties for some applications.

FR4 is inexpensive and find use in many commercial applications below 1 GHz.

The material can be used for some wireless applications, but great care must be taken to

budget and minimize the losses when it is used as a substrate of PTFE and Epoxy glass

(FR4) which has the desirable properties of FR4 with lower loss.

Alumina has desirable microwave properties for applications which require a

relatively high dielectric constant εr ~ 10.0 and low loss tangent. Its drawbacks are the

difficulty involved in machining it and its brittleness. Alumina has good thermal

conductivity and in some aerospace applications it more readily dissipates heat and

remains cooler than other common microwave substrates. In some missile applications

where high temperatures may compromise solder joints alumina is a viable option for the

dissipation of heat. Alumina’s dielectric constant is very sensitive to the processing used

to produce the alumina.

All substrates and laminates have different requirements for the processing.

Details of fabrication issues and methods may be found in the literature and directly from

manufacturers. Other fabrication options such as screen printing conductive inks directly

on substrates have also been investigated.

4.2 Design procedure for Rectangular Microstrip Antenna

4.2.1 Considered Values

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

Antenna:

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

selected appropriately. Since we developing antenna for microwave applications

we choose design an antenna in s-band which ranges from 2 GHz to 4 GHz. We

designed microstrip antenna at 2.25 GHz..

Dielectric constant of the substrate (εr): There are many dielectric substrates

available in the market having different dielectric constant and thickness. Of them

RT Duroidd provides the best results but is highly costly and hence the dielectric

material selected for our design is FR4 (Fiber-reinforced plastic) which has a

dielectric constant of 4.4. This substrate is selected since it can obtain better

results and is cost effective.

Height of dielectric substrate (h): The height of the selected dielectric material

is 1.6mm which is optimal for having maximum radiation and has less leaky

waves. This provides a balance between conductor and dielectric loss and hence

we choose FR4 material dielectric substrate with 1.6mm thickness.

4.2.2 Initial Design Values

There are many analysis methods for the design of antenna which are discussed

later. From them we use transmission line analysis method for our antenna.

Step 1: Calculation of the Width (W)

The width of the Microstrip patch antenna is given as:

…………………………… (4.1)

Where,c is velocity of light

fo is Resonant Frequency

εr is Relative Dielectric Constant

Figure 4.1 Variation of Width with Frequency

Of course other widths may be chosen but for widths smaller than those selected

according to equation (4.1), radiator efficiency is lower while for larger widths, the

efficiency are greater but for higher modes may result, causing field distortion. As a

result design aid, equation (4.1) is plotted for the common dielectric substrates. If other

materials are employed equation (4.1) should be used with appropriate value of ε r. In this

work upon Substituting c=3.0×10^(11)mm/s, εr = 4.4 and fo = 2.25 GHz, we get:

W = 38.5 mm

Step 2: Calculating the Length (L)

Effective dielectric constant (εeff)

Once W is known, the next step is the calculation of the length which involves

several other computations; the first would be the effective dielectric constant. The

dielectric constant of the substrate is much greater than the unity, the effective value of

εeff will be closer to the value of the actual dielectric constant ε r of the substrate. The

effective dielectric constant is also a function of frequency.

As the frequency of operation increases the effective dielectric constant

approaches the value of the dielectric constant of the substrate is given by:

…………………..

(4.2)

In our design for the above mentioned values the effective dielectric is found to be

εeff = 4.100

Effective length ( Leff)

The effective length is:

……………………….. (4.3)

Which is found to be Leff = 32.92mm

Length Extension (∆L)

Because of fringing effects, electrically the micro strip antenna looks larger than

its actual physical dimensions. For the principle E – plane (x-y plane), where the

dimensions of the path along its length have been extended on each by a distance, ∆L,

which is a function of the effective dielectric constant and the width-to-height ratio

(W/h).The length extension is:

..….……………………… (4.4)

Substituting εeff = 4.4, W = 40.57 mm and h = 1.6 mm we get:

∆L = 0.739 mm

Calculation of actual length of patch (L)

Because of inherent narrow bandwidth of the resonant element, the length is a

critical parameter and the above equations are used to obtain an accurate value for the

patch length L.

Figure 4.2 Variation of Length with the Frequency

Fig 4.2 which is a plot of L versus frequency for the various substrates and for

chosen substrate may then be used to verify the design.

The actual length is obtained by:

………………………….. (4.5)

Substituting Leff = 32.92 mm and ∆L = 0.7391 mm we get:

L = 31.44mm

Step 3: Calculation of the Gain (G)

The gain of the micro strip antenna is given by the following formula

G = 4 πA

λg2 ………………..……………………. (4.6)

where A = L*W = 31.44*40.57 =1275.6556

λg=λ0

√ε r ………..……………………..…. (4.7)

= 133.33

√4.4 = 63.56 mm

By substituting the above values we get

G = 4 dB

Figure 4.3 Variation of Gain with the Frequency

Step 4: Calculation of the Beam Width (θ)

The beam width of a micro strip element can be increased by choosing a smaller

element, thus reducing W and L. For a given resonant frequency, these dimensions may

be changed by selecting a substrate having a higher relative permittivity. In many

applications, a decrease in physical size is desirable.

Beam Width in H-Plane

θBH=2 cos−1( 1

21+W K 0

2 )1 /2

……………………....... (4.8)

θBH-Beam Width in H- Plane

Substituting W = 40.57 mm and Ko=0.047 we get:

θBH = 89.29 degrees

Beam Width in E-Plane

θBE = 2cos−1( 7.033K 0

2W 2+K 02h2 )

1/2

……………………… (4.9)

θBE-Beam Width in E- Plane

Substituting W = 40.57 mm, h=1.6mm and Ko=0.047 we get:

θBE = 77.25 degrees

As beam width increases, element gain and consequently directivity decrease,

however the antenna efficiency remains unaffected.

Step 5: Calculation of the Band Width Percentage (BW %)

The bandwidth of the microstrip antenna gives the range of frequencies for which

the microstrip antenna works that is either transmits or receive and it s given by the

following equation:

BW = 100(S−1)

√S8

3 εr

hλ0

………………………………… (4.10)

Substituting λ0=133.33 mm, h=1.6mm and S=2:1, εr = 4.4 we get:

BW = 0.514%

Figure 4.4 Variation of Bandwidth with Frequency for different dielectric substrate

antennas

4.3 Microwave Co-axial Connector

For high frequency operation the average circumference of a coaxial cable must

be limited to about one wavelength, in order to reduce multimodal propagation and

eliminate erotic reflection coefficients, power losses and signal distortion. The

standardization of coaxial connectors during World War II was mandatory for microwave

operation to maintain a low reflection coefficient or a low voltage standing wave ratio

(VSWR). Since that time many modifications and new designs for microwave connectors

have been proposed and developed. Seven types of microwave coaxial connectors are

described below.

APC-3.5: The APC-3.5 (Amphenol Precision Connector-3.5mm) was originally

developed by Hewlett-Packard, but is now manufactured by Amphenol. The connector

provides the repeatable connections and has very low voltage standing-wave ratio

(VSWR). Either the male or female end of this 50Ω connector can mate with the opposite

type of SMA type connector. The APC-3.5 connector can work at frequencies up to 34

GHz.

APC-7: The APC-7 (Amphenol Precision Connector-7mm) was also developed by

Hewlett-Packard in the mid 1960s, but it was recently improved and is now manufactured

by Amphenol. The connector provides a coupling mechanism without male or female

distinction and is the most repeatable connecting device used for very accurate 50Ω

measurement applications. Its VSWR is extremely low, in the range of 1.02 to 18 GHz.

Figure 4.5 APC-7 Connector

BNC: The BNC (Bayonet Navy Connector) was originally designed for military system

applications during World War II. The connector operates very well at frequencies up to

about 4GHz, beyond that it tends to radiate electromagnetic energy. The BNC can accept

flexible cables with diameters of up to 6.35mm (0.25inches) and characteristic impedance

of 50 to 75Ω. It is now the most commonly used connector for frequencies under 1 GHz.

Figure 4.6 BNC Connector

SMA: The SMA (Sub-Miniature A) was originally by Bendix Scintilla Corporation, but

it has been manufactured by Omni-Spectra Inc. (as the OSM connector) and many other

electronic companies. The main application of SMA connector is on component for

microwave systems.

Figure 4.7 SMA Connector

SMC: The SMC (Sub Miniature C) is a 50Ω connector that is smaller than the SMA. The

connector is manufactured by Sealectro Corporation and can accept flexible cables with

diameters of up to 3.17mm (0.125 inches) for a frequency range of up to 7 GHz.

Figure 4.8 SMC Connector

TNC: The TNC (Threaded Navy Connector) is merely a thread BNC. The function of

thread is to stop radiation at higher frequencies, so that the connector can work at

frequencies up to 12GHz.

Figure 4.9 TNC Connector

Type N: The Type N (Navy) connector was originally designed or military systems

during World War II and is the most popular measurement connector for the frequency

range of 1 to 18GHz. It is 50 or 75Ω connector and its VSWR is extremely low, less than

1.02.

Figure 4.10 Type N Connector

Size Series Coupling Impedance ()

Frequency (GHz)

VSWR (max)

Voltage (V)

Subminiature

Miniature

Medium

Large

SMA

SMB

SMC

BNC

TNC

SHV

BN

MC

C

N

NC

QM

QL

Screw

Snap on

Screw

Bayonet

Screw

Bayonet

Screw

Screw

Bayonet

Screw

Screw

Screw

Screw

50

50

50

50

50

NC

50

50

50

50

50

50

50

12.4/18

4

10

4

11

NA

0.2

0.5

11

11

11

4

5

1.3

1.41

1.6

1.3

1.3

1.3

1.3

1.3

1.35

1.3

1.3

1.3

1.3

500

500

500

500

500

5000

200

200

1500

1000

1000

5000

5000

Table 4.3 Basic Features Of the most Common Connector Series

4.4 FABRICATION PROCEDURE

The first step in the fabrication process is to generate the art work from drawings.

Accuracy is vital at this stage and depending on the complexity and dimensions of the

antenna; either full or enlarged scale artwork should be prepared on Stabiline or Rubilith

film. Using the precision cutting blade of a manually operated coordinagraph, the opaque

layer of the Stabiline or Rubylith film is cut to the proper geometry and can be removed

to produce either a positive or negative representation of the Microstrip antenna. The

design dimensions and tolerances are verified on a Cordax measuring instruments using

optical scanning.

Enlarged artwork should be photo reduced using high precision camera to

produce a high resolution negative, which is later used for exposing the photo resist. The

laminate should be cleaned using the substrate manufacturer recommended procedure to

insure proper adhesion of the photo resist and the necessary resolution in the photo

development process. The photo resist is now applied to both sides of the laminate using

laminator. Afterwards, the laminate is allowed to stand to normalize to room temperature

prior to exposure and development.

The photographic negative must be now held in very close contact with the

polyethylene cover sheet of the applied photo resist using a vacuum frame copy board or

other technique, to assure the fine line resolution required. With exposure to the proper

wavelength light, a polymerization of the exposed photo resist occurs, making it insoluble

in the developer solution. The backside of the antenna is exposed completely without a

mask, since the copper foil is retained to act as a ground plane.

The protective polythene cover sheet of the photo resist is removed and the

antenna is now developed in a developer which removes the soluble photo resist material.

Visual inspection is used to assure proper development. When these steps have been

completed, the antenna is now ready for etching. This is a critical step and requires

considerable care so the proper etch rates are achieved.

After etching, the excess photo resist is removed using a stripping solution. Visual

and optical inspections should be carried out to insure a good product and to insure

conformance with dimensional tolerances, with final acceptance or rejection being based

on resonant frequency, radiation pattern and impedance measurement. For acceptable

units the edges are smoothened and the antenna is rinsed in water and dried.

If desired, a thermal cover bonding may be applied by placing a bonding film

between the laminates to be bonded and placing these between tooling plates. Dowel pins

can be used for alignment and the assembly is then heated under pressure until the bond

line temperature is reached. The assembly is allowed to cool under pressure below the

melting point of the

4.5 STEP BY STEP DESIGN PROCEDURE

DESIGN

MASTER DRAWING

ART WORK LAY OUT

PHOTO REDUCTION

NEGATIVE DEVELOPMENT

LAMINATE CLEANING

RESIST APPLICATION

RESIST EXPOSURE

RESIST DEVELOPMENT

ETCHING

BONDING

FINISHING

INSPECTION

DESIGN

MASTER DRAWING

Figure 4.11Flow chart showing the fabrication process

bonding film and the laminate is then removed for inspection. The above procedure

comprises the general steps necessary in producing a Microstrip antenna. The substances

used for the various processes example cleaning, etching, etc., are the tools used for

machining, etc., depending on the substrate chosen. Most manufacturers provide

informative brochures on the appropriate choice of chemicals, cleaners, etchants, etc., for

their substrates.

INSPECTION

Drilling hole of diameter 1.3mm by using precision drilling machine

SOLDERING

Checking with ohm meter for the patch & centre conductor continuity

Visual inspection of solder point which should be blister

Figure 4.12 Photographic Negative of ground plane Used for Fabrication

Figure 4.13 Photographic Negative of patch Used for Fabrication

CHAPTER 5

MEASUREMENTS, TESTING & RESULT ANALYSIS

5.1 MESUREMENTS

Testing of antenna involves measurement of electrical and electromagnetic

parameters. Electrical parameters involve measurement of Return loss or VSWR,

Impedance and electromagnetic parameters involves the measurement of radiation

pattern in E-plane and H-plane and gain . These measurements have been carried out

for the designed microstrip antenna.

Network Analyzer has been used to measure the return loss, VSWR and

impedance shown in figures 5.3,5.4 & 5.5. Radiation patterns and gain of the antenna at

the designed frequency are done in an anechoic chamber at ACD, Hyderabad .

5.2 TESTING

Here is a description of some of the components used to test various antenna

parameters Return Loss, VSWR, impedance measurements using Smith Chart has been

obtained using the Vector Network Analyzer. Radiation Patterns can be obtained using

the experimental set up containing Anechoic Chamber.

5.2.1 Network Analyzer

The testing of antenna is done using R&S ZVL which is a Two Port Vector

Network Analyzer. R&S ZVL vector network analyzer provides the best combination of

speed and accuracy for measuring multi-port and balanced components such as filters,

duplexers and RF modules up to 6GHz. A vector analyzer provides simple and complete

vector network measurements in a compact, fully integrated RF network. R&S ZVL

vector network analyzer offers built-in source, receiver and s-parameter test set covering

frequencies from 10 MHz to 6 GHz.

The R&S ZVL automatic port extension feature automatically measures and

corrects for fixtures, making measurements of in-fixture devices simple and accurate. The

configurable test set provides access to the signal path between the internal source and

the analyzer's test ports. This option provides the capability to improve instrument

sensitivity for measuring low-level signals, to reverse the directional coupler to achieve

even more dynamic range or to add components or other peripheral instruments for a

variety of applications such as high-power measurements. The extended power range

adds a 60 dB step attenuator internally to the RF source path. This attenuator extends the

source output power range to over 80 dB, allowing for maximum flexibility when

stimulating the device under test.

5.2.2 Elements of Network Analyzer

Figure 5.1 Major elements of Network Analyzer

A Network analyzer measurement system consists of four major parts: a signal

source providing the incident signal, signal separation devices to separate the incident,

reflected and transmitted signals, a receiver to convert the microwave signals to a lower

intermediate frequency (IF) signal, and a signal processor and display section to process

the IF signals and display detected information. The receiver performs the full S-

parameters.

Signal Source: The signal source (RF or microwave) produces the incident signal used to

stimulate device under test (DUT). The DUT responds by reflecting part of the incident

energy and transmitting the remaining part. By sweeping the frequency of the source the

frequency response of the device can be determined. Frequency range, frequency

stability, signal purity and output power level and level control are factors which may

affect the accuracy of a measurement. The source used for network analyzer

measurements is a synthesizer, which is characterized by stable amplitude frequency and

high frequency resolution (less than 100 Hz at microwave range).

Signal Separation: The next step in the measurement process is to separate the incident,

reflected and transmitted signals. Once separated, their individual magnitude and/or

phase differences can be measured. This can be accomplished through the use of

wideband directional couplers, bridges, power splitters.

A directional coupler is a device that consists of two transmission lines that are

configured to couple energy to an auxiliary port if it goes through the main port in one

direction and not in the opposite direction. Directional couplers usually have relatively

low loss in the mainline path and present little loss to the incident power. In a directional

couple structure the coupled arm samples a signal travelling in one direction only. The

coupled signal is at a reduced level and the relative amount of reduced level is called the

coupling factor. For instance a 20 dB directional coupler means that the coupled port

power level is 20 dB below the input, which is equivalent to 1 percent of the incident

power. The remaining 99 percent travels through the main arm. The other key

characteristic of a directional coupler is directivity. Directivity is defined as the

difference between a signal detected in the forward direction and the signal detected in

the reverse direction (isolation between the forward and reverse signals).

The two resistor power splitter is used to sample either the incident or transmitted

signal. The input signal is split equally between the two arms, with the output signal

(power) from each arm being 6 dB below the input. A primary application of the power

splitter is for producing a measurement with a very good source match. If one side of the

splitter output is taken to a reference detector and the other side goes through the device

under test to a transmission detector, a ratio display of transmitted to incident has the

effect of making the resistor in the power splitter determine the equivalent source match

of the measurement. Power splitters are very broadband, have excellent frequency

response and present a good match at the test device input requires a directional device.

Separation of the incident and reflected signals can be accomplished using either a dual

directional coupler or Splitter.

Figure 5.2 Vector Network Analyzer used for testing of our antenna

Receiver: The receiver provides the means for converting and detecting the RF or

Microwave signals to a lower IF or DC signal. There are basically two receiver

techniques used in network analysis. The receivers are broadband tuned receivers that use

either a fundamental mixing or harmonic mixing input structure to convert RF signal to a

lower frequency IF signal. The tuned receivers provide a Narrowband pass IF filter to

reject spurious signals and minimized the noise floor of the receiver. The vector

measurement systems (tuned receivers) have the highest dynamic ranges are less suspect

from harmonic and spurious responses, they can measure phase relationships of input

signals and provide the ability to make complex calibrations that lead to more accurate

measurements.

Table 5.1 specifications of network analyzer

5.2.3 Reflection Measurement

The return loss is the measure of power reflected and is related to the reflection

coefficient ‘Γ’ given by

Return Loss in dB = -20 log Γ

The relation between reflection coefficient and VSWR is given by

VSWR (S) = 1+Γ 1-Γ

Network Analyzer Calibration:

An Agilent R&S ZVL vector network analyzer is employed in the present

measurements. Before measuring the return loss of the antenna, the network analyzer

should be calibrated as explained below:

1. The terminal at the test port at which the test antenna is to be mounted is short

circuited. Now the power fed to the test port travels back through the short

circuits so that there will be no radiation at all. The reflected power will be equal

to the incident power and so the reflection coefficient is equal to 1, which in turn

leads to a return loss of zero dB, therefore, when the test port terminals are short

circuited, we must get a zero dB line on the display.

2. The terminals at the test port are now open circuited. The power fed to the test

port cannot be radiated because there is no load. So all the power reflects back.

The reflection coefficient is 1 and therefore leads to a return loss of 0 dB. Hence

when the terminals at the test port are open circuited the screen should display a 0

dB line.

During short circuit of test port terminals the power reflects back with phase

reversal. During the open circuit the reflected power is in- phase with respect to the

incident power. These two settings are stored in memory and the setup is ready for

practical measurements. The antenna is then connected at the test port and the observed

plot is the return loss of the antenna. The percentage bandwidth at -10dB return loss is%

Bandwidth = (f2-f1)/fr × 100

Where (f2-f1) is the frequency band for which the return loss is less than 10 dB.

Reflection Measurement

Under Reflection measurement we measured Return Loss, VSWR and

impedance.

1. Press Begin, filter and Reflection, the return loss of the antenna is displayed.

2. Press freq and then start 2.1 GHz to 2.3 GHz, scale, Auto scale reflection

coefficient in dB as a function of frequency is displayed. You can save and print

the data observed.

3. Press Format, Line Mag, to get the absolute value of reflection coefficient as a

function of frequency is displayed.

Standing Wave Ratio and Impedance

1. Press Format, and SWR. The SWR as a function of frequency is displayed. one

can save and print the data.

2. Press Format, More formats, Impedance Magnitude to get Z0as a function of

frequency. Save and print the data.

3. Press Format and Smith Chart for getting display of the real and imaginary values

of the impedance of the impedance as a function of frequency. Set the start

frequency to 2.1 GHz and stop frequency to 2.3 GHz, the impedance is about

50Ω’s in the pass band and then save and print the data.

Figure 5.3 Plot of our antenna Return Loss measurement for resonant frequency

Figure 5.4 Plot of our antenna SWR for resonant frequency

Figure 5.5 Plot of our antenna Impedance on a Smith Chart

5.2.4 RADIATION PATTERN MEASUREMENTS

The radiation patterns of an antenna are usually represented graphically by

plotting the electric field of the antenna as a function of direction. This electric field

strength is expressed as volts per meter or normalized field in dB.

A complete radiation pattern comprises the radiation for all the angles of and

and really requires three dimensional presentations. This is quite complicated. For the

practical purposes, the pattern is measured in planes of interest. Cross sections in which

the radiation patterns are the most frequently taken are the horizontal (=90 degrees) and

vertical (=constant) planes. These are called the horizontal patterns and vertical patterns

respectively. The terms commonly used are the E- plane and H-plane and they are the

planes passing through the antenna in the direction of beam maximum and parallel to the

far-field E and H vectors. These patterns are known as the ‘Principal Planes’ patterns.

The radiation patterns of the antenna are measured with the scientific Atlanta

instrumentation in an anechoic chamber. The instrumentation consists of the following

four major parts as shown in below figure.

1. Transmitting System

2. Positioning and Controlling System

3. Receiving System

4. Recording System

Transmitting System:

The transmitting or source instrumentation consists primarily of the RF signal

source and associated transmitting antenna.

Signal Source: The model 2150 signal source provides RF power in the 0.1 to 18 GHz

frequency range. The control unit is located near the operator’s console. The RF

oscillators are installed in the main frame assembly which is mounted near the source

antenna.

Source Antenna: Several types of antennas designed especially for the antenna test

range can be used. These include standard gain horns, dipoles, parabolic reflector

antennas, log periodic arrays and circularly polarized antennas depending upon the

requirement.

Positioning & Controlling System:

The antenna to be tested is mounted on the turntable of the antenna test positioner.

The speed and direction of the rotation of the test antenna can be controlled from the

operator’s console by a direct current motor. A synchro transmitter is mechanically

coupled to the positioner turntable and electrically to a position indicator. The antenna

test positioner is controlled by the series 4100 positioner control unit. Electrical cables

are used to supply power from control system to test positioner.

Indicator system: A position indicator allows remote angle read out of the test

positioner. The synchro transmitter in the test positioner provides the position data to

operate the position indicator.

Receiving System:

The antenna under test usually tested in the receive mode. Therefore a receiving

or detecting system must be connected to the test antenna to convert RF signals to a low

frequency signals which can drive the pen system of pattern recorder. Thus the antenna

must receive an RF signal i.e modulated with an audio signal. The model 2150 signal

source has an audio oscillator as a standard feature. The two types of detectors commonly

used for making antenna measurements are crystal detector and Bolometer. Scientific

Atlanta antenna pattern recorders will operate crystal detectors or Bolometer detectors

directly.

Antenna Pattern Recorder:

The radiation patterns of the antenna are recorded as relative amplitude and / or

phase as a function of the position (or angle). The synchro position data from the test

positioner is connected to the recorder’s chart servo system. The resultant graph is a plot

of the relative amplitude of the received signal as a function of the antenna position (or

angle).

Polarization positioner Azimuth positioner

SIGNAL SOURCE

Source control SA 2150

Remote Positioner Control Unit SA 4110-10

Position indicator

INDICATOR

Position Control Unit SA 4100

Pattern recorder

RECEIVER

ANECHOIC CHAMBER

Figure 5.6 Experimental Set Up For Plotting Radiation Pattern

Figure 5.7 Anechoic chambers with free space environment

Figure 5.8 Anechoic Chamber when our antenna is being tested

Figure 5.9 Plot of our antenna Radiation pattern in E and H plane

5.2.5 Gain Measurement

The setup used for measurement of gain is the same as that used for radiation

pattern measurement given in table (5.2). The gain of the antenna is measured by

replacing the test antenna with a standard antenna (horn antenna in this case) and taking

the pattern of the same. The gain is then calculated by comparing the power level

differences of the test antenna with that of the standard antenna.

Table 5.2 Gain Measurement

Figure 5.10 Bottom (ground plane) view of our antenna

Figure 5.11 Top view (patch) of our antenna

5.3 ANALYSIS

This section deals with the comparing the calculated values with the measured

values. Thus we can analyze the differences between them. The comparison is as follows:

ANTENNA PARAMETE

RS

CALCULATED

EQUATIONS

MEASURED

FIGURE/

TABLE

Length 31.44 mm 4.5 32.09 mm Fig 5.11

Width 40.57 mm 4.1 41.15 mm Fig 5.11

Thickness 1.6 mm - 1.6 mm -

frequency 2250MHz - 2200MHzFig 5.4

Bandwidth 51.556 MHz 4.10 56 MHz Fig 5.3

Beam Width E- plane

76.5(degrees) 4.975.6(degrees

)Fig 5.9

Beam Width H- Plane

89.29 (degrees) 4.881.9(degrees

)Fig 5.10

Gain 6.13 dB 4.9 3.94 dB Tab 5.2

Table 5.3 Comparison of calculated and measured values

From the above we finally conclude that the measured values and the obtained

values are approximately equal. Thus this project has been carried out successfully. The

changes in the measured values are due to the variation of dielectric constant of FR4

material, from actual value at our antenna operating frequency. And also due to slight

changes in dimensions of the patch in the fabrication process which was done at M/S

Sravanthi electronics at UPPAL industries. For Aerospace vehicles smaller bandwidth is

required which have been seen in the Microstrip Antenna.

CONCLUSIONS

A rectangular micro strip antenna is designed using the appropriate design

formulae and is fabricated using the PCB fabrication procedure and is tested by using the

vector network analyzer R&S ZVL. The antenna is designed at frequency 2250MHz

frequency with FR4 (εr=4.4),h=1.6mm,tan =0.02. Even though the antenna is desired to

operate at this frequency, when tested practically it is found that, it is resonating at

2200MHz.

The dielectric constant plays a major role in the overall performance of a patch

antenna. It affects both the width, in turn the characteristic impedance and the length

resulting in an altered resonant frequency. We have used the fiber glass substrate but the

permittivity (εr) alters from batch to batch some times even between different sheets of

substrates. In addition FRP-4 has a high loss tangent and is highly frequency dependent..

And also manufacture recommends this FR4 for use up to 1 GHz only with Eeff 4.36

The bandwidth of the patch antenna depends largely on the permittivity (εr) and

thickness of the dielectric substrate. Ideally a thick dielectric lower permittivity (εr) low

insertion loss is preferred for broad band applications.

From the result 1 observed that the band width of the micro strip element can be

increased by choosing a smaller element, thus reducing W and L. For the given resonant

frequency these dimensions will be changed by selecting a substrate having a higher

relative permittivity. The advantages of the micro strip antenna are that they are low cost,

conformable, light weight and low profile, while both linear and circular polarization is

easily achieved.

This antenna material is also ideal for antenna arrays. Longer ranges, larger areas,

faster assembly line speeds will all benefit from the focused energy and directionality

available through antenna array beam forming. The print and etch process of printed

circuit board is very repeatable and highly cost effective. It eliminates the labor and the

technician work required to insure proper phase matching between elements. It also

reduces energy requirements of the system. The reduced side lobe emissions reduce false

alarms, reduce interference between other antennas and minimize emission in unwanted

directions.

FUTURE SCOPE

The project provides the complete overview of Rectangular Microstrip antenna and also

provides the necessary equations to design a rectangular Microstrip antenna and also

provides the fabrication process of a rectangular Microstrip antenna. This also gives the

necessary information for choosing substrate and their properties for getting better

results.

Future challenges of a Microstrip antenna are:

Bandwidth Extension Techniques

Control of Radiation Patterns

Reducing Losses / increasing efficiency

Improving feed networks

Size reduction techniques

The band width can be increased as follows

By increasing the thickness of the substrate

By use of high dielectric constant of the substrate so that physical dimensions

of the parallel plate transmission line decreases.

By increasing the inductance of the micro strip by cutting holes or slots in it.

By adding reactive components to reduce the VSWR

In order to increase the directivity of the micro strip antennas multiple micro strip

radiators are used to cascade to form an array.

REFERENCES

Books

[1] R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna Design Handbook,

ArtechHouse, 2001.

[2] K. F. Lee, Ed., Advances in Microstrip and Printed Antennas, John Wiley, 1997.

[3] D. M. Pozar and D. H. Schaubert, Microstrip Antennas: The Analysis and Design of

Microstrip Antennas and Arrays, IEEE Press, 1995.

[4] F. E. Gardiol, “Broadband Patch Antennas,” Artech House.

[5] S K Behera, “Novel Tuned Rectangular Patch Antenna As a Load for Phase Power

Combining” Ph.D Thesis, Jadavpur University, Kolkata.

[6] D. R. Jackson and J. T. Williams, “A comparison of CAD models for radiation from

rectangular microstrip patches,” Intl. Journal of Microwave and Millimeter-Wave

Computer Aided Design, Vol. 1, No. 2, pp. 236-248, April 1991.

[7] D. R. Jackson, S. A. Long, J. T. Williams, and V. B. Davis, “Computer- aided design

of rectangular microstrip antennas”, ch. 5 of Advances in Microstrip and Printed

Antennas, K. F. Lee, Editor, John Wiley, 1997.

[8] D. M. Pozar, “A reciprocity method of analysis for printed slot and slot- coupled

microstrip antennas,” IEEE Trans. Antennas and Propagation, vol. AP-34, pp. 1439-

1446, Dec. 1986.

Websites

[9] Over view of microstrip antenna, ”httpwww.ecs.umass.edu/ece/pozar/aperture.pdf”

APPENDICES

Basic Models of Antennas

There are many variations of antennas. Below are a few basic models.

The isotropic radiator is a purely theoretical antenna that radiates equally in all

directions. It is considered to be a point in space with no dimensions and no mass.

This antenna cannot physically exist, but is useful as a theoretical model for

comparison with all other antennas. Most antennas' gains are measured with

reference to an isotropic radiator, and are rated in dBi (decibels with respect to an

isotropic radiator).

The dipole antenna is simply two wires pointed in opposite directions arranged

either horizontally or vertically, with one end of each wire connected to the radio

and the other end hanging free in space. Since this is the simplest practical

antenna, it is also used as a reference model for other antennas; gain with respect

to a dipole is labeled as dBd.

The Yagi-Uda antenna is a directional variation of the dipole with parasitic

elements added which are functionality similar to adding a reflector and lenses

(directors) to focus a filament light bulb.

The random wire antenna is simply a very long (at least one quarter wavelength)

wire with one end connected to the radio and the other in free space, arranged in

any way most convenient for the space available. Folding will reduce

effectiveness and make theoretical analysis extremely difficult.

The horn is used where high gain is needed, the wavelength is short (microwave)

and space is not an issue. Horns can be narrowband or wideband, depending on

their shape. A horn can be built for any frequency, but horns for lower frequencies

are typically impractical. Horns are also frequently used as reference antennas.

The parabolic antenna consists of an active element at the focus of a parabolic

reflector to reflect the waves into a plane wave. Like the horn it is used for high

gain, microwave applications, such as satellite dishes.

The patch antenna consists mainly of a square conductor mounted over a ground

plane. Another example of a planar antenna is the tapered slot antenna (TSA), as

the Vivaldi-antenna.

PROGRAM IN MATLAB

Merits of Programming

The design of the microstrip antenna involves many lengthy and tedious

calculations such as width, length, feed locations, and dimensions of the feed. As these

calculations are cumber some and time consuming when done by hand a computer

programming approach is adopted to simplify the task.

Program to find Width, Length & Feed Point

The width and length of the micro strip antenna are to be calculated from the

corresponding equations as given in chapter 4. The next parameter to be found is the feed

point location. In the project, the coaxial type of feed is chosen to feed the antenna. The

impedance of the feed is 50Ώ. Hence in the program the importance of the antenna is

found at every point along the length of the antenna according to the standard formulae

given in the chapter 4 and the point of feed is hence found.

Thus the program in MATLAB to find the length, width of the micro strip

antenna and also the feed location is given below. It takes the input as frequency of

operation(GHz), substrate thickness (in cm) and dielectric constant.

MATLAB Program

clear allclear k0 f1 f2c=3e11

er=input('enter the er value');h=input('enter the value of h');fr=input('enter the resonant frequency');% width calculationw=c/(2*fr*sqrt((er+1)/2));disp('width=')disp(w)% effective lengthp1=(er+1)/2;p2=(er-1)/2;p3=1/(sqrt(1+((12*h)/w)));eeff=p1+(p2*p3);disp('eeff=')disp(eeff)%delta L calculationp4=h*0.412*(eeff+0.3)*((w/h)+ 0.264);p5=(eeff-0.258)*((w/h)+0.8);dl=p4/p5;disp('del L=')disp(dl)% length calculationp6=c/(2*fr*sqrt(eeff));L=p6-(2*dl);disp('Length=')disp(L)% Area calculationA=L*w;disp('Area=')disp(A)% Gain calculationlg=133.33/sqrt(er);G=(4*pi*A)/(lg*lg);disp('Gain=')disp(G)% Beam Width% H planek0=0.047;p7=1+(w*k0/2);p8=sqrt(1/(2*p7));BWH1=2*(acos(p8));BWH=BWH1*57.18;disp('BEAM WIDTH IN H-PLANE')disp(BWH)% E planep9=(3*k0*k0*w*w)+(k0*k0*h*h);p10=sqrt(7.03/p9);

BWE1=2*(acos(p10));BWE= BWE1*57.18;disp('BEAM WIDTH IN E-PLANE')disp(BWE)% BAND WIDTH CALCULATIONs=2;p11=(8*h)/(3*er*133.33);p12=(100*(s-1))/sqrt(s);BWP = p11*p12;disp('BAND WIDTH')disp(BWP)BW=BWP*2250;disp(BW)OUTPUT OF PROGRAM