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RADIATION PATTERN OF LARGE

PLANAR ARRAYS USING ACTIVE

ELEMENT PATTERN

A PROJECT REPORT

Submitted by

PRIYANKA B

Register No: 14MCO017

in partial fulfillment for the requirement of award of the degree

of

MASTER OF ENGINEERING

in

COMMUNICATION SYSTEMS

Department of Electronics and Communication Engineering

KUMARAGURU COLLEGE OF TECHNOLOGY

(An autonomous institution affiliated to Anna University, Chennai)

COIMBATORE-641049

ANNA UNIVERSITY: CHENNAI 600 025

APRIL 2016

ii

BONAFIDE CERTIFICATE

Certified that this project report titled “RADIATION PATTERN OF LARGE PLANAR

ARRAYS USING ACTIVE ELEMENT PATTERN” is the bonafide work of

PRIYANKA.B [Reg. No. 14MCO017] who carried out the research under my supervision.

Certified further, that to the best of my knowledge the work reported herein does not form

part of any other project or dissertation on the basis of which a degree or award was conferred

on an earlier occasion on this or any other candidate.

HHHH

The Candidate with Register No. 14MCO017 was examined by us in the

project viva –voice examination held on............................

INTERNAL EXAMINER EXTERNAL EXAMINER

SIGNATURE

Dr. K.KAVITHA

PROJECT SUPERVISOR

Department of ECE

Kumaraguru College of Technology

Coimbatore-641 049

SIGNATURE

Dr. A.VASUKI

HEAD OF THE DEPARTMENT

Department of ECE

Kumaraguru College of Technology

Coimbatore-641 049

iii

ACKNOWLEDGEMENT

First, I would like to express my praise and gratitude to the Lord, who has

showered his grace and blessings enabling me to complete this project in an excellent

manner.

I express my sincere thanks to the management of Kumaraguru College of

Technology and Joint Correspondent Shri Shankar Vanavarayar for his kind support

and for providing necessary facilities to carry out the work.

I would like to express my sincere thanks to our beloved Principal

Dr.R.S.Kumar Ph.D., Kumaraguru College of Technology, who encouraged me with

his valuable thoughts.

I would like to thank Dr.A.Vasuki Ph.D., Head of the Department, Electronics

and Communication Engineering, for her kind support and for providing necessary

facilities to carry out the project work.

In particular, I wish to thank with everlasting gratitude to the Project Coordinator

Dr.M.Alagumeenaakshi Ph.D., Asst. Professor-III, Department of Electronics and

Communication Engineering, throughout the course of this project work.

I am greatly privileged to express my heartfelt thanks to my project guide

Dr.K.Kavitha Ph.D., Associate Professor, Department of Electronics and

Communication Engineering, for her expert counselling and guidance to make this

project to a great deal of success and I wish to convey my deep sense of gratitude to all

teaching and non-teaching staff of ECE Department for their help and cooperation.

Finally, I thank my parents and my family members for giving me the moral

support and abundant blessings in all of my activities and my dear friends who helped

me to endure my difficult times with their unfailing support and warm wishes.

iv

ABSTRACT

The study of microstrip patch antennas has made great progress in recent years.

Compared with conventional antennas, microstrip patch antennas have more

advantages and better prospects. In applications that require very high gains, it is

necessary to design antenna arrays to meet the demands of long distance

communication.

The radiation pattern computation for large arrays is usually employed by the

well known active-element pattern method when direct methods become infeasible.

However this method needs to calculate and store the pattern of each and every

individual element in an array. This becomes still tedious in the case of larger arrays.

To overcome this problem, a simplified AEP method which is known as subarray

pattern method can be used. This method predicts the radiation pattern of large arrays

using small subarrays. Eventhough this approach is effective for broadside and

uniform excitation arrays, the process of element-by-element computation is fully

avoided. This method provides faster calculation of radiation from large arrays. In this

paper, the radiation pattern from large array of 6×7 has been computed from subarray

of size 5×5. From the analysis it is seen that high computation time, shortage in

memory and space comes into account because of larger planar arrays.

The aim of this study is to design large antenna arrays with low complex

algorithm for computation and analyze their performance. Consider a microstrip

antenna consisting of a very thin metallic patch which is placed above a conducting

ground plane. The patch and ground plane are separated by a dielectric. The

rectangular microstrip patch antenna array, working especially in the ISM (Industrial,

Scientific and Medical) band, has been designed. The design specifications include

dielectric constant of 2.2, resonating frequency 2.4 GHz, height 0.32cm. The

rectangular microstrip patch antenna array was simulated using a commercial

simulation software HFSS, its performance parameters are measured and the results

are compared for different antenna configurations based on computation.

TABLE OF CONTENTS

CHAPTER

NO.

TITLE PAGE

NO.

ABSTRACT iv

LIST OF FIGURES viii

LIST OF TABLES ix

LIST OF ABBREVIATIONS x

1 INTRODUCTION 1

1.1 PATCH ANTENNAS 1

1.1.1 Definition of Patch Antennas 3

1.1.2 Advantages 3

1.1.3 Disadvantages 4

1.1.4 Applications 4

1.2 ANTENNA ARRAYS 5

1.2.1 Planar Arrays 6

1.3 RADIATION PATTERN 7

1.3.1 Active Element Pattern (AEP)

7

2 LITERATURE SURVEY 9

2.1INTRODUCTION 9

2.2 PLANAR ARRAYS 9

2.3MEASUREMENT OF RADIATION PATTERN 11

2.4 A STUDY ON AEP AND SAP METHODS 12

2.5 FASTER COMPUTATION OF PATTERNS FOR PLANAR

ARRAYS

15

2.6 RELATIVE STUDIES OF MICROSTRIP PATCH ANTENNA

17

3 DESIGN OF RECTANGULAR PATCH ANTENNA 18

3.1 MICROSTRIP PATCH ANTENNA 18

3.2 ANALYTICAL APPROACH - DESIGN EQUATIONS 20

3.3 PROPERTIES OF SUBSTRATE 22

3.4 FEEDING STRUCTURES 22

3.4.1 Probe Feed 23

3.4.2 Microstrip Feed Line 23

3.4.3 Proximity Coupled Feed 24

3.4.4 Aperture Coupled Feed 24

3.5 ANTENNA PARAMETERS AND TERMS 25

3.6 ANTENNA DESIGN SPECIFICATIONS 26

3.6.1 Single Antenna 26

3.6.2 2×2 Antenna 27

3.7 ANTENNA PROPERTIES 28

3.7.1 Operating Frequency 28

3.7.2 Return Loss 28

3.7.3 Bandwidth 29

3.7.4 Antenna Radiation Pattern 29

3.7.5 Half Power Beam Width 30

3.7.6 Gain 30

3.7.7 Directivity 30

3.7.8 Voltage Standing Wave Ratio 31

3.7.9 Resonant Frequency 31

4 METHODOLOGY 32

4.1 ACTIVE ELEMENT PATTERN METHOD 32

4.2 REDUCTION IN COMPUTATION FOR LARGE ARRAYS 33

4.2.1 Subarray Pattern method 33

4.3 5×5 ANTENNA ARRAY 34

4.4 6×7 ANTENNA ARRAY

35

5 SIMULATION RESULTS AND DISCUSSION 37

5.1 HFSS 37

5.2 DESIGN PROCEDURE 37

5.3 RESULTS 38

5.3.1 Return loss 38

5.3.2 VSWR 39

5.3.3 Radiation Pattern 40

5.3.4 3-D Radiation Plot 42

5.3.5 Gain 42

5.4 COMPUTATIONAL ANALYSIS OF PLANAR ARRAYS 43

6 CONCLUSION 45

REFERENCES 46

LIST OF PUBLICATIONS 50

viii

LIST OF FIGURES

FIGURE NO. CAPTION PAGE NO.

1.1 Planar array 6

1.2 Geometry for the active element pattern of uniform array 7

3.1 Proposed Single Antenna 19

3.2 Front view of 2×2 Antenna 27

4.1 Subarray for the construction of larger planar arrays 33



5.1 Return loss of Single Antenna 38

5.2 Return loss of 2×2 Antenna 38

5.3 VSWR of Single Antenna 39

5.4 VSWR of 2×2 Antenna 39

5.5 E-Field pattern 40

5.6 H-Field pattern 41

5.7 3D polar plot 42

5.8 Single Antenna Gain 43

ix

LIST OF TABLES

TABLE NO. CAPTION PAGE NO.

1.1 Characteristics of various type of printed antennas 2

3.1 Dimensions of the Single Antenna 27

3.2 Dimensions of the 22 Antenna 28



5.1 Comparison of antenna based on computation 44

x

LIST OF ABBREVIATIONS

OES Orchard-Elliott-Stern method

WL Woodward-Lawson method

SLL Sidelobe level

AEP Active Element Pattern method

LP Linear Polarization

CP Circular Polarization

LCP Liquid Crystal Polymer

MCCS Modified Capacitive Coupling Structure

SAP SubArray Pattern method

HFSS High Frequency Structural Simulator

UHF Ultra High Frequency

RF Radio Frequency

RL Return Loss

Wi-Fi Wireless Fidelity

ADS Almost Difference Sets

PSL Peak sidelobe levels

BCS Bayesian Compressive Sensing inversion algorithm

PSO Particle Swarm Optimization

MoM Method-of-Moments

PBF Physical Basis Function

CRE Complex Ray Expansion

UTD Uniform Theory of Diffraction

TTD True Time Delay

1

CHAPTER 1

INTRODUCTION

This chapter gives us an overview of patch antennas and its applications,

planar arrays and a detailed description of active element pattern for computation

purpose.

1.1 PATCH ANTENNAS

In the recent years the development in communication systems requires the

development of low cost, minimal weight, low profile antennas that are capable of

maintaining high performance over a wide spectrum of frequencies. This

technological trend has focused much effort into the design of a microstrip patch

antenna. Antennas play a very important role in the field of wireless communications.

Some of them are Parabolic Reflectors, Patch Antennas, Slot Antennas, and Folded

Dipole Antennas.

Patch antennas play a very significant role in today’s world of wireless

communication systems. A Microstrip patch antenna is very simple in the construction

using a conventional Microstrip fabrication technique. The most commonly used

Microstrip patch antennas are rectangular and circular patch antennas. One of the

main advantages of microstrip antenna technology is the ease with which an array

feed network can be fabricated in microstrip form.The basic microstrip antenna suffers

from a number of serious drawbacks, including very narrow frequency bandwidth,

high feed network losses, poor cross polarization and low power handling capability.

The most serious limitation of this technology is its narrow impedance bandwidth of

the basic element. The traditional microstrip patch element typically has an impedance

bandwidth of microstrip antenna is classified by three categories. They are

Impedance Bandwidth: The impedance variation with frequency of the antenna

element results in a limitation of the frequency range over which the element can

be matched to its feed line. Impedance bandwidth is usually specified in terms of

2

return loss or maximum VSWR (typically less than 2.0 or 1.5) over a frequency

range. The relation between VSWR and bandwidth is given by,

𝐵𝑊 =𝑉𝑆𝑊𝑅 − 1

𝑄𝑡 ∗ √𝑉𝑆𝑊𝑅∗ 𝑓𝑜

Pattern Bandwidth: The bandwidth side lobe level and gain of an antenna all vary

with frequency. If any of these quantities is specified as a maximum or minimum,

the operating frequency range can be determined.

Polarization or Axial Bandwidth: The polarization properties (linear or circular) of

an antenna are usually preferred to be fixed with frequency. Specifying a

maximum cross polarization or axial ratio level can be used to find this bandwidth.

Table 1.1 represents the comparison of various types of printed antenna

characteristics.

Table 1.1 Characteristics of various type of printed antennas

Characteristics Microstrip Stripline Cavity Bucked

Printed

Antenna

Printed Dipole

Antenna

1. Profile Thin Not very thin Thick Thin

2. Fabrication Very Easy Easy Difficult Easy

3. Polarization Both linear

and circular

Linear Both linear and

circular

Linear

4. Dual Frequency

Operation

Possible Not possible Not Not

5. Shape

Flexibility

Any Shape Only

Rectangular

Other Shapes

Possible

Rectangular

and Triangular

6. Spurious

Radiation

Exists Exists Doesn’t Exist Exists

7. Bandwidth 1~5% 1~2% ~10% ~10%

3

1.1.1 DEFINITION OF PATCH ANTENNAS

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

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

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

called a ground plane. The two metal sheets together form a resonant piece

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

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

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

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

for the antenna to be resonant, a length of microstrip transmission line slightly shorter

than one-half a wavelength at the frequency is used.

The basic configuration of a microstrip antenna is a metallic patch printed on a

thin, grounded dielectric substrate. Originally, the element was fed with either a

coaxial line through the bottom of the substrate, or by a coplanar microstrip line. This

latter type of excitation allows feed networks and other circuitry to be fabricated on

the same substrate as the antenna element, as in the corporate fed microstrip array.

1.1.2 ADVANTAGES

Microstrip antennas have several advantages compared to conventional microwave

antennas and therefore many applications over the broad frequency range from ~100

MHz to ~50 GHz.

1) Light weight, low volume, low profile plane configuration which can be made

conformal.

2) Low fabrication cost, readily amenable to mass production.

3) Can be made thin; hence they don’t perturb the aerodynamics of host aerospace

vehicles.

4) The antennas may be easily mounted on missiles, rockets and satellites without

major alterations.

5) The antennas have low scattering cross section.

6) Linear, circular polarization is possible with simple changes in feed position.

https://en.wikipedia.org/wiki/Antenna_(radio)

https://en.wikipedia.org/wiki/Ground_plane

https://en.wikipedia.org/wiki/Microstrip

https://en.wikipedia.org/wiki/Transmission_line

https://en.wikipedia.org/wiki/Wavelength

https://en.wikipedia.org/wiki/Resonant

4

7) Dual frequency antennas are easily made.

8) No cavity backing required.

9) Feed lines and matching networks are fabricated simultaneously.

1.1.3 DISADVANTAGES

1) Narrow bandwidth.

2) Loss, hence somewhat lower gain.

3) Most microstrip antennas radiate into half plane.

4) Practical limitation on maximum gain (~20dB).

5) Poor end fire radiation performance.

6) Poor isolation between feed and radiation elements.

7) Possibility of excitation of surface waves.

8) Lower power handling capability.

1.1.4 APPLICATIONS

For many practical designs, the advantages of microstrip antennas far out weight

of their disadvantages. Some notable system applications for microstrip have been

developed include,

1) Personal communication systems.

2) Mobile communications.

3) Satellite communications.

4) Direct broadcast televisions.

5) Wireless local area networks.

6) Intelligent vehicle highway system.

7) Satellite navigation systems.

8) Doppler and other radars.

9) Global positioning system.

5

1.2 ANTENNA ARRAYS

An antenna array is a set of N spatially separated antennas. The number of

antennas in an array can be as small as 2, or as large as several thousand. In general,

the performance of an antenna array increases with the number of antennas (elements)

in the array. The radiation pattern of a single element is relatively wide, and each

element provides low values of directivity (gain). In many applications it is necessary

to design antennas with very high directive characteristics (very high gains) to meet

the demands of long distance communication. This can only be accomplished by

increasing the electrical size of the antenna. Another way to enlarge the dimensions of

the antenna, without necessarily increasing the size of the individual elements, is to

form an assembly of radiating elements in an electrical and geometrical configuration.

In an array of identical elements, there are some controls that can be used to

shape the overall pattern of the antenna. These are:

1. The geometrical configuration of the overall array (linear, circular, rectangular,

spherical, etc.).

2. The relative displacement between the elements.

3. The excitation amplitude of the individual elements.

4. The excitation phase of the individual elements.

An array of identical elements all of identical magnitude and each with a

progressive phase are referred to as a uniform array. The array factor can be obtained

by considering the elements to be point sources. If the actual elements are not

isotropic sources, the total field can be formed by multiplying the array factor of the

isotropic sources by the field of a single element.

The array factor (AF) is given by

𝑨𝑭 = 𝟏 + 𝒆+𝒋(𝒌𝒅𝒄𝒐𝒔𝜽+𝜷) + 𝒆+𝒋𝟐(𝒌𝒅𝒄𝒐𝒔𝜽+𝜷) + ⋯ + 𝒆𝒋(𝑵−𝟏)(𝒌𝒅𝒄𝒐𝒔𝜽+𝜷)

𝑨𝑭 = ∑ 𝒆𝒋(𝒏−𝟏)(𝒌𝒅𝒄𝒐𝒔𝜽+𝜷)𝑵𝒏=𝟏 (1.1)

which can be written as

6

𝑨𝑭 = ∑ 𝒆𝒋(𝒏−𝟏)𝝍

𝑵

𝒏=𝟏

where 𝝍 = 𝒌𝒅𝒄𝒐𝒔𝜽 + 𝜷

1.2.1 PLANAR ARRAYS

Planar arrays are useful to generate radiation pattern of high directivity using

elements of low directivity. Despite planar arrays are more complex and expensive

than linear arrays, they have several advantages: The main lobe can be oriented to any

direction, a better side lobe ratio can be obtained, the radiation pattern of the antenna

can be controlled in a dynamic way, electronic systems can be used to feed the

elements of intelligent antennas. Planar arrays can provide more symmetrical patterns

with lower side lobes. In addition they can be used to scan the main beam of the

antenna towards any point in space. Applications include tracking radar, search radar,

remote sensing, communications and many others.

Fig 1.1 Planar array

Fig 1.1 shows the geometrical disposition of a planar array of the rectangular

type , it can be obtained by collocating N linear arrays perpendicular to the y-axis

separated by dy. Each linear array is made of M elements separated by dx.

7

1.3 RADIATION PATTERN

Radiation pattern refers to the directional (angular) dependence of the strength

of the radio waves from the antenna or other source. The methods for measuring

radiation pattern are: Method of moments, Original induced element pattern method,

Improved induced element pattern method, Pattern multiplication.

1.3.1 ACTIVE ELEMENT PATTERN (AEP)

In the analysis of large arrays there are two main factors namely array factor and

element pattern considered which determine how the far-field pattern of the array will

be created. The element pattern must take into account how the energy emitted from

the single element reacts with the adjacent element and reradiates or absorbs affecting

the pattern of the single element. This single element which considers the reradiating

and mutual coupling effect is termed as “active element pattern”.

Fig 1.2 Geometry for the active element pattern of uniform array

When all the active element factors are approximated as equal then the total

field pattern is the product of the active element factor and the array factor. The array

factor is given by equation (1.1).

Consider a rectangular uniform planar array of MN identical elements. The

array element is placed along x-axis and y-axis defined by column element and row

element respectively. The far field is given by the summation of AEP of all the

elements which can be written in the form,

8

𝐸𝑀×𝑁 (𝜃, 𝜙) = ∑ ∑ 𝐸𝑚𝑛𝑁𝑛=1

𝑀𝑚=1 (𝜃, 𝜙) (1.2)

The AEP approach of determining the radiation pattern of large arrays is time

consuming and requires more computation power. When larger array structures on the

order of hundreds to thousands of elements are to be used, the simulation process will

require each of the element to be placed, radiation pattern computed for each element

with the mutual coupling for all the elements taken into account. Depending on the

computer system, the computation time will be several hours to days.

A new technique of subarray pattern is being employed to reduce the

computation time, memory and space. This method will be described in Chapter 4.

Chapter 2 deals with a brief discussion on planar arrays for the computation of

the radiation pattern, studies related to active element pattern arriving at faster

computation along with the study of patch antennas. Chapter 3 describes the design of

patch antennas and its related concepts. The methodology used is dealt in Chapter 4.

The simulated results of the proposed designs and discussions will be dealt in Chapter

5. Chapter 6 tells about the inference or the conclusion and scope for future work.

9

CHAPTER 2

LITERATURE SURVEY

2.1 INTRODUCTION

This chapter will present a brief overview of planar arrays for the computation of

radiation pattern using active element pattern method. This method is employed to

construct large arrays which reduces computation problem. A study of microstrip patch

antenna is also made.

2.2 PLANAR ANTENNA ARRAYS

J.A.Rodrigruez et al [8] developed a two stage method for the synthesis of planar

arrays with arbitrary geometry that generate footprints of arbitrary shape. The first

consists of obtaining a continuous circular aperture distribution that approximately

affords the desired footprint pattern by truncating the corresponding fourier series. In the

second step this distribution is sampled at the array points and the array element

excitations are then optimized by simulated annealing to improve the performance. The

method has proved to be useful for the synthesis of large satellite array antennas.

J.A.Rodrigruez et al [9] also developed a new method by combining the OES and

WL techniques which can perform rapid synthesis of irregular footprints for arrays that

are too large to allow direct optimization of array excitations by stochastic methods. It is

possible to synthesize any desired footprint at the expense of increasing the antenna size.

The author suggested to find a compromise between the features of the desired pattern

and the number of elements of the antenna. This technique can be applied to conformal

array antennas.

Marcos Alvarez-Folgueiras et al [10] designed linear and planar arrays based on

linear semiarrays composed of a small number of subarrays differing in their internally

uniform element spacing, which was constrained to exceed 0.5λ so as to minimize mutual

10

coupling. It results in a low-dimensional optimization problem that can be rapidly solved

by an appropriate optimization techniques and affords uniformly excited arrays with

excellent predicted performance.

A sidelobe-minimizing method proposed by Balanis and Bevelacqua [11]

efficiently determines the optimal weights given a specified beamwidth for wideband

planar arrays of elementsscanned to broadside. This method can be executed significantly

faster than optimal wideband weighting methods developed previously. This speedup in

computation time allows for simultaneous weight-geometry optimization. Authors [11]

have presented results for wideband arrays of 4-7 elements.

An analytical technique was proposed by Giacomo Oliveri et al [12] based on

almost difference sets (ADS) for thinning planar arrays with well controlled sidelobes.

The method allows one to synthesize bidimensional arrangements with peak sidelobe

levels (PSLs) predictable and deducible from the knowledge of the array aperture, the

filling factor, and the autocorrelation function of the ADS at hand.The numerical

validation, points out that the expected PSL values are significantly below those of

random arrays and comparable with those from different sets (DSs).

Wenji Zhang et al [13] studied the antenna array synthesis problem from the new

perspective of sparseness constrained optimization.By exploiting the a priori information

that the antenna location space is sparse, the antenna array synthesis problem is cast as

sparseness constrained optimization problem and solved with Bayesian compressive

sensing (BCS) inversion algorithm. Authors [13] presented numerical examples to show

the high efficiency of both planar and linear arrays synthesis with sparseness constrained

optimization.

D.M.Pozar [3] in his work discussed the use of the active element pattern for

prediction of the scan performance of large phased array antennas. If all the active

element factors can be approximated as equal, then the pattern of the fully excited

arraycan be expressed as the product of the active element factor and the array factor, in

an analogous fashion to ordinary array theory. This method is used to locate and correct

11

array design problems before the full-scale system is fabricated and reduces the risk of a

costly design failure.

Kai Yang et al [5] proposed a novel embedded element pattern

decompositionmethod to synthesize conformal phased antenna arrays. This method

decomposes the embedded element patterns as a product of a characteristic matrix and a

Vandermonde structured matrix. It is also applicable to the synthesis of a pattern with any

mainlobedirection and optimized polarization. They applied a modified particle swarm

optimization (PSO) method to optimize the weights ofthe modes. The advantages of this

method are low peak side lobe, accurate mainlobe scanning and low cross-polarization.

2.3 MEASUREMENT OF RADIATION PATTERN

Jeong-Hwan Kim and Hong-Ki Choi [14] developed a method to obtain the far-

field radiation pattern of an antenna at a reduced distance (d<10λ) where the far-field

distance condition is not satisfied. An asymptotic antenna transmission formula and

angular mode deconvolution technique has been used to determine the far-field

radiation.This method can be used to measure E-plane and H-plane radiation pattern of a

large size antenna and a low sidelobe level antenna in a small anechoic chamber.

Theodore G.Vasiliadis et al [15] presented a novel technique for the

approximation of three-dimensional (3-D) antenna radiation patterns. The method

combines the two principal cuts in order to acquire an adequate estimate of the 3-D

antenna radiation solid.This technique exhibits low approximation errors and is easily

integrated into 3-D radio propagation planning tools (such as ray-tracing algorithms).

Christian M. Schmid et al [1] presented an analysis of the effects of calibration

errors and mutual coupling on the pattern of an antenna array, based on a statistical,

linear, angle-independent mutual coupling model. They have derived both a worst-case

boundary and statistical properties for general and two common mutual coupling matrix

models. The results show how the design parameters channel weighting, the number of

channels and the tolerances, coupling or isolation affect the beam pattern. They may be

used for analyzing the probability of achieving or exceeding a given SLL or for

specifying array and system requirements.

12

Xue-Song Yang and W.Z.Wang [4] analyzed pyramidal conformal antenna arrays

with seven elements and twelve elements with the use of AEP technique. The results

showed that the AEP technique was effective in predicting the radiation pattern of the

pyramidal conformal array, which is an approximation of a conical conformal array. AEP

requires much less computational time than to simulate the whole array, especially when

the array is very large.

David F. Kelley and W.L.Stutzman [6] introduced a new method ‘the hybrid

active elementpattern method’ which accurately predicts the patterns of small and

medium-sized arrays of equally spaced elements. Example arrays of center-fed dipoles

are analyzed to verify and illustrate the representations. The results can be applied to

arrays of any type of element. The array patterns computed using both the classical

pattern multiplication approach and the methods based on active element patterns are

compared to those computed using accuratenumerical codes based on the method of

moments.

Peter J. Collins and J.P.Skinner [7] developed a hybrid moment method (MM)

based numerical model for the electromagnetic scattering from large finite-by-infinite

planar slot arrays. The model incorporates the novel concept of a physical basis function

(PBF) to dramatically reduce the number of required unknowns. The authors developed

the model by representing an individualslot column with equivalent magnetic scattering

currents on an unbroken perfectly conducting plane. A newly developed one-sided

Poisson sum formula provides a convenient means to calculate the mutual coupling

between the PBF and the slot columns in the presence of a stratified dielectric media.

2.4 A STUDY ON AEP AND SAP METHODS

Shuai Zhang et al [19,20] proposed a simplified AEP method which uses the total

radiation field of four small subarrays to construct the radiation pattern of large planar

arrays. To eliminate the cumbersome process of standard AEP method, which needs to

compute and store the AEP of each subarray element and uses them to construct large

arrays this method has been employed. It is only effective for broadside and uniform

excitation arrays and has the same accuracy as the standard AEP method. From the

13

theoretical derivation, the author verified that the proposed method leads to a significant

saving in memory usage, runtime, and manpower resource. Numerical example shows

that the proposed method can adequately consider the mutual coupling effects. This

method is applicable to any element type and the scattering calculation of large planar

arrays.

A systematic method for designing shaped beam patterns with an array antenna

introduced by Erdinc Ercil et al [22] possibly get realistic antenna patterns including

mutual coupling effects. The method has been verified through antenna pattern

measurements. As the measured active element patterns are used, the synthesized pattern

is very close to measured patterns. Slight difference was observed between the measured

and predicted patterns. This difference might be attributed to two factors: The uncertainty

in measurements, and the different impedances seen by antenna elements during the

element pattern measurement and entire array measurement stages. A drawback of the

method is that the array must be at hand prior to the design of the beamforming network

or the array excitation coefficients.

D. M. Kokotoff et al [21] investigated a procedure for computing the radiated and

scattered fields from a large conformal array of slots including mutual coupling effects

without having to solve a large matrix equation. This approach begins with the radiated

or scattered fields as calculated by the method of moments from individual slot elements

in a subarray. The subarray lattice is identical to the larger array and both of their borders

are isomorphic to the lattice. To compute the fields of the larger array, a mapping

procedure is invoked whereby the fields of each element in the large array are obtained

from a dilated element in the subarray. The computational savings, in terms of matrix

storage and computing speed is enormous, since a much smaller matrix equation is

needed for the subarray calculation. The dilation method agrees well with method of

moments results and is more accurate than array factor calculations based upon single

element patterns.

14

Brockett and Rahmat-Samii [23] investigated various subarray pattern distortions

that can cause the appearance of grating lobes with the aim to provide an insightful and

valuable first-order diagnostic tool for antenna array designers. In typical subarray

configurations, the emergence of undesirable grating lobes is a possibility due to

distortions in the subarray array factor which can be caused by feeding errors, mutual

coupling between elements and/or feed lines, or other discrepancies. The focus has been

made on systematic errors that can arise in subarray designs that feature common element

excitation schemes. Distortions will be categorized by amplitude and phase errors

separately, demonstrating their distinct manifestations in each excitation scheme.

Recognition of these manifestations can lead to better subarray designs and save

significant time in the development of large array antennas. The concepts introduced

were supported by analytical array factor calculations for 1xN linear subarrays, full-wave

simulations of a 1x4 subarray and 1 x16 array, and representative measurements of two

1x16 arrays at Ku-band.

An accurate method to synthesise a shaped-beam flat reflectarray (RA) antenna

based on the phase synthesis of its equivalent aperture was presented by Karimipour et al

[24]. For this purpose particle swarm optimisation was used to determine the optimal

phase distribution on the reflective surface of the antenna. Furthermore, by dividing the

equivalent aperture of the antenna into small parts and by appropriate approximation of

the induced current in each part, the radiation fields have been evaluated via the sum of

the simple integrals. In the proposed method the effects of the feed antenna including the

angle, polarisation, amplitude and phase of the radiated fields from the feed are fully

considered in the synthesis procedure. To verify the synthesis method a RA with flat

reflective surface has been designed and manufactured that shows a good agreement with

the simulation results obtained from commercial full-wave electromagnetic software,

CST Microwave Studio.

The standard active element pattern (AEP) method presented by Shuai Zhang et al

[25] to predict the radiation pattern of large finite arrays. In this method, the AEPs of a

15

large array are deduced from those of a small subarray. Thus, it needs to compute the

AEPs of the subarray element-by-element and costs much CPU time. The author

proposed a simplified AEP (SAEP) method to eliminate this complicated procedure. In

the expression of the SAEP method the radiation field of a large finite array is simply

related to the total radiation field of two small subarrays. Compared with the standard

AEP method, the SAEP method allows us to arrive at a more efficient calculation of the

radiation from large arrays. Numerical results show that the SAEP method has the same

accuracy as the simulator HFSS while maintaining the simplicity of the pattern

multiplication method.

2.5 FASTER COMPUTATION OF PATTERNS FOR PLANAR ARRAYS

A hybrid method developed by P.F.Zhang et al [26] to compute the radiation

pattern of antennas on large complex three-dimension carriers. This involves computing

the radiation fields of the antenna in free space with FEM, characterizing the reflection

and diffraction of the carrier to the radiation fields with CRE (Complex Ray Expansion)

and UTD (Uniform Theory of Diffraction).The shortcomings such as great number of ray

trace, distortion and partly shadowing of the rays etc., are overcome by the use of CRE,

and the time consuming physical-optics-type integration is replaced by the paraxial

approximation of the complex rays. By using the proposed method, the computation of

the three dimension radiation pattern of an antenna in a large ship is finished by a PC in

1671.20 seconds.

Luca Manica et al [27] presented an efficient approach for the synthesis of sub

arrayed monopulse planar antennas. Starting from the guidelines of an effective

procedure previously developed to deal with linear geometries, some innovative features

have been introduced to extend the capability of the approach as well as its efficiency,

thus enabling the synthesis of planar monopulse arrays. As a matter of fact, by exploiting

some features of the solution, a simple and compact representation of the space of

admissible solutions has been defined, which allows a considerable reduction of the

problem complexity as well as a significant saving in terms of storage resources and CPU

time to synthesize the compromise solution.

16

Ricciardi et al [28] demonstrated the capability to quickly simulate, on a desktop

platform, wideband radiation patterns for large phased arrays, with overlapped subarray

architecture, that are subject to various errors. The attained run-times are extremely fast,

thus demonstrating that the simulation has more than sufficient speed to conduct iterative

optimization of wideband array designs. The significant run time improvement is

obtained by implementing the NUG algorithm on the GPU platform to process in parallel

individual far-field observations points for each of the constituent overlapped subarray

patterns.

A multilevel algorithm for the computation of the transient radiation patterns of

true time delay (TTD) conformal arrays over a range of observation and beam steering

directions was presented by Shlivinski and Boag [29]. It is based on hierarchical

decomposition of the array into smaller sub-arrays of elements. At the finest level of

decomposition, the angular temporal radiation patterns of single-element sub-arrays are

obtained over a sparse angular grid of directions and short temporal duration, by either

measurement or calculation. Subsequent steps of the algorithm comprise multilevel

aggregation of delayed sub-array contributions. This process continues until the transient

radiation pattern of the whole array is obtained. This algorithm attains a computational

complexity substantially lower than that of the direct evaluation and is particularly

efficient for large arrays with large numbers of elements.

A fast algorithm for antenna array power synthesis has been presented by Comisso

and Vescovo [30]. It is based on the iterative computation of an auxiliary phase pattern

and can be applied to arrays of arbitrary geometry, including configurations characterized

by a large number of elements. Furthermore, the method usually required less CPU time

as compared to the other considered methods. This is due to the use of a proper weight

function and a simple closed form expression that allows an easy computation of the

auxiliary phase pattern at each iteration, using a low number of samples.

17

2.6 RELATIVE STUDIES OF MICROSTRIP PATCH ANTENNA

Atsuya Ando et al [16] proposed an enhanced microstrip antenna that incorporates

a patch that rotates around the inner conductor of the coaxial line or dielectric shaft and a

novel coaxial line feeding technique that offers constant electromagnetic coupling. This

enhanced patch antenna achieves the antenna gain of approximately 0 dBd, which is the

same as that of the previously proposed antenna, while suffering no significant gain

degradation due to unit inclination over inclination angles from ±45 compared to a

conventional quarter-wavelength whip antenna, which experiences a degradation of

approximately 2.7 dB.

B.T.P. Madhav et al [17] tested the microstrip rectangular patch array for both the

substrate materials of LCP substrate and RT-duroid. It was found that the RT-duroid

substrate antenna has good gain, directivity and bandwidth values compared with LCP

substrate antenna. As the dielectric constant value increases the size of the antenna

decreases as well as its efficiency and vice-versa. Both the substrate materials are having

advantages and disadvantages as per the applications are concerned.

Changliang Deng et al [18] proposed low-profile LP and dual-band CP patch

antennas with vertical monopole-like radiation patterns. They introduced MCCS to feed

these microstrip antennas compactly which enables the polarization flexibility without

changing the near- and far-field characteristics much. Then, four curved branches are

added around the circular radiating patch to employ a horizontal wave of the same

amplitude and 90° phase difference. The concepts of these kinds of antennas can be

applied in GPS communication systems andother wireless communication systems.

Khagindra Kumar Sood et al [2] proposed a waveguide shunt-slot feed for a

microstrip patch antenna and analyzed using a MoM-based formulation. Entire-domain

basis functions are used with a Galerkin procedure to obtain the solution. The developed

analysis is used to analyze a C-band prototype for input characteristics and farfield

patterns. Subsequently, authors [2] carried a parametric study for chief design parameters.

A comparison was made to a previously microstrip patch radiator fed by an endwall iris

and a good match has been seen.

18

CHAPTER 3

DESIGN OF RECTANGULAR PATCH ANTENNA

3.1 MICROSTRIP PATCH ANTENNA

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

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

such as a printed circuit board, with a continuous metal layer bonded to the opposite

side of the substrate which forms a ground plane. Common microstrip antenna shapes

are square, rectangular, circular and elliptical, but any continuous shape is possible.

Some patch antennas do not use a dielectric substrate and instead are made of a metal

patch mounted above a ground plane using dielectric spacers; the resulting structure is

less rugged but has a wider bandwidth. Because such antennas have a very low

profile, are mechanically rugged and can be shaped to conform to the curving skin of a

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

incorporated into mobileradiocommunications devices.

Microstrip antennas are relatively inexpensive to manufacture and design

because of the simple 2-dimensional physical geometry. They are usually employed

at UHF and higher frequencies because the size of the antenna is directly tied to

the wavelength at the resonantfrequency. A single patch antenna provides a maximum

directive gain of around 6-9dBi. It is relatively easy to print an array of patches on a

single (large) substrate using lithographic techniques. Patch arrays can provide much

higher gains than a single patch at little additional cost; matching and phase

adjustment can be performed with printed microstrip feed structures, again in the same

operations that form the radiating patches. The ability to create high gain arrays in a

low-profile antenna is one reason that patch arrays are common on airplanes and in

other military applications. Such an array of patch antennas is an easy way to make

a phased array of antennas with dynamic beamforming ability.

An advantage inherent to patch antennas is the ability to

have polarization diversity. Patch antennas can easily be designed to have vertical,

https://en.wikipedia.org/wiki/Light_beam

https://en.wikipedia.org/wiki/Dielectric

https://en.wikipedia.org/wiki/Printed_circuit_board

https://en.wikipedia.org/wiki/Ground_plane

https://en.wikipedia.org/wiki/Bandwidth_(signal_processing)

https://en.wikipedia.org/wiki/Mobile_radio

https://en.wikipedia.org/wiki/UHF


https://en.wikipedia.org/wiki/Resonance

https://en.wikipedia.org/wiki/Decibel

https://en.wikipedia.org/wiki/Phased_array

https://en.wikipedia.org/wiki/Polarization_(waves)

19

horizontal, right hand circular (RHCP) or left hand circular (LHCP) polarizations,

using multiple feed points, or a single feedpoint with asymmetric patch

structures. This unique property allows patch antennas to be used in many types of

communications links that may have varied requirements.

Microstrip antennas are relatively inexpensive to manufacture and design

because of the simple 2-dimentional physical geometry. They are usually employed at

UHF and higher frequencies because the size of the antenna is directly tied to the

wavelength at the resonant frequency. Patch arrays can provide much higher gains

than a single patch at little additional cost, matching and phase adjustment can be

performed with printed microstrip feed structure, again in the same operations that

form the radiating patches. The ability to create high gain arrays in a low- profile

antenna is one reason that patch arrays are common on airplanes and in other military

applications. Patch arrays an easily be deigned to have vertical, horizontal, right hand

circular, or left hand circular polarization, using multiple feed points, or a single feed

point with asymmetric patch structures.

Fig 3.1 Proposed Single Antenna

The most commonly employed microstrip antenna is a rectangular patch which

looks like a truncated microstrip transmission line. It is approximately of one-half

wavelength long. When air is used as the dielectric substrate, the length of the

rectangular microstrip antenna is approximately one-half of a free-space wavelength.

As the antenna is loaded with a dielectric as its substrate, the length of the antenna

decreases as the relative dielectric constant of the substrate increases. The resonant

https://en.wikipedia.org/wiki/Microstrip


https://en.wikipedia.org/wiki/Dielectric_constant

20

length of the antenna is slightly shorter because of the extended electric "fringing

fields" which increase the electrical length of the antenna slightly. An early model of

the microstrip antenna is a section of microstrip transmission line with equivalent

loads on either end to represent the radiation loss.

3.2 ANALYTICAL APPROACH - DESIGN EQUATIONS

Microstrip antennas are characterized by a larger number of physical

parameters than conventional microwave antennas. They can be designed to have

many geometrical shapes and dimensions but rectangular and circular Microstrip

resonant patches have been used extensively in many applications. The antenna

parameters for the antenna shown in fig 3.1 can be calculated by the transmission line

method.

A design procedure is outlined which leads to practical designs of rectangular

microstrip antennas. The procedure assumes that the specified information includes

the dielectric constant of the substrate (휀𝑟), the resonant frequency (𝑓𝑟), and the height

of the substrate (h). The procedure is as follows

Specify:

휀𝑟 , 𝑓𝑟(in Hz), 𝑎𝑛𝑑 ℎ

Determine:

W, L

Design procedure:

1. For an efficient radiator, a practical width that leads to good radiation efficiencies

is

𝐖=𝒗𝟎

𝟐𝒇𝒓√

𝟐

𝟏+𝜺𝒓 (3.1)

where,𝑣0 is the free-space velocity of light.

2. Determine the effective dielectric constant of the microstrip antenna using

21

𝜺𝒓𝒆𝒇𝒇 = (𝜺𝒓+𝟏)

𝟐 +

(𝜺𝒓 − 𝟏)

𝟐[𝟏 + 𝟏𝟐

𝒉

𝑾]

−𝟏

𝟐 (3.2)

3. Once W is found, determine the extension of the length ∆𝐿 using

∆𝑳 = 𝟎. 𝟒𝟏𝟐𝒉 (𝜺𝒓𝒆𝒇𝒇+ 𝟎.𝟑)(

𝑾

𝒉+𝟎.𝟐𝟔𝟒)

(𝜺𝒓𝒆𝒇𝒇− 𝟎.𝟐𝟓𝟖)(𝑾

𝒉+𝟎.𝟖)

(3.3)

4. The actual length of the patch can now be determined using

𝑳 =𝝀

𝟐− 𝟐∆𝑳 (3.4)

Apart from these parameters, there are some more parameters which are used in the

design of microstrip patch antennas.

5. Ground length

𝑳𝒈 = 𝟔𝒉 + 𝑳 (3.5)

6. Ground Width

𝑾𝒈 = 𝟔𝒉 + 𝑾 (3.6)

7. Feed Length

𝐥𝐟 =𝛌

𝟒 (3.7)

where,

εreff = Effective dielectric constant

εr = Dielectric constant of substrate

h = Height of dielectric substrate

𝑣0 = free space velocity of light (3*10^8)

𝑓𝑟 = Resonant Frequency

22

W, L= width and length of the patch

All measurements are in centimeter.

3.3 PROPERTIES OF SUBSTRATE

• Thickness of substrate should be very much less than guided wavelength

• Dielectric constant ( 휀𝑟) for RF and microwave bands should satisfy the

condition

2.2 ≤ 휀𝑟 ≤ 16

• Dielectric loss tangent which is the imaginary part of 휀𝑟 and denoted as

tan𝛿should be such that

0.0001 ≤ tan𝛿 ≤ 0.06

• High dielectric constant result in low radiation.

3.4 FEEDING STRUCTURES

There are many configurations that can be used to feed microstrip antennas.

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 feeding techniques used are: microstrip

line, coaxial probe, aperture coupling and proximity coupling.

Feeding structure is used to transfer RF or microwave energy from

transmission system to antenna. It is responsible for widening impedance bandwidth

and enhancing radiation performance. Different types of feeding structures are

described below:

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3.4.1 PROBE FEED

Coaxial-line feeds, where the inner conductor of the coax is attached to the

radiation patch while the outer conductor is connected to the ground plane. The

coaxial feed or probe feed is a very common technique used for feeding microstrip

patch antennas. It is also easy to fabricate and match, and it has low spurious

radiation. However, it also has narrow bandwidth and it is more difficult to model,

especially for thick substrates (h < 0.02 𝜆0).

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. 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.

3.4.2 MICROSTRIP FEED LINE

The microstrip feed line is also a conducting strip, usually of much smaller

width compared to the patch connected directly to the edge of the microstrip patch.

This kind of feed arrangement has the advantage that the feedcan be etched on the

same substrate to provide a planar structure.The purpose of the inset cut in the patch is

to match the impedance 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 substrate

thickness increases, surface waves and spurious feed radiation increase, which for

practical designs limit the bandwidth (typically 2-5%). The feed radiation also leads to

undesired cross polarized radiation.

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3.4.3. PROXIMITY COUPLED FEED

This type of feed technique is also called as the electromagnetic scheme. 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. Energy is transferred by means of

electromagnetic coupling between patch and feeding strip. 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 micro strip

patch antenna. This scheme also provides choices between two different dielectric

media, one for the patch and one for the feed line to optimize the individual

performances.

Matching can 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.

3.4.4 APERTURE COUPLED FEED

This feeding structure consists of two substrates separated by a common

ground plane. Radiating patches are on upper substrate while feeding strip on lower

substrate. A narrow slot (non-resonant aperture) cut from ground plane between patch

and feed line. The feeding strip is electromagnetically coupled to patch through this

slot or aperture. The amount of coupling is controlled by aperture size and shape. Her

impedance matching is achieved by optimizing aperture parameters, location and

length of strip or dielectric constant of two substrates. This feeding structure has the

advantage of broad impedance bandwidth and high polarization purity. The

disadvantage of this feeding structure is its higher complexity and cost.

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.

25

3.5 ANTENNA PARAMETERS AND TERMS

• Antenna : A device for the radiation or reception of EM Waves

• Antenna Efficiency : The ratio of the power radiated (𝑃𝑟) to the power fed into

the antenna (𝑃𝑡).

• Antenna Resistance : The real part of the antenna input impedance.

• Array Element : A single radiating element or a convenient grouping of

radiating elements, that have a fixed relative excitation, in an antenna array.

• Array Antenna : An arrangement of antenna elements, usually identical, used

to obtain specific antenna characteristics.

• Antenna Bandwidth : The frequency over which the antenna characteristics

conform to a desired standard.

• Antenna Beam : The major lobe of the radiation pattern of an antenna.

• Broadside Array Antenna : A linear or planar array whose direction of

maximum radiation is perpendicular to the line or plane of the array.

• Directional Antenna : An antenna which radiates or receives electromagnetic

waves more effectively in a perpendicular direction.

• Directivity : The ratio of the maximum intensity to the average radiation

intensity.

• Endfire Array Antenna : A linear array antenna whose direction of maximum

radiation is parallel to the line of array.

• Half Power Beamwidth (HPBW): In a plane containing the direction of the

maximum of a beam, the angle between the two directions in which the

radiation intensity is one half the maximum value of the beam.

• Isotropic Radiator : A hypothetical antenna radiating equally well in all

direction.

• Polarization of an Antenna : This is the polarization of the wave radiated by

the antenna is that particular direction. When the direction is not specified, the

polarization is taken to be the polarization in the direction of maximum

radiation.

26

• Radiation Resistance : The ratio of the square of the RMS antenna voltage to

the power radiated. It may be expressed as, 𝑅𝑟 =𝑉2

2𝑃𝑟.

• Resonant Frequency : A frequency at which the input impedance of the

antenna has no reactive component.

• Scan angle : The angle between maximum of the side lobe and a reference

position.

• Side Lobe : A radiation lobe is any direction other than the intended lobe.

• Side Lobe Level : The relative level to the highest side lobe.

3.6 ANTENNA DESIGN SPECIFICATIONS

3.6.1 SINGLE ANTENNA

A patch antenna is designed using the coaxial probe feed and is placed on the

top of the substrate which is at a height of 0.32cm from the ground of dimension

10*9cm. The substrate is made up of Rogers RT/Duroid material, which should satisfy

the following conditions.

Thickness of substrate should be very much less than guided

wavelength.

Dielectric constant for RF and microwave bands should satisfy the

condition range ( 2.2 ≤εr≤ 16)

Dielectric loss tangent which is the imaginary part of εr , is denoted

astan 𝛿 such that 0.0001≤ tan 𝛿 ≤0.06.

There are three essential parameters required for the design of a rectangular

microstrip patch antenna. They are

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

selected appropriately. The frequencies used for S-band is ranging from 2-4

GHz. Here the ISM band is selected which has frequencies ranging from 2.4-

2.4835 GHz and the resonant frequency of the antenna selected is 2.4 GHz.

27

Dielectric constant of the substrate ( 휀𝑟): The dielectric material used for the

design is Rogers RT/Duroid with 휀𝑟 = 2.2

Height of the substrate (h) : The height of the dielectric substrate chosen is

0.32cm.

An excitation power of 1W is fed to the antenna by means of coaxial probe feed,

whose one end is connected to the substrate while the other is connected to the patch.

A port of 50Ω is connected to the feed line.The design of the single element antenna

with dimensions given in table 3.1 is shown in fig 3.1.

Table 3.1 Dimensions of the Single Antenna

Sl. No Dimensions Values in cm

1 Patch Width, W 4.0

2 Patch Length, L 3.0

3 Ground plane width, Wg 10.0

4 Ground plane length, Lg 9.0

5 Substrate height, h 0.32

6 Dielectric constant, 휀𝑟 2.2 (constant)

3.6.2 22 ANTENNA

A 2 2 patch antenna array is designed using the coaxial probe feed and is

placed on the top of the substrate which is at a height of 0.32cm from the ground of

dimension 20 18cm. The same procedure of single antenna element design is

followed for 22 antenna array. The design of 22 antenna array is shown in Fig 3.2.

Fig 3.2 Front view of 22 Antenna

28

Four antennas are placed at the top of the substrate above a ground plane of

20 18cm dimension with 6cm ( 2/ ) inter-element spacing between them. 1W of

power is fed to all the four antennas using individual coaxial probe feed. The

dimensions of the 22 antenna array is given in table 3.2.

Table 3.2 Dimensions of the 22 Antenna







6 Dielectric constant, 휀𝑟 2.2 (constant)

7 Inter-element spacing 6

3.7 ANTENNA PROPERTIES

There are several important antenna characteristics that should be

considered when choosing an antenna for any application. They are as follows:

3.7.1 OPERATING FREQUENCY

The operating frequency is the frequency range through which the antenna

will meet all functional specifications.It depends on the structure of the antenna in

which each antenna types has its own characteristic towards a certain range of

frequency. The operating frequency can be tuned by adjusting the electrical length of

the antenna.

3.7.2RETURN LOSS

Return loss is the ratio, at the junction of a transmission line and a

terminating impedance or other discontinuity, of the amplitude of the reflected wave

to the amplitude of the incident wave. The return loss value describes the reduction in

29

the amplitude of the reflected energy, as compared to the forward energy. Return loss

can be expressed as,

RL=20log𝒛𝟏+𝒛𝟐

𝒛𝟏−𝒛𝟐

where,

Z1 = impedance towards the source

Z2 = impedance towards the load

3.7.3 BANDWIDTH

Bandwidth can be defined as the range of frequencies within which the

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

specified standard. Bandwidth is a measure of frequency range and is typically

measured in hertz. For an antenna that has a frequency range, the bandwidth is usually

expressed in ratio of the upper frequency to the lower frequency where they coincide

with the -10 dB return loss value. The formula for calculating bandwidth is given as,

BW= 𝒇𝒉−𝒇𝒍

√𝒇𝒉𝒇𝒍× 𝟏𝟎𝟎%

where,

fh= lower frequency that coincide with the -10 dB return loss

fl= upper frequency that coincide with the -10dB return loss

3.7.4 ANTENNA RADIATION PATTERNS

The radiation pattern is a graphical representation of the characteristics

of an antenna radiation in a certain direction as shown in Fig 4.11. These

characteristics include radiation intensity, field intensity and polarization. It is

normally represented withrectangular or polar plots and it is expressed in dB.

The radiation pattern of an antenna is the geometric pattern of the

relative field strengths of the field emitted by the antenna. An antenna radiation

pattern is a 3-D plot of its radiation far from the source. Antenna radiation

30

patterns usually take two forms, the elevation pattern and the azimuth pattern.

The elevation pattern is a graph of the energy radiated from the antenna looking

at it from the side. The azimuth pattern is a graph of the energy radiated from

the antenna as if looking at it from directly above the antenna.

3.7.5 HPBW

The HPBW (Half Power Beam Width) is a way of measuring the antenna

directivity. This means that if the main lobe of an antenna is too narrow, the

directivity is higher. It can be determined by taking out 3dB (half power) with respect

to the main lobe power level.

3.7.6 GAIN

There are two types of gain, Absolute Gain and Relative Gain.

The Absolute Gain of an antenna is defined as the ratio between the

antennas radiation intensity in a certain direction and the intensity that would be

generated by an isotropic antenna fed by the same input power, therefore it can be

given as,

𝑮(𝜽, 𝝋) =𝑼(𝜽, 𝝋)

𝑼𝟎

whereG(𝜃, 𝜑) is the gain of the antenna in a certain direction,𝑈(𝜃, 𝜑) is the radiation

intensity in a certain direction and 𝑈0is the radiation intensity of an isotropic antenna.

The absolute Gain is expressed in dBi as its reference is an isotropic antenna.

The Relative Gainof an antenna is defined as the ratio between the antenna

radiation intensity in a certain direction and the intensity that would be generated by a

reference antenna. The Relative Gain is expressed according to reference antenna.

3.7.7 DIRECTIVITY

The directive gain of an antenna is a measure of the concentration of the

radiated power in a particular direction. It may be regarded as the ability of the

31

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. The maximum

directive gain is called as the directivity of an antenna and is denoted by D. This is an

important parameter that allows us to measure the concentration of radiated power in a

certain direction.

3.7.8 VOLTAGE STANDING WAVE RATIO (VSWR)

The voltage standing wave ratio (VSWR) is defined as the ratio of the

maximum voltage to the minimum voltage in a standing wave pattern. The VSWR can

also be calculated from the return loss (𝑺𝟏𝟏) which means that it is also an indicator of

antennas efficiency. With the return loss we can determine the mismatch between the

characteristic impedance of the transmission line and the antennas terminal input

impedance it is given as

VSWR=𝟏+𝑺𝟏𝟏

𝟏−𝑺𝟏𝟏

The VSWR increases with the mismatch between the antenna and the

transmission line and decreases with a good matching. The minimum value of VSWR

is 1:1 and most equipment scan handle a VSWR of 2:1, the bandwidth of an antenna

can be determined by the VSWR or the return loss. The best performance of an

antenna is achieved when the VSWR under 2:1 or the return loss is -10dB or lower.

3.7.9 RESONANT FREQUENCY

The “resonant frequency” and “electrical resonance” is related to the

electrical length of an antenna. The electrical length is usually the physical length of

the wire divided by its velocity factor (the ratio of the speed of wave propagation in

the wire to the speed of light in a vaccum). Typically an antenna is tuned for a specific

frequency, and is effective for a range of frequencies that are usually centered on that

resonant frequency.

32

CHAPTER 4

METHODOLOGY

This chapter will present a new approach to active-element pattern method for

large planar array antennas for the purpose to have less computation time, memory

storage and space during computation.

4.1 ACTIVE ELEMENT PATTERN METHOD

Antenna array far-field patterns have two parts that make up the pattern that is

seen. The first part is the array factor which is determined by the number of elements

and their spacing. The second is the element pattern and has a large effect on the

overall far-field pattern. When first taught about arrays, the element pattern is the

simple free-space pattern of the specific antenna type. However, once an element is

placed near other radiating elements it is no longer in free-space and the pattern does

not give an accurate representation pattern that should be used with the array factor.

The pattern that should be used is one that takes into the account the effects of the

adjacent elements around the specific antenna and uses that to modify its far-field

pattern. This modified single element far-field pattern is called an active-element

pattern and takes into account all the mutual coupling of the elements and gives the

array far-field pattern a more accurate representation.

An active-element pattern is the radiation pattern of a single live element when

all elements are terminated at the generator load, which is typically determined from

an infinite array excitation. The active-element pattern emerges from the single live-

element radiation and the mutual-coupling effects of the adjacent elements on that

radiation.

There are two problems with this approach to finding active-element patterns

for elements in a large array. The first problem is that the computation power needed

to mesh and calculate the current for a large array is only really achievable by

computers that have massive computation power in the form of RAM or processing

power. This processing power makes it unrealistic to do first-order design or analysis

33

work of antenna arrays. The second problem is the time it takes to complete all the

calculations is quite extreme, once again making the computation method unwanted

when designing or analyzing large arrays.

4.2 REDUCTION IN COMPUTATION FOR LARGE ARRAYS

Large arrays with elements numbering in the hundreds have properties that

allow for some reductions in the number of calculations needed to achieve an accurate

far-field and active-element pattern. There are a few precautions that have to be taken

for these reductions to work properly. First, the elements in the array have to be

identical; there cannot be difference in polarization or structure. Second, all the

elements have to be equally spaced, making the structure of the array periodic.

4.2 .1 SUBARRAY PATTERN METHOD

A new technique of subarray pattern is being employed to reduce the

computation time, memory and space. This method uses the total field pattern of

subarrays to construct the radiation pattern of larger planar arrays. The accuracy of

this is similar to AEP method which is effective only for broadside and uniform

arrays.

Fig. 4.1 Subarray for the construction of larger planar arrays

When the distance between two elements is larger than a certain distance, mutual

coupling effects can be ignored. Thus, the AEPs of the interior elements of large

planar array are assumed to be identical and approximated by the AEP of the central

element of the subarray. For the remaining elements of the large array, the AEP can be

approximated by their corresponding elements in the subarray. It is noted that the

approximated AEP method considers extra phase shift. In this case, the mutual

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coupling effects between two elements are ignored and forced to be zero when their

distances are very much larger. This method converts the radiation pattern

computation of large planar array into a small subarray. This allows a faster

calculation of radiation from large planar arrays.

Consider the subarray composed of S×S identical elements. The three cases in

subarray pattern method include identical row dimension (S×N), identical column

dimension (M×S) and arbitrary dimension (M×N). After analyzing these cases it is

seen that, radiation from large array of M×N elements can be related to the field

radiated by four small subarrays composed of S×S, S×(S+1), (S+1)×S, and

(S+1)×(S+1) elements. Therefore, the SAP method eliminates individual AEP

computation and storage which leads to saving in memory, computation time and

manpower resource.

Another reduction in computation, when finding the active-element pattern, is

that large arrays do not have to take into account the edge effects of the array. Edge

effects for arrays consist of reflected surface waves and the un-uniformity of the

electromagnetic environment around the edge elements that causes the edge element

patterns to be different. However, since large arrays have so many elements the

number of elements that are actually affected by these edge effects is low and can be

ignored. The edge effects can also be mitigated by adding loading elements and using

amplitude tampering in the power applied to elements.

4.3 55 ANTENNA ARRAY

A 55 patch antenna array is designed using the coaxial probe feed and is


dimension 5045cm. The same procedure of single antenna element design is

followed for 55 antenna array. The design of 55 antenna array is shown in Fig 4.2.

All antenna elements are placed at the top of the substrate above a ground plane of

5045cm dimension with 6cm ( 2/ ) inter-element spacing between them. 1W of

power is fed to all the 25 antennas using individual coaxial probe feed.

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The dimensions of the 55 antenna array is given in table 4.1.








6 Dielectric constant, 𝜀𝑟 2.2 (constant)


4.4 67 ANTENNA ARRAY

Consider a 67 elements array as an example. Fig. 4.1 shows that a 55

elements array can be used to construct a larger array of 67 elements. Note that the

approximated AEP should consider the extra phase shift. In this case, the mutual

coupling between two elements in the x–axis and y-axis direction are ignored and

forced to be zero when their distance are larger than 2𝑑𝑥 and 2𝑑𝑦 , respectively. If

the results cannot achieve the desired accuracy, the scale of the small planar array

should be expanded. We shall refer to such a small square array as subarray and

denote the method as subarray pattern method. This method converts the radiation

36

calculation of a large planar array into that of a small subarray and allows us to arrive

at a fast calculation of the radiation from the large planar array when numerical

methods and simulation software are infeasible.

67 antenna array are deducted from 55 antenna elements by SAP

method. A 67 patch antenna array is designed using the coaxial probe feed and is


dimension 6063cm. The design of 67 antenna array is shown in Fig 4.3. All

antenna elements are placed at the top of the substrate above a ground plane of

6063cm dimension with 6cm ( 2/ ) inter-element spacing between them. 1W of

power is fed to all the 42 antennas using individual coaxial probe feed.


The dimensions of the 67 antenna array is given in table 4.1.








6 Dielectric constant, 𝜀𝑟 2.2 (constant)


37

CHAPTER 5

SIMULATION RESULTS AND DISCUSSION

There exists much software such as HFSS, Fidelity, CST, Feko, EMPro,

SIMetric, SuperNEC etc. for the simulation of RF component designs. In this paper,

the antenna has been designed and simulated using HFSS.

5.1 HFSS

HFSS is a commercial finite element solver for electromagnetic structures from

Ansys. ANSYS HFSS software is the industry - standard simulation tool for 3-D

fullwave electromagnetic design. It is one of several commercial tools used for

antenna design, and the design of complex RF electronic circuit elements including

filters, transmission lines, and packaging.

5.2 DESIGN PROCEDURE

The three essential parameters in the design of an antenna are,

Frequency of operation

Dielectric constant of substrate

Thickness of substrate

The designs steps for the antenna is given below:

1) Creation of ground plane

2) Creation of substrate and patch

3) Feed Creation

4) Simulation of antenna using HFSS

5) Measurement of performance parameters

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5.3 RESULTS

5.3.1 RETURN LOSS

It is a measure of the effectiveness of an antenna to deliver power from source

to the antenna.

For a practical antenna, the return loss should be < -10dB.

Fig 5.1 Return loss of Single Antenna

Fig 5.2 Return loss of 2x2 Antenna

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From Fig 5.1: 𝑆11 = -32.9201 dB at 2.4 GHz frequency

From Fig 5.2: 𝑆11 = -26.4807 dB at 2.4 GHz frequency

5.3.2 VSWR

Voltage Standing Wave Ratio (VSWR) is defined as a measurement of the

mismatch between the load and the transmission line. For ideal case the value of

VSWR is 1 and for better matching, VSWR value should be as small as possible.

Fig 5.3 VSWR of Single Antenna

Fig 5.4 VSWR of 2x2 Antenna

40

Here the value of VSWR is less than 2 at the resonant frequency for all the

antenna designs, which is a good performance criterion.

5.3.3 RADIATION PATTERN Radiation pattern refers to the directional dependence of the strength of the

radio waves from the antenna. The E-Field (𝟇=0) and H-Field (𝟇=90) patterns for

2×2, 5×5 and 6×7 arrays are shown in following figures.

(c)

Fig 5.5 E-Field pattern (a) 2×2 array (b) 5×5 array (c) 6×7 array

41

Gain of 13.5329, 18.3501 and 20.6156 has been obtained for 2×2, 5×5 and 6×7 array structures.

(c)

Fig 5.6 H-Field pattern (a) 2×2 array (b) 5×5 array (c) 6×7 array

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5.3.4 3-D RADIATION PLOT

The 3-D radiation pattern of the designed antenna arrays are shown in the

following figures. The designed arrays have the radiation pattern in one particular

direction.

(c)

Fig 5.7 3D polar plot (a) 2×2 array(b) 5×5 array(c) 6×7 array

5.3.5 GAIN

Gain is the ratio of radiation field intensity of test antenna to that of the

reference antenna. It is usually expressed in dB. It measures how much power an

antenna radiates.

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Fig 5.8 Single Antenna Gain

From the above figures it is seen that the gain of an antenna increases with an

increase in the number of elements. It is observed from the results that, there is an

improvement in antenna performance parameters such as return loss, gain and VSWR

as the design enhances from single antenna, 2×2 , 5×5 to 6×7 arrays.

5.4 COMPUTATIONAL ANALYSIS OF PLANAR ARRAYS

One of the most important aspects of this new technique is that it saves time

and computation power. For this research the computer used for the computation had a

2 GHz processor and was always limited due to the restraints of the HFSS version

used on computer.

As expected, when looking at the computation time and power, the power and

time increase as the number of elements increases. The amount of computation power

is not extreme by common computer standards, but then most of these array sizes are

small when compared to real world arrays. Realistic large arrays in use today are

usually on the order of thousands of elements and would easily require several GB of

computation power to work through. The worst part about the larger arrays

computation is the time it takes to complete the simulations. At the smallest number of

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elements it takes about an hour to finish the simulations and at the largest it takes

almost days to complete.

Therefore, the new method has most definitely achieved the goal of reducing

the computation time and power required for a large array on an average PC.

Table 5.1 Comparison of antenna based on computation

Computations/

Dimensions

Computation time Memory Total No. of

elements

Single antenna 1 min 35 sec 7.1309 GB 14174

22 antenna 6 min 47 sec 18.78 GB 61126

55 antenna 3 hr 33 min 31 sec 280.35 GB 751609

Table 5.1 above contains the computation time and memory required to

compute all the data need to find the active-element pattern for all the arrays that are

considered in this research.

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CHAPTER 6

CONCLUSION

6.1 CONCLUSION

Microstrip antenna arrays afford a unique design alternative for applications that

benefit from thin, conformal, rugged antennas with low to moderately high gain or

shaped radiation patterns. The rectangular microstrip patch antenna array was simulated

using a commercial simulation software HFSS. An efficient method called SAP is used

for the calculation of radiation pattern from large planar arrays. In this method, the total

field radiated by larger array is related to small subarrays. This leads to significant saving

in computation time, memory storage and space. To have good accuracy, subarray size

can be increased. The antenna performance parameters are measured and the results are

obtained for different array structures. From the simulated results, it was found that there

is an improvement in gain. High gain antennas can be constructed by forming large

antenna arrays.

This study clearly shows how larger antenna arrays can be successfully designed

with minimum computational complexity using SAP method. There is a scope for future

work to develop larger array structures with other types of antenna configurations to

achieve very high gains. Better results can be obtained by considering further more

mutual coupling effects.

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LIST OF PUBLICATIONS

Conferences

Presented a paper titled “Performance Analysis of Microstrip Patch Antenna Array

using Subarray Pattern method” in the 5th National Conference on Communication,

Information & Telematics-CITEL2016 on 30th-31st March 2016 at Kumaraguru

College of Technology, Coimbatore.

Presented a paper titled “Performance Analysis of Microstrip Patch Antenna Array

using AEP method” in an International Conference on Communication and Security

(ICCS2016) on 17-19 March 2016 at Pondicherry Engineering College,

Pondicherry.

radiation pattern of large planar arrays using … · arrays using active element pattern” is the...

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