Circular_array_antenna_2.docx

ETHIOPIAN INSTITUTE OF TECHNOLOGY-MEKELLE

ELECTRICAL AND COMPUTER ENGINEERING STREM OF ELECTRONICS AND COMMUNICATION ENGINEERING MIN PROJECT project title: CIRCULAR ARRAY ANTENNA SUBMITTED BY: 1.Anwar Beshah

0934/05

2.Yohannes w/gebreal

1891/05

3.Meles Habtu

0392/05

4.Maereg T/Selassie

0333/05

5.Samuel Meles

1775/05

6.Tamrat Belay

0543/05

SUBMITTED TO: Inst. Tekle Birhane

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ACKNOWLEDGEMENTS

First we would like to thank for the Almighty God who helped us in every way of our step. We would like to express our gratitude to our advisor Mr. Tekle Birhane, for his guidance enabled us to know more about this project. The co-operation is much indeed appreciated. Our grateful thanks also go the entire Electronics and Communication Engineering Stream of School of Electrical and Computer Engineering and all lecturers who prepared us from the base of Communication Engineering. We will also like to appreciate our friends, we love you all and thanks for the ideas. Special thanks also to our parents, who encouraged, supported and helped us financially, prayerfully and morally throughout this project.

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ABSTRACT

Antennas are ubiquitous devices in radio, TV, satellite, and mobile communications, and the economic and social impact of these services motivate engineers to improve antenna feasibility and performance. A single element antenna, due to its limited performance, is often not enough to meet technical needs for high gain, narrow and/or steerable beams, pattern nulls, and low side lobes. An array of antennas can, however, cover most of these constraints. Enlarging the dimensions of single elements often leads to more directive characteristics. 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. This new antenna, formed by multi elements, is referred to as an array. In most cases, the elements of an array are identical. This is not necessary, but it is often convenient, simpler, and more practical. The individual elements of an array may be of any form (wires, apertures, etc.)

The number, geometrical arrangement, and relative amplitudes and phases of the array elements depend on the angular pattern that must be achieved. The geometrical arrangements can be linear, circular, planar, etc. However, this paper focuses on uniform circular array antenna. Once an array has been designed to focus towards a particular direction, it becomes a simple matter to steer it towards some other direction by changing the relative phases of the array elements—a process called steering or scanning. The aim of this project is analyses the performance of circular array antenna by varying the distance, radius, number of element and phases of the array element. Simulation study is used to evaluate the performance of the circular array antennas. The simulation results show that the circular antenna have good performance in terms of directivity, side lobes and gain and also shows the direction of the radiated power that is the desired angular sector.

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TABLE OF CONTENTS TITLE PAGE……………………………………………………………………………..i ACKNOWLEDGEMENTS………………………………………………………………ii ABSTRACT………………………………………………………………………………iii TABLE OF CONTENTS…………………………………………………………………iv LIST OF TABLES……………………………………………………………………….vi LIST OF FIGURE……………………………………………………………………….vii

CHAPTER ONE INTRODACTION………………………………………………………………………….1 1.1 Background of the study……………………………………………………………......1 1.2 Statement of the problem……………………………………………………………….1 1.3 Objectives of the study………………………………………………………………….2 1.3.1 General objective …………………………………………………………………2 1.3.2 Specific objective…………………………………………………………………2 1.4 Methodology……………………………………………………………………………2 1.5 Project outline………………………………………………………………………......2

CHAPTER TWO LITERATURE REVIEW………..………………………………………………………3 2.1 Antenna………………………………………………………………………………3 2.2 Types of antenna……………………………………………………………………..3 2.3 Antenna parameters…………………………………………………………………..4

CHAPTER THREE ARRAY ANTANNA………………..…………………………………………………5 IV

3.1 Introduction…………………………………………………………………………..5 3.2 circular array antenna…………………………………………………………………5 3.3 Geometry of Circular Array Antennas………………………………………….….....7 3.4 Array Factor…………………………………………………………………………..7 3.5 Circular array for far field…………………………………………………………….9

CHAPTER FOUR RESULT AND DISCUSSTIONS……………………………………….……………….11 4.1 Mat lab Simulation and analysis…….………………………………………………..11 4.2 Simulation Results…………………………………………………………………….11 4.2.1 Variable input N, constant –a ……………………………………………………….11 4.2.2 Variable input a, constant N…………………………………………………………21 4.3 Discussion on the result……………………………………………………………….24

CHAPTER FIVE CONCLUSION ……………………………………………..………………………….25 5.1 Conclusion……………………………………………………………………………25 5.2 Recommendation…………………………………………………………………….25 5.2.1 Communication application ……………………………………………………….25 5.2.1 Radar application…………………………………………………………………..25 5.2.3 Circular array in direction finding…………………………………………………26

REFERENCES…………………………………………………………………………..27

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LIST OF TABLES Table 4.1: simulation algorithm…………………………………………………………….10

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LIST OF FIGURES Page no. Figure 3.1: Geometry of an N-element circular array……………………………………………7 Figure 3.2: Geometry of an N-element circular array for far file………………………………..9

Figure 4.1: a) Array pattern (N=5, a=1)………………………………………………..12 Figure 4.1: b) Power [dB] pattern (N=5, a=1) ……………………………………….....12 Figure 4.1: c) Polar plot of array pattern (N=5, a=1)…………………………………...13 Figure 4.1 : d) Polar plot for power pattern in dB (N=5, a=1) …………………………13 Figure 4.1: e) Polar plot of element normalized E-fields……………………………….14 Figure 4.1: f) Polar Array factor and total E-fields in dB (N=10, a=1)…………………14 Figure 4.2: a) Array pattern (N=10, a=1)……………………………………………….15 Figure 4.2: b) Power [dB] pattern (N=10, a=1)………………………………………..15 Figure 4.2: c) Polar plot of array pattern (N=10, a=1)…………………………………16 Figure 4.2: d) Polar plot for power pattern in dB (N=10, a=1)………………………..16 Figure 4.2: e) Polar plot of element normalized E-fields……………………………….17 Figure4.2: f) Polar plot array factor and total E-field…………………………..............17 Figure 4.3: a) Array pattern (N=15, a=1)……………………………………………….18 Figure 4.3: b) Power [dB] pattern (N=15, a=1)………………………………………..18 Figure 4.3: c) Polar plot of array pattern (N=15, a=1)………………………………....19 Figure 4.3: d) Polar plot for power pattern in dB (N=15, a=1)…………………………19 Figure 4.3: e) Polar plot of element normalized E-fields……………………………….20 Figure 4.4: f) Polar plot array factor and total E-field………………………………….20 Figure 4.5: a) Array pattern for (a=2 and N=5) ………………………………………...21 Figure 4.5: b) power pattern [dB] for (a=2 and N=5)……………….………………….21 Figure 4.5: c) Polar plot of array pattern (N=15, a=1)…………………………………22 Figure 4.5: d) Polar plot for power pattern in dB (N=15, a=1)………………………..22 Figure 4.5: e) Polar plot of element normalized E-fields………………………………23 Figure 4.5: f) Polar plot array factor and total E-field…………………………………23

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CHAPTER ONE INTRODUCTION 1.1 Background of the study An antenna is a structure, usually made from a good conducting material, that has been designed to have a shape and size such that it will radiate EM power in an efficient manner it is well established fact that time varying currents will radiate EM waves. Thus an antenna is a structure on which time varying currents can be excited with relatively large amplitude when the antenna is connected to a suitable source, usually by means of transmission line or wave guide. There is almost endless variety of structural shapes that can be used for antenna. However, from practical point of view those structures that are simple and economical to fabricate are the ones most commonly used. In order to radiate efficiently, the minimum size of the antenna must be comparable to wavelength. (Robert e. Collin, 1985) The antenna like the eye is a transformation device converting EM photons into circuit currents, but unlike the eye the antenna can also convert energy from circuit into photons radiated into space. In simplest term an antenna converts photons to currents or vice versa (John d. kraus, 1968) For antennas to radiate or propagate signals, there must be a time-varying current or an acceleration (or deceleration) of charge... (C. A. Blanis, 2005) Antennas can be categorized as Wire Antenna, Aperture Antenna, Micro strip Antenna Reflector Antenna, Lens Antenna, Array Antenna, Reflector Antenna. Among these antenna types the circular antenna has been discussed in chapter two with a detail and brief explanation including their performance characteristics.

1.2 Statement of the problem Now a day, most of the communication systems are transformed into wireless so the advantage of circular array can’t be considered as questions. The problem statements are:  There is a poor quality of reception.  There is low gain and directive beam.  There is low capability of scan all azimuth and the beam patter is variant in linear arrays. Due to this, the significance of our study is to give a clear idea in which case the circular array antenna have a good performance.

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1.3 Objectives of the study 1.3.1 General objective The main objective of this Project is to analyses the performance circular array antenna.

1.3.2 Specific objective Specific objectives of the project are:  Study the characteristics of circular array antenna.  Evaluating the performance of circular array antenna.

1.4 Methodology The formal methodologies to be used to achieve objectives of the project are:  Literature review: includes reading books, articles, simulation tools and other resources related to the topic.  System modeling and simulation: includes mathematical expression of the system and simulating the communication system using matlab.  Analysis and Interpretation of the results: the performance of circular array antenna will be explained.

1.5 Project outline There are five chapters contained in this project: Chapter one is the general introduction to the project. Chapter two entails on literature survey, antenna type and antenna performance parameter over. Chapter three describes circular array antenna. Chapter four consists of the simulation results obtained in investigating the performance of circular array, analysis and comparison. Chapter five contains the conclusions of our work.

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CHAPTER TWO LITERATURE REVIEW 2.1 Antenna An antenna is a transducer that converts an electric current into electromagnetic waves which are then radiated into space. Electric charges are the sources of EM fields. If the sources are time varying, EM waves propagate away from the sources and radiation is said to have taken place. Radiation may be thought of as the process of transmitting electric energy. The radiation or launching of the waves into space is efficiently accomplished with the aid of conducting or dielectric structures called antennas. Theoretically, any structure can radiate EM waves but not all structures can serve as efficient radiation mechanisms. An antenna may also be viewed as a transducer used in matching the transmission line or waveguide (used in guiding the wave to be launched) to the surrounding medium or vice versa. The antenna is needed for two main reasons: efficient radiation and matching wave impedances in order to minimize reflection. The antenna uses voltage and current from the transmission line (or the EM fields from the waveguide) to launch an EM wave into the medium. An antenna may be used for either transmitting or receiving EM energy. (Matthew O. Sadiku, 1990) The I EEE Standard Definitions of Terms for Antennas defines the antenna as a means for radiating or receiving radio waves.” In other words, the antenna is the transitional structure between free-space and a guiding device. The guiding device or transmission line may take the form of a coaxial line or a hollow pipe (waveguide), and it is used to transport electromagnetic energy from the transmitting source to the antenna or from the antenna to the receiver. Antennas transmit radio signals by converting electrical currents into electromagnetic waves. Antennas receive the signals by converting the electromagnetic waves back into radio frequency electrical currents. Antennas can function in air, space, under water or other liquid, and even through solid matter for limited distances. Since the beginning of the twentieth century, antenna designers have investigated different antenna architectures to meet the requirements of communication systems. A large variety of antennas have been developed to date; they range from simple structures such as monopoles and dipoles to complex structures such as phased arrays. A detailed study of circular sector patch antenna. This antenna has interesting dimension, so it can be integrated easily in antenna array. Recently, Smart antenna have received increasing interest for improving the performance of wireless radio systems, their application has been suggested for mobile-communications systems, to overcome the problem of limited channel bandwidth, satisfying a growing demand for a large number of mobiles on communications channels. However Conventional Antenna systems, which employ a single antenna, radiate and receive information equally in all directions. In this project the performance circular array antenna is investigated. 2.2 Types of Antennas Antennas are mainly classified into different categories: wire, aperture, loop, Microstrip, array, reflector, smart antennas. Wire antennas are the most common type of antennas. They can be seen on automobiles, buildings, ships, aircraft, spacecraft and many other places. Aperture antennas are mainly used in aircraft and spacecraft applications. Some examples of aperture antennas are the pyramidal horn, the conical horn and the rectangular waveguide antennas. Microstrip patch antennas are mainly used for government and 3

commercial applications. Array antennas are assembly of elements (wire, aperture, rectangular). Rectangular and circular micro strip patch antennas are the most used antennas because of their low crosspolarization. 2.3 Antenna Parameters The performance of an antenna depends on many parameters like: radiation pattern, directivity, antenna efficiency, beam-width and gain. The radiation pattern is a parameter that plays a very important role on the performance of an antenna. The radiation pattern is a graphical representation of the radiation properties of an antenna in terms of space coordinates. The coordinate system used to analyze the radiation of antennas. Most radiation patterns are composed of a major lobe, minor lobes and back lobes. The major lobe or main lobe is the maximum radiation lobe and it is typically pointing in the =0 direction. The back lobe is the lobe located at an angle of 180 degrees with respect to the main lobe, and a side lobe is next to a major lobe, seen in the direction of the main beam. Half Power Beam Width (HPBW) is the angular separation between the half power points on the antenna radiation pattern, where the gain is one half the maximum value. First Null Beam width (FNBW) is the angular width between the first nulls on either side of the main beams. Directivity is the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions. Antenna Efficiency is the product of the conduction efficiency and the dielectric efficiency. Gain is defined as the ratio of the antenna radiated power density at a distant point to the total antenna input power radiated isotopically.

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CHATER THREE ARRAY ANTANNA 3.1 Introduction An array of antenna elements is needed to obtain good adaptive properties and more gain for a smart antenna. These antenna elements play an important role in shaping and scanning the radiation pattern. There are different kinds of antenna elements to form an adaptive array. These include dipoles, micro strips, horns, reflectors and so on.in most cases the elements used to create the array are identical. There are different types of array configurations like linear, planar and circular arrays. An array of identical elements with identical magnitude and each with progressive phase is called as a uniform array. The circular array, in which the elements are placed in a circular ring, is an array configuration of very practical interest. Circular arrays are used in application that require 360◦ coverage in azimuth. Over the years, applications span Radio direction finding, air and space navigation, underground propagation, radar, sonar, and many other systems. More recently, circular array shave been Proposed for wireless communication, and in particular for smart antennas. the basic symmetry of circular arrays offers a number of advantages, which in additional to the 360◦ scan angle already Mentioned can include an ability to compensate for the effects of mutual coupling by breaking down the array excitation into a series of symmetrical spatial components. This can also give rise to directional patterns which remain constant in shape over broad bandwidths.

3.2 circular array antenna The field of circular array (or cylindrical) arrays has received far less attentions than that devoted to linear and planar arrays. At first sight this seems surprising since one of their principal advantage is the ability to detect beams electronically through360° with little change of either beam width or side lobes level. Circular array has been applied, to a limited extent, in both communications systems and navigations aids since the late 1930s. There has, however, been surprisingly little change in their scale of applications since that date, through there are now signs of a significant increase of interests in such arrays for applications to DF (Directional Findings) and ESM ?(Electronic support Measurement) system. The analysis and general understanding of the properties of circular arrays has progressed steadily for many years and the most significant development were probably made by several groups of workers in 1990s when the concept of phase mode excitations was developed. The lack of applications in the past is probably due to the fact that the basic problems of exiting circular arrays with the correct values of amplitude and phase are, in general, more complex than for linear array. Furthermore, electronic scanning of directional patterns for circular arrays may be difficult to implement and require both the amplitude and phase of each elements of the circular array to be changed. The basic symmetry of circular array offers a number of advantages, which in addition to the 360°scan angle already mentioned can includes an ability to compensate for the effect of mutual coupling by breaking down the array excitations into a series of symmetrical spatial components. This can also give to directional patterns which remains constant in shapes over broad bandwidths. These advantages, together with new and more convenient methods of array phasing, are beginning to increase interest in such arrays for a number of potential applications. 5

Early works on circular arrays related to their applications for directional findings and their ability to produce omnidirectional coverage from a cylindrical configurations’ of elements wrapped around a central mast or support structures. This latter was applied in broadcast antenna to avoid shadowing from the basic mast structures which supported the antenna. In this case controlled excitation of the vertical aperture is used to achieve the desired patterns in the vertical plane. This is generally achieved by stacking multiple rings of circular arrays. Other circular array applications have included Wullenweber arrays for direction finding, wide band width HF communications arrays, Wrap-around antenna ship borne communications, navigational aids, spacecraft antenna, and null steering antennas for mobile communications and wide-bandwidth microwave direction-finders. In the fields of radar systems there have been several experimental circular arrays aimed at achieving 360° electronic scanning concepts applied to fairly small apertures containing perhaps 16 or 32 elements. The problems of high-power feeding and phasing for circular array still represent a significant restriction on this type of applications, particularly for wideband operations. For the radar field there is, nevertheless, the possibility of designing circular arrays For reciving only, where the problems of phasing can more easily be achived by array signal processing techniques. There has also been a limited application or circular array configurations to sonar systems although the published materials available in this field is far more limited. In general, the circular array, in which the elements are placed in a circular ring, is an array configuration of very practical interest. Over the years, applications span radio direction finding, air and space navigation, underground propagation, radar, sonar, and many other systems. More recently, circular arrays have been proposed for wireless communication, and in particular for smart antennas. Using circular array for smart and DOA antenna have many advantages:     

Scan beam in any direction, in contrast to linear array. Provides elevation and azimuth coverage possess azimuthal symmetry, and pattern does not change very much when scanned symmetrically. Elements are continuous; those no discontinuity in the distributions and thus possible lower side lobe. Can utilize basic phasing techniques, like linear arrays, to scan the beam. Despite of diametrical elements, which would indicate intense coupling circular arrays possess low coupling because of symmetry which permit the breakdown of the array into a series of symmetrical a spatial component.

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3.3 Geometry of Circular Array Antennas In the circular array, the elements are placed in a circular ring with N number of equally spaced elements. In current wireless communications, circular arrays have been proposed for the smart antenna applications. These circular arrays have the ability to scan a beam azimuthally through 3600 with little change either in the beam width or side lobe level. The geometry of an N-element circular array antenna is shown in Figure1.

Figure 3.1: Geometry of an N-element circular array

3.4 Array Factor Refeerring to Figure 1, let us assume that N isootropic elements are equally spaced on the xy plane along a cirrcular ring of the radius a. The normalized field of the array can be written as

where Rn is the distance from the nth element to the observation point. in general

For r>>a, the above equation reduces to

In a rectangular coordinate system, 7

Therefore,

Or

For the amplitude term, the approximation

is made. Assuming the approximations of the above two equations are valid, the far-zone array field is reduced to

where an is the complex excitation coefficient (amplitude and phase); ɸ𝑛 = 2πn /N is the angular position of the n-th element. In general, the excitation coefficient can be represented as

𝑎𝑛 =𝐼𝑛 𝑒 −𝑖𝑎𝑛 Where 𝐼𝑛 is the amplitude term and 𝑎𝑛 is the phase of the excitation of the n-th element relative to a chosen array element of zero phase,

The AF is obtained as

The above expression represents the AF of a circular array of N equispaced elements. the maximum of the AF occurs when all phase terms in equal unity, or 8

The principal maximum (m = 0) is defined by the direction (0 ,ɸ0 ), for which if a circular array is required to have maximum radiation in the direction (0 ,ɸ0 ). The AF of such an array is

3.5 Circular array (far field)

Figure 3.2: Geometry of an N-element circular array for far file

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The total field for circular array

for phase for amplitude

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CHAPTER FOUR RESULTS AND DISCUSSIONS 4.1 Matlab Simulation and Analysis This Mat-lab simulation gives us the detailed explanation and understandings of the characteristics of circular array antenna and it is also used to evaluate the performance based on the different inputs like number of elements, distance between each element in lambda and the radius of the circle. The general constituent of the code we used to design array antennas are presented based on the following algorithms. Table 4.1: simulation algorithm

Cases

Parameters

Sketched output

Case 1

Phi=60°, theta=45°,

Plot and polar plot

Radius of circle a=1 Number of elements, N=5, 10, 15

Case 2

Theta=45°, 𝑝ℎ𝑖 = 60°

Plot and polar plot

Vary a in terms lambda

4.2 Simulation Results This simulation of circular array antenna is based on the amplitude, array factor total directivity and the half power band width in which some of them are given in numerical Values and the others are provided in diagrammatical illustrations. The results are classified according to the input parameters such as; Nvariable, constant radius; constant- N, variable-radius. 4.2.1 Variable input N, constant-a In section, the simulation results obtained bay varying the value of a are presented. Here, the radius of the circle and the phase angle are taken be constant. Specifically, the value of N was varied from 5to 15 while the value of ‘a’ and theta were taken 1 and 45°respectively. First the performance of the circular array antenna is studied. Here the values taken for simulation are: the number of elements N=5, the radius of the circle is a=1, the angle theta=45° and phi=60°. In order to seen the effect in the performance of the circular array vary the number of elements and radius of the circle. In addition to this to the phase shift can also vary the theta and phi angle value.

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(a)

(b) 12

(c)

(d) 13

(e)

(f) Figure 4.1 a) Array pattern (N=5, a=1) b) Power [dB] pattern (N=5, a=1) c) Polar plot of array pattern (N=5, a=1) d) Polar plot for power pattern in dB (N=5, a=1) e) Polar plot of element normalized E-fields, f) Polar Array factor and total E-fields in dB (N=5, a=1)

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Now vary the number of elements with a constant radius of a circle and phase angle shift. Here the value take for simulation is N=10, a=1, theta=45° and phi=60°.

(a)

(b)

15

(c)

(d) 16

(e)

(f) Figure 4.2 a) Array pattern (N=10, a=1) b) Power [dB] pattern (N=10, a=1) c) Polar plot of array pattern (N=10, a=1) d) Polar plot for power pattern in dB (N=10, a=1) e) Polar plot of element normalized Efields, f) Polar plot array factor and total E-fields in dB (N=10, a=1)

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(a)

(b)

18

(c)

(d)

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(e)

(f) Figure 4.3 a) Array pattern (N=15, a=1) b) Power [dB] pattern (N=15, a=1) c) Polar plot of array pattern (N=15, a=1) d) Polar plot for power pattern in dB (N=15, a=1) e) Polar plot of element normalized Efields, f) Polar plot array factor and total E-fields in dB (N=15, a=1)

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4.2.3 Variable input a and constant N In section, the simulation results obtained bay varying the value of a are presented. Here, the number of antenna elements and the phase angle are taken be constant. Specifically, the value of ‘a’ was varied from 1to 2 while the value of N and theta were taken 10 and –45°respectively.

(a)

(b)

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(c)

(d)

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(e)

(f) Figure 4.4: a) Array pattern (N=10, a=2 and theta=-45°) b) Power [dB] pattern (N=10, a=2) c) Polar plot for power pattern in dB (N=10, a=2) d) Polar plot of element normalized E-fields, array factor and total E-fields in dB (N=10, a=2) e) polar plot of the element pattern, f) polar plot of the normalized E field the and the normalized array factor. 23

4.3 Discussions on the result The element radiation pattern is chosen to be non-directional which is isotropic radiator. Then in this case, the array radiation pattern will be totally determined by the array factor AF. In the first case figure 4.1(a) shows the array pattern of the circular array with one large beam width and other grating lobes almost the same grating lobes with the main beam width and figure 4.1(b) shows the power pattern with the same pattern distribution. Therefore, the normalized E- field and the normalized array factor of circular array antenna which has N= 5 elements with radius of the circle a=1 have similar plot given in figure 4.1(e) that shows the grating lobes are larger. In reference figure 4.2(a-f) shows have the same number of the grating lobe with figure 4.1but the beam width of the grating lobe N=10 is narrow than N=5 elements. In reference figure 4.3 the number of elements increased from N=10 to N=15 with a constant radius of a circle a=1. In that case have better radiation distribution than the N=5 elements and also lower grating lobes with narrow beam width of grating lobes. In addition to these the phase angle also varies it direction. Depend on theta and phi angle. So we can steer the beam in different direction. Therefore, the array factor plots sketched for different number of elements with a constant radius of a circle we can decrease the grating lobes until some extent. But, further increasing the number of element has no any effects on the minimization of the grating lobes. In the other hand, if we increase the radius of a circle with a constant number of elements the grating lobe is increased and also the beam width of the grating lobe is wide. But, it can be more directive and narrow beam width.

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CHAPTER FIVE CONCLUSION 5.1 Conclusion This project described the performance of circular arrays of directional antennas. Also, we have seen that circular array antennas are a very important parts of today’s communications system. The basic symmetry of circular array offers a number of advantages, which in addition to the 360°scan angle already mentioned can includes an ability to compensate for the effect of mutual coupling by breaking down the array excitations into a series of symmetrical spatial components. This can also give to directional patterns which remains constant in shapes over broad bandwidths. From the result obtained we can conclude that increase in the number of elements with a constant radius of circle can minimize the grating lobes whereas increasing a radius of circle with constant number of elements can’t minimize the grating lobes rather than it can be more directive and wide grating beam width. Generally, we can conclude from the result that is obtained the grating lobes and the number of elements have a slightly directly relationship. The circular array antenna has high HPBW.

5.2 Recommendation The rather limited number of applications for circular arrays has been mainly due to the problems and complications of array excitation and been rotation. In the case of beam cophasal patterns this has been particularly difficult and, in general, has been solved by multiple beams or mechanical rotating goniometer. we recommend to use circular array antenna on the following area 1. Communication application 2. Radar application 3. Circular array in direction finding

5.2.1 Communication application Circular array has been used for many years in the HF band for both communication and direction finding the systems. Employ beam cophasal excitation with time delay compensation to achieve broad bandwidth operation. The elements are usually a monopole or a combination of driven and parasitic elements. multi octave performance can also lead to two separate circular arrays covering different parts of the band.

5.2.1 Radar application It is, perhaps, not surprising that circular array have not yet been applied in operational radar systems since the extent of application of electronically-steered linear arrays is still quite limited. nevertheless, several experimental systems and sub systems have been constructed. These have included an array employing diode switching of signals, constructed by wheeler laboratories, and a further switching scheme which could

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also rotate an amplitude taper, developed by the noval electronic laboratory. such switching systems have tended to be complex, particularly where amplitude tapers have been involved. 5.2.3 Circular array in direction finding The simplest example of a circular array used for DF application is probably the 4 or 5 element array used for cathode ray direction finding systems (CRDF). Four dipole elements form a square and are excited as two pairs. A single dipole (or monopole) located in the center of the square is used as a phase reference to remove the 180◦ ambiguity of arrival. these systems are used to provide instantaneous display to air craft controllers of the bearing of an aircraft via the VHF voice link.

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REFERENCES [1] (Robert e. Collin, “Antennas and Radio Wave Propagation”, Mc Graw-Hill, 1985) [2] (John d. Kraus, Antennas, McGraw-Hill, New York, 1968) [3] (C. A. Balanis, Antenna Theory, Analysis and Design, John Wiley & Sons, Inc., New Jersey, 2005.) [4] W. L. Stutzman and G. A. Thiele, Antenna Theory and Design, Wiley, New York, 1998. [5] Matthew o. Sadiku, Elements of electromagnetic, 2nd edition, 1990.

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