Optimization for Spherical Phased Array Antenna

The main feature of the phased array antenna is its ability to control the amplitude and phase excitation of each radiating source in order to form and scan the main beam by electronic control without any mechanical contributions. The phased array is composed of a group of element sources which are distributed and oriented in a linear, two or three dimensional configurations. A comprehensive computer program is developed using matlab software to perform the analysis of linear array (uniform and nonuniform amplitude), planar array, circular array and spherical array to draw the field patterns for the different versions of phased array antennas. The basic parameters of the phased array antenna are calculated and analyses to discuss their effects on beam shaping. Spherical phased array has been developed as three dimensional configurations to perform and enhance maximum beam steering. The general equation for spherical phased array (SPA) antenna is derived. The program GPA–2D can draw the array factor in 2Dimension with respect to linear (uniform and nonuniform amplitude), planner, circular and spherical phased array antennas. However, the program GPA– 3D can draw the array factor in 3Dimension with respect to planar, circular and spherical phased array antennas. Analysis of developed spherical phased array antenna and optimization technique is performed to enhance beam steering capabilities to get the optimized results for 5-sections and 7-sections of SPA antenna (Broad side array). KeywordsPhase Array Antenna, Matlab, Linear Array , Plannar Array , Circular Array, Spherical Phase Array 1.Introduction An antenna acts to convert guided waves on a transmission structure into free space waves. As part of a transmitting or receiving system, it is designed to radiate or receive electromagnetic waves. Phased array antennas play a major role in the recent and future advanced radars and communication systems [1]. Basically, the phased array is composed of a group of element sources which are distributed and oriented in a linear, two or three dimensional configurations. The main feature of the phased array antenna is its ability to control the amplitude and phase excitation of each radiating source in order to form and scan the main beam by electronic control without any mechanical contributions [2]. The total field of the array is determined by the vector addition of all fields radiated by the individual elements. To provide very directive patterns, it is necessary for these fields to interfere constructively (add) in the desired direction and Interfere destructively (cancel each other) in the remaining space. We introduce the parameters that characterize the antennas and then array elements and feeding Structures for Phased Arrays [5]. The basic parameters of the phased array antenna are the array factor, radiation pattern, directivity, beam width and impedance [2]. These parameters can be controlled by a number of controls that can be used to shape the overall pattern of the antenna. These parameters are the geometrical configuration of the overall array ( linear, planar, circular, and spherical ), the relative displacement between the element sources, the excitation amplitude of the individual elements, the excitation phase shift of the individual elements, and the relative pattern of the individual elements. To simplify the presentation and give a better physical interpretation of the techniques, a two-element array has first been considered and Pattern Multiplication takes place. The analysis of uniform and nonuniform linear arrays with any desired number of elements is discussed with maximum radiation that can be oriented in any direction to form a scanning array [3]. In addition to placing elements along a line (to form a linear array), individual radiators can be positioned along a rectangular grid to form a rectangular or planar array [3]. Planar arrays provide additional variables which can be used to control and shape the pattern of the array. Planar arrays are more versatile and can provide more Optimization for Spherical Phased Array Antenna www.irjes.com 55 | Page 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. The spherical phased array antenna (SPA) is designed to operate in microwave range in order to maximize beam steering [4]. The spherical phased Array antenna is composed of identical feeding sources distributed over the surface of a sphere. Proposed spherical array model is adopted using the Array Factor equation ) , (   AF for general spherical phased array antennas, where it can be segmented into many sections with each one as a circular array. The general equation for spherical phased array (SPA) antenna is derived. A comprehensive computer program is developed using matlab software to perform the analysis for different phased array configurations such as linear array (uniform and nonuniform), planar array, circular array and spherical array, including calculation and drawings of the array factor, then optimizing the spherical phased array (SPA) antenna of 5-sections and 7-sections, respectively. 1.1Antennas and phased Array antenna In addition to receiving and transmitting energy, an antenna is usually required to direct the radiated energy in some directions and suppress it in others. Arrays of antennas can be arranged in space and inter-connected to produce a directional radiation pattern. Such a configuration of multiple radiating elements is referred to as an ARRAY ANTENNA. Rather than increasing the size of an antenna to get more directive characteristics, we use an assembly of radiating elements in an electrical and geometrical configuration to achieve this goal. Basically, the phased array antenna is composed of a group of individual radiators which are distributed and oriented in a linear, two or three dimensional spatial configurations. The amplitude and phase excitations of each radiator (element) can be individually controlled to form a radiated beam of specific desired shape in space. The position of the beam in space is controlled electronically by adjusting the phase of excitation signals of the individual radiators. Hence beam scanning is accomplished with the antenna structure remaining fixed in space without the involvement of mechanical motion in the scanning process. 1.2 Linear Phased Array Antenna The total field of the array is determined by the vector addition of the fields radiated by the individual elements. This assumes that the current in each element is the same as that of the isolated element. This is usually not the case and depends on the separation between the elements. To provide very directive patterns, it is necessary that the fields from the elements of the array interfere constructively (add) in the desired directions and interfere destructively (cancel each other) in the remaining space. Ideally this can be accomplished, however practically it is only approached. In an array of identical elements, there are five 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 5. The relative pattern of the individual elements. 1.2.1 N-Element Linear Array Uniform Amplitude and Spacing Now the arraying of elements has been introduced and it was illustrated by the two-element array, let us generalize this method to include N elements. Referring to the geometry of Figure 2.2(a), let us assume that all the elements have identical amplitudes but each succeeding element has a progressive phase lead current excitation relative to the preceding one (  represents the phase by which the current in each element leads the current of the preceding element). An array of identical elements all of identical magnitude and each with a progressive phase is 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 n single element. This is the pattern multiplication rule of equation (1.5), and it applies only for arrays of identical elements. Optimization for Spherical Phased Array Antenna www.irjes.com 56 | Page E(total) = [E(single element at reference point)] × [array factor] (1.5) Figure 2.2, Far-field geometry and phasor diagram of N-element array of isotropic sources positioned along the z-axis The array factor is given by ) cos )( 1 ( ) cos ( 2 ) cos ( ... 1                 kd N j kd j kd j F e e e A       N n kd n j F e A 1 ) cos )( 1 (   (1.6) which can be written as [3],