A nonuniformly spaced linear antenna array with broadside radiation characteristics is synthesized using firefly algorithm and particle swarm optimization. The objective of the work is to find the optimum spacing between the radiating antenna elements which will create a predefined arbitrary radiation pattern. The excitation amplitudes of all the antenna elements are assumed to be constant. The optimum spacing between the array elements are obtained using firefly algorithm. The minimum allowed distance between the antenna elements is defined in such a way that mutual coupling between the elements can be ignored. Numerical analysis is performed to calculate the far-field radiation characteristics of the array. Two numerical examples are shown to form two different desired predefined radiation patterns. The performance of the firefly algorithm and particle swarm optimization is compared in terms of convergence rate and global best solution achieved. The performances of the optimized nonuniformly spaced arrays are analyzed. Finally, contour plots of the radiated power from the optimized array in the horizontal plane and vertical plane in the far-field region are provided. 1. Introduction Multiple antennas can be arranged in space in various geometrical configurations to form an antenna array with highly directive radiation pattern [1, 2]. The radiation characteristics of the antenna array depend on some input parameters. These parameters are the relative magnitude and phase of the excitation current of each radiating element, radiation characteristics of each radiating element, the geometrical configuration of the array, and the separation distance between the array elements [2]. An antenna array can be designed to produce almost any arbitrary prescribed pattern by controlling these parameters. For this reason, antenna arrays find application in RADAR and wireless communication systems [3, 4]. Most antenna arrays are designed to produce a directive beam at a particular direction and while keeping the sidelobe level (SLL) small to avoid interference with other radiating sources. In most cases, this is achieved by controlling the magnitude and phase of the excitation amplitudes [5, 6]. In most cases, a relatively simple geometry is considered where the distance between two consecutive radiating elements is constant. However, exact control of phase and magnitude of excitation current of array elements requires complex and expensive electronic circuitry [4]. In case of phased arrays, where the direction of the main beam needs to be controlled electronically in
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