Simultaneous Improvement of array factor directivity and side lobe level of time‐modulated linear antenna arrays using opposition‐based harmony search algorithm

Abstract

SummaryIn this paper, simultaneous improvement of array factor directivity and side lobe level of time‐modulated linear antenna arrays using opposition‐based harmony search algorithm has been dealt with. Because of the periodic function of switching time, the same antenna array will radiate at fundamental (center) frequency as well as its harmonic frequencies. The first two harmonic frequencies are (f0 + Fp) and (f0 + 2Fp), where f0 and Fp are operating frequency and pulse repetition frequency, respectively. Four case studies have been adapted; Case‐1: optimal switching time sequence of each element; Case‐2: optimal switching time sequence of each element and optimal non‐uniform inter‐element spacing; Case‐3: optimal switching time sequence of each element, optimal excitation phase of each element, and optimal uniform inter‐element spacing; Case‐4 refers to optimal switching time sequence of each element and optimal uniform inter‐element spacing. Simulation results reflect that Case‐4 outperforms Case‐1, Case‐2, and Case‐3. The objective function was judiciously chosen in such a way that it can simultaneously improve the array factor directivity as well as side lobe level. Considered for the analysis was 16‐element linear antenna array. Various simulation results are presented showing better side lobe performance, better side band performance, and improved array factor directivity with respect to the uniform array having the same number of elements. The numerical results show the power radiated by any harmonic frequency is less as compared with the power radiated at the center frequency called the fundamental frequency. It has also been observed that as the harmonic frequency increases, sideband level and power radiated by the antenna at its harmonic frequency decrease. Copyright © 2015 John Wiley & Sons, Ltd.