Research Article A Comparative Study on Sideband Optimization in Time-Modulated Arrays Ertugrul Aksoy and Erkan Afacan Department of Electrical & Electronics Engineering, Faculty of Engineering, Gazi University, 06570 Ankara, Turkey Correspondence should be addressed to Ertugrul Aksoy; ertugrulaksoy@gazi.edu.tr Received 29 November 2013; Accepted 19 March 2014; Published 29 April 2014 Academic Editor: Paolo Rocca Copyright © 2014 E. Aksoy and E. Afacan. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A comparative analysis of the three diferent methods known as sideband level suppression (SBL), sideband radiation suppression (SR), and sideband bound suppression (SB) which are used in sideband calculations for time-modulated arrays (TMAs) is presented. he three methods are investigated in terms of sideband level, sideband power, time average directivity, and solution time for TMAs so as to show the performances and potentialities of these distinct techniques. he problems of interference suppression, sidelobe cancelling, and joint interference suppression and sidelobe cancelling are analyzed for a time-modulated linear array. In the linear array 30 elements are used and the interelement spacing is determined to be a half-wavelength. During the investigations, diferential evolution (DE) algorithm is chosen as the optimization tool. he common variable aperture size (VAS) time schemes are optimized to synthesize the desired goals in order to compare the techniques. he results show that the SB method is more convenient than the other two compared methods. 1. Introduction he application of time as a fourth design parameter has been irst suggested by Shanks and Bickmore in the late 1950s [1]. his irst work has been followed by the work of Kummer et al. in 1963 in which time parameter is used to obtain an ultralow sidelobe pattern for a linear 8-element slot array [2]. Ater these works the time parameter has begun to be used for the improvement of the properties of antenna arrays [3]. he research in this area has gained acceleration especially with the advancement of calculation speed and with the emergence of new optimization techniques in the early 2000s. he irst works were about obtaining the desired pattern at the operating frequency and controlling sidebands simultaneously [4–8] and also about investigating several switching sequences such as variable aperture size (VAS) [9], pulse shiting [10], and pulse splitting [11–14]. Also the time modulation implementation of several optimization methods such as diferential evolution (DE) [4, 5], particle swarm optimization (PSO) [6], or simulated annealing (SA) [7] may be considered amongst the early studies. Time modulation has been also used in interference suppression and adaptive beamforming applications [15–18]. Sidebands occurring due to the periodic nature of time modulation are generally evaluated as a loss in many standard applications, but in the work of Tennant and Chambers, it is shown that these sidebands can be used on purpose [19]. Firstly, it is proposed that for a two-element time-modulated array a steerable deep null at the irst harmonic frequency can be found and used in direction inding applications [19], and then this is proved experimentally in [20]. Later Li et al. have suggested that the main beam of the irst harmonic can be steered without using phase shiters and can be used for communications [21]. Other direction inding applications using time modulation are given by Li et al. [22] and Hong et al. [23]. Recent studies about time modulation can be expressed as follows: gain improvement by using single- pole double-throw switches is investigated in [24]; relector arrays with time modulation are investigated in [25]. he optimization of switching durations so as to maintain main beam directivity constant is given in [26]. Instead of switching functions with ideal rectangulars, more realistic modellings Hindawi Publishing Corporation International Journal of Antennas and Propagation Volume 2014, Article ID 290737, 14 pages http://dx.doi.org/10.1155/2014/290737