Array thinning, sideband analysis and pulse optimization for time modulated antenna arrays

The subject of time modulated antenna arrays is already a hot research topic. In time modulation, switching causes sidebands to occur and these sidebands are generally considered as loss. Usually this wasted power is aimed to be suppressed and these process is made via sidelobe-like calculations. In this study an inequality which can be used for the suppression of sidebands of time modulated arrays is derived and by using this inequality time consuming calculations are aimed to be simplified. Considering the radiated total time average power, sideband radiation under symmetric pulse distributions is examined in the literature. It is shown in this study that the expression given in the literature for symmetric pulse distributions is not valid for the asymmetric cases. This expression is generalized to linear and planar arrays placed on an arbitrary grid, under asymmetric pulse distributions, in a way to cover the older forms. By this way, the computability of time average total power radiated at sidebands, which was incalculable for asymmetric pulse distribution, is achieved.An array thinning method for time modulated arrays is proposed. It is shown that linear and planar arrays can be thinned directly by using a penalty function via a continuous optimization process without using a binary mask. Differential evolution algorithm is selected as the continuous optimization tool. The proposed method is compared with binary optimization methods and thinning procedures encountered in the literature.Pattern nulling in time modulated antenna arrays is examined and it is shown that sideband radiations must be taken into account for time modulated arrays. A two-step optimization procedure is proposed and the applicability of this procedure is shown by examples and simulations.Sideband suppression with pulse splitting under static fundamental radiation is investigated. It is shown that splitting the pulses produces 3 dB better results than pulse shifting, which is known as the best sideband suppression method. Generally it is accepted that the first sideband is always bigger than others. Simulations have shown that this idea is not always true for pulse splitting. Pulse splitting is also shown to provide independent sideband control.Key Words : Antenna arrays, Time modulation, Sideband radiation