An Expression for Evaluating Directivity of Non-uniform Period Time Modulated Linear Arrays

In this paper, the expression for directivity of nonuniform period time-modulated linear antenna array is obtained and its variations with inter-element spacing is presented. In the case of uniform period time-modulated array (UTMA), due to the same time-modulation frequency to each antenna element, different harmonic signals from different time-modulated elements radiate at the same frequency and accumulate in space. In contrast to UTMA, the harmonic signals of different time modulated elements in the non-uniform period time-modulated array (NTMA), are spread in space because of different modulation frequencies for the different individual elements. Therefore, the sideband power calculation, as well as the directivity calculation in NTMA, is different from that of UTMA, and this is considered for the first time in this paper.