An optimal far-field radiation pattern synthesis of time-modulated linear and concentric circular antenna array

In this paper, an optimal far-field radiation pattern synthesis by using time modulation technique is carried out for linear antenna array (LAA), and concentric circular antenna array (CCAA) designs using a stochastic optimization method called grey wolf optimization (GWO). An improved far-field radiation characteristic mainly depends on the synthesis of low side lobe level (SLL) and narrow first null beam width (FNBW). A low SLL is a requirement to reduce the interference by the other systems operating in the same frequency band. A narrow FNBW is necessary to obtain a high directivity. In time modulation technique, "time" has a most significant role. It is considered as the fourth-dimensional parameter as it plays the role of an additional degree of freedom to achieve an improved radiation pattern. The time-modulated antenna array (TMAA) radiates at various harmonic frequencies for the periodic switching time sequence. In this paper, the generation of radiation pattern only at the fundamental/central frequency and at its first two harmonic frequencies are considered. The GWO algorithm is a flexible and robust search algorithm and is applied here to find out the optimum sets of switching on-time duration for each array element and to determine the optimum inter-element separation between two array elements of the 16-element time-modulated linear antenna array (TMLAA) and the nine-ring time-modulated concentric circular antenna array (TMCCAA). The GWO algorithm-based results show a substantial improvement in far-field radiation pattern synthesis compared with the uniform radiation pattern and those of the methods reported in state-of-the-art literature.