Subarrayed time-modulated arrays with minimum power losses

In recent years, several works have been devoted to show the potentialities of time-modulated arrays (TMAs) [1][2]. It is now well-established that TMAs synthesize low-sidelobe average patterns by using a set of simple on-off radio-frequency (RF) switches that modulate the static excitation weights. Moreover, a fast and simple control of the radiation pattern is enabled by just modifying the pulse sequence of RF switches. By exploiting this latter property, it would be of great interest for practical array applications the possibility of reconfiguring the pattern just modifying a reduced number of control elements [3][4] in order to simplify the overall feeding network architecture. Towards this end, this work presents an innovative two-step strategy for the synthesis of sub-arrayed time-modulated antenna arrays where RF switches are used at the sub-array level. The problem is formulated as the retrieval of the “best” sub-arraying configuration and pulse sequence generating a desired pattern at the working frequency with minimum power losses in the harmonic radiations (called sideband radiation -SR) generated by the periodic modulation of the static array excitations. At the first step, the sub-array configuration is determined by means of a “pulse matching” approach that exploits the guidelines of the Border Element Method (BEM) presented in [5] and recognized for its effectiveness in dealing with both small and large arrays. At the second step, a strategy based on a Particle Swarm Optimizer (PSO) has been used to determine the pulse sequence minimizing the amount of the power losses where an effective analytical relationship [6] has been taken into account to count the energy in the SR.