In this paper we investigate the possibility to generate a multisine signal source, to enhance conversion efficiency in low-power wireless power transfer scenarios. A time modulated array composed by three microstrip patch antennas operating at 868 MHz is chosen. The time modulation is performed by 3 switch diodes, one for each antenna, with properly designed periodic on/off sequences of period equal to 1μs. The multisine behavior of the radiated field is obtained by exploiting the intrinsic generation of sideband harmonics, with 5 frequency bins equally spaced by 1 MHz all directed toward the broadside direction. To obtain this behavior, we design the modulation sequences with a genetic algorithm to produce a broadside radiation at the fundamental and the desired higher harmonics. Realistic antenna radiation patterns for the array structure are simulated with CST Microwave Studio and used as input of the optimization procedure. Preliminary results show the feasibility of the proposed concept.