Multiple Beamforming Using Multi-Tone Signals for Microwave Power Transfer System

This article proposed a multiple beamforming scheme using a multi-tone for microwave power transfer (MPT). To simultaneously transmit power to multiple targets, it is necessary to form a multibeam. It can be formed by generating multi-tone signals with frequency offset in each channel of an array antenna. For
$K$
targets,
$K$
-tone signals are generated, and the directions of the formed
$K$
beams are changed by adjusting the weights of the signals. Therefore, we introduced a multi-tone modulation scheme based on a matrix calculation to express the modulated multi-tone signal for an
$M \times N$
planar array antenna (PAA). Moreover, for comparison with conventional beamforming using a continuous-wave (CW) signal, the multi-tone signal was analyzed in the time domain according to the directions of the multibeam. For verification, a
$4\times $
4 digital beamforming (DBF) system operating at 5.8 GHz capable of generating multi-tone signals in each channel was designed. Based on the relative received power, beam patterns were measured for two, three, and four beams. When 39 dBm of RF power was radiated from a transmitting antenna located 1 m from a receiver, an average RF power of 14.7 dBm was received for four beams. We confirmed that the DBF system using the proposed scheme can concurrently transmit power for up to four receivers.