Retro-reflective Beamforming to Multiple Targets Based on Time-reversal for Microwave Power Transmission

This paper presents an experimental retro-reflective beamforming system based on time-reversal for wireless power transmission to multiple target devices. In this experiment, the wireless power transmitter with a four-element antenna array receives pilot signals from three targets, each at a unique frequency. The pilot signals containing multiple frequencies are down-converted to baseband, and then, an FPGA is used to re-verse the baseband signal in time to achieve phase conjugation of the signals at all frequencies. With a digital beamforming circuit architecture, the reversed signals are up-converted, and after amplification, fed to the antenna array. As a result, multiple ret-ro-reflective beams are formed, each at a unique frequency and toward a different target. The results show that the experimental system is able to simultaneously focus power onto three targets dynamically, which validates the effectiveness of the multi-target retro-reflective beamforming schemes.