Retro-reflective Beamforming based on a Frequency Division Scheme for Microwave Power Transmission to Multiple Targets

This paper presents an experimental retro-reflective beamforming system for wireless power transmission to multiple targets (with “targets” standing for “wireless power receivers” in this paper). In our experiments, each target broadcasts a pilot signal at a unique frequency. The pilot signals from multiple targets are received by a wireless power transmitter. After analyzing the pilot signals, the wireless power transmitter configures one power beam toward each target at its pilot signal's frequency based on phase-conjugation. With a digital beamforming circuit architecture, multiple retro-reflective beams at multiple frequencies can be formed simultaneously. Experimental results demonstrate that the proposed retro-reflective beamforming scheme based on frequency division could track multiple targets' location and construct multiple power beams accordingly.