Retro-directive beamforming versus retro-reflective beamforming for wireless power transmission

This paper studies the difference between retro-directive beamforming technique and retro-reflective beamforming technique in the context of wireless power
transmission applications. In all of our studies, a wireless power receiver broadcasts continuous-wave pilot signal, the wireless power transmitter receives and analyzes the pilot signal, and finally the wireless power transmitter transmits continuous-wave power with phase profile conjugate to that of the received pilot
signal. Our study demonstrates that, a linear equi-spaced array configuration employed by the wireless power transmitter behaves as a retro-directive beamformer when the wireless power receiver resides in the far-zone of the wireless power transmitter, whereas it behaves as a retro-reflective beamformer when the wireless power receiver is not in the far-zone. Our studies further
show that, far-zone gain could be reduced by adjusting the array’s geometrical configuration without affecting focusing in the near-zone. All the conclusions drawn in this paper are supported by numerical results as well as experimental results.