Ultra-compact concurrent multi-directional beamforming receiving network for high-efficiency wireless power transfer (WPT)
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This thesis demonstrates an all-passive ultra-compact low-loss array-based beamforming rectenna array for high-efficiency wireless power transfer (WPT). The detailed circuit analysis and theoretical derivation are presented in the paper, showing that the proposed circuit can achieve full field-of-view (FoV) WPT operation with scalable array-based RF-to-DC efficiency improvement. A proof-of-concept 4-element rectenna design example at 2.4GHz is implemented in a 4-layer FR4-Rogers hybrid PCB. The compact transformer-based 4×4 Butler matrix design with at least 100× size reduction as the passive beamformer is implemented in the WPT design for supporting concurrent multi-direction beam reception. At 2.4GHz, measurement for the Butler matrix exhibits an insertion loss of 0.8dB, a return loss better than 10dB (DC-3GHz), and a peak-to-null ratio > 35dB. Then, with the proposed passive beamformer, the measurement results of the proposed WPT network achieves at least full-FoV 2.4× and a peak 3× RF-to-DC efficiency enhancement compared to conventional rectenna array design. To the best of our knowledge, this is the first complete analysis and demonstration of a compact scalable N-element array-based beamforming rectenna array network for full-FoV high-efficiency WPT.