Inho Park

한국전자파학회논문지 (The Journal of Korean Institute of Electromagnetic Engineering and Science)

In this study, we propose a digital beamforming system for microwave power transfer with a real-time beam-scanning algorithm for tracking a moving receiver. To perform scanning, each channel in the transmitter generates and converts a baseband signal for the allocated beam direction based on the pilot slots in a frame structure. An initial timer reset process and a preamble are included in the algorithm to maintain time synchronization among units of the scanning period in a wireless environment. The average received power is simulated, and the optimal frame configuration is derived by considering the proportion of an energy transmission slot in the frame. For experimental verification, we design a 4 × 4 digital beamforming system operating at 5.8 GHz and a receiver. The scanning performance is experimentally validated with various numbers of scanning beams and placements of the receiver. Moreover, when radiating 16 W of RF power, an RF power of 100 mW or more is received in all sections for the scenario of the receiver moving in a 1 m distance using 1 second period beam scanning. The proposed microwave power transfer system with a real-time beam scanning algorithm is verified to track the moving receiver in a wireless environment and perform optimal microwave power transfer.

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.