On the Deployment of Distributed Antennas of Power Beacon in Wireless Power Transfer

Wireless power transfer (WPT) has drawn significant attention in the last decade and more and more literatures are arising on related research topics such as microwave power transfer and wireless powered communications network. The extremely low efficiency of WPT is regarded as the major bottleneck thus becoming the main task that researchers need to tackle. In this paper, we propose a novel distributed antenna power beacon (DA-PB) whose antennas are uniformly distributed on a circle with the same height when performing WPT. Closed-form expression of antenna height for DA-PB is derived to make the radio frequency (RF) electromagnetic radiation power density at any location of the charging cell lower than the safety level given by federal communications commission. In addition, we get the closed-form expression of average harvested direct current (DC) power per user in the charging cell for path-loss exponent 2 and 4. In order to maximize the average efficiency of WPT, the optimal radius for distributed antennas elements is derived when the path-loss exponent takes the typical value 2 and 4, which could be lower bound and upper bound for common path-loss exponent. Conventional colocated antenna (CA) PB is also analyzed as a benchmark for our proposed DA-PB. Simulation results verify our derived theoretical results. And it is shown that the proposed DA-PB indeed achieves larger average harvested dc power per user and efficiency of WPT than conventional CA-PB.