Methods for Improving the Transmission-Conversion Efficiency From Transmitting Antenna to Rectenna Array in Microwave Power Transmission

This letter describes two methods for improving the transmission-conversion efficiency in microwave power transmission (MPT). On one hand, according to the obtained formula, the transmission-conversion efficiency can be improved by optimizing the amplitude distribution and phase distribution on the aperture of the transmitting antenna. On the other hand, when the distribution of the aperture is fixed and the equal amplitude with in-phase distribution is taken as an example, the transmission-conversion efficiency can also be improved by adopting nonuniform rectenna array. The transmission-conversion efficiency formula is rederived for this case since the size of partial units increases. Lastly, an MPT system is established, and the corresponding transmission-conversion efficiencies are calculated. Compared with the initial case where the transmitting antenna has an equal amplitude with in-phase aperture distribution and the receiving aperture is composed of a uniform rectenna array, the obtained transmission-conversion efficiencies of optimizing aperture distribution and nonuniform rectenna array increased by 25% and 24.9%, respectively. However, if the transmitting antenna is far from the rectenna array, the transmission-conversion efficiencies in these three cases tend to be the same.

I. Introduction

Microwave power transmission (MPT) has received much attention in recent decades. As a special way to transfer energy over long distances, MPT can deliver energy for mobile platforms and to some areas where it is difficult or impossible for people to reach [1]– [3]. In the design of MPT system, efficiency is one of the most important indexes. Many methods have been studied to improve the efficiency of MPT. The aperture distribution of the transmitting antenna is optimized to improve the ratio of power irradiated on the receiving aperture [4], [5]. Besides, flat beampattern in the near field is designed to improve the total microwave–dc efficiency of rectenna array [6]. The study on improving the maximum conversion efficiency of rectenna unit has been done for a long time [7], [8]. However, the methods used to improve MPT efficiency are only concerned with one aspect of MPT and are not comprehensive enough.