On the Design of Discrete Apertures for High-Efficiency Wireless Power Transfer

This communication deals with the design of discrete apertures (DAs) for wireless power transfer (WPT) within the Fresnel region and provides some design guidelines to enhance WPT efficiency. In fact, although the aperture excitations optimization problem, given two specific continuous or DAs, has been already researched, the effect of antenna arrays design choices (such as the number of antenna elements or their spacings) on the WPT efficiency has not been investigated yet. In order to do that, WPT efficiency formulation has been theoretically analyzed to understand the different antenna parameters contributions to the power transfer efficiency (PTE). After that, the problem of the array excitation optimization in the sense of maximum PTE has been revisited including cases with or without perfect impedance matching. Finally, different array designs and relative achievable PTEs have been compared systematically, and it is shown that arrays with interelement spacing in the order of 0.3 lambda-0.4 lambda (tightly coupled arrays) provide the largest PTE (also for oblique WPT cases) when the array excitation is calculated taking into account the impedance mismatching.