An active retrodirective antenna element for circularly polarized wireless power transmission

This paper presents a novel retrodirective array (RDA) circuit and antenna system for microwave wireless power transmission. Thanks to the principle of phase conjugation in mixers, retrodirectivity can be achieved in the far-field. More specifically, the proposed architecture in this article deals with an active transmitter module to retrodirect a received tone, with increased power, from a mobile unit and with circularly polarized (CP) radiation. Initial simulations predict an error below 4° with respect to the desired retrodirected phase at a different transmit frequency. In order to achieve this operation, it is necessary to use notch filters before and after the mixers, basically to avoid improper signal phase conjugation as well as unwanted signal re-radiation. To the authors' knowledge none of the reported RDAs designs found in the literature are able to provide similar functionality in terms of compactness and planar implementation as well as CP operation. Other applications for the proposed RDA circuit element include target tracking, low-cost sensor charging, and other wireless systems.