Target Localization Based on Intermodulation Feedback for Multisine Wireless Power Transmission Using a Time-Modulated Array

To achieve accurate power feeding to a terminal (e.g. rectenna) in the far-field wireless power transmission (WPT), a new method is proposed to locate the terminal so that the base station can adaptively adjust its beam steering and transmitting power to satisfy the high-efficiency power conversion conditions of the rectifier. In this work, the generated intermodulation (IM) signal at rectenna under multisine incidence is employed to establish the feedback link with the base station. A linear time-modulated array (TMA) is exploited to generate two-tone multisine wave by the optimized modulation sequence thanks to its multi-beam radiation behavior at the base station side. In the terminal end, the IM signal is spontaneously produced due to the nonlinearity of power rectifying under two-tone incidence and employed as the feedback. To highly isolate the two tones and IM signal, a dual linear polarized (DLP) antenna is designed to ensure a compact system design for both sides. By this way, the feedback IM signal carrying the terminal's direction and distance information is sensed by orthogonally polarized antenna pairs. Then the direction of terminal is obtained by the proposed high-accuracy direction of arrival (DoA) estimation method using a multi-baseline TMA, which is realized by a two-stage single-pole-double-throw (SPDT) switching network. Regarding the imperfection of RF switches, a compensation method is proposed. With estimated DoA, the distance between terminal and base station is evaluated based on the received signal strength indicator (RSSI) method. To verify the feedback mechanism, a prototype is fabricated and tested.