Radiative Wireless Power-Transfer System Using Wideband, Wide-Angle Slot Arrays

This paper analyzes the benefits of using wideband, wide-angle arrays in radiative wireless power-transfer systems. A physical optics (PO) code is used to investigate the focusing capabilities and operating range of two 2-D antennas: Van Atta arrays and phase-conjugate/time-reversal arrays. In the PO analysis, the antennas are assumed to be ideal mirrors, which do not backscatter the impinging energy but rather completely absorb and reemit it. Sources located in both the near and far field of the antennas are considered. It is shown that for distances larger than the mirror size, the two antennas have similar focusing capabilities. In such scenarios, a Van Atta approach is preferred over a phase-conjugate approach due to its ease of implementation. Antenna elements used to realize these arrays/mirrors are typically resonant and exhibit strong backscatter, a limited field of view, and small bandwidth. To overcome these limitations, we propose an array/mirror consisting of long slots fed by parallel plate waveguides. A spectral Green's function approach is used to derive the scattering performance of the infinite array in reception. It is shown that the array can collect the total power impinging from a remote source over a large field of view and bandwidth. The conclusions arrived at for the infinite case are extended to the finite case through full-wave simulations. It is shown that the array can refocus the energy impinging from a close source over a large bandwidth. An infinite magnetic line source is considered as an example. An accurate expression is provided for the voltage distribution across the feed lines of the array. The proposed solution paves the way toward the practical implementation of ideal Van Atta and time-reversal/phase-conjugate mirrors. The wideband behavior of the array may enable high-power, pulsed retrodirective arrays.