Electrically small array for microwave energy harvesting

In this paper, we propose a three-dimensional antenna resonator consisting of a pair of inverted L-shaped wires sharing a common part, a continuous metallic ground slab, and a coaxial port loaded with a lumped matching resistor to mimic the input impedance of a rectifier. Such a resonator array can function as an efficient RF energy receiving aperture in the long-distance wireless power transmission system. Unlike the conventional receiving array, where the distance between adjacent elements is half wavelength to reduce the mutual coupling, here the distance between the receiving elements is electrically very small to achieve good impedance matching between free space and energy output port. An equivalent circuit model is proposed to explain the energy capture mechanism. Simulation results show that near unity energy capture efficiency at resonant frequency is obtained under incidence of both normal and oblique incident wave.