A terrestrial microwave power transmission system is considered as an effective method for collecting natural energy. In this system, frequency dependence of the refractive index and multipath propagation due to the ground surface poses problems. In the study, a single-frequency retrodirective system was proposed with a beam pilot signal using dual-mode dielectric resonator antenna elements. The results confirmed that the beam pilot signal radiated from the entire surface of the receiving antenna and accurately used the same propagation space as that of microwave power by beam propagation method simulation. A dual-mode dielectric resonator antenna was proposed as a common array antenna element for the beam pilot signal and microwave power. This involves a cross-shaped hemispherical dielectric resonator structure, and an isolation level exceeding 60 dB was experimentally measured between the orthogonal ports of the fabricated antenna. The dual-mode dielectric resonator antenna with an isolation exceeding 60 dB was successfully developed as an enabling device to realize a single-frequency retrodirective system with a beam pilot signal.

Voltage doubler rectifiers are usually applied to systems with high voltage and low current requirement. An X band voltage doubler rectifier has been developed with 72% conversion efficiency. To the best of our knowledge, the obtained rectifying efficiency is the maximum reported to date at X band with Schottky diodes. The working characteristics of the diodes in the voltage doubler rectifier are analyzed in detail. Closed-form equations of diode input impedance and rectifying efficiency are presented and validated using Advanced Design System simulations. The matching network design of the proposed rectifier is based on the closed-form equations. The preliminary rectifying efficiency is predicted by the closed-form equations as well. Measured and simulated results are in good agreement.

A novel wireless sensor network system with compatibility of microwave power transmission (MPT) using a Gallium Nitride (GaN) power amplifier has been fabricated and tested. The sensor node operates using electrical power supplied by the MPT system. Time- and frequency-division operations are proposed for the compatibility. Under the frequency-division operation, receiving signal strength indicator of −85 dBm and packet error rate of <1% were measured when the available DC power of a rectifier with 160 mW output power. Under 120-min measurement, sustainable power balance between radio-frequency–DC conversion and power consumption in stable operation of the sensor node was achieved.

We propose a wireless power distribution system (WPDS) operating at 2.45 GHz CW in buildings instead of wired power distribution in order to reduce the initial cost of the building. Required technologies for the WPDS are (a) low-cost and low-loss deck plate waveguide, (b) variable microwave power distributor for the waveguide, and (c) high-power (>100 W) rectifier at the outlet. We developed and tested the deck plate waveguide, power distributor, and high-power rectenna consisting of 256 Si Schottky barrier diodes and newly developed GaN diodes. Finally, a test WPDS was built and microwave power transmission experiments were conducted. The total efficiency of the test WPDS was estimated to be 52%.