Wireless Power Transfer at Higher Frequency for SPS and for Commercial WPT

One of the promising future power stations is a solar power satellite (SPS) station in geostationary orbit (36,000 km above the surface of Earth) that uses wireless microwave power-transfer technology. In this system, the power generated would be transmitted to the ground by a microwave beam. The SPS would be a very large satellite with a large transmitting phased-array antenna that would work at 2.45 or 5.8 GHz. The size of the transmitting antennas is theoretically determined by Maxwell’s equations. However, we must reduce the size of the antennas to reduce the cost and to produce a small prototype satellite as a first step to the SPS. The only way to reduce the size of the antennas is to use a higher frequency. We developed rectennas that are optimized for 24 and 60 GHz transmission. In addition, we developed a monolithic microwave integrated circuit (MMIC) rectenna for 24 GHz transmission and with dimensions of 1 mm × 3 mm. The maximum radio-frequency to direct-current (RF-DC) conversion efficiency is 47.9% for a 210 mW microwave input power with a 120  load. We also designed a rectenna for 60 GHz transmission whose maximum RF-DC conversion efficiency is 46.2% for a 80 mW input power at 60 GHz with a 100  load. Finally, based on rectenna technology, we propose other satellite experiments.