Study on Multipath Retrodirective for Efficient and Safe Indoor Microwave Power Transmission

This paper shows that multipath retrodirective improves the efficiency and safety of indoor microwave power transmission (MPT). The retrodirective array antenna sends back the power signal toward the pilot signal transmitted from the receiver. In a room, there are many propagation paths (multipath) besides the line of sight between the receiver and the transmitter. Simulating multipath retrodirective, we verified the power signal reproduces the multipath of the pilot signal. By utilizing multipath, the efficiency was better than MPT using single beam. We also simulated cases that a water cuboid exists between the receiver and the retrodirective array. Since the cuboid intercepted the direct path of the pilot signal, the multipath power signal formed in a way to avoid it. This result shows not only that target tracking is possible even when the receiver is not on the direct line of sight, but also that multipath retrodirective will realize safe indoor MPT even when people are close to the system, because multipath power signal formed in a way to avoid them.