Efficient microwave power transfer system using retrodirective antenna array

In this paper, we present a design method for a highly efficient retrodirective array (RDA)-based microwave power transfer (MPT) system for the mMTC scenario, and evaluate its characteristics through experiments. Long-range wireless power transfer is required to effectively support the mMTC situation. RDA-based MPT controls and tracks the power beam towards the device within a certain range and it enables efficient power transfer. The overall link budget analysis is examined first and the required antenna gain is calculated. The required antenna gain can be secured using multiple-antenna modules. So, it is possible to design an RDA-based MPT system. In this paper, we implement a reduced RDA-based MPT system and evaluate its characteristics to confirm the feasibility of this design method. Through experiments, it has been confirmed that additional gain can be secured by using multiple antenna modules, and the RDA function can be effectively operated to effectively make a power beam in the direction of the power receiver. Conclusively, the gain of about 2.2dB increased whenever the number of antennas is doubled. The experimental results also show that the RDA-based MPT system designed in this paper is capable of adaptive power beamforming from -30 degrees to 30 degrees.