A Beamforming based Wireless Energy Transmitter and Energy Harvester for IoT/M2M Applications

This paper presents a beamforming-based Korea LoRa band (i.e. 920 - 925MHz) wireless power transmitter and receiver chain for IoT/M2M applications. To complete wireless power harvesting, major key elements are: First one is a 6-bit active phase shifter to improve directivity between sensor-node and master-node using beamforming. The other one is an RF to DC converter to rectify RF and achieve the battery charging voltage. To reduce a phase error of active phase shifter because an IQ phase imbalance, an IQ phase calibration technique that maintaining the 1 of Q-factor is used. In addition, to improve the RF power harvesting distance, the rectifier is designed with a resonating single to differential (S2D) matching network for getting higher DC voltage than the RF input peak voltage. As the Q-factor of active phase shifter maintains 0.98 - 1.03, the maximum phase error is approximately 1.5deg for -10 to 100 temperature. The minimum input power that can be harvested is about -13dBm from EIRP 26dBm, 915MHz. The minimum output voltage of the boosted rectifier is 0.8V from -13dBm input. The RF to DC converter output voltage range is 3.0 to 5.5V. The maximum RF to DC power conversion efficiency is about 55% from 4 to 6dBm input.