Design of a Beamforming Tri-Band Rectifier for RF Energy Harvesting

Ambient RF energy is considered as one of the most promising resources for powering low-power electronics, especially in IoT and wireless sensor network applications. One of the most significant challenges in RF energy harvesting is the low ambient RF power density which decreases the conversion efficiency of the rectifiers. Another problem is that RF power is spread over different frequency bands in our surroundings. In response to these challenges, this paper focuses on designing a beamforming tri-band harvester capable of capturing RF energy from GSM-900, DCS-1800, and WiFi-2400 frequency bands. This rectifier consists of a novel tri-band Butler matrix with asymmetric hybrid couplers as the beamforming network to maintain high gain harvesting while ensuring proper spatial coverage. Additionally, a tri-band rectifying circuit utilizing a new single branch impedance matching network has been designed to convert RF power to DC at three frequency bands. The measured power conversion efficiency of this beamforming rectifier is found to be 53.4%, 44%, and 16.8%, respectively at the three frequency bands for an ambient RF power level of -15 dBm and also the maximum PCE of 67% for -5 dBm input power. The proposed tri-band Butler matrix along with the tri-band rectifier circuit is then fabricated on RT-duroid 5880 and RO4003C substrates. Comparison done between measured and simulated results validates that the proposed network is able to harvest incoming RF energy efficiently from different directions at three desired frequency bands.