Using 2.4 GHz load-side voltage standing waves to passively boost RF-DC voltage conversion in RF rectifier

Abstract

A novel, dual-band, voltage-multiplying (RF-DC) rectifier circuit with load-tuned stages resulting in a 50 Ω input-impedance and high RF-DC conversion in 2.4 and 5.8 GHz bands for wireless energy-harvesting is presented. Its novelty is in the use of optimal-length transmission lines on the load side of the 4 half-wave rectifying stages within the two-stage voltage multiplier topology. Doing so boosts the rectifier's output voltage due to an induced standing-wave peak at each diode's input, and gives the rectifier a 50 Ω input-impedance without an external-matching-network in the 2.4 GHz band. Comparisons with other rectifiers show the proposed design achieving a higher DC output and better immunity to changing output loads for similar input power levels and load conditions. The second novelty of this rectifier is a tuned secondary feed that connects the rectifier's input to its second stage to give dual-band performance in the 5.8 GHz band. By tuning this feed such that the second stage and first stage reactances cancel, return-loss resonance in the 5.8 GHz band is achieved in addition to 2.4 GHz. Simulations and measurements of the design show RF-DC sensitivity of −7.2 and −3.7 dBm for 1.8V DC output, and better than 10 dB return-loss, in 2.4 and 5.8 GHz bands without requiring an external-matching-network.