A UHF rectifier with one octave bandwidth based on a non-uniform transmission line

Ambient RF energy especially in urban settings is suitable for scavenging and harvesting scenarios provided one is able to collect signals from a large number of frequency bands and consequently spanning a large aggregate bandwidth. In this work a broadband rectifier is designed capable of harvesting RF energy in the 400 MHz - 1 GHz range, which includes the analog and digital TV bands and the UHF ISM 900 MHz band. In order to obtain a sufficiently large rectifier bandwidth, a matching network based on a non-uniform transmission line is considered. A charge pump rectifier is used and the number of diodes in the circuit is optimized in order to facilitate impedance matching based on the Bode-Fano limit. A prototype is fabricated and characterized. The rectifier has a measured efficiency above 5% from 470 MHz to 990 MHz at -20 dBm input power, which increases above 60% at 10 dBm input power over a band from 470 MHz to 860 MHz.