RF-Powered-Tag Intermodulation Uplink With Three-Tone Transmitter for Enhanced Uplink Power

An intermodulation RF-powered-tag uplink (UL) that exploits the rectifier third-order intermodulation (IM3) has been recently proposed. The key features for the IM3 ULs to outperform the conventional backscattering ULs are the frequency-division duplexing downlink/UL operation and the passive reuse. While the previously reported IM3 UL systems only transmit two-tone waveforms, this paper demonstrates that under a given transmitter (Tx) peak power and a given Tx average power, transmitting an optimized three-carrier Tx waveform can improve the IM3 UL power and the receiver signal-to-noise ratio without compromising the rectifier harvested dc power. The developed theory is based on power series analysis and is verified by nonlinear simulation and experimental results, which include two RF-powered reader-tag systems: The first one employs a custom designed ultra-high frequency (UHF) PCB rectenna and the second one uses a commercial Gen-2 UHF radio-frequency identification inlay.