Single-Antenna FDD Reader Design and Communication to a Commercial UHF RFID Tag

This letter demonstrates a new radio frequency identification (RFID) reader architecture improving the uplink (UL) quality and is compatible with a commercial ultra high frequency Gen2 RFID inlay. The reader transmits a weak auxiliary carrier in addition to the main carrier. The tag nonlinearity generates a new frequency component at the third-order intermodulation (IM3) frequency for UL communication, where the on-tag backscatter works as an on-off-keying modulator at the newly generated IM3 carrier. Since the UL and downlink frequencies are slightly offset, the passives are reused efficiently and the transmitter-to-receiver (Tx-to-Rx) noise/leakage can be eliminated by employing a duplexer, which results in a low-noise and low-interference Rx.