A Carrier Extraction Cancellation Circuit in RFID Reader for improving the Tx-to-Rx isolation

A novel high-isolation leakage carrier cancellation system, which is highly required in the ultra-high frequency (UHF) radio frequency identification (RFID) reader circuit, is presented here. First, a novel deformed microstrip rat-race circuit (RRC) is designed to take the place of traditional circulator. The microstrip device is integrated in the leakage carrier extraction circuit, which is connected in the receiver and balanced by the open-loop circuit. One of the advantages of the delicately designed system is that no need of real-time tracking to balance the variations of the amplitude and the phase of the leakage carrier. Results demonstrate that the leakage carrier with the leakage carrier extraction cancellation circuit (CECC) is improved to be 108 dB in UHF RFID narrow bands from 920 to 925 MHz and to be 117 dB at the centre frequency point. The Tx-to-Rx isolation is improved to be 48–70 dB higher than that of other cancellation circuits. The proposed leakage carrier cancellation system shows obvious improvement on the efficiency of the isolation. Both the experiment and simulation demonstrate the merits of properties of the novel designed system with the benefits of improved isolation and lower cost.