Adaptive TX Leakage Canceler for the UHF RFID Reader Front End Using a Direct Leaky Coupling Method

This paper presents a new adaptive leakage canceler based on a direct leaky coupling method for an RF front-end circuit of an ultrahigh-frequency radio-frequency identication (UHF RFID) reader. For better receiver sensitivity, the leakage signal from a transmitter (TX) to a receiver (RX) should be suppressed. Compared with conventional methods, the proposed TX leakage canceler has a much simpler circuit configuration due to the direct leaky coupling circuit (LCC) and the phase shifter on the RX path. The LCC includes a variable resistor, a variable capacitor, and an inductor, which allow us to control the magnitude and the phase of the coupled TX signal. The phase shifter that is located on the RX path even before the low-noise amplifier controls the phase of the TX leakage signal. For the worldwide RFID bands that spans from 840 to 960 MHz, the canceler must be adaptively controlled by using a microcontroller and control circuits. For the experimental verification, an RF front-end circuit with the proposed adaptive TX leakage canceler was designed and implemented for the UHF RFID reader. The implemented RF front-end block occupies only 54 ×54 mm², except for the control block. From 840 to 960 MHz, the adaptively controlled RF front-end circuit exhibited significant cancelation characteristics for the TX-RX leakage signals. This results in more than twice longer reading distances for the commercial RFID tags compared with the cases without the adaptive canceler.