Electrically tunable bandpass filter with integrated carrier suppression for UHF RFID systems

One of the most critical points in designing a RFID system based on the backscattering process is the limitations in the system dynamic resulting from the Tx-Rx-leakage, principally over the circulator and partly through environmental reflections. This signal can overshadow the modulated tag reply, which is generally at a maximum of only a few hundred kilohertz apart. This paper presents a novel patented hardware based solution, which combines the bandpass filtering of the operational channel required for a multi-reader environment with the suppression of the carrier leakage, leading to an improvement in the system dynamic of over 50 dB. Experimental results verifying the proposed architecture are presented. The relative bandwidth of the measured filter is under 0.03% as compared to the center frequency of 866.5 MHz, corresponding to the European RFID band.