Perfect Isolation: Dealing with Self-Jamming in Passive RFID Systems
; Santos, J.
; Boaventura, A.
IEEE Microwave Magazine Vol. 17, Nº 11, pp. 20 - 39, November, 2016.
ISSN (print): 1527-3342
Journal Impact Factor: 1,975 (in 2015)
Digital Object Identifier: 10.1109/MMM.2016.2600942
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Passive RF identification (RFID) readers transmit a continuous wave (CW) powering signal to remotely power up batteryless transponders, while simultaneously receiving a backscattered signal at the same frequency . To separate the transmitter and receiver paths, readers use either a bistatic or monostatic antenna configuration. The first configuration employs two separate antennas, one to transmit and one to receive; in the second, the transmitter and receiver share a common antenna by means of a coupler or circulator. Both cases, however, suffer from poor transmitter-to-receiver isolation: strong CW signals can leak into the receiver, degrading its sensitivity to the weak transponder backscattered signals. Receiver sensitivity degradation occurs due to the leaked local oscillator (LO) phase noise  and also to the saturation of the front end caused by strong CW leakage. This requires high-dynamic-range capability in the RF stage [the low-noise amplifier (LNA) and mixer] as well as in the baseband stage [the amplifiers and analog-to-digital converters (ADCs)].