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Perfect Isolation: Dealing with Self-Jamming in Passive RFID Systems

Carvalho, N.B.C. ; Santos, J. ; Oliveira, A. ; Boaventura, A.

IEEE Microwave Magazine Vol. 17, Nº 11, pp. 20 - 39, November, 2016.

ISSN (print): 1527-3342
ISSN (online): 1527-3342

Journal Impact Factor: 1,975 (in 2015)

Digital Object Identifier: 10.1109/MMM.2016.2600942

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Abstract
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 [1]. 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 [1] 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)].