Broadband suppression properties of active leaking carrier cancellers

In passive UHF RFID systems backscattering is used for tag to reader communication. This technique relies on a continuous wave signal being transmitted by the reader during the tag's data transfer. In order to separate transmission and reception paths circulators, directional couplers or disjoint transmit and receive antennas can be used. Perfect isolation is not achievable with any of those approaches. So a leaking carrier is present at the receiver in any case. It is possible to reduce the interference from this signal by some kind of leaking carrier cancellation. Such a cancellation prevents receiver blocking and reduces the baseband hardware's requirements, depending on the receiver concept. Usually, the narrowband properties of carrier cancellers are studied. This is only sufficient for conventional RFID systems, if the transmitter noise can be neglected. Broadband RFID systems, as recently discussed in literature, also require broadband leaking carrier cancellers. In this paper the broadband suppression properties of carrier cancellers are first investigated theoretically. Further a hardware implementation is presented and characterized. Finally, measurement results are compared to the theoretical findings.