1-TX and 2-RX in-band full-duplex radio front-end with 60 dB self-interference cancellation

This paper presents experimental results of self-interference cancellation of a full-duplex radio front-end. The proposed RF front-end uses three antennas for a 1-TX and 2 (primary and diversity)-RX MISO system without RF circulators. Transmitting signals are fed to two identical antennas through a rat race coupler with 180° phase difference, resulting in the signal cancellation at the RX diversity antenna which is equally spaced from transmitting antennas. Using the isolation port of the rat race coupler, the two TX antennas can also be used for RX primary antenna maintaining its own function of transmitting. The remaining self-interference signals are further canceled by tunable RF cancellation circuits, which consist of variable attenuator, phase shifter, and true time delay. After optimizing RF cancellation circuits, the measured results show 60-dB self-interference cancellation over 80-MHz and 60-MHz bandwidth in RX diversity and RX primary paths, respectively.