Full-Duplex Architecture With Broadband Suppression of Reflected Transmit Signal

The RF front end of a broadband full-duplex communication architecture is described, in which one antenna simultaneously transmits and receives signals that can overlap spectrally to any extent. This architecture not only minimizes the power of the transmitted signal at the receiver in the ideal, purely hypothetical case in which the antenna has infinite return loss, but also successfully suppresses the portion of the transmitted signal reflected off an actual antenna of finite return loss while successfully recovering received signals at the same frequency. The hardware that separates the transmit signal reflected off the antenna from a same-frequency signal received by that antenna performs this separation purely in the analog domain without the need for a control circuit or any other digital-domain hardware. The authors know of no other antenna interface that distinguishes the reflected transmit signal from a same-frequency receive signal in the analog domain. This innovative antenna interface has been used to demonstrate single-antenna in-band full-duplex capability with better than 30 dB of analog transmit/receive isolation nearly everywhere between 1 and 18 GHz. In any subband within this 17 GHz-wide instantaneous bandwidth, additional analog and digital techniques can be applied to further improve the aggregate transmit/receive isolation.