Filtering Antenna Approach for In-Band Full-Duplexing Systems

Self-interference cancellation (SIC) is critical for In-Band Full-Duplexing (IBFD) systems, which facilitate doubling of the spectrum efficiency [1] . Propagation-level SIC methods are especially attractive as they ease the required dynamic range of the receiver (Rx) hardware. While the multi-antenna solutions increase the form factor of transmitter (Tx) – Rx system, the single antenna configurations typically employ expensive and bulky circulators. Polarization-based isolation has been previously shown for a two-antenna system by employing an active-component loaded stub-resonator [2] . However, the design requires multiple-layers of thick substrate to provide both the matching and directivity to the antennas. In addition, the reflections from the stub resonator interfere with the Tx antenna patterns and the distortions produced by the active component propagate through the Rx chain, degrading its sensitivity.