Circuits and methods for antenna-based self-interference cancellation are provided. In some embodiments, circuits for antenna-based self-interference cancellation are provided, the circuits comprising: a transmit antenna having a transmit port that receives a transmit signal; a receive antenna having a receive port that is cross-polarized with respect to the transmit port and having an auxiliary port that is co-polarized with respect to the transmit port; and a termination connected to the auxiliary port that reflects a signal received at the auxiliary port as a reflected signal, wherein the reflected signal counters interference caused by the transmit signal at the receive port.