An apparatus for simultaneous transmit and receive is provided. The apparatus is capable of rejecting or passing transmitter and receiver signals. The apparatus includes: a transmitter; an antenna (e.g., a shared antenna); a receiver including switches controllable by time varying signals; and a quadrature coupler including first, second, third, and fourth ports, wherein the first port is coupled to the transmitter, wherein the second port is coupled to the antenna, and wherein the third and fourth ports are coupled to the receiver.