A circulator system for use in a simultaneous transmit and receive system includes a transmitter port connected to a first port of a circulator component by a phase shifter and possibly a pre-conditioning impedance, an antenna port connected to a second port of the circulator component by a pre-conditioning impedance, and a receiver port connected to a third port of the circulator component by a phase shifter and a pre-conditioning impedance. A loop with an impedance is connected between the transmitter port and the receiver port. A double loop circulator system includes further phase shifters and impedances at the first and third ports of the circulator component and a second loop with an impedance connected signal paths for the transmitter and receiver ports, being connected between the phase shifters in the signal paths. High isolation between the transmitter and receiver ports is provided.