Patent ID: 7092684

Claim:
An interference canceller for reducing the level of an interfering signal comprising: a circulator comprising a transmitter port, a receiver port and an antenna port; a transmission line comprising a first end coupled to the transmitter port and a second end for coupling to a signal source; and a circuit, having an input and an output, the input coupled to the receiver port and the output coupled to the transmission line, for providing a phase shifted version of a signal coupled to the input at the output: wherein an interfering signal at the antenna port is coupled to the transmission line by the circulator and the circuit so as to reduce an amplitude of the interfering signal at the second end of the transmission line that results from the interfering signal being coupled from the antenna port to the transmitter port of the circulator; and wherein the circuit comprising a directional coupler for coupling to the transmission line; a variable attenuator for level shifting a signal at the antenna port coupled to the transmission line by the circulator and the circuit; a variable phase shifter for phase shifting the signal at the antenna port coupled to the transmission line by the circulator and the circuit, all series coupled between the input and the output; and a calibration apparatus comprising: a sensor coupled to the transmission line, for providing a sensing signal, the sensing signal corresponding to a combination of the interfering signal at the antenna port coupled to the transmission line by the circulator and circuit and the interfering signal at the second end of the transmission line that results from the interfering signal being coupled from the antenna port to the transmitter port of the circulator; and a control circuit coupled to the sensor operable to adjust one of the variable attenuator and the variable phase shifter according to the sensing signal.