substantial improvements in frequency reuse in microwave communications systems is achieved by canceling co - channel interference and transmitter leakage . interferometric beam - narrowing reduces beamwidth without reducing peak magnitude of the beam pattern . frequency - dependent beam - shaping compensates for frequency - dependent distortions of the beam pattern thereby improving bandwidth . a spatial demultiplexing technique utilizes spatial gain distributions of received signals to separate signals , even from co - located transmit sources , and uses microwave lensing to enhance received spatial gain distributions . predetermined cross - polarization interference is used to separate differently - polarized receive signals . a reference branch provides a cancellation signal to a receiver to cancel transmitter leakage signals . an error signal controls an impedance - compensation circuit that is responsive to changes in antenna impedance but not to receive signals . a dc bias magnetic field applied to a magnetic permeable material adjusts non - linear distortion in a cancellation circuit for canceling distortion in a transmitter leakage signal . discreet impedance elements approximate a circuit having distributed impedance .