A doppler radar module consisting of transmitting and receiving diodes disposed within adjacent sections of wave guide with the transmitter diode disposed a half wave length away from a shorting end of the transmitter section of wave guide, and a receiver diode disposed a quarter wave from a shorting end of the receiver portion of the guide. The receiver section and the transmitter section of the wave guides being separated by a common wall; coupling aperture disposed in the common wall substantially one wave length from the end of the transmitter section of wave guide for coupling a small portion of transmitter energy into the receiver portion of wave guide and for coupling substantially all reflected energy into the wave guide section.