Abstract: A microwave transmitter/receiver unit consisting of a hollow waveguide member closed at one end and open at the other is divided longitudinally by an internal dividing plate into two waveguides, one for transmitting microwave radiation to the open end and the other for receiving such radiation from the open end. A Gunn diode is mounted in a cavity in the transmitting waveguide and at least one detector diode is mounted in the receiving waveguide. The unit is of an inherently compact nature and has particular application to doppler radars, two way communication links and distance measuring radars.