A motion detection unit for detecting motion by means of Doppler frequency shift which comprises: a microwave circuit board (1) comprising an oscillator (14), a hybrid coupler circuit element (11) and a mixer (12); an antenna board (2) comprising at least one transmit and receive antenna (4, 5); and a ground plane layer, the two boards (1, 2) being superimposed with the ground plane layer intervening, wherein, in operation, the hybrid coupler circuit element (11) divides power from the oscillator (14), into power for the antenna transmission signal and local oscillator (LO) power to the mixer (12), and directs a received signal from the antenna (4, 5) to the mixer (12), the local oscillator (LO) power and the received signal being combined in the mixer (12) to produce a Doppler signal output.