IMPROVEMENTS IN OR RELATING TO RADAR SYSTEMS

1285890 Pulse radar; frequency modulation PLESSEY CO Ltd 24 Nov 1969 [6 Dec 1968] 57982/68 Headings H4D and H3R [Also in Divisions H1] A system comprises a transmission line means connected to the output of an oscillator and means for accelerating an effective short circuit along the line towards the oscillator to produce a Doppler shift in the wave reflected from the short circuit before it is fed to an aerial. In a transmitter for a pulse compression radar, a magnetron 4 is pulsed by pulser 5 and a length of waveguide attached to the output of the magnetron is divided into two sections 1, 3, the section 1 being sealed at 9 and evacuated through part 10. Before the magnetron 4 is pulsed a mass of hydrogen is injected through a hollow electrode 6 into the waveguide 1. A pulse tapped from the pulser 5 ionizes the gas thereby short-circuiting the waveguide. A magnetic field applied transversely to the waveguide accelerates the ionized gas column towards the oscillator. The R.F. pulse from the magnetron is reflected from the short circuit and undergoes a Doppler shift due to the movement thereof. The waveguide may be replaced by a coaxial cable, wherein the gas forms an annulus which is accelerated along the line by a current along the centre conductor.