GB596657A - Improvements in or relating to radar systems - Google Patents

Abstract

596,657. Radiolocation. BAILEY, A. E., and RHODERICK, E. H. Feb. 19, 1945, No. 4198. [Class 40 (v)] The invention relates to a pulse radiolocation system in which reference oscillations at the receiver intermediate frequency are mixed with signals at intermediate frequency derived from received echo signals, the Doppler shift being made use of to discriminate between moving and stationary reflecting objects. Use is made of a reference oscillation generator which oscillates continuously and since the oscillations generated by the transmitter start up at random, the reference oscillations must be brought into a particular relationship as regards phase with the transmitter. For this purpose oscillations from the receiver local oscillator are mixed with radio-frequency oscillations from the transmitter and the resulting intermediate frequency oscillations are employed to control the phase of the reference oscillation generator. In the drawing, a pulse transmitter 1 feeds an aerial system 2, 3. Common T and R working is employed using a receiver blocking device 4 which may be a gas-filled rhumbatron device. Reflected signals received by the aerial 'system 2, 3 are fed through the blocker 4 to a crystal mixer to which the output of a local oscillator 6, preferably a triode, is also fed. The . intermediate frequency output of the mixer 15 is fed to an I.F. amplifier 7. The output of the amplifier 7 is fed to a detector 8 and the final output which corresponds to transmitter pulses and any echoes is passed to utilisation or display circuits. Radio-frequency energy derived from the transmitter 1 is also fed to a mixer 9 to which a second output of the local oscillator 6 is fed. The output of the mixer 9, which is at intermediate frequency is fed to a low-gain amplifier 10. An oscillator 11 which is of the electron-coupled Hartley type produces oscillations at the intermediate frequency which serve as the reference oscillations for determining the Doppler shift when mixed with intermediate frequency signals derived from moving objects. The amplifier 10 is loosely coupled to the grid circuit of this oscillator 11 and thereby locks it relatively to the radiofrequency of the transmitter 1. The output of the oscillator 11 is fed through a buffer amplifier 12 to the detector 8 as shown, or it may be fed to a suitable point in the I.F. amplifier 7. 13 is a stabilised power pack supplying both the local oscillator 6 and the reference oscillation generator 11. The output of the detector includes two components, one being of constant amplitude and corresponding to echoes from stationary objects and the other being amplitude modulated due to the Doppler effect and corresponding to echoes from moving objects. This output may be used in various ways to give a P.P.I. display free from clutter, e.g. as disclosed in Specifications 596,649 and 596,651. The Specification discusses conditions for the stability of the reference oscillation generator 11 and the local oscillator 6. Specification 596,650 also is referred to in the Provisional Specification.