Patent GB-722858-A (GB)
Title: Improvements in or relating to radar display systems
Inventor: KEMP ROLAND JOHN
IPC: G01S7/06
Filed: 1952-10-07
Abstract: 722,858. Radar. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 15, 1953 [Oct. 7, 1952], No. 25130/52. Class 40 (7). [Also in Group XL (b)] Relates to radar systems in which a large volume of space is floodlit by the transmitter and the receiver comprises a rectangular array of receiving elements located in the focal plane of a directional device, e.g. a lens, the azimuth and elevation of reflecting objects being displayed on a cathode-ray tube by intensity modulation of a rectangular raster. According to the present invention, the receiving elements are connected to the grid of the display tube via individual gates which are opened sequentially by the pulse outputs from a corresponding array of photo-cells which are scanned by a light beam or spot synchronously with the display raster. The invention is applicable to pulse or unmodulated C.W. systems and it is described as applied to unmodulated C.W. Doppler systems in which the receiving elements comprise a 5 x 5 square array of crystal mixers in which the received waves are heterodyned with the transmitted waves to give Doppler beat frequencies. In some of the embodiments the beat frequencies are applied via band-pass filters to differently-coloured cathode-ray tube displays indicating responses due to targets of different radial velocity. In all the embodiments, the columns of the photo-cell array MPT, Fig. 2 (not shown), are scanned in sequence, each column being scanned successively ten times before the next column is scanned. In the embodiment described with reference to Figs. 1-7, the scanning light spot is produced by a light source LS, Fig. 5, and optical system CL, PM in conjunction with a motor-driven apertured drum AD shown in developed form in Fig. 3. The number of lines in the rectangular display raster is equal to the total number of apertures in the drum, i.e. 500, and the raster is synchronized with the drum by line and frame pulses generated by a toothed wheel, Fig. 4 (not shown), driven by the motor so that the signal from any one crystal is displayed on a corresponding rectangular element of the complete raster, the form of the intensity modulation being indicative of the beat frequency and hence of the radial velocity of the target. In Fig. 8 the light spot scanning device comprises a cathode-ray tube LCRT, with the array of photo-cells MPT mounted on the screen, the line and frame deflecting waveform from LPG and SFPG being respectively sawtooth and stepped so that the photo-cells are scanned as in the previous embodiment. The gating pulses from the photo-cells are applied via amplifiers GA1 ... GA25 (GA1 and GA2 only shown) to gates G1 ... G25 and the crystal mixers XI ... X25 are connected in parallel via the respective gates and a common amplifier PRA to three filters F1 ... F3 having pass-bands of 0-600, 600-1200 and 1200- 2000 c/s. respectively, the outputs from the filters being applied via amplifiers FA1 ... FA3 to the grids of three cathode-ray tubes DTR, DTB and DTG which have red, blue and green filters LFR, LFB and LFG respectively and which are scanned in synchronism with the photo-cell scan by conventional saw-tooth line and frame deflecting waveforms from generators LPG and FPG synchronized by a master generator MSPG. The tubes may be viewed separately but a better discrimination between discrete targets and clutter is obtained by viewing them in optical superimposition through half-silvered mirrors MM1 and MM2; alternatively the tubes may have coloured phosphors or a single three-colour tube may be employed. In a modification, Fig. 9 (not shown), the filters precede the gates, three filters and three gates being provided for each crystal which is separately coupled to each of the three tubes via a corresponding filter and gate. Fig. 10 (not shown) illustrates the use of the cathode-ray tube light spot scan of Fig. 8 in conjunction with a single monochrome display.