Patent GB-737818-A (GB)
Title: Improvements in or relating to radar systems
IPC: G01S7/06
Filed: 1953-03-23
Abstract: 737,818. Radar. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. March 23, 1953 [April 17, 1952], No. 7946/53. Class 40 (7). A radar display system is arranged to indicate the azimuth, elevation (or height), and range of an object by representing two of these factors as the position co-ordinates of a luminous spot on a display screen and the third by variation of the colour of the spot. In a first embodiment a narrow beam directional aerial system is arranged to scan a volume of space by repeatedly sweeping out a rectangular raster (Figs. 1 and 3, not shown) and the screens K1 and K2 of two cathode-ray tubes are scanned in synchronism with the aerial scanning to give two identical azimuth-elevation type displays. The transmitter trigger pulses are fed to two multivibrator pulse generators 171 and 172. M1 produces a series of pulses commencing with the transmission of a pulse and extending for two-thirds of the pulse repetition period whilst M2 produces a series of pulses of similar length but commencing one-third of the repetition period after the transmission of a pulse and ending with the transmission of the next pulse. These two series of pulses are used respectively to open gates P1 and P2 controlling the passage of the received signals to intensity-modulate the cathode-ray tubes. If the screen K1 fluoresces red-orange and K2 blue and an optical system is used effectively superposing the two images on a joint display screen E then it willbe seen that the images caused by objects in the first third of the maximum range of the radar will appear only on screen K1 and will be red-orange in the final display. Similarly objects in the most distant third of the range covered will appear only on screen K2 and be blue in the final display. Images corresponding to objects at ranges in the intermediate third will appear on both screens and the final display will have an indication compounded of both colours. Thus images may be in three different colours on the screen according to whether they represent near objects, distant objects, or those at intermediate distances. The sub-ranges need not be of equal size. In a modification the colour of the displayed image is arranged to vary continuously in accordance with range variation. In this modification two tubes with different coloured screens scanned in correspondence with the aerial scan and whose joint images are viewed on a screen E are used as before. The tubes, however, are constructed to give a spot luminous intensity as near as possible proportional to the time duration of the applied signal. Reference pulses corresponding in time to the transmitted pulses and received echo pulses from receiver R are applied to two pulse generating circuits B1, B2 which respectively give pulses of time duration commencing with the echo signal and ending with the next reference pulse and commencing with a reference pulse and ending with the echo signal. These output pulses are applied respectively to intensity modulate the red-orange tube and the blue tube to produce images of an intensity inversely proportional to range and proportional to range. The colour of images on the screen E is thus graded from red-orange for near objects to blue for distant ones and range may be determined by comparison of image colour with a calibrated colour filter. The use of the system in connection with passive reflector beacons marking a landing runway is described with reference to Figs. 9 and 10 (not shown). The sensitivity of the receiver may be reduced for a short time after transmission of a pulse so that echoes corresponding to close objects are not displayed.