GB1103632A - Improvements in radars and particularly in optical radars - Google Patents

Abstract

1,103,632. Photo-electric position and velocity determination. COMPAGNIE FRANCAISE THOMSON HOUSTON-HOTCHKISS BRANDT. 2 June, 1965 [2 June, 1964], No. 23571/65. Heading H4D. In an optical radar system utilizing the Doppler effect, a beam from a coherent source such as a laser 10 is projected via a scanning device 11 and an optical system 12. Reflected beams from targets are received by an optical system 13 and are taken to a light adder 14 which is also fed directly from the beam from the laser 10, and an output beam containing light from both beams passes through a device 15, for reducing background solar interference, to a photomultiplier 16. The electric signal output from the photo-multiplier 16 contains the Doppler frequencies due to the movements of the targets and is taken to a filter system 17 comprising three band-pass filters 30, 31, 32, Fig. 3 (not shown), which supply, respectively, the colour input terminals of a tri-chromatic cathode-ray tube contained in an oscilloscope 18. In this way, the representation of a target is seen in a colour corresponding to one of three distinct speed ranges. Finer resolution of speed is obtained by means of a device 110, comprising a plurality of band-pass filters 40, 41 . . . 4n, Fig. 4 (not shown), connected to gates 410, 411 . . . 41n which mark targets according to their speeds. The photomultiplier 16 also supplies a distance and angular position measuring system 19. The scanning device 11 may provide scanning in two dimensions by mechanical means or may operate electronically with " staircase " waveforms, the light beam being interrupted by a modulator during transitions. A scanning means using a vibrating quartz crystal to set up standing waves in a strip of transparent material whose refractive index varies with stress is described. The anti-interference device 15 and the photomultiplier 16 may be combined so that a casing has at one end a photocathode (20), Fig. 2 (not shown), from which electrons proceed to a screen (23) with an aperture (24). A deflection system (22) moves the electron beam in synchronism with the beam from the laser so that only electrons corresponding to the target pass through the aperture (24), and are received by a photomultiplier (21). Distance is determined from the time of transit of the leading edge of a light pulse to a target and back by reflection to the radar system. Angular position may be determined by moving an observation gate provided with rectangular co-ordinate counters to the image of the target, in a similar way to that described in French Specification 1,404,558.