Patent GB-654293-A (GB)
Title: Improvements relating to the stereoscopic production of images of objects
IPC: G01S7/20
Filed: 1944-08-14
Abstract: 654,293. Radiolocation. SPERRY CORPORATION. Aug. 14, 1944, No. 15506. Convention date, Aug. 14, 1943. Addition to 616,520. [Class 40 (vii] A radiolocation system gives a stereoscopic image representing the positions of objects relative to a reference plane, and an image of objects in the reference plane may be simultaneously displayed. For example, for airport traffic control, images showing the relative heights of aircraft may be superposed on a map of the area surrounding the airport or, on an aircraft, images representing the relative distances of objects ahead may be displayed against an image of the outline of the aircraft. In the system shown, scanning means comprises a reflector 12 mounted on a horizontal axis 14 about which it is " nodded " by a motor 25, the whole structure being simultaneously "spun" about a vertical axis 19 by a motor 21 so that a large solid angle which may be substantially a hemisphere, is spirally scanned. Pulses from a transmitter 31 are led over wave-guides 33 ... 37 to an antenna 11 and reflected pulses pass back over the wave. guide system to receiver 43 where they are detected and applied to the control electrodes of cathode-ray tubes 47, 48. The beams of both tubes are given similar rotating radial deflections by saw-tooth generators 72, 73 synchronized by pulse generator 32, and fed with alternating currents in quadrature derived from a generator 53 driven by the "spin" motor 21. The amplitude of the radial deflection is made dependent on the angle of "nod" by feeding the stator 58 of generator 53 from a generator 61 driven by the " nod # motor. Thus the direction of the radial sweep at any instant indicates the azimuth of the radiated beam and the length of the sweep is proportional to the projection of a finite radiated beam on to a horizontal plane, i.e. to the cosine of the angle of " nod." To produce the stereoscopic effect, additional horizontal deflections in opposite directions are given to the cathode-ray beams by a further saw-tooth generator 74 also fed from generator 61 so that at the instant when the beams are brightened by the receipt of a reflected pulse the additional deflections will be proportional to the time of transmission multiplied by the sine of the angle of " nod," i.e. to the vertical height. The output of sawtooth generator 74 is led through a balanced amplifier 102 provided with control knobs 103, 104 for varying the direct-current level and the amplification factor. By reversing leads 105, 106, objects nearer the scanning antenna can be made to appear to be more distant, e.g. to simulate the view of an observer looking down from an aircraft. The screens 49, 51 of the tubes are projected through polarizing screens 111, 112 on to a projection screen 115 and observed through polarizing discs 116, 117 associated with the separate eyes. A map of the associated area may be superimposed on the stereoscopic images by placing photographic records thereof on the screens 49, 51, the tubes being so adjusted that there is normally a dull glow over the whole surfaces of the screens to illuminate such records. Specification 583,362 is referred to.