Patent GB-592393-A (GB)
Title: Radio navigational system
IPC: G01S13/91
Filed: 1943-06-04
Abstract: 592,393. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd. June 4, 1943, No. 9027. Convention date, Mareh. 23, 1942. [Class 40 (v)] A landing area is provided with a plurality of spaced reflecting or re-radiating units 11, 12, 13, the signals from which enable a pilot to observe his position relative to the units and thereby to descend in a correct glide-path. In the system shown, one unit 11 is arranged centrally of the desired landing direction 14 and is buried just below ground level, and two other units 12, 13 are mounted on towers on either side of the landing strip and ahead of the landing position, the three units defining a plane in which the aircraft should descend for safe landing. Fig. 2 shows the apparatus provided on the aircraft. The antenna, assembly, which may be fixed or universably mounted, comprises a forward transmitting antenna 20 and four receiving antenna 21,. 24 directed up and down and right and left in pairs as shown. The receiving antennae;are connected to detector-amplifiers 27 ... 30 over circuits including quarter-wavelength blocking means 25 controlled from impulse-generator 18, so that pulses sent out from antenna 20 are not picked up directly. The output circuits from detector-amplifiers 27 @... 30 are combined in pairs to get, respectively, the total left, right, down and up reception of the reflected signals and these are again combined in pairs with inversion of one member of a pair so that potentials corresponding to the resultant right (or left) and up (or down) reception are produced in circuits 42 and 36. These potentials are applied to pairs of plates 37, 43 of a cathoderay oscillograph 31 causing deflection of the beam to a point indicating graphically the position of a reflecting unit relative to the line of flight. The cathode-ray beam is caused to traverse the tube vertically by a saw-tooth generator 44 under the control of impulse generator 18, but the ray is normally suppressed by bias on the grid 46 and rendered operative (over circuit 47) just before the deflecting potentials are applied to the plates 37, 43. Fig. 5 shows the correct indications on the cathode-ray tube when tlie aircraft is following the glide path, the spot 50 indicating that reflector 11 is directly ahead whilst lines 48, 49 indicate that reflectors 12, 13 are symmetrically located on either side and nearer. As the aircraft passes between the reflectors 12, 13, the lines 49, 48 disappear and the pilot should then prepare to land. If the pilot is above or below the glide plane 11, 12, 13, the lines 49, 48 are inclined to the horizontal and if he is to left or right of the centre line, the lines are of unequal length. Line 68 corresponds to reflection from the ground and gives an altitude indication. To avoid confusion due to reflections from trees &c., the units 11 ... 13 may be constructed as relay units. In one such arrangement, Fig. 3, signals received on antenna 51 are detected at 52 and control, over a delay circuit 57,. a transmitter 55. The .detected signals also control a multi-vibrator 60 which produces through a clipper 61 and an inverter-clipper 62 potentials controlling blocking devices 58, 59 associating the receiver and transmitter with the common antenna 51. The timing of the control circuit is such that the receiver circuit will be blocked for a period sufficient to prevent response to the transmissions from the other two re-radiating units. In one unit, the antenna may be non-directional to provide an indication of the landing area when approached from any direction and a keying unit 66 may be added to give identification. In an alternative re-radiating unit, Fig. 3a (not shown), received signals are amplified at radio-frequency, the input and output circuits of the amplifier being associated with the aerial over a conjugate network, and the receiving circuit being blocked during re-radiation in a manner similar to that shown in Fig. 3. Instead of units 12, 13 being mounted on towers, all three units may be at ground level. In this case, the correct indication for an aircraft in the glide-path will be as shown at 79, 80, Fig. 11, and lines 81 are superimposed on the screen of the cathode-ray tube to indicate the correct angle for lines 79. Where it is desired that landing should. take place at the near end of the field in the vicinity of units 12, 13, the lines 81 near the bottom of the screen are flattened. To prevent the signals from units 12, 13 cancelling one another and producing a spot instead of lines 48, 49, Fig. 5, a keyer 99, Fig. 1, may render the units operative alternately at a very rapid rate. Alternatively, the delay networks 57, Fig. 3, may have different time constants in which case the lines 48, 49 will be staggered on the screen. For landing on water, the units 11 ... 13, preferably reflectors, may be mounted on buoys, and for use on an aircraft carrier, two additional lateral units are preferably used. The pulse-transmission systems described may be replaced by a varying - frequency system. Specification 574,676 is referred to.