Patent GB-633832-A (GB)
Title: Improvements in or relating to navigation aiding radio systems
IPC: G01S19/15
Filed: 1946-08-20
Abstract: 633,832. Radio navigation. RADIO CORPORATION OF AMERICA. Aug. 20, 1946, No. 24856. Convention date, Oct. 18, 1945. [Class 40 (vii)] In a radio aircraft-landing system comprising a radar station on the ground with two cathoderay tube displays, one of which presents azimuth and range information of the aircraft using the system and the other presents corresponding elevation and range information, images of the two displays are transmitted to the aircraft by television and there reproduced in superimposed relationship, the range-scale of the second display being so distorted in accordance with the angle of elevation of the aircraft that registration between the two displays is obtained only when the correct glide-path is being followed. The pulse radar station 5 comprises two transmitters operating on different frequencies and radiating from aerials 7 and 9 respectively. Aerial 7 provides a directional radiation pattern that is broad in azimuth and narrow in elevation and aerial 9 provides a pattern that is narrow in azimuth and broad in elevation. These patterns are swept to and fro in elevation and azimuth respectively. Echo signals received by the system using aerial 9 are displayed as intensity modulations upon a cathode-ray tube as shown in Fig. 3. Steady potentials applied to the deflecting plates deflect the origin of the display to the point 93. A constant amplitude sawtooth waveform -is applied to the vertical deflecting plates to provide a range scale and a synchronized sawtooth waveform whose amplitude is caused to vary with the oscillation of the directional beam of the aerial 9 is applied to the horizontal deflecting plates, so that the position of the indication 99 upon the display indicates the range and azimuth of the aircraft. This display is projected optically on to the pick-up electrode of a television camera, on to which are also projected optically lines such as 89, 91, 115, representing the runway, the end of the runway, and the position at which an aircraft following the glide-path reaches a height of 200 feet, respectively. The signals received upon aerial 7 are displayed as shown in Fig. 4, wherein the origin is deflected to the point 101 and horizontal deflection measures range and vertical deflection measures elevation. A further horizontal deflection, which increases with the angle of elevation is introduced so that the broken lines such as 109 represent lines of constant range. The line 105 indicates the elevation angle for which the range scales on the two displays are equal. This display is projected on to the pick-up electrode of a television camera by an optical system including a cylindrical lens so that the image of the indication 103 is drawn out into a vertical line. The output signals of the two cameras are combined and the composite television signal is transmitted to the aircraft. The second television camera is so arranged that the reproduction obtained therefrom is turned through 90 degrees so that the display received by the aircraft is as shown in Fig. 6, the image of the origin 101 coinciding with that of the origin 93 and the image 113 of the vertical line obtained from the spot 103 now lying horizontally. The correct course is followed when the spot 99 lies on both the line 89 and the line 113; as shown, the aircraft is to the right of and below this course. In the case where the ground station is displaced from the touchdown point, the elevation of the glide-path as measured from the ground station varies from point to point along the path. In order to compensate for this, means may be provided for displacing the origin 101 of the elevation display horizontally in accordance with the instantaneous elevation angle of the aerial 7.