Patent GB-1030872-A (GB)
Title: Improvements in or relating to aerial structures
Inventor: BURR DONALD WILLIAM
IPC: H01Q15/14
Filed: 1962-03-08
Abstract: 1,030,872. Aerials; direction finding. MINISTER OF AVIATION. March 6, 1963 [March 8, 1962], No. 8926/62. Headings H4A and H4D. [Also in Divisions G1 and G3] The invention relates to a large steerable aerial, e.g. a radio telescope or radar tracking aerial, having a flexible reflector which is maintained in shape by photo-electrically comparing its profile with a standard profile generated by a rotating beam of light and using the difference signal to automatically control hydraulic or gear-driven jacks and which is maintained in its true tracking position by additional servo assisted systems some of which are also controlled photo-electrically. The reflector comprises three-sided panels, Fig. 1 (not shown), of aluminium honeycomb sandwich or metallized glass fibre having an adjustable jack 2, Fig. 2, positioned at each apex. A half-silvered rotating mirror 6 positioned in a central aperture 3 of the reflector directs a beam of light from a source at A through the circumferential slit 7 to produce a conically scanned beam 8 which defines a datum surface for the desired profile 5 of the reflector. The actual positions of the reflector panels are compared with the required profile 5 by a pair of photo-cells 19, 20, Fig. 3, disposed on each jack 2 and differentially connected to a servomotor 22, 23, which drives the jack so that each cell of the pair is equally illuminated. Some of the light from the source at A passes through the mirror 6 to fall on a cluster of photo-cells (not shown) the output from which is used to maintain the rotation axis of the mirror 6 coincident with the axis AB of the light beam. For command tracking, Fig. 5 (not shown), the orientation of the aerial system is controlled in accordance with the input command # IN  by a main servo 29 ... 31A, the actual direction # OUT  of the aerial beam is determined by a data extraction unit 26 as a function of the position of the aerial feed element 24 (see below) and any error e =  IN -# OUT  obtained in a difference circuit 28 controls an auxiliary servo which adjusts the position of the feed 24 to reduce the error to zero. For automatic tracking, Fig. 6 (not shown), the difference e between the actual beam direction # OUT  and the direction # IN  of a target is determined directly by a " split system " coupled to the feed 24 and is (1) applied to the auxiliary servo 25, and (2) added to the output # OUT  from the data extraction unit to give the command signal # IN  for the main servo. The actual direction of the aerial beam is given by the position of a " virtual " feed D, Fig. 7 (not shown), located at the optical image of the actual feed C, i.e. the displacements of C and D from the axis AB of the reflector 5 are diametrically opposite. Two horizontally spaced light sources E and F, Fig. 8 (not shown), are mechanically linked with the actual feed so that the mid-point of the base line EF always coincides with the virtual feed D and the beams 45, 46, Fig. 9, from these sources are directed (by means of lens and mirror systems 45A, 46A mounted on a horizontal shaft 43) on to a horizontally stabilized rotatable platform 38 located in the region of the intersection of the main turning axes of the aerial and carrying two diametrically shaped diamond clusters 39, 40 of light-sensitive elements 1 . . . 4 and 5 ... 8, Fig. 10. The angular position of the platform 38 is controlled by an azimuth servo (not shown) responsive to a combination of outputs of light -sensitive elements (1 + 2 + 5 + 7) -(3+4+6+8) and the angular position of the shaft 43 is controlled by an elevation servo (not shown) responsive to a combination of outputs of light-sensitive elements (2+6)- (3+7). The corresponding azimuth and elevation of the aerial beam are then given by data units 41 and 44 mounted respectively on the platform 38 and shaft 43.