GB1194535A - Improvements relating to Satellite Tracking Arrangements - Google Patents

Abstract

1,194,535. Aerials. PLESSEY CO. Ltd. 31 July, 1967 [29 July, 1966], No. 34107/66. Heading H4A. A geostationary satellite executes a small figure-of-eight movement relative to the earth during one revolution of the latter, due to slight earth #wobble"; such a satellite is tracked by an aerial system incorporating a dish reflector, the dish structure first being moved coarsely about an axis, then being locked against such movement, and finally the dish is moved in azimuth and elevation to track the figure-ofeight movement. In one embodiment the coarse movement is about an axis 4, Fig. 1, parallel to the earth's polar axis, mount 3 being fixed to a shaft 5 mounted for rotation in pedestal bearings 6, 7. Mount 3 may be filled with concrete to counterbalance structure 1, 2. Thrust on bearing 7 is relieved by free-running rollers, e.g. 8, which bear against semicircular surface 9 of mount 3. The drive for mount 3 is electric via a gear-box and chain drive, Fig. 6 (not shown). Locking of the mount is effected by bolting contoured plates to a concrete bollard forming part of tower structure 19, see also Fig. 6B (not shown). The fine movement of dish 1 is done by two ball screw-jacks, e.g. 23, see also Fig. 4 (not shown); a movement of about 15 degrees in two directions is arranged for. Movement of one jack or both together affords elevational movement of dish 1 about bearings, e.g. 25, having an axis perpendicular to polar axis 4; differential movement between the jacks gives azimuth displacement about an axis 27. The aerial arrangement includes a horn 35, Fig. 5, a waveguide circular polarizer 36, a diplexer 37, and a waveguide feeder 39. Two test horns 41 are added. Waveguides pass into a hollow cylinder 42 having its axis coincident with polar axis 4 and carrying a cabin 43 housing receiving apparatus; dish 1 can rotate about axis 4 without corresponding movement of cabin 43. However, the waveguide structure and receiving apparatus in the cabin rotate: hence the waveguide structure need not be modified for different coarse settings of mount 3. To accommodate cabin movement as the aerial moves in elevation whilst giving access from tower 19, Fig. 1, a concertina passageway 45 is provided. Tower 19 has several floors for housing apparatus. To cater for upward thrust on upper bearing 6 in high winds corresponding rollers may be added. In another embodiment the supporting tower comprises an open framework 51, Figs. 8, 9, incorporating a triangular upper frame 53. A "tilt" frame 54 is connected to frame 53 at points 55, 56 so that frame 54 can pivot about an axis 57 by means of a ball screw-jack 58 generally the same as in the first embodiment. A further ball screw-jack 61 is incorporated. The initial, coarse, setting of the aerial is effected by rotating tower 51 about a vertical axis: the tower is jacked up on to rollers, rotated manually and lowered off the rollers on to the ground. Adjusting reflector profile, Fig. 9.-The reflecting surface of the dish may be made from panels secured to a support framework. A panel 65 includes a support 66 of honeycomb construction to which is attached a reflecting sheet 67. Metal members, e.g. 69, are set by epoxy resin 68; a universal joint structure 70 at one end of a threaded bolt 71 is received by a bore. Annular member 72 swivels on a ball 73 and is locked in the bore of member 69 by a clip 74. The lower end of bolt 71 threads into a block 75 which can swivel about a bolt 76 passing through a flange 77 of a channel-shaped bracket 78; that bracket is attached to one of the frame members of the supporting structure. When the desired reflecting surface profile is achieved, corresponding swivel blocks and brackets are welded together.