GB1272570A - Improvements in or relating to automatic tracking radio equipments - Google Patents

Abstract

1,272,570. Radio direction finding; aerials. MARCONI CO. Ltd. 2 Sept., 1969 [17 Oct., 1968], No. 49364/68. Headings H4A and H4D. Tracking equipment, particularly for use at a ground station co-operating with a communications satellite, has an aerial, such as a horn 2, Fig. 3, which is coupled to a circular waveguide 3. A resonant cavity 5 is also coupled to the waveguide 3, through a slot 4. Received signal set up TE 11 and TE 21 mode waves in the circular waveguide, and the latter excite the cavity, which thereupon re-radiates TE 11 mode waves into the waveguide. Means are provided for rotating the said waveguide, and a resultant output is obtained therefrom of amplitude modulated TE 11 mode waves. From these output waves, and from signals (obtained from suitable means) which are indicative of the angular position of the waveguide 3, tracking error signals are derived. As described, the slot 4 is longitudinal, the cavity 5 is rectangular, and is provided with a tuning plunger 6 at one end. The waveguide 3 is coupled through a rotatable choked coupling 7 to a second circular waveguide 8 which terminates in a diplexer 9, the diplexer having a rectangular waveguide output 11 and a rectangular waveguide input 12. A polarizer 10 is positioned in the circular waveguide 8 for ensuring correct polarization of transmitted signals. The horn 2 is positioned in operation to receive signals from and to transmit signals to a parabolic reflector (Fig. 1, not shown). Said horn 2, the waveguide 3, the cavity 5 and the movable part of the choked coupling 7 are rotated about the axis of the waveguide by a motor 13, Fit. 5. Synchros spaced 90 degrees apart are associated with the choked coupling 7. Output from the port 11 is taken to a filter 16, which blocks signals at the frequency of transmission, and thence to a parametric amplifier 17, which gives an output of communication signals to a filter 18, and an output of directional signals to a mixer and local oscillator 20. The directional signals are taken through filters 21, 22 to phase and amplitude comparison circuits 14, 15, which also receive respective inputs from the synchros indicative of the position of the waveguide 3. The circuits 14, 15 give signals representative of the H and E plane errors, and these can be applied to aerial drive means, to maintain tracking. It is stated that the equipment will function with either linearly or circularly polarized signals transmitted by the satellite. In a modification, two slots and two cavities are utilized, spaced circumferentially 90 degrees apart on the circular waveguide.