Patent GB-1344092-A (GB)
Title: Antenna tracking systems
IPC: H01Q25/04
Filed: 1971-03-31
Abstract: 1344092 Radio direction finding; aerials DEFENCE SECRETARY OF STATE FOR 21 March 1972 [31 March 1971] 8304/71 Headings H4D and H4A Apparatus controlling a steerable aerial comprises a circular waveguide 1, a mode coupler 2 which gives an output when TM 01  mode waves are sustained within the waveguide 1 as a result of the aerial axis pointing near to, but not at, a target source, and a modulator 4 having one input from the mode coupler 2 and another from a modulating control source over a transmission line 9. The waveguide 1 also sustains circularly polarized TE 11  mode waves when the aerial axis is pointing at or near to the target and linearly polarized signals derived from these are combined in a square section waveguide 6 with output signals from the modulator 4, thereby forming an amplitude modulated resultant signal. A detector circuit is provided, which derives tracking control signals, from said resultant signal, which are related to misalignment parameters such as #, #, where # = angle between the aerial axis and the sight line to the target, and # = angle between a plane containing said axis and said line, and a reference (e.g. horizontal) plane. As described, the steerable aerial receives circularly polarized waves from, for example, a satellite relay transponder. The output from the TM 01  mode coupler 2 is connected via a rectangular waveguide 3 to the modulator 4, which is of the ferrite phasemodulation type, and which receives a sawtooth waveform signal over the co-axial line 9 from a generator 14. The circular waveguide 1 is continued in a polarizer section 7, which converts the circularly polarized TE 11  mode waves into linearly polarized waves, a transition section 8, and the square waveguide 6, which also receives the output of the modulator 4 via a rectangular waveguide 5. The combined signals from the waveguide 6 are coupled through a diplexer 10 to a microwave receiver 12, which has two outputs. One output is fed directly to a tracking control system 15, to provide an indication of the parameter 0, and the other output is compared in phase in a detector 13 with the signal from the generator, the output of said detector being fed to the system 15 to provide an indication of the parameter #. A transmitter 11 is also coupled to the diplexer 10, signals being conveyed along the waveguides 6, 8, 7 and 1 to the aerial. It is stated that the modulator 4 may alternatively be of frequency changing balanced diode type, supplied by a sine wave control source. In another embodiment, a generator (14<SP>1</SP>), Fig. 5 (not shown), supplies a staircase waveform signal to the modulator, so that it effects four equal duration steps of 90 degrees phase change per cycle (Fig. 6, not shown). The generator also supplies respective trains of enabling pulses, each corresponding to successive steps of a particular phase level, to four synchronous detectors, which also receive input from the microwave receiver. The output of each detector is integrated, and is fed to an input terminal of one of two difference amplifiers. The outputs of said amplifiers, which are fed to the tracking control system, are related to misalignment parameters in two orthogonal planes. Specification 1,171,401 is mentioned.