Patent GB-1082183-A (GB)
Title: Waveguide mode coupler for monopulse tracking system
IPC: G01S13/44
Filed: 1966-01-31
Abstract: 1,082,183. Moriopulse tracking system. COMMUNICATIONS SATELLITE CORPORATION. Jan. 31, 1966 [June 24, 1965], No. 4164/66. Heading H4D. The invention relates to an improvement on a tracking system such as is described under the title " The Autotrack System" in the Bell System Technical Journal, July 1963, Part 2, pages 1283-1307, wherein ideally circularly polarized beacon signals, received from the satellite S to be tracked, are passed down a circular waveguide and mode coupler means 10 are used to extract from the waveguide:- (a) Propagation modes, such as TM 01  and TE 01  which have an intensity, Fig. 2 (not shown), which drops to zero when the satellite is on the boresight axis of the receiving antenna 11, and are used, like the difference signal in overlapping beams monopulse systems, for tracking purposes, and (b) Orthogonal components TE 11x  and TE 11y  of a propagation mode which can be used like the sum signal in overlapping beams monopulse systems. When the received signal is elliptically polarized however the minimum (n<SP>1</SP>) in the intensity of the TM 01  and TE 01  modes is reduced to (n) and becomes less well defined. This may be considered to be due to the contamination of the extracted TM 01  and TE 01  modes by the modes TE 11x  and TE 11y . The invention thus extracts controlled amounts of the TE 11x  and TE 11y  modes from the extracted TM 01  and TE 01  modes to produce uncontaminated modes TM 01  and TE 01 which exhibit the null point (n<SP>1</SP>). The means to perform this extraction process is a mode compensating network 30 which comprises four identical combining networks 31, 32, 33 and 34. The contaminated TM 01  mode is applied to one input of hybrid junction 35 and the TE 11x  is applied to the other input thereof via phase shifting means 40. Sum and difference signals respectively appear at the two outputs of the hybrid, and the difference signal is passed to one input of a second hybrid 36. The sum signal is passed to the other input of the hybrid 36 via a phase-shifter 37. By suitable adjustment of phase-shifters 40 and 37 the difference output of hybrid 36 comprises the TM 01  force of any TE 11x  contamination, and the sum output comprises the TE 11x  mode. The partly decontaminated TM 01  mode is passed to a second network 32, to which the TE 11 y mode is also applied, such that the difference output of hybrid 43 comprises the pure TM 01 <SP>1</SP> mode and the sum output comprise the TE 11y  mode. The TE 01  mode is similarly decontaminated by first use of network 33 and second, use of network 34. The action of the networks 31, 32, 33 and 34 are explained with reference to Fig. 3 (not shown) by feeding the pure TM 01 1 mode with hybrid 36 and producing the contaminated TM 01  mode from hybrid 35, and assuming that the action of the network is reciprocal. The TE 11x <SP>1</SP>, TM 01 <SP>1</SP>, TE 11y <SP>1</SP> and TE 01 <SP>1</SP> signals are now passed to an error signal processing network. The TE 11x 1 and TE 11y <SP>1</SP> signals are passed to the inputs of a hybrid 12, directly and via a phase shifter 13. The outputs of the hybrid indicate the amount of right-hand circular polarization and left-hand circular polarization respectively present and are selectable by switch 17. Similarly the TM 01 <SP>1</SP> and TE 01 <SP>1</SP> signals are passed, the latter via a phase-shifter 14, to a hybrid 15, to produce right-hand and left-hand polarization outputs selectable by switch 16. The selected signals are brought to standard levels in normalizers 18 and 19 and are then applied to product detectors 20 and 21, detector 21 having a 90 degrees phase shifter 22 at its input. The outputs of the detectors produce orthogonal correction signals for the antenna direction, a switch 23 in co-operation with 180 degrees phase shifter 24, operating in synchronism with switches 16 and 17 to permit the phase of one correcting signal to be reversed.