Patent GB-1179937-A (GB)
Title: Radio Navigation System.
Inventor: EARP CHARLES WILLIAM
IPC: G01S1/02
Filed: 1967-11-16
Abstract: 1,179,937. Radio navigation. STANDARD TELEPHONES & CABLES Ltd. 16 Nov., 1967, No. 52142/67. Heading H4D. The Specification describes a radio navigation system comprising, on the ground, an arrangement of omnidirectional antennµ 1, 2, 3, Fig. 1, sequentially radiating for periods of 1/30 second each, C.W. of 1500 Mc/s. and on a co-operating aircraft, a commutated antennµ direction finding array 4, Fig. 2, having a commutation rate of 1 kc/s. and providing on a C.R.T. or meters the spacial directions of each ground antenna thereby providing from the average of and the difference of said directions, respective indications of the aircraft's bearing and range with respect to the ground antennµ. The direction finder is of the Doppler type, producing at the output of frequency discriminator 13 and 1 kc/s. filter 14, a 1 kc/s. signal having amplitude and phase (with respect to the commutating cycle) representing functions of the radiating ground antennµ bearing with respect to the aircraft's heading. The commutation signal from oscillator 8 is fed directly to phase detector 15 and via 90-degree phase shifter 17 to phase detector 16. The phase detectors also receive the filter 14 output and so produce signals e.g. Fig. 4a, representing the horizontal and vertical components respectively of the ground antenna's bearing. Each phase detector output is in three parts corresponding to the successive radiations from the three ground antennµ. Thus the outputs may be fed to respective horizontal and vertical deflection plates of a C.R.T. to provide a display of three spots, representing the aspect of the ground antennµ as seen from the aircraft, and indicating: (a) From the centre position of the display with respect to the C.R.T. centre, the bearing of the ground antennµ; (b) From the distance between the spots 2<SP>1</SP> and 3<SP>1</SP> representing antennµ 2 and 3, the reciprocal of the range to the ground antennµ; (c) From the ratio of said distance to the distance of spot 1<SP>1</SP> above the line joining spots 2<SP>1</SP> and 3<SP>1</SP>, the slope angle of the aircraft; (d) From the horizontal deflection of spot 1<SP>1</SP> with respect to spots 2<SP>1</SP> and 3<SP>1</SP>, the angular track deviation from a line bisecting line joining antennµ 2 and 3; (e) From the tilt of the display, the aircraft banking. By making the ratio in (c) equal to 1 for a predetermined glide slope, the deviation of the aircraft from said glide slope can also be determined. At some distance from the ground antennµ, the spots merge, and a meter display 20, 21, 22, 28 takes over. The D.C. component of the horizontal bearing signal represents (a) and is extracted by a detector and displayed on centre zero housing indicator 20. The A.C. component of said bearing signal represents (b) and is extracted by an A.C. amplifier and displayed on range meter 21. Asymmetry of the A.C. component indicates an angular deviation as in (d) and is detected by a positive/negative peak detector and comparator 23 and displayed on track deviation indicator 22. The ratio of the A.C. components of the horizontal and vertical bearing signals represents (c) and with suitable amplification ratios can be used to energize a glide slope deviation indicator 28. To aid initial acquisition of the ground antennµ, a horizontal direction finder 37 may be used.