Patent GB-1375221-A (GB)
IPC: G01S13/91
Filed: 1972-02-04
Abstract: 1375221 Radio navigation; pulse radar THOMSON-CSF 4 Feb 1972 [4 Feb 1971] 5389/72 Heading H4D In a pulse radar aircraft landing system, cooperating with reflectors disposed about a runway, several bearings of the aircraft relative to the reflectors are obtained at different times, but used simultaneously for computing purposes, correcting means being provided to take into account change in the bearings due to yaw and horizontal movement of the aircraft between bearing measurement and computation. The system comprises dual channel radar, Fig. 12(a) having an antenna 1 which is scanned in azimuth to give horizontal bearing information with respect to reflectors B1 to B3, its elevation angle being fixed. Information about the aircraft elevation with respect to the reflectors is obtained by a monopulse technique. The antenna is stabilized against roll and pitch by inputs I R , I P . The radar may be used as a simple detector of, e.g. clouds by switches 9, 14, which when in their lower positions enable sum channel 11 to feed weather radar receiver 15. In this mode, the antenna scanning rate is lower, the sweep is greater and the radar pulse length and duration are longer. Inputs 61, 62 control the pulse repetition rate and length. Reflector bearings g 1 , g 2 , g 3 , obtained at different times from position detector 25, are fed to correcting means and reflector distances r 1 , r 2 , r 3 , runway parameters I RW  i.e. length, width &c., aircraft yaw I y , elevational data #S 1  to #S 3 , and reflector parameters i.e. their geometrical disposition, are fed to a computer 26. Computer 26 provides a signal ro giving the distance to desired landing point Bo (Figs. 8, 9, not shown). In Fig. 12b computer 26 is again shown, together with further units 201 to 205 and unit 26a. Unit 203, detailed in Fig. 16 (not shown), utilizes the data available to produce a synthetic runway display (Fig. 17, not shown) on a cathode-ray tube. Unit 204 provides a signal D s  giving estimated stopping distance of the aircraft after touch down and unit 205 gives an indication if the aircraft comes within collision distance of obstacles along the flight path, Fig. 21 (not shown) illustrating a modified form of the circuit in Fig. 12 using a device similar to unit 205 to control receiver 15. Computer 26 provides a signal #S 0  related to the elevation of the aircraft with respect to point B 0 . Unit 26a utilizes this value, together with elevation information #S 3 , distance r 3 , and runway length L to compute a value # (Fig. 9, not shown) giving the aircraft elevation with respect to the ground. Unit 202 has inputs for reflector parameters a, b &c. (e.g. see Fig. 14, not shown), bearings g 1  to g 3  and aircraft course, the unit 310 constituting the correcting means of the invention. Unit 202 is illustrated in Fig. 15 and comprises devices 401 to 403, each corresponding to one of g 1 , g 2 , g 3 . The instantaneous aircraft course deviation #C is obtained from unit 303 and is fed into units 401 to 403 and added to inputs g 1  to g 3  to compensate for yaw variations. The units 401 to 403 determine the mean bearings G1 to G3 from n echoes. Figure 14 illustrates the situation when the aircraft is on or near the runway axis, as in the landing phase, A being the projection of the aircraft position on to the runway. The angle G 1  gives the bearing of reflector B 1 relative to the aircraft axis and is G<SP>1</SP> 1 , the bearing relative to the runway axis. G<SP>1</SP> 1  can be obtained from a, b/2 and t 0  which is equated to AB 0  G<SP>1</SP> 2  can be similarly obtained for reflector B2. The rates of charge of G<SP>1</SP> 1 , G<SP>1</SP> 2  are obtained in units 405, 406, G<SP>1</SP> 3  being ignored as B 3  is on the runway axis. #G<SP>1</SP> 1 /#t and #G<SP>1</SP> 2 /#t approximate to the rate of charge in G 1 , G 2  and are added to G 1 , G 2  in 401, 402. The compensated G 1 , G 2  values are then used in computer 408 simultaneously to compute G 0 , the bearing of point B 0  relative to the aircraft. Figure 13 (not shown) illustrates the circuits of Fig. 15 in greater detail. The available data is fed into device 201 which computes X 0 , Y 0 , Z 0  the aircraft co-ordinates with respect to the runway, r 3 -e, the distance of the aircraft from the end of the runway, e being the distance between B 3  and the runway limit (Fig. 10, not shown), angle γ giving the aircraft bearing relative to the runway axis (Fig. 10, not shown),  G 3  the reflector B 3  bearing, angle ## (Fig. 10, not shown) giving the angle through which the aircraft must be turned to align with the runway axis and angle 8, the deviation of the aircraft flight path with respect to the desired theoretical glide path T (Fig. 9, not shown).