Patent GB-880142-A (GB)
Title: Improvements in or relating to radar apparatus
Inventor: MATTHEWS ROBERT
IPC: G01S1/02
Filed: 1956-10-22
Abstract: 880,142. Radar. DECCA RECORD CO. Ltd. Jan. 20, 1958 [Oct. 23, 1956], No. 32190/56. Class 40(7). Relates to a system for navigating a craft in relation to a predetermined track in which the position of the craft is determined by a control primary or secondary pulse radar having a P.P.I. display produced by a C.R.T. with fixed orthogonal x and y deflectors and the position of the craft relative to a predetermined point on the track is transmitted to the craft as a pilot instruction (speech or meter display) or for automatic control of the craft. According to the present invention x and y voltages controlling the position of an electronic interscan marker are adjusted manually or automatically to maintain the marker coincident with the craft response on the P.P.I., a line trace representing the track is produced on the P.P.I. by applying repetitive interscan waveforms to the x and y deflectors and the differences between the x and y marker position voltages and x and y voltages corresponding to a predetermined point on the track trace are determined and applied through resolvers to combining circuits to give the components of the distance of the marker from the predetermined point along and perpendicular to a reference direction, e.g. the direction of the track or the direction of movement of the marker. In Fig. 2 the x and y voltages corresponding to the predetermined point in the track are produced by sampling the track waveforms at the appropriate instant in each cycle of their generation. Fig. 1, rectilinear track. As shown two generators 15 and 16 are coupled to the x and y deflector coils 17, 18 of the P.P.I. C.R.T. 14, each generator producing a sawtooth output having a starting level dependent on an input shift voltage and a slope dependent on an input rate voltage as described in Specification 818,477. With the switches 22 in the left-hand position, the generators 15, 16 produce an electronic interscan marker, e.g. a small circle, as described in Specifications 744,640 and 837,201 whose position is controlled by x and y D.C. position voltages from a position signal generator 20 to coincide with the craft response on the P.P.I. display; the generator 20 may comprise a manually adjusted resolver with a manually variable input or an automatic tracking arrangement as described in Specification 867,361. With the switches 22 in their right-hand position, the generators 15, 16 produce an electronic interscan rectilinear trace representing the desired track, the position of the origin of the trace being determined by x and D.C. position voltages from a generator 21 applied to the shift inputs of the generators 15, 16 and the direction of the trace being determined by applying to the rate inputs of generators 15, 16 the D.C. outputs from a sin-cos generator 23 controlled by a manual control 24. Voltages proportional to the x and y co-ordinates of the craft marker relative to the origin of the track trace are produced by applying the outputs from the generators 20, 21 to subtraction circuits 27, 28 and the resultant difference voltages are resolved into components along and perpendicular to the track by resolvers 29, 30 controlled by the manual control 24, the outputs from the resolvers 29, 30 being combined in circuits 31, 32 to give signals representing the component distances of the marker from the origin of the track trace along and perpendicular to the track. These signals are displayed on meters 32, 34 and transmitted by a radio link to the craft for display on similar meters 39, 40. The rate of change of deviation of the craft from the track may be obtained by differentiating the deviation voltage. The craft may be navigated along a path differing from that represented by the track trace by controlling it to maintain the track deviation at some predetermined, and possibly varying, value. A plurality of craft can be controlled from a single radar display if separate components 20, 27-31, 33 are provided for each craft marker. Figs. 2, 3, 4, non-rectilinear track. In this embodiment x and y components of a curved track 76, Fig. 3, are represented by synchronized repetitive waveforms 79, 80, Fig. 4(a) and (b), produced during each interscan period B, Fig. 4, by means of integrators 70, 71, Fig. 2, to each of which is applied a D.C. rate control voltage which is varied continuously or in steps during the interscan period B to produce the required track curvature. The starting levels of the waveforms 79, 80 are defined by D.C. shift control voltages applied to the integrators 70, 71 during an initial period t1, Fig. 4. During other interscan periods A, Fig. 4, a circular craft marker 78, Fig. 3, is produced by generators 65 corresponding to generators 15, 16 in Fig. 1, the x and y voltages 81, 82 Fig. 4(a) and (b) controlling the position of the marker being produced as in Specification 837,201 by generating at 61 voltages proportional to the x and y components of the speed of the craft and integrating these speed voltages in integrators 62, 63 whose starting levels are controlled by the x and y outputs from an initial-position signal generator 60. In order to determine the distance of the craft marker 78 from a predetermined point on the track, the track waveforms 79, 80, Fig. 4, are sampled in demodulators 85, 86 of the type described in Specification 867,361 by a sampling pulse, Fig. 4(d), to give x and y D.C. position voltages which are subtracted at 87 and 88 from the x and y marker position voltages from the integrators 62, 63, the resultant difference voltages being resolved and combined to give voltages representing components of the required distance along and perpendicular to a direction determined by the setting of the resolvers 89, 90 which may be controlled manually in accordance with the directional setting of the craft speed and direction signal generator 61 or automatically in accordance with the direction of the track as determined by pulse sampling the rate voltage inputs to the track waveform generators 70, 71. If it is required to display the track 76, Fig. 3, on the C.R.T. 54 the input control voltages to the track waveform generators 70, 71 are also applied to the marker generators 65 during the track interscan periods B and in this case the generators 70, 71 may be omitted, the track voltage inputs to the demodulators 85, 86 being taken from the generators 65. The sampling pulses, Fig. 4(d), applied to the demodulators 85, 86 are generated by applying to a coincidence comparator 96 (1) a linear sawtooth timing waveform 95, Fig. 4(c), produced during each interscan period and (2) a varying D.C. voltage 101, Fig. 4(c), from a control circuit 97 such that an output pulse is generated when the instantaneous amplitudes of the inputs 95 and 101 are equal. The circuit 97 may comprise a manual potentiometer but as shown it comprises an integrator 98, the starting level and slope of the output waveform 101 being controlled respectively by potentiometers 99 and 100 in accordance with the initial position and the speed of the craft so that the predetermined point on the track from which the distance of the craft marker is measured is the position that the craft would have reached if it had followed the track.