Patent GB-937845-A (GB)
Title: Improvements in or relating to radar display apparatus
Inventor: BOLLARD DAVID ROOKSBY
IPC: G01S13/70
Filed: 1959-07-01
Abstract: 937,845. Pulse radar; pulse circuits. DECCA Ltd. Oct. 3, 1960 [July 1, 1959], No. 20286/59. Classes 40 (6) and 40 (7). Relates to an automatic tracking system which generates a D.C. voltage representing the predicted co-ordinate position of a moving echo on a pulse radar display and in which said predicted position voltage is periodically corrected by an error voltage representing the difference between the predicted co-ordinate and the actual co-ordinate as determined by the radar. According to the present invention the actual co-ordinate is represented by the instantaneous amplitude of a sawtooth timebase voltage 105, Fig. 4 (a), at the instant when the echo is received and the timebase voltage 105 and the predicted co-ordinate D.C. voltage 106, Fig. 4 (a), are applied respectively to the grids of two valves 60, 61, Fig. 2, connected as a long-tail pair such that in the region of the cross-over of the two input voltages the instantaneous difference between the anode voltages 107 and 108 of the valves 60 and 61, respectively, is proportional to the co-ordinate error corresponding to an echo received at that instant, the actual error corresponding to a selected echo being determined by applying the anode outputs from the valves 60, 61 through a balanced amplifier 62, 63 to charge respective storage capacitors, e.g. 65, 66, Fig. 2, associated with means providing an output representing the difference A-B, Fig. 4 (j), of the charges A and B, Figs. 4 (f) and (g), on said capacitors, the balanced amplifier 62, 63 having a normally blocked triode cathode load 64 which is unblocked by applying the selected echo, Fig. 4(e), to its control grid. When determining a range co-ordinate the sawtooth timebase voltage is synchronized with the pulse transmission and when determining a bearing co-ordinate the timebase is synchronized with the aerial rotation. The invention is described as applied to plan position tracking systems using cartesian coordinates such as disclosed in Specifications 937,846 and 937,847 in which separate error sensing circuits are used in the X and Y tracking channels, the slopes of the timebase voltages in the two channels being proportional respectivelv to sin # and cos #, where # is the instantaneous bearing of the rotating aerial and the echo which unblocks the triode 64 in each channel being selected by a gate 50 which opens upon coincidence of x and y gate pulses corresponding respectively to the predicted x and y co-ordinates. The predicted co-ordinate voltages may be used (1) to control a marker on a P.P.I. display, (2) to provide information on another display, or (3) as control signals; when a resolved P.P.I. display is used having x and y timebases these may be derived from the error sensing timebases. As shown, a triangular x gate pulse, Fig. 4 (c), produced by combining the anode outputs of valves 60 and 61 through rectifiers 82 and 83 and a corresponding y gate pulse derived from the long tail pair 80, 81 in the Y channel are applied to a coincidence circuit 84, 87 to produce the gating pulse, Fig. 4 (d), for the gate 50, the width of the gating pulse being controlled by the bias applied on a lead 79. As the aerial beam sweeps through a target an echo will be produced in each of a plurality of successive pulse recurrence periods and if it is desired to integrate the errors during the sweep through period, the anodes of the balanced amplifier 62, 63 are coupled through diodes 67, 68 to the storage capacities 65, 66 which are shunted by high resistances 69, 70 forming long-time-constant input circuits to a differential amplifier 71, 72 producing an output representing the integrated co-ordinate error, as shown in Fig. 4 (j). Alternatively. Fig. 3 (not shown), the storage capacities may be connected across the anode resistors of the balanced amplifier 62, 63 to form shorttime constant circuits which are D.C. coupled to the differential amplifier to produce a pulse error output.