Patent GB-937848-A (GB)
Title: Improvements in or relating to radar apparatus
Inventor: KNOWLES PHILIP NEVILLE GEORGE
IPC: G01S13/72
Filed: 1961-03-22
Abstract: 937,848. Pulse radar. DECCA Ltd. March 16, 1962 [March 22, 1961], No. 10489/61. Class 40 (7). In a pulse radar automatic tracking system which incorporates a repetitively scanning directional aerial, gating means define an area around the expected position of a target in order to select the target echo signal, comparator means compares the tracked position of the target with the instantaneous values of time base scans in one or more co-ordinate directions at each instant when the target echo signal is obtained so as to produce output signals representative of position errors in the one or more co-ordinate directions, the position errors are summed, counting means count the video signals received from the gated area in each aerial scan, and means operative after the completion of the aerial scan across the gated area effects correction of the tracked position of the target by an amount proportional to the sum of the appropriate error signals and inversely proportional to the sum of the appropriate error signals and inversely proportional to the number of video signals received from the gated area during the aerial scan. Thus the present arrangement is more satisfactory than that disclosed in Specification 937,847, when the aerial beam width is relatively wide, since the tracking will now be towards a position in the centre of the beam. In the detailed embodiment tracking is in plan Cartesian co-ordinates and a resolved-time-base P.P.I. display is afforded; in a height-finding radar, height tracking is in one co-ordinate direction, the display having height and range as two co-ordinates. In the general arrangement, Fig. 1, identical devices 14, 15 provide separate tracking of two targets. The video-frequency output of pulse radar receiver 13, and X and Y time-base sawtooth scans from resolving bearing data unit 16, are fed to device 15 included within which there are X- and Y-velocity integrators 20, 21 giving outputs representing the tracked position and to each of which is applied the velocity component from velocity store 24 or 25 and the position correcting signal from correction circuit 26 or 27. The outputs of the velocity integrators are compared with the respective time-base sawtooth voltages in a double comparator 28 which produces an output only when the two pairs of compared voltages are equal; this output gates the required video signal in a circuit 29 and the " normalized " video output is utilized to gate separate X- and Y-comparators 30, 31 which compare the X- and Y-component tracked position signals with the respective X- and Y- sawtooth signals to provide error signal outputs from correction circuits 26, 27. In Fig. 2 only the separate circuits for X-tracking are shown; those for Y-tracking are similar. Velocity integrator 20 comprises an amplifier 32 with a capacitative feed-back 33. The double comparator 28 incorporates.long-tailed pairs 36, 37 and 38, 39; when the X- and Y-components of the tracked position are simultaneously equal to those of time-base voltage a signal is producedat the point earthed by resistor 41 and fed to amplifier 42 to form a gating pulse for gate 45. The gate width is adjustable by a grid bias on line 43. Radar video signals are amplified by variable-gain amplifier 44 and are " bottomclipped " to remove noise before being fed to gate 45; the gate output triggers a regenerator 46 to form standardized video echo pulses. X-comparator 30 consists of valves 50, 51, connected to respective anodes of valves 36, 37 and having a common cathode circuit incorporating a valve 52 controlled by regenerator 46 output; the difference between the comparator 30 outputs is proportional to the direction and amplitude of the X-component position error, for each echo received from the target. Capacitors 59, 60 charge to ultimate voltages proportional to the sums of the outputs at the anodes of respective valves 50, 51. After the aerial beam has swept through the gated area a relay 58/3 is operated and so connects capacitors 59, 60 as to extract the algebraic sum of the X-position errors, the resultant error voltage being fed to the second input of amplifier 32. Relay 63/3 is operated for a time which is inversely proportional to the total number of echo signals received by a control unit 64 which is described in detail with reference to Fig. 3 (not shown), and which includes operation of a further relay if there are less than a predetermined number of target responses, to prevent the velocity integrators and velocity stores corrections being effected. Also if there are more than a further predetermined number of " target " responses, arising from noise or interference, a relay is actuated to ensure rejection of the radar data. Predetermined position and velocity values may be set into corresponding stores 20, 24. The gating pulse for gate 45 may be automatically controlled by a relay, Fig. 3 (not shown), so as to be wide if no target is detected. The valve circuits may be replaced by transistor circuits.