Patent GB-716197-A (GB)
Title: Improvements in and relating to pulse radar systems
Inventor: WHITELEY JOSEPH WILLIAM
IPC: G01S13/526
Filed: 1952-09-16
Abstract: 716,197.. Pulse radar. COSSOR, Ltd., A. C. Sept. 16, 1952 [Oct. 15, 1951], No. 24045/51. Class 40 (7) Relates to pulse radar systems for indicating moving targets only in which the received R.F. echo pulses are applied to a phase sensitive detector 15 together with the output, Fig. 2 (b), from a coherent oscillator 16 phase locked to the transmitted pulses, Fig. 2 (a), the output from detector 15 being applied to a full-wave rectifier 17 whose output, Fig. 2 (c), is applied directly and via a delay device 22 (delay equal to pulse recurrence period) to a differential detector 21 which produces an output only in response to signals from moving targets since for stationary targets waveform, Fig. 2 (b) is identical during successive recurrence periods but a moving target causes a change (dotted portion 103). In such systems an unstable pulse recurrence frequency (P.R.F) results in a spurious output from the differential detector and according to the present invention this is prevented by interrupting the output from the full-wave rectifier 17 by a blanking waveform, Fig. 2 (d), and integrating the resultant signal, Fig. 2 (f), before application to the display unit, the blanking waveform being such that it is in a fixed phase relation to the time of pulse transmission, its recurrence frequency is much greater than the system P.R.F. and each blanking period (negative portion of Fig. 2 (d) waveform) is less than the duration of the transmitted pulse. As shown, 'the transmitter magnetron 12 is controlled by a pulse generator 10 and modulator 11, the output from modulator 11 being also applied to trigger a pulse generator 26 which gates on oscillator 27 whose output, Fig. 2 (b), is applied to a waveform generator 28 producing the blanking wave, Fig. 2 (d), which is applied together with the output, Fig. 2 (c), from rectifier 17 to an input gate 18. The intercepted output, Fig. 2 (f), from gate 18 is modulated at 20 on to a carrier from oscillator 19 and applied to the differential detector 21 directly and indirectly via supersonic delay line 22, amplifier 23 and matching delay line 24 which have a total delay time equal to the pulse recurrence period. The free-running period of generator 10 is slightly greater than the required recurrence period and the generator is triggered by the direct pulse from magnetron 12 applied thereto via components 14, 15, 17, 18, 20, 22 and 23, the recurrence period being then determined by the transmission time round the loops 10, 11, 12, 14, 15, 17, 18, 20, 22, and 23. The output, Fig. 2 (g), from detector 21 comprises a wanted portion 103' due to the moving target and spurious signals 104, 104<SP>1</SP>, 105, 105' due to P.R.F. filter and the spurious signals may be removed by integration. As shown the integration is effected by two separate integrators A and B, 33, 34 to which the interrupted wave, Fig. 2 (g), is applied via gates 29, 30 which are operative alternately at the interruption frequency. The A gate 29 is controlled by a gating wave, Fig. 2 (e), from generator 28 and the gated output, Fig. 2 (h), is applied to integrator A, 33, whose output, Fig. 2 (j), is clamped to a datum level just prior to each gating period by a clamp 31 actuated by clamping pulses, Fig. 2 (i), from generator 28. The result of integration during the gating periods t0-t1, t8-t9, appears during the succeeding blanking periods t1-t2, t9-t10, and is seen to be zero except when the moving target signal 103' occurs in gating period t8-t9, a signal 10b then appearing in the succeeding blanking period t9-t10 and such signals are selected by applying the output, Fig. 2 (1), from integrator A to an output gate 35 controlled by a gating wave, Fig. 2 (h), from generator 28 of opposite phase to the A integrator gating wave, Fig. 2 (e), the selected output, Fig. 2 (b), being applied to control a final gate 39 to which the output, Fig. 2 (g), from differential detector 21 is applied via delay 40 (delay equal to the interruption period) so that the moving target signal 103' of wave, Fig. 2 (g), is selected and appears as a delayed signal 103" in the output, Fig. 2 (m), from gate 39, this output being applied to the display unit 38. Moving target signals occurring during periods t1-t2, t3-t4 &c. are detected in a similar manner by integrator B34, and its associated clamp 32 and output gate 3b, the B control waves (not shown) being 180 degrees phase displaced from the corresponding A control waves. Alternatively the outputs from the A and B output gates 35, 36 are applied directly to the display unit.