GB807022A - Improvements in radar circuits - Google Patents

Abstract

807,022. Radar. COSSOR Ltd., A. C. Sept. 20, 1956 [June 22, 1955], No. 18116/55. Class 40 (7). In pulse radar protection against false warning due to " second - time - round " echoes (S.T.R.'s) is arranged by varying the pulse recurrence period, storing a control signal representative of echo time interval, providing a gate opened by the control signal only during short periods around the end of that time interval in several successive recurrence periods, and passing received echoes to a warning device only when the gate is open. The embodiments described apply to an aircraft tail - warning radar. ' First embodiment (see Figs. 1 and 4, and Figs. 2 and 3 (not shown)). The pulse recurrence periods begin at To (see Fig. 4) and are alternated between two different values P1, P2 and a range gate n is used. A wanted echo is shown at t and S.T.R.'s at S1, S2. Pulses To cause gnerator 12 to generate a linear sawtooth as a time-scale arranged to terminate automatically at the end of the range gate in the absence of a received echo within that gate. Video echo signals are applied to gate 14 opened by comparator 15 and if open when a video echo signal arrives a " lengthened-signal " generator 16 terminates the time-scale sawtooth (see also Fig. 4b) whose attained voltage is stored in memory 17; the resetting of the time-scale generator 12 passes a pulse to the comparator to close gate 14 shortly after it has passed the echo signal. The comparator passes a pulse to memory re-set gate 21 to prevent memory re-set multivibrator 20 erasing the store in the memory. When the next To pulse arises the time-scale generator gives a new sawtooth compared in the comparator with the voltage from the memory. Immediately prior to the instant at which an echo signal from the same target as previously considered is due, as determined by the memory, the comparator opens gate 14 and via multivibrator 22 opens gate 18 briefly; if an echo signal arrives at this time a lengthened pulse is generated and fed through gate 18 to a counter. If no echo signal arrives at the expected time gate 14 remains open and an echo signal arriving later within the range gate operates the lengthened signal generator, gate 18 being closed, and the range of the new echo signal is stored in the memory. If no echo signal arrives during the range gate, the memory capacitor is discharged and the time scale generator re-sets. The circuit of Figs. 2 and 3 (not shown), differs in that lengthened signal pulse generator 16 is omitted and gates 14, 18 are combined in the same valve; it is arranged that the time-scale sawtooth always begins with a fixed voltage step (see Fig. 4 (b)), to ensure that however soon after To an echo signal arrives the memory capacitor has sufficient charge to carry out its required functions. Preferred embodiment.-In the preferred embodiment (see Figs. 5 to 8, not shown), the major difference from the above arrangement is that a separate multi-vibrator is triggered five microseconds before To and its period is longer than the range gate by the duration of a lengthened signal pulse; this ensures that when a lengthened signal pulse occurs at minimum range the memory capacitor is sufficiently charged to carry out its required functions. Warning of wanted received echoes.-The warning device (not described) is triggered only after a predetermined number of lengthened pulses have been applied to the counter.