GB980440A - Improvements to radar data extraction systems - Google Patents

Abstract

980,440. Pulse radar. SOC. NOUVELLE D'ELECTRONIQUE ET DE LA RADIOINDUSTRIE. March 30, 1962 [April 17, 1961; May 23, 1961], No. 12298/62. Heading H4D. In order to remove spurious signals from wanted echo signals in pulse radar, the detected signals are subjected to successive " coincidence " searches in the first of which relatively long time gates q 1 , Fig. 2a, are utilized and in the second of which time gates q 2 , Fig. 2b, not longer than the radar pulse duration are utilized, the second coincidence search being made only for those signals found in the first coincidence search, and the wanted signals are fed to a memory device. The video echo signals on line 1, Fig. 1, below an amplitude threshold S 1 , Fig. 2a, are rejected by a device 2 which additionally amplifies signals above that threshold to a fixed amplitude S 2 , Fig. 2b; Fig. 2 shows sequencies of echo signals in successive repetition periods I, II, III, IV, the signals in corresponding periods being designated by letters a, b, c, d. A circuit 6 causes the signals to be delayed by the quantum q 2 and also causes signals occupying two quanta to issue in the positions of two adjoining quanta as depicted in Fig. 2c. Circuit 3 includes a matrix of ferrite cores each of which changes state in response to a signal corresponding to a quantum magnitude q 1 , the signals being delayed by q 1 as shown in Fig. 2d. Fig. 2e represents the signals of Fig. 2b which have been delayed by a quantum q 1 and advanced by a quantum q 2 . Circuit 3 makes the first coincidence search from the second repetition period to the first &c., the signals, Fig. 2f, ensuing and being switched by a circuit 4 to the small-quantum coincidence search circuits 5 from whose output circuit 7 issues the signals shown in Fig. 2g. In an alternative embodiment the signals from circuit 3 are applied to a range counter feeding a switching circuit connected to registers each of the latter controlling a " conditioner" such that when the range counter passes through a state corresponding to that of one of the registers in the next recurrence period the conditioner delivers a pulse to an output circuit via an AND circuit, Fig. 3 (not shown). In order to assist differentiation of wanted echoes from clutter, the signals selected by the two coincidence searches are applied to a delay line 18, Fig. 5, consisting of elements 19 each of which imparts a delay of one quantum q 2 ; the delay line outputs are connected as shown to a summation circuit 21 and a differential amplifier 22 the other input to which is a D.C. reference voltage. Amplifier 22 and the mid-point of the delay line are connected to AND circuit 23 the output from which is sent to utilization means. The theory of operation of Fig. 5 is described with reference to Fig. 4 (not shown).