GB1058667A - Improvements in pulse radar systems - Google Patents

Abstract

1,058,667. Pulse radar. COMPAGNIE FRANCAISE THOMSON-HOUSTON. Feb. 19, 1964 [Feb. 19. 1963], No. 6940/64. Heading H4D. In a pulse radar receiver long echoes due to extended non-useful objects such as clouds on " window " are eliminated by quantizing the echoes in each return binarily in amplitude in dependance on whether their amplitudes are above or below a given threshold, determining the percentage duration of a return during which the echoes have amplitudes above the said threshold, making a partial long echo decision when the said percentage becomes greater than a given amount, and making a final long echo decision when a minimum number of successive returns give the same partial decision. An example of such time measurement and amplitude quantization of echo pulses is shown in Fig. 1 (not shown), wherein the echoes (a) are quantized in time in periods of (T) duration and are compared with a threshold amplitude (V). The quantized result is shown at (b) wherein a time quantum is of unity amplitude when part of the preceding echo time quantum is above the threshold (V) and of zero amplitude when none of the said echo time quantum is above the said threshold. The quantized signal shown at (Fig. 1b) may be fed to the counting circuit of Fig. 4 (not shown), which comprises a shift register 1 comprising a plurality (1À1) (1À2), (1À3) . . . (1Àn), where (n) is the number of time quanta used, of cascaded bi-stable circuits, the first such circuit having one input controlled by the quantized signal whilst the second input of this and all the other circuits are controlled by clock pulses on line (3) occurring once each time quantum. A logic circuit (4) determines the total number of 1 type signals stored in the register and feeds a threshold decision circuit (5) which produces a partial long echo rejection signal at output (7) when the said total number becomes greater than a given threshold number. When the quantized signal is equal to zero the clock pulses have no effect on the bi-stable circuits. When the quantized signal becomes of unity amplitude, the first circuit (1À1) is switched, and the next clock pulse switches back the said circuit and also switches the second circuit (1À2). The quantized signal thus proceeds along the register to emerge at output (6). Alternatively, Fig. 5 (not shown), the output (6) may be taken from an intermediate point of the register. Alternative to Fig. 4, a circuit (40), Fig. 6 (not shown), may count the difference between the number of 1 signals entering the register and the number leaving it. The register can then be replaced by a delay line (100), Fig. 7 (not shown), having its input and output fed to (40) and the signal output (6) taken from an intermediate part thereof. In Fig. 8 (not shown) the time and amplitude quantized signal as fed to a plurality of delay lines in parallel (1À1), (1À2) . . . (1Àn) having delays successively increasing by one repetition period. The outputs of the delays, together with the undelayed signal are combined in logic circuit (4) and a final long echo decision is produced by a threshold circuit (5) at the output of the logic circuit. The partial long echo decision may be used to block the corresponding long echo in the return, Fig. 9 (not shown). Quantized echo signals and the corresponding partial long echo decisions may be cumulatively stored over say eight repetition periods and a final long echo decision taken by means of threshold circuits at the output of the storing means, Fig. 12 (not shown). In stacked beam radar, Fig. 13 (not shown), a long echo may be detected on one beam and not on another. Each beam is provided with a circuit such as shown in (Fig. 12) and the final long echo decisions therefrom combined in an OR circuit, Fig. 13 (not shown).