GB1445184A - Continuous wave radar system and method for obtaining range discrimination therewith - Google Patents

Abstract

1445184 FM-CW radar INTERNATIONAL STANDARD ELECTRIC CORP 2 Nov 1973 51020/73 Heading H4D In a "range limited" FM-CW radar system, of the kind wherein the beat signal is passed through a filter to select a particular modulation side band, which side band varies in amplitude according to a Bessel function of the target range, e.g. as shown in Fig. 3 for the first order side band, the largest amplitude peak 22 occurring at close range, enables, in conjunction with a detection threshold 26, the limitation of target detection to said close range. A very good reflector, e.g. sea, at a greater range, may however produce an echo which, even when weighted by a lesser peak, 23, may come above the threshold and cause an erroneous detection. To overcome this, it is proposed to produce a delay between the transmitted signal and that used for beating with the echo signal, such that a beat signal side band of the sixth order on higher, e.g. the tenth, having an amplitude which varies with distance as shown in Fig. 4 when no delay is introduced, now has an amplitude variation as shown in Fig. 5, the "mirror" peak 33 of Fig. 4 having being "shifted" to the right by a "range" equivalent to the delay. The delay is chosen such that the peak 33 in Fig. 5 extends over the required near range zone of investigation and the next peak 28 is at such a large range that no sufficiently large echoes therefrom could cause interference.