GB1095355A - - Google Patents

Abstract

1,095,355. Continuous wave radar. DORNIER SYSTEM G.m.b.H. April 29, 1965 [May 22, 1964; Aug. 27, 1964], No. 18088/65. Heading H4D. The Specification describes a radar system whereby a hit or the miss-distance of a missile relative to a target may be detected. Two frequencies differing by for example 5 mc/s. are radiated omnidirectionally from the target and after reflection thereby are received back with corresponding doppler frequency shifts fd, and fd2 (a and b, Fig. 7). These are converted into corresponding square waves c and d by limiters B, Fig. 5, and passed to a digital phase discriminator P. This produces pulse train e, indicating the phase differences between corresponding pulses in trains c and d, which is passed through a gate T, controlled by amplitude threshold means AS, such that it is open only when signals above noise level are being received and by frequency threshold means FS which limits the width of pulses arising from the region of signals a and b, corresponding to the nearest approach of the missile and exhibiting an inaccurate phase reversal, to that shown in pulse train f. Pulse train f is passed through a low-pass filter TP, having a limiting frequency lower than the lowest pulse repetition frequency expected in train f, to produce a mean level output g, the final value of which represents the miss-distance of the missile. This value is stored at SP, the store being cleared at the beginning of the next missile passage. To extend the speed range of the system filter TP may be replaced by three low-pass filters in parallel (Fig. 6, not shown), having pass bands such that low speed, medium speed and high speed missiles are respectively allowed for. To allow fine and coarse miss distance measurements three frequencies may be transmitted, two having a large frequency difference and giving a fine but ambiguous measurement, and another two having a small frequency difference, giving a coarse measurement.