Patent GB-1103510-A (GB)
Title: Moving target electromagnetic detection system
IPC: G01S13/64
Filed: 1965-04-15
Abstract: 1,103,510. Pulse doppler radar. STANDARD TELEPHONES & CABLES Ltd. (Laboratoire Central de Telecommunications). 15 April, 1965, No. 16170/65. Heading H4D. In a coherent pulse doppler radar, of the type wherein the output of the receiver phase discriminator is applied to a channel comprising a band pass filter 31/35, Fig. 5, to extract the doppler signals (waveform K, Fig. 8), a rectifier 51/55, (waveform L) and a low pass filter 61/65 to remove the doppler ripple (waveform M) and produce a signal for an M.T.I. A-type display 71/75, a plurality of said channels is provided fed by the phase discriminator output via a plurality of gating switches, each switch being gated open once per repetition period at a time which walks through the repetition period and which progressively lags by equal amounts from one switch (21) to the next (22). The time bases of the oscilloscopes have time repetition frequencies equal to the strobing frequency of the switch gates, or a multiple thereof, such that displays are built up at said repetition frequency as a result of the successive strobing of a plurality of successive echo returns. In a first embodiment, Figs. 5, 6, 7, 11, the transmitted pulses are at a repetition frequency Fr (waveform A, Fig. 7) and a strobing pulse train with a repetition frequency of M (Fr-fe) (waveform C) is produced by a rotary phase shifter 18 where M is the number of display channels used, e.g. 5, and fe is a small fraction of Fr, e.g. 1/6. The waveform C is fed to five AND gates 26/30 and to a 1: M divider 46 which produces waveform B with a repetition frequency of (Fr-fe). Waveform B is fed to trigger a monostable circuit 36 to produce a gating pulse train D each pulse train having a width just greater than 1/MFr. Pulse train D is fed to gate 26 such that pulses E in the strobing pulse train C are gated through to output terminal 41 and also trigger input of monostable circuit 37. The gating pulse train F from circuit 37 in turn gates pulses G through gate 27 to output 42. Thus there are produced at terminals 41/45 a series of strobing pulses for application to respective switches 21/25, having periods of 1/Fr - fe and so walking through the echo return period 1/Fr with a period of 1/fe, and being successively delayed from one switch to the next by intervals of 1/5(Frfe). Thus if the screen of each display C.R.T. 71/75 is divided into five parts and each C.R.T. is supplied with a sweep voltage 69 of period 1/fe, then the A type display on the C.R.T., is as shown in Fig. 11. On each C.R.T., particular attention is paid to the first fifth of the display to be traced. Thus to C.R.T. 71 is allocated the first fifth of the range, to C.R.T. 72 the second fifth, and so on. Thus the entire range is displayed between the five C.R.T.s in the time taken to display only a fifth of said range. In a second embodiment, Figs. 9, 10 (not shown), each channel deals with and displays only a respective fifth of the range, the strobing pulses for any particular channel sweeping through the respective range fifth with a period of 1/5-fe. Each C.R.T. is provided with a sweep voltage with a frequency of 5fe such that the first fifth of the range is spread out to cover all of the first C.R.T. 71, and successive fifths of the range are displayed on successive C.R.T.s.