Patent GB-1004873-A (GB)
Title: A system responsive to the distance between two objects in relative motion
IPC: G01S13/50
Filed: 1961-12-11
Abstract: 1,004,873. Distance measurement by Doppler effect. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Dec. 11, 1961 [Dec. 16, 1960], No. 44299/61. Heading H4D. In a system responsive to the distance between two relatively moving objects, two U.H.F. signals are transmitted from one of the objects and mixed with the respective echo signals from the other object to detect the two Doppler beat frequency signals which are fed to individual means producing pulses each time the signals cross zero, which are in turn fed to an AND gate controlling a counter, counting the zero pulses from one of the Doppler signals such that the first simultaneous reception by the AND gate of a zero pulse from both signals starts the counter whilst the second such reception stops it, the the counter reading being indicative of the closest approach of the two objects. The first simultaneous reception by the AND gate of a zero pulse from both Doppler signals, may actuate a control, e.g. firing device. In the vector diagram of Fig. 1, which is for a target C transmitting a signal, frequency f 1 , to a missile E at a   distance r, the echo signal vector #E lags the transmitted signal vector by an angle # where The inphase component of E is thus equal to   zero for #=#/2(2K+1) or r 0 =(2K+1)# 1 /8   giving Fig. 3 which shows a family of r 0  circles separated by # 1 /4. The transmission of a second   frequency f 2  < f 1  results in a second family of circles (not shown), coinciding for a common value of r 0  given by In Fig. 4 the two frequencies F 1  and F 2  are fed by transmitters 1 and 2 to aerial 3 and are mixed (as soon as the missile nears the r 0 . COIN  circle) with the respective echo signals F 1D  and F 2D , received by aerial 4, in mixer 5. The resulting beat frequencies (F 1  - F 1D ) and (F 2  - F 2D ) are transformed into I.F.'s by local oscillator 6 and as (f 1 -f 2D ) and (f 2  - f 2D ) are amplified in 11 and 12 and amplitude detected in 21 and 22 to produce the required in-phase components of   vectors #E 1  and #E 2 . The resulting sine waves are squared off in clippers 31 and 32 and the zero crossings are located by pulses produced by differentiators 41 and 42. The two series of pulses are fed to an AND gate 7 which upon simultaneous reception of pulses from both clippers, caused by the missile crossing the r 0 . COIN  circle, turns on a counter 8 which then commences to count the pulses produced by differentiator 41. The counter is switched off by the second coincidence of pulses in the gate at the r 0 . COIN  circle. Thus knowing the value of r 0 . COIN  and # 1  the distance of the missile from the target is fixed every time the counter receives a pulse from differentiator 41, the total count registered by the counter also indicates to # 1 /4 the nearest approach of the missile to the   target. The count may be fed to transmitter 1, for transmission to the ground or a separate transmitter may be used, Fig. 6 (not shown). The apparatus may be mounted in the missile and operate a proximity fuse as soon as the missile is at a distance r 0 . COIN  from the target, Fig. 7 (not shown). Separate counters may be used for each differentiation.