GB1351096A - Radar distance measuring apparatus - Google Patents

Abstract

1351096 Radar HONEYWELL GmbH 5 July 1972 [6 July 1971] 31366/72 Heading H4D Distance measuring apparatus in which two signals are correlated, one being a delayed version of the transmitted pseudo-random sequence of pulses the other being the received signal and wherein the delayed signal is progressively delayed by a given time interval per period of pulse sequence and the delay for maximum correlation is measured to indicate the distance. Generators 2, 3 produce identical pseudo-random sequences under the timing control of clock 1. The signal X(t) is used to modulate the radar transmitter 4 and received signals are demodulated and passed to one input of sign logic 11. Generator 3 produces a signal Z(t) at the end of every completed pseudorandom sequence which advances counter 14 by one and is fed to the J input of bi-stable 21. During the next clock pulse from clock 1, generator 3 is held reset by the Q output of bi-stable 21 and thus is delayed in recommencing the next pseudo-random sequence. Generator 2 however continues to recycle without delay since the J input to bi-stable 23 is held continuously at "0". Thus the signal X(t - #) fed to the second input of logic 11 has a progressively increasing delay with respect to the transmitted signal during successive sequences. Logic 11 detects whether the instantaneous values of the two inputs A and B are identical and produces a corresponding + or - output which is fed to up-down counter 12. Since the auto-correlation function of a pseudo-random code is zero except at coincidence counter 12 content will vary about zero for the sequences before coincidence and during the period when the delay of the comparison signal equals the echo time of the received signal will rise to a maximum. At maximum count, a signal V12 stops period counter 14 and resets generators 2 and 3 to recommence their cycles. The output of counter 14 is transferred into a memory and decoder 16 which drives a digital indicator 17. The two correlated signals are also fed to an analogue correlation chain 25, 26 which drives an A-D converter 27 whose output provides a further digit 28 for the distance indication. During the sequence in which coincidence of the two signals occurs the analogue correlation provides a finer resolution of the range. A further increase in resolution may be obtained by increasing the clock frequency at the expense of loss of maximum range. Light or acoustic waves may also be used. Device may be used for anti-collision in all types of vehicle or for a fuse.