Patent GB-1509138-A (GB)
Title: Anti-collision radar
IPC: G01S13/58
Filed: 1976-03-30
Abstract: 1509138 Anti-collision radar INTERNATIONAL STANDARD ELECTRIC CORP 30 March 1976 [4 April 1975] 12719/76 Heading H4D In an anti-collision radar, particularly for automobiles, of the type utilising a sawtooth frequency modulated CW device for simultaneously measuring the distances and relative speeds of targets within a range to be monitored and wherein a beatnote signal (video signal) containing the information on distance and relative speed is generated in a first mixer 6 by superposition of a signal SR reflected from a target and a signal SM coupled out of the radar transmitter, the said range is divided into several distance ranges which are cyclically searched, a second mixer 9 being provided wherein the video signal is converted up with cyclically changed frequencies (from an oscillator bank 10) allotted to one distance range each so that if several targets are present the relative speed of at least one target is measured, and the distance and relative speed are determined simultaneously from the frequencies of a given partial range of the frequency spectrum of the output signal of the second mixer 9. The radar described measures only the relative speed of the closest target, but it may be adapted to measure the speeds of several or all targets in the monitored range. The cyclical search is interrupted for measurement only when a target is detected. The given partial range of the frequency spectrum of the output signal of mixer 9 is filtered out by a steep-slope band-pass filter 11 whose output is allotted to one distance range. A signal appears at the output of filter 11 only if the video signal was mixed in mixer 9 with the frequency allotted to the distance range in which a target is located. Thus, if the mixing frequency is known, it will be known in which distance range the target is located. The filter output signal is converted down in a mixer 12 and fed to distance evaluating unit 16 and relative speed evaluating unit 17 and subsequent signal processing units 18, 19, and an indicating unit 20. To avoid disturbing superpositions during the return of the modulating signal a switch 21 controlled at the repetition rate of the modulation frequency by a one-slot multivibrator 8 prevents the video signal from being passed on to an amplifier 7 during this time. The distance evaluating units 16 (see also Fig. 3, not shown) produces signals SF1, SF2 and SE according to whether the target is in the first or second of two partial distance ranges or exceeds a threshold value. The relative-speed evaluating unit 17 (see also Fig. 4, not shown) includes a band-pass filter which filters out the frequency range corresponding to the Doppler shifts to be expected and the Doppler shift is determined using a turnable N-path filter controlled by a voltage-controlled oscillator. A signal SDV goes to unit 18 when the output of the band-pass filter exceeds a threshold value and a signal SD is transmitted to unit 19 when the output of the N-path filter exceeds a threshold value. A signal SVCO with the frequency of the voltagecontrolled oscillator also goes to unit 19. Signal SD is present only when the centre frequency of the N- path filter corresponds to the frequency of the Doppler-shifted spectral line. The relative speed is determined by measuring the frequency at which the VCO oscillates when signal SD is present. The distance signal processing unit 18 (see also Fig. 5, not shown) receives signals SF1, SF2, SE, SDV, and a clock signal which cyclically switches a control device producing output signals El to E12 which control the oscillator bank 10, such switching ceasing during speed evaluation. An output signal ST goes to unit 19. The relative speed signal processing unit 19 (see also Fig. 6, not shown) receives signals ST, SVCO, SD and E12, and determines the relative speed and direction of the closest target. The indicating unit 20 has a display giving the relative speed (and sign) as well as the distance of the target.