Patent GB-928426-A (GB)
Title: Vehicle radar system
IPC: G01S13/931
Filed: 1960-09-13
Abstract: 928,426. Automatic relative speed control. BENDIX CORPORATION. Sept. 13, 1960 [Oct. 2, 1959], No. 31539/60. Class 38 (4). [Also in Group XL (c)] In a vehicle mounted Doppler radar system for warning the vehicle driver of the proximity of a preceding vehicle and for automatically braking the vehicle and/or controlling the speed to maintain a fixed predetermined separation between the vehicles the radio-frequency energy forming the radar beam is single side-band modulated. With this arrangement the Doppler frequency components (derived by demodulation of the reflected energy) due to " closing " and " opening " relative velocity are situated in separate frequency bands positioned in different portions of the frequency spectrum so that separation of the components indicative of a " closing " velocity may be separated by means of a band-pass filter. As shown in Fig. 1, an R.F. carrier oscillator 20 is amplitude modulated in 24 by a constant frequency signal from oscillator 22 and the modulated wave is radiated by a forwardly directed aerial 26 mounted on the front of the vehicle. Reflected energy, received by an aerial 28 (preferably coaxial with 26) is fed to a homodyne detector 34 together with a portion of the carrier from 22 via directional couplers 30, 32 and the output from detector 34, consisting of the modulating signal together with a Doppler component, is supplied to a band-pass amplifier 36. The latter, which has a pass-band extending from somewhat less than the modulating signal frequency to the sum of the latter plus the maximum Doppler frequency increment that may arise, supplies a discriminator 40 and an adjustable band-pass amplifier 38 which, as described above, separates out the Doppler frequency components caused by a " closing " relative Velocity. Two operating modes are described. In the first mode (termed " warning " mode) the switches 48, 52, 54 are (as shown) on their a contacts and the system operates to supply a warning signal and/or to apply the vehicle brakes when a predetermined minimum separation between the vehicles has been reached. This is achieved by supplying the output of the filter 38 to a phase comparator 42 which has, as a second input, a single from the modulating oscillator 22 delayed in 44 by an interval controlled by a coupling from the speed indicator 46 such that it corresponds to a minimum safety separation which increases with increase of speed. When the separation becomes less than this value the output of the comparator 42 operates a warning and/or braking device 50. By including a variable attenuator between the comparator 42 and the device 50 the attenuation of which is reduced (controlled by an output from filter 38) as the Doppler frequency indicative of a " closing " frequency increases, the warning and/or braking action may be made to occur more promptly at high than at low speeds (Fig. 2, not shown). In the second operating mode (termed " tracking " mode) switches 52, 54 are positioned on their b contacts and switch 48 on either a or b optionally and the system operates to control the vehicle speed control 46 to maintain a constant separation, predetermined by manual setting of delay device 44, between vehicles (switch 48 on contact b) or to maintain a separation which increases with increase in speed (switch 48 on contact a). This is achieved by utilizing the output of discriminator 40, which supplies distinguishable signals (e.g. + and -) when the input from amplifier 36 represents a " closing " or an " opening " relative velocity to operate the speed control device 46 to reduce such relative velocity to zero. At the same time, the output of the comparator 42, independently, controls the vehicle speed device 46 in accordance with the predetermined delay in delay device 44. Specification 888,975 is referred to.