Patent GB-1495387-A (GB)
Title: Road vehicle radar system
IPC: G01S13/931
Filed: 1973-12-22
Abstract: 1495387 Radar JOSEPH LUCAS Ltd 2 Dec 1974 [22 Dec 1973] 59667/73 Heading H4D A road vehicle radar system comprises a radar transmitter arranged to transmit continuous waves which are modulated in frequency by a waveform which has periods of linear increase, periods of linear decrease, and periods without change. The system also comprises a radar receiver and a control unit whereby the parts of the received modulated waveform corresponding to said periods are separately processed to give independent outputs which are related to the range and relative velocity of an obstruction. A computer is fed with the range and relative velocity signals and also receives a signal representative of the actual speed of the vehicle. The computer provides an output as a function of the three inputs. As described, two identical aerials 22, 24, Fig. 1, are of printed circuit type construction, and are used, respectively, for transmission and reception. An oscillator 20 feeds the aerial 22 through a coupler 25, which diverts a small part of its output to a mixer 23. The echo signals received by the aerial 24 provide another input to said mixer. The oscillator 20 is a Q-band Gunn diode varactor, and is set to a centre frequency of 34À8 GHz. It is frequency modulated by a modulator 21 to provide an output which is represented by the solid line in Fig. 3. This envelope comprises successive rising and falling portions with a flat portion between each falling portion and the subsequent rising portion, all portions being of equal durations. Control logic 11 drives the modulator 21 by means of square wave 1 to 1 mark/space ratio pulses which operate a modulo-3 counter. One output of the counter drives an integrator provided with a D.C. bias to produce the increasing and decreasing modulation value periods, and another output of the counter drives a hold switch to hold the output of the integrator for the constant modulation value periods (Fig. 9, not shown). The broken line in Fig. 3 represents the modulated frequency of the received echo waves for an obstruction which has a relative motion towards the vehicle. The Doppler effect causes an increase f d  in the frequency of the received waves of 2f 0 . V/C, where f 0  = carrier frequency, V= relative velocity, C= velocity of light. The time t, taken by the waves to travel from the vehicle to the obstruction and back is 2h/C, where h is the range. This is equivalent to a frequency change of f r  in the rising and falling parts of the modulation waveform of where #f= difference between maximum and minimum transmitted frequencies, and t 2  = length of triangular part of the waveform.f r  is negative for rising parts of the waveform and is positive for falling parts of the waveform. If the relative motion of the obstruction should be away from the vehicle, the sign of f r  is positive for said rising parts and negative for said falling parts (Fig. 4, not shown). Output signals from the mixer 23 are amplified by an amplifier 28, which has a rising gain/frequency characteristic to compensate for low level signals at large ranges, and are fed through a low pass filter 29 to a zero-crossing detector 26 and a counter 27 (controlled by the control logic circuit 11) to provide a digitized input to a computer 10. An alternator 30 is driven through gearing by the speedometer cable of the vehicle and its output is digitized by means of a limiter 31, a monostable 32, and a counter 33 to provide another input to the computer 10. The computer functions according to a specified equation to give an output which is a function of range, relative velocity and vehicle speed, and in which weighting factors take account of vehicle characteristics and stability of control. A converter 12 produces analogue equivalents of the digital outputs of the computer and, as shown, in Fig. 1, these are applied through respective comparators 15, 16 to operate either the brakes or the throttle of the vehicle. Alternatively, they may be arranged to operate a visual and/or audible warning (Fig. 1a, not shown).