Patent GB-1382039-A (GB)
Title: Multiple frequency doppler radar system for vehicle passengers
IPC: G01S13/931
Filed: 1973-05-23
Abstract: 1382039 Doppler radar system NISSAN MOTOR CO Ltd 23 May 1973 [26 May 1972] 24608/73 Heading H4D A Doppler radar system for passenger vehicles, such as automobiles, detects the distance between a vehicle and an object in its path by transmitting two separate signals which have slightly different frequencies, and producing a phase difference signal from the two Doppler signals corresponding to said transmitted signals. A first means converts each Doppler signal into a pulse signal consisting of pulses which appear during alternate half-waves thereof. A second means produces a train of pulses of the same polarity, each appearing when either one of the two pulse signals appears, and a third means averages said train of pulse to produce said phase difference signal. As described, a signal generator 13, Fig. 1, is controlled by a switching pulse generator 11 and produces two pulse trains alternating with each other and each carrying an R.F. signal. Said trains are coupled through an isolator 14 and a tuner 16 to an aerial 17. Doppler shifted reflected signals from the object are received by an aerial 18 and signals at the Doppler frequencies are produced by a mixer 20, which also has an input from the isolator 14. A switching circuit 23 controlled by the switching pulse generator 11 selectively passes pulse signals modulated in amplitude by one Doppler signal to a line 25, and by the other Doppler signal to a line 25<SP>1</SP> (Figs. 4C, 4D, not shown). The said signals are then applied through respective hold circuits 26, 26<SP>1</SP>, each of which is arranged to hold its output level during a predetermined time following an input, to respective bandpass filters 28, 281 and amplifiers 30, 30<SP>1</SP>. Bipolar (e.g. sinusoidal) signals from said amplifiers (Figs. 4E, 4F, not shown) are applied to respective limiters 32, 32<SP>1</SP> which produce rectangular pulses during positive half-cycles of said signals, said pulses corresponding to one Doppler signal being displaced with respect to the pulses corresponding to the other Doppler signal by an amount which depends upon the distance to the object (Figs. 4G, 4H, not shown). The two pulse trains are applied to the two inputs of an exclusive OR gate 34, the pulsed output from which is averaged in a smoothing circuit 36 (having an associated control circuit 38) to produce a signal proportional to said distance (Fig. 4G, 4H, 4J, not shown). A signal proportional to the relative speed of the object is produced by a frequencyto-voltage converter 41, which is connected to the output of the limiter 32 or 32<SP>1</SP>. Said distance and velocity signals may be utilized for operation of a safety device of the vehicle. A circuit for the limiters 32, 32<SP>1</SP> is described which produces a pulse rising up when the intensity of the input signal exceeds a predetermined value and falling down when it is below a predetermined value (Figs. 2, 3, not shown). The smoothing circuit or averaging means 36 comprises a resistor-capacitor integrator fed through an amplifier with a transistor having its emitter earthed, and providing output through a transistor emitter-follower circuit (Fig. 9, not shown). The control circuit 38 comprises a capacitor which charges up through a resistor in the absence of output from the gate 34, and disables the circuit 36 by virtually earthing the input to its integrator.