Abstract

A radar system mounted on a vehicle and having an RF signal transmitted preferably in a confined beam in front of the vehicle and reflected from obstacles in the path of the beam to be reflected back to the vehicle. The system includes an asymmetrical magic tee which receives both the transmitted and received signals and provides a pair of Doppler frequency signals whose relative phase relationship determines whether the signal is an opening or closing Doppler signal. The signal employs a diplex Doppler detection scheme for providing both range and rate data. Under an imminent collision situation the system provides control signals to power means for pulsating the brakes of the vehicle to thereby avoid a collision. To minimize false target detections and to provide target discrimination, there is provided in this system both a range gated circuit for detecting normal closing rates and an amplitude gated circuit that is operable primarily for detecting fast closing rates such as may occur when a vehicle is stopped in the roadway. A ground speed detector is provided and has an output analog voltage which is usable as a gain control voltage for the range and amplitude gated circuits. The system is also provided with means for inhibiting braking action below a predetermined vehicle speed for use in slow traffic, and means for altering the braking action at speeds above a predetermined speed such as on the order of 35 MPH.