Abstract: A vehicle collision preventing apparatus determines the danger by an output of a radar for detecting the distance to an obstacle and the relative velocity in a danger determining circuit wherein the distance to the obstacle and the relative velocity at the present are estimated from the data given before disappearing the data of the radar by an estimate arithmetic circuit when a signal reflecting from the obstacle reduces to be incapable of detecting the obstacle by the radar.

Abstract: A radar apparatus comprises a microwave head portion in which a solid state oscillator, such as a Gunn oscillator, is utilized to generate a transmitting signal wave to be transmitted toward a target as well as a local oscillation signal wave by which an intermediate frequency signal is obtained upon a receipt of a reflected wave from the target. A transmission-reception switch means connected to a hybrid coupler constitutes a switching means for switching the operation of the radar apparatus between a transmitting mode and a receiving mode. A signal processing portion is provided in which the instantaneous amplitude value of the intermediate frequency signal according to a phase variation of the intermediate frequency signal due to the movement of the target is obtained by sampling the intermediate frequency signal with sampling pulses, whereby the velocity and moving direction of the target are determined and, by combining such information, an alarm is actuated.