Abstract: In an anticollision device, a moving object heading in a given direction along a movement vector and having a relative speed vector directed towards an obstacle is fitted out with at least two antennas sending out a microwave signal liable to be received by the obstacle. The device furthermore comprises reception means and means to analyze the echoes received from the obstacle, the analyzing means determining the variation with respect to time of the angle .theta. between the movement vector and the relative speed vector, a substantially zero variation of the angle .theta. indicating a risk of collision. Application to the equipment of motor vehicles to prevent collisions, notably in the event of poor visibility.

Abstract: The distance between the target and the measurement means is segmented into adjacent distance compartments, the first one of which starts at the zero distance. Each distance compartment has an associated energy level obtained by the demodulation of the delay measurement signal resulting from the product of correlation between the emitted signal and the received signal reflected by the target. The disclosed method consists in creating two distinct aliasings of the spectrum of the signal measurement signal, the energy level of which corresponds to the first distance compartment, these aliasings being achieved on the part of the spectrum corresponding to negative distances. This two distinct aliasings make it possible to obtain two distinct energy levels on the totality of the first distance compartment, and thus enable the measurement of all the distances on this first distance compartment, including the very small distances, even almost zero distances, by comparisons and analyses of the two energy levels.