Abstract: An auto-test device for a radar includes at least one transducer located in the field of radiation of the radar microwave transmission, the transducer being configured to intersect a part of the radiated energy and to send it back to a receiver so as to create, in the receiver, a test signal modulated by beats of the transducer. The device further includes a synchronism mechanism configured to excite the transducer in synchronism with a sub-multiple of the frequency of sampling of a reception signal. The transducer is placed such that the receiver receives a test signal with a mean value close to zero.

Abstract: Disclosed is a radar for the detection of obstacles. The radar uses at least four frequencies referenced F.sub.1, F.sub.2, F.sub.3, F.sub.4 such that:F.sub.1 -F.sub.3 =F.sub.2 -F.sub.4and such that:(F.sub.1 +F.sub.3)-(F.sub.2 +F.sub.4)=Cte where Cte represents a constant frequency value, the measurement of distance from the target being done on the basis of the difference in phase between two signals of which the first (r.sub.1 (t)-r.sub.3 (t)) is constituted by the difference between two received signals corresponding respectively to the frequencies F.sub.1 and F.sub.3 and the second (r.sub.2 (t)-r.sub.4 (t)) is constituted by the difference between two received signals corresponding respectively to the frequencies F.sub.2 and F.sub.4. Application in particular to automobile speed control.