A protective device and protective measure for a radar system is provided that includes an active countermeasure by using passive emitter and/or decoys. Decoys are thereby utilized that function according to the reflection principle. These decoys are thereby radiated by the vehicle's radar. The radiation reflected by the decoys in the direction of the ARM has the same characteristic as the direct radiation from the radar itself. Thus, the ARM is unable to discriminate between decoys and the actual radar.