Abstract: A radar system is capable of detecting and classifying rotating targets such as rotating antennas. Particularly, unfriendly radar installations can be detected and classified by a synthetic aperture radar system, which may be carried by an aircraft.The radar reflection signal (echo) received by a synthetic aperture radar system and reflected from a rotating object will appear as a series of image points, or pulses, at the same range, but spaced apart by some apparent distance or frequency. By knowing the apparent distance (d) between adjacent image points, the range (R) to the target, the time of integration (T.sub.o) of the radar system, the velocity (V.sub.o) of the detecting aircraft, the angle (B.sub.o) to the target, and the wavelength of the aircraft's radar signal (.lambda.