RADAR TECHNIQUES FOR DETECTION OF PARTICULAR TARGETS

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.), the rate of rotation (F) of the target may be determined from ##EQU1## where S is the azimuthal resolution expressed by ##EQU2## Furthermore, by knowing the azimuthal extent (W) of the apparent target (namely, the apparent width of the entire set of image points), the width or diameter (L) of the target may be ascertained ##EQU3## Apparatus for classifying rotating targets is provided to permit on-board determination of the class of target detected.