Patent US 4,348,674

Method and apparatus for passive classification of moving targets which uses pulse Doppler radar wherein in addition to the primary Doppler echo the radar echo signals of the moving targets also contain periodically repeating Dopplers side line frequencies which can be utilized for classification of the targets. These Doppler side lines occur because of the periodic change of reflectivity of the target as, for example, due to rotating parts on the target and in the invention are investigated by means of spectral analysis for identification of the target. For example, land vehicles, wheeled and track vehicles can be easily distinguished with the invention and a first rough evaluation and in a fine detail evaluation, can be classified for every target type.