Joint time-frequency micro-Doppler analysis of electromagnetic backscattering from micro-motion object

Mechanical vibration or rotation of structures in a target may induce frequency modulation on returned signals and generate side-bands about the center frequency of the target´s body Doppler frequency. The modulation due to vibrations, which is usually at very low frequencies relative to the body Doppler frequency, is called micro-Doppler phenomenon. Radar cross section (RCS) of an object is a function of aspect angle and frequency. When the object is rotating or has a rotating structure on it, the electromagnetic (EM) backscattering is subjects to modulations simultaneously in amplitude and phase that result in asymmetric Doppler spectra about the carrier frequency. The characteristics of the spectra are determined by the geometry, dimension, and the rotation rate of the rotating part.