Employing microdoppler of radar signal to extract the characteristics of helicopter rotor

Microdoppler is a new subject in radar signal processing with a research history of about twenty years. Radial velocity of targets relative to radar position, causes doppler frequency shift of return signal to radar. In addition to radial velocity of target fuselage, many targets consist of components which have small scale motions which results in frequency modulation around the main doppler frequency shift. Vibrations of the motor components and fuselage of airplanes and blade rotation of helicopters are some examples of these types of small scale motions which produce periodic doppler shifts known as microdoppler. Extraction of microdoppler shift and its properties is very important in target classifications and estimating many parameters of the target. In this study we focus on microdoppler properties of return signal of radar from helicopter. Estimation of helicopter parameters such as number of blades, their length and velocity of angular rotation and finally identification of helicopter type are aims of this research. For this purpose, the previous methods for estimating the helicopter parameters are reviewed and classified.