Radar signatures of helicopter rotors in great bistatism

Electromagnetic signatures of helicopter rotors have been the subject of numerous theoretical and experimental studies. This research arises from the individual characteristics of helicopter radar echoes that facilitates their identification. Indeed, the radar cross section (RCS) of a helicopter may be separated into a fuselage component at the incident wave frequency and a series of harmonics arising from the amplitude and phase modulations of the scattered signal. These harmonics are functions of the blade number and the angular rotational frequency. A high frequency model, based on the physical theory of diffraction (PTD), has been developed to calculate the time-dependent bistatic: RCS of helicopter rotors. The problem is treated using the quasi-stationary approach and a realistic blade cinematic. Then, the spectral responses are analyzed through 3D "time-frequency" maps or images. Finally, results are given where the temporal and spectral characteristics of a generic rotor are studied versus the bistatic configuration. Particularly attention is given to the RCS and spectrum phenomena in great bistatism.