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For the typical multi-component periodic micro-Doppler signal parameter estimation, a helicopter rotor feature extraction method based on flicker phenomenon and phase compensation is proposed in this paper. The method firstly analyzes the formation mechanism of helicopter rotor flicker phenomenon in time domain and time-frequency domain through the integral model. Then the demodulation operator of the micro-Doppler signal is constructed for the phase compensation of the echoes with respect to the time-frequency flicker characteristics and the phase information of the slow time dimension of the target echoes. The parameter combination of the possible number of blades and rotational speed is predicted using the time domain flicker interval, and the phase compensation process is evaluated and optimized to significantly reduce the amount of computation. Finally, the parameter estimation of rotor blade number, blade length and rotational speed is acquired by calculating whether the center frequency of each flicker after phase compensation is periodically focused to zero frequency. The simulation results show that the method can effectively estimate the main parameters of helicopter rotor blades, and the processing results of the measured data show that the proposed method has more stable performance compared with OMP algorithm and Hough transform, which provides a new technical way for helicopter rotor blade feature extraction.

Constructing the mapping between the geometric object and its corresponding 3D scattering response is a fundamental but challenging task in the domain of electromagnetic scattering, which is crucial for radar target recognition and the 3D structure interpretation. In recent years, the analytic physical optics, as a typical analytic solution, has been successfully utilized to produce the parsimonious, physically relevant 3D bistatic scattering models for standard dihedral and obtuse dihedral. In this paper, the scattering mechanism of separated dihedral, as a canonical structure that often appears in the actual targets, is investigated and its corresponding bistatic 3D scattering model is derived and established by the combination of geometric optics and physical optics method. First, the single and double-bounce reflection, as well as the occlusion occurred under different incident wave angles for the separated dihedral are analyzed in detail. Consecutively, the bistatic 3D scattering responses for different reflection cases are derived by the physical optical integration. Finally, the closed-form solution to bistatic 3D scattering model of separated dihedral is presented. The experiments with the two state-of-the-art electromagnetic calculation methods, shooting and bouncing rays and method of moments, validate the effectiveness of the proposed model. Especially, the experimental results also manifest that the standard dihedral is the specific case of the proposed model.