Time-frequency Characteristic Analysis of Near-field Rotating Blade Echoes Based on Attribute Scattering Centers

Time-frequency analysis provides a crucial mathematical approach for quantifying and inverting scattering characteristics. This paper focuses on conducting a detailed time-frequency analysis of near-field rotating blade echoes. By establishing an attribute scattering centers model for such blades, it overcomes limitations of existing models, including neglect of blade occlusion, blade disk influence, and geometric oversimplification of blade tips. Starting from a single blade, based on the scattering centers theory, the geometric features of the blade are analyzed to determine that the scattered waves of the blade mainly originate from the side sliding-distributed scattering centers, root local scattering centers, tip face distributed scattering centers, and static echoes from the blade disk. The illuminated range of the blade and the activation/deactivation moments of each scattering centers are precisely determined according to the relative position between the blade and the radar. Notably, during blade rotation, when the line passing through the radar is tangent to the circle of the blade disk, the root and side scattered waves appear or disappear simultaneously. When tangent to the circle of blade tips, the appearance and disappearance of side and tip face scattered waves vary depending on the blade's movement direction relative to the probe. Building on the single-blade research, the shielding effect of multiple blades on electromagnetic waves is considered to analyze their scattering characteristics, and theoretical echo models for single and multiple blades are proposed. Electromagnetic simulations and experiments are carried out, with time-frequency analysis performed based on the short time Fourier transform (STFT). The results demonstrate excellent consistency among the time-frequency characteristics of theoretical echoes, electromagnetic simulation echoes, and measured echoes. These findings validate that the proposed attribute scattering centers model for blades can comprehensively explain the time-frequency characteristics of echoes, outperforming existing multi-scattering point models. This study refines rotating blade scattering research to the individual blade level, offering new perspectives for near-field scattering and time-frequency characteristic analysis.