基于局部散射中心的近、远场微动回波时频分布特性的解析表达

微多普勒效应是由目标(或其部件)的转动、振动、进动等微动引起的频率调制现象，能够反映目标的几何结构和运动状态。该文全面分析了近、远场探测条件下目标扇叶转动引起的微动回波的时频分布特性。首先建立了近、远场雷达微动回波模型。然后从远场微动回波模型中推导其瞬时频率表达式，结果表明远场微动回波的时频图中包含由叶尖散射点、叶彀散射点和镜面反射点引入的正弦型flash、零频flash和矩形flash。最后，在近场条件下，直接推导得到上述3类局部散射点的瞬时频率表达式，表明近场微动回波时频图呈现类正弦型flash，零频flash和部分余弦型flash的组合。该文还从积分运算性质和电磁散射理论两方面解释了上述flash的形成机理，揭示了它们与扇叶数目、尺寸、转速等参数之间的关系。该文结果将有助于目标精细化建模、分类识别等应用。仿真和实测数据结果均证明了分析结果的正确性。

Analytical Expression of the Time-Frequency Features of the Near-Field and Far-Field Micro-Motion Echo Based on Local Scattering Centers

Micro-Doppler effect is a frequency modulation phenomenon caused by the rotation, vibration, precession or other micro-motions of targets (or their components), which is able to reflect the geometric structure and motion state of the target. In this paper, the time-frequency distribution characteristics of micro motion echo induced by the rotation of target fan blades under near-field and far-field conditions are analyzed comprehensively. First, the signal models of the near-field and far-field radar micro motion echo are established. Then, the instantaneous frequencies are derived from the signal model of the far-field micro motion echo. The results show that the spectrogram of the far-field micro motion echo is composed of the sinusoidal flashes, zero-frequency flash, and rectangular flashes induced by the tip scattering points, hub scattering points, and mirror reflection points, respectively. Finally, the instantaneous frequencies corresponding to the above three kinds of local scattering points under near-field condition are directly derived, which indicates that the spectrogram of the near-field micro motion echo behaves as the combination of the sine-like flashes, zero-frequency flash, and partial cosine flashes. The formation mechanisms about the above flashes are explained from the perspectives of the integral operation properties and electromagnetic scattering theories. Also, the relationship between the flashes and the number, size, rotation velocity of the blades is revealed. This paper will be helpful to the applications of target fine modeling, target classification and recognition. The correctness of the analyses is validated by simulated and field experimental data.