米波雷达低仰角目标多径模型及其反演方法研究

现有的低仰角测高方法多采用镜面反射模型，将直达波与多径简化为两远场点源；然而实际中不规则反射面使多径回波波前畸变，远场点源模型难以完全描述多径信号。针对此模型失配问题，该文重点研究低仰角目标多径模型，首先分析经典多径模型，对反射系数和反射面高度进行参数反演；然后提出一种扰动多径模型，将反射面对多径回波的影响建模为扰动反射系数，并利用最大似然算法反演扰动反射系数。计算机仿真结果验证了参数反演方法的有效性；实测数据验证了复杂情形下所建模型的合理性和反演方法的有效性，提高了低仰角测高算法在实际阵地的适用性。

Multipath Model and Inversion Method for Low-angle Target in Very High Frequency Radar

The existing methods of altitude measurement for low-angle targets adopt the specular reflection surface model, and the direct and multipath signals are considered as two correlated far-field point sources. However, in reality, the wavefront of multipath signal is distorted by irregular reflection surface, and the far-field point source model is not enough to describe the multipath signal. To deal with this model mismatch problem, the low-angle multipath model is mainly studied. This paper begins with a discussion of classical multipath model and is followed by the inversion method of reflection coefficient and the height of reflection surface. Then the perturbation of the multipath signal caused by irregular reflection surface is modeled as perturbational reflection coefficient and a perturbational multipath model is developed with a maximum likelihood method to invert the proposed parameter. Simulation data processing results validate the effectiveness of the inversion method. The effectiveness of the proposed model and inversion method are validated by measured data processing results. These research results can provide valuable information for enhancing the applicability of the low-angle altitude measurement method in practical situations.