毫米波段OAM域临近空间高超声速目标电磁散射特性研究

The complicated scattering characteristics of hypersonic targets in the near space make their radar detection difficult. Different OAM modes of electromagnetic vortex can provide a new way of carrying radar echo information. By exploring the advantage of OAM beam in radar detection, the effective and precise detection of hypersonic target may thus be implemented, which is one of the key tasks urgently to be solved in the development and utilization of near space. In this project, the radar echo characteristics of vehicle with electrically large size covered by plasma sheath are analyzed under different modes of incident vortex beam in millimeter wave band by the theoretical modeling and simulation; it is explored that the interaction mechanism between near space object and vortex electromagnetic wave. Specially, the distribution of plasma sheath flow field and dielectric property is simulated in different flight and environment parameters, and then the exact composite target model is created. On the basis, GLMT and PO method are developed to study the electromagnetic scattering characteristics of hypersonic targets with simple and complicated shapes under LG vortex beam with arbitrary incident direction, and the effectiveness of the PO method is verified by GLMT. The differences of the scattering characteristics of conventional plane wave, Gaussian beam, and the OAM beam are discussed. The influence of the inhomogeneous plasma sheath electromagnetic model built by partition method on the composite vehicle RCS is focused for the regional feature of the space variation of flow field. The project will provide theoretical guidance for feature extraction of near space hypersonic target by new radar system based on OAM.

临近空间高超声速目标的复杂散射特性造成现有雷达目标探测困难。电磁涡旋的不同OAM态可携带新维度的雷达回波信息，挖掘OAM波束的雷达探测优势，实现高超声速目标精确有效探测是临近空间开发利用中亟待解决的关键问题之一。本项目拟通过理论建模仿真手段开展毫米波段不同涡旋波束模式下等离子体鞘套包覆电大尺寸飞行器的雷达回波特征分析，探索临近空间目标与涡旋电磁波的作用机理。具体包括通过模拟不同飞行及环境参数下的鞘套流场和介电特性分布，建立组合体目标的准确模型。在此基础上，采用GLMT和PO方法研究任意方向LG涡旋波束入射下高超声速简单及复杂形状目标的电磁散射特性，通过GLMT验证PO方法的有效性。比对传统平面波、高斯波束及OAM波束散射特性的差异，着重研究考虑流场空间分布区域化特征建立的非均匀鞘套电磁模型对飞行器组合体RCS的影响，对基于OAM的新体制雷达系统临近空间高速目标特征提取具有指导性意义。

电磁涡旋的不同轨道角动量(OAM)态可携带新维度的雷达回波信息。以高超声速目标雷达精确探测和识别的迫切需求为牵引，本项目通过理论建模仿真手段开展了不同涡旋波束模式下简单导体目标、复杂形状飞行器及其组合体目标的电磁散射特性研究。建立了可以精确拟合流场的等离子体鞘套物理模型及组合体目标模型，在物理光学法的非均匀分区等离子体鞘套介电模型基础上计算了高超声速目标散射特性，研究了非均匀弱电离(尘埃)等离子体鞘套目标电磁散射。结合角谱展开法，采用广义洛伦兹Mie理论(GLMT)计算了不同波形涡旋波束对导体球、介质球及等离子体球的散射解析解。利用物理光学法(PO)研究了任意入射LG涡旋电磁波束对电大尺寸复杂目标的散射、OAM波束在轴入射与离轴入射时飞行器目标的散射特性以及涡旋波束对等离子体鞘套包覆目标的电磁散射。本项目中，通过涡旋高斯波束入射下金属球的RCS与解析法GLMT计算结果进行比较，验证了涡旋波束散射的PO算法计算精度和有效性。详细分析了涡旋波束参数(OAM态数、径向量子数、波束中心位置、雷达频段、入射角)、等离子体鞘套参数(电子密度、碰撞频率)及飞行参数(飞行速度、飞行高度)不同时目标RCS的变化规律及物理机制。.另外本项目超额完成的工作：基于目标远区散射场强度和相位分布，运用螺旋谱展开法分析了目标形状(对称、非对称)及离轴入射对涡旋波束场OAM谱特性的影响。为了全面地反映场的模态信息，采用全区域相位采样方法计算了球形目标散射场的OAM谱，并与圆周相位采样方法做了仿真比较。.本项目的研究将为基于OAM的新体制雷达目标精确探测及特征提取提供理论依据。