【作者】 李永祯；

【导师】 庄钊文；

【作者基本信息】 国防科学技术大学 ， 信息与通信工程， 2004， 博士

【摘要】 随着现代战场电磁环境的日趋复杂恶劣,用动态的、统计的观点研究时变电磁波的极化现象,揭示波极化变化的内在规律,挖掘蕴含其间的物理本质,探究雷达目标与环境极化散射的特征机理,建立雷达目标极化散射统计特性的有效表征方法,最大限度的发掘和利用雷达传感系统所获得的电磁信息,使之能够适应复杂多变的战场环境、具备智能化的探测识别能力,已经成为雷达极化信息处理技术领域所面临的基础课题和紧迫任务。 为了能够有效提取和利用蕴含在随机极化波和起伏目标极化散射中的内在规律和丰富信息,以统计的、动态的观点来重新审视、研究了电磁波和雷达目标电磁散射的时变极化特性,建立了瞬态极化统计学理论的基础框架。在此基础上,针对导弹、飞机等空间/空中目标,对极化雷达中的弱目标检测、真假目标鉴别及目标识别等应用问题进行了系统深入的研究,为雷达系统削弱恶劣电磁环境的影响、对抗有源干扰、反隐身和识别真假目标等方面提供了新颖的、极具潜力的技术途径。 具体内容可分为理论研究和应用研究两个方面: 在理论研究方面,以瞬态极化理论为基点,以时变电磁波和雷达目标极化散射为对象,研究了瞬态极化的统计特性,建立了瞬态极化统计学理论的基础框架,深刻地揭示出时变电磁波和雷达目标极化散射的统计规律,为时变电磁波极化表征以及雷达目标极化散射特性的刻划提供了有力的理论工具。具体内容包括:①研究了随机极化波瞬态极化的统计特性,提出了电磁波瞬态极化相似系数、极化起伏度和极化采样序列等新概念,研究了正交极化基的选择对瞬态极化描述子的影响,阐释了瞬态Stokes矢量和瞬态极化投影矢量等表征参量的物理内涵及其性质,导出了零均值和非零均值随机极化波在正态分布假设条件下幅度、相位、幅度比、相位差、瞬态Stokes矢量以及瞬态极化投影矢量等的概率密度分布,分析了随机极化波瞬态极化投影矢量数字特征与波的极化参数(如极化度)之间的依赖关系;②从确定性和统计性两个角度分别研究了雷达目标的时变电磁散射极化特性的表征问题,深入研究了在时变电磁波激励下雷达目标的瞬态极化表征方法,提出了雷达目标瞬态极化散射的特征参量描述和目标间极化散射相似性度量等表征方法;在此基础上,提出并深入研究了雷达目标的瞬态极化Wigner-Ville时频分布及瞬态极化一般类时频分布;最后,给出了起伏目标瞬态极化散射矩阵的统计描述方法,研究了典型电磁波激励下雷达目标散射波的统计特性,分析了雷达目标瞬态极化散射的统计特性与入射波之间的依赖关系。 这些概念和方法构成了雷达瞬态极化统计理论的基本内容,为随机极化波和雷达目标电磁散射的极化特性分析、特征提取等研究提供了理论依据和有力工具,为随后的极化信更多还原

【Abstract】 In modern warfare, the electromagnetic (EM) environments have been more and more complicated and adverse. In order to exploit and utilize the EM information utmost, that is, to let the radar sensing system can adapt adverse battleground environments with intelligent detection and recognition capability, some problems are becoming a groundwork and impendent mission in radar polarization information processing. These problems mainly include studying the polarization phenomena of time-varying EM waves from dynamic and statistical viewpoints, revealing the inherent rules of random EM waves, exploring polarization scattering characteristics of radar targets and environments, and founding effectual descriptive means of polarization statistics of radar targets.The dissertation can be divided into two sections. Firstly, the instantaneous polarization(InPol) statistical theory is founded, which is based on InPol theory. From the statistical viewpoint, polarization characteristics of time-varying EM waves and radar target scattering are studied. Thereby, using the theory above, target detection, multi-decoy discrimination, target recognition and other applications have been studied according to polarimetric radar systems and aerial targets (e.g. missiles). The methods and conclusions in this thesis can proffer some novel and promising techniques for weakening the influences of adverse EM environments, confronting active jamming, detecting concealed targets and recognizing targets and other applications.The main contributions of the thesis are as follows:In theory, the radar InPol statistical theory has been founded and InPol theory also has been developed deeply. The main contents include:1) The polarization characteristics of random EM waves are studied from dynamic and statistical viewpoints. Firstly, polarization similar degree, polarization fluctuant degree(PFD) and polarization sampling sequences and other conceptions are presented in this thesis. Secondly, the influences of orthogonal polarization basis to InPol descriptions have been discussed, and the properties of instantaneous Stokes vector or InPol projection vector (IPPV) and other descriptions have been explained. Thirdly, the probability density functions(PDFs) and joint PDFs of amplitude, phase, amplitude ratio, difference of phase, instantaneous Stokes vector and IPPV of random EM waves have been derived in the condition of Gaussian hypothesis, and one moment, variance, compounded moment characteristics of these parameters are also presented. Fourthly, the relation between moment characteristics of IPPV of random EM waves and its polarization parameters (such as degree of polarization) are analyzed. At last, statistical distributions and numerical characteristics of polarization sampling sequences are also analyzed.2) The description problem of time-varying polarization scattering of radar target have been respectively studied from determinate and statistical viewpoints. Firstly, the characteristic descriptions of instantaneous polarization scattering of radar target are derived. Secondly, InPol time-frequency distributions of radar target are presented and the properties of InPol Wigner-Ville distribution or general time-frequency distribution of radar target are also derived. Thirdly, statistical descriptions of instantaneous polarization scattering matrix of radar target have been presented and statistical properties of scattered wave of radar target inspirited by typical electromagnetic wave are given.These conceptions and conclusions proffer theoretical foundations and avail tools for polarization characteristic analyzing of random EM waves or radar target scattering, feature extraction and other applications. And these are possessed of practical significance to engineering applications.In application, the InPol statistical properties of radar targets and electro-jamming are presented, and their applications in target detection, discrimination of active-decoy and radar target, classification and recognition of targets in modern warfare are also studied. The main achievements include:1) Statistical and power properties of radar target scattering signal and receiver noise are analyzed respectively based on narrowband polarimetric radar systems. Then, their different statistical properties in IPPV series or instantaneous sub-Stokes series are analyzed and two kinds of detection problems are studied when signal polarization is known or not. Two novel and promising detection algorithms of dim targets are presented by polarization accumulating, which are based on IPVS and PFD respectively. Theories and simulation results show that it can improve the detection performance greatly by optimizing the receiver’s bandwidth and transmit pulse width.2) Aiming at coherent pulse radar systems, utilizing the correlation difference between radar targets and receiver noise, a novel dim target detection algorithm which can extract targets’ motion information has been presented by "polarization accumulation". Theoretical results and computer simulations show that the detection performance is greatly improved compared to the conventional detector.3) The discrimination problem of radar targets and any elliptic polarized active-decoys is studied. Firstly, polarization scattering characteristics of radar targets and active-decoys are analyzed. Aiming at different polarimetric measuring systems (such as narrowband full-polarimetric radar, narrowband timesharing polarization measurement radar and broadband timesharing polarization measurement radar), several polarimetric discriminators are designed. Then, the usage of these polarization discriminators are analyzed too. And computer simulations indicate that polarimetric radars have potential to distinguish active multi-decoy from radar targets.4) The problem of feature-extraction and recognition of ballistic missile targets is studied in this thesis. Firstly, based on instantaneous polarization scattering matrix of radar targets, the descriptions of its polarization scattering characteristics are presented by theory of matrices. Then, the first and second order polarization measures of radar targets are extracted with measured data of warhead targets, which are insensitive with radar targets’ pose. Finally, missile targets classification and identification problem are studied through nearest neighbor recognition methods and satisfied recognition results are achieved.更多还原