动态分形粗糙海面散射的遮蔽效应和多普勒谱研究

利用粗糙面电磁散射中的基尔霍夫近似,结合粗糙面遮蔽函数和分形粗糙海面特征函数的计算,导出了考虑遮蔽效应情况下导体分形粗糙海面散射截面的近似公式。研究了海面不同均方根斜率对遮蔽效应的影响。比较了毫米波入射时高斯粗糙面和分形粗糙海面的散射截面分布情况。分析了不同分维下分形海面双站散射截面的角分布情况。详细讨论了不同入射角和不同分维及遮蔽效应对分形海面散射回波多普勒谱的影响。     

海面对低空目标短波散射特性的影响

海上目标散射特性的分析在短波超视雷达的应用中起着极其重要的作用。本文从求解半空间散射问题的矩量法出发，分析研究了海面对目标后向散射截面的影响。数值结果表明，海面与目标间的耦合导致后向散射截面围绕某一固定值上下波动，随高度的增加波动幅度逐渐减小，结合目标在自由空间中的双站散射特性，文中给出了分析和判定海面影响的近似方法。     

箔条云团RCS的概率分布

严格证明了在满足大数定理的条件下箔条云团的单站及双站雷达散射截面积(Radar Cross Section,RCS)的概率分布均为指数分布,箔条云团中偶极子的空间分布形式、空间取向及偶极子之间的互耦对RCS概率分布函数形式没有影响,这些因素的影响只体现在指数分布的数字特征上.     

双站散射模式响应的分析与应用

基于电磁散射积分方程求解的矩量法,将入射和散射的平面波分解成含有Bessel函数的模式叠加,提出了目标双站散射模式响应的概念,得到目标远场双站雷达散射截面(RCS)与模散射响应之间成傅立叶变换的关系.根据基函数的性质阐明了模散射响应矩阵具有带限低通特性、互易对称性和近似成对角分布稀疏特性.模式散射响应是与外在观测角无关...     

海面上电大尺寸目标电磁散射特性研究

基于几何光学法(GO)、物理光学法(PO)、射线弹跳法(SBR)和等效电流法(MEC),提出了一种快速计算金属海面上电大尺寸目标电磁散射的解析算法。该算法考虑了阴影效应,运用GO/PO+SBR计算了目标与海面的镜面反射以及它们之间的多次相互作用,并运用MEC计算了目标的棱边绕射以改进计算结果。应用该算法计算了平板上方规则金属目标的双站雷达散射截面(RCS),并与传统矩量法(MoM)进行比较,验证了算法的有效性。最后,计算了PM(Pierson-Moskowitz)海浪谱的随机海洋粗糙面上舰船模型目标的散射特性,并对计算结果进行了分析,讨论了海洋面以及入射波参数对散射结果的影响。     

箔条感应电流分布和散射特性研究

推导了箔条雷达散射截面(RCS)的计算公式及其衍生的公式;基于矩量法和伽略金法,计算和比较了箔条散射与振子辐射的感应电流分布和远场方向图的差异,讨论了箔条空中姿态对感应电流分布及远场方向图的影响;给出了单站散射和双站散射情形单根箔条平均有效雷达截面的定义和计算公式.     

粗糙海面上舰船Kelvin尾迹的电磁散射仿真

基于点源扰动方法建立了舰船的Kelvin尾迹模型, 模拟了不同船速下的Kelvin尾迹.实际中, 舰船尾迹除了受到舰船自身参数影响外, 还会受到风驱海浪的调制.为了建立更为符合实际的Kelvin尾迹模型, 借助PM(Pierson-Moscowitz)海谱生成粗糙海面, 将其与Kelvin尾迹模型进行线性叠加后, 得到了粗糙海面上舰船尾迹.在该复合模型基础上, 利用物理光学法获得了不同入射情况下的单站、双站的雷达散射截面, 实现了海面舰船尾迹电磁散射的模拟仿真.这一过程的实现, 有利于更好地模拟舰船尾迹在合成孔径雷达(Synthetic Aperture Radar, SAR)中的成像仿真, 同时为SAR成像中舰船尾迹以及舰船自身的识别奠定了基础.     

数值模拟低掠角入射海面与船目标的双站散射

为研究风驱粗糙海面上有船目标时的双站散射,提出了一种结合广义前后的迭代方法（GFBM）与谱加速算法（SAA）快速求解双站散射的Monte Carlo数值方法,计算了在TE、TM锥形波低掠角入射在一维Pierson-Moskowitz谱粗糙导体海面以及船目标存在时的双站散射,数值模拟了在低掠角入射条件下,包含多次散射传播的粗糙海面与目标的双站散射与极化、频率、视角和海面风速等参数的关系。     

基于改进物理光学法的电大目标双站RCS的预估

研究了电大尺寸目标双站电磁散射的改进物理光学法。针对以往双站高频算法由于忽略阴影区电流影响,导致大双站角下计算误差有所增大的问题,提取电流步进法中的迭代算子,考虑阴影区不同面元的耦合影响,与图形电磁计算方法相结合,推导出了改进的物理光学公式。分别提取照明区和阴影区面元,按照入射波方向进行排序迭代求解,快速有效地计算了电大目标的双站雷达散射截面(RCS)。通过与多层快速多极子,以及高低频混合方法进行对比,验证了该方法的有效性和准确性。     

磁化等离子体覆盖导体散射问题的FE/BI方法分析

基于矢量有限元方法和边界积分方程,推导了分析三维导体表面覆盖各向异性磁化等离子体电磁散射问题的矢量有限元/边界积分(FE/BI)方法公式,并将该方法推广到外磁场沿任意方向时磁化等离子体的情形。应用该方法计算了磁化等离子覆盖导体目标的双站雷达散射截面(RCS),分析了等离子体厚度、密度、碰撞频率和外磁场方向对雷达散射截面的影响。数值计算结果表明:在导体表面覆盖各向异性磁化等离子体并且选取合适的参数,能够有效地减少雷达散射截面。     

航天器起伏表面的红外辐射特性

采用随机表面的计算机生成方法模拟了卫星表面起伏形貌;考虑了空间环境的辐射热流,采用蒙特卡罗法计算起伏表面面元间的辐射传递系数,完成了起伏表面的温度分布计算;考虑表面双向反射分布函数,建立了起伏表面随方向变化的红外辐射强度计算模型,并且以卫星常用的镀铝聚酰亚胺薄膜材料为例,分析了空间目标起伏表面的红外辐射特性。计算结果表明:随机起伏表面的红外辐射特性与理想平面的红外辐射特性差别明显;表面温度分布和红外辐射分布与表面的起伏形貌特征相关性很强。其结果可以为空间目标红外探测技术的研究提供更加有效的支撑。     

平面平行真空微电子二极管中二分之三次方关系式的应用

在一定的假定条件下，考虑空间电荷影响，平面平行真空微电子（P—VMD）二极管中电流一电压近似按二分之三次方关系式工作。本文在此关系式及Forler—Nordheim场发射方程的基础上，通过解简化立方方程，进一步推导出管内的电位、电场强度、电子速度和空间电荷密度的分布函数。P-VMD二极管在保持管内结构与阴极表面电场强度不变，并工作在典型工作状态（归一化电位系数P=2／3）情况下，考虑空间电荷影响时的阳极电压、阳极电场强度和阳极电子速度分别比无空间电荷影响时增加约50．00％，73．21％和22．47％。P—VMD二极管内的空间电荷密度分布函数为正割函数，在阳极表面附近为最小，在阴极表面处为无穷大，这是由于本文假设在阴极表面处的电子初速度为零的缘故。     

Theoretical and practical investigation of the thermal generation in gate controlled diodes

The different components of thermal generation in a gate controlled diode are studied theoretically and experimentally. Expressions for the generation current in the space charge layer, the diffusion current from the quasi-neutral bulk and the surface generation current are derived for a gated-diode. The width of the generation zone within the space charge layer is calculated as a function of the energy level of the trap and the diode reverse voltage. This leads to a characteristic of the leakage current as a function of the space charge layer width. It is pointed out that the diffusion current can influence the leakage current and cannot be neglected in structures with a low dark current. In the second part the gate controlled diode is used to characterize the thermal generation in structures with a homogeneous and low dark current. A generation lifetime of 5.5 msec and a surface generation velocity at a depleted surface of 1.5 cm/sec is derived. The generation lifetime is found to be constant as a function of depth into the substrate. A considerable diffusion current is measured which is comparable to the generation current in the space charge layer.     

A surface integral equation approach to the scattering andabsorption of doubly periodic lossy structures

The scattering and absorption of a doubly periodic array of absorbers, either placed in free space, backed by a perfect conductor or by a half-infinite space with the same material properties as the elements forming the array, is analyzed with a surface integral equation approach (SIE). The use of a suitable periodic Green's function as kernel of the SIE reduces the formulation of the problem to a single absorber. A set of equivalent electric and magnetic currents on the surface of the absorber is discretised using Glisson functions and the SIE is solved with Galerkin's method. The validity and flexibility of the SIE approach is exemplified by comparing numerical results with measurement data for a family of commercially available absorbers     

Electromagnetic field inside a surface current distribution

The electromagnetic field and a generalised electric Green's dyad, when the field point is inside a surface current distribution are derived. The Green's dyad is represented by the sum of the dyadic Green's function in free space and a source dyad determined by the shape of the principal area that surrounds the singularities of the Green's function.<>     

HSC分类法及其在海量数据分类中的应用

使用支持向量机对非线性可分数据进行分类的基本思想是将样本集映射到一个高维线性空间使其线性可分.本文则基于Jordan曲线定理,提出了一种通用的基于分类超曲面的分类方法,简称HSC分类法,它是通过直接构造分类超曲面,根据样本点关于分类曲面的围绕数的奇偶性进行分类的一种新分类判断算法,与SVM方法相比,不需要考虑使用何种核函数,不需要做升维变换,直接解决非线性分类问题.对数据分类应用的结果说明:HSC可以有效地解决非线性数据的分类问题,并能够提高分类效率和准确度.     

On the possibility of recording the radiation of the electromagnetic pulses generated by the electric discharges on board of a space vehicle by the ground-based radars

Necessary conditions are determined for recording the radiation of the electromagnetic pulses generated by the electric discharges on board of a space vehicle by the ground-based radars. The mean power-flow density of electric discharges at the Earth’s surface is obtained as a function of the discharge power and the altitude of the space vehicle trajectory. The minimum power-flow density of electric discharges at the Earth’s surface that can be recorded in the presence of the solar radiation is also found. The sensitivity of radar receivers that allows recording the radiation pulses generated by such electric discharges is estimated.     

Anomalous mutual coupling between microstrip antennas

An asymptotic expansion of the microstrip Green's function is used to facilitate a study of mutual coupling between two printed antennas, and coupling versus element separation is presented for substrate parameters of practical interest. For certain substrate parameters, it is found that the magnitude of mutual coupling does not decay monotonically with increasing element separation. Instead, the magnitude exhibits a quasi-periodic oscillation which can be attributed to the interference of surface and space waves. The presentation and discussion of this anomalous behavior is the purpose of the paper. The asymptotic representation of the Green's function, which differentiates space wave terms from surface wave terms when source and observation points are largely separated, is used to characterize the behavior of mutual coupling in the principal planes     

Retrieval of symmetrical image blur using zero sheets

The analytically continued Fourier transform of a two-dimensional image vanishes to zero on a two-dimensional surface embedded in a four-dimensional space. This surface uniquely characteristics the image and is known as a `zero sheet'. Since the manipulation of a function in four-dimensional space is cumbersome, the projections of zero sheets, known as `zero tracks' are calculated. This knowledge of zero sheets can be extended to a number of practical applications including image processing. Image restoration can be realised without prior knowledge of the point spread function, i.e. blind deconvolution is possible even when only a single blurred image is given. If the blurred image concerned contains a point spread function with diagonal symmetry, the point zeros calculated row-wise and column-wise contain some similarities, which supports retrieval of both the true image and a point spread function. This novel scheme performs the separation effectively in the absence of contamination     

半导体少子产生区宽度线性模型的研究

基于对半导体表面产生区宽度特点的分析，提出了与表面空间电荷区宽度呈线性关系的产生区宽度新模型。该模型形式简单，精度较高。数理统计分析结果表明，该线性模型是合理的。