精糙介质面对高斯波束的散射

该文研究了当入射场为光波束时粗糙介质面的散射问题,利用波束的平面波谱展开方法及基尔霍夫近似理论导出了散射场和非相干截面计算公式,并对后向非相干截面进行了数值计算,最后对其结果进行了分析讨论。     

二维粗糙面两束波束散射特性研究

基于Kirchhoff近似,推导两束波束散射强度相关系数的表达式,数值计算漫射强度及散射强度相关系数随角度差、相关长度及粗糙度变化情况。结果表明:散射角对粗糙表面相干散射强度与光滑表面相干散射强度的比值有影响,当两束波束的入射角、方位角均相等,意味着两束波束相互重合且散射强度比值为单波束比值的四倍;当两束波束的入射角、方位角中有一个角度不相等,由散射场干扰效应的影响,相干散射强度比值都会减小。相关长度的变化与漫射强度和散射强度相关系数均成正比;随着入射角度差增大,漫射强度的后向散射效应增强,且散射强度相关系数变小,说明两束波束的干扰越严重;随着散射角的增大,总散射强度受干扰项散射强度影响较大,则后向散射效应增强。     

椭圆高斯波束中小粒子的一阶散射特性

研究电磁波束的小粒子散射特性在环境监测等领域有着广泛的应用。将电磁波束做级数展开,给出了各项对应电磁波的物理意义及粒子内电场的解析式。以椭圆高斯波束为例,对粒子内电场以及后项与前项电磁波束中粒子内电场的大小的比值随照射距离、频率的变化做了仿真。研究了椭圆高斯波束中小粒子的散射特性,通过仿真分析了波束腰宽和频率对散射特性的影响,验证了算法的有效性。研究表明,波束腰宽可以改善粒子的识别性能,粒子对高阶项的散射场远小于对次阶项的散射场,瑞利粒子内场表达式中坐标的幂次与外场波束表达式中坐标的幂次相同。所提方法简单,为研究电磁波束的粒子散射特性探索了新的途径。     

单根箔条平均雷达截面研究

箔条干扰是最为常用的无源干扰方式之一,主要依靠其电磁散射特性实现对雷达接收机的干扰。对箔条散射雷达截面进行研究,利用非相干模型推导了不同入射极化条件下单根箔条平均雷达截面,得到了箔条极化散射矩阵,并对单根箔条极化散射特性进行分析。提出了相干条件下的理想摆放模型,得到了更贴近实际使用的单根箔条平均雷达截面数值,为充分发挥箔条无源干扰效能打下基础。     

电波传播

0319926雨介质中简单目标的相干散射场[刊]/李应乐//电波科学学报.—2003,18(2).—200～202,215(L)利用叠加原理,导出了离散雨介质中相干散射场与目标散射场的具体表达式,数值计算了雨介质中相干散射场与降雨率的关系,计算结果表明:波的衰减不     

粗糙球体和锥体目标激光散射非相干分量比

为了研究激光散斑对目标探测的影响,采用物理光学近似方法,进行了平面波激光照射在粗糙球体和圆锥体目标时对散射场统计特性的理论分析,推导了粗糙体目标散射场量的二阶统计矩, 数值计算了粗糙球体和锥体的非相干散射分量比随粗糙度、散射角、半径及目标材料的变化情况。结果表明,散射角的变化对粗糙球体散射非相干分量比有影响,粗糙度变大,目标的非相干分量占总散射分量的比重越大;随着粗糙球体半径变小,球体表面越粗糙;圆锥体目标散射非相干分量比的峰值位置随粗糙度变化而不同,但其峰值均位于镜反射方向上;金属类材料比非金属抛光铝材料的非相干分量比小,且半径变化与非相干分量比成正比。该研究结果可为更复杂目标激光散射特性和激光散斑探测、识别的研究提供一定的参考价值。     

部分空间相干光经准均匀介质的散射

基于一阶波恩近似,研究了部分空间相干平面光经准均匀介质的散射特性,得到了远场散射光谱强度和光谱相干度的解析表达式。讨论了入射光的空间相干性和介质特性对散射场光谱强度和光谱相干度的影响。比较了入射光是完全相干光和部分相干光时,散射场光谱强度和相干度的区别。研究结果表明:入射光的空间相干性对散射场光谱强度的分布有重要影响;随着入射光空间相干长度的增大,光谱宽度减小;光谱相干度随着入射光束腰宽度或介质有效半径的增大而减小。当准均匀介质的有效半径和相干长度、入射光的空间相干长度满足一定条件时,散射光是完全相干光。     

手征涂覆球对高斯波束的散射

在广义米理论的基础上,通过把入射高斯波束、散射场和内部场用适当的球矢量波函数展开,给出了一种求解手征涂覆球对高斯波束散射的解析方法。待定的展开系数可由从边界条件得到的线性方程组求出。对于波束的区域近似模型,给出了微分散射截面的数值结果。结果表明：与介质涂覆的情况相比,手征涂覆对微分散射截面和散色场的极化特性都产生了较大的影响。     

在轴零阶贝塞尔波束对手征介质球的散射特性分析

贝塞尔波束自产生以来,凭借其无衍射、自修复特性已经获得了越来越多学者的关注。基于广义洛伦兹米理论, 将在轴贝塞尔波束与手征介质球相互作用的入射场及散射场展开为球矢量波函数的表达式。结合球矢量波函数的正交完备性及电磁场的连续性边界条件,推导出了在轴零阶贝塞尔波束对手征介质球电磁散射的解析解。数值模拟了散射强度随散射角的分布,将在轴贝塞尔波束退化为平面波照射手征介质球的散射结果与文献比较,吻合得较好。分析了波束及介质球参数、介质球偏离波束中心位置对散射强度的影响。该理论为手征材料和手征涂覆目标在微波工程及目标隐身中的应用提供了很好的理论应用价值。     

用复射线展开法分析目标的雷达截面

本文根据复射线分析和场的高斯波束展开,提出了一种计算复杂目标电磁散射特性的简便方法。由于复射线法不受目标形状的限制,因此该方法可用于任意形状的目标。本文以矩形进气道为例,进行了雷达截面分析计算,并将计算值与测试值比较,结果表明这种方法是可行的。     

Scattering of an incident Gaussian beam by a perfectly conductingrough surface

The modifications of the regular full wave theory for rough surface scattering by an incident Gaussian beam instead of a plane wave are developed. The Gaussian beam is produced by a large circular aperture that has a Gaussian illumination. It is shown that provided the incident Gaussian beam has a plane phase front over the extent of the rough surface patch and the linear dimensions of the rough patch are large compared with the surface height correlation length, the normalized scattering cross-section is the same as for an incident plane wave     

Calculations of Infrared Laser Beam Scattering from Rough Dielectric Objects

The coherent and incoherent scattering cross sections of Infrared Laser Gaussian beam scattering from arbitrarily shaped convex dielectric objects with rough surfaces are investigated by using plane wave spectrum method and physical optics approximation. In the paper, the infrared laser scattering cross sections of rough sphere are calculated at 10.6 μm , and the influence of the beam size, permittivity, and polarization as well as roughness parameters is analyzed numerically. When the beam size is much larger than the size of object, the results in the paper can reduce to those of an incident plane wave. On the other hand, for the case of roughness statistical parameter close to zero, only the forward scattering has a parent difference compared with the result of gaussian beam scattering from smooth sphere.     

圆锥后向激光雷达散射截面非相干分量的理论研究

本文根据粗糙表面的电磁散射理论计算了圆锥的后向激光雷达散射截面（ＬＲＣＳ）的非相干分量，分析了其随表面粗糙度的变化规律，并对非相干分量的概念进行了较为详细的阐述，希望能对外场全尺寸目标测量及实验室缩比模型的ＬＲＣＳ测量研究，提供一定的参考依据。     

Scattering, transmission, and absorption by a rough resistive sheet - E polarization

Motivated by the use of thin conducting textiles in absorbers, the interaction of electromagnetic waves with a rough resistive sheet is examined. Expressions for the fields above and below the sheet are derived in terms of an equivalent current using Gaussian beam illumination. These field expressions are then used with equations derived from the conservation of energy to find the distribution of scattered, transmitted, and absorbed power using an exact numerical solution and the Kirchhoff approximation. As a consequence of the lack of refraction, the Kirchhoff single scattering solution produces strong coherent transmitted intensities at the forward angles with an attendant minimum in the incoherent intensity. A second minimum in the incoherent intensity is observed in the antispecular direction. Fields arising from multiple scattering interactions are observed independent of the Kirchhoff single scatter contributions at these angles for surfaces of large root-mean-square slope. An increase in the absorption in the sheet is also observed as surface roughness is increased. The increase in absorption is believed due to multiple scattering interactions on the surface.     

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。     

一维指数型导体粗糙面与其上方矩形截面柱的复合电磁散射研究

采用Monte Carlo方法模拟了一维指数型导体粗糙面,运用矩量法研究了一维指数型导体粗糙面与其上方矩形截面柱的复合电磁散射。通过数值计算得到了复合散射系数随散射角和入射波频率的变化曲线,讨论了粗糙面高度起伏均方根、相关长度、矩形截面中心距粗糙面的高度、矩形截面长、矩形截面宽、入射波频率对散射系数的影响,得出了一维指数型粗糙面与其上方矩形截面柱的复合电磁散射特征。结果表明,粗糙面高度起伏均方根、相关长度、矩形截面中心距粗糙面的高度、矩形截面长、矩形截面宽、入射波频率对复合散射系数的影响是比较复杂的。     

A numerical study of scattering from an object above a rough surface

A numerical model is applied in a Monte Carlo study of scattering from a three-dimensional penetrable object above a lossy dielectric rough interface. The model is based on an iterative method of moments solution for equivalent electric and magnetic surface current densities on the rough interface and equivalent volumetric electric currents in the penetrable object. Both time-and frequency-domain results are investigated to illustrate the relative importance of coherent and incoherent scattering effects in the sample problem considered. Results show that a four-path model using a reduced-reflection coefficient can be reasonable for coherent scattering predictions and that incoherent object/surface interaction effects can make significant contributions to received cross sections.     

Tilt modulation of high resolution radar backscatter crosssections: unified full wave approach

The unified full wave approach is used to determine the tilt modulation of the like- and cross-polarized (high-resolution) radar backscatter cross sections for the rough sea surface. Real or synthetic aperture radars (SARs) with small effective footprints (resolution cells) are considered. Since the unified full-wave approach accounts for Bragg scattering as well as specular point scattering in a self-consistent manner, it is not necessary to adopt a two-scale model for the rough sea surface. The sea surface slope probability density function is assumed to be Gaussian. The backscattering cross sections are evaluated for all angles of incidence (normal to grazing). For tilts in the plane of incidence, the modulation of all the cross sections is largest at angles of incidence of 10°. The cross-section modulation due to tilts perpendicular to the plane of incidence critically depends on the incident and scattered polarizations. The effective filtering of the large-scale spectral components of the rough sea surface by the high-resolution radar is accounted for, and the dependence of the cross-section tilt modulation on the size of the effective footprint is determined     

粗糙金属和介质目标的太赫兹散射特性分析

太赫兹频段金属和介质粗糙目标的散射特性是研究太赫兹雷达目标特性的重要基础。当目标表面的主曲率半径远远大于入射波长,且粗糙表面高度起伏与斜率起伏远小于入射波长时,根据稳定相位法和标量近似法,可获得粗糙金属和介质目标的相干散射截面和非相干散射截面。基于稳定相位法,任意目标的相干散射截面可退化为粗糙导体、光滑介质和粗糙介质目标的相干散射。该文分析了电大尺寸光滑金属铝和介质白漆球的散射截面,与Mie理论计算的介质球的散射特性吻合,散射截面误差小于0.1 dBm2。采用朗伯定理,验证了粗糙介质球的太赫兹非相干散射精确解,当目标表面剖分精度越高,非相干散射的计算精度越高。该文数值计算了粗糙介质球的太赫兹相干和非相干散射特性,分析了表面粗糙度和表面材料对散射特性的影响,为电大尺寸空间目标太赫兹散射特性分析提供了理论基础。