时域混合算法在一维海面与舰船目标复合电磁散射中的应用

采用时域积分方程(TDIE)与时域基尔霍夫近似(TDKA)的混合算法研究粗糙海面与舰船目标的复合瞬态电磁散射.该方法将舰船目标及其近邻海面划分为TDIE区域,用TDIE方法精确求解;将剩余电大尺寸的粗糙海面划分为TDKA区域,采用高效的TDKA电流近似求解.通过混合算法和传统TDIE算法结果的对比,表明TDIE-TDKA混合算法能保证计算的精度,同时具有较高的计算效率.最后,讨论了海面上方有无目标、海面上方风速、电磁脉冲入射角、舰船目标尺寸、吃水深度对后向散射磁场的影响.     

海面与其上方双矩形截面柱复合散射的混合算法研究

采用Pierson-Moscowitz(PM)海谱和Monte Carlo方法模拟实际的粗糙海面, 基于矩量法和基尔霍夫近似的混合算法研究了海面与其上方双矩形截面导体柱的复合电磁散射特性, 得出了复合散射系数的角分布曲线, 计算了复合散射系数随海面参数、矩形截面柱参数以及入射波参数的变化情况, 并做了详细分析与讨论, 得到了PM谱海面与其上方双矩形截面柱复合散射特性. 结果表明, 与单纯的矩量法相比较, 采用基于矩量法和基尔霍夫近似的混合算法, 既可获得较高的准确性, 同时又可减少计算时间和内存占用量, 而且粗糙面尺度越大该优势越明显.     

二维随机粗糙面上导体目标复合瞬态散射的混合算法

提出用时域积分方程法(TDIE)与时域基尔霍夫近似法(TDKA)的混合算法来求解二维导体随机粗糙面及其上方二维导体目标的复合瞬态散射,推导出了在TM波入射情形下显式及隐式格式的时间步进方程.将粗糙面与目标分别进行TDKA和TDIE计算,并考虑目标与粗糙面之间的耦合,对TDKA和TDIE进行混合迭代,既大大降低了粗糙面求解的复杂度,又保证了计算精度.数值算例中,考虑了角反射器(开放体)和圆柱(封闭体)两种目标,分别计算了目标表面电流响应和电场远场响应.计算结果表明,和单纯TDIE法相比,本文混合方法计算效率 关键词： 随机粗糙面 复合瞬态散射 时域积分方程法和时域基尔霍夫近似法 混合算法     

有限元/边界积分方法在海面及其上方弹体目标电磁散射中的应用

本文将有限元/边界积分方法(FE/BIM)结合区域分解方法引入到粗糙海面及其上方目标 的电磁散射问题的研究中. 由于积分边界可以以任意形状设置在距模型表面任意远的距离处, 故本文采用共形人工边界结合区域分解建模方法截断模型的开放计算区域以减少求解未知量, 在截断区域内部采用有限元方法求解, 而计算区域的边界条件通过边界积分方程方法得到. 通过与矩量法获得的数值计算结果进行比较, 证明了该混合算法及模型处理方法的正确性, 进而研究了海面上方弹体目标的电磁散射特性, 并讨论了其双站散射系数随电磁波入射角度、目标高度、海面风速以及弹体尺寸的电磁散射特性变化情况. 本文结果可用于反演复杂背景下的目标信息及目标探测等领域. 关键词： 电磁散射 粗糙海面 目标 有限元/边界积分方法     

二维导体微粗糙面与其上方金属平板的复合电磁散射研究

研究了二维导体微粗糙面与其上方金属平板复合电磁散射特征.应用互易性原理使求解二次散射场简化为求解包含平板上的极化电流和微粗糙面散射场的积分方程，从而降低了求解难度.应用物理光学近似和微扰法分别求解了平板上的极化电流和粗糙面的电磁散射场，得到了复合散射截面计算公式并进行了数值计算.尤其对该复合模型后向耦合电磁散射结果进行了详细分析和讨论. 关键词： 互易性原理 复合电磁散射 微粗糙面 平板     

二维粗糙海面散射回波多普勒谱频移及展宽特征

基于二维线性海面模型及粗糙面电磁散射的一阶小斜率近似公式,研究了海面回波各阶多普勒谱的频移特性,得到了多普勒谱频移所对应的理论公式,与经典多普勒频移公式相比考虑到了风速、大尺度波浪轨道运动等因素对多普勒谱频移的影响;同时根据粗糙面的双尺度模型,基于多普勒谱频移的物理机理,给出了求解散射场多普勒谱展宽的理论公式.最后将理论公式计算所得结果与模拟结果及实测数据进行了比较,讨论了风速、入射波频率及入射角等因素对多普勒频移及多普勒谱展宽的影响.通过比较可以发现,给出的理论公式可以对多普勒谱频移和展宽进行一定程度的预测. 关键词： 粗糙海面 电磁散射 多普勒谱     

二维导体粗糙面电磁散射的分形特征研究

采用二维归一化带限Brown分形函数来模拟二维分形粗糙面,主要利用基尔霍夫近似给出了该导体粗糙面的电磁散射场.导出了平均散射场、平均散射系数和散射强度方差的计算公式.讨论了散射场分布与分维的关系,获得了散射场波峰拟合线的斜率与分维D满足线性关系这一重要结论. 关键词：     

基于压缩感知的一维海面与二维舰船复合后向电磁散射快速算法研究

矩量法作为数值方法中积分方程方法的代表, 具有计算精度高、所用格林函数自动满足辐射条件、无须额外设置边界条件等优点. 但是在舰船目标与海面复合后向电磁散射仿真中, 传统矩量法需针对每个入射角反复求解矩阵方程组, 导致其在处理后向散射问题时计算量大, 耗时长, 仿真效率低下. 为解决上述问题, 本文提出了一种基于压缩感知技术的矩量法的改进算法. 该算法在求解复合后向散射问题时, 首先利用观测矩阵与传统矩量法中的电压矩阵相乘, 得到一组新的低维度的电压矩阵; 其次通过求解新电压矩阵下的矩阵方程组, 获得电流矩阵的观测值; 最后利用恢复算法(本文采用正交匹配追踪算法)重构出所需的原始入射源照射下的电流系数. 通过与传统矩量法的计算结果对比, 表明本文所提算法能够在保证计算精度的前提下, 明显减少计算时间, 提高计算效率.     

气泡/泡沫覆盖粗糙海面电磁散射的修正双尺度法研究

提出了风驱粗糙海面覆盖水气泡层的‘体-面’复合模型.基于修正的双尺度粗糙面散射理论、MIE理论和矢量辐射传输理论,比较了水气泡与实心水粒子的电磁散射特性的差异,分析了海面泡沫覆盖率与风速、气-海温差的关系.在有、无泡沫层情形下,采用高斯和经验海谱,讨论了单站、双站散射系数与入射角、方位角、风速、风向、极化等参量的关系,并将数值计算的结果与相关文献的测量值进行了比较和分析. 关键词： 电磁散射 海面复合模型 修正双尺度法 MIE     

粗糙海面与其上方多目标复合散射的混合算法

针对粗糙海面与其上方多目标复合的情形,常用算法存在计算量过大、计算时间太长等缺点,本文采用基尔霍夫近似法与矩量法结合的混合算法可以大大简化计算量、节省时间.本文首先通过蒙特卡罗的方法模拟一维PM粗糙海面,并与粗糙海面上方多目标建立复合模型;然后对矩量法结合基尔霍夫近似法的混合算法做了详细的公式推导,得到了复合散射系数,并且分析了不同入射角、目标高度、目标间距、目标尺寸、风速等参数对复合电磁散射特性的影响.实验结果表明,针对粗糙海面与其上方多目标复合的情形,采用矩量法结合基尔霍夫近似法的混合算法不但可以保证准确性,而且可以大幅度减少计算所用时间(混合算法用时占矩量法的19%),对大尺寸粗糙面和复杂的复合模型优势尤为明显.     

Hybrid method for investigation of electromagnetic scattering from conducting target above the randomly rough surface

A current based hybrid method (HM) is proposed which combines the method of moment (MOM) with the Kirchhoff approximation (KA) for the analysis of scattering interaction between a two-dimensional (2D) infinitely long conducting target with arbitrary cross section and a one-dimensional (1D) Gaussian rough surface. The electromagnetic scattering region in the HM is split into KA region and MOM region. The electric field integral equation (EFIE) in MOM region (target) is derived, the computational time of the HM depends mainly on the number of unknowns of the target. The bistatic scattering coefficient for the infinitely long cylinder above the rough surface with Gaussian roughness spectrum is calculated, and the numerical results are compared and verified with those obtained by the conventional MOM, which shows the high efficiency of the HM. Finally, the influence of the size, location of the target, the rms height and correlation length of the rough surface on the bistatic scattering coefficient with different polarizations is discussed in detail.     

An angular cutoff composite model for investigation on electromagnetic scattering from two-dimensional rough sea surfaces

Based on the local configuration angle division to select the corresponding method for electromagnetic scattering calculation from rough sea surface,this paper presents an angular cutoff composite model:when the local scattered angle is in the specular region that is given by an approximately 20 degrees cone around the specular direction,the Kirchhoff approximation is applied to evaluate the specular reflection,which dominates the total scattering in this region;the small perturbation method is employed to handle the diffuse reflection which is predominant as the local scattered angle is situated out of the specular region.Numerical results are compared with those of experimental and theoretical models in several configurations as a function of incident angle,wind speed,wind direction.The comparison of numerical results of other experimental and theoretical models in several configurations shows that the new composite model is robust to give accurate numerical evaluations for the sea surface scattering.     

双尺度动态分形粗糙海面的电磁散射及多普勒谱研究

利用更为符合海面实际散射场计算的双尺度法分析并计算了一维动态分形粗糙海面的后向散射截面，同时与微扰法有关结果进行了比较.研究了动态分形海面后向散射信号的多普勒谱分形特征，分析了不同极化状态下后向散射截面和多普勒谱谱宽随入射角及分维的变化规律，最后详细讨论了多普勒谱中心频率与海面Bragg谐振频率间的关系. 关键词： 双尺度模型 分形海面 电磁散射 多普勒谱     

Investigation of composite electromagnetic scattering from ship-like target on the randomly rough sea surface using FDTD method

Composite electromagnetic scattering from a two-dimensional (2D) ship-like target on a one-dimensional sea surface is investigated by using the finite-difference time-domain (FDTD) method. A uniaxial perfectly matched layer is adopted for truncation of FDTD lattices. The FDTD updated equations can be used for the total computation domain by choosing the uniaxial parameters properly. To validate the proposed numerical technique, a 2D infinitely long cylinder over the sea surface is taken into account first. The variation of angular distribution of the scattering changing with incident angle is calculated. The results show good agreement with the conventional moment method. Finally, the influence of the incident angle, the polarization, and the size of the ship-like target on the composite scattering coefficient is discussed in detail.     

Application of the method of equivalent edge currents to composite scattering from the cone-cylinder above a dielectric rough sea surface

Compared with scattering from a rough surface only, composite scattering from a target above a rough surface has become so practical that it is a subject of great interest. At present, this problem has been solved by some numerical methods which will produce an enormous calculation amount. In order to overcome this shortcoming, the reciprocity theorem (RT) and the method of equivalent edge currents (MEC) are used in this paper. Due to the advantage of RT, the difficulty in computing the secondary scattered fields is reduced. Simultaneously, MEC, a high-frequency method with edge diffraction considered, is used to calculate the scattered field from the cone-cylinder target with a high accuracy and efficiency. The backscattered field and the polarization currents of the rough sea surface are evaluated by the Kirchhoff approximation (KA) method and physical optics (PO) method, respectively. The effects of the backscattering radar cross section (RCS) and the Doppler spectrum on the size of the target and the windspeed of the sea surface for different incident angles are analysed in detail.     

Investigation on global positioning system signal scattering and propagation over the rough sea surface

This paper is devoted to the study of polarization properties, scattering properties and propagation properties of global positioning system (GPS) scattering signal over the rough sea surface. To investigate the polarization and the scattering properties, the scattering field and the bistatic scattering coefficient of modified Kirchhoff approximation with using the tapered incident wave is derived in detail. In modeling the propagation properties of the GPS scattering signal in the evaporation duct, the initial field of parabolic equation traditionally computed by the antenna pattern with using fast Fourier transform (FFT) is replaced by the GPS scattering field. And the propagation properties of GPS scattering signal in the evaporation duct with different evaporation duct heights and elevation angles of GPS are discussed by the improved discrete mixed Fourier transform with taking into account the sea surface roughness.