IPO+FMM混合方法结合GRI和级联技术计算电大腔体的RCS

采用快速方法(FMM,RPFMM,FaFFA)加速迭代物理光学法(IPO)的迭代过程,可以快速计算电大腔体的电磁散射特性.采用广义互易积分,用靠近腔体终端的一个St面将腔体分成两段,形状简单光滑的腔体前端用IPO结合快速算法处理,而腔体终端单独分析.为了能够处理深腔体和进一步加快计算速度,将腔体前端进一步分成几个子腔体,每一个子腔体独立分析,通过一个级联方法求得腔体前端在St面产生的辐射场,最终在St面用广义互易积分求得腔体的RCS.数值计算结果表明该方法是准确的,同时能有效地提高计算速度.     

物理光学迭代法的子域连接法

本文提出的物理光学迭代法的子域连接法不但适用对电大尺寸一般腔体雷达截面的计算,而且能有效降低数值计算时间.它是将腔体分成若干个子腔体,每个子腔体用物理光学迭代法分析,子腔体之间电磁耦合通过对整个腔体循环迭代计入.数值结果验证了本文方法的正确性.     

快速预测干扰下斜开孔腔体屏蔽效能的模型

提出一种针对复杂干扰下斜开孔金属腔体屏蔽效能的计算模型。该模型可快速精准地计算出任意金属材料腔体,任意开孔位置,任意观测点位置,任意入射、极化平面波照射以及斜开孔阵腔体的屏蔽效能。首先依据磁流原理和镜像原理将斜开孔腔体等效为两个水平开孔腔体,然后基于Robinson的等效电路法分别求解各自的屏蔽效能,再利用公式换算求得斜开孔金属腔体的屏蔽效能。随后针对腔体会面临的不同干扰,给出不同情况下屏蔽效能的计算方法。考虑多种干扰叠加的复杂工况,将该模型利用Matlab 进行编程,并将计算结果同全波仿真软件CST中的时域传输线矩阵法和频域有限元法的仿真结果进行对比,验证了所提模型的可行性。该模型在保证计算精度的同时,在计算效率上表现出极大的优势。     

改进的IPO-CBFM 分析电大尺寸腔体的RCS

计算电大尺寸复杂腔体电磁散射时,迭代物理光学法与矩量法的混合方法（IPO-MM）是有效方法之一。为 了提高该算法的效率,在IPO 中使用快速远场近似（FAFFA）技术加速,在腔体复杂部分的MM 中使用特征基函数法 （CBFM）技术加速。在新的IPO/FAFFA-CBFM 混合法中,利用分块技术对求解矩阵进行降秩,使用传统的求解方法 即可求解方程,而不需要预条件处理与低频法的迭代求解方法。结果表明,新的混合方法有更高的计算效率和在单机 平台上解决更大复杂腔体电磁问题的能力。     

基于时间门方法的随机耦合模型在复杂腔体电磁预测中的应用

利用随机耦合模型（random coupling model,RCM）预测复杂腔体电磁效应时,通常要通过测量辐射阻抗来实现,但实验过程中满足混沌腔体以及耦合通道的腔体加工、实验过程模拟等条件要求较高,且实验步骤繁琐. 为了克服上述问题,文中采用时间门方法（time gating method,TGM）,通过对散射参数进行频域-时域-频域转换,结合门控函数,计算腔体辐射散射参数,并分析了门控时间对计算结果的影响. 不同频段内TGM计算结果与实验结果的统计特性,验证了该方法的适用性. TGM与RCM相结合用于复杂金属屏蔽腔体电磁脉冲耦合效应的研究,可以简化原有RCM的繁琐过程.     

E/H面不连续腔体的雷达散射截面分析

应用散射参数的级联特性分析不规则腔体的雷达散射截面。针对进气道前端的不规则矩形管道结构，采用全波模式法精确分析了E／H面任意不连续矩形腔体散射参数的求取，再根据等效网络的级联特性求得任意组合不规则矩形管道的散射矩阵，在保持计算精度的条件下克服了模式法只能精确计算规则腔体结构的限制。数值结果验证了该方法的正确性。     

小孔矩形腔体屏蔽特性的研究

本文提出了有孔腔体远、近场电磁屏蔽效能的计算方法，体研究了矩形腔体的屏蔽特性，讨论了各类孔对屏蔽能的影响程度。数值结果表明，理论计算与实验数据吻合较好。     

电大尺寸开口腔体电磁散射的子结构法研究

将子结构法与矢量有限元法相结合对无限大接地的三维开口腔体的电磁散射特性进行分析.将原尺寸较大的腔体分解成若干个不重叠的子腔体,在各子腔体内应用矢量有限元法进行分析,在原腔体开口面应用边界积分方程描述.通过求解容量矩阵获得子腔体之间连接边界上的场值,可以快速获得腔体开口面上的场值,极大地减少了存储量和计算量,易于对电大尺寸腔体的电磁散射问题进行分析.数值算例验证了该方法的准确性和高效性.     

腔体模式下表面等离子激元共振的仿真研究

为了分析腔体模式下表面等离子激元共振情况,介绍了电介质球腔体本征模式的多重散射解析方法和有限元数值计算方法(comsol软件),运用有限元法建立简单模型进行数值仿真,简要分析腔体模式与金属表面等离子激元的耦合,重点分析了小球半径与表面等离子波长的关系,提出了改变小球半径来影响表面等离子波长的构想,并提出了近似的公式。     

电大尺寸复杂结构腔体电磁散射的IPO/FEM混合法研究

该文将物理光学迭代法（IPO）的子域连接法与矢量有限元法（FEM）相结合，提出了一种新的混合方法用于分析计算电大尺寸复杂结构腔体目标的电磁散射特性，对于腔体内部适合用高频方法处理的部分采用IPO方法分析；对于具有复杂结构和材料特性的部分，采用矢量有限元法进行研究，利用交界面上的连续性条件实现这两种方法的耦合，为了验证理论模型的正确性，该文对某一矩形空腔及底部加载金属台阶的腔体进行了分析，计算结果与文献数据以及用时域有限差分法所得结果一致，并具有很好的收敛效果。在此基础上，对底部加载介质层的复杂结构腔体进行了分析计算，结果表明这种混保方法对于分析电大尺寸复杂结构腔体的散射特性是行之有效的。     

FMM用于快速计算电大腔体的RCS

利用迭代物理光学法(IPO)计算一般电大尺寸腔体的电磁散射特性,在迭代过程中用快速多极子方法(FMM)加速计算.在雅可比最小残差法(JMRES)的积分运算中引入FMM并与共扼梯度法(CG)的计算效率进行了比较.采用结构化分组,利用转移因子的平移不变性对计算和存储进行了优化.计算结果表明这些加速方法是有效的并能极大地提高计算效率.     

Analysis of the numerical dispersion of the 2Dalternating-direction implicit FDTD method

The numerical dispersion property of the two-dimensional alternating-direction implicit finite-difference time-domain (2D ADI FDTD) method is studied. First, we notice that the original 2D ADI FDTD method can be divided into two sub-ADI FDTD methods: either the x-directional 2D ADI FDTD method or the y-directional 2D ADI FDTD method; and secondly, the numerical dispersion relations are derived for both the ADI FDTD methods. Finally, the numerical dispersion errors caused by the two ADI FDTD methods are investigated. Numerical results indicate that the numerical dispersion error of the ADI FDTD methods depends highly on the selected time step and the shape and mesh resolution of the unit cell. It is also found that, to ensure the numerical dispersion error within certain accuracy, the maximum time steps allowed to be used in the two ADI FDTD methods are different and they can be numerically determined     

An Alternative Algorithm for Both Narrowband and Wideband Lorentzian Dispersive Materials Modeling in the Finite-Difference Time-Domain Method

In this study, an alternative algorithm is proposed for modeling narrowband and wideband Lorentzian dispersive materials using the finite-difference time-domain (FDTD) method. Previous algorithms for modeling narrowband and wideband Lorentzian dispersive materials using the FDTD method have been based on a recursive convolution technique. They present two different and independent algorithms for the modeling of the narrowband and wideband Lorentzian dispersive materials, known as the narrowband and wideband Lorentzian recursive convolution algorithms, respectively. The proposed alternative algorithm may be used as a general algorithm for both narrowband and wideband Lorentzian dispersive materials modeling with the FDTD method. The second-order motion equation for the Lorentzian materials is employed as an auxilary differential equation. The proposed auxiliary differential-equation-based algorithm can also be applied to solve the borderline case dispersive electromagnetic problems in the FDTD method. In contrast, the narrowband and wideband Lorentzian recursive convolution algorithms cannot be used for the borderline case. A rectangular cavity, which is partially filled with narrowband and wideband Lorentzian dispersive materials, is presented as a numerical example. The time response of the electric field z component is used to validate and compare the results     

Forward-backward iterative physical optics algorithm for computing the RCS of open-ended cavities

The forward-backward methodology is combined with the iterative physical optics (IPO) algorithm to improve convergence for cavity scattering problems. Wave propagation inside elongated cavities, such as jet engine inlet ducts, follows a predominant down-and-back path. The forward-backward method allows the IPO currents on the cavity walls to be updated sequentially (forward) and reverse-sequentially (backward) along the waveguide axis. A relaxation parameter is introduced to help control the convergence characteristics, making the new algorithm mathematically equivalent to the classical iterative method of symmetric successive over-relaxation. The fast far-field approximation (FaFFA) accelerates the matrix-vector products in the IPO formulation, and an equivalent surface impedance is used to characterize thin material linings in the cavity.     

有限元方法计算介质腔谐振频率和品质因子

采用有限元方法计算了二维方形介质腔和二维微盘的谐振频率和品质因子,并给出了两种腔中磁场、电场振幅分布图,介质腔中的谐振问题对应亥姆霍兹波动方程的本征值问题,本征值的实部和虚部与谐振腔Q值关联;比较了近似解析解、FDTD解、FEM解的结果,对于谐振频率比较,FEM和解析解更接近,对于品质因子比较,低Q值结果FDTD和FEM结果相近,高Q值结果两者相差较大。通过比较知道,FEM方法比时域有限差分方法计算更准确,求解速度更快。     

Design of cavity-backed slot antennas using the finite-differencetime-domain technique

A cavity-backed slot antenna is thought to be one of the most suitable elements for the wireless transmission of microwave energy. A design technique is developed for the cavity-backed slot antenna using the finite-difference time-domain (FDTD) method. The technique is effective in characterizing antenna performance such as the input impedance and the far-field pattern since it takes into account the geometry of the feeder as well as the cavity. We present a method that overcomes difficulties when the FDTD method is used to design the antenna. Moreover, we discuss how to determine the calculation parameters used in the FDTD analysis. Several numerical results are presented, along with measured data, which demonstrate the validity, efficiency, and capability of the techniques. The paper proposes a new prediction method for the frequency characteristics of the cavity-backed slot antenna, which applies computational windows to time-sequence data. It is emphasized that windowing the slow decaying signal enables the extraction of accurate antenna characteristics. We also discuss how to estimate the antenna patterns when we use a sinusoidal voltage excitation     

Incorporation of Conductor Loss in the Unconditionally Stable ADI-FDTD Method

A surface-impedance boundary condition (SIBC) is presented for an unconditionally stable alternating-direction implicit (ADI) finite-difference time-domain (FDTD) method. The conformal SIBC formulation based on locally conformal grids is capable of modeling the conductor loss of arbitrarily-shaped lossy metal structures. The work is described in the framework of the finite-integration technique (FIT) formulation of the ADI-FDTD. The paper focuses on the proposed ADI-FDTD SIBC formulation and its extensive validation. For this purpose, cylindrical and spherical cavity resonators are used for numerical tests. The quality factor $Q$ is directly proportional to wall loss and is particularly sensitive to the accuracy of loss calculation. The resonator structure consists only of a vacuum-filled metal cavity and is thus free of additional sources of error that are caused by other extensions to the basic ADI-FDTD algorithm. The formulation is validated by comparison with analytic results and numerical data calculated using CST Microwave Studio (MWS). The convergence rate of the results is of second order, i.e., the error reduces to one quarter as the mesh resolution is doubled.      

应用改进迭代物理光学方法分析电大尺寸开口腔体散射

为了克服用IPO法处理电大尺寸形状相对复杂的腔体散射时会出现迭代收敛慢甚至发散现象,本文引入松弛因子、异步迭代以及继承迭代等措施改进迭代的收敛性,所得结果与其它方法或实验结果符合很好。