A macro-element compression for the moment method

A new approach based on QR compression of the off-diagonal blocks of the impedance matrix arising in integral equations solutions of electromagnetic (EM) scattering problems, previously implemented for finite and irregular gratings, is extended here to an arbitrarily shaped obstacle. The main tool consists in dividing the entire surface scatterer into subdomains and in assembling the global impedance matrix as a combination of the macromatrices associated to each interaction of any patch on the other. The correlation between compression rate and accuracy of field computation is drawn up. An experimental study is performed to optimize the method relatively to the two competing parameters: accuracy and cost. Finally, it is shown that this method works equally well in both the high and the low frequency domain and also with an inclusion of a small detail in a large object     

Multimode moment method formulation for waveguide discontinuities

A computationally efficient method for analyzing waveguide discontinuities is presented. The method is based on Galerkin's moment method formulation. The generalized scattering matrix of a waveguide discontinuity is derived. A generalized equivalent circuit is constructed which gives physical insight to the problem. The method is found to be several times faster than the well-known mode matching technique. The accuracy of the proposed method is demonstrated by comparing the numerical result with the measured return loss of a multisection iris-coupled filter     

A moment method analysis for coplanar waveguide discontinuityinductances

Based on the concept of duality, the quasi-static equivalent inductance of a coplanar waveguide discontinuity is determined from the equivalent capacitance of its complementary structure, i.e., a coplanar strip discontinuity in free space. For the capacitance calculation, an integral equation governing the excess charge distribution near the discontinuity is solved by the method of moments together with Galerkin's approach. Numerical results for the short end and symmetric step change are presented. The good agreement with the data available from the full-wave analyses reveals that this approach is simple, accurate, and very suitable in the CAD for MMICs     

基于分数低阶矩的非整数时间延迟估计方法

依据信号的噪声特性和分数低阶矩理论,提出一种基于最小平均p范数的非整数时间延迟估计方法(称为LMPFTDE算法)。该算法是对直接估计非整数采样间隔的时间延迟估计算法(ETDGE)的广义化,运用最小分散系数准则,通过使误差的p阶矩最小得到非整数时间延迟估计值。理论分析和计算机仿真结果都表明该方法不仅可以在高斯噪声环境下工作,而且在脉冲噪声下也具有良好的健壮性。     

Space-domain finite-difference and time-domain moment method for electromagnetic simulation

A hybrid time-domain numerical method based on finite-difference technique and moment method is proposed. Starting from Maxwell's differential equations, our method uses Yee's finite difference scheme in the space domain, but does not utilize the customary explicit leap-frog time scheme. Instead, in the time domain, the fields are expanded in a series of basis functions and treated by a moment method procedure. By choosing appropriate basis functions and testing functions, the conventional finite-difference time-domain (FDTD) formulation and the order-marching unconditionally stable FDTD scheme can be derived from our method as two special cases. Finally, we use triangle basis functions and Galerkin's testing procedure to get an implicit formulation. To verify the accuracy and efficiency of the new formulation, we compare the results with the FDTD method. Our method improves computational efficiency notably, especially for multiscale problems with fine geometric structures, which is restricted by stability constrain in the FDTD method.     

偶极子天线矩量法分析

基于矩量法对细直天线的电流分布及输入阻抗进行了分析，并与理论计算进行比较，结果表明：矩量法在计算较细的半波振子天线时，有较好的计算结果，对粗振子的结果误差比较大。     

Incompleteness of the periodic moment method

The periodic moment method predicts zero mutual impedance between expansion and test dipoles that are perpendicular. A new term has been added for this case, with nonzero results that agree precisely with spatial domain mutual impedance summations.<>     

Error analysis of the moment method

Because of the widespread use of the Method of Moments for simulation of radiation and scattering problems, analysis and control of solution error is a significant concern in computational electromagnetics. The physical problem to be solved, its mesh representation, and the numerical method all impact accuracy. Although empirical approaches such as benchmarking are used almost exclusively in practice for code validation and accuracy assessment, a number of significant theoretical results have been obtained in recent years, including proofs of convergence and solution-error estimates. This work reviews fundamental concepts such as types of error measures, properties of the problem and numerical method that affect error, the optimality principle, and basic approximation error estimates. Analyses are given for surface-current and scattering-amplitude errors for several scatterers, including the effects of edge and corner singularities and quadrature error. We also review results on ill-conditioning due to resonance effects and the convergence rates of iterative linear-system solutions.     

非线性散射介质内辐射传递的积分矩方法

提出了求解非线性散射介质内辐射传递的积分矩方法.将辐射传递方程中散射相函数的积分项转化为辐射强度各阶矩的线性组合.散射相函数为勒让德多项式展开形式,辐射强度矩的最高阶数与散射相函数的展开项数相同.将原本复杂的积分微分方程转化为微分方程,通过积分法求解此方程.积分矩方法不需要对立体角进行离散,不会引起射线效应.积分矩方法...     

采用矩不变量的激光雷达距离像匹配方法

为了解决激光成像雷达距离像匹配中的尺度和旋转不变性问题,提出了一套完整的距离像匹配方法,主要包括图像比例调整、Krawtchouk矩不变量提取、构造特征空间及搜索匹配4部分内容.以仿真激光成像雷达距离像为实验数据,通过调整实时图与参考图之间的比例缩放、提取两图的Krawtchouk矩不变量并以此构造特征向量进行匹配.实现了仿真激光雷达距离像的景象匹配.实验结果表明,该算法在一定比例的缩放和任意角度旋转的情况下,匹配正确率和匹配精度都较高,算法的抗高斯噪声能力较好.     

The moment method solution for printed wire antennas of arbitraryconfiguration

A printed wire antenna of arbitrary configuration is analyzed. The electric field tangential to the wire is derived using the current expanded by piecewise sinusoidal functions. These functions are also used to form the impedance matrix elements. Use of the stationary phase method leads to a simple expression for the radiation field. Numerical analyses based on the present formulation yield radiation characteristics of a zigzag dipole antenna, a loop antenna, and a round spiral antenna     

An accurate moment method model for the tapered slot antenna

A moment-method model is presented for the radiation characteristics of the tapered slot antenna. It overcomes the shortcoming of an earlier theory. The method is rigorous for the air dielectric antennas. For dielectric-supported antennas, the method is approximate but accurate. The method is particularly accurate for antennas etched on substrates that are electrically thin or have a low dielectric constant, within the limits of (ε_r-1)d /λ₀⩽0.1. Numerical results are presented for the radiation pattern and compared with experimental results to validate the model     

Problem-matched basis functions for moment method analysis-anapplication to reflection gratings

In the evaluation of the frequency response of a scattering object by the integral equation technique, generally a large linear system of equations has to be solved for each frequency point. This paper deals with a technique that drastically reduces the size of the linear system without loss of accuracy, The key point is the definition of a set of problem-matched basis functions. These basis functions are extremely efficient in the representation of the unknown in the parameter range of interest. In this way, the central processing unit (CPU) time required in the response evaluation is drastically reduced. Examples of application concerning reflection gratings are reported     

Reduced-reference image quality assessment using moment method

Reduced-reference image quality assessment (RR IQA) aims to evaluate the perceptual quality of a distorted image through partial information of the corresponding reference image. In this paper, a novel RR IQA metric is proposed by using the moment method. We claim that the first and second moments of wavelet coefficients of natural images can have approximate and regular change that are disturbed by different types of distortions, and that this disturbance can be relevant to human perceptions of quality. We measure the difference of these statistical parameters between reference and distorted image to predict the visual quality degradation. The introduced IQA metric is suitable for implementation and has relatively low computational complexity. The experimental results on Laboratory for Image and Video Engineering (LIVE) and Tampere Image Database (TID) image databases indicate that the proposed metric has a good predictive performance.     

柱形等离子体天线辐射特性的矩量法分析

基于矩量法计算了当等离子体天线工作频率远小于等离子体频率时,密度均匀分布的柱形等离子体天线表面电流分布、辐射方向图、输入阻抗及天线效率等天线参数.计算结果表明:等离子体天线具有与金属铜天线类似的辐射特性,并且随等离子体参数变化而改变.此外既可以通过等离子体天线的动态重构,也可以在损失部分效率的前提下选取固定的等离子体参数,获得天线的宽带特性.     

A moment method approach using frequency-independent parametricmeshes

A moment method (MM) formulation using nonuniform rational B-splines (NURBS) parametric surfaces is introduced to analyze radiation and scattering from arbitrarily shaped conducting bodies. A feature of the technique presented is the independence of the geometrical model from the frequency which avoids the regeneration of the geometry model when the frequency changes. This feature is obtained by defining new sets of basis and testing functions that extend over subpatches in each NURBS. The proposed approach is accurate, flexible, and efficient     

Robust use of supplementary conditions for moment method solutionnear internal resonances

A robust and efficient general method is presented for stabilizing moment method calculations using supplemental information. This method is then applied to the problem of exterior calculations using the electric field integral equation and the magnetic field integral equation for closed conducting bodies at frequencies near those of interior resonances. A large number of well-known techniques provide supplemental information. Thus, this paper shows how the information in each of these may be used more efficiently in the sense of a smaller operation count. The mathematical method used here is the modified truncated singular value decomposition, which is both numerically stable and describes whether the supplemental conditions used are sufficient to allow an accurate solution of the integral equation. The surface currents associated with the (nearly) resonant interior mode(s) are explicitly computed by this method     

Nonlinear extension to a moment method iterative reconstruction algorithm for microwave tomography

An iterative nonlinear algorithm for microwave image reconstruction based on moment method solutions to field problems has been suggested. The algorithm has been simplified significantly considering the effects due to the dominant nonlinear terms only. The results obtained using it have been compared with those reported earlier using a simpler algorithm.     

Input impedance of thin dipoles by moment method

The input impedance of half-wave dipoles with decreasing diameters has been calculated using the moment method of analysis with a stepped approximation of the current distribution. It is shown that the solution becomes increasingly inaccurate when the wire radius decreases and only a few segments for the antenna are used, and that it also diverges from the accurate answer when the length/diameter ratio of each segment is such that the axial-line-current and charge approximations become insufficient.