一种改进稳定性的时域电场积分方程法

研究了时域电场积分方程隐式MOT算法中时间基函数对其稳定性的影响,由理论分析和数值结果得出了选用高频分量较少的时间基函数不利于隐式MOT算法稳定性的结论.在此基础上,将一种多项式时间基函数与新的时间平均方法相结合,提出了一种改进稳定性的隐式MOT算法,计算实例表明比先五步后三步平均法更加精确,比以前的隐式MOT算法更加稳定.     

时域积分方程MOT算法的推迟位时间卷积数值积分新方法

通过变量代换平滑三角形上推迟位（标量位函数和矢量位函数）并消除推迟矢量位旋度的奇异性,使得采用数值积分法就能够精确快速地计算任意正则时间基函数与推迟位函数及推迟矢量位旋度之间的时间卷积运算,可用于基于任意类型时间基函数的时域电场、时域磁场及其混合场积分方程时间步进（MOT ）算法。与时间卷积运算的解析法对比分析表明,该时间卷积数值积分方法能够精确快速地计算基于任意类型时间基函数和不同时间步长条件下时域积分方程MOT算法的阻抗矩阵元素;而具体的计算实例也表明,阻抗矩阵的精确计算显著地提升了时域积分方程MOT算法的后时稳定性和求解精度。     

TDEFIE的奇异性积分的精确快速计算

利用时域积分方程(TDIE)法模拟时域散射现象越来越受到学者们的关注.用于求解TDIE的时间步进(MOT)算法的后时不稳定性严重阻碍了TDIE法的广泛应用和发展.本文首先利用参数坐标和Duffy坐标变换将TDEFIE的奇异性积分转换成非奇异性积分,然后根据时间基函数的特点将该积分转换成可以快速精确计算的分区域积分.数值结果表明,该方法大幅提高了利用MOT算法求解TDE-FIE的MOT算法的后时稳定性和计算精度.     

任意形状导体与线天线组合目标的瞬态特性分析

本文采用微分形式的时域电场积分方程(TDEFIE)时间步进算法(MOT)对任意形状导体与线天线组合目标的电磁瞬念特性进行了分析.针对组合目标的复杂特性,使用细金属带状线模拟线天线,采用统一的RWG基函数表示表面电流分布,采用三阶内插时间基函数并通过恰当的时间步长选取对该问题进行分析求解.同时给出了线面连接处单元的剖分方法,基函数的设置.线面连接处电源激励模型的添加以及输入阻抗计算方法,最后给出了验证算法的数值结果.     

基于时域多分辨法微带线串扰分析

时域多分辨分析法作为一种时域计算方法,其吸收边界直接影响到计算的准确度。采用具有紧支撑性和对称性的CDF(2,6)尺度函数作为基函数得到了三维各向异性完全匹配层吸收边界;将时域多分辨分析法应用于微带线串扰分析中,给出了适用于任意尺度函数的集总电阻和阻抗电压源模拟方法,并用该方法分析了某印刷电路板上两根平行微带线的串扰问题。仿真结果表明:与传统的时域有限差分算法相比,以CDF(2,6)尺度函数为基函数的时域多分辨分析法只需要其一半的网格数,计算速度提高三倍,同时具有内存使用少、利用率高等特点。     

基于时域有限差分法的广义传输矩阵的研究

文章研究了基于时域有限差分法的时域广义传输矩阵方法,时域广义传输矩阵在包含散射体的惠更斯等效面上计算和提取,通过时域积分方程和时域有限差分法的混合应用计算得出。本文同样给出了一个在等效面上RWG基函数和FDTD网格上的变换算法。基于时域有限差分法的时域广义传输矩阵方法比基于时域步进法（MOT）和积分方程的广义传输矩阵方法更加稳定。     

一种改进的RRT路径规划算法

本文以自主驾驶车辆为实际应用背景.提出了一种改进的RRT(快速随机搜索树)路径规划算法.该路径规划算法将非完整性约束条件与双向多步扩展RRT搜索算法相结合,在提高搜索效率的同时保证了规划路径的可行性.同时将路径点作为B样条基函数的控制点,用三次B样条函数来拟合控制点生成平滑可跟踪的路径.通过在平面障碍物环境下实验,验证了该算法的有效性.     

基于三次B样条提升方案的图像融合算法

提出了一种基于三次B样条提升方案的图像融合算法,该算法是对三次B样条小波基进行提升,采用一定的融合决规则对高频分量和低频分量进行融合.高频分量采用多尺度下邻域方差法来计算,低频分量采取求平均的方法进行融合,最后将三次B样条提升算法与传统的小波变换算法的融合图像和参数指标进行比较,实验表明不论从视觉效果,还是采用信息熵,联合熵和平均梯度作为评价标准,都优于传统的小波变换法.     

精确稳定求解时域电场积分方程的一种新方法

时域电场、磁场和混合场积分方程已被广泛用来分析散射体的时域散射响应.基于适当的空间积分方法和隐式的时间步进算(MOT)法在求解时域磁场和混合场积分方程时总是稳定的,然而在求解TDEFIE时则是不稳定的.在本文中,时域电场积分方程的非奇异性积分采用标准的高斯求积法来计算;而利用参数坐标变换和极坐标变换将其奇异性积分转换成为可以分区域精确快速计算的非奇异性积分.通过数值实验表明,利用该方法可以非常精确稳定地求解时域电场积分方程,即使是在时间迭代后期也不必采用任何求平均的过程;另外,该方法可以用于任意时间基函数并可以推广到高阶空间基函数的情形.     

一种加快时间步迭代的加窗技术

提出了一种基于时域矩量法(TD-MOM)时间步迭代(MOT)的加速算法.通过在时间步迭代上加时间窗,从而剔除对于当前时间步没有贡献的迭代计算,达到加速的效果.仿真结果与一般MOT算法非常吻合,证明方法有效.     

A new temporal basis function for the time-domain integral equationmethod

A new temporal basis function that has all-order continuous derivative has been constructed using a nonlinear optimization scheme. This new basis function provides a much more stable explicit marching-on-in-time (MOT) solution, based on the time-domain integral equation (TDIE) method, than that presently available. Two examples are presented to illustrate the superior stability of the proposed temporal basis function     

Transient electromagnetic scattering from dielectric objects using the electric field Integral equation with Laguerre polynomials as temporal basis functions

In this paper, we propose a time-domain electric field integral equation (TD-EFIE) formulation for analyzing the transient electromagnetic response from three-dimensional (3-D) dielectric bodies. The solution method in this paper is based on the Galerkin's method that involves separate spatial and temporal testing procedures. Triangular patch basis functions are used for spatial expansion and testing functions for arbitrarily shaped 3-D dielectric structures. The time-domain unknown coefficients of the equivalent electric and magnetic currents are approximated using a set of orthonormal basis function that is derived from the Laguerre functions. These basis functions are also used as the temporal testing functions. Use of the Laguerre polynomials as expansion functions for the transient portion of response enables one not only to handle the time derivative terms in the integral equation in an analytic fashion but also completely separates the space and the time variables. Thus, the time variable along with the Courant condition can be eliminated in a Galerkin formulation using this procedure. We also propose an alternative formulation using a different expansion of the magnetic current. The total computational cost for this new method is similar to that of an implicit marching-on in time (MOT)-EFIE scheme, even though at each step this procedure requires more computations. Numerical results involving equivalent currents and far fields computed by the two proposed methods are presented and compared.     

Solution of time domain electric field Integral equation using the Laguerre polynomials

In this paper, we propose a numerical method to obtain a solution for the time domain electric field integral equation (TD-EFIE) for arbitrary shaped conducting structures. This method does not utilize the customary marching-on in time (MOT) solution method often used to solve a hyperbolic partial differential equation. Instead we solve the wave equation by expressing the transient behaviors in terms of Laguerre polynomials. By using these causal orthonormal basis functions for the temporal variation, the time derivatives can be handled analytically. In order to solve the wave equation, we introduce two separate testing procedures, a spatial and temporal testing. By introducing first the Galerkin temporal testing procedure, the MOT procedure is replaced by a recursive relation between the different orders of the weighted Laguerre polynomials. The other novelty of this approach is that through the use of the entire domain Laguerre polynomials for the expansion of the temporal variation of the current, the spatial and the temporal variables can be separated and the temporal variables can be integrated out. For convenience, we use the Hertz vector as the unknown variable instead of the electric current density. To verify our method, we compare the results of a TD-EFIE and inverse Fourier transform of a frequency domain EFIE.     

基于特定导频OFDM信道估计的研究

在OFDM系统中,准确的信道估计是对抗瑞利衰落信道中信道干扰的关键。提出了一种对OFDM信道估计的新方法,利用CR Spline函数的插值方法,设计一个特定的导频结构,从而导出信道估计的CR Spline函数形式,用该函数近似信道衰落包络。实验结果表明,仅用少量导频就可以近似出信道特性,并具有良好的平滑性。计算机仿真证明了提出算法的有效性。     

A stable solution of time domain electric field Integral equation for thin-wire antennas using the Laguerre polynomials

In this paper, a numerical method to obtain an unconditionally stable solution of the time domain electric field integral equation for arbitrary conducting thin wires is presented. The time-domain electric field integral equation (TD-EFIE) technique has been employed to analyze electromagnetic scattering and radiation problems from thin wire structures. However, the most popular method to solve the TD-EFIE is typically the marching-on in time (MOT) method, which sometimes may suffer from its late-time instability. Instead, we solve the time-domain integral equation by expressing the transient behaviors in terms of weighted Laguerre polynomials. By using these orthonormal basis functions for the temporal variation, the time derivatives can be handled analytically and stable results can be obtained even for late-time. Furthermore, the excitation source in most scattering and radiation analysis of electromagnetic systems is typically done using a Gaussian shaped pulse. In this paper, both a Gaussian pulse and other waveshapes like a rectangular pulse or a ramp like function have been used as excitations for the scattering and radiation of thin-wire antennas with and without junctions. The time-domain results are compared with the inverse discrete Fourier transform (IDFT) of a frequency domain analysis.     

基于样条函数Renyi熵的时间分集小波盲均衡算法

针对时间分集分数间隔判决反馈盲均衡算法(TD)计算量大、收敛速度慢的缺点,该文提出了一种基于样条函数Renyi熵的时间分集小波盲均衡算法。该算法直接把定义的样条函数Renyi熵作为代价函数用于TD的权向量更新,利用分数间隔获得更详细的信道信息;由正交小波变换降低输入信号的自相关性,以加快收敛速度;利用时间分集和判决反馈结构来降低多径衰落对通信质量的影响。水声信道盲均衡的仿真实验,验证了该算法的有效性。     

基于海情和三次样条插值算法的舰船雷达散射截面优化分析方法

不同风浪等级下的海面会对船舰目标雷达散射截面(RCS)分析产生强烈影响。该文建立了一种船舰模型,利用物理光学法与矩量法的混合算法(PO-MOM)分析了不同海情下的船舰目标远场单站RCS。之后研究了海情对船舰目标RCS测试结果的影响。最后提出了基于3次样条插值(Cubic Spline Interpolation, CSI)算法的优化补偿方法。结果表明,随着海情等级的增加,舰船RCS降低;利用3次样条插值算法进行补偿,其补偿结果的平均值误差小于0.38 dBsm,最大值误差小于0.05 dBsm,因此能有效地减少海情对船舰RCS测试结果的影响。     

An accurate scheme for the solution of the time-domain Integral equations of electromagnetics using higher order vector bases and bandlimited extrapolation

Despite the numerous advances made in increasing the computational efficiency of time-domain integral equation (TDIE)-based solvers, the stability and accuracy of TDIE solvers remain problematic. This paper introduces a new numerical method for the accurate solution of TDIEs for scattering from arbitrary perfectly conducting surfaces. The work described in this paper uses the higher order divergence-conforming basis functions of Graglia et al. for spatial discretization and bandlimited interpolation functions for the temporal discretization of the relevant integral equations. Since the basis functions used for the temporal representation are noncausal, an extrapolation scheme is employed to recover the ability to solve the problem by marching on in time. Numerical results demonstrate that the proposed method is stable and that it exhibits superlinear convergence with regard to the spatial discretization and exponential convergence with respect to the temporal discretization.     

修正自适应Chirplet分解法及其快速实现

为克服时频关系为线性的基函数的不足,该文提出一种新的信号分解算法修正自适应Chirplet分解法,将Chirplet基函数推广到三次相位信号的形式,因此可以逼近信号中的非线性时变结构成分。同时提出了一种快速分解算法,该算法通过计算信号的三次相位函数,可得到其能量分布集中于信号的瞬时频率变化率曲线上的结论,此时通过谱峰检测可同时获得基函数的二、三次相位系数,时间中心以及幅度的估计;进而通过解调频技术获得其初始频率和时间宽度的估计。文中给出了实现该方法的具体步骤,并分别以仿真信号和蝙蝠回声定位信号为例验证了该算法的有效性。