基于FDTD的约瑟夫森结与超导传输线协同分析方法

为实现高性能处理器,超导RSFQ（快速单磁通量子）电路被提出.该电路主要由超导约瑟夫森结和超导无源传输线组成,对其建模分析是超导RSFQ电路设计的基础.本文提出了基于FDTD（时域有限差分）的约瑟夫森结与超导传输线的协同分析方法.该方法采用FDTD数值方法求解超导传输线的电报方程.在超导传输线与约瑟夫森结交界处的非线性边界条件上,采用了Newton-Raphson迭代算法.数值结果表明,本文提出的约瑟夫森结和超导传输线的协同分析方法与WRspice仿真软件相比具有相同精度,且运算效率显著提高.     

三维PML吸收边界条件在微带线不连续性问题分析中的应用

将完全匹配层(PML)吸收边界条件从求解二维TE/TM模问题推广到求解三维混合模传输线问题.通过对各种三维微带线不连续性结构散射特性的计算表明,文中给出的电磁PML吸收边界条件保持了二维情况下宽带、高精度的优点,在复杂结构的FDTD分析中具有重要的实用意义.     

FDTDSIBC混合方法计算近地导线表面电流

通过在FDTD方法中引进时域表面阻抗界条件来研究瞬态电磁脉冲对有耗地面附近电缆线耦合问题。由频域表面阻抗出发通过拉氏变换得到时域表面阻抗边界条件（SIBC）,并将这种边界条件应用于FDTD方法中来模拟有耗地面的反射。计算结果表明了些方法的有效性。     

基于高阶时域有限差分法与改进节点分析法混合求解复杂传输线网络瞬态响应

该文提出一种用于求解复杂传输线网络瞬态响应的新型混合算法.通过构建混合单端口网络模型将传输线分布参数系统与集总电路分开,分别采用高阶FDTD(2,4)与改进节点电压分析法(MNA)分析传输线与端口电路瞬态响应.与以往暂态分析方法相比,高阶FDTD(2,4)的低数值色散特性,使得求解传输线时可采用粗网格离散,能方便处理电长度较长的传输线.同时直接采用电路分析方法求解端口电路,能够获取电路中各节点的电压电流波过程.通过几组数值实例验证了该方法的有效性及准确性.     

一种高精度的稳定的色散边界条件

本文给出了一种高精度的稳定的色散边界条件(DBC),可应用于传输线的时域有限差分法(FDTD)的分析之中。我们用一个新的二阶差分式代替了边界条件中的微分算子。与P。Y。Zhao等人(1994)提出的色散边界条件相比,本文中的边界条件具有相同的绝对稳定特性,但具有更好的吸收性能。     

任意截面的非平行多导体传输线瞬态分析

以分析多导体传输线的时域有限差分(FDTD)法为基础,在考虑任意截面传输线分布参数无法直接计算的情况下,提出MOM-FDTD 混合方法对不平行多导体传输线进行瞬态分析。首先,利用FDTD建立多导体传输线时域差分模型,然后用MOM 法计算任意截面形状的非平行传输线的分布参数,并且与FDTD法混合进行瞬态分析计算。此算法相对于全波算法,在时间与存储空间消耗上具有很大的优势,并且满足精度要求。最后通过同轴传输线与矩形带状线的例子验证这个方法是正确有效的。     

三维PML吸收边界条件在微带线不连续性问题分析中的应用

将完全匹配层（PML）吸收边界条件从求解二维TE／TM模问题推广到求解三维混合模传输线问题,通过对各种三维微带线不连续性结构散射特性的计算表明,文中给出的电磁PML吸收边界条件保持了二维情况下宽带、高精度的优点,在复杂结构的FDTD分析中具有重要的实用意义。     

一种时间序列预测方法在二维时域有限差分法中的应用

本文将一种时间序列预测方法与二维时域有限差分(FDTD)法相结合,并应用于均匀微波平面传输线的特性参数计算。该混合方法特别适用于尺寸很细微的MMIC传输线,而且可以精确地计算非理想导体的损耗。与传统的FDTD法相比,大大节约了计算时间,提高了效率。计算结果与测量非常一致。     

有耗平面和三维目标复合散射的FDTD分析

采用FDTD方法计算了有耗地面与三维目标的复合散射,对吸收边界条件,连接边界条件和近远场变换作了细致讨论.吸收边界使用了广义PML吸收层,它对电磁波有较好的吸收效果.连接边界处则利用解析入射波和三波迭加技术,上半平面用入射波和反射波、下半平面用透射波作为对目标的外加场进行计算.得到近场数据后,为避免出现复杂的Sommerfeld积分,用互易原理简化了外推过程.FDTD算法与矩量法和快速多层多极子相比,具有节省内存,计算时间短等优点.通过地上物体和地下物体的计算验证了FDTD方法的精确性,讨论了散射体离地高度对后向RCS的影响.     

用修正特征法模型求解高速VLSI中有耗互连线的瞬态响应

本文提出了用于高速集成电路系统中有耗互连线瞬态响应求解的一个计算模型及其相应的算法。传统的特征法在用于求解无耗传输线或满足ＬＧ＝ＲＣ的有耗传输线时具有简单的递归形式和较高的计算效率,但不能用于一般的有耗传输线。本文在特征法的基础上,通过适当的参数修正,建立了一般有耗传输线瞬态响应的近似特征模型,导出了其对时间变量递归形式的计算公式。     

压电陶瓷振子中的损耗及其对振子特性的影响

分析了压电材料中的损耗现象,并用复数表示有损压电振子的各种参数。文章从压电振子的阻抗（或导纳）方程出发,详细分析了纵效应振动及横效应振动模式振子的谐振（或反谐振）频率、频率偏移量与损耗大小、机电耦合系数大小的关系。     

Triangle impulse response (TIR) calculation for lossy transmission line simulation

Triangle impulse responses (TIRs) for lossy transmission lines are accurately calculated using both an inverse fast Fourier transform algorithm and an accelerated inverse Laplace transform algorithm. Frequency dependent transmission line parameters, i.e., R, L, G, and C, are employed to model the skin effect and the frequency dependent electrical properties of the substrate material. The calculated TIR can be further used to carry out time domain simulations for a large number of lossy transmission lines. Frequency dependent line parameters, R, L, G, and C should be used in specific cases to assure the causality of signal waveform, the accuracy of the time delay, and the amplitude of the waveform evaluations in the time domain.     

Modelling of dielectric losses in microstrip patch antennas: application of FDTD method

A frequency dependent complex permittivity is used to describe the dielectric losses of a microstrip patch antenna. The theoretical and experimental results for the usual parameters (input impedance, reflection coefficient and radiation pattern) of a rectangular microstrip patch are compared for a lossy and a nonlossy dielectric. Good agreement is obtained between the experimental measurements and theoretical results when the dielectric losses are considered.<>     

Stability Analysis of a Second Harmonic Coaxial-Waveguide Gyrotron Backward-Wave Oscillator

This study analyzes the stability of a Ka-band second harmonic gyrotron backward-wave oscillator (gyro-BWO) with a coaxial interaction waveguide. All of the possible competing modes in the frequency tuning range are considered. To suppress various competing modes, the downstream part of the coaxial interaction waveguide is loaded with distributed losses. Although the competing modes have different kinds of transverse field distributions, simulation results show that the losses of the outer cylinder and those of the inner cylinder serve as complementary means of suppressing the competing modes. The losses can stabilize the competing modes while having minor effects on the start-oscillation current of the operating mode. Detailed investigations were performed involving the dependence of the start-oscillation currents on the parameters of the lossy inner cylinder and the lossy outer cylinder, including the resistivity and the length of the lossy section. Moreover, under stable operating conditions, the performances of the second harmonic coaxial gyro-BWO with different sets of circuit parameters are predicted and compared.     

High-frequency scattering by objects buried in lossy media

The uniform geometrical theory of diffraction (UTD) is extended so that it can be used to calculate the scattering from an object buried in a lossy medium. First, the accuracy of this high frequency method is examined by comparing numerical results for the scattering by a polygonal cylinder in a lossy medium of infinite extent with calculations based on a method of moments (MoM) solution. Next, the more difficult scattering problem of a polygonal cylinder in a lossy half space is treated. The UTD solution for the unbounded region is employed together with the fields of rays introduced by the interface between air and the lossy medium to obtain expressions for the scattered field in air and in the lossy medium     

Simulation models of a dissipative transmission line above a lossyground for a wide-frequency range. I. Single conductorconfiguration

The simulation model of a single conductor dissipative line above a lossy ground, based on the exact formulation of the Maxwell equations, is proposed for a wide frequency range. The transmission-line (TL) and fast-wave (FW) propagation constants of the line are computed by solving the modal equation coming from the continuity of the tangential component of the electric field at the air-wire interface. Three different expressions of the distributed line impedance and admittance are suggested with reference to different definitions of the line voltage. Moreover, logarithmic approximations of the Sommerfeld integrals are proposed in order to obtain an easy-to-implement formulation of the simulation models for use in computer codes. Comparisons between the proposed models and the Carson (1926) approach are carried out with reference to a single conductor line above a lossy earth, considering different values of the line geometrical parameters and ground conductivity and permittivity     

Lossy dielectric and thin lossy film models for 3D steady state TLM

The 3D steady state TLM technique (SS-TLM) is extended to provide TLM models for lossy materials and thin lossy films in the frequency domain. The models are evaluated by comparing with time domain TLM (TD-TLM) and analytic solutions.<>     

New canonic lossy inductor using a single CDBA and its application

A new lossy inductor (parallel R-L type) using single current differencing buffered amplifier (CDBA) is presented, which employs only two resistors and a grounded capacitor. The proposed lossy inductor is shown to be useful in realizing an oscillator circuit, which provides quadrature voltage outputs using only two CDBAs, three resistors and two grounded capacitors and offers independent control on condition of oscillation and frequency of oscillation up to a frequency of 61 MHz. Detailed non-ideal analysis including single-pole model for voltage and current gain has also been carried out. SPICE simulation results and experimental results based upon the CDBA constructed from commercially available IC AD844 have been included which confirm the practical workability of the proposed lossy inductor and quadrature oscillator circuit.     

Some measurement results for frequency-dependent inductance of ICinterconnects on a lossy silicon substrate

Frequency dependent measurements of scattering (S) parameters using a vector network analyzer (VNA) have been performed on IC interconnects on a lossy silicon substrate. The multiline calibration method has been used to perform the de-embedding of the line parameters, from which the line inductance is extracted. A highly accurate closed-form approximation for frequency-dependent impedance per unit length of a lossy silicon substrate for IC interconnects has been used to compare with the measurements performed     

Electromagnetic wave transmission in a well logging cable-theory

A well logging cable is idealized as a uniform cylindrical structure consisting of N axial dielectric-coated thin wires in a lossy medium, all encased by a metallic sheath. A general modal equation which is specialized to low frequencies where quasi-static conditions prevail is developed. It is pointed out that the line parameters are spatially dispersive, in addition to being frequency dependent. The formulation differs from most multiconductor transmission theories because of the presence of the lossy filler material, which actually allows for a simplification of the working mode equation, which is an N-order polynomial