Effects of Randomization on Periodic Coupling

Previous analyses of periodically coupled multimoded systems have assumed equal spacing of the coupling points. In this paper, explicit simple formulas are developed to account for randomized variations of a periodically coupled system. This analysis is useful in multimoded transmission systems utilizing circular waveguides or fiber optics and in active systems such as traveling wave tubes and surface acoustic wave devices.     

二维周期结构色散特性的矢量理论分析

在矢量衍射理论基础上给出了任意斜入射下二维周期结构(网格光栅)的角色散表达式。研究表明，二维周期结构的色散特性分析可以将一维光栅涵盖在其中。并阐述了(m，0)级和(0，n)级衍射波的角色散彼此不相关的独立性原理。     

圆柱形微带,耦合线的色散特性分析

本文利用一种全波分析方法－－柱面坐标中的二维时域有限差分法，数值模拟了圆柱形均匀微带线和耦合线的色散特性。讨论了柱面坐标二维时域有限差分（ＦＤ－ＦＤ）法的基本理论和处理方法，并给出不同带宽的圆柱形微线和不同耦合宽度与耦合间隙的圆柱形合线的色散特性。这些结果对微波与毫米波集成电路过渡区的设计是有价值的。     

Analysis of Dispersion Characteristics for a Circular Dielectric Rod Waveguide with Periodic Corrugations

The dispersion characteristics of a circular dielectric rod waveguide with period corrugations are analyzed with the mode matching method. After obtaining the rigorous dispersion equation, the dispersion curve for TE₀₁ mode exciting is calculated by the improved Newton's method. The variations of the normalized center frequency and width as well as the maximum attenuation constant of the stopband with the geometry parameters of the periodic corrugation structure are given respectively. The convergence properties of numerical solutions are also discussed. Based on the analysis, some useful guidelines for the design of the band-rejection filters consisting of the periodic structure are thereby suggested.     

Variational Principles and Mode Coupling in Periodic Structures

Variational techniques are used in analyzing periodic "cold" microwave structures for the angular frequency, omega, as a function of assumed phase shift per periodic cell. Two variational expressions are given: one for omega in terms of the E- and H-fields, and one for k² = omega²µ epsilon in terms of the E-field. For structures with relatively light coupling between cells, the trial fields to be used with the variational expressions are composed of closed cavity modes, phase shifted by phi radians from cell to cell. Both variational expressions yield determinantal equations for k²(phi) which agree with equations previously derived from a mode coupling point of view. One form of an equivalent lumped circuit is given to represent the structure within one of its pass bands. Curves compare the variational-mode coupling expression for k²(phi) of a periodically lumped loaded transmission line with exact expressions.     

Dispersion Characteristics of Arbitrary Periodic Structures with Rectangular Grooves

The dispersion characteristics of a circular cylindrical waveguide with periodic surface corrugations consisting of rectangular grooves with smoothing are examined using the Space Harmonic Method (SHM). The whole structure is divided into two regions, one describing the propagation volume and one inside the grooves. In the first region, the Floquet theorem is applicable and the field distribution is expressed as a summation of spatial Bloch components, whereas in the second one an appropriate Fourier expansion of standing waves is used. Applying the boundary conditions an infinite system of equations is obtained, which is solved numerically by truncation. Several cases are considered, including the limiting cases of a sinusoidal and a rectangular corrugation profile, to check the accuracy of the method proposed as well as its dependence on the corrugation profile. Numerical results are presented only for transverse magnetic modes, although the formalism can be easily extended to include all kinds of waves that can in principle propagate in such a structure.     

基于热-流-力耦合计算的多芯片组件布局构形优化

基于构形理论和多物理场耦合数值计算方法,建立了自然对流条件下均匀产热的多芯片组件模型,给定印刷电路板面积和芯片总占地面积为约束条件,分别以最高温度、最大应力和最大形变为优化目标,以芯片个数及芯片长宽比为设计变量,研究了芯片布局演化对系统性能的影响.结果 表明:不同优化目标下,最优构形均为芯片长宽比为2.1的8芯片布局方式,多芯片组件的最高温度、最大应力和最大形变分别最多可降低16.5％,28.3％和26.9％.对芯片个数和芯片长宽比双自由度的优化效果要明显优于仅对芯片长宽比的单自由度优化.     

螺旋带色散特性和耦合阻抗的精确计算

应用一种改进的计算螺旋带色散和耦合阻抗的方法,对面电流密度进行Chebyshev多项式展开后,去除了螺旋带上的面电流密度假设。在介质的高阶径向分层时为了避免高阶矩阵的求逆运算,采用转移矩阵和连接矩阵处理边界的场匹配。编写可径向任意分层的普适性程序,计算了螺旋线行波管的一些典型结构。研究表明：该理论的计算结果与实验结果有很好的一致;谐波次数以及面电流Chebyshev展开的项数完全可以依据结果的收敛性进行选取;分层的数目主要与结构的径向规则程度有关,径向越不规则,所要求的分层数目越多。     

螺距对螺旋慢波系统色散和耦合阻抗的影响

螺距是慢波系统的一个重要参数,直接影响螺旋慢波系统的色散特性和耦合阻抗.严格求解螺距对慢波系统色散和耦合阻抗的影响是不方便的,而通过计算机模拟可以方便快速地研究螺距对慢波系统色散和耦合阻抗的影响.模拟结果表明,对于工程项目当螺距变化小于4%时,螺距对色散和耦合阻抗的影响是很小的.     

Dispersion Diagram Characteristics of Periodic Array of Dielectric and Magnetic Materials Based Spheres

In this paper, the characteristics of electromagnetic (EM) waves supported by three dimensional (3D) periodic arrays of dielectric and magneto-dielectric spheres are theoretically investigated. The sphere particles have the potential to offer electric and magnetic dipole modes, where their novel arrangements engineer desired metamaterial performance. A full wave spherical modal analysis is applied to express the electromagnetic fields in terms of the electric and magnetic dipole modes and the higher order terms. Imposing the boundary conditions, determine the required equations for obtaining $kd-beta d$ dispersion characteristics. A metamaterial constructed from unit-cells of two different spheres is created, where one set of spheres develops electric modes, and the other set establishes magnetic modes. It is demonstrated that such a composite of high dielectric spheres provides double negative (DNG) metamaterial in a narrow frequency band spectrum where $kd,beta d≪ 1$. We also investigate the dispersion diagram for a 3D array of one-set of highly coupled dielectric spheres. Here, the couplings between the electric and magnetic dipoles of the spheres generate hybrid modes, resulting in a backward wave medium for $kd> 1$. The developments of DNG and backward wave metamaterials utilizing 3D array of magneto-dielectric spheres located inside space, and dielectric spheres embedded in a negative $mu$ host, are also addressed. The use of magnetic materials allows accomplishing wider dispersion characteristic bandwidths and tunable feasibility.      

声表面波色散换能器的分析

根据定义，采用等效电路法计算出色散换能器的声导纳。根据电荷叠加原理，计算出色散换能器的电容，从而得到器件的Y11和Y22，同样，采用等效电路法，Y12和Y21也可计算出来，这样，可预计整个器件的频率响应。     

Large Negative Dispersion in Dual-Core Photonic Crystal Fibers Based on Optional Mode Coupling

Chromatic dispersion of dual-concentric-core photonic crystal fibers (PCFs), which have an inner low-index core and an outer high-index core, is investigated based on a full vector finite-element method. Large negative dispersion can be obtained by introducing avoided crossing between modes of the two asymmetric cores. While increasing the negative dispersion, larger effective mode area is also possible by choosing a higher order mode in the outer core to couple with the fundamental inner core mode. During the analysis, a dual-core PCF with a dispersion peak value of -36 000 ps/(nmldrkm) and effective mode area of 34.8 mum² is presented.     

螺旋带径向厚度对色散和耦合阻抗的影响

该文将有限厚度的实际螺旋带等效为存在无限薄螺旋带的等厚真空层,从场分析和软件模拟两个方面研究了等效慢波结构的色散特性和耦合阻抗.将理论计算、软件模拟和实验测试结果进行了比较,结果表明,用真空层等效有限厚度的实际螺旋带时,将无限薄螺旋带置于等厚真空层的中央,其螺旋慢波结构的色散特性和耦合阻抗的理论计算、软件模拟和实验测试结果三者取得了很好的一致.     

DCF色散补偿性能的研究

分析了光纤色散和非线性效应。研究了利用色散补偿光纤(DCF)进行色散补偿的三种方案,数值模拟了采用这三种方案对在G.652光纤上传输375 km速率为10 Gb/s和40 Gb/s光信号进行色散补偿时入纤光功率对系统误码性能的影响,并分析了模拟结果,筛选出其中一种最好的方案,给出了具体的入纤光功率的取值范围。     

Dispersion Relation and Loss of Subwavelength Confined Mode of Metal-Dielectric-Gap Optical Waveguides

We have investigated the dispersion relation of a novel metal-dielectric-gap optical waveguide. This structure confines the optical field strongly in the gap region between metals and dielectric materials, and its size can be reduced to less than the wavelength of the transmitted light. In addition, the propagation length of light extends much greater than that of the surface plasmon modes on metal surfaces. We show that this mode of propagation has a cut-off at zero wavenumber, and that it is hollow-waveguide-like for small wavenumbers, while it approaches a surface-plasmon-like mode for large wavenumbers. A typical propagation length at around the communication wavelength is 10–20 $mu$m, and optical fields are confined into an approximately $100times 200 hbox{nm}^{2}$ cross section.      

相干耦合场作用下介质色散和吸收的改变

对Ｖ型三能级原子系统在相干耦合场作用下的吸收和色散特性进行了研究，由原子密度矩阵方程计算出原子相干生成于下两能级时介质极化强度振幅的实部和虚部，讨论了不同耦合场强度和不同非相干泵浦速率对原子系统吸收和色散的影响．     

等离子体中电磁波色散关系的PIC粒子模拟

等离子体参数的变化对在其中传播的电磁波有重要影响,文章采用周期性边界条件的二维PIC粒子模拟程序对电磁波在等离子中的传播过程进行了数值模拟,给出了电磁波在不同密度等离子体中传播的色散关系,得到了电磁波在等离子体中的传播特性。其结果,将作为进一步实现电磁波与等离子体中空间电荷波产生波-波相互作用过程模拟的基础。     

DDS信号的杂散及抑制分析

DDS（直接数字频率合成器）技术由于有诸多优点而得到广泛的应用。但因其固有的数字特性,使其输出信号存在大量的杂散,如何抑制DDS技术产生的杂散问题,是当前研究的热点问题之一。文中在介绍DDS工作原理的基础上,分析了其输出频谱杂散的来源,进而提出了几种抑制杂散的方法,通过加扰动源破坏杂散的周期性,压缩数据和增大ROM的相对容量等,有效地改善了DDS频谱质量,对基于DDS技术的频率源的设计有一定的实用性和指导意义。     

菲涅耳波导的波导色散特性分析

采用转移矩阵法对菲涅耳波导的波导色散特性进行了分析，讨论了波长、波导宽度和折射率差异参数对其波导色散的影响，并指出菲涅耳波导在色散补偿方面的应用。