Equivalent circuit representation of lossy coplanar waveguides

The study of the dispersion properties of planar transmission lines including metallic losses with the generalized transverse resonance method is formalized in building an equivalent network of the cross-section which specifies the relationships between the tangential components of the fields on each side of the interfaces. Virtual sources represent the trial quantities chosen to describe the problem. With twoport type boundary conditions, the trial quantities are not easily defined from physical considerations, but the virtual sources obey to specific rules. This purpose is illustrated in studying the attenuation in lossy suspended coplanar transmission lines.     

Spectral clustering steered low-rank representation for subspace segmentation

Low-rank representation (LRR) and its variations have achieved great successes in subspace segmentation tasks. However, the segmentation processes of the existing LRR-related methods are all divided into two separated steps: affinity graphs construction and segmentation results obtainment. In the second step, normalize cut (Ncut) algorithm is used to get the final results based on the constructed graphs. This implies that the affinity graphs obtained by LRR-related algorithms may not be most suitable for Ncut, and the best results are not guaranteed to be achieved. In this paper, we propose a spectral clustering steered LRR representation algorithm (SCSLRR) which combines the objection functions of Ncut, K-means and LRR together. By solving a joint optimization problem, SCSLRR is able to find low-rank affinity matrices which are most beneficial for Ncut to get best segmentation results. The extensive experiments of subspace segmentation on several benchmark datasets show that SCSLRR dominates the related methods.     

Analysis of hollow conducting waveguides using superquadricfunctions-A unified representation

Waveguides of various geometries have found many applications. The analysis of the wave modes inside these waveguides are usually subject to cross sections of the waveguides and specific, but convenient, coordinate systems have to be chosen in the analysis. In this paper, the boundary geometries of waveguides (which include rectangular, circular, elliptical, triangular, coaxial, etc.) are represented in a unified manner by a superquadric function. In this paper, with the Rayleigh-Ritz method, the wave propagation characteristics in a hollow conducting waveguide of the superquadric cross section are analyzed in a unified manner. From the analysis, it is realized that the superquadric function can be utilized to accurately model the boundary of various waveguide structures through variation of the shape parameters. The comparisons between the analytical and computational results show this method is accurate and efficient     

Spectral analysis of Serpinskij carpet-like prefractal waveguides and resonators

Exact results on some modal properties of waveguides and resonators is studied, whose geometry is derived from "Serpinskij carpet-like" prefractals (Serpinskij carpet and sponge; Menger sponge). The study is biased to the closed-form computation of specific resonances and eigenmodes (called "dia-periodic"), and to the relation existing between their topology and the existence of a finite set of transverse electromagnetic modes.     

Spectral representation of a periodic nonstationary random process

This paper deals with the periodic nonstationary process, the mean value and the correlation function of which are invariant under shift by a multiple of a certain period. The spectral representation is derived by making use of Loève's harmonizability theorem on a second-order nonstationary process. The process is represented as a sum of infinite stationary processes among which covariances exist. Each stationary process has a nonoverlapping frequency band of equal width, the center of which corresponds to a harmonic of the fundamental frequency determined by the period. The correlation function, dependent on two points, is represented in terms of a matrix-valued spectral density that is hermitian and nonnegative definite. The representations in other possible forms are also given. Finally some properties, special processes, and examples produced by a certain stationary random sequence are discussed.     

Multimode network representation of multiple inductive andcapacitive obstacles in parallel plate waveguides

In this paper the multimode network formulation is used to characterize a multiple obstacle or aperture discontinuity in parallel plate waveguide. The procedure leads to a frequency-independent integral equation. This equation is solved numerically by using the method of moments, allowing for the implementation of a very general and efficient code. The frequency-independent integral equation formulation and its numerical solution are first outlined. Then, we discuss the convergency properties of the procedure, and compare its results with other theoretical results available     

Spectral representation of fractional Brownian motion in ndimensions and its properties

Fractional Brownian motion (fBm) provides a useful model for processes with strong long-term dependence, such as 1/f^β spectral behavior. However, fBm's are nonstationary processes so that the interpretation of such a spectrum is still a matter of speculation. To facilitate the study of this problem, another model is provided for the construction of fBm from a white-noise-like process by means of a stochastic or Ito integral in frequency of a stationary uncorrelated random process. Also a generalized power spectrum of the nonstationary fBm process is defined. This new approach to fBm can be used to compute all of the correlations, power spectra, and other properties of fBm. In this paper, a number of these fBm properties are developed from this model such as the T^H law of scaling, the power law of fractional order, the correlation of two arbitrary fBm's, and the evaluation of the fractal dimension under various transformations. This new treatment of fBm using a spectral representation is extended also, for the first time, to two or more topological dimensions in order to analyze the features of isotropic n-dimensional fBm     

Spinor formalism for waveguides

The authors first prove that there exists a close relationship between the spinor fields and the electromagnetic transverse fields TE, TM.Then the spinor formalism is applied to the waveguide theory and explicit formulae are given for waveguides with rectangular or circular cross section. An interesting feature of the spinor formalism is to require only two components.     

The integral equation method in problems of the theory of nonuniformly filled waveguides

A technique based on the integral equation method is developed for simulation of nonuniformly filled waveguides. It is shown that integral equations ensure a more accurate calculation of the field distribution in the neighborhood of the interface of inhomogeneous media.     

TEM waveguides for EMC measurements

An overview of TEM waveguide electromagnetic compatibility (EMC) test facilities applicable to radiated emission and immunity measurements is given. Measurements of the field homogeneity in two TEM waveguides of different style are discussed. A statistical weighting of the measured electrical field is used to compare the results with standards requirements     

Filter synthesis for coupled waveguides

The synthesis of realistic coupled waveguide filters is considered. The emphasis is on the synthesis of physical devices, rather than on the approximate coupled-mode representations. For this purpose, variational optimization is combined with the normal-mode analysis of interacting waveguides. Physical effects such as the change in coupling strength with waveguide or material dispersion are naturally taken into account. The beam propagation method (BPM) is used to verify the effectiveness of the designs and thus lends a measure of confidence of the applicability of the method to realistic devices     

Loss calculations for antiresonant waveguides

The authors present a theoretical study of antiresonant waveguides, in cylindrical and planar geometry, using leaky mode solutions of the vector wave equation. General analytical expressions are derived to describe the attenuation coefficients of TE, TM, HE, and EH modes of multilayered leaky waveguides, taking into account material absorption. Results obtained with these expressions are compared to numerical solutions and found to be accurate when the leakage loss is low.<>     

Dielectric waveguides for millimetre-wavelength transmission

The letter describes the salient features of a parametric study of dielectric waveguides intended for millimetre-wavelength microwave transmission. The waveguide is an analogue of the monomode optical waveguide, and, if core and cladding are made from foam materials, with loss tangents of order 10?5, the HE11 mode attenuation is about 40 dB/km, and the group delay change is 0.35 ns/km over 1 GHz bandwidth centred at 40 GHz.     

Fusion junctions for glass-fibre waveguides

Various ways of making fused joints in a monomode glass-fibre waveguide have been tried. The highest efficiencies have been about 80%, with a joint in which the end faces are lightly fused together after the cores have been aligned for optimum transmission.     

Matrix analysis of discontinuities in nonreciprocal waveguides: analytical description for magnetooptical slab waveguides

A new analytical formalism to study the effect of discontinuities in a nonreciprocal waveguide has been developed. The analysis is based on 1) the general orthogonality relation obtained from the reciprocity theorem, 2) the modal expansion of the transverse electromagnetic fields within the waveguide, and 3) the continuity of the tangential components of such electromagnetic fields at both sides of the discontinuity. The formalism is presented in a matrix form, which allows the treatment of several discontinuities as a simple summation and product of coupling and propagation matrices. The matrix formalism is developed for magnetooptic waveguides in the three different orientations of the magnetization, and, within this context, two practical applications of magnetooptic isolators are studied.     

Spectral and time domain approaches to some inverse scattering problems

Four methods of electromagnetic probing of an inhomogeneous plane stratified medium are presented. They differ by the nature of the incident wave used in the diagnostic. In the first method, the medium is considered as a structure propagating guided modes, and permittivity profiles are determined from the knowledge of one of the guided modes. In the next three, the medium is considered as a scatterer illuminated by a plane wave. Two of them are devoted to reconstruction of conductivity or permittivity profiles from time domain analysis of the reflected field. The last one allows one to obtain permittivity profiles from spectral domain analysis of the reflection coefficient. In spite of their apparent diversity, all these methods are issued from integral representations of the electromagnetic fields. These representations provides the simulated experimental data for the inverse problems. The behavior of these processes has been examined when parameters of practical interest are varied.     

About coupled-mode theories for dielectric waveguides

A critical examination is made of recent works on coupled-mode theory for dielectric waveguides with strongly overlapping fields. It is shown that there is no best formulation. In each case, explicit or implicit approximations lead to errors that are difficult to estimate. An investigation is made of the accuracy of coupled-mode formulas, in the case of strong guidance, for TM waves along coupled slabs or for HE11 modes along circular rods. Contrary to a previous prediction, there is no breakdown of coupled-mode formulas when the guidance is increased. The coupled-mode equations are applied to the problem of nonparallel waveguides in optical directional couplers. Comparison between coupled-mode predictions and beam-propagation-method simulations shows that bending effects in converging and diverging sections affect the accuracy. An improved coupled-mode theory is proposed in order to take these effects into account     

Athermal waveguides for temperature-independent lightwave devices

The central waveguide of narrowband optical filters is quite sensitive to temperature. This is an obstacle to the broad use of optical frequency-division multiplexing (FDM) systems. Since this undesired characteristic is caused by the temperature dependence of optical path length in the filter, one can stabilize the filtering characteristics if such dependence is successfully eliminated. Thus, a temperature-independent optical waveguide (athermal waveguide), with an optical path length independent of temperature obtained by canceling out the positive dependence of ordinary optical materials with the negative temperature coefficient of the refractive index of some special materials like polymers, is proposed. The experimental result shows that the temperature dependence of optical path length is reduced to -7% of that of conventional glass waveguides