Analysis of Wave Propagation in Inhomogeneous Dielectric Slab Waveguides

The propagation characteristics of the guided modes in an inhomogeneous dielectric slab waveguide are analyzed by tbe regularized WKBJ method. The corrected propagation constants of the guided modes in a near parabolic index medium are derived in analytic form. The effects of the refractive index profile and the homogeneous cladding on the guided modes can be expressed in terms of the mode indices and evaluated numerically.     

Uniform Asymptotic Technique for Analyzing Wave Propagation in Inhomogeneous Slab Waveguides

The guided modes of inhomogeneous dielectric slab waveguides are analyzed by a uniform asymptotic technique based on the related equation method. This technique gives highly accurate solutions in the sense of asymptotic expansion. The algorithm for calculating the guided modes of slab waveguides with an even polynomial refractive-index medium is presented. As an example, we calculate the third-order approximate solutions for the guided modes in an analytic form. The results show that the WKB solutions for higher order modes are more accurate than for the lower order modes and the correction to the WKB solutions is significant for the lower order modes. The numerical result for eigenvalues and modal fields confirms that the third-order asymptotic solution is accurate for all the guided modes of the near-parabolic profile waveguides and for higher order modes in the case of the quasi-Gaussian profile.     

A Variational Theory for Wave Propagation in Inhomogeneous Dielectric Slab Loaded Waveguides

A novel numerical technique based on the variational formulation defined only in the slab is developed to study the loaded rectangular waveguide with an inhomogeneous dielectric slab. The variational equation for the boundary value problem is formulated and solved numerically, using the finite element method with piecewise quadratic trial functions. A comparison of this new technique with the conventional variational ones is presented. Various propagation characteristics, such as the phase constant, useful bandwidth, power handling capacity, and attenuation constants due to conductor and dielectric losses, are investigated for the waveguide centrally loaded with a slab of parabolic dielectric profile. The effects of changes in dielectric profiles are discussed by examining the results for the slabs with constant and parabolic profiles.     

Propagation of Cladded Inhomogeneous Dielectric Waveguides

An approximate theory on the propagation of modes in an arbitrarily inhomogeneous optical waveguide embedded in a homogeneous medium is presented. Simple formulas are given, whereby the propagation constants can be determined assuming that the analytic solution is known in the absence of cladding. The results obtained applying the theory to a truncated parabolic-index profile are shown to be in good agreement with those obtained by the rigorous analysis. The theory is also applied to the propagation of TE and TM waves in truncated near-parabolic-index media.     

A Perturbation Method for the Analysis of Wave Propagation in Inhomogeneous Dielectric Waveguides with Perturbed Media

This paper presents a perturbation method for determining the modes and the propagation constants of TE and TM waves in inhomogeneous dielectric waveguides whose index distributions depart from well-known profiles; e.g., a parabolic profile for which exact solutions can be obtained. Applying the variable-transformation technique to the wave equations, the wave-equation problem is transformed into the related-equation problem. The approximate solutions of the wave equations are obtained solving the related equation. The method is applied to the analysis of lower order mode propagation in a near-parabolic-index medium. The first-order field functions and the second-order propagation constants are given.     

Propagation in Rectangular Waveguide Containing Inhomogeneous, Anisotropic Dielectric

The Wentzel, Kramers and Brillouin (WKB) approximation is used to solve the wave equations for propagation of guided waves in rectangular waveguide containing an inhomogeneous dielectric. The simplest form of anisotropy is used to characterize the relative dielectric constant, i.e., it is assumed that the relative permittivity tensor is diagonalized with respect to the waveguide coordinants. Each of the elements of the relative permittivity tensor is allowed to vary continuously across the broad dimension of the waveguide. The TE/sub nm/ and TM/sub nm/ cases are analyzed for the instance of completely filled guide, while the TE/sub no/ modes are considered for slab-loaded guide.     

The Diffraction of Electromagnetic Waves by Dielectric Steps in Waveguides

The problem of determining the scattered electromagnetic fields when a dielectric step discontinuity is placed in a waveguide is considered. Although an exact method of solution is not presently known, the recently introduced modified residue-calculus technique (MRCT) can be successfully extended to obtain a very accurate and numerically efficient approximate solution of the semi-infinite dielectric step. A still further extension of the modified residue-calculus method yields the approximate solution for the case of a finite dielectric step. A unique advantage of the present methods is that the degree of accuracy obtained is independent of the relative permittivity of the dielectric material and of the frequency. Thus very high permittivities or frequencies can be considered without an attendant increase in computational complexity. Numerical data are presented which confirm the accuracy of the method.     

Waves and Evanescent Fields in Rectangular Waveguides Filled with a Transversely Inhomogeneous Dielectric

A numerical-calculation method for rectangular waveguides containing a transversely inhomogeneous dielectric is presented. The method is not restricted to the cutoff case or to special inhomogeneities. The relative permittivity of the dielectric can be an arbitrary function of the cross-sectional coordinates. The electric-and magnetic-field strengths, the dispersion characteristics of the propagating modes, and the attenuation constants of the evanescent modes result from the solution of a matrix eigenvalue problem with typically 8000 matrix elements. Propagating and evanescent modes in a waveguide containing a longitudinal semicircular dielectric rod are calculated as examples. The accuracy of the calculation method is confirmed by measurements and by calculating a special example with an exactly known solution. The error of the field intensities is typically 5 percent; the error of the dispersion characteristics and of the attenuation constants is typically 0.5 percent.     

Propagation, Attenuation, and Dispersion Characteristics of Inhomogeneous Dielectric Slab Waveguides

A numerical method based upon invariant imbedding and the transverse impedahce concept is applied to the problem of calculating various properties of inhomogeneous slab waveguides. The approach appears not only to be rapidly convergent but is also capable of giving arbitrary accuracy for any given mode. In particular, some interesting properties of a class of asymmetric profiles are pointed out, relating to discussions of lossy structures, temporal pulse distortion, and spatial broadening.     

传输均匀场的加载介质壁矩形波导的研究

本文给出了一种能够传输均匀场的介质壁矩形波导，在数值计算的基础上得出了其结构参数；并进一步分析了加载工作物质对其场型的影响。     

Application of Generalized Characteristic Vectors to Problems of Propagation in Clad Inhomogeneous Dielectric Waveguides

A transformation matrix that uses generalized characteristic vectors is used to convert Maxwell's equations into a set of loosely coupled equations for the wave amplitudes. This transformation is suitable for permittivity profiles with turning points. In earlier full-wave solutions to these equations, several special functions that account for the local features of the permittivity profile, especially near the turning points, were used to obtain appropriate expansions of the fields. The transverse field components, the propagation coefficients, as well as the phase and group velocities, are computed for both horizontally polarized (TE) and vertically polarized (TM) modes of the dielectric waveguides using the full-wave approach. These solutions are compared with analytic solutions for waveguides with special permittivity profiles. They are also compared with recently published results based on a perturbational approach.     

损耗介质周期加载圆柱波导场分析

本文利用傅立叶级数将损耗介质周期加载圆柱波导结构的场展开,通过分界面上场匹配的模式分析方法得出了TMOn模的色散曲线、电磁场分布以及品质冈数等特性参量.编写了程序DDET-TM并计算TM01模的各特性参量,得到的结果与HFSS的仿真结果吻合较好,验证了本方法的适用性.     

Comments on "Ridged Waveguides with Inhomogeneous Dielectric Slab Loading" (Letters)

In the above paper/sup1/, Magerl derives dispersion equations for TE/sub m0/ modes of ridged waveguide with inhomogeneous dielectric-slab loading. The existence of TE modes was evidently assumed a priori (a seemingly natural assumption); unfortunately, true TE modes do not exist in this waveguide (with a singuIar exception to be noted).     

Composite Dielectric Waveguides

Composite dielectric waveguides, or a class of dielectric waveguides made of a few dielectric materials, are described. A composite circular dielectric waveguide (CCDW) is treated with the the point-matching method. Computed values of the propagation constant of the CCDW are compared with those of the homogeneous circular dielectric waveguides (HCDW). Microwave experiments carried out to comfirm the theory are discribed.     

Solutions of the Vector Wave Equation for Inhomogeneous Dielectric Cylinders--Scattering in Waveguide

Some solutions of the vector wave equation for an inhomogeneous dielectric cylinder, suitable for numerical calculations of the scattered electromagnetic (EM) field in waveguide, are presented in cases where the cylinder axis is parallel, or perpendicular, to the incident electric field vector. The scattered field, given in terms of normal modes of the rectangular waveguide, permits easy determination of the transmission and reflection coefficients for the structure. The dielectric susceptibility may be considered as variable along the cylinder radius according to a parabolic function (Luneberg-type profile). Finally, numerical results of the scattered near field are presented for Teflon cylinders of different diameters, in the case of parallel polarization. They are compared with laboratory measurements in the microwave X band made as a reliability test of the computational program. The agreement between measured and computed values is satisfactory within a deviation of 10 percent in the whole frequency band.     

电磁波在均匀磁化等离子体中的衰减与反射

等离子体覆盖住金属导体,通过等离子体对入射电磁波的折射、吸收,使得入射波功率衰减,降低了反射功率,起到减小目标RCS的作用.对于均匀磁化等离子体,针对介电常数与等离子体粒子密度、外加磁场强度、电子碰撞频率以及入射波频率的关系,仿真计算了不同的等离子体粒子密度、外加磁场强度、电子碰撞频率以及不同等离子体厚度在毫米波波段对电磁波的衰减和反射特性的影响.     

Bends in Nonradiative Dielectric Waveguides

An experimental study was made of bends in the nonradiative dielectric waveguide (NRD-guide) at 50 GHz. The main cause of the bending losses was found to be due to the reflection at the transitions between the straight and curved waveguides rather than due to the radiation. The width of the dielectric strip was experimentally optimized in order to reduce the reflection, and a bend with a curvature radius as small as one guide wavelength could be realized. The experimental results are examined theoretically. The theory implies that the NRD-guide has a favorable tendency to suppress not only the radiation but also the reflection at the curved sections. It is also shown that the field maximum moves outwards or inwards from the mean path of the curved guide according to whether the dielectric strip is wider or narrower than a certain critical width. This critical width can be adopted as a design criterion for a low loss, very sharp NRD-guide bend.     

Ridged Waveguides with Inhomogeneous Dielectric-Slab Loading

The dispersion equation of the ridged waveguide with inhomogeneous dielectric-slab Ioading is derived. Numerical results for the cutoff frequencies of the three lowest order TE/sub m0/ modes are given which substantiate the feasibility of the modal expansion and field-matching technique employed. For a Teflon-slab loaded ridged waveguide, a 40-percent decrease of dominant-mode cutoff frequency, simultaneously providing 20-percent enhanced TE/sub 20/-mode separation compared to an empty ridged waveguide, is demonstrated.     

Dielectric Loaded Elliptical Waveguides

Wave propagation in a metallic elliptic waveguide loaded with a dielectric rod or a dielectric lining is investigated theoretically. The mode spectrum for both slow and fast hybrid modes is obtained by numerical solution of the characteristic equations. Correspondence is established between the modes of the loaded and unloaded elliptical waveguides. Typical field plots for /sub e/HE/sub 01/ and /sub 0/EH/sub 01/ modes are presented. Power flow, power loss, and attenuation are obtained using a perturbation method.