Analysis of Radiation Phenomena in a Wedge Ended Dielectric Slab Waveguide

Radiation phenomena observed in a wedge shape ended dielectric slab waveguide are analyzed using mode matching technique. The case of transverse electric polarization (TE) being parallel to dielectric slab waveguide is assumed. In order to describe the fields in the wedge region, a stack of dielectric plates is assumed and in each layer the fields are expanded in terms of the mixed spectrum of guided and radiated modes. A similar expansion is used in the constant thickness slab waveguide while in free space medium a continuous-radiation mode expansion is used. Then a mode matching approach is applied, incorporating the orthogonality properties of mixed spectrum modes, in order to compute the wave fields inside the dielectric slab waveguide and wedge medium. Mode matching is achieved by discretizing the continuous radiation mode spectrum leading into a numerically stable solution provided a sufficient large number of points are used to convert integrals into finite summations. Numerical computations are carried out for various wedge geometries and shapes including linear and exponential profiles.     

Scattering of Surface Waves at a Dielectric Discontinuity on a Planar Waveguide

A theoretical treatment is presented of the scattering of a surface-wave mode on a planar surface waveguide at an abrupt axial transition. The latter is due to a dielectric obstacle that covers the line completely up to a given height. The analysis involves the matching of the tangential fields, expressed in terms of complete sets of eigenmodes, on the transition plane. The problem arises in certain obstacle detection schemes currently being proposed for guided transportation, which use the principle of guided RADAR.     

Rigorous Analysis of the Step Discontinuity in a Planar Dielectric Waveguide

Planar dielectric waveguides play an important role in electrooptics and in the submillimeter regions. In many laser configurations and integrated optical components, grooves are etched in the planar surface or overlays are deposited on it. The step is an idealization of such discontinuity. In this paper, the problem of an arbitrary large step under multimode excitation is solved by means of a rigorous variational approach. A rapidly converging expression for the scattering matrix of the step is derived, which is analogous to the one previously derived for transverse discontinuities in closed waveguides. Two choices as to the basis functions are compared: one is constituted by optimally scaled Laguerre functions and the other by the surface waves of both slabs complemented by Laguerre functions. Both the electric field and the magnetic field formulations of the problem have been investigated for the TE case. Numerical results are presented for the scattering matrix of the step under monomode and multimode excitation as well as for its radiation pattern. The accuracy and limitations of existing small step approximations are discussed. The technique is applicable to other transverse discontinuities in open structures.     

Scattering of Guided Modes Caused by an Arbitrarily Shaped Broken End in a Dielectric Slab Waveguide

Electromagnetic scattering of guided modes in a dielectric slab waveguide caused by an arbitrarily shaped broken end is analyzed theoretically by using the integral equation method. By solving the integral equations iteratively, the tangential components of the electric and magnetic fields on the broken end surface are determined, from which the reflected mode power, the radiation wave power and field patterns, and the total scattered power are obtained. Numerical results are presented for the plane-perpendicular, plane-tilted, and arc-shaped end surfaces. Both TE and TM modes are assumed as an incident wave.     

Coupling Between an Abruptly Terminated Optical Fiber and a Dielectric Planar Waveguide

The coupling between an optical fiber and a dielectric planar waveguide is analyzed when both guides are terminated abruptly and are facing each other. Mixed spectrum eigenwave representations of fields are employed inside the waveguides while Fourier integrals are utilized to describe the field in the space between the two guides. A coupled system of integral equations is derived by satisfying the boundary conditions on the terminal planes of both waveguides. A weak guidance approximation is assumed to facilitate the analysis. Numerical results are presented for several coupling geometries. Misalignment losses and coupling optimization phenomena are investigated.     

Rigorous Analysis of Electromagnetic Wave Propagation in Cylindrical Dielectric Waveguide Array

Cylindrical Dielectric Waveguide Array(CDWA) should be considered as a kind of two-dimensionally periodic(2DP) medium. Based on the established rigorous theory for 2DP medium, a great amount of numerical results for CDWA were presented. Wave propagation in CDWA was analyzed in detail in this paper. Firstly, given the longitudinal wave vector (k _z=0), Brillouin dispersion relations between transverse wave vectors were analyzed when modulation coefficients or the rate of different dielectric areas in a unit cell varied. Interactions between space harmonics were also studied. Secondly, when the area of dielectric cylinder in the unit cell varied within a given range, CDWA dispersion relations were compared with Rectangle Dielectric Waveguide Array's, some interesting conclusions were obtained.     

Analysis of Electromagnetic Waves Scattering by a Finite Size Dielectric and Metal Cylinder in a Rectangular Waveguide

The paper presents a rigorous solution of the scattering problem by a circular dielectric and perfectly conducting cylinders of any radius and any height in the rectangular waveguide oriented perpendicularly to a wall. The method is based on the representation of fields in waveguide and dielectric medium by cylindrical eigenfunctions and application of boundary conditions on surfaces of the cylinder to evaluate the fields inside and outside the cylinder. The reflection and transmission coefficients are expressed through the fields. As an example the reflection and transmission coefficients versus frequency for various dielectric and metallic cylinders are computed. The comparison of numerical with experimental data is presented.     

Comments on "Scattering of Surface Waves at a Dielectric Discontinuity on a Planar Waveguide" (Letters)

An analysis of the problem of scattering of surface waves at a dielectric discontinuity on a planar waveguide has recently appeared in this TRANSACTIONS. (Letters)     

Propagation in Dielectric Slab Loaded Rectangular Waveguide

Propagation in dielectric loaded rectangular waveguide is investigated theoretically for varying slab thickness and dielectric constant. The slabs are placed across the center of the waveguide in the E plane. This geometry is found to offer bandwidths in excess of double that of rectangular waveguide for dielectrics having dielectric constants of approximately 18. Power handling capacities which are double or triple that of standard waveguide are achievable using the dielectric loaded waveguide. In addition to the theory, design curves of bandwidth, guide wavelength, cutoff wavelength, impedance, power handling capacity, wall losses, and dielectric losses are presented and compared to experiment where possible.     

Scattering of Surface Waves on Transverse Discontinuities in Symmetrical Three-Layer Dielectric Waveguides

This paper presents a rigorous Wiener-Hopf solution to the problem of transverse discontinuities in a symmetrical three-layer dielectric waveguide excited by the dominant TE mode. Fourier transformation and the proper boundary conditions provide the Wiener-Hopf equation for the Fourier components of the scattered fields at the interface between the free space and the dielectric waveguide. A formal solution to this equation is derived by conventional factorization methods, and an iterative method is proposed to calculate the reflected, transmitted, and radiated fields numerically.     

Parametric Equations for Surface Waves In Dielectric Slab (Short Paper)

For the dielectric slab it is shown that 1) the dispersion curve for the nth surface wave can be found using parametric equations in which the normalized inside wavenumber K/sub xl/ and the mode number are the parameters, 2) the dispersion curve for the nth surface wave mode can also be found by using parametric equations in which the mode number and a modified wavenumber x' with common domain [0, pi/2] are the parameters, and 3) an TE or all TM dispersion curves for surface waves are related to each other by a simple algebraic equation using the mode numbers and the normalized propagation constants K/sub 0/ and Beta as the variables.     

Rigorous Hybrid-Mode Analysis of the Transition from Rectangular Waveguide to Shielded Dielectric Image Guide

The transition waveguide to shielded and dielectric image guide is analyzed by the rigorous hybrid-mode field expansion technique where higher order mode coupling effects are taken into account directly, also below the corresponding cutoff frequency. The solution of the related eigenvalue problem includes waves with a complex propagation constant although the guide is assumed to be lossless. Calculated diagrams of the propagation constant as a function of frequency, as well as of the permittivity, illustrate the complicated mode conversion between evanescent modes, complex waves, backward waves, and propagating waves. For the three-dimensional scattering problem, the calculated magnitude of the input reflection coefficient agrees well with measurements, whereas the transmission-line theory applied to this structure leads to wrong results.     

Scattering of Unidirectional Surface Waves

A perfectly conducting plane screen embedded in a gyrotropic medium is shown to be able to support a unidirectional surface wave. Such a surface wave is assumed to be incident on the top of a semi-infinite screen. At the edge the incident power is converted partly into a reflected surface wave which travels on the bottom of the screen and partly into a space wave. The angular distribution of the radiated energy as well as the power-reflection and the power-transmission coefficients are evaluated. Total reflection is shown to occur for a certain band of frequencies.     

Rigorous Analysis of the Disk-Loaded Waveguide Slow-Wave Structures

Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). Although TM ₀₁ mode is it's main mode, the asymmetry mode may be excited by slight asymmetry of the structure, misalignment of the beam, or the asymmetry associated with the input or output structure. So research about asymmetry mode of disk-loaded waveguide is necessary. The general dispersion equation and interaction impedance expression of disk-loaded waveguide is obtained with accurate field theory for the first time. Based on these results, a broadband and a narrowband disk-loaded waveguides are designed which can be used in the Ka band HPTWT. Moreover, the theoretical calculated results are compared with the simulated results from the HFSS (High Frequency Structure Simulator) code using finite element method. It is found that frequency domain overlapped by these two modes of the narrowband structure is very narrow, so the HEM ₁₁ mode may be ignored when calculating Beam-wave interaction. In the other hand, the interaction impedance of HEM ₁₁ mode is very low generally.     

斜入射情况下介质周期结构三维散射问题的严格求解

本文采用多模网络与严格模匹配相结合的方法,以介质周期结构在平面波沿主平面二维斜入射情况下散射特性的分析为基础,经过巧妙的数学处理,严格求解了三维斜入射情况下介质周期结构的散射问题,从而为毫米波和光集成电路中有关介质周期结构的精确分析和奠定了基础.     

Tapping of Love Waves in an Isotropic Surface Waveguide by Surface-to-Bulk Wave Transduction

A theoretical study of tapping a Love wave in an isotropic microacoustic surface waveguide is given. The surface Love wave is tapped by partial transduction into a bulk wave at a discontinuity. It is shown here that, by careful design of the discontinuity, the converted bulk wave power and the radiation pattern may be controlled. General formulas are derived for the calculation of these important characteristics from a relatively general surface contour deformation.     

Air-Gap Effect in Rectangular Waveguide Containing a Lossy H-Plane Dielectric Slab

The propagation coefficient for a partially filled rectangular waveguide containing a lossy H-plane slab against the broad wall can be significantly altered if an air gap exists between the slab and the wall of the waveguide. The solutions of the dispersion equation show that the attenuation and phase coefficients may be increased as well as decreased by the presence of an air gap. For a fully filled waveguide the effect of an air gap is maximized if the gap is equally distributed at the top and bottom of the sample.     

对称非线性薄膜波导TE模的色散特性

用均匀（重整化）微扰方法分析Ｋｅｒｒ型非线性薄膜两侧为折射率相等的包层与衬底情形ＴＥ模的传播特性，传播常数用表征非线性的功率密度极值作为参数来表示。在微扰法失效情况下，用数值积分法求解。本文方法简便，节省机时，对典型实例的计算结果与精确数值计算结果十分符合。     

Analysis of Coupling and Radiation Properties for an Improved Dielectric Waveguide Directional Coupler Utilizing a Tapering Left-Handed Slab Core

The coupling and radiation characteristics of an improved dielectric waveguide directional coupler with a tapering left-handed slab core located in the coupling region are analyzed by the staircase approximation method, which combines the building block approach and multi-mode network theory with a rigorous mode-matching procedure. Particular attentions are directed toward the radiation characteristics under different structural parameters of the coupler. Numerical results indicate that the proposed coupler is very promising by shortening the coupling length significantly while keeping the radiation loss at a low level.