Features of Radiation of Electromagnetic Waves from a Thin Electric Antenna in a Planar Waveguide with Inhomogeneous Filling

We consider the problem of radiation of electromagnetic waves from a thin electric antenna located in a planar waveguide with perfectly conducting walls filled with an inhomogeneous dielectric. Cases where the antenna is fed by a time-harmonic e.m.f. and a bell-shaped impulse signal are analyzed. The current distribution along the antenna, its input admittance, the longitudinal component of the electric field, and the total complex power of the antenna are calculated numerically. We compare the antenna characteristics for waveguides with homogeneous and inhomogeneous filling.     

Characteristics of an Electric Dipole in a Plane Waveguide with an Inhomogeneous Filling in the Long-Line Approximation

Within the framework of the long-line approximation, we obtain the expressions for the current distribution, input impedance, and admittance of a nonsymmetric thin electric dipole whose ends are connected to perfectly conducting walls of a plane waveguide filled by an inhomogeneous dielectric. The use of this approximation allows one to qualitatively interpret the results of rigorous solution of the problem of the effect of the medium inhomogeneity on the radiation characteristics of the antenna.     

Propagation of an ultrashort laser pulse in a waveguide of rectangular cross section

The propagation of a spikelike ultrashort laser pulse in a mirror waveguide of rectangular cross section with perfectly conducting walls is considered. An algorithm for the calculation of the propagation of a field pulse in such a waveguide is designed. The general approach is illustrated by calculation of the propagation of a p-polarized field pulse shorter than the dimensions of the waveguide cross section.     

Interference of co-and counterpropagating waveguide modes in a planar structure

Interference between inhomogeneous waves in a planar waveguide placed in a perfectly conducting environment is studied. It is shown that the interference flux of copropagating waveguide TM modes behaves like counterpropagating homogeneous volume waves. The longitudinal and transverse components of the interference fluxes of co-and counterpropagating waves in the general case result from interference between both the active and reactive components of the field. The interference flux of waveguide modes may also be observed when the partial fluxes of the modes equal zero.     

Scattering losses from planar waveguides with material inhomogeneity

Abstract

We consider the propagation of guided waves in a planar waveguide that has a finite-length segment of inhomogeneous media. Except for the inhomogeneous segment, which varies in length from 0 to 160λ, the waveguide is piecewise homogeneous everywhere. The inhomogeneity is modelled by two-dimensional random permittivity fluctuations that are numerically generated from an assumed Gaussian correlation function.

In 2D, the Maxwell equations are solved in the frequency domain for both TE and TM polarization by using modal expansion methods, perfectly matched absorbing boundary layers and the R -matrix transfer matrix algorithm. The guided waves are excited by a Gaussian beam incident on the waveguide aperture. For various waveguide design parameters, numerical results are given for waveguide power loss per unit length of waveguide inhomogeneity. The power loss curves are calculated as the average from numerous realizations of the random permittivity and the coefficient of variation is also given.     

Estimation of field in plane impedance waveguide with local geometrical inhomogeneity. I

The effect of an inhomogeneity in the form of a circular cylinder the properties of whose base are described by a certain impedance and whose lateral surface is ideally conducting on the field of a point source in a plane impedance waveguide is studied. In a scalar approximation, the problem is reduced to a two-dimensional integral equation over the surface of the inhomogeneity. A solution is constructed by the method of successive approximations; the solution of the problem for a regular impedance waveguide is used as an initial approximation. The effect of a local ionospheric inhomogeneity on the field of an electrical dipole in the earth-ionosphere waveguide is estimated.Leningrad State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 8, pp. 908–918, August, 1991.     

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.     

Scattering losses from planar waveguides with material inhomogeneity

We consider the propagation of guided waves in a planar waveguide that has a finite-length segment of inhomogeneous media. Except for the inhomogeneous segment, which varies in length from 0 to 160λ, the waveguide is piecewise homogeneous everywhere. The inhomogeneity is modelled by two-dimensional random permittivity fluctuations that are numerically generated from an assumed Gaussian correlation function.

In 2D, the Maxwell equations are solved in the frequency domain for both TE and TM polarization by using modal expansion methods, perfectly matched absorbing boundary layers and the R-matrix transfer matrix algorithm. The guided waves are excited by a Gaussian beam incident on the waveguide aperture. For various waveguide design parameters, numerical results are given for waveguide power loss per unit length of waveguide inhomogeneity. The power loss curves are calculated as the average from numerous realizations of the random permittivity and the coefficient of variation is also given.     

On solution of the vector 3-D locally irregular waveguide problem

The vector 3-D problem of a point-source field in a plane waveguide with a large-scale local inhomogeneity on one of its walls is considered. The field components on the boundary surfaces comply with the Leontovich conditions, which are used as a basis for obtaining expressions for the derivatives of the field vectors normal to the boundaries; these expressions reflect the 3-D nature of the inhomogeneity. The problem is reduced to a system of 2-D integral equations allowing for overexcitation and depolarization of the field scattered by the irregularity. The system of 2-D integral equations is asymptotically transformed over the inhomogeneity region on the surface of the walls bounding the waveguide space into a system of linear integral equations, for which the integration contour is represented by the line between the source and observation point, as well as by the linear geometric contour of the irregularity.State University, St. Petersburg. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 8, pp. 785–803, August, 1995.     

平面光波导结构的FDTD分析

将各向异性理想匹配层(APML)吸收边界条件用于平面光波导结构的时域有限差分法(FDTD)分析中,导出了APML媒质中适用于角域和边缘的通用差分方程,并对平行介质带定向耦合器进行了数值模拟和验证,所得数值解与解析解非常一致.该方法可用于任意复杂结构的平面光波导的计算机辅助设计与分析.     

Calculation of VLW fields in a waveguide with A 3-D local inhomogeneity

The problem of a point-source field in an irregular impedance waveguide is solved. The 3-D inhomogeneity of one of the walls of the waveguide is given by an area-inhomogeneous impedance. To obtain a solution within the framework of the method of integral equations, we develop a procedure for asymptotic transformation of the 2-D equation into an 1-D equation with allowance for the waves reflected from all the inhomogeneity boundaries. The obtained 1-D integral equation for points that belong to both the path line and boundary contour of the inhomogeneity is solved numerically using an original algorithm. The results of model calculations in a near-earth waveguide for the case of ionospheric perturbations that are large on the wavelength scale are given.State University, St. Petersburg. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 12, pp. 1312–1322, December, 1995.     

Field Structure in the Cross Section of a Ferrite Inhomogeneous Anisotropic Insert of a Rectangular Waveguide

We develop a physico-mathematical model describing excitation and distribution of electromagnetic waves in an anisotropic waveguide or resonator in the three-dimensional case. We develop a theoretical approach for discretization of the Maxwell equations in an arbitrary medium in the presence of bounding walls of a waveguide or resonator. The resulting system of linear algebraic equations for the electric-field components in an inhomogeneous anisotropic medium is solved by the method of biconjugate gradient. The results of calculating the electric field lines in the cross section of an anisotropic insert of a rectangular waveguide are presented.     

Stability of hydromagnetic Dean flow between two arbitrarily spaced concentric circular cylinders in the presence of a uniform axial magnetic field

The effect of a uniform axial magnetic field on the stability of the flow of an incompressible viscous electrically conducting fluid between two arbitrarily spaced concentric circular cylinders driven by a constant azimuthal pressure gradient is studied. The linearized stability equations for steady axisymmetric disturbances form an eigenvalue problem, which are solved by using a classical Runge–Kutta scheme combined with a shooting method, termed unit disturbance method. It is observed that for fixed gap width, the magnetic field has a stabilizing influence on the flow for both perfectly conducting and nonconducting walls. It is also found that for a given value of magnetic parameter, stabilization is more as the gap width increases. Further the electrically nonconducting walls are found to be more destabilizing than the perfectly conducting walls. The critical value of the radii ratio (0<η<1) beyond which the first unstable mode becomes nonaxisymmetric is determined for various values of the magnetic parameter.     

Hybrid Modes in a Square Corrugated Waveguide

By using two scalar eigenfunctions, electric and magnetic fields in the rectangular (or square) corrugated waveguide are analyzed. In a rectangular corrugated waveguide, the boundary conditions on two corrugated and two smooth walls can be satisfied to excite the hybrid mode. In a highly oversized waveguide where the wavelength of dominant mode is close to that in vacuum, two smooth walls can be exchanged with the corrugated walls because the boundary condition at those walls is satisfied approximately. The replacement is possible due to almost no penetration of the electromagnetic fields into the gap of the replaced walls when the direction of main electric field is parallel to the gap of replaced walls. This characteristic enables us to rotate the polarization of the hybrid mode in the oversized square waveguide with all four corrugated walls and is applicable to the remote steering antenna for electron cyclotron heating in the ITER.     

Dipole-exchange spin wave spectrum in an anisotropic ferromagnetic waveguide with a rectangular cross section

A theory has been constructed that strictly describes the spectrum of dipole-exchange spin waves in an arbitrarily magnetized anisotropic ferrite waveguide with a rectangular cross section. The theory takes into account the spatial inhomogeneity of the internal magnetic field in the waveguide cross section. The influence of parameters of the ferrite waveguide on the distribution of the internal magnetic field in the waveguide cross section is analyzed. The dispersion characteristics of two waveguide types most widely used in practice are investigated. The dipole-exchange spin wave spectra calculated for a transversely magnetized waveguide are presented and the distributions of the dynamic magnetization in the waveguide cross section for several types of volume and localized spin-wave modes are constructed.     

Full-vectorial mode solver for anisotropic optical waveguides using multidomain spectral collocation method

A full-vectorial mode solver in terms of the transverse magnetic field components for optical waveguides with transverse anisotropy is described by using the multidomain spectral collocation method based on Chebyshev polynomials. The waveguide cross section surrounded by the perfectly matched layers is divided into suitable number of homogeneous rectangles, and then connected with by imposing the continuities of the longitudinal field components at the dielectric interfaces shared by the adjacent rectangles, resulting in a generalized matrix eigenvalue problem. To validate the established method, results of an anisotropic square waveguide and a magnetooptic rib waveguide are presented and compared with those from the full-vectorial finite difference method, full-vectorial beam propagation method, and the experimental data.     

Space-charge field of a photorefractive grating in a planar waveguide based on a cubic crystal

We consider the initial stage of formation of photorefractive gratings in planar waveguides based on cubic electrooptic crystals. We have obtained solutions for the components of the space-charge field for arbitrary ratios between parameters characterizing the spatial inhomogeneity of the light interference pattern in the waveguide as well as the diffusion length. The dependence of the component of the space-charge field parallel to the grating vector on its period in the initial section of the recording is also determined by the sum and difference of the transverse propagation constants of the interacting waveguide modes. We show that for waveguide interactions characterized by a small transverse scale of spatial inhomogeneity, the distributions of the space-charge field and the light intensity in the interference pattern are substantially different. These effects must be considered in analysis of the nonlinear interactions occurring in a refractive index grating due to the electrooptical effect. Tomsk University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, pp. 65–73, June, 1997.     

Dispersion relation for space-charge waves in a warm plasma-filled elliptical waveguide in an infinite axial magnetic field

A perfectly conducting elliptical cylinder filled with a warm plasma and immersed in an infinite axial magnetic field is considered. Using Maxwell’s equations and dielectric tensor, a Mathieu differential equation for axial component of electric field is obtained. Considering the boundary conditions, dispersion relation for waves in a plasma of warm electrons and immobile ions, which fills an elliptical waveguide and it is under the action of infinite axial magnetic field are calculated. Furthermore, dispersion relation and scalar potential in the quasi-static approximation in a cold magnetized plasma elliptical waveguide is calculated. The obtained results are graphically presented.     

An Exact Solution of the Problem on Dynamics of an Electromagnetic Field in a Cylindrical Resonator with Moving Boundaries

The dynamics of an electromagnetic field in an unsteady cylindrical resonator with perfectly conducting and impedance walls is considered. Exact solutions are found for fields as functions of time. Conservation of photon numbers during the compression is shown.