Hyperbolic Secant Coupling In Overmoded Waveguide

This work presents a new solution of the coupled-mode equations for a hyperbolic secant spatial variation of the coupling between two modes. An analytic expression is given for the transmission coefficient for arbitrary complex differential propagation constant and coupling strength. The expression is particular simple in the case when the differential attenuation between the modes is negligible. Design curves are presented in terms of normalized parameters. The hyperbolic secant coupling may be truncated and still yield virtually the same transmission as for infinite couping length. The required coupling length is indicated by a comparison of the ideal expression with the results of numerical integration of the coupled-mode equations. Hyperbolic secant coupling can be particularly useful for the design of short low-loss broad-band bends, twists, and mode-selective couplers in overmoded waveguide. Results of tests on 90-degree bends in rectangular and corrugated circular waveguide are consistent with the theory.     

Ionosphere effects on navigational and positioning signals full-wave solutions

Full-wave, numerical, and analytical solutions are obtained for navigational signals reflected or transmitted through an inhomogeneous anisotropic layer such as the ionosphere. The transfer functions used in these solutions are obtained by using a nonsingular transformation matrix to convert Maxwell's equations (for the transverse electromagnetic field components) into a set of loosely coupled first-order differential equations for the forward and backward traveling ordinary and extraordinary wave amplitudes. These transformation matrices which are also suitable for critical coupling regions (characterized by strong reflections or coupling between the ordinary and extraordinary waves) are constructed through the use of generalized characteristic vectors. Analytical and numerical techniques are used to obtain the signal distortions and instantaneous phase anomalies due to the medium. These are used to determine the time of the third zero crossing, which is generally regarded as the effective arrival time of the signal.     

电离层中ELF辐射源向下传播衰减理论分析

利用大功率高频（HF）电波调制加热电离层可在电离层中有效形成辐射源,并用于辐射ELF电磁波.本文基于磁流体力学的基本方程通过对电离层中极低频（ELF）辐射源的辐射场分析,获得ELF电磁波在电离层中传播的色散关系式,建立电离层中的ELF辐射源向下传播衰减模型.并依据建立的传播衰减模型,分析不同纬度地区传播衰减的差异,以及传输频率和背景电离层参数对传播衰减的影响.     

Guided Waves in Inhomogeneous Focusing Media Part I: Formulation, Solution for Quadratic Inhomogeneity

This work is a theoretical study of waves in a circular-cylindrical radially inhomogeneous guiding medium. A vector theory based upon Maxwell's equatious is used to derive linear homogeneous fourth-order equations satisfied by the longitudinal electric and magnetic field components for a medium in which the permittivity decreases monotonically from the propagation axis. The percentage change of permittivity from the guide axis to some radius a is assumed small. For modes with propagation constants approximately equal to the wave number at guide center, all field components are shown to satisfy second-order differential equations. In particular, all transverse field components are proportional to a single scalar function. In a Iossless system with no containing boundary, a new class of polynomial-Gaussian solutions describes the longitudinal fields for the case of a quadratically decreasing permittivity, while the transverse fields are Gaussian-Laguerre. Mode patterns, propagation constants, and orthogonality relations are given. It is shown analytically that the modes tend to TE or TM as the mode order increases. Moreover, the transverse fields become dominant at large wave numbers, and the fields become tightly bound to the guide axis as the wave number and/or inhomogeneity increases. Studies of more general permittivity variations and wall effects will be reported shortly.     

Field distribution in a circular waveguide with a corrugateddielectric lining

The problem of wave propagation through a circular cylinder with a periodically interrupted dielectric lining is solved by a boundary value approach by considering the region between the corrugations as a medium with a tensor permittivity. The characteristic equation for the phase constant is derived by matching the field components. Solutions for the phase constant are obtained and the variation of the phase constant with the physical parameters is studied. The variation of the axial and circumferential electric field components in the transverse plane is also studied     

隧道中低频导行电磁波的传播特性

在低频段上，导行电磁波的衰减率很小，随频率的升高而缓慢增加，不论单线波模还是双线波模其近壁效应都很小。用数值分析方法术解了单线波模方程和双线波模方程，得出的主要结论为它们的衰减率与隧道壁电导率和隧道半径有撤弱依赖关系。理论分析含单导体的任意横截面隧道可知低频段上导行电磁波的衰减率与隧道横截面积大小有微弱依赖关系，而与横截面形状无关。     

波在暖电离层中的传播和耦合

本文研究了波在暖电离层中的传播。文中导出了用拆射率n表示的波的色散关系,并由此推导出分层暖电离层中q的方程。所有这些方程都被用于用射线方法研究波在暖电离层中的传播,模式联接和波的线性耦合。 本文还讨论了波方程的奇点、等离子体波与电磁波的耦合。在波耦合区中,波的场可以通过求解波方程在奇点附近的解而求得。文中比较了用射线方法和全波方程研究波耦合时电波传播的结果。 本文所得结果对研究用无线电波加热电离层实验中的吸收区域是有用的。     

Nonuniform Layer Model of a Millimeter-Wave Phase Shifter

The electromagnetic wave propagation of millimeter waves in dielectric waveguides with thin surface plasma layers is characterized. The phase and attenuation of a 94-GHz wave are computed for various surface plasma layer thicknesses as a function of earner density levels. The electron/hole pairs generated in the vicinity of the dielectric waveguide surface by photo excitation are assumed to have an exponential profile due to either carrier diffusion or the exponential absorption of the optical field. Field computations made for a uniform plasma layer are compared with those of the nonuniform plasma to illustrate the effects of the exponential tails of the carrier profiles on both the phase and attenuation of the millimeter wave. The thin plasma layers slightly affect the field profile of the transverse electric modes (fields polarized parallel to the plasma layer). The transverse magnetic fields are highly distorted at plasma densities greater than 10/sup 16/ cm/sup -3/.     

On Inhomogeneously Filled Rectangular Waveguides (Short Papers)

A method is given for determining the characteristic equations and field components of the LSE and LSM modes in rectangular waveguides filled with a dielectric which is inhomogeneous in one transverse dimension. The method is exact and yields solutions for a nearly arbitrary variation in permittivity across the waveguide.     

Concerning lossy, compressible, magneto-ionic media-General formulation and equation decoupling

The governing equations for electromagnetic phenomena in lossy, compressible, magneto-ionic media are formulated in terms of a newly introduced compressivity tensor. The matrix forms of both the permittivity tensor and the compressivity tensor are given. From the new governing equations, a three-dimensional vector wave equation and a dispersion equation are derived. In a source-free region, a set of three simultaneous wave equations in the longitudinal components of the electric and magnetic fields and in the pressure distribution can be written. These equations can be decoupled in the lossless case by effecting a transformation. The required transformation matrix and the resulting uncoupled, second-order, differential equations are given. Formulas for the determination of the transverse components of the electric and magnetic fields are also derived.     

A numerically efficient finite-element formulation for the generalwaveguide problem without spurious modes

A numerically efficient finite-element procedure without spurious modes is presented for the analysis of propagation characteristics in arbitrarily shaped metal waveguides loaded with linear materials of arbitrary complex tensor permittivity and permeability. The method is straightforwardly derived from the first-order Maxwell curl equations and comprises both the transversal and longitudinal components of the electric and magnetic fields. Hence, all necessary boundary conditions on the tangential field components are a priori satisfied by the trial functions. With this formulation, an absence of spurious modes has been found. Furthermore, by imposing the additional boundary conditions on the normal components of the magnetic induction and electric displacement fields, the dimension of the resulting matrix equation can be significantly reduced. For the fundamental modes, both the convergence order and the accuracy of the presented method are found to be significantly higher than those of comparable methods when applied to some numerical examples     

Radiowave propagation in a coal seam with inhomogeneous rock walls

An idealized slab model of a horizontal coal seam is adopted. The structure is laterally uniform, but the media within and outside the slab are allowed to be inhomogeneous in the vertical direction. A general mode equation is obtained, and simplifications are made to facilitate computation of the propagation constant of the dominant mode. Using an exponential variation of the rock conductivity, it is shown that the frequency dependence of the attenuation rate is strongest for a conductivity increasing with distance into the rock media     

An E-J Collocated 3-D FDTD Model of Electromagnetic Wave Propagation in Magnetized Cold Plasma

A new three-dimensional finite-difference time-domain (FDTD) numerical model is proposed herein to simulate electromagnetic wave propagation in an anisotropic magnetized cold plasma medium. Plasma effects contributed by electrons, positive, and negative ions are considered in this model. The current density vectors are collocated at the positions of the electric field vectors, and the complete FDTD algorithm consists of three regular updating equations for the magnetic field intensity components, as well as 12 tightly coupled differential equations for updating the electric field components and current densities. This model has the capability to simulate wave behavior in magnetized cold plasma for an applied magnetic field with arbitrary direction and magnitude. We validate the FDTD algorithm by calculating Faraday rotation of a linearly polarized plane wave. Additional numerical examples of electromagnetic wave propagation in plasma are also provided, all of which demonstrate very good agreement with plasma theory.      

Combined doping and geometry effects on transferred-electron bulk instabilities

The behavior of transferred-electron bulk negative differential conductivity devices with nonuniform geometries and various doping profiles is analyzed. Computer solutions were obtained for appropriate transport equations generalized by a scheme to simulate arbitrary areal variation. The solutions show that the effects of doping and geometrical nonuniformities on domain dynamics are similar. The product of doping and transverse area plays an important role in determining the space-charge properties. An important practical implication of the above result is demonstrated by a scheme for device design using combinations of geometrical and doping nonuniformities to achieve a desired control characteristic. Various equivalent device configurations yielding a linear frequency-voltage characteristic over a wide frequency range are proposed.     

Electromagnetic scattering from anisotropic materials, part II: Computer code and numerical results in two dimensions

The two-dimensional problem of oblique scattering by penetrable cylinders of arbitrary cross section made of materials which are linear, lossy, anisotropic and possibly inhomogeneous is considered. The materials are characterized by arbitrary tensor susceptibilitiesbar{x}_{ec}andbar{x}_{m}. The frequency-domain volume integrodifferential equations satisfied by the electric and magnetic fields and obtained in a previous paper (Part 1) are analyzed numerically. Optimal ordering of the unknowns and transverse electric-transverse magnetic (TE-TM) decomposition in the matrix formulation of the problem are discussed. The cross section of the scatterer is broken down into a triangular mesh. The field components at the vertices of the triangles are the unknowns; within each triangle, each field component is a linear combination of its values at the vertices. Computed field distributions inside the scatterer are found to be in excellent agreement with results obtained by other methods.     

A set of integral equations for electromagnetic wave radiation from an arbitrary source in a linear, lossy, inhomogeneous, cold magnetoionic medium

By decomposing the permittivity tensor into its isotropic, longitudinal, and transverse parts (with respect to the static magnetic field), a set of simultaneous integral equations are derived for the electric field components in a linear, lossy, inhomogeneous, cold magneto-plasma. The developed integral equations are useful to obtain an approximate solution for electromagnetic radiation as well as scattering problems in such a medium.     

Reverse transient characteristics of a P-N junction diode due to minority carrier storage

Analysis of the transient switching characteristics of a p-n junction diode is considered a boundary value problem; solution of this problem yields mathematical equations applicable to the design of high-speed computer components. This analytical technique is used to establish the transient current of a semiconductor diode when an external biasing potential is rapidly switched from the forward to the reverse direction. Using a one-dimensional model of finite geometry, minority-carrier storage is assumed within a region of arbitrary lifetime, bounded on one side by the junction and on the other side by an ohmic contact of arbitrary recombination velocity. Further, this region of carrier storage is assumed to contain a drift field of constant magnitude as would result from an exponential type of conductivity grading. Mathematical equations are presented which characterize this transient situation from its initiation until the junction current has decayed to some arbitrary magnitude. Applications of this analysis are illustrated in graphical form throughout a range of parameters characterizing practical semiconductor devices.     

Propagation and coupling characteristics of microstrip lines withlaminated ground plane

In this paper, we analyze the effect of laminated ground plane on the propagation and coupling characteristics of microstrip lines. Each lamina is modeled as an anisotropic layer, and transition matrix is used to relate the tangential field components in different laminae. An integral equation is formulated in the spectral domain, and the Galerkin's method is applied to solve the integral equation for the phase and the attenuation constants of several microstrip line structures. The effects of substrate dielectric are also studied. The attenuation constant variation thus obtained will be useful in circuit board design and in studying signal transmission in lamina environment     

Reflection of electromagnetic wave from a time-varying medium

For the purpose of radiowave propagation in the ionosphere, in a plasma and in other media, the reflection and transmission of an electromagnetic wave from a suddenly changed conductivity, when a plane wave is normally incident upon an interface separating two conducting media, are studied. The field expressions are exactly obtained through the use of the Laplace transform. The discussion is primarily on the time behaviour of the reflected wave.     

The wave propagation and mode coupling in warm ionosphere

The wave propagation in warm ionosphere is studied in both homogeneous and inhomogeneous ionosphere. When the temperature of electrons are taken into account, the plasma wave is a propagating wave. The dispersion relation of waves in warm ionosphere has been derived. It is an algebric equation which is analogue to the Appleton-Hartree equation, but in higher order. In a stratified warm ionosphere, the equation forq (Booker’sq) is an algebric equation. Both of these equations are used in study of the wave propagation in the ionosphere by means of ray tracing method. The wave mode linking in homogeneous ionosphere and mode coupling in stratified ionosphere are studied. The mode coupling between plasma wave and electromagnetic wave is discussed through the discussion of singularity of the wave equation. The wave fiold near the wave transformation region can be found out by solving the wave equation near the singularity. The justification of study mode conversion by ray tracing is explained. The results could be useful in the study of wavo absorption process and radio heating experiments in the ionospheres.