Radiation of elementary sources in a chiral medium

The classical problem of radiation of elementary sources is generalized to the case of a chiral medium. The electromagnetic fields of right- and left-hand polarized waves are expressed in terms of vector potentials, and formulas for the components of the fields radiated by a vertical electric dipole in a chiral medium are obtained.     

Microwave attenuation and cross polarization in dust storms

Some of the electrical and mechanical properties of dust are discussed. An expression for optical visibility during storms is given in terms of the relative volume occupied by dust. Expressions for attenuation and phase shift constants for a medium with precipitating dust particles are derived in terms of visibility and wavelength for both vertical and horizontal polarizations. Expressions for the attenuation and cross polarization of circularly polarized waves are also derived. Computations show that linearly polarized waves suffer but little effect. Circularly polarized waves on the other hand are significantly cross polarized.     

Plane waves in a magnetoionic medium

With a view to elucidating the difficulties inherent in the treatment of wave propagation in a magnetoionic medium in terms of homogeneous plane waves, the theory of homogeneous plane waves in such a medium is reviewed with particular emphasis on the properties of the time-averaged Poynting vector.     

Radio wave propagation along mixed paths through a four-layeredmodel of rain forest: an analytic approach

This paper presents a novel full-wave analysis of the radio waves that are excited from a dipole antenna located in the trunk layer and propagate inside a four-layered forest medium. The dyadic Green's functions for the four-layered geometry are applied first to derive the integral expression of the electric fields. The closed form of the electric fields is then obtained by using the quasi-static approximation, saddle-point technique, and branch-cut integrations in the complex plane and, hence, expressed in terms of direct waves, multiple reflected waves, and lateral waves. Two kinds of images, i.e., the quasi-dynamic and complex images, are considered in the integration in the complex plane. Among those waves excited by a dipole antenna in the four-layered medium, it is shown theoretically and numerically that the lateral wave along the upper-side air-canopy interface plays a role of dominant modes. The propagation mechanism of other lateral waves due to the air-canopy, canopy-trunk, and trunk-ground interfaces is also discussed and analyzed so as to gain an insight into the wave characteristics. Transmission losses of the lateral waves are calculated numerically     

Scattering characteristics of two-dimensionally periodic impedancesurface

We present an exact formulation for the three-dimensional (3-D) boundary-value problem of plane wave scattering by a two-dimensionally (2-D) periodic impedance surface in a uniform medium. The scattering characteristics of such a structure are rigorously analyzed in terms of the complete set of both TE- and TM-polarized plane waves in the uniform medium. Extensive numerical results are given to illustrate physical phenomena associated with the structure     

The effect of diffusion on space-charge waves in a very thin semiconductor layer†

Convective and absolute instabilities associated with space-charge waves are described in a very thin layer of a semiconductor with negative differential mobility and embedded in an infinite dielectric region. Thermal diffusion of carriers plays an important role in the evaluation of the range of existence of convectively unstable space-charge waves,

Within the range of our approximations the forward growing space-charge waves are shown to exhibit a maximum growth rate for a frequency which is determined in terms of diffusion and parameters of the semiconductor find the surrounding dielectric medium.     

波导参数和传播常数对光折变表面波的影响

基于质点振荡的模型和数值模拟的方法,研究了波导参数和传播常数对光折变晶体与线性电介质界面光折变表面波类型和局域表面波模的影响。当波导参数大于传播常数时,在光折变晶体与线性电介质界面可以产生非局域表面波。当波导参数小于传播常数时,在光折变晶体与线性电介质界面可以产生振荡表面波和局域表面波。在局域表面波形成的系统内,正波导参数的光波能量比负波导参数的光波能量在光折变晶体内聚集得多。在给定一个局域表面波形成的物理系统,传播常数越大,表面波在线性电介质和光折变晶体中衰减就越快,对应表面波模的波峰离界面就越近。     

Electrodynamics of anisotropic media with space and time dispersion

The average stress tensor, power-flow density, momentum density, and energy density for electromagnetic waves in a linear stationary anisotropic medium with space and time dispersion are clarified with the help of the second-order nonlinear terms in the equation of motion for polarization. The wave fields are connected with the medium-mass motion through the nonlinear terms; the net force between the fields and the medium mass plays a crucial role in interpreting the stress tensor and the wave momentum. Asymmetry in the space-space part of the energy-momentum tensor, which is quadratic in the field fluctuations, is ascribed to anisotropic restoring forces of the polarizations; asymmetry in the space-time part is attributed to nonvanishing average forces between the fields and the medium-mass motion.     

A spectral-domain method for multiple scattering in continuousrandomly irregular media

A spectral-domain method for computing the first and second-order moments of a scalar wavefield propagating in a continuous randomly irregular medium is described. The scattering is characterized by the moments of incremental forward and backward scattering functions. Approximate forms for these moments are given in terms of the spectral density function of the relative permittivity fluctuations. Solutions are developed for incident plane and spherical waves. Well-known results that are usually derived from the parabolic wave equation using the Markov approximation are easily recovered from the general solutions. The results show that backscatter enhancements depend on the correlation between the forward and backward scattered waves. Computations are performed to illustrate the effects of backscatter on VHF transionospheric radiowaves     

Transverse Magnetic Wave Propagation in Sinusoidally Stratified Dielectric Media

The problem of the propagation of TM waves in a sinusoidally stratified dielectric medium is considered. The propagation characteristics are determined from the stability diagram of the resultant Hill's equation. Numerical results show that the stability diagrams for Hill's equation and those for Mathieu's equation are quite different. Consequently, the dispersion properties of TM waves and TE waves in this stratified medium are also different. Detailed dispersion characteristics of TM waves in an infinite stratified medium and in waveguides filled longitudinally with this stratified material are obtained.     

Electromagnetic fields of buried sources in stratified anisotropic media

A general formulation to the problem of the radiation of arbitrary distribution of buried sources within a horizontally stratified anisotropic medium is presented. The fields are obtained in terms of appropriately defined electric and magnetic types of dyadic Green's functions which are dual to each other. The formulation is considerably simplified by the resolution of these dyadic Green's functions into transverse electric (TE) and transverse magnetic (TM) waves and by the existing duality between them. A systematic procedure for deriving the fields in an arbitrary layer in terms of the primary source excitation and appropriately defined wave amplitude matrices is described.     

Wave Propagation in Sinusoidally Stratified Dielectric Media

The dispersion properties and the fields of electromagnetic waves are investigated for propagation in a stratified infinite medium. The stratification is characterized by a dielectric constant which, along one coordinate, is modulated sinusoidally about an average value. A systematic and comprehensive study is presented for the case of H modes for which the pertinent wave equation is in the form of a Mathieu differential equation. The modes and dispersion characteristics are analyzed in terms of a "stability" chart, which is customary in the study of the Mathieu equation. Results are obtained for an unbounded medium and for a waveguide filled with the modulated medium. Also, the reflection occurring at an interface between free space and a semi-infinite medium of this type is examined. In addition to these rigorous results for arbitrary values of modulation, simple analytical expressions are given for all of these cases where the modulation in the dielectric is small. It is shown that the fields are then expressible in terms of the fundamental and the two nearest space harmonics. The fields within a unit cell in the stratified medium are calculated for both small and large modulation and for frequencies up through the second pass band. It is of interest that the variation of the fields is not, in general, simply related to the variation of the dielectric constant within a cell.     

Electromagnetic field of a horizontal electric dipole buried in a medium covering one-dimensionally anisotropic medium

The electromagnetic fields of a horizontal electric dipole buried in a medium covering one-dimensionally anisotropic medium are studied. There are three media, one-dimensionally anisotropic medium covered with a dielectric under the air. The electromagnetic field components are complex because of the multiple reflections from the up and down boundaries. The electromagnetic field components between air and one-dimensionally anisotropic medium are given, the trapped surface waves and lateral waves along the dielectric-anisotropic medium boundary are computed. The results have some practical applications in the communication in sea or lake above one-dimensionally anisotropic earth or sediments.     

On Guided Waves in Moving Anisotropic Media

Based upon the Maxwell-Minkowski theory, the equations governing the propagation of electromagnetic waves in a cylindrical waveguide of an arbitrary cross section filled with a moving anisotropic medium are derived. The governing equations are reducible to a pair of coupled wave equations in the axial components of the electric and magnetic fields, which in turn can be solved through the solution of a single second order scalar homogeneous Hehnholtz equation. For a general anisotropic medium no pure TM or TE modes can exist in the waveguide. However, if the moving medium is uniaxially anisotropic, TM and TE modes are possible. It is interesting to note that the cutoff frequencies are always lowered by a factor which depends upon the velocity of the medium and is independent of the guide geometry. The formulas for the characteristic wave impedance and power flow in a waveguide for a moving uniaxial medium, if expressed in terms of the new cutoff frequency, have the same forms as those for a moving isotropic medium. The propagation characteristics of waveguides of rectangular and circular cross sections filled with a moving uniaxial gyroelectric medium are discussed.     

A MIMO Propagation Channel Model in a Random Medium

Multiple input-multiple output systems have received considerable attention because of their potential to achieve high channel capacity. This paper presents a study of the effects of a random scattering medium on channel capacity. Formulations are given including stochastic Green's functions and mutual coherence functions. Transmitter and receiver characteristics are included and analytical formulation for eigenvalues and channel capacities are given in terms of the medium scattering characteristics, optical depth, frequency, number of transmitter and receiver elements, transmitting power, and noise spectral power. As an example, we show 500 m link at 60 GHz through rain. The eigenvalues and the channel capacity are calculated in terms of SNR and the rain rate representing the optical depth. It is shown that as the rain rate increases, the correlation of waves at antennas decreases and the capacity increases. However, at high rain rate, the capacity tends to decrease due to the absorption and scattering.      

Wave diffraction by a rough boundary of an arbitrary plane-layeredmedium

The problem of electromagnetic (EM) wave scattering by a slightly rough boundary of an arbitrary layered medium is solved by a small perturbation method. The bistatic amplitude of scattering as well as scattering cross sections for a statistically rough surface are calculated for linear and circular polarized waves. Along with the scattering into the upgoing waves in the homogeneous medium, the scattering cross sections in the downgoing waves into a layered medium are obtained. Analytical results are applied to the modeling of natural layered media (ice and sand layers) remote sensing problems employing global positioning system (GPS) technics     

Comparison Identities for Wave Propagation in a Time-Varying Plasma Medium

An unbounded space-invariant but time-varying medium conserves the wave number k of the wave but alters the frequency of the wave. Thus a switched medium acts like a frequency transformer, the frequencies of the newly created waves (output waves) are easily computed. The amplitudes of the output waves depend on the rise time Tr of the profiles of the parameters of the switched medium.     

有耗表面反射波的极化特性研究

文中对有耗媒质界面反射波的极化特性进行了较详细的分析与计算，指出此时反射波的极化与入射波的极化是不同的，给出这种变极化特性随媒质参数及入射角的各种关系曲线，这些曲线对分析雷达目标的散射极化特性是很有意义的。     

Transmission des signaux perpendiculairement à un milieu stratifié périodique: étude fréquentielle

The authors consider the propagation of electromagnetic and elastic waves in a medium consisting of alternating layers of two different homogeneous isotropic and nonabsorbing substances. The waves are assumed harmonic and plane and their propagation is perpendicular to the layers. They show the existence of frequency ranges for which the wave propagation is possible and other ones where the waves are vanishing. The dispersion property of this medium is analysed; for low frequencies, the propagation velocity is shown smaller than the expected mean velocity. At last, a detailed work gives the transfer functions for transmission and reflection of the double linear filter constituted of the layered medium set between two homogeneous isotropic media. They pay attention to the isochronous layered medium.