Plane wave pulse propagation through random media

The theory of plane wave pulse propagation through a random medium, under the forward-scattering assumption is presented. Since pulse propagation characteristics are determined by two-frequency mutual coherence functionGamma, a set of normalized curves is given forGammafor different propagation parameters (operating frequency, propagation distance, turbulence strength or density of scatterers, etc.). From the curves one can obtain the coherence bandwidth of a wave for a variety of situations. A received pulse form due to an input delta function is given in a normalized form which is applicable to the whole range of strong fluctuation. The results are applied to optical pulse propagation in dense clouds. It is shown that the high data rate optical pulse communication through clouds may be limited due to a narrow coherence bandwidth of the order of megahertz. A good agreement between the theoretical prediction and the available experimental data has been demonstrated for both the received pulse shapes and the pulse durations of an optical pulse in clouds.     

Phase-space asymptotic analysis of wave propagation in homogeneous dispersive and dissipative media

Arising naturally in the study of one-dimensional pulse propagation in homogeneous dispersive and/or dissipative media are certain classes of oscillatory and/or diffusion integrals which encompass the canonical diffraction catastrophe integrals due originally to Thorn and Arnold. This is especially evident within the framework of a phase-space asymptotic analysis. Depending on the order of approximation of the exact solution beyond the Liouville or "first-order quasiparticle" limit, one recognizes caustic-like structures smoothed over by hyperdiffusion. Asymptotic series for these structures, which essentially define new basic functions, have been derived, but will not be presented here. Only the salient features of these structures will be reviewed briefly, and they will be illustrated by means of several simple canonical problems. Also, their applicability to other physical areas (e.g., wave propagation in deterministically and/or randomly varying channels, diffraction, etc.) will be pointed out.     

多层双各向同性媒质中电磁波的传输特性

用不对称传输线模型分析了平面电磁波垂直入射于多层双各向同性媒质的反射和透射问题，导出了形式上较简单的计算多层双各向同性媒质界面反射和透射系数公式。为了便于和已有的文献结果相比较，给出计算实例，结果表明，用此公式得出的结果和文献结果一致，为计算多层双各向同性媒质的反射和透射带来方便；同时，对双各向同性媒质，非互易参数和手征参数的改变对反射和透射系数都有较大的影响。     

在时域内计算色散媒质中光脉冲的传输

得到了时域内色散媒质中光脉冲传输的计算公式，并提出了时域内色散媒质中显式的光束传播法。计算了短脉冲在具有二阶色散效应的定向耦合器内的传输、计算结果同参考文献中的一致，但本文的计算方法简单、方便、实用。     

The energy characteristics of wave propagation through interfaces of media with complex parameters

With the use of the 1D wave equation as an example, the wave incidence on one interface and on two interfaces of media with arbitrary complex parameters is analyzed. It is noted that, when the energy reflection, transmission, and absorption coefficients are calculated by means of traditional techniques, their sum exceeds unity if the wave number in the first medium is complex. The complex character of the energy balance on the media interfaces is revealed. Definitions are introduced and the properties of complex reflection, transmission, localization, reactivity, and absorption are considered.     

Radio wave propagation through woods

In 1997 and 1998, measurements were made of radio wave attenuation through a cottonwood plantation at the University of Illinois at Urbana-Champaign, on a number of frequencies between 27 and 411 MHz. Based on these measurements, an empirical formula that describes radio wave attenuation was developed     

Millimeter wave propagation through a chiral medium model of human trunk

That millimeter wave propagation through a chiral medium of human trunk has been discussed by obtaining the electromagnetic filed, absorbent power, specific absorption rate, temperature field and their distribution in a human trunk model with plane strati calate homogeneous tissues under a normal incidence plane wave. The chiral medium is described electromagnetically by the constitutive relationsD=εE+εβB andB=μH+μβE. The constantsε, μ andβ ate real and have values that are fixed by the size, the shape, and the spatial distribution of the elements that collectively compose the medium. Also, the principle of thermal therapeutics for millimeter wave is discussed preliminaryly.     

Electromagnetic wave propagation in almost periodic media

The problem of electromagnetic wave propagation in almost periodic media is investigated, and a solution is obtained directly from Maxwell's equations. The evaluation of this solution involves a generalization to almost periodic media of the Brillouin diagram of periodic media. The Brillouin diagram is used to place in evidence similarities and differences of wave propagation in periodic and almost periodic media. It is shown that although the periodic and almost periodic theories agree in many cases of interest, there exist cases in which distinct differences appear. In particular, these distinctions become apparent for media with closely spaced tones.     

Laser wave propagation through the atmosphere

Communications with coherent light through the atmosphere bring out new system limitations besides the ones imposed by attenuation and scattering normally associated with incoherent waves. This is so because the laser directivity and coherence responsible for increased channel capacity are easily destroyed or at least degraded by the presence of random thermal turbulences. Simple expressions describing the effects of atmospheric turbulence on laser beam propagation are obtained. Corresponding calculations yield the order of magnitude of such random phenomena as beam scanning, phase variation, beam cross-section change, amplitude and frequency modulation. In particular, the polarization fluctuation is predicted quantitatively in terms of the atmosphere mean square refractive index and its turbulence correlation length.     

Nonlinear wave propagation phenomena in left-handed transmission-line media

This paper introduces nonlinear transmission lines based on left-handed (LH) media and simulates harmonic generation and parametric generation in a material that, in two dimensions, could also focus microwaves. This paper discusses physical phenomena that lead to and affect self-supporting harmonic generation and parametric generation in LH nonlinear transmission-line media and outline advantages of these media for developing new types of compact and efficient frequency multipliers and "active lens" devices.     

Electromagnetic wave propagation in spherically stratified isotropic media

The general electromagnetic field can be resolved into two components represented by electric and magnetic Hertz vectors, both vectors being parallel to the radial direction. Very few exact solutions for the radial variation of fields of the electric type have been found hitherto. Generalised refractive-index profiles permitting exact transcendental solutions are presented.     

Optical wave propagation in form-birefringent media and waveguides

Characteristics of a periodic structure waveguide with a finite width are studied theoretically and numerically. Propagation constants of two orthogonally polarized fundamental modes converge to values which are different from each other, when the total periodic structure width exceeds twice the wavelength. The asymptotic characteristic equation is derived analytically. The normalized frequencyVof the high-index layers must be less than unity in order that the optical energy does not localize in the high-index layers. Both the magnitude of the birefringence and the effective refractive index in the form-birefringent media can be controlled by varying the thickness of the high-index layer and the thickness ratio of the high- and low-index materials.     

Electromagnetic wave propagation in cylindrically stratified isotropic media

The general electromagnetic field, when independent of axial distance, may be expressed as the sum of E parallel and H parallel partial fields. Exact solutions of the wave equation for the radial variation of the H parallel field are not numerous. Generalised refractive-index profiles are presented which permit transcendental solutions to be made.     

A general method for FDTD modeling of wave propagation in arbitraryfrequency-dispersive media

A general formulation is presented for finite-difference time-domain (FDTD) modeling of wave propagation in arbitrary frequency-dispersive media. Two algorithmic approaches are outlined for incorporating dispersion into the FDTD time-stepping equations. The first employs a frequency-dependent complex permittivity (denoted Form-1), and the second employs a frequency-dependent complex conductivity (denoted Form-2). A Pade representation is used in Z-transform space to represent the frequency-dependent permittivity (Form-1) or conductivity (Form-2). This is a generalization over several previous methods employing either Debye, Lorentz, or Drude models. The coefficients of the Pade model may be obtained through an optimization process, leading directly to a finite-difference representation of the dispersion relation, without introducing discretization error. Stability criteria for the dispersive FDTD algorithms are given. We show that several previously developed dispersive FDTD algorithms can be cast as special cases of our more general framework. Simulation results are presented for a one-dimensional (1-D) air/muscle example considered previously in the literature and a three-dimensional (3-D) radiation problem in dispersive, lossy soil using measured soil data     

Line-of-sight wave propagation through the turbulent atmosphere

A review of the recent developments in the field of random fluctuations of an electromagnetic wave propagated over a line-of-sight path is presented. The major interest is in the optical to millimeter wavelength range where fluctuations in amplitude, phase, and angle-of-arrival are important system considerations. It is assumed that the fluctuations are the result of variations in the refractive index caused by turbulence in the atmosphere. The review concentrates on the major approximations involved in the theoretical developments, and in particular, attempts to put in perspective the arguments over Rytov's method. The paper includes a number of previously untranslated results from the Russian literature, and some previously unpublished results of the author's. A brief assessment of new theoretical approaches and a discussion of some extremely important experimental work are given.     

Radio wave propagation through rain forests of India

A radio wave attenuation measurement survey program was undertaken for the tropical rain forests of India. Measurements were taken at frequencies from 50 to 800 MHz, for antenna heights from 1.5 to 16.5 m above the ground with both horizontally and vertically polarized emissions, and at various separation distances varying from 40 to 4000 m. There were 96 combinations of system parameters for each selected distance between transmitting and receiving locations. In addition to the copolar measurements, cross-polar measurements were carried out to study cross-polar phenomenon in the presence of vegetation. The results of the studies are discussed, covering scatter of the data, lack of homogeneity of the foliage, variation in foliage proximity of the antenna, scattering of radio waves, effect of antenna beamwidth, effect of changes in wind velocity, frequency and polarization dependence of the basic transmission loss, seasonal variation of the loss, effect of climate and type of vegetation, foliage loss, specific attenuation, and effect of increased antenna height in the forest. An empirical model derived from these measurements is proposed     

电波传播模型的本地化研究

根据目前常用的电波传播模型，研究并提出了对本地化传播模型进行验证评估的方法，使本地化传播模型能更加适合无线电管理工作的需要。