Propagation modeling over terrain using the parabolic wave equation

We address the numerical solution of the parabolic wave equation over terrain using the Fourier/split-step approach. The method, referred to as a shift map, generalizes that of Beilis and Tappert (1979) who introduced a coordinate transformation technique to flatten the boundary. This technique is extended to a wide-angle form, allowing larger propagation angles with respect to the horizon. A new impedance boundary condition is derived for electromagnetic waves incident on a finitely conducting surface that enables solution of the parabolic wave (PWE) using the previously developed mixed Fourier transform. It is also shown by example that in many cases of interest, the boundary may be approximated by discrete piecewise linear segments without affecting the field solution. A more accurate shift map solution of the PWE for a piecewise linear boundary is, therefore, developed for modeling propagation over digitally sampled terrain data. The shift-map solution is applied to various surface types, including ramps, wedges, curved obstacles, and actual terrain. Where possible, comparisons are made between the numerical solution and an exact analytical form. The examples demonstrate that the shift map performs well for surface slopes as large as 10-15° and discontinuous slope changes on the order of 15-20°. To accommodate a larger range of slopes, it is suggested that the most viable solution for general terrain modeling is a hybrid of the shift map with the well-known terrain masking (knife-edge diffraction) approximation     

采用随机射线方法预测城市环境的无线电波传播

根据无线电波在城市环境传播的随机特性，使用随机射线方法研究无线电波的传播规律，得到二维传播环境中平均接收功率的计算模型和路径损耗预测模型。讨论了该模型中三个参数的选择方法，并通过实验数据验证了路径损耗模型。     

森林中电波传播的抛物方程法

抛物方程法能处理非均匀介质环境中的电波传播问题,并可用FFT步进算法快速求解,在电波传播中得到了广泛运用.该文用抛物方程法求解了森林中的电波传播问题,并将计算结果与Tamir侧面波模型的结果进行比较,二者吻合很好.最后用抛物方程法分析了森林中电波传播的特性.     

抛物方程法在森林环境电波传播特性预测中的应用

为提高大区域森林环境电波传播特性预测的准确性,研究抛物方程（PE）法在森林环境电波传播特性预测中的应用,提出了基于抛物方程的森林模型。该模型采用PE法实现准确快速求解,考虑森林在垂直方向上的非均匀性,引入森林分层模型,将森林分为树冠、树干两个均匀有耗介质层,并根据森林区域的特性参数确定各有耗介质层的等效介电常数,相比于传统将森林等效为一个给定介电常数的均匀有耗介质层,能够更准确地描述森林对电波传播的影响。将其应用于三种常见绿叶林的电波传播特性预测中,仿真结果表明,该模型能够反映不同区域、不同植被种类的森林对电波传播的影响差异,有效预测大区域森林环境电波传播特性。     

太赫兹波大气衰减的抛物方程模型

抛物方程是一种模拟电波传播特性的高效模型,但目前抛物方程模型在模拟电波传播时,主要考虑大气的折射效应而忽略了其吸收作用,然而太赫兹波的大气衰减较为严重。通过引入大气分子吸收的复折射率,实现了应用抛物方程模型计算太赫兹波的大气衰减。该模型考虑了大气压强、温度和水汽密度等气象参数随高度变化对大气衰减的影响,且能够针对不同地区和季节的气象条件对大气衰减进行计算,与真实环境更加符合。最后利用该模型仿真分析了0.14 THz波的传播特性,给出了传播损耗随距离和高度的变化,并与忽略大气衰减的结果进行了对比,结果表明抛物方程模型能同时体现太赫兹的大气吸收效应和多径传播效应。     

3D parabolic equation model of EM wave propagation in tunnels

To describe radio wave propagation in curved oversized lossy waveguides of arbitrary cross-section, a vectorial parabolic equation (PE) has been derived and applied to modelling UHF/VHF radio communication in tunnels. Numerical results are presented for curved tunnels with rectangular cross-section.     

非线性光孤子传输方程的研究

本文在从描述光孤子在单模光纤中的非线性传输方程（ＮＬＳ，即非线性薛定谔方程）出发，利用Ｍａｘｗｅｌｌ方程和慢变包络近似性，导出ｐｓ量级光孤子高阶修正的非线性薛定谔方程（ＨＭＮＬＳ）可进一步研究色散，损耗等高价效应对孤子传输造成的影响。     

电波传播抛物方程模型在航空通信中的应用

针对航空通信中电波传播损耗预测需要满足精确性、实时性及复杂环境适应性的要求,在分析电波传播损耗对航空通信系统作用范围的影响基础上,采用抛物方程模型研究了航空通信中电波在空间区域的传播特性。该模型利用分步傅里叶算法实现快速求解,采用边界平移法处理复杂地形边界,并通过非均匀网格技术提高空间任意一点的场强计算精度,从而改善了复杂环境下电波传播损耗预测的精确性和实时性。将该模型应用于真实地形环境下的航空通信仿真算例中,仿真结果表明：该模型能有效预测复杂环境下电波的传播损耗,评估在正常通信条件下飞行器的飞行范围、最大飞行距离以及最低飞行高度等性能。     

Propagation characteristics of magnetoelastic surface wave

The propagation characteristics of a magnetoelastic surface wave in ferrites are described using numerical calculations pertinent to gallium-y.i.g.     

矩形波导中电磁波传输特性研究

本文基于功率流分别讨论了在矩形波导横截面积一定,TEm0和TMmn模式单独传输时,宽长尺寸比的最优解问题,得到了TEm0波传播时,其宽长比应趋近于0;TMmn波传播时,m＜n,仅TM12的宽长比为1;m≥n,宽长比为n/m.所得结果对矩形波导尺寸的选择和设计有潜在的应用价值.     

Optimal second-order small-signal model for long- and short-channelthree-terminal MOSFET/MODFET wave equation

An optimal second-order small-signal model is developed for the long-channel three-terminal MOSFET/MODFET wave equation. The resulting Y parameters admit the correct fourth-order frequency power series expansion and exhibit a graceful degradation at high frequencies compared to a previously reported second-order model. This model can be integrated in the velocity-saturated MOSFET/MODFET equivalent circuit and is demonstrated to greatly improve the frequency range of validity of this short-channel model. The excellent results obtained demonstrate the validity of both the equivalent-circuit synthesis procedure and the correctness of the equivalent circuit proposed     

Riccati form of the wave equation

The use of the Riccati form of the wave equation is discussed with reference to the reflection coefficients of atmospheric ayers. The basic principles are established for vertical incidence and can be readily extended to more general cases and analogous problems in other fields, including transmission-line and waveguide theory.     

A simplified mode equation for electromagnetic wave propagation in an asymmetrical coal seam

Attention is drawn to an earlier publication of the eigenvalue/eigenvector solution given in Schmidt's 1979 paper.     

Thermal networks from heat wave equation

In this paper passive and reciprocal thermal networks are introduced which model the finite velocity of heat propagation. In particular it is shown that the theory of distributed and discretized thermal networks deduced from the heat diffusion equation and the multi-point moment matching technique for deriving approximated lumped thermal networks of small state-space dimensions can be extended to thermal networks ruled by the hyperbolic heat equation.     

Improved small-signal equivalent circuit model and large-signalstate equations for the MOSFET/MODFET wave equation

A simple non-quasi-static small-signal equivalent circuit model is derived for the ideal MOSFET wave equation under the gradual channel approximation. This equivalent circuit represents each Y-parameter by its DC small-signal value shunted by a (trans) capacitor in series with a charging (trans) resistor. A large-signal model for the intrinsic MOSFET is derived by first implementing this RC topology in the time domain. Modified state equations are then introduced to enforce charge conservation. Transient simulations with this approximate large-signal model yield results that are compared with reported exact numerical analysis for the long channel MOSFET for a wide range of bias conditions. This unified small- and large-signal model applies to both the three- and four-terminal intrinsic MOSFET in the region of the channel where the gradual channel approximation is applicable. A non-quasi-static small-signal equivalent circuit for the velocity-saturated MOSFET wave equation is also reported     

核电磁脉冲地波传播规律

介绍了核电磁脉冲地波传播的理论计算方法,研究了当大地电导率大于0.005 S/m时,地波传播函数随频率及传播距离的变化规律,并计算了不同传播距离核爆电磁脉冲的地波电场。结果表明,频率越高,传播距离越远,传播函数的幅值越小;核爆电磁脉冲的传播距离为500 km时,电场的幅度会有大于一个量级的衰减。     

AN APPROXIMATE SOLUTION OF NONLINEAR WAVE EQUATION

A uniformly valid approximate solution of a kind of nonlinear wave equations is studied. The research results indicate that the solution of this kind of equations can be represented by Airy function approximately. The usually used W. K. B. approximation is the first order approximation of the present result in the region far away from the turning point of refractivity. At the turning point of refractivity, the present result is still valid.     

Three-dimensional wave equation computations on vector computers

There are now several laboratories worldwide which routinely perform three-dimensional (3D) physical modeling of acoustic phenomena of interest to seismologists. Corresponding computerized mathematical models have been limited to two dimensions on conventional computers due to the immense computational requirements of accurate full-size problems. The introduction of high-performance vector processors in the 100 + MFLOP range has at last made 3D computerized models a practical reality. Several major oil companies and large seismic contractors have installed such processors and are contributing to research and development in this area as an improved tool in the search for fossil energy sources. We now have such models and we have some limited experience in using them, however, much more work is required before these mathematical models can routinely supplant the physical ones. Here we describe one such model which was developed for the Cyber 205. A two-dimensional (2D) model for the VAX-11 with FP5-100 Array Processors was modified to three dimensions and vectorized suitably for the larger system. We state the acoustic wave problem in mathematical form and present the algorithm used for its solution. We then review the theoretical justification for selecting this particular algorithm. We also discuss the most important technical aspects of implementing the algorithm in vector form on the Cyber system. We present typical output and finally we give timing results for several model sizes, both 2D and 3D, on the Cyber 205 and 2D on the VAX-11 with FPS-100 Array Processors.     

Boundary control of the one-dimensional wave equation

Through the method of characteristics, literal-form expressions are derived for the one- and two-boundary controls of the one-dimensional wave equation. These formulas offer a basis for solution of a number of optimal control problems.