部分森林覆盖山区电波传播特性预测的快速算法

为提高部分森林覆盖山区电波传播特性预测的时效性,提出了一种基于宽角抛物方程(PE)的快速预测算法。采用PE通过分步傅里叶变换(SSFT)求解;在SSFT步进迭代过程中,根据传播路径上森林的等效介电常数、地形的起伏情况,动态选择PE的水平步长。通过对部分森林覆盖的不规则地形条件下的电波传播特性进行仿真,探讨了该方法的可行性和有效性。结果表明：相比于均匀大步长算法,该方法更准确;而相比于均匀小步长算法,该方法能够保证抛物方程的计算精确度,同时极大地提高计算效率。     

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.     

基于分形的粗糙海面三维抛物方程模型及其应用

风驱海浪随机起伏变化是海面环境的典型特征之一, 而较大的风浪通常会给海面无线通信带来重要的影响.传统的抛物方程(Parabolic Equationmethod, PE)模型在预测粗糙海面的电波传播时, 未能充分考虑海浪的电磁散射以及阴影效应等.针对以上不足, 文中基于三维抛物方程, 引入动力学分形方法, 对传统的抛物方程模型进行了改进研究.相比传统的Miller-Brown近似方法, 改进后的预测模型能更好地反映出海浪几何特征对电磁波传播的影响.最后以舰载雷达的有效探测范围为计算背景, 对粗糙海面的电波传播特性进行了仿真分析, 结果表明了该模型在区域级海面环境电波预测的可行性.     

基于PE模型的电波传播特性预测技术研究

PE模型已经被广泛地应用于电波传播特性预测技术的研究,并成为解决电波传播问题的主要工具。通过对抛物方程推导过程中由于对伪微分算子Q的处理而产生的误差进行分析,表明PE模型在预测小仰角的电波传播时具有很好的计算精度。对基于PE模型的电波传输损耗理论模型进行计算机仿真,得到电波传播损耗的理论计算值,通过与实测数据进行对比,验证了PE模型用于电波传播特性预测的正确性,并且对理论模型的计算结果稍微偏小的原因做了分析。     

抛物方程的动态网格模型及其应用

针对大尺度不规则地形条件下电波传播特性预测的准确性与时效性问题,在非均匀网格技术的基础上,提出了抛物方程的动态网格模型,并通过对刃峰地形条件下的电波传播特性进行仿真,探讨了动态网格模型的可行性和有效性。结果表明:在计算精度相似的情况下,相对于均匀细网格和非均匀网格,动态网格模型缩短了抛物方程的计算时间,具有更高的时效性;相比均匀粗网格具有更高的计算精度。可见,抛物方程的动态网格模型在预测大尺度不规则地形条件下电波传播特性时具有高效性。     

基于圆柱抛物方程的城市环境电波预测模型

提出了一种三维实体重建技术与柱坐标抛物方程结合的城市环境电波传播预测方法。从数字地图 中提取城市建筑物高程矢量数据,建立立体光刻文件的拓扑数据结构,将其转化为抛物方程模型对应的扇形栅格数 据,实现城市建筑群的三维几何模型重构。同时结合聚类算法并利用城市影像信息对地表环境进行分类,对不同类 型的地表媒质赋予不同电磁参数,实现真实城市环境下同时包含建筑物信息和地表媒质参数的一体化电磁建模。 最后,采用分步傅里叶圆柱坐标系抛物方程法,对三维城市环境中电波的传播特性进行仿真分析。数值计算结果表 明,相较于传统经验模型,该方法能够考虑电波的反射、折射和衍射效应,可准确预测真实城市环境下的电波传播规 律,且具有较高计算效率。本模型可为无线网络规划、电磁频谱地图构建等提供指导。     

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。     

基于柱坐标抛物方程的海上雷达覆盖范围研究

为预测雷达波在海面的全向传播特性,提出了基于柱坐标抛物方程(parabolic equation,PE)的电波传播模型,用于海上雷达覆盖范围的研究.从亥姆霍兹方程出发,推导出柱坐标系下的前向PE形式.再利用PE通解中三角函数的正交性,求解各电波传播模式的激励系数,结合分步傅里叶变换实现柱坐标PE的步进迭代算法,以预测电...     

典型场景下电波传播特性建模

为了解决某些典型场景(如海上、山区、丘陵、城区)下无法使用已有基础模型来全面表达电波传播特性的问题,建立了一种在典型场景下,基于确定性抛物方程、适用于多个传输场景的统一电波传播模型。把典型场景等效为损耗介质层来求解边界条件,利用Fourier分步步进法得到相应解,然后得到电波在典型场景下的传播损耗,并进行了理论分析和实验验证。结果表明,在不同传输场景下,将统一电波传播模型与Miller-Brown模型、射线追踪模型进行比较,结果较吻合,验证了其正确性。这一结果对建立一种求解典型场景下电波传播衰落问题的统一电波传播模型是有帮助的。     

基于抛物方程法的部分森林覆盖山区电波传播分析

基于Fourier分步步进法的抛物方程模型求解了山区不规则地形部分森林覆盖环境的电波传播,并分析了森林对电波传播的影响.模型中为了简化边界条件,地形用分段线性函数来近似.然后预测了一个山区部分针叶林覆盖环境的电波传播,得到的结果与实测数据进行对比,二者吻合很好.最后对算法的稳定性与误差进行了分析,本文的模型能处理不规则地形、森林等复杂环境且算法效率高.     

A parallel-plate waveguide model of lossy microstrip lines

An improved semi-analytical model of a lossy microstrip transmission line is proposed. The model is based on the theory of the fundamental transverse magnetic mode of a lossy parallel-plate waveguide whose dielectric medium is assigned the effective permittivity of the respective lossless microstrip line. The complex propagation constant of the fundamental mode is computed by imposing the Leontovitch boundary condition at the upper and lower plates whose impedances take into account the thickness of the conductors and the current crowding effect. The dielectric loss is computed by perturbation formulas. The proposed model features high accuracy and computational efficiency at frequencies up to 100 GHz.     

基于全局透射边界条件的宽角抛物方程电波预测模型

提出了一种新型的基于全局透射边界条件（non-local boundary condition,NLBC）的Greene近似宽角抛物方程（wide-angle parabolic equation,WAPE）电波预测模型,用于求解对流层远距离复杂环境中的电磁波传播特性.采用有限差分法（finite difference method,FDM）求解WAPE得到了三对角线性方程组,可以快速地求解整个空间的电场分布,也可以对不规则的地表环境进行精确建模.本文提出的WAPE模型解决了传统的PE离轴传播角度偏小的问题,将电波的最大传播仰角提升至约50°,同时大大减小了计算区域中上边界吸收层的设置尺寸,从而提高了PE的计算效率.实验证明,当伪微分算子的相位误差不超过0.002时,Tappert、Claerbout和Greene近似形式得到的最大传播角分别为20°、35°和45°.最后,通过与经典的光学双射线模型进行对比,证明本文提出的基于NLBC的Greene近似WAPE模型的可计算传播仰角更大,对上边界处反射电磁波有良好的吸收效果.因此,本文的模型适用于对流层远距离复杂环境中电磁波传播特性的精确预测.     

Clutter return from vegetated areas

An analytical stochastic model to predict relevant statistical scattering features of electromagnetic waves propagating within vegetated environments is presented. The propagation phenomena are described by formulating the scattering associated with random permittivity fluctuations superimposed on a lossy deterministic background slab. The distorted wave Born approximation is employed to determine the backscattered power, and its temporal spectrum.     

Modal Transition and Reduction in a Lossy Dielectric-Coated Waveguide for Gyrotron-Traveling-Wave Tube Amplifier Applications

A metal cylindrical waveguide coated with an inside layer of lossy dielectric which affects the propagation characteristics of a guided electromagnetic mode is investigated for gyrotron-traveling-wave tube (gyro-TWT) amplifier applications. This paper reveals a series of novel phenomena. The dispersion curve of a higher order mode has a turning point during its evolvement from the fast wave region to the slow wave region. An electromagnetic mode in the lossy dielectric-coated waveguide exhibits a transverse partial-standing-wave distribution. The dielectric loss induces modal transition which results in the dispersion curves of a pair of nearby modes crossing each other and interchanging mode structures. Modal reduction caused by strong dielectric loss merges a pair of nearby modes into one. In this one merged mode, the dielectric-coated waveguide is equivalent to a conventional cylindrical waveguide with imperfect conducting wall. This improved understanding of lossy dielectric-coated metal cylindrical waveguide is of value and usefulness for application toward gyro-TWTs capable of high-power and wide bandwidth.     

几种抛物方程形式的相位误差分析

近轴近似是引起抛物方程（parabolic equation, PE）自身固有相位误差的根本原因. 为选取适合目标场景中的最优PE形式,基于色散分析方法,推导了现有六种PE形式的色散关系,评估出折射率和传播仰角对各PE形式相位误差的影响,进而分析出对流层电波传播、水下声波传播、森林电波传播三种典型场景中各PE形式的精度. 研究发现,对于对流层电波传播场景,Lin-Duda型PE精度最高,Feit-Fleck型PE和Tappert型PE的精度几乎完全相同,紧随其后的是Padé型PE;对于水下声波传播场景,Padé型PE和Lin-Duda型PE最为准确;对于森林电波传播场景,Lin-Duda型PE的精度依旧是最高的. 进一步地,通过固定相位误差限给出了不同PE形式的适用仰角范围.     

Physically consistent transmission line models for high-speed interconnects in lossy dielectrics

The development of a physically consistent multiconductor transmission line model for high-speed interconnects in lossy, dispersive dielectrics is presented. Based on this model, a methodology is presented which constructs SPICE-compatible equivalent circuits that take into account dielectric loss and dispersion. Simulations using wideband measurement data of alumina demonstrate the effect of the Debye based permittivity model.     

Exact formulas for wave impedance and propagation constants ofhomogeneous, lossy dielectric and/or magnetic materials

Calculations of propagation constants for lossy materials are performed under the approximations of low loss (or high conductivity). To improve the understanding and better predict the analysis of such materials, exact formulation for wave impedance and propagation constants of homogeneous, lossy, dielectric/magnetic materials are proposed. Formulation is based on dielectric and/or magnetic loss tangent of the material     

An ADI-PE Approach for Modeling Radio Transmission Loss in Tunnels

Alternate direction implicit (ADI) method is used to study radio wave propagation in tunnels using the parabolic equation (PE). We formulate the ADI technique for use in tunnels with rectangular, circular and arched cross sections and with lossy walls. The electrical parameters of the lossy walls are characterized by an equivalent surface impedance. A vector PE is also formulated for use in tunnels with lossy walls. It is shown that the ADI is more computationally efficient than the Crank Nicolson method. However, boundary conditions become more difficult to model. The boundary conditions of the ADI intermediate planes are given the same boundary conditions as the physical plane and the overall accuracy is reduced. Also, when implementing the ADI in tunnels with circular cross sections the order at which the line by line decomposition occurs becomes important. To validate the ADI-PE, we show simulation results for tunnel test cases with known analytical solutions. Furthermore, the ADI-PE is used to simulate real tunnels in order to compare with experimental data. It is shown that the PE models the electric fields most accurately in real tunnels at large distances, where the lower order modes dominate.      

Simulation of a periodic dielectric corrugation with an equivalent anisotropic layer

A periodic, corrugated, dielectric layer is simulated by an anisotropic dielectric layer of equal thickness. The tensor elements of the equivalent dielectric layer are given in terms of the permittivity of the dielectric material, the period of the surface corrugation, and the width of the corrugations. The validity of this technique is verified by comparing the reflection coefficient of the equivalent layer with that of the corresponding corrugated layer using the moment method. Employing a multiple layer approach, the technique is extended to handle periodic surfaces with arbitrary cross sections which can be used to design millimeter wave dielectric plate polarizers and absorbers.