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Rough surface scattering and propagation over rough terrain in ducting environments.

机译：管道环境中的粗糙表面散射和在粗糙地形上的传播。

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摘要

The problem of rough surface scattering and propagation over rough terrain in ducting environments has been receiving considerable attention in the literature. One popular method of modeling this problem is the parabolic wave equation (PWE) method. In this method, the Helmholtz wave equation is replaced by a PWE under the assumption of predominant forward propagation and scattering. The resulting PWE subjected to the appropriate boundary condition(s) is then solved, given an initial field distribution, using marching techniques such as the split-step Fourier algorithm. As is obvious from the assumption on which it is based, the accuracy of the PWE approximation deteriorates in situations involving appreciable scattering away from the near-forward direction, i.e. when the terrain under consideration is considerably rough. The backscattered field is neglected in all PWE-based models.; An alternative and more rigorous method for modeling the problem under consideration is the boundary integral equation (BIE) method, which is formulated in two steps. The first step involves setting up an integral equation (the magnetic field integral equation, MFIE, or the electric field integral equation EFIE) governing currents induced on the rough surface by the incident field and solving for these currents numerically. The resulting currents are then used in the appropriate radiation integrals to calculate the field scattered by the surface everywhere in space. The BIE method accounts for all orders of multiple scattering on the rough surface and predicts the scattered field in all directions in space (including the backscattering direction) in an exact manner.; In homogeneous media, the implementation of the BIE approach is straightforward since the kernel (Green's function or its normal derivative) which appears in the integral equation and the radiation integrals is well known. This is not the case, however, in inhomogeneous media (ducting environments) where the Green's function is not readily known. Due to this fact, there has been no attempt, up to our knowledge, at using the BIE (except under the parabolic approximation) to model the problem under consideration prior to the work presented in this thesis.; In this thesis, a closed-form approximation of the Green's function for a two-dimensional ducting environment, formed by the presence of a linear-square refractivity profile (n2( z) = 1 − ϵz, where ϵ is a constant called the ducting parameter), is derived using the asymptotic methods of stationary phase and steepest descents. This Green's function is then modified to more closely model the one associated with a physical ducting medium, in which the refractivity profile decreases up to a certain height, zo, beyond which it becomes constant. This modified Green's function is then used in the BIE approach to study low grazing angle (LGA) propagation over rough surfaces in the aforementioned ducting environment. The numerical method used to solve the MFIE governing the surface currents is MOMI, which is a very robust and efficient method that does not require matrix storage or inversion.; The proposed method is meant as a benchmark for people studying forward propagation over rough surfaces using the parabolic wave equation (PWE). Rough surface scattering results obtained via the PWE/split-step approach are compared to those obtained via the BIE/MOMI approach in ducting environments. These comparisons clearly show the shortcomings of the PWE/split-step approach.
机译：管道环境中的粗糙表面散射和在粗糙地形上传播的问题在文献中已引起相当大的关注。建模此问题的一种流行方法是抛物线波动方程（PWE）方法。在这种方法中，在主要向前传播和散射的假设下，用PWE代替了亥姆霍兹波方程。然后，使用行进技术（例如分步傅里叶算法），在给定初始场分布的情况下，求解经受适当边界条件的所得PWE。从其所基于的假设可以明显看出，在涉及从近前方向明显散射的情况下，即当所考虑的地形相当粗糙时，PWE近似的精度会降低。在所有基于PWE的模型中，后向散射场均被忽略。用于建模所考虑问题的另一种更严格的方法是边界积分方程（BIE）方法，该方法分两步制定。第一步涉及建立一个积分方程（磁场积分方程，MFIE或电场积分方程EFIE），以控制由入射场在粗糙表面上感应的电流，并通过数值方式求解这些电流。然后，将得到的电流用于适当的辐射积分中，以计算空间中空间各处被表面散射的场。 BIE方法考虑了粗糙表面上多次散射的所有阶数，并以精确的方式预测了空间中所有方向（包括反向散射方向）的散射场。在均质介质中，BIE方法的实现非常简单，因为众所周知的是出现在积分方程和辐射积分中的核（格林函数或其正导数）。但是，在不容易了解格林函数的不均匀介质（导电环境）中，情况并非如此。由于这个事实，据我们所知，在本文提出的工作之前，没有人尝试使用BIE（抛物线近似除外）对所考虑的问题进行建模。本文通过线性平方折射率分布（ n 2 （ ）= 1-＆epsiv; z ，其中＆epsiv;是称为管道参数的常数），是使用固定相和最速下降的渐近方法得出的。然后修改格林函数，以更紧密地模拟与物理导管介质相关联的函数，其中折射率分布降低到一定高度， z o 它变得恒定。然后，将这种修改后的格林函数用于BIE方法中，以研究上述导管环境中低掠角（LGA）在粗糙表面上的传播。用于解决控制表面电流的MFIE的数值方法是MOMI，这是一种非常强大而有效的方法，不需要矩阵存储或求逆。所提出的方法是人们研究抛物线波动方程（PWE）在粗糙表面上向前传播的基准。将通过PWE /分步方法获得的粗糙表面散射结果与在管道环境中通过BIE / MOMI方法获得的粗糙表面散射结果进行比较。这些比较清楚地表明了PWE /分步方法的缺点。

著录项

  • 作者

    Awadallah, Ra'id Suleiman.;

  • 作者单位

    Virginia Polytechnic Institute and State University.;

  • 授予单位 Virginia Polytechnic Institute and State University.;
  • 学科 Engineering Electronics and Electrical.
  • 学位 Ph.D.
  • 年度 1998
  • 页码 172 p.
  • 总页数 172
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 无线电电子学、电信技术;
  • 关键词

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