High Frequency Techniques: the Physical Optics Approximation and the Modified Equivalent Current Approximation (MECA)
High Frequency Techniques: the Physical Optics Approximation and the Modified Equivalent Current Approximation (MECA)
复制标题
高频技术：物理光学近似和改进的等效电流近似 (MECA)
DOI：
10.5772/17307
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发表时间：
2011
影响因子：
2
通讯作者：
F. Las
中科院分区：
文献类型：
--
作者：
J. Gutierrez;J. Martinez;F. Las
在大多数电磁问题中，当天线、设备或场景的尺寸增加或工作频率变得更高时，用于评估散射场的未知数的数量增加。在这种情况下，严格的全波方法-例如。矩量法（MoM）、快速多极法（FMM）（Engheta等人，1992）、时域有限差分法（FDTD）（Taflove和Umashankar，1987）或频域有限差分法（FDFD）（Rappaport和McCartin，1991）、有限元法（FEM）（Kempel等人，1998年）-不能处理的分析，这样的问题超出了上限所确定的计算要求的时间和内存。高频技术包括麦克斯韦方程的渐近估计。因此，它们在处理电大尺寸几何形状时提供了良好的精度，同时相对于上述方法减少了计算需求。在高频技术中，几何光学（GO）和物理光学（PO）近似是最广泛的方法，由于在各个领域，如雷达散射截面（RCS），反射面天线的设计或无线电覆盖计算获得成功的结果。由于物理光学近似在下面的部分中详细描述，因此简要总结几何光学。在GO中的主要兴趣在于，入射，反射和透射电磁波的研究基于能量通量的守恒沿着一个源和一个观察点之间的射线管。因此，几何光学通常被称为射线光学。GO包括两种不同的方法（Rossi & Gabillet，2002）：射线跟踪（Glassner，1989）-起点是接收器或观察点，并通过分析墙壁，建筑物，山脉上的反射来寻找到源的路径-和射线发射-从源发射多条射线，因此它们独立地跟随直到到达观察点或接收器。GO的常见应用之一是评估无线电覆盖或城市场景中的信道特性。GO和PO技术都需要一种额外的方法来计算由于衍射现象的贡献。GO可以通过衍射的几何理论（GTD）（Keller，1962）或衍射的统一理论（Uniform Theory of Diffraction）来补充。
In most of the electromagnetic problems, the number of unknowns to evaluate the scattered fields grows whenever the size of the antenna, device or scenario increases or the working frequency becomes higher. In this context, the rigorous full-wave methods –e.g. Method of Moments (MoM), Fast Multipole Method (FMM) (Engheta et al., 1992), Finite-Difference Time-Domain (FDTD) (Taflove & Umashankar, 1987) or Finite-Difference FrequencyDomain (FDFD) (Rappaport & McCartin, 1991), Finite Element Method (FEM) (Kempel et al., 1998) – can not tackle the analysis of such problems beyond an upper limit determined by the computational requirements in terms of time and memory. High frequency techniques consist in the asymptotic evaluation of the Maxwell’s equations. As a consequence, they provide good accuracy when dealing with electrically large geometries meanwhile the computational needs diminish with respect to the aforementioned methods. Within the high frequency techniques, the Geometrical Optics (GO) and the Physical Optics (PO) approximation are the most extended methods due to the successful results obtained in various fields such as Radar Cross Section (RCS), design of reflector antennas or radioelectric coverage calculation. Since the Physical Optics approximation is detailed in the following section, the Geometrical Optics is briefly summarised. The main interest in the GO lies in the fact that incident, reflected and transmitted electromagnetic waves are studied based on the conservation of the energy flux along a ray tube between a source and an observation point. Therefore, the Geometrical Optics is usually referred to as Ray Optics. The GO comprises two different methodologies (Rossi & Gabillet, 2002): Ray Tracing (Glassner, 1989) – the starting point is the receiver or observation point and a path to the source is sought analysing the reflections on walls, buildings, mountains – and Ray Launching – multiple rays are launched from the source, so they are independently followed until an observation point or the receiver is reached. One of the common applications of the GO is the evaluation of radio electric coverage or the channel characterization in urban scenarios. Both the GO and the PO techniques require of an additional method to compute the contribution due to the diffraction phenomenon. The GO can be complemented by means of the Geometrical Theory of Diffraction (GTD) (Keller, 1962) or the Uniform Theory of