9.4.1 Diffraction Phenomena

On the way from the satellite to the receiver the radiated signal encounters obstacles. These could be natural obstacles like trees or human-made obstacles like buildings. The term “diffraction” in general refers to a phenomenon that occurs when the wave interacts with an obstacle. Figure 9.4.1 illustrates the case. Here the electromagnetic field of an incident wave is illustrated by a plurality of wavefronts shown in solid lines. As a result of this interaction, a so-called diffraction field is generated. Diffraction wavefronts are shown as dashed lines. The diffraction field affects the amplitude and phase distribution of the incident field. Diffraction phenomena occur with waves of any kind, such as acoustic, electromagnetic, or say water surface waves. A commonsense example could be ocean waves interacting with an isolated rock in a bay. The branch of science treating diffraction phenomena is known as wave diffraction theory. A complete list of references on this subject would be endless. In regard to electromagnetics, the foundations are provided by Morse and Feshbach (1953), Felsen and Marcuvitz (2003), Fock (1965), Keller (1962), Ufimtsev (2003), Kouyoumjian and Pathak (1974), Balanis (1989), and references therein. One is to note that so-called strict analytical or closed-form solutions are available for a very limited number of obstacle models such as spheres, cylinders, or wedges. For cases where obstacles are much smaller or much larger ...

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