Date

2007

Author

Pelgur, Ali

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Calculation of electromagnetic wave propagation over irregular terrain is an important problem in many applications such as coverage calculations for radars or communication links. Many different approaches to this problem may be found in the literature. One of the most commonly used methods to solve electromagnetic boundary value problems is the Method of Moments (MoM). However, especially at high frequencies, the very large number of unknows required in the MoM formulation, limits the applicability of this method, since the memory requirement and the operation count increases by O(N2) and O(N3), respectively, where N is the number of the unknowns. Several approaches have been proposed in the literature to reduce the memory requirement and the operation count of the MoM. These approaches rely on the special structure of the impedance matrix generated by the MoM. The Conjugate Gradient (CG) method is a non stationary iterative technique that can be used to solve general asymmetric/non-Hermitian systems with an operational cost of O(N2) per iteration. Furthermore, the computational time can be improved by the Fast Fourier Transform (FFT) algorithm to perform the matrix vector multiplication that appear in any iterative technique. This approach has been successfully used in the literature to solve scattering from electrically large objects and it has been shown that the computational cost and memory requirement can be reduced to O(KNlogN) with K being the number of iterations. In this thesis, CG method accelerated with Fast Fourier Transform (CG FFT) method is applied to the problem of electromagnetic propagation over irregular terrain. Applications for electrically large rough terrain profiles are presented. The accuracy of the method is compared to the direct solution of the MoM, CG method and Free Space model with recoveries by Hata model or multiple knife-edge diffraction and reflection. The solution works on quasi-planar surfaces and profiles with small deviation like little breezy sea surface properly.

Subject Keywords

Electrical Engineering., Electronics., Nuclear Engineering.

URI

http://etd.lib.metu.edu.tr/upload/12608830/index.pdf
https://hdl.handle.net/11511/16967

Collections

Graduate School of Natural and Applied Sciences, Thesis