Browsing by Subject "Method of Moments (MoM)"
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Item Open Access Application of iterative techniques for electromagnetic wave scattering from dielectric random rough surfaces(Bilkent University, 2005) İnan, KıvançMobile radio planning requires accurate prediction of electromagnetic field strengths over large terrain profiles. However the conventional method of moments (MoM) becomes unsuitable for electrically large rough dielectric surfaces, because of the O(N³) computational cost due to the large number of surface unknowns N. Iterative Methods are beneficial methods for faster electromagnetic problem solutions. By using such methods, very accurate results can be achieved, causing a computational cost of O(N²). In this work, among the stationary iterative methods; Forward-Backward Method (FBM), and among the nonstationary iterative ones; Conjugate Gradient Squared (CGS), BiConjugate Gradient Stabilized (Bi-CGSTAB) and Quasi Minimal Residual (QMR) Methods are presented to investigate the electromagnetic wave scattering from dielectric random rough surfaces. These techniques are compared to each other over various kinds of surface models that reflect the real terrains to find out the best solution methodologies. Furthermore, efficiency of the methods are assessed by comparing the obtained scattering results, normalized radar cross sections (NRCS) of the surfaces considered, with the numerically exact ones computed by employing the MoM.Item Open Access Comparison of two physical optics integration approaches for electromagnetic scattering(Bilkent University, 2008) Öztürk, EnderA computer program which uses two different Physical Optics (PO) approaches to calculate the Radar Cross Section (RCS) of perfectly conducting planar and spherical structures is developed. Comparison of these approaches is aimed in general by means of accuracy and efficiency. Given the certain geometry, it is first meshed using planar triangles. Then this imaginary surface is illuminated by a plane wave. After meshing, Physical Optics (PO) surface integral is numerically evaluated over the whole illuminated surface. Surface geometry and ratio between dimension of a facet and operating wavelength play a significant role in calculations. Simulations for planar and spherical structures modeled by planar triangles have been made in order to make a good comparison between the approaches. Method of Moments (MoM) solution is added in order to establish the accuracy. Backscattering and bistatic scattering scenarios are considered in simulations. The effect of polarization of incident wave is also investigated for some geometry. Main difference between approaches is in calculation of phase differences. By this study, a comprehensive idea about accuracy and usability due to computation cost is composed for different PO techniques through simulations under different circumstances such as different geometries (planar and curved), different initial polarizations, and different electromagnetic size of facets.