Dünya Yüzeyi Üzerindeki Bir Hedeften Elektromanyetik Saçılımın Modellenmesi İçin Karma Nümerik Yöntemlerin Geliştirilmesi

Abstract

In electromagnetic wave propagation problems, when there is a target above the Earth’s surface, it is necessary to consider all wave phenomena between the transmitter and the target to model the electromagnetic scattering and to calculate the radar cross section of the target. The wave phenomena, such as reflection from the Earth’s surface, atmospheric refraction, wavelength, shape/size/position of the target, diffraction, the range between the source and the target etc. affect the wave propagation and the radar cross section of the target.

In long range electromagnetic problems, the Split-Step Parabolic Equation (SSPE) method is an efficient method which is capable of handling both forward and backward scattered waves and modeling the vertical-varying refractivity profile in the troposphere. This method can effectively model the scattering effects in a propagation problem, but it is hard to implement the boundary conditions if there exist air targets in the domain. Additionally, the standard SSPE method employs staircasing approach for modeling slanted/curved surfaces and this approach may cause staircasing error. In this thesis, a new hybrid method, called SSPE+MoM, is proposed by combining SSPE and MoM (Method of Moments) to model electromagnetic scattering from irregular terrains. This hybrid method decreases the staircasing error and improves the performance of the SSPE method. The results of the hybrid SSPE+MoM method are compared with those of the standard SSPE and those obtained with another hybrid method which is Geometric Optic (GO) + Uniform Theory of Diffraction (UTD). To obtain the results of the GO+UTD hybrid method, the “GO+UTD Toolbox for Electromagnetic Propagation (ver 1.0)” is employed. The algorithm of this tool which can model the electromagnetic scattering over a terrain on the Earth’s surface is rearranged to model the electromagnetic scattering from the knife-edges located above the Earth’s surface.