Browsing by Subject "Physical Optics"

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Open Access
Application of characteristic basis function method for scattering from and propagation over terrain profiles
(2009) Yağbasan, Atacan
A computationally efficient hybrid method, that combines the characteristic basis function method and the physical optics as well as the forward backward method, is applied for the solution of integral equations used to investigate the electromagnetic scattering from and propagation over large scale rough terrain problems. The method utilizes high-level basis functions defined on macro-domains (named as blocks) namely characteristic basis functions that are constructed by aggregating low-level basis functions (i.e., conventional sub-domain basis functions). In the construction of the abovementioned characteristic basis functions, forward backward method as well as the physical optics approach (when applicable) are used. The conventional characteristic basis function method originally developed by Prakash et al. is slightly modified to handle large terrain problems, and is further embellished by accelerating it and by reducing its storage requirements via the use of an extrapolation procedure. Numerical results for the induced currents, total fields and path loss are presented and compared with either measured or previously published reference solutions to assess the efficiency and the accuracy of the method. Besides, certain parametric studies and convergence tests have been carried out.
Open Access
Development and implementation of SBR technique for scattering and RCS problems
(2016-09) Dağdelen, Murat Erdal
Full wave solution techniques are preferred to calculate the electromagnetic characteristic of an object. These methods give very accurate results. However, when the object is electrically large regarding wavelength, computation time may take very long, or required computer resources may not be provided. In this case, high-frequency approximation techniques are employed to solve electromagnetic scattering problems involving electrically large objects. Shooting and Bouncing Ray (SBR) method is a high-frequency technique that combines Geometric Optics (GO) and Physical Optics (PO). It can be used for the solution of electrically large objects. Multiple re ection feature of SBR makes it possible to calculate current distribution accurately on the target for the complex objects. In this study, an SBR code is developed in MATLABR which solves di erent kinds of problems that involve electrically large objects. Required formulas are derived and implementation procedure of the code is discussed. Radar Cross Section (RCS) of some basic shapes is calculated using SBR. An RCS reduction technique is explained and implemented. As the antenna-platform interaction, di erent kind of antennas are placed on a tank-like and a ship-like object to observe the e ect of a scatterer on antenna pattern. An antenna coupling formula is derived. This formula is used to calculate coupling between two antennas in di erent environments. Results show fairly good agreement with Method of Moment (MoM) solutions.