Browsing by Subject "Physical Optics (PO)"

Now showing 1 - 4 of 4

Open Access
Comparison of two physical optics integration approaches for electromagnetic scattering
(2008) Öztürk, Ender
A 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.
Open Access
Implementation of physical theory of diffraction for radar cross section calculations
(2002) Öztürk, Alper Kürşat
A computer program which uses the Physical Theory of Diffraction (PTD) method to calculate the Radar Cross Section (RCS) of perfectly conducting targets with arbitrary shape is developed. Given an arbitrary surface, it is first meshed using planar triangles. The area of each triangle is restricted to be smaller than 0.005λ 2 in order to obtain a good approximation to the actual surface. After meshing, Physical Optics (PO) surface integral is numerically evaluated over the whole surface. If the surface has edges or wedges, diffractions originating from these edges play a significant role in the overall scattered field. This part of the diffracted field is calculated using PTD-EEC method. Calculation of the edge currents is made possible by canonically modelling the arbitrary-shaped edge. If the surface of the scatterer has thin wires attached to it, then the thin wire scattering formulation in the literature is applied. Expressions for scattering mechanism on a straight wire are based on diffraction, attachment, reflection and launch. The results get sufficiently accurate especially for electrically large bodies.
Open Access
Polarization included geometry based channel modeling for MIMO systems
(2008) Akkaya, Keziban
Most of the studies in the literature about channel modeling do not include the polarization. Aiming to develop a more realistic geometric model including polarization, the channel characteristics are examined using measurement data. Each multipath in the measurement data is modeled with a scatterer. Locations of scatterers are determined in the geometry based single bounce model. Then, each scatterer is replaced by a thin impedance disc. Electrical properties, sizes and orientations of discs are obtained using physical optics approximation. Using the channel model, XPD characteristics of the environment are examined. As a result of this study, a channel model for characterizing the general scenarios as much as possible is developed.
Open Access
RCS computations with PO/PTD for conducting and impedance objects modeled as large flat plates
(2005) Albayrak, N. Aslıhan
Calculation of Radar Cross Section (RCS) of arbitrary bodies using Physical Optics (PO) Theory and Physical Theory of Diffraction (PTD)is considered. For bodies with impedance surface boundary condition, only PO is used. Analytical approach to PO integral is used to achieve faster computations. A computer program has been developed in Fortran in order to calculate the Radar Cross Section (RCS). Arbitrary shape is modeled as triangular facets of any area by the help of graphical tools. Given the triangular meshed model of an arbitrary body, Physical Optics(PO) surface integral is numerically evaluated over the whole surface. There is no limitation on the size of the triangles, as soon as the total surface does not retire from the original one. Shadowing algorithm has been used in order to have more accurate solutions. Additionally, flash points of PO are visualized over the surface of targets, hence local nature of high-frequency phenomena is proved. Induced surface currents, edge currents and RCS have been calculated for some basic shapes and the fuel tank model of F-16 airplanes. Induced surface currents have been visualized over the surface of the particular targets using Matlab.