ELECTROMAGNETIC SCATTERING FROM FINITE-DIMENSION STRUCTURES
NEO CHYE POH
NEO CHYE POH
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Abstract
The thesis reports the results of an investigation of electromagnetic scattering from finite-dimension structures of various shapes by solving the governing electric field integral equation (EFIE). In the first part of the thesis, the induced current on a centrally-loaded cylinder illuminated by a plane wave at angles of incidence, other than the special case of 90 degrees considered by others, was determined theoretically from the governing EFIE. The magnitude and phase of the induced current can be greatly changed by the impedance loading, wave illumination angle and operational frequency. In view of this, the optimum loading to achieve zero back scattering in the illumination direction from a thin cylinder shorter than two wavelengths over a wide range of frequencies was determined. It was found that an optimum impedance is required to achieve zero back scattering for a given set of wave illumination angle and frequency. Results are also presented for a central impedance which gives the best overall monostatic radar cross-section (RCS) performance for all wave incident angles and over a wide range of frequencies. In the second part of this thesis, a numerical scheme to obtain the RCS of conducting plate, thin dielectric plate and three-dimensional structures of resonant size and arbitrary geometry is described. The three-dimensional structures can be of arbitrary material composition. The RCS is obtained by solving the EFIE using the conjugate gradient-fast Fourier transform method (CG-FFT). The accuracy of this method is checked by comparisons with the RCS measurements or predictions by other methods. It is then extended to study the RCS performance of a rectangular plate, with different shapes at its leading edge, and the bistatic RCS of some new structures. In the last part of this thesis, the CG-FFT method, a scheme which avoids the storage of large matrices and reduces the computational time by orders of magnitude, is employed to compute the reflection coefficient of infinite and finite frequency selective surfaces (FSS). The reflection coefficient is obtained by solving the EFIE and the computed results (infinite case) are checked against the available published data. The CG-FFT method is then extended to show that the specular reflection coefficient of the finite free standing FSS can be approximated by its infinite array case when the number of patches is sufficiently large, greater than 12 x 12 for a square FSS array.
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Date
1999
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Thesis