Browsing by Author "Nosich, A. I."

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Open Access
Accurate simulation of reflector antennas by the complex source-dual series approach
(Institute of Electrical and Electronics Engineers, 1995-08) Oğuzer, T.; Altıntaş, A.; Nosich, A. I.
The radiation from circular cylindrical reflector antennas is treated in an accurate manner for both polarizations. The problem is first formulated in terms of the dual series equations and then is regularized by the Riemann-Hilbert problem technique. The resulting matrix equation is solved numeridy with a guaranteed accuracy, and remarkably Little CPU time is needed. The feed directivity is included in the analysis by the complex source point method. Various characteristic patterns are obtained for the front and offset-fed reflector antenna geometries with this analysis, and some comparisons are made with the high frequency techniques. The directivity and radiated power properties are also studied.
Open Access
Analysis of an arbitrary conic section profile cylindrical reflector antenna, H-polarization case
(IEEE (Institute of Electrical and Electronics Engineers), 2004) Oğuzer, T.; Nosich, A. I.; Altintas, A.
Two-dimensional scattering of waves by a perfectly electric conducting reflector having arbitrary smooth profile is studied in the H-polarization case. This is done by reducing the mixed-potential integral equation to the dual-series equations and carrying out analytical regularization. To simulate a realistic primary feed, directive incident field is taken as a complex source point beam. The proposed algorithm shows convergence and efficiency. The far field characteristics are presented for the reflectors shaped as quite large-size curved strips of elliptic, parabolic, and hyperbolic profiles.
Open Access
Analysis of an arbitrary profile reflector antenna having resistive-type surface-H-polarization case
(IEEE, 2008-06-07) Oǧuzer, T.; Altıntaş, Ayhan; Nosich, A. I.
A regularization-based numerical solution is obtained for arbitrary-shape conic section profile reflector antenna in 2-D, for the H-polarization case. New point is that the reflector surface is assumed a resistive-type material. The problem is treated by reducing the singular integral equation obtained from the boundary condition to the dual series equations and application of the Riemann Hilbert Problem (RHP) technique. The resulting matrix equation has regularized form. Sample numerical results are obtained for various values of the eccentricity of the conic section contour of reflector and the resistivity of its surface. © 2008 IEEE.
Open Access
Analysis of an arbitrary profile reflector antenna system having resistive type surface–E-polarization case
(IEEE, 2006-06) Oǧuzer, T.; Altıntaş, Ayhan; Nosich, A. I.
The regularized solution is performed for arbitrary shape conic section profile geometry. In this case the reflector surface is taken as made up of resistive type material. The problem is formulated depending on the circular In periodicity and then Fourier series coefficients of the surface current density are obtained. The resultant matrix equation is in the regularized form. Then the various numerical results are obtained for different eccentricity factor of the conic section and the resisitvity of the reflector surface. © 2006 IEEE.
Open Access
Analysis of radome covered circular reflectors by complex source-dual series approach
(IEEE, 1994) Oğuzer, T.; Altıntaş, A.; Nosich, A. I.
Radiation from a two dimensional reflector antenna covered by a cylindrical radome is analyzed by the complex dual series approach. It is only performed for the electrically polarized incident field. The approach is based on the analytical numerical type regularization technique and not on the moment method. This method gives the exact solution with any desired accuracy and the directivity of the feed antenna can be modelled by using this method. The results can be thought as a reliable data for the validity of approximate solutions. The lossy case and the multilayer radome problems can be solved by the same method.
Open Access
Analysis of the elliptic-profile cylindrical reflector with a non-uniform resistivity using the complex source and dual-series approach: H-polarization case
(Springer, 2013) Oğuzer, T.; Altintaş, A.; Nosich, A. I.
An elliptic-profile reflector with varying resistivity is analyzed under the illumination by an H-polarized beam generated by a complex-source-point (CSP) feed. The emphasis is done on the focusing ability that is potentially important in the applications in the optical range related to the partially transparent mirrors. We formulate the corresponding electromagnetic boundary-value problem and derive a singular integral equation from the resistive-surface boundary conditions. This equation is treated with the aid of the regularization technique called Riemann Hilbert Problem approach, which inverts the stronger singular part analytically, and converted to an infinite-matrix equation of the Fredholm 2nd kind. The resulting numerical algorithm has guaranteed convergence. This type of solution provides more accurate and faster results compared to the known method of moments. In the computations, a CSP feed is placed into a more distant geometrical focus of the elliptic reflector, and the near-field values at the closer focus are plotted and discussed. Various far-field radiation patterns including those for the non-uniform resistive variation on the reflector are also presented.
Open Access
Analytical regularization based analysis of a spherical reflector symmetrically illuminated by an acoustic beam
(IEEE, 2000) Vinogradov, S. S.; Vinogradova, E. D.; Nosich, A. I.; Altintaş, A.
A mathematically accurate and numerically efficient method of analysis of a spherical reflector, fed by a scalar beam produced by a complex source- point feed, is presented. Two cases, soft and hard reflector surface, are considered. In each case the solution of the full-wave integral equation is reduced to dual series equations and then further to a regularized infinite- matrix equation. The latter procedure is based on the analytical inversion of the static part of the problem. Sample numerical results for 50-λ reflectors demonstrate features that escape a high-frequency asymptotic analysis. (C) 2000 Acoustical Society of America.
Open Access
A comparative study of RCS predictions of canonical rectangular and circular cavities with double-layer material coating
(Denshi Jouhou Tsuushin Gakkai,Institute of Electronics Information and Communication Engineers, 1997-11) Koshikawa, S.; Çolak, D.; Altıntaş, A.; Kobayashi, K.; Nosich, A. I.
A rigorous radar cross section (RCS) analysis is carried out for two-dimensional rectangular and circular cavities with double-layer material loading by means of the Wiener-Hopf (WH) technique and the Riemann-Hilbert problem (RHP) technique, respectively. Both E and H polarizations are treated. The WH solution for the rectangular cavity and the RHP solution for the circular cavity involve numerical inversion of matrix equations. Since both methods take into account the edge condition explicitly, the convergence of the WH and RHP solutions is rapid and the final results are valid over a broad frequency range. Illustrative numerical examples on the monostatic and bistatic RCS are presented for various physical parameters and the far field scattering characteristics are discussed in detail. It is shown that the double-layer lossy material loading inside the cavities leads to the significant RCS reduction.
Open Access
E-polarized beam scattering by an open cylindrical PEC strip having an arbitrary "conical-section" profile
(John Wiley & Sons, Inc., 2001) Oğuzer, T.; Nosich, A. I.; Altintaş, A.
Two-dimensional (2-D) scattering of waves by a conducting strip with a canonical profile is simulated in the E-polarization case. This analysis is performed by reducing a singular integral equation (IE) to the dual-series equations, and making their analytical regularization. Furthermore, the incident field is taken as a complex source point (CSP) beam. This is an extension of our previous studies about circular and parabolic reflector antennas. The algorithm features are demonstrated. Far-field characteristics are presented for quite large-size curves strips of elliptic, parabolic, and hyperbolic profiles.
Open Access
Effect of imperfect flat earth on the vertically polarized radiation of a cylindrical reflector antenna
(IEEE, 2000-02) Boriskina, S.; Nosich, A. I.; Altintas, A.
The radiation of a circular cylindrical reflector antenna in the presence of imperfect flat earth is treated in an accurate manner. The boundary value problem is formulated in terms of a full-wave integral equation converted to the dual-series equations and then regularized by using analytical inversion of the static part. The resulting Fredholm second-kind matrix equation is solved numerically with guaranteed accuracy. The feed directivity is included in the analysis by using the complex source-point method. Various antenna features, which include the overall directivity, efficiency, gain, and radiated and absorbed power fractions have been calculated and compared with the free-space antenna characteristics. They show some phenomena not predicted by approximate techniques.
Open Access
Enhancement of plasmon resonances in the wave scattering by finite grids of circular silver wires
(IEEE, 2010-09) Natarov, D. M.; Benson, T. M.; Altıntaş, Ayhan; Sauleau, R.; Nosich, A. I.
Using the field expansions in local coordinates and addition theorems for cylindrical functions, we consider the problem of the H-polarized plane wave scattered by a finite chain of circular wires. The absorption and scattering cross-sections are found numerically and plasmon and grating-type resonances are studied for the grids of silver nano-size wires. © 2010 IEEE.
Open Access
Integral equation anlaysis of an arbitrary-profile and varying-resistivity cylindrical reflector illuminated by an E-polarized complex-source-point beam
(Optical Society of America, 2009-06-09) Oguzer, T.; Altintas, A.; Nosich, A. I.
A two-dimensional reflector with resistive-type boundary conditions and varying resistivity is considered. The incident wave is a beam emitted by a complex-source-point feed simulating an aperture source. The problem is formulated as an electromagnetic time-harmonic boundary value problem and cast into the electric field integral equation form. This is a Fredholm second kind equation that can be solved numerically in several ways. We develop a Galerkin projection scheme with entire-domain expansion functions defined on an auxiliary circle and demonstrate its advantage over a conventional moment-method solution in terms of faster convergence. Hence, larger reflectors can be computed with a higher accuracy. The results presented relate to the elliptic, parabolic, and hyperbolic profile reflectors fed by in-focus feeds. They demonstrate that a partially or fully resistive parabolic reflector is able to form a sharp main beam of the far-field pattern in the forward half-space; however, partial transparency leads to a drop in the overall directivity of emission due to the leakage of the field to the shadow half-space. This can be avoided if only small parts of the reflector near the edges are made resistive, with resisitivity increasing to the edge.
Open Access
Lasing modes of infinite periodic chain of quantum wires
(IEEE, 2009-06-07) Byelobrov, V. O.; Benson, T. M.; Sewell, P.; Altıntaş, Ayhan; Nosich, A. I.
In this paper, we study the scattering and eigenvalue problems for a periodic open optical resonator that is an infinite chain of active circular cylindrical quantum wires standing in free space. The scattering problem is solved by the method of partial separation of variables. The eigenvalue problem differs from the first one by the absence of the incident field and presence of "active properties" of cylinders and yields the frequencies and thresholds of lasing. ©2009 IEEE.
Open Access
Lens or resonator? Electromagnetic behavior of an extended hemielliptic lens for a sub-millimeter-wave receiver
(John Wiley & Sons, 2004) Boriskin, A. V.; Nosich, A. I.; Boriskina, S. V.; Benson, T. M.; Sewell, P.; Altintas, A.
The behavior of a 2D model of an extended hemielliptic silicon lens of a size typical for THz applications is accurately studied for the case of a plane E-wave illumination. The full-wave analysis of the scattering problem is based on the Mutter's boundary integral-equations (MB1E) that are uniquely solvable. A Calerkin discretization scheme with a trigonometric basis leads tu a very efficient numerical algorithm. The numerical results related to the focusability of the lens versus its rear-side extension and the angle of the plane-wave incidence, as well as near-field profiles, demonstrate strong resonances. Such effects can change the principles of optimal design of lens-based receivers.
Open Access
Low-threshold Lasing eigenmodes of infinite periodic chain of quantum wires
(Optical Society of America, 2010-10-26) Byelobrov, V.; Ctyroky, J.; Benson, T. M.; Sauleau, R.; Altintas, A.; Nosich, A. I.
We study the lasing eigenvalue problems for a periodic open optical resonator made of an infinite grating of circular dielectric cylinders standing in free space, in the E- and H-polarization modes. If possessing a “negative-absorption” refractive index, such cylinders model a chain of quantum wires made of the gain material under pumping. The initial-guess values for the lasing frequencies are provided by the plane-wave scattering problems. We demonstrate a new effect: the existence of specific grating eigenmodes that have a low threshold of lasing even if the wires are optically very thin.
Open Access
Manipulation of backscattering from a dielectric cylinder of triangular cross-section using the interplay of go-like ray effects and resonances
(Institute of Electrical and Electronics Engineers, 2015) Sukharevsky, Ilya O.; Nosich, A. I.; Altıtaş, Ayhan
A triangular dielectric cylinder (dielectric prism) of the size, in cross-section, comparable to or moderately larger than the wavelength is a scatterer, which blends together two different types of electromagnetic behavior: geometrical optics (GO) and resonance. As shown in this paper, the first is responsible, for instance, for enhanced reflection from an isosceles 90° prism, if illuminated from the base. The second is responsible for the peaks in the total scattering and absorption cross-sections (ACSs) at the natural-mode frequencies. The numerical analysis is performed by solving the well-conditioned Muller-type boundary integral equation (IE) discretized using an algorithm with controlled accuracy.
Open Access
The method of analytical regularization in the electromagnetic wave scattering by thin disks
(Institution of Engineering and Technology, 2007) Balaban, M. V.; Nosich, A. I.; Altıntaş, Ayhan; Benson, T. M.
We consider the problem of diffraction of an arbitrary electromagnetic wave by a thin disk made from different materials and located in free space. Here we imply a zero- thickness perfectly electrically conducting (PEC) disk, and also thin electrically resistive (ER) and dielectric disks whose thickness is much smaller than the disk radius and the free space wavelength, and also much smaller than the skin-layer depth in the ER disk case. The method used for the modeling is based on the integral equation (IE) technique and analytical regularization. Starting with Maxwell's equations, boundary conditions and the radiation condition at infinity we obtain a set of coupled dual IEs (DIEs) for the unknowns and then reduce this set of equations to the coupled IEs of the Fredholm second kind. To verify our results we calculate the far field characteristics in the case of the PEC disk with the incident field being the field of horizontal electrical dipole located on the disk axis.
Open Access
The method of regularization and its application to some EM problems
(Springer, 2000) Altıntaş, Ayhan; Nosich, A. I.; Uzunoğlu, N. K.; Nikita, K. S.; Kaklamani, D. I.
The regularization of the integral equations for the solution of electromagnetic problems is discussed. The technique includes a semi-analytic inversion of the integral operator resulting in equation of the Fredholm second kind, which can be solved using numerical inversion. The procedure is employed through Riemann-Hilbert Problem technique for the electromagnetic problems that can be put into a dual-series equation form. An example of the method is described for the E-wave scattering from a cavity-backed aperture.
Open Access
Modelling a resistive-reflector antenna by the complex source-dual series approach: the 2-D case of H-polarization
(IEEE, 1995) Altıntaş, Ayhan; Nosich, A. I.; Yurchenko, V. B.
The simulation of reflector antenna is normally conducted under an assumption of the perfect conductivity of reflector. This paper presents an analysis of resistive reflector beamforming using modified method of regularization for solving the scattering from a curve resistive strip. Besides, to simulate a directive feed in equally accurate manner, the Complex Source Method is used.
Open Access
Numerically exact analysis of a two-dimensional variable-resistivity reflector fed by a complex-point source
(Institute of Electrical and Electronics Engineers, 1997-11) Nosich, A. I.; Yurchenko, V. B.; Altintaş, A.
Accurate numerical analysis of a two-dimensional (2-D) variable-resistivity reflector has been carried out by the method of regularization based on the analytical inversion of the corresponding static problem. The complex source-point model has been used to account for the directivity of the feeder and both the H- and E-polarization cases are considered. Far-field radiation patterns, directivity, and total radiative power have been computed for reflectors of uniform and nonuniform complex resistivities. The concept of edge loading for the control and improvement of antenna characteristics is confirmed by this numerically rigorous technique.