Browsing by Subject "Moment methods"
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Item Open Access Analytical evaluation of the MoM matrix elements(Institute of Electrical and Electronics Engineers, 1996-04) Alatan, L.; Aksun, M. I.; Mahadevan, K.; Birand, M. T.Derivation of the closed-form Green's functions has eliminated the computationally expensive evaluation of the Sommerfeld integrals to obtain the Green's functions in the spatial domain. Therefore, using the closed-form Green's functions in conjunction with the method of moments (MoM) has unproved the computational efficiency of the technique significantly. Further improvement can be achieved on the calculation of the matrix elements involved in the MoM, usually double integrals for planar geometries, by eliminating the numerical integration. The contribution of this paper is to present the analytical evaluation of the matrix elements when the closed-form Green's functions are used, and to demonstrate the amount of improvement in computation time. © 1996 IEEE.Item Open Access Capacity of printed dipole arrays in the MIMO channel(Institute of Electrical and Electronics Engineers, 2008-10) Tunc, C. A.; Aktas, D.; Ertürk, V. B.; Altintas, A.Moments performance of printed dipole arrays in the MIMO channel is investigated using a channel model based on the Method of solution of the electric-field integral equation. Comparisons with freestanding dipoles are given in terms of channel capacity. Effects of the electrical properties (such as the dielectric thickness and permittivity) on the MIMO capacity are explored. Various dielectric-substrate configurations yielding high-capacity MIMO arrays are presented.Item Open Access Closed-form Green's functions for general sources and stratified media(Institute of Electrical and Electronics Engineers, 1995-07) Dural, G.; Aksun, M. I.The closed-form Green's functions of the vector and scalar potentials in the spatial domain are presented for the sources of horizontal electric, magnetic, and vertical electric, magnetic dipoles embedded in general, multilayer, planar media. First, the spectral domain Green's functions in an arbitrary layer are derived analytically from the Green's functions in the source layer by using a recursive algorithm. Then, the spatial domain Green's functions are obtained by adding the contributions of the direct terms, surface waves, and complex images approximated by the Generalized Pencil of Functions Method (GPOF). In the derivations, the main emphasis is to put these closed-form representations in a suitable form for the solution of the mixed potential integral equation (MPIE) by the method of moments in a general three-dimensional geometry. The contributions of this paper are: 1) providing the complete set of closed-form Green's functions in spectral and spatial domains for general stratified media; 2) using the GPOF method, which is more robust and less noise sensitive, in the derivation of the closed-form spatial domain Green's functions; and 3) casting the closed-form Green's functions in a form to provide efficient applications of the method of moments.Item Open Access Improved testing of the magnetic-field integral equation(Institute of Electrical and Electronics Engineers, 2005) Ergül, Özgür; Gürel, LeventAn improved implementation of the magnetic-field integral equation (MFIE) is presented in order to eliminate some of the restrictions on the testing integral due to the singularities. Galerkin solution of the MFIE by the method of moments employing piecewise linear Rao–Wilton–Glisson basis and testing functions on planar triangulations of arbitrary surfaces is considered. In addition to demonstrating the ability to sample the testing integrals on the singular edges, a key integral is rederived not only to obtain accurate results, but to manifest the implicit solid-angle dependence of the MFIE as well.Item Open Access Numerical diffraction synthesis of 2-D quasioptical power splitter(IEEE, 2007-06) Nosich, A. A.; Gandel, Y. V.; Magath, T.; Altıntaş, AyhanA new diffraction synthesis method is proposed for computing quasioptical 2-D reflector beam splitters in the E-polarization case. It is a combination of a numerical gradient (NG) optimization and an efficient analysis method based on singular integral equations (SIEs) which are discretized using a fast and accurate numerical Nystrom-type method of discrete singularities (MDS). The results of design are shown for a 40-quasioptical power splitter obtained from an offset parabolic reflector fed by in-focus beam source.Item Open Access Numerical optimization of a cylindrical reflector-in-radome antenna system(IEEE, 1999-04) Yurchenko, V. B.; Altintaş, A.; Nosich, A. IAccurate numerical optimization based on rigorous solution of the integral equation using the method of analytical regularization is performed for a cylindrical reflector antenna in a dielectric radome. It is shown that the multiple scattering in this system is more significant for the optimum radome design than any nonplane-wave effects or the curvature of the radome. We claim that, although the common half-wavelength design is a good approximation to avoid negative effects of the radome (such as the loss of the antenna directivity), one can, by carefully playing with the radome thickness, its radius, reflector location, and the position of the feed, improve the reflector-in-radome antenna performance (e.g., increase the directivity) with respect to the same reflector in free-space.Item Open Access A numerically efficient technique for the analysis of slots in multilayer media(Institute of Electrical and Electronics Engineers, 1998-04) Kınayman, N.; Dural, G.; Aksun, M. I.A numerically efficient technique for the analysis of slot geometries in multilayer media is presented using closed-form Green's functions in spatial domain in conjunction with the method of moments (MoM). The slot is represented by an equivalent magnetic-current distribution, which is then used to determine the total power crossing through the slot and the input impedance. In order to calculate power and current distribution, spatial-domain closed-form Green's functions are expanded as power series of the radial distance />, which makes the analytical evaluation of the spatial-domain integrals possible, saving a considerable amount of computation time.Item 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.Item Open Access On the capacity of printed planar rectangular patch antenna arrays in the MIMO channel: analysis and measurements(IEEE, 2010) Tunc, C. A.; Olgun, U.; Ertürk, V. B.; Altintas, A.Printed arrays of rectangular patch antennas are analyzed in terms of their MIMO performance using a full-wave channel model. These antennas are designed and manufactured in various array configurations, and their MIMO performance is measured in an indoor environment. Good agreement is achieved between the measurements and simulations performed using the full-wave channel model. Effects on the MIMO capacity of the mutual coupling and the electrical properties of the printed patches, such as the relative permittivity and thickness of the dielectric material, are explored.Item Open Access Singularity of the magnetic-field integral equation and its extraction(Institute of Electrical and Electronics Engineers, 2005) Gürel, Levent; Ergül, ÖzgürIn the solution of the magnetic-field integral equation (MFIE) by the method of moments (MOM) on planar triangula-tions, singularities arise both in the inner integrals on the basis functions and also in the outer integrals on the testing functions. A singularity-extraction method is introduced for the efficient and accurate computation of the outer integrals, similar to the way inner-integral singularities are handled. In addition, various formulations of the MFIE and the electric-field integral equation are compared, along with their associated restrictions.