Browsing by Subject "Method of moments"
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Item Open Access Analysis of cylindrically conformal antennas using closed-form Green's function representations(IEEE, 2015-04) Kalfa, Mert; Karan, S.; Ertürk, Vakur B.Probe-fed microstrip patch antennas and slotted sectoral waveguide array antennas embedded in cylindrically stratified media are analyzed with a hybrid Method of Moments/Green's function technique, where closed-form Green's function representations for electric and magnetic current sources are used as the kernel of the associated integral equations. Various patch and slot antennas are analyzed using the proposed method. Numerical results in the form of input impedance, S-parameters, and radiation patterns are presented and compared to the results obtained from CST Microwave Studio™ and HFSS™.Item Open Access Analysis of finite arrays of axially directed printed dipoles on electrically large circular cylinders(IEEE, 2004) Ertürk, V. B.; Rojas, R. G.; Lee, K. W.Various arrays consisting of finite number of printed dipoles on electrically large dielectric coated circular cylinders are investigated using a hybrid method of moments/Green's function technique in the spatial domain. This is basically an "element by element" approach in which the mutual coupling between dipoles through space as well as surface waves is incorporated. The efficiency of the method comes from the computation of the Green's function, where three types of spatial domain Green's function representations are used interchangeably, based on their computational efficiency and regions where they remain accurate. Numerical results are presented in the form of array current distributions, active reflection coefficient and far-field pattern to indicate the efficiency and accuracy of the method. Furthermore, these results are compared with similar results obtained from finite arrays of printed dipoles on grounded planar dielectric slabs. It is shown that planar approximations, except for small separations, can not be used due to the mutual coupling between the array elements. Consequently, basic performance metrics of printed dipole arrays on coated cylinders show significant discrepancies when compared to their planar counterparts. © 2004 IEEE.Item Open Access Analysis of finite arrays of circumferentially oriented printed dipoles on electrically large cylinders(Wiley, 2004) Ertürk, V. B.; Güner, B.An efficient and accurate hybrid method of moments (MoM)/Green's function technique in the spatial domain is developed for the rigorous analysis of large, finite phased arrays of circumferentially oriented printed dipoles on electrically large, dielectric-coated, circular cylinders. Basic performance metrics (in the form of array current distribution, active reflection coefficient, far-field patterns, and so forth) of several arrays have been obtained and compared with similar printed arrays on grounded planar substrates. Certain discrepancies have been observed and discussed. © 2004 Wiley Periodicals, Inc.Item Open Access Analysis of input impedance and mutual coupling of microstrip antennas on multilayered circular cylinders using closed-form green's function representations(Institute of Electrical and Electronics Engineers Inc., 2014) Karan, S.; Erturk, V. B.Closed-form Green's function (CFGF) representations for cylindrically stratified media are developed and used in conjunction with a Galerkin method of moments (MoM) in the space domain for the analysis of microstrip antennas on multilayered circular cylinders. An attachment mode is used in the MoM solution procedure to accurately model the feeding of probe-fed microstrip antennas. The developed CFGF representations are modified in the source region (where two current modes can partially or fully overlap with each other during the MoM procedure) so that singularities can be treated analytically and hence, the proposed CFGF representations can be safely used in this region. Furthermore, accurate CFGF representations for the probe-related components (necessary for probe type excitations including the attachment mode) are obtained when the radial distance between the source and field points is electrically small or zero. Numerical results in the form of input impedance of various microstrip antennas and the mutual coupling between two antennas are presented showing good agreement when compared to the available published results as well as the results obtained from CST Microwave Studio.Item Open Access Analysis of slotted sectoral waveguides embedded in cylindrically stratified media using closed-form Green's function representations(IEEE, 2013) Kalfa, Mert; Erturk, Vakur B.Slotted waveguide antenna arrays with dielectric covers are widely used in both military and civil applications due to their low-profile, high power handling capacity, and the ability to conform to the host platform. Conformity is especially required for air platforms where aerodynamics and radar cross section (RCS) of the vehicle are of utmost importance. For an air platform, one or more dielectric layers (monolithic or sandwich radomes) can be used to protect the antenna from the extreme flight conditions. Although the accurate and efficient design and analysis of low-profile conformal slotted waveguide arrays is of great interest, available solution methods in the literature usually suffer in terms of efficiency and memory requirements. Among the available solution methods, one of the widely used solvers are integral equation (IE) based ones that utilize the method of moments (MoM). However, the IE solvers suffer from long matrix fill times, especially when cylindrically stratified media are considered. © 2013 IEEE.Item 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.Item Open Access Applications of hybrid discrete Fourier transform moment method to the fast analysis of large rectangular dipole arrays printed on a thin grounded dielectric substrate(Wiley, 2002) Chou, H.-T.; Ho, H.-K.; Civi, O. A.; Erturk, V. B.Recently a discrete Fourier transform-method of moments (DFT-MoM) scheme was developed for fast analysis of electrically large rectangular planar dipole arrays, which has been shown to be very efficient in terms of number reduction of unknown variables and computational complexity. The applications of this DFT-MoM to treat dipole arrays printed on a grounded dielectric substrate are examined in this Letter. Numerical results are presented to validate its efficiency and accuracy.Item Open Access A closed‐form solution to the asymptotic part of the MOM impedance matrix and the MOM excitation vector for printed structures on planar grounded dielectric slabs(John Wiley & Sons, Inc., 2007) Bakýr O.; Ertürk, V. B.In the spectral domain method of moments (MoM) solution of printed structures on planar grounded dielectric slabs, the infinite double integrals which appear in the asymptotic parts of the MoM impedance matrix and the MoM excitation vector elements, have been previously transformed to one-dimensional finite integrals, which have been numerically computed using the highly specialized "International Mathematics and Statistics Library" subroutines. In this paper, these one-dimensional integrals are evaluated in closed-form, resulting in an improved efficiency and accuracy for the rigorous investigation of printed antennas and complex millimeter and microwave integrated circuits. Numerical results in the form of mutual impedance between two expansion functions and input impedance of various microstrip antennas are presented to assess the accuracy of these closed-form expressions.Item Open Access Computing moments of first passage times to a subset of states in Markov chains(SIAM, 2005) Dayar T.; Akar, N.This paper presents a relatively efficient and accurate method to compute the moments of first passage times to a subset of states in finite ergodic Markov chains. With the proposed method, the moment computation problem is reduced to the solution of a linear system of equations with the right-hand side governed by a novel recurrence for computing the higher-order moments. We propose using a form of the Grassmann-Taksar-Heyman (GTH) algorithm to solve these linear equations. Due to the form of the linear systems involved, the proposed method does not suffer from the drawbacks associated with GTH in a row-wise sparse implementation. © 2005 Society for Industrial and Applied Mathematics.Item Open Access Design and analysis of finite arrays of circumferentially oriented printed dipoles on electrically large coated cylinders(Bilkent University, 2004) Güner, BarışConformal antennas and arrays are used in a wide range of applications including mobile communication systems, missiles, aircrafts and spacecrafts. In these applications, the conformality is required for aesthetic and aerodynamic constraints and reducing the radar cross-section. Antennas and arrays conformal to the cylindrical host bodies are particularly important since cylindrical geometry can be used to approximate most of the practical problems and it is a canonical geometry. However, the available design and analysis tools for antennas/arrays conformal to cylindrical host bodies are either approximate methods or restricted to small arrays. Recently, a hybrid method based on Method of Moments (MoM) combined with a Green’s function in space domain is proposed to solve the aforementioned problem. In this work this method is used to analyze finite, phased arrays of circumferentially oriented printed dipoles conformal to the dielectric coated electrically large circular cylinders. The accuracy and efficiency of the method comes from the computation of the appropriate Green’s function which is the kernel of the electric field integral equation to be solved via MoM. There are three different high-frequency based representations for the Green’s function in the spatial domain which are valid in different but overlapping regions: Planar representation, steepest descent path (SDP) representation and the Fourier Series (FS) representation. These different representations are used interchangeably to obtain the most accurate solution that requires the least amount of computational time. Several modifications on the method are made in this work to increase the efficiency and accuracy of the solution. The effects of the array and host body parameters on the performance of the array are presented. The results are compared with a previously published spectral domain solution to show the accuracy of the method. Also, performance comparisons with those of the cylindrical arrays of axially oriented dipoles and planar arrays are made to observe the effects of curvature and the dipole orientation on the performance of the array.Item Open Access Design and analysis of slotted sectoral waveguide array antennas embedded in cylindrically stratified media(IEEE, 2014-07) Kalfa, Mert; Ertürk Vakur B.Slotted waveguide antennas are being widely used in military and commercial applications for many decades. Low cross-polarization, high power capacity, ease of fabrication in microwave bands, and the ability to form arrays make them excellent candidates for phased array antennas in radar applications. However, due to slots being highly resonant (narrow-band, high Q) radiators, their design parameters are very sensitive; hence, accurate design and analysis methods are required for a successful antenna design. Moreover, slotted waveguide array antennas are low-profile structures, which makes them suitable candidates for conformal and structure-integrated applications. Conformal and structure-integrated system solutions are especially required for air platforms, where aerodynamics, radar cross-section (RCS) and efficient use of real estate are of utmost importance. Although the accurate and efficient design and analysis of low-profile conformal slotted waveguide arrays are of great interest, available solution methods in the literature usually suffer in terms of efficiency and memory requirements. Among the available solution methods, one of the widely used solvers are integral equation (IE) based ones that utilize the method of moments (MoM). However, IE solvers suffer from long matrix fill times, especially for matrix entries related to the cylindrically stratified media. © 2014 IEEE.Item Open Access Effect of the off-focus shift of the feed on the radiation characteristics of a 2-D parabolic reflector antenna(IEEE, 2010) Oğuzer, T.; Altıntaş, A.; Nosich, AlexanderThe parabolic reflector antennas are widely used in the telecommunication systems and generally have large aperture sizes like 50λ to 80λ and larger. Their reliable full-wave analysis with the conventional Method of Moments (MoM) or with the other numerical methods is difficult because of inaccessible speed and accuracy. This statement is valid both for 3D and 2D reflector antennas in both polarizations. The Method of Analytical Regularization (MAR) constitutes an alternative solution compared to the ordinary MoM, which can provide only 1-2 digit accuracy. It provides finer accuracy within a reasonable computation time because the computational error can be decreased simply by increasing the matrix size in MAR. We have previously developed this method for the accurate simulation of the arbitrary conical section profile 2D reflector antennas, and the corresponding codes have provided us with accurate benchmark data. Here we study a similar problem however with the feed simulated by Complex Source Point (CSP) source located at an off-focus point on the symmetry axis of a front-fed reflector antenna. The numerical results are presented for the radiation characteristics including the forward and backward directivities and the radiation patterns in all directions. © 2010 IEEE.Item Open Access Efficient analysis of large finite arrays via mom formulation with dft based acceleration algorithms(2003) Çivi, Ö. A.; Ertürk, Vakur B.; Chou, H.-T.A DFT based acceleration algorithm is combined with iterative methods to accelerate the computation of Method of Moments (MoM) analysis of electromagnetic radiation/scattering from large, finite free-standing and printed elements of phased arrays. Computational complexity of this approach is O(Ntot), where Ntot is the number of unknowns. Numerical results are presented to validate the efficiency and accuracy of the method.Item Open Access Efficient analysis of large phased arrays using iterative MoM with DFT-based acceleration algorithm(John Wiley & Sons, Inc., 2003) Ertürk, V. B.; Chou, H-T.A discrete Fourier transform (DFT)-based iterative method of moments (IMoM) algorithm is developed to provide an O(Ntot) computational complexity and memory storages for the efficient analysis of electromagnetic radiation/scattering from large phased arrays. Here, Ntot is the total number of unknowns. Numerical results for both printed and free-standing dipole arrays are presented to validate the algorithm's efficiency and accuracy.Item Open Access Efficient and accurate EM simulation technique for analysis and design of MMICs(John Wiley & Sons, Inc., 1997) Kınayman, N.; Aksun, M. I.A numerically efficient technique for the analysis and design of MMIC circuits is introduced and applied to some realistic problems. The formulation is based on the method of moments (MoM) in the spatial domain, and utilizes closed-form Green's functions. Incorporating the closed-form Green's functions into the MoM has resulted in an efficient and accurate CAD algorithm. This is because use of the closed-form Green's functions not only eliminates the calculation of the spatial-domain Green's functions, but also makes it possible to evaluate the MoM matrix elements analytically We have demonstrated the application of this method here for some stripline and microstrip geometries, and compared the results with those obtained from commercial EM software, em (Sonnet Software, Inc.)Item Open Access Efficient computation of surface fields excited on a dielectric-coated circular cylinder(IEEE, 2000-10) Erturk, V. B.; Rojas, R. G.An efficient method to evaluate the surface fields excited on an electrically large dielectric-coated circular cylinder is presented. The efficiency of the method results from the circumferentially propagating representation of the Green’s function as well as its efficient numerical evaluation along a steepest descent path. The circumferentially propagating series representation of the appropriate Green’s function is obtained from its radially propagating counterpart via Watson’s transformation and then the path of integration is deformed to the steepest descent path on which the integrand decays most rapidly. Numerical results are presented that indicate that the representations obtained here are very efficient and valid even for arbitrary small separations of the source and field points. This work is especially useful in the moment-method analysis of conformal microstrip antennas where the mutual coupling effects are important.Item Open Access Efficient evaluation of spatial-domain MoM matrix entries in the analysis of planar stratified geometries(IEEE, 2000) Kinayman, N.; Aksun, M. IAn efficient hybrid method for evaluation of spatial-domain method-of-moments (MoM) matrix entries is presented in this paper. It has already been demonstrated that the introduction of the closed-form Green's functions into the MoM formulation results in a significant computational improvement in filling up MoM matrices and, consequently, in the analysis of planar geometries. To achieve further improvement in the computational efficiency of the MoM matrix entries, a hybrid method is proposed in this paper and, through some examples, it is demonstrated that it provides significant acceleration in filling up MoM matrices while preserving the accuracy of the results.Item Open Access An efficient method for electromagnetic characterization of 2-D geometries in stratified media(IEEE, 2002) Aksun, M. I.; Çalışkan, F.; Gürel, LeventA numerically efficient technique, based on the spectral-domain method of moments (MoM) in conjunction with the generalized pencil-of-functions (GPOF) method, is developed for the characterization of two-dimensional geometries in multilayer planar media. This approach provides an analytic expression for all the entries of the MoM matrix, explicitly including the indexes of the basis and testing functions provided that the Galerkin's MoM is employed. This feature facilitates an efficient modification of the geometry without the necessity of recalculating the additional elements in the MoM matrix. To assess the efficiency of the approach, the results and the matrix fill times are compared to those obtained with two other efficient methods, namely, the spatial-domain MoM in conjunction with the closed-form Green's functions, and a fast Fourier transform algorithm to evaluate the MoM matrix entries. Among these, the spectral-domain MoM using the GPOF algorithm is the most efficient approach for printed multilayer geometries.Item Open Access Efficient methods for electromagnetic characterization of 2-D geometries in stratified media(Bilkent University, 1997) Çalışkan, FatmaNumerically efficient method of moments (MoM) algorithms are developed for and applied to 2-D geometries in multilayer media. These are, namely, the spatial-domain MoM in conjunction with the closed-from Green's functions, the spectral-domain MoM using the generalized pencil of functions (GPOF) algorithm and a FFT algorithm to evaluate the MoM matrix entries. These approaches are mainly to improve the computational efficiency of the evaluation of the MoM matrix entries. Among these, the spectral-domain MoM using the GPOF algorithm is the most efficient approach for printed multilayer geometries. The assessment of the efficiency of this method is performed on several problems, by comparing the matrix fill times for these three approaches. In addition a new iterative algorithm is developed to solve the MoM matrix equation, which is based on dividing a large object into subregions and solving the matrix equation on each subregion by considering the effects of other regions. This iterative algorithm is applied to some large geometries and is compared to a traditional LU decomposition algorithm for the assessment of its numerical efficiency. It is observed that the iterative algorithm is numerically more efficient as compared to the LU decomposition.Item Open Access Efficient use of closed-form Green's functions for the analysis of planar geometries with vertical connections(Institute of Electrical and Electronics Engineers, 1997-05) Kınayman, N.; Aksun, M. I.An efficient and rigorous method for the analysis of planarly layered geometries with vertical metallizations is presented. The method is based on the use of the closed-form spatial-domain Green's functions in conjunction with the method of moments (MoM). It has already been demonstrated that the introduction of the closed-form Green's functions into the MoM formulation results in significant computational improvement for the analysis of planar geometries. However, in cases of vertical metallizations, such as shorting pin's, via holes, etc., there are some difficulties in incorporating the closed-form Green's functions into the MoM formulation. In this paper, these difficulties are discussed and their remedies are proposed. The proposed approach is compared to traditional approaches from a theoretical point of view, and the numerical implementation is demonstrated through some examples. The results are also compared to those obtained from the commercial software em by SONNET.