Browsing by Author "Aksun, M. İrşadi"
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Item Open Access Closed-form green's functions of HED, HMD, VED, and VMD for multilayer media(IEEE, 1993-06-07) Aksun, M. İrşadi; Dural, G.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 a general, multilayer, planar medium. The spectral domain Green's functions in a arbitrary layer are obtained through the Green's function of the source layer by using a recursive algorithm.Item Open Access Comparative evaluation of absorbing boundary conditions using Green's functions for layered media(IEEE, 1995) Aksun, M. İrşadi; Dural, G.Absorbing boundary conditions are comparatively studied using the Green's functions of the vector and scalar potentials for multilayer geometries and general sources. The absorbing boundaries are introduced as additional layers with predefined reflection coefficients into the calculation of the Green's functions. The Green's functions are calculated using different reflection coefficients corresponding to different absorbing boundaries and compared to those obtained with no absorbing boundary. This approach provides an absolute measure of the effectiveness of different absorbing boundaries.Item Open Access Comparative evaluation of absorbing boundary conditions using Green's functions for layered media(Institute of Electrical and Electronics Engineers, 1996-02) Aksun, M. İrşadi; Dural, G.Absorbing boundary conditions are comparatively studied using the Green's functions of the vector and scalar potentials for multilayer geometries and general sources. Since the absorbing boundaries are introduced as additional layers with predefined reflection coefficients into the calculation of the Green's functions, this approach provides an absolute measure of the effectiveness of different absorbing boundaries. The Green's functions are calculated using different reflection coefficients corresponding to different absorbing boundaries and compared to those obtained with no absorbing boundary. It is observed that the perfectly matched layer (PML) is by far the best among the other absorbing boundary conditions whose reflection coefficients are available.Item Open Access Efficient and robust approach for the derivation of closed-form Green's functions(IEEE, 1995) Aksun, M. İrşadiSpatial domain Green's functions for multilayer, planar geometries are cast into closed forms with two-level approximation of the spectral domain representation of the Green's functions. This approach is very robust and much faster compared to the original one-level approximation.Item Open Access Efficient methods for electromagnetic characterization of 2-D geometries in stratified media(IEEE, 1998) Çalışkan, Fatma; Aksun, M. İrşadi; Gürel, LeventNumerically 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-form Green's functions, the spectral-domain MoM using the generalized pencil of functions (GPOF) algorithm and 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.Item Open Access Fast multipole method in layered media: 2-D electromagnetic scattering problems(IEEE, 1996) Gürel, Levent; Aksun, M. İrşadiIn this study, the Fast Multipole Method (FMM) is extended to layered-media problems. As an example, the solution of the scalar Helmholtz equation for the electromagnetic scattering from a two-dimensional planar array of horizontal strips on a layered substrate is demonstrated.Item Open Access Hybrid model for probe-fed rectangular microstrip antennas with shorting pins(IEEE, 2000) Mutlu, Selma; Aksun, M. İrşadiFor a probe-fed microstrip antenna, it is quite common to employ the cavity model to find the field distribution under the patch and other electrical properties. Therefore, a multiport analysis technique based on the cavity model is usually employed to predict the input impedance of a probe-fed microstrip antenna with shorting pins. However, this approach does not provide any information about the field distribution under the patch with the shorting pins, which is usually used to calculate the radiation properties of the patch antenna. In this study, shorting pins are considered as current sources with unknown amplitudes, and the field distribution under the patch is obtained as a linear superposition of the contributions from each source via cavity model. Then, the unknown current densities over the shorting pins are determined by implementing the boundary condition of the tangential electric field on the pins. This is a hybrid approach because the field distribution is calculated from the cavity model, and the current densities over the shorting pins are obtained from the point matching of the resulting field distributions over the shorting conductors. The input impedance results found from this approach agree extremely well with those obtained from the multiport analysis, which shows that the proposed approach predicts both the input impedance and the field distribution under the patch. In addition, since the feeding probe is also made of PEC, the electric field under the patch should satisfy the boundary condition on this conductor as well. In the application of the cavity model, this is always ignored, with the assumption that the source probe is too thin to affect the field distribution under the patch significantly. In this study, the boundary condition of the electric field is implemented over the source, and its effect on the field distribution, in turn on the resonant frequency, is demonstrated.