Browsing by Author "Kalfa, M."

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Open Access
Analysis of slotted sectoral waveguide arrays with multilayered radomes
(Institute of Electrical and Electronics Engineers Inc., 2016) Kalfa, M.; Ertürk, V. B.
A method of moments/Green's function (MoM/GF) technique in the space domain is used for the rigorous and fast analysis of cylindrically conformal slotted sectoral waveguide arrays (SSWGAs) in the presence of multilayered cylindrical dielectric radomes. Representing the slots by fictitious magnetic currents via the equivalence principle, the geometry is divided into two regions and separate GF representations for each region are developed to be used in conjunction with the MoM procedure. Particularly, in the region that constitutes the cylindrically stratified medium, the newly developed closed-form GF representations for magnetic currents are valid for all source and observation points, including the source region (where source and observation points are on the top of each other). Basic performance metrics of an SSWGA such as equivalent slot currents, S-parameters, radiation patterns in the presence of a multilayered cylindrical radome are presented to assess the accuracy and efficiency of the proposed technique. © 1963-2012 IEEE.
Open Access
Closed-form green's function representations for mutual coupling calculations between apertures on a perfect electric conductor circular cylinder covered with dielectric layers
(IEEE, 2011-06-07) Akyüz, M. S.; Ertürk, V. B.; Kalfa, M.
Closed-form Green's function (CFGF) representations are developed for tangential magnetic current sources to calculate the mutual coupling between apertures on perfectly conducting circular cylinders covered with dielectric layers. The new representations are obtained by first rewriting the corresponding spectral domain Green's function representations in a different form (so that accurate results for electrically large cylinders, and along the axial line of a cylinder can be obtained). Then, the summation over the cylindrical eigenmodes is calculated efficiently. Finally, the resulting expressions are transformed to the spatial domain using a modified two-level generalized pencil of function method. Numerical results are presented showing good agreement when compared to CST Microwave Studio results.
Open Access
Error control of multiple-precision MLFMA
(Institute of Electrical and Electronics Engineers, 2018) Kalfa, M.; Ergül, Ö.; Ertürk, Vakur
We introduce and demonstrate a new error control scheme for the computation of far-zone interactions in the multilevel fast multipole algorithm when implemented within a multiple-precision arithmetic framework. The proposed scheme provides the optimum truncation numbers as well as the machine precisions given the desired relative error thresholds and the box sizes for the translation operator at all frequencies. In other words, unlike the previous error control schemes which are valid only for high-frequency problems, the proposed scheme can be used to control the error across both low- A nd high-frequency problems. Optimum truncation numbers and machine precisions are calculated for a wide range of box sizes and desired relative error thresholds with the proposed error control scheme. The results are compared with the previously available methods and numerical surveys.