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    A compact 4 x 4 reconfigurable MIMO antenna design with adjustable suppression of certain frequency bands within the UWB frequency range
    (Elsevier Gmbh, 2023) Durukan, Tulun; Altuncu, Yasemin
    This paper introduces a novel 4 x 4 multiple-input multiple-output (MIMO) antenna design with a reconfigurable operating band within the Ultra-Wideband (UWB) range. The antenna consists of four rectangular radiating elements arranged symmetrically and orthogonally on a defected ground plane. The design incorporates switching elements that allow adjustable and reversible suppression of specific bands within the UWB range, enabling the antenna to operate in three different modes: UWB, X-band, and dual-band with sub-6GHZ and X-band. Thus, a single UWB antenna can serve as three different antennas, suppressing certain frequencies as required. To mitigate mutual coupling between adjacent antenna elements, four thin stubs are strategically placed at the center of the ground plane, forming a square with open corners. When one of the antenna elements is excited, this structure acts as an insulator, ensuring that the surface current is confined solely to that element and not induced in others. Experimental verification of the proposed design was performed by fabricating and testing the antenna. The results indicated good agreement between simulation and measurement data for various parameters, including S-parameters, radiation patterns, gains, and MIMO parameters such as envelope correlation coefficients (ECC), diversity gain (DG), mean effective gain (MEG), and total active reflection coefficient (TARC).
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    Reconstruction of Two-Dimensional Objects Buried into Three-Part Space with Locally Rough Interfaces via Distorted Born Iterative Method
    (Emw Publishing, 2019) Altuncu, Yasemin; Durukan, Tulun; Akdogan, Riza Erhan
    In this paper, the reconstruction problem of inaccessible objects buried into a three-part space with locally rough interfaces is solved by Distorted Born Iterative Method (DBIM). DBIM requires the calculation of the background electric field and Green's function in every iteration step via the solution of the direct scattering problem. Here, they are calculated numerically by using the buried object approach (BOA) which is very useful in the solutions of the problems including stratified media with locally rough interfaces. Various numerical applications have been performed to demonstrate the applicability and efficiency of the method. The method was found to be very successful in reconstructing moderate contrast objects when they were buried in the middle space. In this case, the method works effectively even if the buried objects and interface roughnesses have complex geometric structures. Moreover, the multiplicity of buried objects has no negative effect on the reconstruction results. Nevertheless, the results of reconstruction deteriorate when objects are buried in the bottom space. However, the accuracies of them are still on an acceptable level in this situation.
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    Reconstruction of two-dimensional objects buried into three-part space with locally rough interfaces via distorted born iterative method
    (Electromagnetics Academy, 2019) Altuncu, Yasemin; Durukan, Tulun; Akdogan, Riza Erhan
    In this paper, the reconstruction problem of inaccessible objects buried into a three-part space with locally rough interfaces is solved by Distorted Born Iterative Method (DBIM). DBIM requires the calculation of the background electric field and Green’s function in every iteration step via the solution of the direct scattering problem. Here, they are calculated numerically by using the buried object approach (BOA) which is very useful in the solutions of the problems including stratified media with locally rough interfaces. Various numerical applications have been performed to demonstrate the applicability and efficiency of the method. The method was found to be very successful in reconstructing moderate contrast objects when they were buried in the middle space. In this case, the method works effectively even if the buried objects and interface roughnesses have complex geometric structures. Moreover, the multiplicity of buried objects has no negative effect on the reconstruction results. Nevertheless, the results of reconstruction deteriorate when objects are buried in the bottom space. However, the accuracies of them are still on an acceptable level in this situation. © 2019, Electromagnetics Academy. All rights reserved.