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    The effects of bends in waveguides for aviation and non-aviation applications / Dalga kılavuzlarındaki bükülmelerin havacılık ve havacılık dışı uygulamalara etkileri
    (İnan Eryılmaz, 2020) Doğan Çelenk, Esra; Ege, Tuncay; Ünal, Emin
    Waveguides, one of the most effective ways to carry electromagnetic energy, have application areas such as microwave communication systems, internet networks, radars, space exploration, optics and aviation. Sudden changes in the size or shape of the waveguides, such as bends and twists, can cause reflections and overall loss of efficiency. When such a change is required, the bends and twists of the waveguides must provide certain conditions to prevent reflections. This paper describes a new method to evaluate the attenuation constant for a circular dielectric or metallic waveguide having uniform curvature. When the radius of curvature “Ro” is large compared to the radius “a” of the waveguide field components can be obtained directly using toroidal coordinate system for the curved section of the waveguide instead of obtaining from those obtained for straight waveguide using perturbation techniques. Results obtained show excellent agreement with those given in the literature.
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    New generation WIMAX antenna based on metamaterial superstrate
    (INOE, 2013) Doğan Çelenk, Esra; Ünal, Emin; Kapusuz, Dilek
    In this study, a microstrip patch antenna system based on metamaterial superstrate (PAMS) is proposed. Patch antennas suffer from low gain and directivity. A significant study is realized to circumvent this drawback by implementing a patch antenna based on metamaterial superstrate. The effective medium parameters of the unit cell are retrieved and planar three-layer metamaterial composed of unit cell arrays are used as a superstrate for gain and directivity enhancement of a microstrip patch antenna at 5.6 GHz. The gain and directivity efficiency of the proposed system is about 13.474 dB and 12.40 dB, respectively at 5.6 GHz. In this study, Simulation and measurement results are also presented. The PAMS consists of periodically arranged metamaterial array unit cells as a superstrate and patch antenna. The system is designed to operate from 5.2 GHz to 6 GHz with a return loss of -32.174 dB at first mode (5.6 GHz). Both simulation and measurement results of the PAMS show that this configuration is able to realize a broadside gain 72% of the maximum gain from the metamaterial superstrate. The effects of the compactness of the arrays are also investigated. It is observed that return loss is directly proportional with the compactness of the superstrate. The maximum return loss (-32.174 dB) is obtained with seven arrays of metamaterial.