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    Development of extraction techniques for dielectric constant from free-space measured S-parameters between 50 and 170 GHz
    (Springer, 2017) Ozturk, Turgut; Elhawil, Amna; Uluer, Ihsan; Guneser, Muhammet Tahir
    This paper is a comprehensive study on Newton-Raphson technique used in millimeter wave frequencies for material characterization. Various algorithms are used for extracting the complex permittivity of a material from measured S-parameters. Efficiency of the methods depends on the initial guess and the accuracy of measured S-parameters for each thickness and frequency band. In this paper, we suggest the initial-value estimation method that helps to estimate a proper value for starting the algorithm. Moreover, an alternative extraction process is modelled that does not require new measured S-parameters or extracting process for each frequency band and thickness with a composed database. The estimation process is conducted partially as V (50-75 GHz), W (75-110 GHz), and D (110-170 GHz) frequency bands.
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    Extracting the dielectric constant of materials using ABC-based ANNs and NRW algorithms
    (Taylor & Francis Ltd, 2016) Ozturk, Turgut; Elhawil, Amna; Dugenci, Muharrem; Unal, Ilhami; Uluer, Ihsan
    Five different Nicolson-Ross-Weir (NRW) extracting techniques are used to extract the dielectric constants of Teflon, Rexolite, Glass (borosilicate and soda-lime), Paper, and Ultralam 3850HT from S-parameters. The results of these extraction techniques are used to train the Artificial Neural Networks. In order to improve the accuracy of the results, the weights of ANNs are calculated using artificial bee colony estimation method. The results are compared with that obtained using NRW, Newton-Raphson, and genetic algorithm. The obtained results indicate that the proposed model gives good extracted parameters as compared with the previously published results.