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    A Dual-Band Patch Antenna with Improved Gain and Group Delay Characteristics for C-Band and X-Band Applications
    (2021) Gençoğlan, Duygu Nazan; Çolak, Şule
    In this study, a dual-band patch antenna with improved gain and group delay characteristics is proposed for C-band and X-band applications in radar and satellite communications. In the study, conventional square patch antenna is modified by partially removing the ground plane and rounding the patch corners. The radius of the rounded patch corners is determined by parametric study to achieve the best antenna performance. According to this parametric study, the value of the radius is set to 2 mm. Antenna performance is analysed both in frequency and time domains. Return Loss, Voltage Standing Wave Ratio, gain, radiation pattern, and group delay are investigated via CST Microwave Studio program. Experimental study is also performed to verify the simulation results. The results show that the designed antenna with rounded patch corners and partial ground plane has dual band characteristic. The two resonance frequencies are 6.85 GHz and 9.1 GHz in the simulation results, and 6.56 GHz and 9.12 GHz in the measurement results. The antenna has maximum gain of 5.8 dB. Additionally, group delay variation is very small in the related frequency range. Thus, it is verified that, the proposed antenna has enhanced bandwidth, improved gain and more uniform group delay as compared to the conventional square patch antenna. The proposed dual-band antenna is a quite promising structure with its appropriate gain and uniform group delay characteristics for C-band and X-band applications in radar and satellite communications.
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    A programmable digital metasurface structure designed using ANN technique
    (Taylor and Francis Ltd., 2023) Altıntarla, Gizem; Ünal, Emin; Altıntaş, Olcay; Gençoğlan, Duygu N.; Çolak, Şule; Nazeri, Amir H.; Alkurt, Fatih Özkan
    In this paper, an 8-bit programmable digital metasurface is designed in the operating frequency range from 4 to 7 GHz. A monopole antenna operating at 5 GHz is characterised by using a metasurface structure as the ground plane. Various combinations of the metasurface structure are examined by altering the state of each unit-cell between ‘ON (1)’ and ‘OFF (0)’ in the coding matrix. The purpose of the 8-bit programmable digital metasurface is to control the electromagnetic wave effectively in the frequency range of interest. Dynamically controllable metasurface structure is utilised to change the unit cells’ configurations. In addition, the proposed adjustable metasurface is capable to control the monopole antenna directivity, gain and main lobe magnitude, efficiently. According to various via conditions, different metasurface-based antenna parameters such as return loss (S11), radiation pattern, directivity and surface current distribution are investigated by means of the commercial numerical simulation software, CST microwave studio. Employing the simulation results of the metasurface-based antennas, the artificial neural network (ANN) data set is obtained. 128 activation conditions are trained and tested by Levenberg Marquart learning algorithm. During the ANN procedure, MATLAB is used to obtain accurate results by changing the rate of test and training data set. © 2022 Informa UK Limited, trading as Taylor & Francis Group.
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    Design of Notched Rounded Bowtie Antenna for Ultra-Wideband Communication Systems
    (2019) Gençoğlan, Duygu Nazan; Çolak, Şule
    In this paper, a modified bowtie antenna structure is proposed for Ultra-Wideband communicationsystems. This antenna is obtained by rounding and notching the edges of antenna arms. Antennaparameters for the designed structure are examined according to the restrictions specified by FederalCommunications Commission. Thus, Return Loss (S11), Voltage Standing Wave Ratio (VSWR), gain,radiation pattern and impedance are observed in the 3.1 GHz - 10.6 GHz frequency range. Additionally,the effect of arm length and dielectric material on antenna performance are interpreted in the same range.According to obtained results, the proposed structure satisfies the bandwidth requirements for Ultra-Wideband systems. Gain and impedance variations are also in acceptable limits for Ultra-Widebandapplications. The proposed antenna is analyzed through CST Microwave Studio program.
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    Improvement and optimization of thin dipole for UWB applications
    (Islamic Azad University, 2018) Gençoğlan, Duygu Nazan; Çolak, Şule
    In this paper, thin dipole is investigated in the 3.1-10.6 GHz Ultra-Wide Band frequency range. The study includes the design of half wave dipole antenna with different dipole radii to improve the antenna characteristics. Antenna parameters including return loss, Voltage Standing Wave Ratio, -10 dB bandwidth and radiation pattern are examined according to Federal Communication Commission regulations and Ultra-Wide Band system requirements in this frequency range. Additionally, two optimization techniques, Genetic Algorithm and Particle Swarm Optimization are applied to obtain the best dipole radius. CST Microwave Studio, an electromagnetic simulation program, is used for the design of the antenna structure and the simulation purposes. The simulation is performed in transient mode. The results show that the antenna performance can be improved by selecting the suitable antenna dimensions. Additionally, Genetic Algorithm and Particle Swarm Optimization techniques are compared in terms of time consumption to obtain the best VSWR and return loss values. The results also depict that Genetic Algorithm yields better results for the proposed structure. © 2017 Majlesi Branch, Islamic Azad University.
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    Investigation of Origami Inspired Sub-6 GHz Accordion Monopole Antenna for 5G Applications
    (2021) Gençoğlan, Duygu Nazan; Çolak, Şule
    This study presents an origami inspired sub-6 GHz accordion monopole antenna for 5G applications. Parametric study is performed by varying monopole height, fold width and bevel angle to examine the antenna performance in the 1 GHz - 6 GHz frequency range. The proposed antenna is designed with the values that yield the best performance in accordance with the results of parametric study. Antenna behavior is then evaluated in terms of Return Loss, gain and radiation pattern. The proposed antenna operates in 1.22 GHz - 6 GHz frequency range which covers almost the entire sub-6 GHz range with an approximate impedance bandwidth of 132%. Hence, the designed antenna structure has a good performance in the sub-6 GHz and it is a promising design for 5G applications.
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    Optimizing the Gain and Directivity of a Microstrip Antenna with Metamaterial Structures by Using Artificial Neural Network Approach
    (Springer, 2021) Sağık, Metin; Altıntaş, Olcay; Ünal, Emin; Özdemir, Ersin; Demirci, Mustafa; Çolak, Şule; Karaaslan, Muharrem
    The purpose of this study is to improve the gain and directivity of the microstrip patch antenna by means of metamaterial (MTM) structures. As it is known, antennas have power densities in a certain direction, and the radiation curves of the antennas are shaped by orienting them according to this power density. Based on this feature of the antennas, it is aimed to improve the gain and directivity of microstrip patch antennas with the most suitable structures thanks to metamaterial (MTM) structures. The MTM structures designed are interacted with the antenna. Then, the frequency, gain and directivity of the antenna are trained by the artificial neural network technique to estimate the most appropriate values. As a result, the gain and directivity of the antenna are improved by the interaction of microstrip patch antenna and MTM structures and the results are interpreted on the figures. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.
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    Pandemik Hastalıkların Kesin Epidemiyolojik Özelliklerini Taşıyan Kapsamlı Parametrik Modelin Sınırlı Matematiksel Ve Meta Sezgisel Optimizasyon Yöntemleri Ile Geliştirilmesi
    (2023) Tutsoy, Önder; Balıkçı, Kemal; Çolak, Şule
    Pandemi hastalıklarının çok boyutlu tahmin modelleri, kendilerine has epidemiyolojik karakterlerini yansıtacak şekilde kurgulanmalıdır. Bu yazıda, büyük ölçekli bir epidemiyolojik modelin bilinmeyen parametrelerini öğrenmek için grafik teorisi tabanlı kısıtlı çok boyutlu (CM) matematiksel ve meta-sezgisel algoritmalar (MA) oluşturulmuştur.
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    Radar and Non-Contact Sensing
    (Elsevier, 2022) Ebrahim, Malikeh P.; Tom, Neil; Gençoğlan, Duygu Nazan; Çolak, Şule; Yuce, Mehmet R.
    Radar systems have received attention extensively in recent years for remote detection and monitoring for healthcare and security applications. Monitoring the primary vital signs is essential to evaluate people’s physical and occasionally mental health, to assess potential symptoms of diseases and to follow up on patients’ recovery. Human activity sensing plays a vital role in intelligent home and health monitoring applications. Data observed from human activities is appropriated for improving our lifestyle. In this work, recent implementations of both contact and remote radar systems are presented. The article also discusses required antennas’ specifications for mentioned applications. © 2023 Elsevier Ltd. All rights reserved
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    Stokastik, Kararsız, Değişken Zaman Kontrol Sinyali Gecikmeli ve Belirsiz Değişkenli Doğrusal Sistemlerde Öğrenme Temelli Kontrolör Tasarımı ve Analizi
    (2017) Tutsoy, Önder; Bankana, Duygun Erol; Çolak, Şule
    Bu projenin ilk asamasında, sensör ölçümleri kullanarak sistem tanımlama/modelleme algoritmaları (system identification) olan çıkıs hatası (output error), öz baglanımla degisen ortalama (autoregressive moving average), harici girisli öz baglanımla degisen ortalama (autoregressive moving average with exogenous input) sistemleri için uyarlamalı tahminci tasarlanmıs ve analiz edilmistir. Hem sistem tanımlama temelli modeller ile hem de uyarlamalı tahminci ile elde edilen Q-fonksiyonu ve kontrol sinyal sonuçları analiz edilmis ve bu sonuçlar gerçek sistem parametrelerinin kullanılması durumunda elde edilen sonuçlar ile karsılastırılmıstır. Projenin ikinci asamada, parametrik ve parametrik olmayan degiskenlerin bulunması durumunda birinci basamakta tasarlanan uyarlamalı tahminci gelistirilerek, simülasyon çalısmaları ile kararlılık, ögrenme ve kontrol performansı test edilmistir. Ayrıca, stokastik, kararsız, dogrusal sistemin kontrol sinyalinde zamanla degisen bir gecikme olması durumu da bu kapsamda dikkate alınmıs, ve gerek ögrenme gerekse de kontrol sonuçları analiz edilmistir. Projenin üçüncü asamada, uyarlamalı tahminci kontrol sinyali hakkında herhangi bir varsayım yapılmadan Q-fonksiyon ile birlikte kontrol politikasını da ögrenebilecek sekilde gelistirilmis ve simülasyon ortamında uygulanmıstır. Dördüncü asamada ise çok girisli ve çok çıkıslı sistemler için uyarlamalı tahminci yeniden tasarlanmıs ve simülasyon sonuçları (ögrenme süresi, kullanılan fonksiyon yaklasımının etkinligi, kesif amaçlı eklenen gürültünün rolü gibi) analiz edilmistir. Her bir durum için tasarlanan uyarlamalı tahmincinin optimum düzeyde ögrenme ve kontrol sonuçları üretebilmesi için uyarlamalı tahminciye ait parametrelerin rolü, ve deger aralıkları ayrıca belirlenmistir.
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    Tunable left-hand characteristics in multi-nested square-split-ring enabled metamaterials
    (Central South University of Technology, 2020) Abdulkarim, Yadgar. I.; Deng, Lian-wen; Yang, Jun-liang; Çolak, Şule; Karaaslan, Muharrem; Huang, Sheng-xiang; He, Long-hui
    Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring resonators on the top side and a set of wires on the back side is proposed. Scattering parameters are retrieved by high-frequency structure simulator (HFSS) software based on the finite element method. Effects of square-split-ring number on the left-hand characteristics containing negative values of permittivity, permeability, and refractive index have been intensively investigated. Simulated results show that obvious resonant left-hand characteristics could be observed within 8–18 GHz, and the resonant frequency counts are inclined to be in direct proportion to the square-split-ring number over 8–18 GHz. Besides, the proposed sandwiched metamaterial with three square-split-ring resonators and three wires presents the widest frequency band of left-hand characteristics in a range of 8–18 GHz. Further, electromagnetic field distributions demonstrated that the induced magnetic dipole dominates the resonant absorption. The multi-peak resonance characteristics of square-split-ring resonant structure are considered to be a promising candidate for selective-frequency absorption or modulation toward microwave frequency band. © 2020, Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature.