LEE- Telekomünikasyon Mühendisliği Lisansüstü Programı

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http://hdl.handle.net/11527/19468

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Konu "anten" ile LEE- Telekomünikasyon Mühendisliği Lisansüstü Programı'a göz atma
  • Öge
    5G uygulamaları için dairesel polarizasyonlu ve metayüzeyli mikroşerit MIMO anten tasarımı
    (Lisansüstü Eğitim Enstitüsü, 2023) Koçer, Mustafa ; Günel, Murat Tayfun ; 782952 ; Telekomünikasyon Mühendisliği Bilim Dalı
    Bu tez çalışmasında, 6 GHz altı 5G frekans spektrumuna yönelik n78 bandı olarak adlandırılan 3.3-3.8 GHz frekans aralığında 4x4 çok girişli çok çıkışlı bir anten tasarımı hedeflenmiştir. Öncelikle çok girişli, çok çıkışlı anten tasarımında kullanılacak olan mikroşerit anten tasarımı gerçekleştirilmiştir. Mikroşerit antenin dairesel polarizasyonda çalışması için kare yama tercih edilmiştir. Tercih edilen kare yamanın köşelerinde sol el dairesel polarizasyona yönelik kesik daire ve kesik üçgen kullanılmıştır. Yapılan tasarımlara göre köşelerinden kesik daire kullanılarak yapılan mikroşerit anten tasarımı kesik üçgen kullanılarak yapılan tasarıma göre daha iyi sonuç vermiştir. Sol el dairesel polarizasyona yönelik köşelerinde kesik daire oluşturularak tasarlanan mikroşerit antenin performansını artırmak için üzerine hava boşluğu olmadan 4x4 metayüzey yerleştirilmiştir. Böylece metayüzeyin oluşturduğu yüzey dalgalarının kesim frekanslarında mikroşerit anten rezonansa girmiştir. Mikroşerit antenin istenilen yansıma katsayısı ve eksenel oranı aşağı frekansta (3.4 GHz) iken metayüzeyin yüzey dalgaları yukarı frekanslardadır (3.9-4 GHz). Bu sayede anten geniş bantta çalışmaktadır. Kullanılan metayüzey sayesinde FR-4 alttaş malzemesi ile tasarlanan bu antenin verimliliği, kazancı artmıştır ve geniş bantta dairesel polarizasyonda çalışması sağlanmıştır. Ayrıca mikroşerit yama antenin ortasında çapraz yarık oluşturularak metayüzeyli mikroşerit anten daha düşük yansıma katsayısına sahip olmuştur. Metayüzeyli mikroşerit antenin tasarımında kullanılan alttaş malzemesinin kalınlıkları ve kullanılan alttaş malzemesinin performansa etkileri incelenmiştir. Ayrıca tasarımda kullanılan 4x4 metayüzeyin köşelerinden kesik daire şekli oluşturularak antenin dairesel polarizasyon bant genişliği artırılmış ve daha geniş bantta yüksek kazanç elde edilmesi sağlanmıştır. TLC-32 alttaş malzemesi kullanılarak tasarlanan metayüzeyli mikroşerit anten ile 6 GHz altı 5G uygulamalarına yönelik 3.3-3.8 GHz' te dört kapılı (iki kapı sağ el dairesel, iki kapı sol el dairesel polarizasyon) olacak şekilde MIMO anten tasarımı gerçekleştirilmiştir. Tasarlanan MIMO antenin 1. ve 3. kapıları sol el dairesel polarizasyona yönelik iken 2. ve 4. kapıları sağ el dairesel polarizasyona yöneliktir ve her kapı kendi aralarında 90° döndürülerek tasarlanmıştır. MIMO antenin izolasyonunu artırmak için MIMO antenin ortasında alttaşa entegreli dalga kılavuzu yapısı kullanılmıştır. Buna ek olarak mikroşerit anten katmanına ve metayüzey katmanına parazitik elemanlar eklenmiştir. Böylece tasarımı gerçekleştirilen MIMO anten yüksek izolasyonlu ve kapılarının hepsi yüksek kazançlı olacak şekilde dairesel polarizasyonda çalışmaktadır.
  • Öge
    A new antenna design methodology based on performance analysis of MIMO and defining novel antenna parameters
    (Graduate School, 2024-05-08) Yussuf, Abubeker Abdulkerim ; Paker, Selçuk ; 504122305 ; Telecommunications Engineering
    The rapid growth of wireless technology has created a significant demand for the design of Multiple-Input Multiple-Output (MIMO) antennas for wireless devices. MIMO antennas play a crucial role in meeting the requirements of current and future wireless standards, as they can maximize data rates in wireless communication systems by utilizing multiple channels within the same bandwidth. However, designing MIMO antennas for compact devices presents considerable challenges. The limited space between antennas leads to increased coupling and high correlation, which can negatively impact their performance. To address these challenges, this thesis proposes a new antenna design methodology based on MIMO performance metrics and defining antenna parameters. Existing metrics for conventional antenna systems are insufficient for fully assessing MIMO antenna performance. This methodology provides a systematic approach to optimize antenna configurations, mitigate mutual coupling, and achieve desired performance characteristics, paving the way for enhanced system capacity. The thesis introduces a novel methodology for designing MIMO antennas that relies on crucial performance metrics and defining parameters. These parameters include factors such as antenna spacing, slot dimensions, strip placements, and parasitic element sizes, which are important for meeting the requirements of modern wireless standards within the LTE and sub-6 GHz 5G bands. The research presents five distinct MIMO antenna designs, each optimized for specific requirements and validated through simulations and experimental measurements. Firstly, the dual-band Vivaldi-shaped MIMO antenna covers the 5G NR bands n78 and n79, boasting gains of over 7.63 dBi and 8.5 dBi respectively, while maintaining mutual coupling below -30 dB. Secondly, the concentric octagonal-shaped MIMO antenna is designed for 5G UE applications in the n38 band, achieving a gain of over 5 dBi and mutual coupling below -25 dB. Thirdly, the compact quad-element MIMO antenna is designed for LTE/Wi-Fi applications, exhibiting high isolation exceeding 17 dB and a channel capacity loss lower than 0.6 b/s/Hz. Fourthly, the wideband MIMO antenna is a single-element design with quad-ports, operating in the 2.1/2.3/2.6 GHz and 2.4 GHz bands. It offers an operating bandwidth of 2-3.0 GHz, reflection coefficients below -10 dB, isolation under -25 dB using synthesized pi-networks TL-based decoupling network, and a diversity gain of approximately 10 dB. Finally, a quad-element MIMO antenna utilizing a modified Apollony fractal, designed for 5G wireless communications, achieves S11 below or equal to -10 dB within the impedance bandwidth, with low mutual coupling below -20 dB. The thesis explores various decoupling strategies to mitigate mutual coupling and enhance antenna performance. These strategies include antenna placement and orientation, parasitic elements, neutralization, and synthesized Pi-networks TL-based decoupling network topology. Each design is thoroughly evaluated through simulations and experimental measurements, with performance metrics including S-parameters, envelope correlation coefficient (ECC), channel capacity, total active reflection coefficient (TARC), and diversity gain. The research demonstrates the feasibility and effectiveness of the proposed methodology for designing compact MIMO antennas that offer improved performance metrics, making them well-suited for use in 5G and beyond wireless communication systems.
  • Öge
    Antenna design for breast cancer detection and machine learning approach for birth weight prediction
    (Graduate School, 2024-01-03) Kırkgöz, Haluk ; Kurt, Onur ; 504201348 ; Telecommunications Engineering
    With the advancement of technology in the biomedical field, new diagnostic and treatment methods and new devices are being developed day by day. However, although this situation seems mostly advantageous, the development of technology in some areas poses some difficulties for both patients and doctors in terms of diagnosis and treatment. For example, electromagnetic radiation used for diagnostic purposes can be harmful to patients. In addition, the precision and accuracy of the results of the techniques used also contain a margin of error, and it becomes important for doctors to consider these margins of error in the decision-making process. Based on the briefly mentioned problems, alternative methods are proposed for two different fields in this thesis. In the first study, an alternative method different from standard methods for breast cancer diagnosis will be proposed, and in the second study, machine learning approaches that can determine the baby's birth weight with high accuracy will be presented. Breast cancer remains a major global health problem and requires continuous improvements in diagnostic and control methods to achieve better patient outcomes during treatment and early detection of the disease. As breast cancer is one of the most common and dangerous diseases among women worldwide, it is therefore critical to diagnose it quickly. Considering that breast cancer is the second-leading cause of cancer-related mortality in women, the need for efficient and non-invasive diagnostic methods has become greater. The negative consequences of conventional approaches in terms of their operating principles or application methodologies give rise to this demand. In response to the limitations inherent in traditional diagnostic techniques, microwave imaging methods have been developed for effective diagnosis of breast cancer. The feasibility and efficacy of using microstrip patch antennas for breast cancer detection are especially examined in the first section of this thesis, which explores an alternative medical method. These antennas can be considered an important development in the medical industry as they are able to detect small electromagnetic oscillations that are indicative of early-stage cancer. This study introduces the design and simulation of a rectangular microstrip patch antenna on an FR-4 substrate operating at 2.45 GHz in the ISM band for breast cancer detection. Utilizing the Computer Simulation Technology (CST) software, both the proposed antenna and a five-layer breast phantom, with and without a 5 mm-radius tumor, were comprehensively designed. A breast phantom modeled as a hemisphere and an embedded tumor modeled as a sphere with different dielectric characteristics were successfully simulated. The antenna's performance was evaluated at varying distances from the phantom, revealing alterations in parameters such as electric field, return loss, voltage standing wave ratio, efficiency, specific absorption rate, etc., in the presence of a tumor. The simulation results at different antenna locations show discernible differences in values with and without tumors, indicating that a tumor significantly influences power reflection back to the antenna. The VSWR of the antenna, lower than 2, aligns with acceptable VSWR limits. Furthermore, the proposed antenna demonstrates increased electric field strength in the presence of a tumor. In addition, simulation outcomes in free space and with a 3-D breast phantom indicated that the antenna, positioned 20 mm from the breast phantom, is more efficient in tumor identification compared to the one located at 40 mm. Given its tumor detection capability and satisfactory SAR values, the proposed antenna emerges as a promising tool in biomedical applications. Future studies will explore alternative antenna geometries and techniques to enhance performance and increase tumor detection sensitivity. Birth weight is a critical indicator of both pregnancy progress and infant development, exerting a substantial influence on short- and long-term health conditions in newborns. In other words, fetal weight emerges as a pivotal indicator of short- and long-term health problems in newborns, both in developed and developing countries. Understanding the contributing factors to low birth weight (LBW) and high birth weight (HBW) can inform the implementation of optimal interventions for the population's health. In the second study, we present our research on the prediction of birth weight classification through the application of various machine learning algorithms. For this investigation, 913 medical observation units, each characterized by 19 features encompassing actual birth weight information and ultrasound measurements, were employed. In the study, a number of data preprocessing steps were performed on the data set before the data set was directly used to train the classifier models. To address the issue of imbalanced data across classes, we implemented the synthetic minority oversampling technique (SMOTE). Additionally, feature scaling was applied to standardize numerical attributes within a particular range in the dataset, as there are different physiological variables with different units and orders of magnitude. In this work, nine different machine learning classifier models are used. They are decision tree, discriminant analysis, naive bayes, support vector machine, k-nearest neighbor, kernel approximation, ensemble classifier, artificial neural network, and logistic regression. The hyperparameters of each model were kept at default values, and no hyperparameter tuning was made. To evaluate the performance of nine distinct supervised machine learning algorithms, we compared birth weight classification models with and without feature selection, utilizing numerous evaluation metrics. These different metrics are accuracy, sensitivity, specificity, positive predictive value, negative predictive value, F1 score, and area under the receiver operating curve. Referring to the Pearson correlation coefficient technique applied to the data set, abdominal circumference, head circumference, biparietal diameter, femur length, and hemoglobin levels at the 0th and 6th hours are highly correlated with birth weight. The results of our analysis highlight that the subspace kNN-based ensemble classifier outperforms other machine learning models, achieving the best macro-average accuracy of 99.87% without feature selection and 99.75% with feature selection. Additionally, we observed that the bilayered neural network exhibits similar performance to the kNN-based model, with the best macro-average accuracy of 99.62%, irrespective of feature selection. Furthermore, principal component analysis (PCA) was applied to the data set as an unsupervised method for birth weight classification. The outcome clearly demonstrates the successful classification of most data points by PCA. The findings of this study underscore the potency of machine learning as a robust and non-invasive method for accurately predicting the birth weight classification of infants. In light of these factors, a health program could be devised to prevent the occurrence of LBW and HBW since recognition of LBW or HBW in a newborn may signal potential problems that could manifest immediately after birth or later in life. At the end of the thesis, performance improvement methods have been proposed based on the two studies we conducted, and we hope that the results of our research will shed light on future studies.
  • Öge
    Measurement-based antenna misalignment analysis and angle of arrival estimation for terahertz wireless communication systems
    (Graduate School, 2023-09-07) Nayir, Hasan ; Kurt Karabulut, Güneş ; 504201323 ; Telecommunication Engineering
    As the demand for instant information and faster data transmission rates increases, the bandwidth requirements of wireless communication systems are predicted to exceed the capabilities of current millimeter-wave (mm-Wave) systems. To address this need, Terahertz (THz) wireless communication systems have emerged as a promising option for 6G and future wireless systems, offering a large contiguous bandwidth in the range of 0.1 THz - 10 THz that is applicable for both indoor and outdoor communication. However, the implementation of THz communication systems presents challenges due to substantial propagation losses, molecular absorption, and the effects of antenna misalignment on system performance. This master's thesis focuses on addressing the aforementioned challenges in THz communication systems. Our primary objective is to analyze the effects of antenna misalignment on system performance. To achieve this, we have designed and implemented a comprehensive measurement system capable of accurately characterizing the impact of misalignment on THz communication channels. By conducting extensive experiments and measurements, we aim to quantify the degradation in system performance caused by antenna misalignment and establish a thorough understanding of the underlying mechanisms. Furthermore, we aim to develop novel angle of arrival (AoA) estimation techniques specifically tailored for THz communication systems. These techniques will leverage advanced signal processing algorithms and innovative antenna array designs to accurately estimate the arrival angles of incoming signals, even in the presence of misalignment. By improving the accuracy of AoA estimation, we anticipate significant advancements in beamforming, spatial multiplexing, and other key aspects of THz system design. Through our research efforts, we strive to contribute to the development of more efficient and reliable THz wireless communication systems for future generations. By mitigating the impact of antenna misalignment and enhancing the accuracy of AoA estimation, we envision THz systems that can achieve higher data rates, improved coverage, and enhanced overall system performance. This work has the potential to revolutionize wireless communication and pave the way for the seamless integration of THz technology into various applications, including 6G networks, ultra-fast wireless links, and high-capacity communication systems. As a result, this master's thesis examines the potential of the THz band for wireless communication systems in the face of growing demand for data capacity in mobile networks. The study highlights the limitations of conventional frequency spectrums, such as the mm-Wave systems, and demonstrates how the THz band can overcome these limitations. The importance of comprehensive measurement campaigns and new algorithms to estimate the AoA and address antenna misalignment in THz wireless communication systems is emphasized. The thesis proposes a new algorithm, the AoSA-gold-MUSIC, which is designed specifically for THz-enabled space information networks (SINs) and is able to estimate AoA accurately while being computationally efficient. The analysis of channel impulse and frequency responses from the measurement campaign provides valuable insights into the behavior of electromagnetic waves in different scenarios and shows how the THz band could pave the way for next-generation wireless communication systems with disruptive metrics. These metrics include data rates of up to 100 Gbps, latency as low as 0.1 ms, and high spectrum efficiency.