Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Access type: Open accessSubject: search.filters.subject.Antennas (Electronics)

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Now showing 1 - 3 of 3
  • Master Thesis
    Wireless Physical Layer Network Coding for Multiple Antenna Systems
    (01. Izmir Institute of Technology, 2020) İlgüy, Mert; Özbek, Berna; Özbek, Berna; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Wireless networks are prone to interference due to their broadcast nature. In the design of most of the traditional networks, this broadcast nature is perceived as a performance-degrading factor. However, physical layer network coding (PNC) exploits this broadcast nature by enabling simultaneous transmissions from different sources and facilitates an increase in the spectral efficiency of the wireless networks. Besides, the massive multiple input multiple output (MIMO) is considered as one of key technologies to improve the spectral efficiency for wireless communication systems. The combination of PNC and multi-user massive MIMO in the sixth generation (6G) networks can increase further the spectral efficiency. In this thesis, PNC based systems are examined via bit error rate (BER) and coverage probability by focusing on the BER of the network coded symbol (NCS). Hence, PNC based systems are compared with network coding (NC) and conventional schemes. The influence of the signal-to-noise ratio (SNR) differences of the users are examined on the BER performances. Thereby, an alternative method to estimate NCS is proposed for the MIMO-PNC systems without using log likelihood ratio (LLR). We derive a closed form expression for the coverage probability in PNC based multi-user massive MIMO systems by employing zero forcing (ZF) equalization. The non-orthogonal multiple access (NOMA) based PNC system is proposed. We show the applicability of the PNC in the NOMA based MIMO systems by giving the the BER performance results.
  • Master Thesis
    Novel rectangular spiral antennas
    (Izmir Institute of Technology, 2008) Saynak, Uğur; Kuştepeli, Alp; Kuştepeli, Alp; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Round spiral antennas are generally designed by using Archimedean spiral geometries which have linear growth rates. To obtain smaller antennas with nearly the same performance, square spiral Archimedean geometries are also widely used instead. In this study, novel square antennas are proposed, designed and examined. At first two similar but different approaches are employed to design new antennas by considering the design procedure used to obtain log-periodic antennas. Then, the performance of these antennas is improved by considering another property of log-periodic antennas. Simulations are performed by using two different numerical methods which are Finite Difference Time Domain Method (FDTD) and Method of Moments (MoM). The results obtained from the simulations are compared with those of the Archimedean spiral antennas in terms of the frequency dependency of fundamental antenna parameters such as antenna gain and radiation pattern. The simulation results are compared with the ones obtained from the experimental study.
  • Master Thesis
    Fibonacci fractal tree antennas
    (Izmir Institute of Technology, 2004) Özbakış, Başak; Kuştepeli, Alp; Kuştepeli, Alp; 03.05. Department of Electrical and Electronics Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Fractal geometry is first defined by Benoit Mandelbrot. A fractal structure is generated with an iterative procedure of a simple initiator by replicating many times at different scales, positions and directions. Fractal structures generated with this method are generally self-similar and the dimensions of these structures cannot be defined with integers. Koch, Minkowski and Sierpinski structures are the most known fractal structures. These structures are commonly used as multiband and wideband antenna designs because of the self-similarity. Furthermore, their special geometry is useful to obtain small antennas which are resonant at lower frequencies. Lowering the resonant frequency has the same effect as miniaturizing the antenna at a fixed resonant frequency. Other important and interesting fractal structures used in antenna designs are the various types of the fractal trees. However, in recent studies the branch length ratios of the fractal tree antennas are taken constant. In this study fractal tree antennas with nonuniform branch length ratios are investigated. By changing the geometry and number of branches of the fractal tree structures the antenna characteristics are examined. The branch lengths and number of branches of the fractal tree antennas are determined by using the Fibonacci sequence. Leonardo Fibonacci (1170 - 1240), a famous Italian mathematician, dealt with geometry and developed a number sequence while observing the nature. Fractal tree antennas are designed with two different geometries in order to improve the resonance behavior of the antennas. The number of branches is decreased, so that less complex fractal tree antennas with the similar performance can be obtained.