Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
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Conference Object Citation - WoS: 5Citation - Scopus: 33A New Narrow Band Dual-Mode Microstrip Slotted Patch Bandpass Filter Design Based on Fractal Geometry(Ieee, 2012) Eyyuboğlu, Halil Tanyer; Mezaal, Yaqeen S.; Eyyuboglu, Halil Tanyer; Elektronik ve Haberleşme MühendisliğiA narrowband, compact, and easily fabricated microstrip bandpass filter design is introduced in this paper as a candidate for use in modern wireless systems. The proposed filter design is based on the use of dual-mode (two pole) square slotted microstrip resonator. This microstrip bandpass filter has the advantages of possessing much narrower and sharper performance responses than those of the single mode resonator and conventional square patch filter. The proposed microstrip filter structure is fractally generated using Sierpinski fractal curve geometry applied to the conventional square microstrip patch. Filter structures resulting from the successive iterations in the fractal generation process show a considerably low insertion loss, and sharper response of about 1% fractional bandwidth as compared with the conventional microstrip square patch filter of 3% fractional bandwidth designed at the same frequency using the same substrate material. The performance of filter structures, based on dual-mode resonators up to the third iterations, has been evaluated using a full-wave based electromagnetic simulator Sonnet software package. Performance simulation results show that these filter structures offer narrower fractional bandwidth percentages as compared with other types of non- fractalized filter structures.Conference Object Citation - WoS: 2Flat-Topped Field Correlations in Extremely Strong Turbulence(Electromagnetics Acad, 2011) Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik MühendisliğiIn extremely strong turbulent horizontal atmospheric optical links, field correlations of flat-topped Gaussian incidence are evaluated. Field correlations are represented versus the diagonal distance at the receiver plane, for variations in the number of beams forming the flat-topped structure, receiver points, source sizes, link lengths, structure constants and the wave-lengths. Our results in extremely strong turbulence are compared to their free space counterparts which only reflect the diffraction patterns at the receiver plane. The effects of the inner scale of turbulence on the field correlations in extremely strong turbulence are examined in detail and it is observed that the size of the inner scale in extremely strong turbulence can considerably influence the field correlations of flat-topped beams.Article A Novel Method To Solve 2nd Order Neumann Type Boundary Value Problems in Electrostatics(Applied Computational Electromagnetics Soc, 2017) Sener, Goker; Şener, Göker; Elektrik-Elektronik MühendisliğiIn this paper, the numerical method of nonpolynomial spline approximation is used to solve 2nd order Neumann type boundary value problems (bvp's) in electrostatics. This new approach provides more accurate results than the polynomial approximations and the spectral methods. The literature contains very little on the solution of Neumann type bvp's because of the fact that a unique solution does not exist for all problems. In electrostatics, Neumann type bvp's are encountered for finding the electrostatic potential inside closed surfaces where the normal derivative of the electric potential is specified everywhere on the surface. Two examples are presented to prove the accuracy of the proposed method. In these examples, the governing differential equation is solved to find the electrostatic potential inside a region bounded by conductors that are maintained at constant voltages. The results are compared with the analytic solutions.Conference Object Citation - WoS: 1Citation - Scopus: 3Hyperspectral Image Compression Using an Online Learning Method(Spie-int Soc Optical Engineering, 2015) Ulku, Irem; Toreyin, B. UgurA hyperspectral image compression method is proposed using an online dictionary learning approach. The online learning mechanism is aimed at utilizing least number of dictionary elements for each hyperspectral image under consideration. In order to meet this "sparsity constraint", basis pursuit algorithm is used. Hyperspectral imagery from AVIRIS datasets are used for testing purposes. Effects of non-zero dictionary elements on the compression performance are analyzed. Results indicate that, the proposed online dictionary learning algorithm may be utilized for higher data rates, as it performs better in terms of PSNR values, as compared with the state-of-the-art predictive lossy compression schemes.Article Citation - Scopus: 9Improvement of Underlay Cooperative Cognitive Networks Bandwidth Efficiency Under Interference and Power Constraints(Ksii-kor Soc internet information, 2019) Preveze, Barbaros; Alkhayyat, Ahmed; Al-Mishmish, Hameed R. M.The definition of the bandwidth efficiency (BE) of cognitive cooperative network (CCN) is the ratio between a number of the licensed slot(s) or sub-channel(s) used by the unlicensed users to transmit a single data packet from the unlicensed transmitter to unlicensed destination, and from unlicensed relay(s) to unlicensed destination. This paper analyzes and improves the BE in the underlay CCN with a new reactive relay selection under interference and power constraints. In other words, this paper studies how unlicensed cooperative users use the licensed network slot(s) or sub-channel(s) efficiently. To this end, a reactive relay selection method named as Relay Automatic Repeat Request (RARQ) is proposed and utilized with a CCN under interference and power constraints. It is shown that the BE of CCN is higher than that of cooperative transmission (CT) due to the interference and power constraint. Furthermore, the BE of CCN is affected by the distance of the interference links which are between the unlicensed transmitter to the licensed destination and unlicensed relay to the licensed destination. In addition, the BE for multiple relays selection over a CCN under interference and power constraints is also analyzed and studied, and it is shown that the BE of CCN decreases as the number of relays increases.Article Citation - WoS: 3Citation - Scopus: 2Snr Advantage of Anisotropy in Oceanic Optical Wireless Communications Links(Optical Soc Amer, 2019) Baykal, YahyaSignal-to-noise ratio (SNR) of an optical wireless communication (OWC) link that operates in anisotropic oceanic turbulence is evaluated. To find the SNR advantage of the anisotropy in the oceanic turbulent medium, SNR in anisotropic oceanic turbulence is normalized by the SNR in isotropic oceanic turbulence. The dB values of this normalized SNR are examined versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, the rate of dissipation of kinetic energy per unit mass of fluid at various oceanic anisotropic factors, the avalanche multiplication factors, the radii of receiver aperture, link lengths, and detector responsivity values. It is found that as the oceanic turbulence becomes more anisotropic, at any link parameter, the SNR of the OWC link becomes advantageous over the isotropic counterpart. (c) 2019 Optical Society of AmericaArticle Entangled Two-Photon Interference(Elsevier Gmbh, 2019) Salmanogli, AhmadThis article proposes a theoretical solution to one of the original problems of the double-slit experiment, which expresses that it is impossible to identify the photon's path without disturbing it We contend that using the entangled two-photon (signal and idler photons) and inserting a double-slit into the beam of signal (idler) photon, it is possible to distinguish the path of signal (idler) photon, just by the detection of the idler (signal) photon. Basically, the signal and idler photons are highly correlated to each other due to the momentum conservation. Indeed, the photon-photon correlation originates the nonlocal interference effect, so using this effect, lets us know about which path the photon goes through, with its conjugate photon's position detection rather than its detection.Article Citation - WoS: 5Citation - Scopus: 5Plasmonic Effect on Quantum-Dot Photodetector Responsivity(Ieee-inst Electrical Electronics Engineers inc, 2019) Salmanogli, Ahmad; Gokcen, Dincer; Gecim, H. Selcuk; Selcuk Gecim, H.In this paper, we analyze and simulate the plasmonic effect on the quantum-dot photodetector responsivity. For this purpose, a plasmonic-based quantum-dot photodetector is designed in which a few quantum dots are embedded in the hot-spot regions of the plasmonic nanoparticles, wherein a high-intensity localized field is created. Notably, due to the maximum overlapping of the plasmonic field with the quantum dots at the hot spot, some of the optical characteristics of the quantum dot, particularly the spontaneous emission decay rate, are changed. This paper focuses on the engineering of the decay rate, through which we found that the quantum-dot photodetector responsivity is strongly enhanced with the order of 100 times at the visible range. For analyzing the proposed system, we first work on the plasmonic effect of the nanoparticle on the quantum-dot lifetime using the Heisenberg-Langevin equations. It is shown that by embedding the quantum dots at the hot spot of the nanoparticle, the decay rate of the quantum dot is dramatically influenced. In the following, plasmonic-quantum dot system responsivity is theoretically examined using a time-varying perturbation theory. Using this approach is necessary because the spontaneous emission cannot be analyzed with the classical methods. Consequently, it is proved that using plasmonic effect leads to enhanced photodetector responsivity, suggesting that even very small incoming signals are detectable.Article Citation - WoS: 13Citation - Scopus: 13Field Correlation of Flat-Topped Beams in Anisotropic Non-Kolmogorov Turbulent Atmosphere(Taylor & Francis Ltd, 2019) Baykal, Yahya; Ata, YalcinField correlation of flat-topped beams in anisotropic non-Kolmogorov turbulent atmosphere is formulated and evaluated. Larger anisotropic factor causes higher field correlations. Smaller field correlations are seen when the transverse distance at the receiver plane increases. Smaller field correlations are observed at large off-axis transverse receiver points, which are valid for any anisotropic factor and for any power-law exponent of non-Kolmogorov turbulence. When the flat-topped beam is composed of large number of Gaussian beams, the field correlation becomes smaller. In anisotropic non-Kolmogorov turbulence, longer propagation distances, larger structure constants, smaller inner scales and smaller source sizes decrease the field correlation. Larger power law exponent of non-Kolmogorov turbulence increases the field correlations at any anisotropic factor.Conference Object Citation - WoS: 6Citation - Scopus: 8Performance Analysis of Mimo Fso Systems With Radial Array Beams and Finite Sized Detectors(Spie-int Soc Optical Engineering, 2014) Kamacioglu, Canan; Uysal, Murat; Baykal, Yahya; Gokce, Muhsin C.; Kamacıoğlu, CananMultiple-input multiple-output (MIMO) systems are employed in free space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, we consider a MIMO FSO system with practical transmitter and receiver configurations that consists of a radial laser array with Gaussian beams and finite sized detectors. We formulate the average received intensity and the power scinitillation as a function of the receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens-Fresnel principle. Then, integrations over the finite sized multiple detectors are performed and the effect of the receiver aperture averaging is quantified. We further derive an outage probability expression of this MIMO system in the presence of turbulence-induced fading channels. Using the derived expressions, we demonstrate the effect of several practical system parameters such as the ring radius, the number of array beamlets, the source size, the link length, structure constant and the receiver aperture radius on the system performance.