Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
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Article Citation - WoS: 91Citation - Scopus: 96Scintillation Index of Elliptical Gaussian Beam in Turbulent Atmosphere(Optical Soc Amer, 2007) Cai, Yangjian; Chen, Yuntian; Eyyuboglu, Halil T.; Baykal, YahyaA tensor method is used to formulate the on-axis scintillation index for an elliptical Gaussian beam (EGB; astigmatic Gaussian beam) propagating in a weak turbulent atmosphere. Variations of the on-axis scintillation of an EGB are studied. It is interesting to find that the scintillation index of an EGB can be smaller than that of a circular Gaussian beam in a weakly turbulent atmosphere under certain conditions and is closely related to the ratio of the beam waist size along the long axis to that along the short axis of the EGB, the wavelength, and the structure constant of the turbulent atmosphere. (C) 2007 Optical Society of America.Article Citation - WoS: 87Citation - Scopus: 95Off-Axis Gaussian Schell-Model Beam and Partially Coherent Laser Array Beam in a Turbulent Atmosphere(Elsevier, 2007) Cai, Yangjian; Lin, Qiang; Baykal, Yahya; Eyyuboglu, Halil T.The propagation of an off-axis Gaussian Schell-model (GSM) beam in a turbulent atmosphere is investigated based on the extended Huygens-Fresnel integral formula. Analytical formulae for the cross-spectral density and corresponding partially coherent complex curvature tensor of an off-axis GSM beam propagating in a turbulent atmosphere are derived. Based on these formulae, the propagation properties of such kind of beam in a turbulent atmosphere are investigated in detail. Furthermore, the methods are extended to investigate the propagation properties of a partially coherent laser array beam in a turbulent atmosphere. The properties of an off-axis GSM beam and a partially coherent laser array beam in a turbulent atmosphere are closely related with the beam parameters and the structure constant of the turbulent atmosphere. (c) 2007 Elsevier B.V. All rights reserved.Article Citation - WoS: 41Citation - Scopus: 46Transmittance of Partially Coherent Cosh-Gaussian, Cos-Gaussian and Annular Beams in Turbulence(Elsevier Science Bv, 2007) Eyyuboglu, Halil T.; Baykal, YahyaAverage relative power transmittance is evaluated, by incorporating atmospheric turbulence, for partially coherent cosh-Gaussian, cos-Gaussian, Gaussian and annular beams. For all the collimated versions of these beams, against the increasing propagation length, there is a typical trend of the decrease in the relative average power transmittance with incremental drop being much less for partially coherent cos-Gaussian beams. The change in the transmittance versus the propagation length will be similar to the corresponding collimated cases, when these beams are focused at a certain focal length. Also partially coherent beams are less sensitive to propagation length changes, except for cos-Gaussian case. Partially coherent cosh-Gaussian beams exhibit a drop in the transmittance as the displacement parameter of the beam is made larger, whereas this trend is just the opposite for partially coherent cos-Gaussian beams. When examined versus the source size, for all the four types of beams, the transmittance has a similar behavior, i.e., it becomes high at small source sizes, falling with increasing source size, and following a dip, it starts to rise, eventually approaching the plane wave limit of unity. The occurrence of the dip coincides with the smallest source size for cosh-Gaussian, with the largest for cos-Gaussian, and about the same source size for Gaussian and annular beams. In general, the average relative power transmittance of coherent beam is affected much more than the partially coherent beams against the variations in source properties. (c) 2007 Elsevier B.V. All rights reserved.Article Citation - WoS: 12Citation - Scopus: 33Investigation of New Microstrip Bandpass Filter Based on Patch Resonator With Geometrical Fractal Slot(Public Library Science, 2016) Mezaal, Yaqeen S.; Eyyuboglu, Halil T.A compact dual-mode microstrip bandpass filter using geometrical slot is presented in this paper. The adopted geometrical slot is based on first iteration of Cantor square fractal curve. This filter has the benefits of possessing narrower and sharper frequency responses as compared to microstrip filters that use single mode resonators and traditional dual-mode square patch resonators. The filter has been modeled and demonstrated by Microwave Office EM simulator designed at a resonant frequency of 2 GHz using a substrate of epsilon(r) = 10.8 and thickness of h = 1.27 mm. The output simulated results of the proposed filter exhibit 22 dB return loss, 0.1678 dB insertion loss and 12 MHz bandwidth in the passband region. In addition to the narrow band gained, miniaturization properties as well as weakened spurious frequency responses and blocked second harmonic frequency in out of band regions have been acquired. Filter parameters including insertion loss, return loss, bandwidth, coupling coefficient and external quality factor have been compared with different values of perturbation dimension (d). Also, a full comparative study of this filter as compared with traditional square patch filter has been considered.Article Citation - WoS: 15Citation - Scopus: 17Scintillation Analysis of Hypergeometric Gaussian Beam Via Phase Screen Method(Elsevier, 2013) Eyyuboglu, Halil T.We give a scintillation treatment of hypergeometric Gaussian beams via the use of random phase screens. In particular, we analyse the on-axis, point-like and aperture averaged power scintillation characteristics of this beam that cannot be undertaken easily by analytic means. Within the range of examined source and propagation parameters, our evaluations show that there will be less scintillation, with increasing hollowness at small source sizes and zero topological charge. At larger source sizes or topological charges, this is reversed and decreasing hollowness will reduce scintillation. More or less the same trend is observed for aperture averaging such that at small source sizes and zero topological charge, increased hollowness will result in lower scintillation. At larger source size and topological charges, there will be a transition from the case of smaller values of hollowness giving rise to less scintillation at smaller aperture openings to the case of larger values of hollowness giving rise to less scintillation at larger aperture openings. In general nonzero topological charges will produces more scintillations, both in on-axis and aperture averaged cases. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 87Citation - Scopus: 94Scintillation Index of a Multi-Gaussian Schell-Model Beam in Turbulent Atmosphere(Elsevier, 2013) Yuan, Yangsheng; Liu, Xianlong; Wang, Fei; Chen, Yahong; Cai, Yangjian; Qu, Jun; Eyyuboglu, Halil T.Multi-Gaussian Schell-model (MGSM) beam was introduced recently [Sahin and Korotkova, Opt. Lett. 37 (2012) 2970; Korotkova et al., J. Opt. Soc. Am. A 29 (2012) 2159]. In this paper, an explicit expression for the scintillation index of a multi-Gaussian Schell-model (MGSM) beam in weakly or extremely strong turbulent atmosphere is derived with the help of a tensor method. Applying the derived formulae, the scintillation properties of a MGSM beam and a GSM beam in weakly or extremely strong turbulent atmosphere are studied numerically and comparatively. Our results show that a MGSM beam has advantage over a GSM beam for reducing turbulence-induced scintillation, which will be useful for long-distance free-space optical communications. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 20Citation - Scopus: 21Apertured Averaged Scintillation of Fully and Partially Coherent Gaussian, Annular Gaussian, Flat Toped and Dark Hollow Beams(Elsevier Science Bv, 2015) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.Apertured averaged scintillation requires the evaluation of rather complicated irradiance covariance function. Here we develop a much simpler numerical method based on our earlier introduced semianalytic approach. Using this method, we calculate aperture averaged scintillation of fully and partially coherent Gaussian, annular Gaussian flat topped and dark hollow beams. For comparison, the principles of equal source beam power and normalizing the aperture averaged scintillation with respect to received power are applied. Our results indicate that for fully coherent beams, upon adjusting the aperture sizes to capture 10 and 20% of the equal source power, Gaussian beam needs the largest aperture opening, yielding the lowest aperture average scintillation, whilst the opposite occurs for annular Gaussian and dark hollow beams. When assessed on the basis of received power normalized aperture averaged scintillation, fixed propagation distance and aperture size, annular Gaussian and dark hollow beams seem to have the lowest scintillation. Just like the case of point-like scintillation, partially coherent beams will offer less aperture averaged scintillation in comparison to fully coherent beams. But this performance improvement relies on larger aperture openings. Upon normalizing the aperture averaged scintillation with respect to received power, fully coherent beams become more advantageous than partially coherent ones. (C) 2014 Elsevier B.V. All rights reserved.Article Citation - WoS: 10Citation - Scopus: 34Wide Bandpass and Narrow Bandstop Microstrip Filters Based on Hilbert Fractal Geometry: Design and Simulation Results(Public Library Science, 2014) Mezaal, Yaqeen S.; Eyyuboglu, Halil T.; Ali, Jawad K.; Zhang, FuliThis paper presents new Wide Bandpass Filter (WBPF) and Narrow Bandstop Filter (NBSF) incorporating two microstrip resonators, each resonator is based on 2nd iteration of Hilbert fractal geometry. The type of filter as pass or reject band has been adjusted by coupling gap parameter (d) between Hilbert resonators using a substrate with a dielectric constant of 10.8 and a thickness of 1.27 mm. Numerical simulation results as well as a parametric study of d parameter on filter type and frequency responses are presented and studied. WBPF has designed at resonant frequencies of 2 and 2.2 GHz with a bandwidth of 0.52 GHz, -28 dB return loss and -0.125 dB insertion loss while NBSF has designed for electrical specifications of 2.37 GHz center frequency, 20 MHz rejection bandwidth, -0.1873 dB return loss and 13.746 dB insertion loss. The proposed technique offers a new alternative to construct low-cost high-performance filter devices, suitable for a wide range of wireless communication systems.Article Citation - WoS: 4Citation - Scopus: 4Complex Degree of Coherence and Power Moments of Cylindrical Sinc Gaussian Beam(Elsevier Science Bv, 2015) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.Complex degree of coherence and power moment aspects of cylindrical sinc Gaussian beam are investigated. To do this, we have used the random phase screen approach. It is seen that on the source plane, cylindrical sinc Gaussian beam has zero on-axis intensity and the sidelobes resemble the sinc or the Gaussian profile depending on the relative magnitudes of width parameter and the source size. Upon propagation in turbulent atmosphere, the initially flat complex degree of coherence becomes curved as the beam propagates, it then partially follows the intensity profile, and eventually turns into a delta function. Power moments are evaluated up to the fifth degree and over two different aperture sizes. In the aperture size of pointlike scintillations, the behaviors of power moments are similar to those of intensity moments. In aperture averaging conditions however, the differences between the variations of moments with respect to the propagation distance and degree of the moments become much less. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 38Citation - Scopus: 42Propagation Factor of Partially Coherent Flat-Topped Beam Array in Free Space and Turbulent Atmosphere(Elsevier Sci Ltd, 2012) Yuan, Yangsheng; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Chen, JunAnalytical expressions for the propagation factor of partially coherent radial flat-topped (FT) beam array in free-space and turbulent atmosphere are derived. Our formulae can be applied to study the beam propagation factors of partially coherent Gaussian beam, partially coherent FT beam and partially coherent radial Gaussian beam array. The evolution properties of the propagation factors of those beams in turbulent atmosphere are studied numerically and comparatively. From the aspect of the propagation factor, our results show that partially coherent radial FT beam array is less affected by turbulence than partially coherent Gaussian beam, partially coherent FT beam and partially coherent radial Gaussian beam array. (C) 2011 Elsevier Ltd. All rights reserved.
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