PubMed İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8650
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Article Citation - WoS: 45Citation - Scopus: 50Scintillations of Incoherent Flat-Topped Gaussian Source Field in Turbulence(Optical Soc Amer, 2007) Baykal, Yahya; Eyyuboglu, Halil T.The intensity fluctuations of incoherent flat-topped Gaussian beams are evaluated when such sources are used in weakly turbulent horizontal atmospheric links. The formulation is developed for a detector having a response time much longer than the source coherence time. The flat-topped Gaussian profile is obtained by superposing many Gaussian beams, then the incoherence is introduced through delta correlation in space. The scintillation index of the incoherent flat-topped Gaussian beams is found to be smaller than the scintillation index of the corresponding incoherent Gaussian beams at the same link length, source size, and wavelength. When compared with the coherent counterparts, the intensity fluctuations of the incoherent flat-topped Gaussian beams are much smaller, yielding the same value only at the spherical wave limit, as expected. Transmitter aperture averaging is a special case of our solution. (c) 2007 Optical Society of America.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: 64Citation - Scopus: 70Complex Degree of Coherence for Partially Coherent General Beams in Atmospheric Turbulence(Optical Soc Amer, 2007) Eyyuboglu, Halil T.; Baykal, Yahya; Cai, YangjianWith the use of the general beam formulation, the modulus of the complex degree of coherence for partially coherent cosh-Gaussian, cos-Gaussian, Gaussian, annular and higher-order Gaussian optical beams is evaluated in atmospheric turbulence. For different propagation lengths in horizontal atmospheric links, the moduli of the complex degree of coherence at the source and receiver planes are examined when reference points are taken on the receiver axis and off-axis. In the on-axis case, it is observed that in propagation, the moduli of the complex degree of coherence are symmetrical and look like the intensity profile of the related coherent beam propagating in a turbulent atmosphere. For all the beams considered, the moduli of the complex degree of coherence profiles turn into Gaussian shapes beyond certain propagation lengths. In the off-axis case, the moduli of complex degree of coherence patterns become drifted at the earlier propagation lengths. Among the beams investigated, the cos-Gaussian beam is found to be almost independent of the changes in the source partial coherence parameter, and the annular beam seems to be affected the most against the variations of the source partial coherence parameter. (c) 2007 Optical Society of America.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: 34Citation - Scopus: 34Scintillation Analysis of Truncated Bessel Beams Via Numerical Turbulence Propagation Simulation(Optical Soc Amer, 2013) Eyyuboglu, Halil T.; Voelz, David; Xiao, XifengScintillation aspects of truncated Bessel beams propagated through atmospheric turbulence are investigated using a numerical wave optics random phase screen simulation method. On-axis, aperture averaged scintillation and scintillation relative to a classical Gaussian beam of equal source power and scintillation per unit received power are evaluated. It is found that in almost all circumstances studied, the zeroth-order Bessel beam will deliver the lowest scintillation. Low aperture averaged scintillation levels are also observed for the fourth-order Bessel beam truncated by a narrower source window. When assessed relative to the scintillation of a Gaussian beam of equal source power, Bessel beams generally have less scintillation, particularly at small receiver aperture sizes and small beam orders. Upon including in this relative performance measure the criteria of per unit received power, this advantageous position of Bessel beams mostly disappears, but zeroth- and first-order Bessel beams continue to offer some advantage for relatively smaller aperture sizes, larger source powers, larger source plane dimensions, and intermediate propagation lengths. (C) 2013 Optical Society of AmericaArticle Citation - WoS: 11Citation - Scopus: 12Bit Error Rate Analysis of Gaussian, Annular Gaussian, Cos Gaussian, and Cosh Gaussian Beams With the Help of Random Phase Screens(Optical Soc Amer, 2014) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.Using the random phase screen approach, we carry out a simulation analysis of the probability of error performance of Gaussian, annular Gaussian, cos Gaussian, and cosh Gaussian beams. In our scenario, these beams are intensity-modulated by the randomly generated binary symbols of an electrical message signal and then launched from the transmitter plane in equal powers. They propagate through a turbulent atmosphere modeled by a series of random phase screens. Upon arriving at the receiver plane, detection is performed in a circuitry consisting of a pin photodiode and a matched filter. The symbols detected are compared with the transmitted ones, errors are counted, and from there the probability of error is evaluated numerically. Within the range of source and propagation parameters tested, the lowest probability of error is obtained for the annular Gaussian beam. Our investigation reveals that there is hardly any difference between the aperture-averaged scintillations of the beams used, and the distinctive advantage of the annular Gaussian beam lies in the fact that the receiver aperture captures the maximum amount of power when this particular beam is launched from the transmitter plane. (C) 2014 Optical Society of AmericaArticle Citation - WoS: 33Citation - Scopus: 38Propagation Analysis of Ince-Gaussian Beams in Turbulent Atmosphere(Optical Soc Amer, 2014) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.We analyze the properties of Ince-Gaussian beams propagating in turbulent atmosphere. Due to analytic difficulties, this analysis is done with the aid of a random phase screen setup. Intensity profile, beam size, and the kurtosis parameter are evaluated against the changes in beam orders, propagation distance, and turbulence levels. It is found that when propagating in turbulence, Ince-Gaussian beams will no longer keep their beam profile invariant like in free space but will experience beam profile changes. These changes will cause additional beam spreading, as well as an increase in beam size and the kurtosis parameter. (C) 2014 Optical Society of AmericaArticle 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: 96Citation - Scopus: 101Twist Phase-Induced Reduction in Scintillation of a Partially Coherent Beam in Turbulent Atmosphere(Optical Soc Amer, 2012) Wang, Fei; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, YahyaThe scintillation index of a Gaussian Schell-model beam with twist phase (i.e., twisted GSM beam) in weak turbulent atmosphere is formulated with the help of a tensor method. Variations of the scintillation index of a twisted GSM beam on propagation in turbulent atmosphere are studied in detail. It is interesting to find that the scintillation index of a twisted GSM beam can be smaller than that without twist phase in weak turbulent atmosphere. Thus, modulation of the twist phase of a partially coherent beam provides a new way to reduce turbulence-induced scintillation. (C) 2012 Optical Society of AmericaArticle Citation - WoS: 80Citation - Scopus: 85Propagation of an Airy Beam Through the Atmosphere(Optical Soc Amer, 2013) Ji, Xiaoling; Eyyuboglu, Halil T.; Ji, Guangming; Jia, XinhongIn this paper, the effect of thermal blooming of an Airy beam propagating through the atmosphere is examined, and the effect of atmospheric turbulence is not considered. The changes of the intensity distribution, the centroid position and the mean-squared beam width of an Airy beam propagating through the atmosphere are studied by using the four-dimensional (4D) computer code of the time-dependent propagation of Airy beams through the atmosphere. It is shown that an Airy beam can't retain its shape and the structure when the Airy beam propagates through the atmosphere due to thermal blooming except for the short propagation distance, or the short time, or the low beam power. The thermal blooming results in a central dip of the center lobe, and causes the center lobe to spread and decrease. In contrast with the center lobe, the side lobes are less affected by thermal blooming, such that the intensity maximum of the side lobe may be larger than that of the center lobe. However, the cross wind can reduce the effect of thermal blooming. When there exists the cross wind velocity v(x) in x direction, the dependence of centroid position in x direction on v(x) is not monotonic, and there exists a minimum, but the centroid position in y direction is nearly independent of v(x). (C) 2013 Optical Society of America
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