Yegin, K.

Article | 2007 | IEEE Antennas and Wireless Propagation Letters6 , pp.488 - 491

Although GPS antennas are commonly used for vehicle applications, their on-vehicle gain patterns are not known well. Especially, when the antenna is mounted at locations other than the roof center, the antenna gain becomes directional at mid-to-low elevation angles. The goal of this letter is to investigate the GPS passive antenna performance at its actual, on-vehicle mounting locations. For four different antenna locations on a sedan vehicle with sunroof, the antenna gain is measured in a quasi-far-field antenna range. The results are also compared to those of finite ground plane, anechoic chamber measurements. © 2007 IEEE.

Öztürk, H. | Nazli, H. | Yegin, K. | Biçak, E. | Sezgin, M. | Dag, M. | Türetken, B.

Conference Object | 2013 | Proceedings of SPIE - The International Society for Optical Engineering8709 , pp.488 - 491

Millimeter wave absorption relative to background soil can be used for detection landmines with little or no metal content. At these frequencies, soil and landmine absorb electromagnetic energy differently. Stepped frequency measurements from 20 GHz to 60 GHz were used to detect buried surrogate landmines in the soil. The targets were 3 cm and 5 cm beneath the soil surface and coherent transmission and reflection was used in the experimental setup. The measurement set-up was mounted on a handheld portable device, and this device was on a rail for accurate displacement such that the rail could move freely along the scan axis. Measure . . .ments were performed with network analyzer and scattering data in frequency domain were recorded for processing, namely for inverse Fourier Transform and background subtraction. Background subtraction was performed through a numerical filter to achieve higher contrast ratio. Although the numerical filter used was a simple routine with minimal computational burden, a specific detection method was applied to the background subtracted GPR data, which was based on correlation summation of consecutive A-scan signals in a predefined window length. © 2013 SPIE Daha fazlası Daha az

Bilgic, M.M. | Yegin, K.

Article | 2013 | Microwave and Optical Technology Letters55 ( 6 ) , pp.1291 - 1295

Aperture coupled microstrip antenna is presented for Ku band phased-array applications. We show that radial open circuit terminated microstrip feed and hourglass aperture shape provide better coupling, high gain, wide bandwidth and small in-band gain variation. Eight-element antenna array with fixed beam tilt is formed and measured to validate simulations. Copyright © 2013 Wiley Periodicals, Inc.

Şişman, I. | Yegin, K.

Article | 2017 | International Journal of Antennas and Propagation2017 , pp.1291 - 1295

We propose a simple solution for jamming mitigation of L1 band GPS by electronically switching antenna beam for wide and narrow beamwidths. Assuming the jamming signal is directed from low elevation angles, antenna reception can be made significantly lower at these angles by electronically reconfiguring the antenna beamwidth. Four-element antenna array and one of the elements of the array are designated as antijam (array) mode and normal mode of the antenna. The antenna is placed on a degenerate-ground with symmetric slots in the ground. Front-end configuration for this antenna is also discussed. Simulations and measurements are per . . .formed to validate the proposed design. The antenna achieves more than 15 dB rejection in measurements and more than 20 dB cross-polarization improvement compared to standalone (normal mode) antenna. The system can easily be replaced with existing active antenna to improve antijam capability of the receiver. © 2017 İsmail Şişman and Korkut Yegin Daha fazlası Daha az

Isenlik, T. | Yegin, K.

Article | 2013 | IEEE Transactions on Plasma Science41 ( 2 ) , pp.296 - 304

We present a simple design method for the hole-slot-type cavity magnetron. Our design model includes all principal parts of magnetron, namely, the cathode, the resonant system, the interaction space, and the magnetic circuit. We first find structural, electrical, and magnetic parameters using empirical formulas. Then, using empirical values as initial guesses, we build and simulate the 3-D model of magnetron in CST Particle Studio. In CST, we show that the eigenmode solver is essential for proper mode excitation; then, we use particle tracking and particle-in-cell simulations for the desired magnetron operation. For a fast convergen . . .t result, we study the impact of design parameters on the magnetron performance. We apply this design procedure to an X-band hole-slot-type magnetron with eight resonators. We believe that our method provides designers a simple, fast, and reliable tool for hole-slot-type magnetron design. © 2012 IEEE Daha fazlası Daha az

Kocakarin, I. | Yegin, K.

Article | 2012 | International Journal of Antennas and Propagation2012 , pp.296 - 304

Surface plasmon-enhanced gold nanoantenna structures on glass substrate are studied for increased localized electric field and fluorescence at the feed gap locations of the antennas. Dipole, Archimedean balanced spiral, and bowtie and double bowtie geometries are studied for surface plasmon effect. Different flare angles for bowtie geometries are compared to each other. Double bowtie geometry with dual polarization capability exhibited superior performance with almost 56 dB field enhancement factor. We also studied the effect of substrate thickness on electric field enhancement and we found that glass thickness plays a critical role . . . for coherent addition of surface plasmons at the feed gap location. The surface plasmon effect is proven by considering perfect electric conductor model of gold instead of its modified Drude model. © 2012 Isa Kocakarin and Korkut Yegin Daha fazlası Daha az

Yegin, K. | Kavak, A. | Cayirci, E. | Dandekar, K.

Editorial | 2014 | International Journal of Distributed Sensor Networks2014 , pp.296 - 304

[No abstract available]

Yegin, K.

Article | 2013 | IEEE Transactions on Antennas and Propagation61 ( 9 ) , pp.4775 - 4782

A diversity antenna system with antennas embedded in rear view mirrors of a vehicle is proposed for satellite digital audio radio system. Antenna diversity is needed because hidden antennas exhibit limited capability and composite body vehicles have poor reception due to no ground plane availability. Pattern gain diversity achieved with the proposed system is proven with on-vehicle antenna simulations and gain measurements. Selection combining diversity receiver architecture is also proposed and the system is tested in real time under two fading scenarios: weak satellite signal in dense foliage and multipath terrestrial environment . . .with frequent satellite blockages. In both cases, the diversity system outperformed the reference antenna system with less mutes times (0.6% versus 0.8% in multipath, 0.1% versus 0.25% in dense foliage) and Reed-Solomon block errors (1.75% versus 2.18% in multipath, 0.87% versus 1.18% in dense foliage). The proposed rear-view mirror location is ideal for minimum signal degradation compared to windshield, backlite, and dashboard antenna installations. © 1963-2012 IEEE Daha fazlası Daha az

Tas, M. | Dasdag, S. | Akdag, M.Z. | Cirit, U. | Yegin, K. | Seker, U. | Eren, L.B.

Article | 2014 | Electromagnetic Biology and Medicine33 ( 3 ) , pp.216 - 222

The purpose of this study is to bridge this gap by investigating effects of long term 900 MHz mobile phone exposure on reproductive organs of male rats. The study was carried out on 14 adult Wistar Albino rats by dividing them randomly into two groups (n: 7) as sham group and exposure group. Rats were exposed to 900 MHz radiofrequency (RF) radiation emitted from a GSM signal generator. Point, 1 g and 10 g specific absorption rate (SAR) levels of testis and prostate were found as 0.0623 W/kg, 0.0445 W/kg and 0.0373 W/kg, respectively. The rats in the exposure group were subject to RF radiation 3 h per day (7 d a week) for one year. F . . .or the sham group, the same procedure was applied, except the generator was turned off. At the end of the study, epididymal sperm concentration, progressive sperm motility, abnormal sperm rate, all-genital organs weights and testis histopathology were evaluated. Any differences were not observed in sperm motility and concentration (p > 0.05). However, the morphologically normal spermatozoa rates were found higher in the exposure group (p < 0.05). Although histological examination showed similarity in the seminiferous tubules diameters in both groups, tunica albuginea thickness and the Johnsen testicular biopsy score were found lower in the exposure group (p < 0.05, p < 0.0001). In conclusion, we claim that long-term exposure of 900 MHz RF radiation alter some reproductive parameters. However, more supporting evidence and research is definitely needed on this topic. © 2014 Informa Healthcare USA, Inc. All rights reserved: reproduction in whole or part not permitted Daha fazlası Daha az

Bayrakceken, F. | Yegin, K.

Article | 2012 | International Journal of Photoenergy2012 , pp.216 - 222

Microwave irradiation at GSM 900/1800 MHz mobile phone frequencies affects the electronic structure of cresyl violet in solution. These changes are important because laser-dye cresyl violet strongly bonds to DNA- and RNA-rich cell compounds in nerve tissues. The irradiation effects on the electronic structure of cresyl violet and its fluorescence data were all obtained experimentally at room temperature. For most laser dyes, this is not a trivial task because laser dye molecules possess a relatively complex structure. They usually consist of an extended system of conjugated double or aromatic ?-bonds with attached auxochromic (elect . . .ron donating) groups shifting the absorption band further towards longer wavelength. Because of the intrinsically high degree of conjugation, the vibrational modes of the molecular units couple strongly with each other. We found that the fluorescence quantum yield was increased from 0.54 ± 0.03 to 0.75 ± 0.01 due to intramolecular energy hopping of cresyl violet in solution which is exposed to microwave irradiation at mobile phone frequencies, and the photonic product cannot be used as a laser dye anymore. © 2012 Fuat Bayrakceken and Korkut Yegin Daha fazlası Daha az

Isenlik, T. | Yegin, K.

Article | 2010 | Electromagnetics30 ( 7 ) , pp.589 - 608

A three-dimensional dyadic Green's function is derived for electromagnetic scattering due to a point electric current source radiating in the vicinity of a wedge with anisotropic impedance and perfect electric conductor faces. The anisotropic impedance face is characterized by surface impedances along directions parallel and orthogonal to the edge axis (principal anisotropy axis). Arbitrary surface impedance is assumed in one direction only (either parallel or orthogonal to principal anisotropy axis), and vanishing impedance is assumed on the other. Assuming reactive surface impedance, the derived forms involve a summation over an a . . .ngular wavenumber and a longitudinal spectral integral, which may be evaluated asymptotically to describe the fields in paraxial region, where the source and observation points are in close proximity to the apex but widely separated. The final asymptotic result reveals three different scattering mechanisms: edge-guided waves, surface waves, and guided waves in the classical sense. Numerical simulations are performed for capacitive and inductive surfaces using the asymptotic results. Simulation results are also compared to those of a commercially available electromagnetic field solver, which assumes uniform surface impedance. Copyright © Taylor & Francis Group, LLC Daha fazlası Daha az

Kocakarin, I. | Yegin, K.

Article | 2013 | International Journal of Antennas and Propagation2013 , pp.589 - 608

Several nanoantennas for infrared energy harvesting applications at 30 THz are studied. Contrary to usual antenna designs, we implemented glass superstrate as opposed to glass substrate for better antenna performance. We defined a figure of merit (FOM) which includes antenna fractional bandwidth, peak gain, and half-power beamwidth of the antenna under consideration. Three different antenna structures with glass superstrate and one of them with glass substrate are studied in detail. According to our FOM definition, the Archimedean balanced spiral antenna exhibited superior performance among other structures with less sensitivity to . . .the incoming polarization of the electromagnetic wave. © 2013 Isa Kocakarin and Korkut Yegin Daha fazlası Daha az