Seçmen, Mustafa
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01.01.09.02. Elektrik- Elektronik Mühendisliği
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90
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299
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207
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293
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2.20
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18
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| Journal | Count |
|---|---|
| Radio Science | 4 |
| Gazi Üniversitesi Mühendislik Mimarlık Fakültesi Dergisi | 2 |
| 23nd Signal Processing and Communications Applications Conference (SIU) | 2 |
| Physica Scripta | 2 |
| IEEE Antennas and Wireless Propagation Letters | 2 |
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94 results
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Now showing 1 - 10 of 94
Conference Object Location Independent Radar Target Classification Method with Strategy Specific Late-Time Intervals(IEEE, 2014) Salih Poyraz; Mustafa Secmen; Poyraz, Salih; Secmen, Mustafa; A Kurowska; J MisiurewiczThis work expounds a target classification method in the resonance scattering region having reduced target's distance aspect angle and noise dependencies. In the given method crucial optimum late-time intervals of the scattered signals are determined by using time-frequency representations. The time instants belonging to maximum and mean power values in time-frequency distributions are used which are independent from targets' positions. Then the feature vectors are formed for each target by using the given time-frequency distributions over these selected late-time regions at several different reference aspects and they are eventually used for the classification in test stage. In this study two different strategies having target-specific and signal-specific late-time intervals are designed. The simulations are carried out with lossless dielectric spheres being challenging targets in terms of scattering mechanism. The performances of designed strategies as well as other similar methods in the literature are compared for different popular time-frequency representations. It is found the strategy with target-specific late-time intervals combined with the Wigner-Ville distribution have better results such that it gives more than 70 percent accuracy for the noisy signals of SNR = 5 dB.Conference Object Real Time Classification of Targets Using Waveforms in Resonance Scattering Region(IEEE, 2015) M. Alper Selver; E. Yesim Zoral; Mustafa Secmen; Selver, M. Alper; Zoral, E. Yesim; Secmen, MustafaThe classification of similar shaped objects from scattered electromagnetic waves is a difficult problem as it heavily depends on the aspect angle. The reduction of the adverse effects of the aspect angle is possible by extracting distinguishable features from the scattered signals. In this paper we propose a target identification method in resonance scattering region using a novel structural feature set based on scattered signal waveform. The feature set carries out a triangularization process to model the hills and valleys of the scattered signal. Once these sub-waveforms are identified their peaks widths increase and decrease rates are calculated for each of them. Together with the inter-distance between the sub-waves feature vector is constructed. Then cross validation strategies are used to design a classifier using multi-layer perceptron network. The simulations performed by two different target libraries, dielectric rods with different permittivity and small scale aircraft models show very high accuracy of the proposed system in real time.Conference Object Citation - Scopus: 1Ultra-Wideband Antenna Design and Optimization for Constant 10-dB Beamwidth in E-Plane(Institute of Electrical and Electronics Engineers Inc., 2024) Mustafa Pehlivan; Jian Yang; Yavuz Öztürk; Mustafa Seçmen; Yang, Jian; Secmen, Mustafa; Pehlivan, Mustafa; Ozturk, YavuzThe quad ridged horn antenna (QRHA) is designed with constant 10 dB beamwidth in the E-plane over 1 - 19 GHz band. The antenna is occurring from 2 parts which are coaxial to a waveguide adapter and a flare section. Higher order modes are suppressed by minimum of 16 dB using pyramidal back cavity in the adapter section. The VSWR of the antenna is below 2 in range of 2 - 20 GHz. The average of 10 dB beamwidth of the antenna is about 125°with maximum deviation of 9% in the desired band. Also the phase center variation is below λ/4 for the entire band. © 2024 Elsevier B.V. All rights reserved.Conference Object The Calculation of Target Poles with Wavelet Transform for Electromagnetic Target Discrimination(2012) Seçmen, Mustafa; Özkurt, NalanConference Object Citation - WoS: 1Citation - Scopus: 1Metamaterial Characteristics of Dielectric Resonator Arrays in Rectangular Waveguide and Free space(IEEE, 2015) Gizem Kalender; Mustafa Secmen; Emine Yesim Zoral; Zoral, Emine Yesim; Secmen, Mustafa; Kalender, GizemThe study demonstrates the metamaterial characteristics of the arrays containing dielectric resonators by evaluating the permittivity and permeability coefficients of the array structures in rectangular waveguide and free space. For this purpose the array with two closely spaced dielectric resonators is setup and placed both in a rectangular waveguide and free space one by one. The scattering parameters in both structures are extracted with full-wave simulations (CST Microwave Studio) and supported with measurement results. Then the effective relative permittivity and permeability values are obtained with the deembedding technique and retrieval method. According to the results the structures show double negative (DNG) characteristics at some frequencies. Therefore the array with dielectric resonators is shown to have metamaterial characteristics. Besides the DNG frequencies of both (waveguide and free space) structures are found to be consistent to each other. This means that the metamaterial behaviour of the dielectric resonator array is highly insensitive to the wave excitation where TE10 and TEM modes are excited in rectangular waveguide and free space respectively.Article Compact and Wideband Cavity-Backed Antenna With Elliptical Coupling Slot and Elliptical Aperture for Satellite Communications Transceiver Applications(John Wiley and Sons Inc, 2025) Yavuz Asci; Ceyhan Türkmen; Mustafa Seçmen; Asci, Y.; Secmen, M.; Turkmen, C.A wideband full-metal cavity-backed antenna with elliptical coupling slot and elliptical aperture is proposed. The antenna consists of two elliptical structures a coupling slot and a radiating aperture which are placed on the feed waveguide side and the load side of a rectangular metal cavity resonator respectively. By using an elliptical slot/aperture the impedance bandwidth and gain of the antenna are found to be considerably improved in the same footprint and without increasing complexity compared to rectangular slot/aperture and also circular aperture. A prototype of the proposed wideband antenna is fabricated by using the additive manufacturing techniques of 3D printing with polylactic acid (PLA) material which is covered with aluminum tape to validate the design at Ku-band for satellite communication (SatCom). The measured results show that the antenna has an impedance bandwidth of 4 GHz (10.86–14.86 GHz for |S11| < −15 dB) which gives a fractional bandwidth (FBW) of 31.1%. With low cross-polarization being less than −25 dB at broadside the antenna has a peak gain of 9 dBi. The proposed antenna is also compact with a total volume of about 1.1λ03 at the center frequency. © 2025 Elsevier B.V. All rights reserved.Doctoral Thesis Mı̇krodalga frekanslarında karbon bazlı elektromanyetı̇k gı̇rı̇şı̇m kalkanlama malzemeleri tasarımı ve gerçekleştirilmesi(2024) Ertekin, Zeynep; Seçmen, MustafaThe exchange of electromagnetic signals is fundamental to personal devices such as computers and telephones, as well as more complex systems such as antennas and radars used in applications such as weather forecasting, satellite communications, navigation and national security. It is essential that these devices operate within the limits of electromagnetic compatibility (EMC). This prevents them from interfering with or damaging each other. However, interference and interaction can sometimes occur when electromagnetic signals are exchanged at close frequencies. These disturbances can be the cause of equipment or system malfunction or data corruption or loss. This is why protecting equipment which uses electromagnetic signals is vital. This thesis investigates the development, optimisation and implementation of two novel electromagnetic shielding composites, both of which use expanded graphite as a conductive filler in polymer matrices to provide effective shielding against electromagnetic interference (EMI). The focus of the research is on the actual EMI shielding performance of the composites rather than ideal conditions. Scattering data were collected using a vector network analyser, microwave parameters calculated using the Nicolson-Ross-Weir algorithm and simulations performed in CST to reduce experimental material costs and improve accuracy and efficiency of the proposed composite. The first of these composites, composed of ionic liquid and expanded graphite co-doped PVDF (Poly(vinylidene difluoride)), demonstrated sufficient electromagnetic shielding success in the 8-18 GHz range. However, it was discarded due to its high cost. The second composite, a structure containing 11 wt.% expanded graphite embedded in screen printing ink, proved to be both cost-effective and successful in broadband applications, providing effective electromagnetic shielding as confirmed by both simulation and experimental methods. Electromagnetic analyses were carried out under both ideal conditions (waveguide) and realistic lossy conditions (free space). A total of seven different methods were used - three experimental and four simulation techniques. As a contribution to the literature, the electromagnetic homogeneity of the novel composite material was evaluated for the first time using two different methods. Homogeneity percentages were obtained over a broadband frequency range (2-30 GHz). For a real-world application, a cube made from the designed composite structure was tested in both experimental and simulation environments. Several antennas operating in different frequency regimes were placed inside the cube to assess its protection from electromagnetic signals. The extent to which these antennas were affected by external electromagnetic signals was investigated. This cube application is a contribution to the literature by demonstrating its use in both electromagnetic shielding and absorption test applications. The material characterisation of this composite structure, presented for the first time in the literature, has also been carried out, underlining its potential effectiveness and practical application.Conference Object A Dual-Band Circularly Polarized Bi-Sectoral Waveguide Horn Antenna for High Power LEOP TT&C Systems(Institute of Electrical and Electronics Engineers Inc., 2022) Esra Alkın; Ceyhan Türkmen; Mustafa Seçmen; Secmen, Mustafa; Turkmen, Ceyhan; Alkin, EsraIn this study a dual-band circularly polarized bi-sectoral waveguide antenna is proposed which is used launch and early orbit phases (LEOP) of telemetry tracking and command (TT&C) applications of satellite systems to almost cover full space together with omni-directional (toroidal) antennas. The structure consists of four parts (pyramidal horn antennas) each having excited by a single inclined slot being cut over circular waveguide. However because the overall antenna is only fed with a single rectangular waveguide it works as transceiver (in TX and RX bands simultaneously). The parts belonging to each band have bi-directional patterns being opposite to each other. Therefore instead of using four separate antennas each being fed by separate rectangular waveguide to cover both directions in dual band (TX and RX bands) in 3D space one antenna with just one feed is demonstrated as being sufficient for same purpose. For this purpose an antenna is designed for a Ku-band TT&C application. The results show that the antenna is dual-band over 500 MHz bandwidth around 11.75 GHz (TX) and 13.75 GHz (RX) center frequencies. The antenna has more than 9.5 dBi peak gain in both main lobes and 15 dB return loss at TX band, and has more than 10 dBi peak gain and 10 dB return loss at RX band. Besides it has less than 3 dB and 3.5 dB axial ratio (AR) values at TX and RX bands within almost 45º and 60º azimuth and elevation beamwidth values respectively. © 2022 Elsevier B.V. All rights reserved.Master Thesis Uydu haberleşme sistemleri için yönsüz antenler(2016) Türkmen, Ceyhan; Seçmen, MustafaIn this thesis, the design, production and measurements of Ku-Band, omnidirectional and circularly polarized antennas, which can be used in satellite communication applications as receiver and/or transmitter, are explained. Ku-Band is a commonly used frequency band in satellite communication applications. These antennas consist of inclined slots (slotted array) placed with a circular symmetry on a circular waveguide. The antenna structures are fed by a special transition from standard rectangular waveguide to this circular waveguide, where the rectangular waveguide is the standard WR75 used frequently in Ku-Band applications. The electromagnetic wave propagates in only dominant TE10 mode inside the rectangular waveguide (main feed of the antenna), while propagating in the second higher order mode of TM01 inside circular waveguide. This TM01 mode is nondominant for circular waveguide; but has circular symmetry in the excitation of the slots on the antenna array, which provides omnidirectional pattern. The mentioned special transition effectively suppresses the dominant TE11 mode and other higher order modes such as TE21 in the circular waveguide, which disturbs symmetry (omnidirectionality) in the radiation pattern. In order to make the antennas circularly polarized, the slotted array elements are designed as inclined way, and parallel metallic plates (disks) are placed around the slotted arrays. Three different versions of the proposed antenna are designed, simulated and implemented. The first one is designed just for transmitting purpose from the satellite to earth, and operates at the frequency about 11.75 GHz. Similarly, the second antenna is realized just for the receiving purpose from the ground segment to satellite. This antenna operates at the frequency about 14.00 GHz. The last antenna design is more sophisticated than the other ones such that it works as a transceiver carrying out transmission at 11.75 GHz and reception at 14.00 GHz simultaneously. According to results obtained for the first two designs, the return loss, which is better than 10 dB, is provided around the frequency regions of both transmitter (11.75 GHz) and receiver (14.00 GHz) within approximately 3 percent frequency bandwidth. In addition, axial ratio is lower than 1 dB in the azimuth plane and lower than 4 dB in a wide beamwidth of elevation plane at the center frequencies. Omnidirectional radiation pattern is provided at azimuth plane such that the variation of gain is about 0.7 dBi at this plane. The transceiver version of the design has frequency bandwidth of about 350 MHz and 500 MHz for the maximum 10 dB return loss around the center frequencies of 11.75 GHz and 14.00 GHz, respectively. The axial ratio values are found to be lower than 2 dB in the azimuth plane for both center frequencies, which corresponds to good circular polarization performance. The values in the radiation patterns change at most 3 dB at the same plane.Article Predicting S-Parameters in Microstrip Trisection Passband Filter Using a S-KNN Algorithm(International Academy of Microwave and Optical Technology (IAMOT), 2024) Senasli Lamia; Mohammed Chetioui; Mehdi Damou; Senasli Nour El Houda Sarah; Abdelhakim Boudkhil; Mustafa Seçmen; Abdelhakim, Boudkhil; Mohammed, Chetioui; Lamia, Senasli; Secmen, Mustafa; Sarah, Senasli Nour El Houda; Mehdi, DamouIn the field of microwave modelling and design the Supervised K-Nearest Neighbor (S-KNN) algorithm has emerged as a valuable tool. An S-KNN based approach to the modelling of passband trisection filter components with emphasis on the optimization of the hyperparameter K is presented in this paper. Our technique introduces a novel S-KNN topology specifically designed for parametric modeling of microwave components with S-parameters as outputs. Unlike previous methods which often rely on manual parameter tuning or lack robust hyperparameter optimization our optimized S-KNN model achieves high accuracy (0.9429) and low mean squared error (0.0109) by tuning K to the specific dataset. The study compares various distance metrics and employs Euclidean distance for predictions. Results demonstrate that the optimized S-KNN model achieves strong alignment with electromagnetic (EM) simulations with an average accuracy of 94.29% offering a faster and potentially more efficient alternative to traditional design techniques. © 2024 Elsevier B.V. All rights reserved.
