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Conference Object COMPARISON OF COMPUTER-BASED PROPAGATION MODELS WITH EXPERIMENTAL DATA COLLECTED IN AN URBAN AREA AT 1800 MHz(Ieee, 2015) Acar, Tarik; Caliskan, Fatma; Aydin, ElifNowadays a lot of models are set for the efficient and economic usage of frequency band since the band is a limited source. Therefore, the propagation models created for this purpose were studied in the literature. These models are Free Space Path Loss (Fspl) + Reflection plus Multiple Diffraction (RMD), COST-Hata and COST-WI models. In order to compare the success of the models, electric field strength measurements were taken in a chosen district (Mustafa Kemal Mahallesi Ankara, Turkey) where an irregular structure style can be observed. First set of measurements were recorded at random coordinates and second set of measurements were collected by the following coordinates tracking on a single line. As a conclusion, measured values were compared with the results which were taken from the mentioned models with graphical presentations. The most appropriate model was tried to be found and as another aim of the study, a correction factor was generated as a modification for COST-Hata propagation model.Article Comparative Assessment and Performance Analysis of Interference Mitigation Techniques for Co-Existent Non-Geostationary and Geostationary Satellites(Wiley, 2024) Ozturk, Faik; Aydin, Elif; Kara, AliIn recent years, technological developments with user demands, reduced production, and launch costs have rapidly increased the number of Low Earth Orbit (LEO) satellites in space. Since LEO satellites use the same frequency band as existing Geostationary Earth Orbit (GEO) satellites, the interference coordination between the two satellite networks is vital. In order to minimize the co-existent interference between these satellite networks, studies perform on different interference mitigation strategies. In this paper, analysis and comparative assessment of these interference mitigation techniques are presented for the co-existent Non-Geostationary Earth (NGEO) and GEO systems. More specifically, power control (PC) and spatial isolation-based link adaptation (SILA) techniques are studied comparatively for the performance evaluation. It is shown that the communication link bandwidth is more efficiently utilized in the SILA technique when compared with the PC technique. Moreover, the multi-objective optimization problem (MOP) approach in the SILA technique is demonstrated to be more effective when compared with the single-objective optimization problem (SOP) approach used in the PC technique as the simultaneous prioritizing objective functions outperforms single prioritization. Finally, it is shown that when the PC technique is applied together with the SILA technique, the exclusive angle (EA) can be reduced up to 8% for 100 Mbps, and 8.5% for 200 Mbps transmission bit rates in different operational scenarios. The presented performance evaluation in this paper may help the satellite operator or decision-maker gain insights on which mitigation technique can be used in the case of a co-existent interference. This paper proposes analysis and comparative assessment of interference mitigation techniques for the co-existent Non-Geostationary Earth (NGEO) and Geostationary Earth Orbit (GEO) systems. Spatial isolation-based link adaptation (SILA) and power control (PC) techniques are studied comparatively for the performance evaluation. The obtained optimization results show that the communication link bandwidth is more efficiently utilized in the SILA technique when compared with the PC technique because of the simultaneous prioritizing of objective functions. imageConference Object Citation - WoS: 1Design and Analysis of Rectangular Dielectric Rod Antennas(Ieee, 2015) Demir, Mahmut; Ozkok, M. Aybars; Caliskan, Fatma; Aydin, ElifIn this study, rectangular dielectric rod antennas with different dimensions and different shapes are designed and analyzed using HFSS simulation software. To analyze the effects of these changes, five different antennas are designed and antenna gains and return loss values are compared.Article Citation - WoS: 8Citation - Scopus: 12Computation and Optimization of Resonant Frequency and Input Impedance of a Coax-Fed Circular Patch Microstrip Antenna(John Wiley & Sons inc, 2007) Gurel, Cigdem Seckin; Aydin, Elif; Yazgan, ErdemMicrostrip antennas are important elements of today's wireless communication networks. In their various applications, it is critical to provide wide hand operation around the resonant frequency providing good impedance match between the antenna element and the feed. In this study, new, simple, arid accurate computation of resonant frequency and input impedance of double-layered, coaxial fed circular disk microstrip antenna with air gap is performed. In the analysis, new effective radius and permittivity expressions are used in simple and modified form including modal effects. Then, a new approach is proposed to provide input impedance matching (it resonant frequency via the application of microgenetic algorithm for wide hand operation. The accuracy of theoretical calculations and impedance matching approach are presented for various,structural parameters and operational modes of the antenna. (C) 2007 Wiley Periodicals, Inc.Article Low Signature UAVs: Radar Cross Section Analysis, Simulation, and Measurement in X-Band(Springer London Ltd, 2025) Unalir, Dizdar; Yalcinkaya, Bengisu; Aydin, ElifThe increasing prevalence of unmanned aerial vehicles (UAVs) is driving the development of radar systems capable of detecting them. This hampers the deployment of UAVs in military operations. While radar cross section reduction (RCSR) can be a valuable solution, the research on this subject is inadequate. This paper presents an RCSR approach adopting a shaping technique for UAVs, demonstrating the proposed approach's efficacy through simulations and actual experimental measurements performed in X-Band on a four-legged UAV model. Using electromagnetic computational instruments, the shaping is applied to the designed UAV model with parameter-based simulations, the simulated radar cross section (RCS) values are derived, and the comparative analysis of these instruments is conducted. Experimental measurements are performed in laboratory conditions using a vector network analyzer. Actual measurement results are validated by simulative findings with the examination of the influence of frequency, polarization, and aspect angle on RCS. The demonstrated measuring approach allows cost-effective and easily applicable research on RCS in X-Band, a commonly utilized frequency range in military. An average RCSR of 10 dBsm has been accomplished with the presented shaping approach.Conference Object Analysis of the Parameters That Effects the Operating Frequencies and Bandwidth of a Cpw-Fed Patch Antenna(Ieee, 2013) Dagdeviren, Birkan; Kapusuz, K. Yavuz; Can, Sultan; Aydin, ElifIn this study, the analysis of the effect of antenna parameters to the operating frequency is performed in a coplanar waveguide fed patch antenna. The effect of the size and the substrate of the design dual frequency antenna to the operating frequency and bandwidth are also evaluated. Bandwidth of the upper and lower frequency is also investigated and results are demonstrated. The method to increase the bandwidth is also presented by using the chosen parameters.Article Citation - WoS: 6Citation - Scopus: 9Comparative Assessment of Electromagnetic Simulation Tools for Use in Microstrip Antenna Design: Experimental Demonstrations(Wiley, 2019) Bilgin, Gulsima; Yilmaz, Vadi Su; Kara, Ali; Aydin, ElifThis paper presents a better understanding of the use of finite integration techniques (FIT) and finite element method (FEM) in different types of microstrip antennas in order to determine which numerical method gives relatively more accurate results. Although the theoretical formulation based on Maxwell's equations of both FEM and FIT are approached from different aspects in the literature, there is still a lack of comparison of the same antenna type using different numerical methods employing FEM and FIT. Therefore, in this study, FEM and FIT were applied to two different types of microstrip antennas, and their simulation and experimental results was compared. For the first antenna demonstration, a multilayer structure was chosen to achieve one of the significant parameters. Then, a microstrip antenna with a compact structure was used in the second demonstration. Using these two antennas, the accuracy of FEM and FIT in different structures were compared and all simulated return loss and gain results were verified by the measured results. The experimental demonstrations show that FEM performs better for both types of microstrip antennas while FIT provides an adequate result for two-layer microstrip antennas.Conference Object Citation - WoS: 2Citation - Scopus: 2Radar Cross Section Studies of Low Signature UAVs in X-Band: Simulation, Measurement and Performance Evaluation(IEEE, 2024) Unalir, Dizdar; Gokdogan, Bengisu Yalcinkaya; Aydin, ElifIn this study, the effectiveness of a radar cross section (RCS) reduction method based on a proposed shaping technique for four-legged unmanned aerial vehicles (UAV) has been proven with simulation tools and experimental measurements in X-Band. Simulative RCS values were obtained with CST and HFSS electromagnetic calculation tools, and the advantages of these tools compared to each other were examined. Experimental measurements were carried out in a laboratory environment with a vector network analyzer (VNA) and confirmed with simulation results. The effects of frequency, polarization and aspect angle factors on RCS were examined. It has been shown that with the proposed measurement method, low-cost and easily applicable RCS analysis can be performed in X-Band, one of the frequency bands frequently used in the defense industry. With the proposed shaping method, RCS reduction in the range of 5-10 dBsm was achieved.Conference Object An Algorithm for Passive Rfid Based Location Estimation(Ieee, 2014) Ozyurt, Erdem; Aydin, Elif; Yapici, A. CagriIn this study, an indoor localization system is developed for the mobile robots. The localization system consists of a passive RFID tag and a reader. The passive RFID tag is placed on the robot and reader antennas are spatially dispersed into the room. For the localization, Selective Adaptive Weighted Centroid Localization (SAWCL) algorithm is used. Performance of the localization system is evaluated for the different tags.Conference Object Citation - WoS: 2Citation - Scopus: 3Design Considerations for Sub-Ghz Multilayer Microstrip Antenna for Near Ground Communication Links in Rural Areas(Ieee, 2017) Bilgin, Gulsima; Yilmaz, Vadi Su; Aydin, Elif; Kara, Ali; Department of Electrical & Electronics Engineering; Electrical-Electronics EngineeringThis paper presents some preliminary results of design and development of sub-GHz multilayer microstip antenna for use in near ground communication applications. In design stage of the antenna, iterative approach was applied. Firstly, a two layer microstrip antenna design process is presented. Next, the corners of the patch were cut, and a vertical wall on all sides of the antenna were introduced. In this way, both the size and resonant freqeuncy can be tuned. Moreover, as an application specific requirement, it is intended to embed this antenna into a metal box in order to protect it from man-made and natural environmental effects. This was also studied, and effects of the embedding ground on the antenna characteristics were examined. It is shown that the designed antenna provides -27dB resturn loss, and 7.3dB peak gain at 915MHz with the dimension of 150x200x13mm. Some preliminary measurements have proven the simulations.
