Design of an S-band power combiner system with two parallel power amplifiers and phase shifters

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Science of Bilkent University, 2011.Thesis (Master's) -- Bilkent University, 2011.Includes bibliographical references leaves 70-72.RF power amplifiers are important blocks in a wireless communication system that play a vital role in determining the level of overall performance. In some situations, more power than a single power amplifier can alone provide is required in applications such as a radar or a space communication system. In such cases, power combiners that can surpass the maximum output power level of a single power amplifier should be used. In this thesis, we study the performance of a power combiner built in classical binary structure. The combiner operates at 3 GHz (S-band) and comprises two power amplifiers which can supply up to 38 dBm of saturated power. Wilkinson power dividers/combiners are utilized at the input/output respectively in order to divide and combine the input and output signals. While building a power combiner, one should also note that the phases of the amplified signals should be matched at the output or else the level of combining loss can reach significant levels. At a phase difference of 180◦ , the signals will be completely out of phase and will combine destructively at the output. Therefore, in our study, in order to be able to control the phases at each arm of the power combiner, two tunable microwave phase shifters are placed before the active devices. The phase shift generated by these shifters are controlled via voltage, hence a desired level of phase shift can be obtained. By this, we demonstrate that phase shifters are also important structures for a power combiner that are instrumental in accomplishing a phase balance between the two arms. The idea behind the work displayed here can be extended to applications requiring much higher power levels or operating at higher frequencies.Özbey, BurakM.S

Yapısal sağlık izleme için kablosuz pasif bir algılayıcı sistemin tasarlanması ve gerçekleştirilmesi

Cataloged from PDF version of article.Thesis (Ph.D.): Bilkent University, Department of Electrical and Electronics Engineering, İhsan Doğramacı Bilkent University, 2016.Includes bibliographical references (leaves 128-140).Structural health monitoring (SHM) aims to ensure detection and prevention of damage in structures and protection of human life via observation of certain damage indicators. In SHM, one of the most important damage indicators is the strain forming on the steel reinforcing bars (rebars) embedded inside concrete. This strain can slowly develop over time, or can suddenly occur due to an overload such as an earthquake. In this dissertation, a novel wireless passive sensing system is presented for detecting and measuring the level of strain and relative displacement in structures. The sensing system comprises a nested split-ring resonator (NSRR) probe along with a transceiver antenna. These two elements form an electromagnetically coupled system that yields very high sensitivity and resolution of displacement and strain sensing accompanied with a wide dynamic range of measurement. Using this wireless system, it is possible to track strain/displacement in both the elastic (reversible-linear) and plastic (irreversiblenonlinear) deformation regions of steel rebars. In the dissertation, the results of the following experiments are presented: Characterization experiments carried out on a translation stage in laboratory environment, tensile test experiments where a rebar is loaded with a pulling force until fracture, and simply supported beam experiments where a beam undergoes loading, which leads to tensile strains on rebars at the bottom of the beam. Especially, the simply supported beam experiments constitute a decisive step toward a real-life application of the proposed sensing system. The sensing system is shown to acquire accurate data until the end of the measurements in which the wired devices such as strain gages break down and fail to capture. Furthermore, the eects of the complex electromagnetic medium formed by the rebars and the concrete on sensing are investigated. In addition, a multi-point sensing capability via multiple probes and single antenna is proposed and experimentally demonstrated, which can be used in 2-D surface strain mapping with further improvements. Finally, an equivalent circuit model is given for the NSRR structure, the results of which are compared to and found to be in good agreement with full-wave simulations and measurements. This study shows that the designed sensing system has the potential to be an alternative for both microstrain-level SHM and large displacement measurements, which can be useful for post-earthquake damage assessment.by Burak Özbey.Ph.D

Evaluation of antegonial angle and antegonial depth to estimate sex in a prepubertal turkish population

This retrospective study aimed to measure the antegonial angle (AGA) and antegonial depth (AGD) on panoramic radiographs in a Turkish subpopulation and to determine how those measurements relate to sex before puberty. A total of 600 patients were divided into 3 age groups (5, 6, or 7 years), and each group consists of 100 boys and 100 girls. For each patient, AGA and AGD indices in panoramic radiograph were measured by an oral radiologist and pediatric dentist. To our knowledge, this is the first study measuring AGA and AGD parameters on prepubertal subjects and identifying sex differences in these parameters. The data were analyzed by independent t test, Mann-Whitney U test, Spearman correlation analysis, and intraclass correlation coefficient for interobserver compliance using the SPSS software program. In all age groups, a statistically significant difference was found between the prepubertal boys and girls in both AGA andAGDparameters (P < 0.05).Our findings support the conclusion that, in addition to adults, AGA and AGD indices can be used to determine the sex of prepubertal Turkish children. These parameters can be used to determine the sex in forensic investigations of victims in whose age or pubertal condition are not known. © 2020 Wolters Kluwer Health, Inc

Status of the Focal Plane Instrumentation (FPI) Project of the 4 m DAG Telescope

DAG (Eastern Anatolia Observatory in Turkish) will be the newest and largest (4m) observatory of Turkey in both optical (VIS) and near-infrared (NIR) Owith its robust observing site infrastructure. The telescope is designedOto house 2 Nasmyth platformes which will be dedicated to NIR and VIS observations. A collaboration has recently been established among four Turkish universities including FMV Isik University (for adaptive optics systems), Middle East Technical University (fort measurement, test and calibration purposes), Istanbul University (for new technology instruments, e.g. MKIDs) and as the coordinator Ataturk University (for obtaining NIR and VIS instruments). In this paper the status of the recently approved FPI project and its aims are presented and possible collaboration opportunities are emphasized.Publisher's Versio

Social Capital, Rurality, and Accessibility: A Comparative Study Between Turkey and Italy

Over the past years, we have observed a growing interest among social scientists and policy makers in deepening their understanding of the importance of the social capital concept, against the background of a broad set of socio-economic experiences in various countries. The concept is popularly defined as a set of individual and societal gains embedded in social ties and networks. The extent to which societies produce and benefit from social capital depends, inter alia, on locational characteristics such as human capital accumulation, segregation, employment rates, the wellbeing of individuals, as well as daily and periodic mobility patterns in relation to the job/housing balance, commuting distances, and in a general sense, rural-urban differences. The aim of this chapter is to examine the impact of job accessibility on social capital at a regional scale, with special attention to rural areas. Job accessibility is considered as an indicator of spatial connectivity, and thus it can strongly relate to social capital. The associated analyses will be done by empirically studying Turkish and Italian provinces (on the basis of the European Union-NUTS3 level regions). A quantile regression model is employed to examine job accessibility and rurality in relation to social capital in 81 Turkish and 110 Italian provinces. In the analysis, social capital is measured by a community resilience index based on a set of relevant data on civic infrastructure, metropolitan stability, home ownership, and political participation. The empirical analysis is carried out for Italy and Turkey. In the last few decades, both countries have experienced a decline in rural livelihood and now have a similar percentage of rural population. Meanwhile, mainly due to the geographical and socio-economic structure, the two countries show different patterns and development characteristics of accessibility. The findings of this paper highlight these differences and similarities, and show social capital variations in response to accessibility and rurality in both Turkey and Italy