1,720,957 research outputs found
A multiple beamforming network for unequally spaced linear array based on CORPS
Get PDF"This paper proposes an alternative and innovative way to design a simpler beamforming network (BFN) based on balancing alternated power combiners and dividers, to feed a nonuniformly spaced linear array with Gaussian amplitude and coherent (inphase) signals. Thus, a two-beam design configuration of the feeding network for a nonuniform array with beam steering capability is proposed and analyzed. The nonuniform aperture and the complex inputs of the feeding network are optimized by means of a differential evolution algorithm. In addition, a comparative analysis between a uniform and nonuniform linear array with the proposed feeding network is performed. Simulation results show the advantages and effectiveness of the proposed feeding network exploiting the nonuniformity of the antenna elements, in terms of side lobe level and directivity. Furthermore, research results show an inherent reduction in hardware complexity of the network.
A New Approach in the Simplification of a Multiple-Beam Forming Network Based on CORPS Using Compressive Arrays
Get PDF"This research paper deals with a innovative way to simplify the design of beam-forming networks (BFNs) for multibeam steerable antenna arrays based on coherently radiating periodic structures (CORPS) technology using the noniterative matrix pencil method (MPM). This design approach is based on the application of the MPM to linear arrays fed by CORPS-BFN configurations to further reduce the complexity of the beam-forming network. Two 2-beam design configurations of CORPS-BFN for a steerable linear array are analyzed and compared using this compressive method. Simulation results show the effectiveness and advantages of applying the MPM on BFNs based on CORPS exploiting the nonuniformity of the antenna elements. Furthermore, final results show that the integration of CORPS-BFN and MPM reduces the entire antenna system including the antenna array and the beam-forming network subsystem resulting in a substantial simplification in such systems.
Array antennas synthesis using stochastic optimization
No full textLa aplicación de antenas inteligentes en los sistemas de comunicaciones celulares, ha sido de gran interés, debido a sus múltiples prestaciones. En las cuales destaca en la generación de diagramas de radiación adaptables según las condiciones del medio en el cual se transmiten. Por lo cual, en los últimos años la investigación de posibles métodos y tecnologías capaces de mejorar estas características, a través del estudio de la síntesis de agrupamiento de antenas ha sido de vital importancia para el desarrollo tecnológico. Este problema de diseño ha implicado el establecimiento de la geometría del agrupamiento y la determinación de las distribuciones de amplitud y fase en cada elemento de antena dentro del agrupamiento, con el propósito de satisfacer una serie de especificaciones de diseño, en las cuales destaca el ancho de haz, nivel de lobulos laterales, dirigibilidad, directividad, o nuevas restricciones de diseño al diagrama de radiación que involucran la optimización de varios parámetros de diseño a través de la inclusión de máscaras con límites impuestos al factor de agrupamiento. Debido a lo anterior dicha síntesis, requiere examinar todas las posibles soluciones al problema, lo que resulta en un problema con un espacio de búsqueda de solución muy grande, esta tesis se propone el uso de métodos de optimización metaheurísticos, como herramienta eficiente para resolver el problema de diseño de agrupaciones de antenas, y particularmente, la aplicación de optimización con enjambre de partículas, ya que se erige como una alternativa eficiente y atractiva a otros métodos estocásticos mucho más extendidos, tales como algoritmos genéticos. Por lo cual la motivación y el reto en esta tesis es efectuar una comparación entre ambos métodos de optimización con el objetivo de comprobar si pueden aplicarse eficientemente a problemas de síntesis de alimentaciones de agrupaciones lineales de antenas. Los resultados obtenidos en este trabajo, muestran las ventajas y limitaciones de ambos métodos en la aplicación de la síntesis de agrupación lineal de antenas.The application of smart antennas on cellular communications systems, has been of great interest, due to its multiple benefits. In which it emphasizes the generation of adaptable radiation patterns according to the conditions of the environment in which they transmit. Thus, in the last couple of years the investigacion of possible methods and technologies able to improve these characteristics, through the study of array antennas synthesis has been of vital importance for the technological development. This design problem has implied the establishing of array geometry and the amplitude and phase distribution determination in each antenna element within the array, ir order to satisfy a series of design specifications, emphasizing the beamwidth, side lobe level, dirigibility, directivity, or new design restrictions to the radiation pattern, which involve the optimization of several design parameters through the inclusion of masks with limits imposed to the array factor. Therefore this synthesis, it requires to examine all the possible solutions to the problem, which is a problem with a huge solution space search. This thesis proposes the use of metaheuristic optimization methods, as efficient tools to solve the design problem of antenna array, and particularly, the application of particle swarm optimization, since it is an efficient and attractive alternative to other stochastic methods more extended, such as genetic algorithms. Thus the motivation and the challenge in this thesis are to carry out a comparison between both methods of optimization with the objective to verify if they can be applied efficiently to synthesis problems that involve feeding linear array antennas. The results obtained in this work, show the advantages and limitations of both methods in the application of linear array antennas synthesis
Contribuciones al diseño y aplicación de redes conformadoras de haces basadas en estructuras periódicas de radiación coherente
No full textEl incremento de tecnologías que requieren características avanzadas en sistemas modernos de antenas, tal y como la capacidad de redirigir y reorganizar sus servicios combinada con la capacidad para generar múltiples haces independientes, necesitan de soluciones que integren estas características eficientemente. Tal es el caso de redes de formación de haz de múltiples haces (M-BFN). En este contexto, un área de investigación en sistemas modernos de antena está asociada a la reducción y simplificación de la red de formación de haz con el propósito de reducir el peso, tamaño y costo del sistema completo de antenas. Basados en estas problemáticas, en este trabajo se presenta el concepto de estructuras periódicas de radiación coherente (CORPS) aplicado a redes de formación de haz (BFN), para el diseño de redes de formación de haz múltiples haces. De esta manera, una red de alimentación CORPS es empleada como una red de formación de haz alternativa, eficiente y novedosa para sistemas de antena multihaz. Por lo cual, la motivación y reto de este proyecto fue el diseño y estudio de diferentes configuraciones de CORPS-BFN. Incluyendo el análisis de esta red en diferentes geometrías de agrupación de antenas y el uso de diferentes enfoques de optimización evolutiva para lograr metas específicas de diseño. Del mismo modo, una de las principales metas fue la introducción de las redes de formación de haz CORPS y sus características particulares en sistemas de comunicaciones móviles celulares como un enfoque original no presentado antes en la literatura.The increase of technologies that require advanced features in modern antenna systems such as the dynamic redirection and reorganization of its services combined with the ability to handle multiple independent beams, require solutions that integrate these characteristics efficiently. Such is the case o multiple-beam forming networks (M-BFN). Based on these problems, this work introduces the concept of coherently radiating periodic structures (CORPS) applied into beam-forming networks (BFN), in order to design multiple-beam forming network. Thus, a CORPS feed network is approached as an alternative beam-forming network, efficient and innovative for multi-beam antenna systems. Therefore, the motivation and challenge of this project was the design and study of different CORPS-BFN configurations. Including the analysis of this network in different antenna array geometries and the use of different evolutionary optimization approaches to achieve specific design goals. Similarly, one of the main goals was the introduction of the CORPS beam-forming networks and its particular features in cellular mobile communication systems as an original approach not presented in the literature previously
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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