1,721,015 research outputs found
Energy-based representation of multiport circuits and antennas suitable for near-and far-field syntheses
No full textAn energy-based representation suitable for the electromagnetic characterization of linear multiport circuits and antenna systems, as well as for the optimization of antenna beamforming and near-field radio frequency-focusing performances, is presented. Radiation, ohmic, dielectric power loss, and reactive power storage are described in the concise matrix form, yielding respective eigenmodes and eigenfields that rigorously account for all energetic processes. Noteworthy eigenfields orthogonality properties are illustrated and employed to maximize (minimize) active power flow through, or to synthesize fields on, arbitrary surfaces. Applications of the proposed formulation include multiport antennas, microwave-sensing devices, microwave hyperthermia applicators, through-the-wall imaging, and wireless power transfer systems. The numerical results illustrate features and performance advantages of the proposed formulation as applied to multiport antennas and lead to define some basic design guidelines
A high-gain mushroom-shaped dielectric resonator antenna for wideband wireless applications
No full textA high-gain mushroom-shaped dielectric resonator (DR) antenna for wideband wireless applications, featuring 65% fractional bandwidth, is proposed. The antenna consists of a low-permittivity hollow cylindrical DR provided with a top-mount spherical cap lens and a metal reflector, excited by means of coaxial probes. Suitable shaping of lens and reflector yields high gain (exceeding 14 dBi) and limited back radiation. The proposed antenna features a broadside radiation diagram with stable radiation patterns and wideband impedance matching. Its potential applications include access points for indoor/outdoor wireless multimedia systems as well as satellite terminal receivers. CST Microwave Studio, implementing a fullwave locally conformal finite integration technique, is employed to design and characterize the antenna, while the singularity expansion method is adopted to express the antenna response to arbitrary excitation waveforms. The numerical results concerning the antenna parameters are found to be in good agreement with the experimental measurements performed on an antenna prototyp
A compact high-gain wideband lens Vivaldi antenna for wireless communications and through-the-wall imaging
No full textCompact high-gain wideband antenna systems for through-the-wall imaging and wireless communications, featuring 160% fractional bandwidth, are presented. Each radiating system, consisting of two orthogonal Vivaldi antennas forming a cross-shaped configuration so to excite linear (horizontal/vertical) and circular polarization (CP), is equipped with a top-mount spherical-axicon dielectric lens. The optimized shaping of the lens and of the outer edge Vivaldi arms allow achieving gain levels exceeding 15dBi with good front-to-back-ratio. The proposed antenna features a broadside gain diagram with stable radiation pattern and wideband impedance matching in the frequency range between 650 MHz and 6 GHz. CST Microwave Studio®, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna and to guide its physical realization. Two-port equivalent circuits were developed to characterize parasitic coupling effects between the Vivaldi antennas ports, while a full-wave analysis allowed characterizing their frequency and time domain behaviors. The numerical results concerning the antennas parameters, illustrating the suitability of the proposed antennas to support narrow and ultra-wideband signal waveforms, are found to be in good agreement with the experimental measurements performed on an antenna prototype
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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