1,721,103 research outputs found
Generalized Symmetrical 3 dB Power Dividers with Complex Termination Impedances
Full text linkThe paper introduces a class of two-way, 3 dB narrowband power dividers (combiners), closed on complex termination impedances, that generalizes a number of topologies presented during past years as extensions of the traditional Wilkinson design. Adopting even-odd mode analysis, we demonstrate that, under very broad assumptions, any axially symmetric reactive 3-port can be designed to operate as a 3 dB two-way power divider, by connecting a properly designed isolation impedance across two symmetrically but arbitrarily located additional ports. We show that this isolation element can be evaluated by a single input impedance or admittance CAD simulation or measurement; moreover, an explicit expression is given for the isolation impedance. The theory is shown to lead to the same design as for already presented generalizations of the Wilkinson divider; further validation is provided through both simulated and experimental case studies, and an application of the theory to the design of broadband or multi-band couplers is suggested
TCAD-based Pseudo-Common-Gate X-PAR Model for GaAs Stacked Power Amplifier Design
Full text linkSeries device stacking has proved to be a very interesting solution for developing high-voltage high-power microwave amplifiers in low-breakdown technologies. The availability of 3-terminal device nonlinear models that are accurate and reliable, yet computationally efficient, in simulating a pseudo-common-gate stage are of crucial importance for developing a stacked power amplifier. This work presents the extraction and validation of a 3-terminal X-parameter model of a GaAs MESFET from physics-based simulations. Remarkable accuracy can be obtained by properly selecting the port terminations, accounting for the peculiar circuit scheme adopted for model extraction
Revisiting the Power Gains of a Loaded Two-Port: Is There a Missing Element?
Full text linkIn microwave electronics, the power gains of a linear two-port are customarily defined as the ratio of an output port and input port power, where such powers are intended either as operational or as available. Two input and two output powers are thus introduced, with four possible combinations of output/input power ratios, but only three are practically exploited, the well-known operational power gain, available power gain, and transducer power gain. In the present paper, we provide a comprehensive review of gain definitions (including the less commonly exploited added-power gains) and finally consider the missing fourth element (defined as the ratio of the output available power and of the input operational power), derive a few mathematical properties of it, both in the general and in the unilateral case, and ultimately justify the reason why this fourth gain G4 which, following the suggestion of an anonymous reviewer, we will call apparent power gain, Gapp, has little interest in the optimization of the power transfer between the generator and the load. Nevertheless, the definition and analysis of Gapp, besides being formally useful to complete the gain family, may yield a deeper insight into the very nature of power transfer optimization in a loaded two-port
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
GaAs-based serial-input-parallel-output interfaces for microwave core-chips
Full text linkMicrowave core-chips are highly integrated MMICs that are in charge of all the beam-shaping functions of a transmit-receive module within a phased array system. Such chips include switches, amplifiers and attenuators, phase shifters, and possibly other elements, each to be controlled by external digital signals. Given the large number of control lines to be integrated in a core-chip, the embedding of a serial to parallel interface is indispensable. Digital design in compound semiconductor technology is still rather challenging due to the absence of complementary devices and the availability of a limited number of metallization layers. Moreover, in large arrays, high chip yield and repeatability are required. This paper discusses and compares challenges and solutions for the key sub-circuits of GaAs serial to parallel converters for core-chip applications, reviewing the pros and cons of the different implementations proposed in the literature
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