1,720,990 research outputs found
A greedy approach for reducing data in near-field measurements
No full textIn this paper, a sampling strategy which allows to take advantage of all a priori information available on the Antenna under test in reducing the measurement number is proposed. Experimental results show that the required sampling points returned by the proposed method are lower than the ones needed by the standard warping and half-wavelength sampling
Additive-oriented spiral antennas with infinite Balun
No full textSpiral antennas have been widely investigated over
the last decades, thanks to wide operative frequency range with
stable antenna parameters. With the recent advance of the
additive manufacturing processes, the antenna design and
realization techniques can be adapted to save production costs and
time. In this contribution, a novel spiral antenna realization is
investigated with an additive-oriented approach. A full-wave
numerical comparison between the classical Equiangular and
Archimedean spiral is presented. Wide operative bandwidth and
stable antenna radiation pattern are achieved. A strong
dependency of the antenna radiating efficiency by the material
losses is found, thus imposing an accurate choice of the geometrical
aspects of the spiral
Warping-Driven Greedy Method for Data Reduction in Planar Near-Field Antenna Measurements
No full textNear-field techniques for antenna testing can require the collection of a very large amount of data when the working frequency increases and/or the antenna is large in terms of wavelength. To mitigate such a drawback, a greedy method, which we call the warping-driven maximum noise propagation error (MNPE) algorithm, is introduced. Antenna under test (AUT) diagnostics is cast as the reconstruction of an equivalent surface current. Starting from a densely populated initial grid, the algorithm selects the sampling points one by one till the noise factor (NF), a figure that controls the propagation of noise from data to the source reconstruction and does not meet a slowly varying region. Hence, the procedure is arrested since no relevant further NF reduction would be obtained. It is shown that MNPE allows for a significant data reduction compared to other literature methods, especially when the starting grid is chosen according to the recently introduced warping sampling theory. Moreover, the initial grid selected according to the warping sampling, in turn, allows to dramatically reduce the computational cost of the selection procedure. A distinctive feature of the MNPE is that a priori information about the AUT can be easily included by projecting the unknown current onto properly selected base functions. As an example of that, we exploit the a priori information concerning the size of the source and the measurement aperture that leads to the radiation pattern being reliable within a bounded part of the visible spectrum (i.e., the so-called valid angle region). Extensive numerical analysis and a few experimental results pertaining to planar scanning confirm the effectiveness of the proposed method in dramatically reducing the amount of data without incurring performance degradation while estimating the source spatial spectrum
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
Digitally Synthesized Antenna Test Bench for Next Generation Phased Array Systems
No full textWith the increasing digitalization of radar new test benches must be employed for antenna measurements. The conventional antenna testing approach cannot be applied to fully digital phased array antenna systems. This paper explores the new challenges regarding the testing of a digital array radar which cannot be performed using a legacy antenna test bench operating in the RF domain only. The measurement setup is based on a couple of generator/I -Q analyzer that have to be locked to the system under test during the measurement in order to ensure phase coherence of the transmitting and receiving pulse. This paper addresses a strategy to generate an auxiliary reference in the RF domain to compensate the phase variation over the measurement time. The proposed test bench can be easily reconfigured for a radar test bench where the main challenges are not seen in terms of phase stability over long measurements, but in many other complex scenarios such as pulse to pulse stability, waveforms agility, jammer interference
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