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1-D Combline Leaky-Wave Antenna With the Open-Stopband Suppressed: Design Considerations and Comparisons With Measurements
No full textThe design of a 1-D planar periodic combline leaky-wave antenna that avoids the open-stopband effects as the beam is scanned through broadside is discussed and verified experimentally. This antenna radiates from nearly resonant stubs, which ensures a small leakage constant and hence a high directivity, and shows a single beam scanning through its n = -1 space harmonic in the X-band frequency range. The open-stopband suppression is obtained by applying a recently proposed matching technique within the unit cell [1] that is experimentally validated here for the first time. Measurements are made of the phase and leakage constants, the S-parameters, and the realized gain patterns. Comparisons are made with numerical values obtained from specialized and commercial software and very good agreement is found in all cases
1-D Combline Leaky-Wave Antenna With the Open-Stopband Suppressed: Design Considerations and Comparisons With Measurements
No full textThe design of a 1-D planar periodic combline leaky-wave antenna that avoids the open-stopband effects as the beam is scanned through broadside is discussed and verified experimentally. This antenna radiates from nearly resonant stubs, which ensures a small leakage constant and hence a high directivity, and shows a single beam scanning through its n = -1 space harmonic in the X-band frequency range. The open-stopband suppression is obtained by applying a recently proposed matching technique within the unit cell [1] that is experimentally validated here for the first time. Measurements are made of the phase and leakage constants, the S-parameters, and the realized gain patterns. Comparisons are made with numerical values obtained from specialized and commercial software and very good agreement is found in all cases
Formulas for the number of surface waves on layered structures
No full textClosed-form expressions are derived for the number of surface waves propagating along a general multilayered structure with media having positive material parameters. The expressions shown here are also useful for the efficient numerical determination and ordering of the cutoff frequencies of surface waves on multilayered structures. The presented formulas are simple but exact. Validation is provided with full-wave dispersive analyses of several types of layered structures
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
Design of a 1-D combline leaky-wave antenna with the open-stopband suppressed
No full textWe discuss and verify experimentally the design of a 1-D planar periodic combline leaky-wave antenna that avoids the open-stopband effects as the beam is scanned through broadside. ©2010 IEEE
Investigation of bound and leaky modes on periodic bidimensional structures using mixed-potential integral equations
No full textIn this paper an original acceleration scheme for the computation of periodic multilayered mixed-potential Green's functions is used to perform numerical dispersive analyses in bidimensional periodic structures embedded in a dielectric slab. The acceleration scheme is first described with reference to the various components of the dyadic and scalar potentials. The Green's functions are then implemented in a method-of-moments code and dispersion curves for both leaky and bound modes (i.e., surface waves) in slabs with periodic inclusions are numerically computed and discussed. ©2010 IEEE
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High directivity in low-permittivity metamaterial slabs: Ray-optic vs. leaky-wave models
Get PDFA study is presented on the directivity of grounded lowpermittivity metamaterial slab structures that achieve highly directive broadside radiation. Two-dimensional (2D) configurations excited by electric line sources are considered, adopting a scalar plasma-like dispersive permittivity for the metamaterial medium that suitably models a wire medium in the presence of a 2D electromagnetic field, with the electric field directed along the wire axes. The role of leaky waves in producing the high directivity attainable with such structures is illustrated by comparing it with a simple ray-optic model for the radiation mechanism. We show how for increasing substrate heights, the leaky-wave effect (dominant for “optimal” thicknesses, and responsible for the very high directivity) evolves into a lensing effect purely explained with ray-optics, when losses are present
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
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