1,720,965 research outputs found
A Low-Cost Suspended Patch Antenna for WLAN Access Points and Point-to-Point Links
No full textIn this letter, a very low-cost antenna is presented for 802.11-b (2.4-2.484 GHz) wireless local area network (WLAN) applications. This antenna can be used in two different configurations. In a stand-alone configuration the antenna has a 12-dBi gain and a 40° half power beamwidth (HPBW) in both E and H planes, thus matching typical requirements for WLAN base stations or access points for indoor WLAN. Furthermore, the same antenna can be used as feeder for a standard TVSAT offset parabolic reflector, thus obtaining a high-gain antenna system configuration (Gain = 23 dBi, HPBW = 12° with a 80 cm reflector) useful for point-to-point connections. The latter configuration provides a very low-cost antenna system useful for Internet service provider to cover the "last mile" toward the customer via a wireless link. A FR4 epoxy-glass substrate is employed providing a solution that is cheap both in material and manufacturing costs. A "suspended" structure allows to synthesize an effective material with low dielectric constant and losses, suitable for antennas application, despite the use of FR4; indeed an 86% loss efficiency is obtained. Some prototypes was realized and measured; their input impedance and gain was found in satisfactory agreement with the numerical predictions provided by the design tools
Efficient Method of Moments Analysis of Radial Line Slot Antennas
No full textIn this paper a computationally efficient method of moments (MoM) formulation is presented for the full-wave analysis and design of radial line slot antennas (RLSAs). The method efficiency is based on an ad-hoc representation of the internal problem (electrically large circular cavity) Green's function, which is split into the sum of a parallel plate waveguide contribution and a rim effect contribution, expanded on radial modes. Comparisons with a commercial general purpose MoM software were performed on a complete RLSA to demonstrate the accuracy and the efficiency of the approac
Planar Radiating Elements for Microwave Smart Array Antennas
No full textIn this paper we present two design experiences of radiating elements for smart antennas at f0 = 4.7 GHz and f0 = 14.925 GHz, respectively, for satellite link application. The first application requires a larger relative bandwidth (13%) so that a cavity backed patch solution was adopted to achieve the desired wide band still preserving a high radiation efficiency and a low inter-element coupling. The proposed cavity backed arrangement avoids surface wave launching, but it maintains a multilayer fully planar structure, easy to be manufactured and assembled. In the second higher frequency application, the requested narrower relative bandwidth (6%) was readily achieved with a standard slot coupled patch arrangement. Both the radiating elements were designed using a commercial simulation tool for planar multilayered structures. The design procedure will be presented as well as the predicted antenna performances, in terms of input and radiation parameters. Some prototypes for single elements and small array configurations are under construction and experimental results will be shown at conference time in comparison with software prediction
Regular-integrand line-integral representation for the PO scattered field, suitable for an efficient numerical integration
No full textWe present a new formulation for providing an exact line integral representation for the PO radiation integral describing the scattering from an aperture in a black screen or by a flat perfectly conducting plate, illuminated by an elementary electric or magnetic dipole, which joins numerical efficiency of Asvestas to the physical appeal and ease of implementation of Rubinowicz; indeed the present formulation overcomes numerical impairments of traditional techniques preserving the physical interpretability of the result. This feature allows us to obtain an efficient tool for numerical scattering computation whose applicability range can also be extended, using typical ray heuristic approximations, to manage scattering by impenetrable or transparent impedance objects, with a well-assessed degree of confidence. Numerical examples show the effectiveness of the presented formulation
Line-Integral Representation for the PO Field Scattered by a Faceted Object, Illuminated by a Complex Point Source
No full textIn this paper a line integral representation of the PO scattered field is presented, which provides an effective modeling tool for the scattering by a complex scenario, represented in terms of faceted surfaces, in which actual antennas operate, efficiently represented via complex source expansion. The present formulation overcomes the numerical impairments of similar past results, by introducing a novel Incremental Geometrical Optics (IGO) contribution, which allows the regularization of the integrand of the line integration which thus becomes suitable for its efficient numerical calculation, drastically reducing the computation effort with respect to the standard surface PO integral. Furthermore, IGO preserve s the physical rayinterpretability of the integrand which is the basis for extending the applicability range of the tool vi a standard ray heuristic approximation, or its analytical continuation for the treatment of complex sources
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
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