1,720,992 research outputs found
A hybrid approach to the synthesis of reconfigurable sparse circular arrays
No full textThe synthesis of sparse reconfigurable arrays is a challenging task. In this contribution we focus in particular on sparse circular arrays, i.e. arrays whose elements are arranged in rings, and we propose a synthesis method capable to provide a layout tailored to the radiation of beams with two different beamwidths. The synthesis method is based on a hybrid approach, that exploits at best the partial convexity of the synthesis problem in order. Numerical examples showing the feasibility of the approach for satellite applications are provided
Advances in the Deterministic Synthesis of Uniform Amplitude Pencil Beam Concentric Ring Arrays
No full textWe present some modifications to the deterministic approach (DA) recently proposed for fast design of aperiodic concentric ring arrays. Such modifications are aimed at improving the array performances in terms of directivity, side lobe level (SLL) and number of control points. In particular, an easy implementation of the size-tapering concept is provided within the processing scheme of the DA procedure; moreover, an improved collocation criterion is presented. Finally, a local optimization procedure, tailored to the concentric ring array case, is addressed
Some recent advances in the synthesis of isophoric sparse arrays for satellite communications
No full textThis paper discusses some recent advances in the synthesis of isophoric sparse arrays, with reference to satellite communications. In particular, we first summarize some of the synthesis algorithm recently proposed, highlighting their advantages and drawbacks. Then, we show that, depending on the particular application scenario for which the sparse array must be designed, a better tailored algorithm exists. The presented analysis is aimed at providing a useful tool for antenna engineers involved in the overall design of sparse arrays for satellite communications
Interleaved isophoric sparse arrays for the radiation of steerable and switchable beams in satellite communications
No full textWe address the synthesis of isophoric sparse ring arrays for full Earth coverage from GEO satellites by means of steerable beams, switchable between two different widths. In particular, we pursue the desired beam zooming/shrinking through two interleaved sparse arrays deployed over the available circular aperture. To this aim, we propose two different antenna architectures: in one case, the two beams are radiated by two separate interleaved arrays; in the other case, the two beams are instead radiated by two interleaved arrays that share a common part of their layouts. Both the proposed architectures allow us to exploit a synthesis procedure that calculates the two interleaved arrays separately, through the cascade of two steps, both implemented with a (computationally) very efficient deterministic density tapering approach. The proposed strategy allows to obtain isophoric sparse layouts satisfying the required design constraints with a significant reduction of the control points with respect to the solution achievable exploiting non-interleaved isophoric sparse arrays
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
Interleaved Isophoric Array Architectures For Reconfigurable Full-Earth Coverage From Geo Satellites
No full textIsophoric Sparse Arrays Ensuring Global Coverage in Satellite Communications
No full textNon-periodic, sparse Direct Radiating Arrays employing equi-amplitude (isophoric) radiators represent an appealing solution to meet the requirements of next satellite services. In this work we address the synthesis of isophoric sparse arrays capable of radiating highly steerable pencil beams, in order to meet the requirement of full Earth coverage from GEO orbits. To this aim, we first of all perform an analytical study that allows assessing the geometrical constraints that the desired beam steerability puts on the design of the array layout. Starting from such results, in the second part of the work we address the actual synthesis of the sparse array. The proposed strategy consists in the synthesis of the optimal radiating feed followed by the synthesis of the array layout capable of taking into account the aforementioned geometrical constraints as well as the feeds' pattern, in such a way to guarantee satisfaction of the side lobe level constraint for every steered beam. Numerical examples demonstrate the effectiveness of the proposed synthesis strategy
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
- …
