1,720,961 research outputs found
Improving the strut modelling of the European Space Agency Deep Space Antennas to evaluate efficiency and sidelobe impact
No full textOn the effects of struts diameter and shape on the European Space Agency deep space antenna directivity and first side lobe
No full textLarge reflector antennas, such as the European Space Agency deep space antennas (DSAs), practically always require struts to support the sub-reflector. While inevitable, they deteriorate the antenna performance. To minimize this deterioration, it is pivotal to understand the role played by different features, including struts diameter and shape. This paper proposes a detailed numerical investigation on the impact of these features on antenna efficiency and side lobes, for a test case comprising both DSA3 and DSA4. It is demonstrated, for the first time in a comprehensive and quantitative way that includes different permutations for the strut design, that both features are significant to define the deterioration, thus providing a significant feedback for struts design
Impact of strut diameter on the European Space Agency Deep Space Antennas efficiency and sidelobes
No full textLarge reflector antennas require the presence of struts to support both feeds and sub-reflectors. Such structures affect the antenna behavior. The present paper proposes an investigation between struts of different radius, considering the structure of the European Space Agency Deep Space Antenna 3 (DSA3), in terms of side-lobes and efficiency. The numerical simulations, which employed Physical Optics, are compared with those related to the DSA4, in order to assess the impact of both the smaller radius and of the different shape of the struts on the antenna performances
Numerical investigation about the impact of struts on the European Space Agency Deep Space Antennas efficiency and sidelobes
No full textLarge reflector antennas require struts to mechanically support feeds or sub-reflectors. In many cases, these affect the antenna performance. This paper proposes a comparison between the European Space Agency Deep Space Antennas (DSAs) 3 and 4, in terms of impact of struts on antenna efficiency and sidelobes. The numerical simulations, carried out on the entire antenna model using Physical Optics, indicates that the struts of the new DSA4 can provide a reduced impact due to the different design
Snow on Polar Radomes and Performance Deterioration at 26 GHz for a Receiving Ground Station: the SNOWBEAR Project
No full textOn De-Pointing Effects Caused by Snow Accumulation on Radomes for Ground Stations Working at K-Band: An analysis of the SNOWBEAR project
No full textGround stations working at high frequencies, such as the K-band, installed at polar latitudes and protected by radomes, are increasingly used to support modern satellites. The effect that snow accumulation may have on the radome is consequently important, as at these frequencies it may jeopardize the satellite link. This article analyses an operative case, referred to as SNOWBEAR (Svalbard grouND StatiOn for Wide Band Earth observation dAta Reception), where a 6.4-m antenna has been installed at Svalbard, Norway, to track an Earth observation (EO) satellite, NOAA-20, for a period of two years. We demonstrate, using experimental data and numerical models, that a chief effect can be described in terms of de-pointing of the main beam, with a particular focus on the difference of de-pointing between the sum and delta modes, and that a real-time, effective, solution is not yet available
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
Comparison between Milling and Wire Erosion for Manufacturing All-Metal High-Pass Dichroic Mirrors
No full textGround stations for space communications are often required to operate at different frequency bands, normally spanning from L band to Ka band. In some cases, especially when they are realized according to a beam-waveguide architecture, dichroic mirrors can be used to insert/extract different bandwidths along the propagation of the beam. As these antennas generally operate high-power transmitting channels, all-metal high-pass dichroic mirrors are usually preferred. This paper presents a quantitative comparison between two possible manufacturing techniques for such mirrors, milling and wire erosion, in terms of manufacturing possibilities, accuracy and surface roughness. To this aim, a test case for dichroic mirrors, aimed at installation in the deep space antennas of the European Space Agency to support future missions to the Moon and designed to be as transparent as possible for the K band, is 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
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