1,721,018 research outputs found
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
A non-redundant sampling representation requiring the same number of spherical near-field measurements for both onset and offset mountings of a Quasi-Planar Antenna
No full textAn effective non-redundant near-field to far-field transformation (NFTFFT) with spherical scan, which accounts for the offset mounting of a quasi-planar antenna and employs the same number of NF data as in the case of onset mounting, is developed in this paper. The interest for this NFTFFT arises from the fact that the mounting where the antenna and the measurement sphere centers coincide could result to be impracticable. In this case, the amount of NF data required by the traditional spherical NFTFFT can significantly increase. In the proposed NFTFFT, this drawback has been overcome by accurately recovering these NF data from the collected non-redundant ones via a sampling expansion, obtained by exploiting the non-redundant sampling representations and assuming the antenna as enclosed in an oblate spheroid. Numerical and experimental results assessing the effectiveness of the developed technique are reported
Near to far-field plane-polar transformation from probe positioning error affected data
No full textIn this article, two efficient approaches for the correction of known positioning errors of the measurement probe in a plane-polar near to far-field (NTFF) transformation, requiring a minimum number of NF data in the case of quasi-planar antennas, are presented and experimentally assessed. Such a NTFF transformation benefits from a non-redundant sampling representation of the voltage detected by the probe got by modeling an antenna with a quasi-planar geometry through a double bowl, a surface consisting of two circular bowls with the same aperture radius, but with lateral bends which may differ to better fit the antenna shape. The uniform samples, i.e., those at the points set by the representation, are accurately retrieved from the collected not regularly distributed ones either by applying a singular value decomposition based approach or an iterative scheme. Then, the input NF data necessary for the classical plane-rectangular NTFF transformation are evaluated from the so retrieved non-redundant uniform samples through a 2-D optimal sampling interpolation formula
An effective iterative algorithm to correct the probe positioning errors in a non-redundant plane-rectangular near-field to far-field transformation
No full textAn algorithm for the effective compensation of known positioning errors, affecting the samples acquired by the probe in a non-redundant plane-rectangular (PR) near-field to far-field (NFFF) transformation, is presented and fully assessed by experimental tests. This transformation adopts a non-conventional PR scan, named planar wide-mesh scan (PWMS), characterized by meshes widening more and more as their distance from the measurement plane center increases, and uses a nonredundant sampling representation of the probe voltage. Such a representation is obtained by considering the antenna as contained in an oblate spheroid, to precisely determine the input NF data for the traditional PR NFFF transformation from the PWMS samples. These samples are unavailable in presence of positioning errors, but, as it will be shown, can be effectively retrieved from the errors affected ones by applying an iterative procedure
A spherical near-to-far-field transformation using a non-redundant voltage representation optimized for non-centered mounted quasi-planar antennas
No full textThis research falls in the antenna measurements related topic, and deals with the problem occurring in the classical spherical near-to-far-field (NTFF) transformation, when it becomes unpractical to mount the antenna under test (AUT) with its center at the center of the scanning sphere. This issue reflects in a growth of the number of near-field (NF) samples to be acquired, since this number depends on the radius of the minimum sphere, which contains the antenna, and is centered at the scanning sphere center. The non-redundant sampling representations of the electromagnetic field are conveniently exploited, to develop an effective spherical NTFF transformation for non-centered AUTs with quasi-planar geometry, requiring a minimum amount of NF samples, and nearly the same as that for a centered mounting of the AUT. Then, the NF data needed to perform the classical NTFF transformation are determined in efficient way from the acquired non-redundant NF samples by employing an accurate 2-D sampling interpolation scheme. Thus, it is possible to significantly save measurement time. Some simulation and laboratory results are reported to show the effectiveness of the developed technique, which takes into account a non-centered AUT mounting
On the correction of the probe positioning errors in a non-redundant bi-polar near to far-field transformation
No full textAn effective procedure allowing one to correct the positioning errors in a bi-polar near to farfield transformation (NTFFT) technique, that requires a minimum number of near-field (NF) data, has been here assessed from the experimental viewpoint. This NTFFT utilizes an optimal sampling interpolation formula, got by considering the antenna under test as contained in an oblate spheroid and applying the non-redundant sampling representation to the probe measured voltage, to precisely determine the NF data needed by the standard NTFFT with plane-rectangular scan from the voltages at the points prescribed by the sampling representation. These voltages are not known and are accurately recovered from the positioning errors affected measured ones by applying an efficient singular value decomposition based technique
A Nonredundant Sampling Representation Managing an Offset Mounting of an Elongated Antenna in a Spherical Near-Field Facility
No full textAn efficient spherical near-field-to-far-field transformation (NFTFFT), which takes into account the offset mounting of an elongated antenna and employs the same nonredundant (NR) amount of near-field (NF) data as in the onset mounting case, is presented. The interest for this NFTFFT is due to the fact that, for practical reasons, a mounting where the antenna and the scan sphere centers coincide is not always possible. In this case, the amount of NF measurements required by the traditional spherical NFTFFT can significantly increase. In the developed NFTFFT, this drawback has been overcome by accurately recovering these NF data from the gathered NR probe voltage samples through a sampling expansion, attained by suitably using the NR sampling representations and assuming the antenna as enclosed in a prolate spheroid. Numerical and experimental results are reported in order to assess the efficacy of the developed technique
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