| 1. |
- Flygare, Jonas, 1988, et al.
(författare)
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Sensitivity simulation and measurement of the SKA Band 1 wideband feed package on MeerKAT
- 2019
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Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019. ; EuCAP 2019
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Konferensbidrag (refereegranskat)abstract
- Advances in wideband feed technology for radio telescopes enable high sensitivity observations over large bandwidths. The wideband quad-ridge flared horn (QRFH) feed package for Band 1 of the Square Kilometre Array (SKA) was optimized for high sensitivity. The 3:1 feed package covers 350-1050 MHz and is a complete room temperature system with low-noise amplifiers integrated inside the ridges of the horn. The QRFH is dual-linear polarized and designed with spline-defined profiles for the horn and ridge shape. Measured feed s-parameters show input reflection less than -11 dB across the band with good port isolation. In this paper we present the first measured sensitivity levels of the Band 1 feed package, which was tested on the SKA precursor reflector MeerKAT. We also present measured aperture efficiency and intrinsic cross-polarization (IXR). The measured results show good agreement with simulations.
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| 2. |
- Bergman, Jan, et al.
(författare)
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DARTS - Distributed Aperture Radio Telescope in Space - First Starlight Explorer
- 2018
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Ingår i: 2018 2nd URSI Atlantic Radio Science Meeting, AT-RASC 2018. - : IEEE. - 9789082598735
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Konferensbidrag (refereegranskat)abstract
- SBERGMANURSIATDARTS1. However, despite the strong science case for the opening up of a brand-new window on the Universe at a low radio frequency that is largely unexplored, mission proposals have been significantly challenged with the lack of flight proven technologies, to implement a space telescope using low cost small spacecraft formations. In recent years, the advent of CubeSat technologies, interplanetary missions and radio frequency inter-satellite link (ISL) technology, have improved to the point that developing a mission where a space radio telescope is formed using a constellation of small satellites is now viable, to bring unique science offerings.
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| 3. |
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| 4. |
- Carozzi, Tobia, 1966, et al.
(författare)
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A Fundamental Figure of Merit for Radio Polarimeters
- 2011
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 59:6, s. 2058-2065
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Tidskriftsartikel (refereegranskat)abstract
- Many modern radio applications, such as astronomy and remote sensing, require high-precision polarimetry. These applications put exacting demands on radio polarimeters (antenna systems that can measure the state of polarization of radio sources), and in order to assess their polarimetric performance, a figure of merit (FoM) would be desirable. Unfortunately, we find that the parameter commonly used for this purpose, the cross-polarization ratio, is not suitable as a polarimetry FoM unless it is given in an appropriate coordinate system. This is because although the cross-polarization ratio is relevant for raw, uncalibrated polarimetry, in general it is not relevant to the quality of the polarimetry after polarimetric calibration. However, a cross-polarization ratio can be constructed from invariants of the Jones matrix (the matrix that describes the polarimetric response of a polarimeter) that quantifies polarimetric performance even after calibration. We call this cross-polarization ratio the intrinsic cross-polarization ratio (IXR) and conclude that it is a fundamental FoM for polarimeters. We then extend the IXR concept from the Jones calculus to the Mueller calculus and also to interferometers, and we give numerical examples of these parameters applied to the Parkes radio telescope, the Westerbork synthesis radio telescope, and the Effelsberg telescope.
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| 5. |
- Carozzi, Tobia, 1966, et al.
(författare)
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Differentially Rotated SKALA4.1 Antennas in Vogel Configurations
- 2023
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Ingår i: 2023 35th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2023.
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Konferensbidrag (refereegranskat)abstract
- We have studied the effects of non-aligned SKALA4.1 antennas in dense arrays with a Vogel layout. We find that the Vogel array is too dense at 2 m minimum inter-element distance for differential alignments to mitigate mutual-coupling, but polarimetric performance can be improved regardless.
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| 6. |
- Carozzi, Tobia, 1966, et al.
(författare)
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Enhancing SKA Band 1 Polarimetry by Using Two Different Feed Rotations
- 2018
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Ingår i: 2018 2nd URSI Atlantic Radio Science Meeting, AT-RASC 2018. - 9789082598735
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Konferensbidrag (refereegranskat)abstract
- We investigate the possibility of enhancing the polarimetric performance of the Square Kilometre Array (SKA) telescope's band 1 by mounting the feeds with two different rotations relative the dish. One rotation aligns the two polarizations along the horizontal and vertical directions and the other rotation is 45 degrees to the horizontal, vertical directions. Taken together, this configuration amounts to introducing a simple and cheap type of polarization diversity. We find that such a configuration can improve polarimetry. This is important since the offset gregorian dish design employed for SKA1-mid tends to produce beam-shapes that are not rotationally symmetric, and thus polarimetry tends to vary azimuthally.
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| 7. |
- Carozzi, Tobia, 1966
(författare)
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Imaging on a sphere with interferometers: The spherical wave harmonic transform
- 2015
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Ingår i: Monthly Notices of the Royal Astronomical Society: Letters. - : Oxford University Press (OUP). - 1745-3925 .- 1745-3933. ; 451:1, s. L6-L10
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Tidskriftsartikel (refereegranskat)abstract
- I present an exact and explicit solution to the scalar (Stokes flux intensity) radio interferometer imaging equation on a spherical surface which is valid also for non-coplanar interferometer configurations. This imaging equation is comparable to ω-term imaging algorithms, but by using a spherical rather than a Cartesian formulation this term has no special significance. The solution presented also allows direct identification of the scalar (spin 0 weighted) spherical harmonics on the sky. The method should be of interest for future multispacecraft interferometers, wide-field imaging with non-coplanar arrays, and cosmic microwave background spherical harmonic measurements using interferometers.
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| 8. |
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| 9. |
- Carozzi, Tobia, 1966
(författare)
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Intrinsic cross-polarization ratio (IXR) for antenna arrays and improving polarimetry via polarization diversity
- 2015
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Ingår i: Proceedings of the 2015 International Conference on Electromagnetics in Advanced Applications, ICEAA 2015. ; , s. 630-633
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Konferensbidrag (refereegranskat)abstract
- I extend the concept of the intrinsic cross-polarization ratio (IXR) to an array of an arbitrary number of antenna elements. IXR is a figure-of-merit for the polarimetric performance of dual-polarized antenna elements, but it is easily generalized to more than two antennas by considering the effective dual-polarized response of polarimetrically beam-formed array. I also show that for a sparse array (i.e. arrays in which mutual-coupling can be ignored) of identical dual-polarized elements all with the same alignment, it is not possible to make the array IXR better than the IXR of dual-polarized element through beam-forming. However, such arrays can be improved by physically rotating the dual-polarized elements such that their alignments are not all the same. An array in which not all the dual-polarized elements do not all have the same alignment is a form of polarization diversity. I argue that polarization diversity is way to improve the polarimetric performance of arrays.
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| 10. |
- Carozzi, Tobia, 1966
(författare)
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New definition for dual-polarized antenna sensitivity
- 2019
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Ingår i: Proceedings of the 2019 21st International Conference on Electromagnetics in Advanced Applications, ICEAA 2019. ; , s. 979-981
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Konferensbidrag (refereegranskat)abstract
- Sensitivity is arguably the single most important defining characteristic of a radio telescope. This is because it sets the threshold for what sources can reasonably be detected. Intuitively, sensitivity is the noise level of an antenna referenced to measurements on the sky. So the lower it is, the easier one would expect to make detections of weak sources, and from this it would make sense to call it loosely the 'detection power' of telescopes. But this sensitivity concept does not take into account the polarization of the source or the polarization of the antenna itself, and could thus lead to problems. The traditionally used definition of sensitivity is namely based on single antennas. This antenna based sensitivity is derived assuming that the two polarized antennas that make up radio polarimeters are orthogonal and have identical amplitude gains. In practice these dual-polarized antennas will have different gains and exhibit polarization leakage due to nonorthogonality. To address these more realistic dual-polarized antennas, I introduce a new definition of dual-polarized (or full-polarization) antenna sensitivity. This new definition of sensitivity is a polarimetric generalization of the scalar, system equivalent flux density (SEFD). The new definition generalizes the total sensitivity, and also provides a quantity that represents sensitivity to purely polarized flux. Based on the new SEFD definition, I find that the intuitive notion that identical and orthogonal antennas should typically have better sensitivity than dissimilar, leaky antennas.
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