| 1. |
- Alef, Walter, et al.
(author)
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BRAND - The next generation receiver for VLBI
- 2018
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In: Proceedings of Science. - Trieste, Italy : Sissa Medialab. - 1824-8039. ; 344
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Conference paper (peer-reviewed)abstract
- The aim of the BRAND EVN project is to build a very wide receiver prototype for primary focus with a frequency range from 1.5 GHz to 15.5 GHz In addition we will investigate solutions for secondary focus telescopes. The project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730562 [RadioNet]. We present the status of the project which was started on January 1st, 2017 and is progressing smoothly: Feed, LNA, filters, major digital components, and some of the firmware are available now. © Copyright owned by the author(s) under the terms of the Creative Commons.
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| 2. |
- Carozzi, Tobia, 1966, et al.
(author)
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Enhancing SKA Band 1 Polarimetry by Using Two Different Feed Rotations
- 2018
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In: 2018 2nd URSI Atlantic Radio Science Meeting, AT-RASC 2018. - 9789082598735
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Conference paper (peer-reviewed)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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| 3. |
- Dong, Bin, 1984, et al.
(author)
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Design of an Asymmetrical Quadruple-ridge Flared Horn Feed: a Solution to Eliminate Polarization Discrepancy in the Offset Reflecting Systems
- 2018
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In: IET Conference Publications. ; 2018:CP741
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Conference paper (peer-reviewed)abstract
- Quadruple-ridge Flared Horns (QRFHs) have been showing qualified performance as the feed antennas for the reflecting systems in the Square Kilometre Array (SKA). However, due to the offset optics of the SKA reflecting system, identical illuminations from dual polarizations of the feed would but result in different system performance. This difference would become more severe towards high frequencies and may cause the worse polarization unqualified for the desired specification. In this paper, an asymmetrical QRFH feed working over Band B (4.6–24 GHz) is proposed and optimized to tackle this problem.The asymmetrical Band-B feed is composed of two different and orthogonal pairs of both ridges and sidewall quad-pieces, so as to provide orthogonal polarizations but different illuminations. Simulated results show that, by this asymmetrical design different beamwidths and different combinations of sub-efficiencies can be provided for two polarizations, so as to eliminate the polarization discrepancy over most of the bandwidth. Benefitting from this elimination, both polarizations of the Band-B feed have now achieved the SKA specification in terms of aperture efficiency.
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| 4. |
- Flygare, Jonas, 1988, et al.
(author)
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Beam pattern measurement on offset Gregorian reflector mounted with a wideband room temperature receiver for the Square Kilometre Array
- 2018
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In: 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting (APSURSI2018). - 9781538671023 ; APSURSI 2018, s. 1759-1760
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Conference paper (peer-reviewed)abstract
- We present measured on-dish beam patterns for a room temperature spline-profile quad-ridge flared horn (QRFH) feed designed for the Square Kilometre Array (SKA) Band 1 covering 350-1050 MHz. The feed and LNA package has been mounted on the offset Gregorian SKA precursor prototype telescope, Dish Verification Antenna 1 (DVA-1) located at the Dominion Radio Astrophysical Observatory (DRAO) near Penticton, British Columbia, Canada. Telescope beam pattern cuts are measured by sweeping over the sun and adding corrections for the solar disk size, elevation and aperture efficiency. Sensitivity calculated with measured receiver noise show good agreement with the predicted performance.
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| 5. |
- Flygare, Jonas, 1988, et al.
(author)
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BRAND: Ultra-Wideband Feed Development for the European VLBI Network - A Dielectrically Loaded Decade Bandwidth Quad-Ridge Flared Horn
- 2018
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In: IET Conference Publications. - : Institution of Engineering and Technology. ; 2018:CP741
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Conference paper (peer-reviewed)abstract
- We present the design of an ultra-wideband dielectrically loaded Quad-Ridge Flared Horn (QRFH) feed for the European Very Long Baseline Interferometry Network (EVN) developed under the RadioNet project BRoad-bAND (BRAND). The feed covers a frequency bandwidth ratio of 10:1 and has an average aperture efficiency of 50 percent simulated in primary focus setup on the Effelsberg telescope (f/D = 0.3). The feed is dual-polarized and has an input reflection better than −10 dB over the whole 1.5–15.5 GHz frequency band. We also introduce an Analytic-Spline-Hybrid (ASH) optimization scheme for the QRFH ridge and sidewall profiles.
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| 6. |
- Flygare, Jonas, 1988, et al.
(author)
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Design trade-offs in feed systems for ultra-wideband VLBI observations
- 2018
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Conference paper (other academic/artistic)abstract
- Due to the advanced capability of today’s ultra-wideband feed systems and low-noise amplifiers, interesting upgrades for future VLBI receiver and tele- scope design should be considered. Multiple input pa- rameters need to be taken into account for optimal sensitivity and applications of the future astronomical and geodetic observational systems. In this paper we present an overview of some trade-offs for wideband systems between SEFD, bandwidth and telescope re- flector optics. We evaluate receiver bandwidths from 3.5:1 to 10.3:1 bandwidth within the frequency range 1.5-24 GHz in different configurations. Due to poten- tial RFI-pollution of the lower frequencies we present potential feed upgrades for the most common reflector geometries ofVGOS and EVN telescopes that mitigate this problem. The results of this work is relevant for fu- ture VLBI stations and telescope design in general. Keywords
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| 7. |
- Flygare, Jonas, 1988
(author)
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Ultra-wideband feed design and characterization for next generation radio telescopes
- 2018
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Licentiate thesis (other academic/artistic)abstract
- Radio telescopes are used as tools for observations in both radio astronomy and geodesy. To observe the weak sources in space, highly sensitive receivers headed by optimized reflector feeds are needed. Wideband and ultra-wideband (UWB) receiver systems enable large continuous frequency bandwidth and reduce the number of receivers that are needed. Therefore, they are attractive for the next generation of large reflector arrays such as the Square Kilometre Array (SKA) and the Next Generation Very Large Array (ngVLA). To achieve highly sensitive wideband and UWB performance with reflector feeds, a near-constant beamwidth and good impedance match are required over large frequency bands. The quad-ridge flared horn (QRFH) is a robust and popular UWB feed technology for this purpose. Typically, the QRFH achieve good performance up to 6:1 bandwidth and are designed for high aperture efficiency. However, due to the very small noise contributions of today's low-noise amplifiers (LNA), it is becoming more relevant to design specifically for high sensitivity. A drawback in existing state-of-the-art QRFH designs, is that they suffer from narrowing beamwidth as the frequency increases over the bandwidth. To meet the demand for high sensitivity observations over large bandwidths, these challenges need to be addressed. In this thesis, the spline-defined QRFH design for the room temperature SKA Band 1 feed package over 350-1050 MHz is presented. The QRFH spline-profile is optimized for high sensitivity over the 3:1 bandwidth for the SKA reflector dish. The thesis also introduces a low-profiled dielectric load at the center of a QRFH design for 10:1 bandwidth for the BRAND project. The dielectric load improves the beamwidth performance over the 1.5-15.5GHz frequency band, while keeping the complexity of the QRFH concept low. Both of the approaches that are introduced here are applicable for any future QRFH design, and are therefore relevant for the community in the hunt for high sensitivity observations.
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| 8. |
- Flygare, Jonas, 1988, et al.
(author)
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Ultra-wideband feed systems for the EVN and SKA - evaluated for VGOS
- 2018
-
Conference paper (other academic/artistic)abstract
- The design of the Square Kilometre Array (SKA) project for radio astronomy is now materializing at a rapid speed; the EU Horizon 2020 RadioNet project BRoad-bAND (BRAND) has the ambition to deliver a decade bandwidth receiver for EVN. The ultra-wideband quad-ridge flared horn (QRFH) feed systems developed for these projects show good performance within the geodetic VLBI Global Observing System (VGOS) frame due to the overlapping frequency bands and reflector geometries. We estimate, through simulation, system equivalent flux density (SEFD) of the two feed systems in the VGOS reflector and compare the it to the existing system installed on one of the 13.2 m diameter reflectors of the Onsala twin telescope (OTT). The two frequency bands analyzed cover 1.5−15.5 GHz and 4.6−24 GHz. Both systems show SEFD better than 1000 Jy over large parts of resp. frequency band - comparable to the 3−18 GHz feed systems. For the SKA QRFH over 4.6−24 GHz, the water vapor absorption line at 22 GHz is within the operational band, therefore we study the application of water-vapor radiometry in line-of-sight of the telescope.
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| 9. |
- Walker, G. W., et al.
(author)
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Optical design and verification of the 4mm receiver for the 20m telescope at Onsala Space Observatory
- 2018
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 10015
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Conference paper (peer-reviewed)abstract
- The work of this research is the design, analysis and verification of the optical performance of a 4 mm receiver channel for the 20 m telescope at Onsala Space Observatory, Onsala, Sweden. The 4 mm (75 GHz) receiver is a newly proposed channel designed to be installed parallel to the existing 3 mm (100 GHz) channel targeting new science at that longer wavelength. Gaussian beam mode analysis is used to produce the fundamental optical design of the system. The design is then analysed more accurately with the physical optics approximation. We report on the comparison of simulation and measurement and verification of the system design.
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| 10. |
- Weinreb, Sander, et al.
(author)
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Cryogenic 1.2 to 116 GHz Receiver for Large Arrays
- 2018
-
In: IET Conference Publications. - : Institution of Engineering and Technology. ; 2018:CP741
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Conference paper (peer-reviewed)abstract
- Current and future large arrays for radio astronomy are compared and the Next Generation Very Large Array, ngVLA, is introduced. Receiver requirements are described and a 4-feed system covering 1.2 to 116 GHz, in a single vacuum cryogenic enclosure is presented followed by description of the reflector optics, the wide-band feeds, and the expected system performance
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