| 1. |
- Atia Abdalmalak, Kerlos, et al.
(författare)
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Ultrawideband Conical Log-Spiral Circularly Polarized Feed for Radio Astronomy
- 2020
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 68:3, s. 1995-2007
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Tidskriftsartikel (refereegranskat)abstract
- In order to meet the requirements of the new generation of radio telescopes, we have developed a new topology called DYQSA, which stands for DYson Quad-Spiral Array. The design exhibits dual circular polarization contrary to dual linear polarization of state-of-the-art feeds. It covers the required ultrawideband (UWB) from 2 to 14 GHz with an almost constant and real input impedance which facilitates the design of the feeding structure and the low-noise amplifiers (LNAs). Different versions are investigated for enhancing feed performance, ensuring higher aperture efficiencies and mechanical stability. The simulation results of the reflector loaded by the proposed feed show an aperture efficiency of 65%±5% with a noise antenna temperature around 14 K and a system equivalent flux density (SEFD) of about 1300 Jy, both averaged over the required bandwidth at zenith. Measurements of the single-element and the four-element feeds are presented. Comparisons with other state-of-the-art feeds are shown in terms of total aperture efficiencies, design adaptability to different reflectors, calibration signal injection, and the required number of LNAs per feed, cost, and physical volume.
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| 2. |
- Flygare, Jonas, 1988, et al.
(författare)
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Dielectrically Loaded Quad-Ridge Flared Horn for Beamwidth Control Over Decade Bandwidth-Optimization, Manufacture, and Measurement
- 2020
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 68:1, s. 207-216
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Tidskriftsartikel (refereegranskat)abstract
- We present the design, manufacture, and measured performance of a dielectrically loaded quad-ridge flared horn (QRFH) feed for decade bandwidth radio astronomy application. The introduction of the dielectric load improves the QRFH beamwidth control in H-plane at the mid and upper frequency range. Consequently on the reflector, illumination efficiency, phase efficiency, and the intrinsic cross-polarization ratio (IXR) have been improved. The dielectric load is made from homogeneous low-loss polytetrafluoroethylene and has a low profile with a cylinder shape for simple installation at the center of the QRFH. The dielectrically loaded QRFH presented here covers 1.5-15.5 GHz with a calculated average aperture efficiency above 50% on a f/D = 0.3 prime-focus reflector. We present a calculation of system noise temperature and sensitivity for the QRFH on a 100 m prime-focus reflector. Measured beam patterns of the QRFH are in good agreement with the simulations over the full frequency band. The input reflection coefficient was predicted to be below -10 dB across the bandwidth. We present a tolerance analysis that explains why the measured one deviates.
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| 3. |
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| 4. |
- Svanelöv, Eric, 1988-, et al.
(författare)
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Funktionshinderidrott ett tveeggat svärd - men de positiva upplevelserna väger över
- 2020
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Ingår i: Idrottsforskning.se. - Stockholm : Centrum för Idrottsforskning. - 2002-3944. ; :8 Aug
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Funktionshinderidrotten är ett tveeggat svärd - den kan både stärka deltagarnas identiteter och sociala relationer, men även upplevas vara exkluderande och marginaliserande från annan idrott. Men i slutändan väger det positiva över, menar deltagarna själva.
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