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Aeff / Tsys evaluation for AAlo sensors

Aeff / Tsys evaluation for AAlo sensors . Cambridge 8th-10th December 2010. Federico Perini 1 , Jader Monari 1 , Giuseppe Virone 2 , Pietro Bolli 3. 1 INAF/IRA-Medicina radio telescopes 2 IEIIT/ CNR-Politecnico di Torino 3 INAF/Osservatorio Astronomico di Cagliari.

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Aeff / Tsys evaluation for AAlo sensors

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  1. Aeff/Tsys evaluation for AAlo sensors Cambridge 8th-10th December 2010 Federico Perini1, Jader Monari1, Giuseppe Virone2, Pietro Bolli3 1 INAF/IRA-Medicina radio telescopes 2 IEIIT/CNR-Politecnico di Torino 3 INAF/Osservatorio Astronomico di Cagliari

  2. Compare differentantennas? White paper on the antenna sub-systems for the SKA project: P.D. Patel, “Antenna Concepts Consideration for SKA”, part of the SKA memo 91, “An SKA Engineering Overview” by P. Hall G. Cortes Medellin, “Antenna Noise Temperature Calculations,” SKA Technical Memo Series n° 95

  3. Zenith D 0 Q 0 Horizon F Direction in the azimuth plane 0 Antenna Temperature General formulation: where Pn(v;q,f) represents the antenna radiation pattern andTb(v;q’,f’), the brightness temperature distribution (here Tb(v;q’)) Pn computation is demanded to an external EM Antenna CAD (GRASP, CST,…) whereas Tb is evaluated by the Matlab code itself

  4. Coordinate reference systems Two different coordinate reference systems: Pn is defined respect to the one related to the antenna itself (z axes = main beam or pointing direction) whereas Tb is defined respect to the Earth (z’ = local zenith) Zenith To compute the integral we need only one coordinate system, so we need the conversion from one to another: Circumference at fixed  correspond to several values of  Ground

  5. Ground contribution The brightness temperature can be split in 2 main contributions: from sky (0° < q’ < 90°) and from ground (90° < q’ < 180°) Moreover the contribution from the ground (emission and scattering), is a polarization dependent process:

  6. Brightness Temperature The Tb model is the one proposed by [Cortes], which includes the effects of the absorption coefficients of water vapour and oxygen, the CMB and the emission from the galaxy Atmosphere temperature Zenithal opacity Effect of Earth curvature Tgo and b are function of the observed sky region [Cortes] suggests reasonable values as: Tgo=20K e b=2.75.

  7. Tbcalculator ftp.ira.inaf.it/pub/outgoing/fperini/

  8. Ta calculatorexample 1: BEST-1 @ 408MHz

  9. Ta calculatorexample 2: 32mt VLBI Dish @ 22GHz

  10. AAlo Vivaldi antenna Pattern at fmax=450MHz For BEST-1 Tcomp=150 min, using two different spacing for Pn, fine (0.04°) for the main beam and coarse (0.68° ) outside the main beam

  11. AAlo Vivaldi antenna

  12. TREC? 50Ohm 75Ohm Trec = TLNA = 30K @ 300K seems reasonable

  13. Aeff/Tsys?

  14. Aeff/Tsys

  15. Double size antenna?

  16. Future works • Tb(v;q’) Tb(v;q’,f’) • Considering the coupling effect • Take in account the array factor at station level (antennas positioning) and at full array level (stations positioning) Stronger collaboration with all partners involved in this task Thanks!

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