Introduction to Radio Telescopes. Frank Ghigo, NRAO-Green Bank. The Fourth NAIC-NRAO School on Single-Dish Radio Astronomy July 2007. Terms and Concepts. Jansky Bandwidth Resolution Antenna power pattern Half-power beamwidth Side lobes Beam solid angle Main beam efficiency
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Frank Ghigo, NRAO-Green Bank
The Fourth NAIC-NRAO
School on Single-Dish Radio Astronomy
Terms and Concepts
Antenna power pattern
Beam solid angle
Main beam efficiency
Aperture illumination function
Verschuur, 1985. Slide set produced by the Astronomical Society of the Pacific, slide #1.
Flux = Power/Area
Flux Density (S) = Power/Area/bandwidth
A “Jansky” is a unit of flux density
Beam solid angle
Pn = normalized power pattern
Kraus, 1966. Fig.6-1, p. 153.
Main beam efficiency, M
Aperture efficiency, ap
Effective aperture, Ae
Geometric aperture, Ag
Power WA detected in a radio telescope
Due to a source of flux density S
power as equivalent temperature.
Antenna Temperature TA
Effective Aperture Ae
Kraus, 1966. Fig.1-6, p. 14.
A gaussian aperture illumination
gives a gaussian beam:
Kraus, 1966. Fig.6-9, p. 168.
Including atmospheric absorption:
Effect of surface efficiency
= total noise power detected, a result of many contributions
Thermal noise T
= minimum detectable signal
For GBT spectroscopy
Thompson, Moran, Swenson, 2001. Fig 2.5, p. 58.
Kraus, 1966. Fig. 3-6. p. 70; Fig. 3-5, p. 69.
For an extended object with source solid angle s,
And physical temperature Ts, then
In general :
Tant = Tcal * (peak-baseline)/(cal – baseline)
(Tcal is known)
Convert counts to T