Felix James “Jay” Lockman NRAO Green Bank, WV Radio Astronomy An Introduction References Thompson, Moran & Swenson Kraus (1966) Christiansen & Hogbom (1969) Condon & Ransom (nrao.edu) Single Dish School Proceedings (2002) ADS GOLDSMITH CAMPBELL LISZT ★★★★
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Radio Astronomy An Introduction · Radio Astronomy An Introduction References Thompson, Moran & Swenson Kraus (1966) Christiansen & Hogbom (1969) ... What does every radio telescope
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Enclose the antenna in a blackbody of temperature Tb
Ta =TbAe
!2
!
4!P"(",#) d!
!a =!
4!P"(!,") d!defining
Ta =Ae
!2
!
4!Tb"(", #) P"(",#) d! (K Hz!1)
But we are looking through the atmosphere!
Specific Intensity (Brightness)
Flux Density
A flux density per unit area is actually a brightness!
I!(!,") (Watts m!2 Hz!1 str!1)
S! =!
!s
I!(!, ") d! (Watts m!2 Hz!1)
Specific Intensity (Brightness)
Flux Density
A flux density per unit area is actually a brightness!
I!(!,") (Watts m!2 Hz!1 str!1)
S! =!
!s
I!(!, ") d! (Watts m!2 Hz!1)
What determines P?
Aperture Plane
“Boxcar” Function
“Sinc” Function
FT
Uniform Illumination
For Uniform Illumination
Airy rings
Main Beam and Sidelobes
Main Beam Efficiency
(from Kraus 1966)
• In the far field, the electric-field pattern, f, of an aperture antenna is the Fourier transform of the electric field illuminating the aperture. And the power pattern, P, is the square of the modulus of f.