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| * Below you find the forward and beam efficiencies upto 280 GHz measured in March 2005 ([http://www.iram.fr/IRAMFR/ARN/aug05/node6.html IRAM Newsletter 8/05]). Values above 300 GHz are predictions based on the observations compiled in the IRAM Annual Report 2007 attachment:IRAM_2007.pdf ). || '''freq''' || '''HPBW''' || '''Beff''' || '''Aeff''' || '''S/TA*''' || '''Feff''' || '''Comments''' || || '''(GHz)''' || '''(arcsec)''' || '''(%)''' || '''(%)''' || '''(Jy/K)''' || '''(%)''' || || || || (1) || (2) || (3) || (4) || (5) || (6) || ||72 (extrapolated) || 34 || 79 || || 6.0 || 95 || || ||77 (extrapolated) || 32 || 79 || || 6.0 || 95 || || ||86 || 29 || 78 || || 6.0 || 95 || || ||110 || 22 || 75 || || 6.3 || 95 || || ||145 || 17 || 69 || || 6.7 || 93 || || ||170 || 14.5 || 65 || || 7.1 || 93 || || ||210 || 12 || 57 || || 7.9 || 91 || || ||235 || 10.5 || 52 || || 8.7 || 91 || || ||260 || 9.5 || 46 || || 9.5 || 88 || || ||279 || 9 || 42 || ||10.4 || 88 || || ||310 || 7.9 || || 37 || || || predicted || ||345 || 7.1 || || 32 || || || predicted || ||360 || 6.8 || || 30 || || || predicted || 1. The '''half power beam width, HPBW''', can be well fitted by: HPBW/arcsec = 2460/freq/GHz. 1. '''Main beam efficiency Beff.''' The data can be well fit by a Ruze function Beff = 1.2 Aeff' exp[-(4pi R sigma/ lambda)^2] with sigma being the rms value of the surface errors of the main dish, R the reduction factor for a steep main reflector, Aeff' is the aperture efficieny of the perfect telescope and lambda the wavelength in mm. The data can be fitted by R*sigma = 0.07 and epsilon = 0.69. 1. '''Aperture efficiency, Aeff.''' The aperture efficiency of the 30m telescope can be obtained via pointings on point-like celestial calibrators like Uranus or Mars. In the approximation that the beam is Gaussian and the edge taper is -14dB, it can also be derived from the beam efficiency using Aeff=Beff*0.80 (attachment:spatial_response_framework_v1.8.pdf) 1. '''Point source sensitivity S/TA*.''' S/TA* is 3.906*Feff/Aeff Jy/K for the 30m (see attachment:cali_rep.pdf). 1. '''Gain-elevation curves.''' The most recent curves are given in the IRAM Annual Report 2007 1. '''Forward efficiency Feff.''' The values for Feff are valid after the 12th of December 2000 when a new reflecting ring was put around the secondary mirror. Forward efficiencies are derived from skydips. 1. '''Error beams.''' A part of the power pattern is distributed in three error beams (see the analysis of attachment:greve_1998.pdf). The size of the described Gaussians is unchanged, however the main beam efficiencies have been improved in the meanwhile, lowering the strengths of the error beams. A new paper is in preparation. Astronomers should take the contribution of the error beam into account when converting antenna temperatures to brightness temperatures, especially when mapping extended sources. 1. Historic values: [http://www.iram.es/IRAMES/telescope/telescopeSummary/beam_effis.html Plot of efficiencies against frequency, measured in 2000], [http://www.iram.es/IRAMES/telescope/telescopeSummary/effi_history.html Compilation of efficiencies obtained in the past till 2001]. ---- New values measured in August 2007: |
=== Efficiencies measured 8/07 (and 6/08) === |
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| || 72 || 33.4 || 98 || 79 || 65 || 5.9 || estimated || | |
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| 1. '''Half power beam width HPBW.''' The HPBW can be well fitted by: HPBW/arcsec=2406/Freq/GHz or HPBW/rad=1.166 W/D, with the wavelength W and the telescope diameter D. | * Measurements were conducted during night time when effects of anomalous refraction and any panel buckling are strongly reduced. In addition, the panel backstructure is heated in a random fashion since 8/05, improving on its thermal balance. (JP, CT, CK 2/09). ABCD receivers were used to observe Uranus and Mars, while small. Receivers were tuned to single sideband. Planetary brightness temperatures Tb from ASTRO/GILDAS: * Mars: 215K constant with frequency * Uranus: 139K at 86GHz, 116K at 145GHz, 102K at 210GHz, 94.5K at 260GHz, 85.6K at 345GHz following Griffin & Orton 1993 1. '''Half power beam width HPBW.''' The observed HPBWs can be well fitted by '''HPBW/arcsec=2406/Freq/GHz''' or HPBW/rad=1.166 Lambda/D, with the wavelength Lambda and the telescope diameter D. |
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| 1. '''Aperture Efficiency Aeff.''' The aperture efficiency of the 30m telescope can be obtained via pointings on point-like celestial calibrators with a well known flux, like Uranus or Mars, when it is small. Aeff can be computed from 3.906 K TA* Feff / Ssou, where K is the correction factor that considers the coupling of the disk size of the planet to the HPBW, TA* is the peak antenna temperature, and Ssou is the intrinsic flux density of the planet. (see Eq.16 in attachment:spatial_response_framework_v1.8.pdf) | 1. '''Main beam efficiency Beff.''' Beff is the ratio of main beam solid angle over the entire antenna pattern solid angle. It is best derived from a source which has a diameter comparable to the size of the main beam. It can be calculated from the peak antenna temperature TA*, the HPBW, the source diameter, and source brightness temperature Tb (see Eq. 18 of [[attachment:cali_rep.pdf]]). For a source which fills the main beam, Beff=TA* Feff/Jnu(Tb), where Jnu(Tb) is the Rayleigh Jeans brightness temperature at frequency nu. Here, we assumed a pure Gaussian beam, HPBW=1.166Lambda/D, and derived the beam efficiency from '''Beff=1.21 Aeff''' (cf. Eq. 5.33 in Baars 2007 "The Parabolical Reflector Antenna in Radio Astronomy and Communication"). 1. '''Aperture Efficiency Aeff.''' Aeff can be obtained via pointings on point-like celestial calibrators with a well known flux, like Uranus or Mars, when it is small. Aeff can be computed from '''3.906 K TA* Feff / Ssou''', where K is the correction factor that considers the coupling of the disk size of the planet to the HPBW, TA* is the peak antenna temperature, and Ssou is the intrinsic flux density of the planet. (see Eq.16 in [[attachment:cali_rep.pdf]] or [[attachment:spatial_response_framework_v1.8.pdf]]) 1. '''Point source sensitivity S/TA*.''' S/TA* is expressed as '''3.906 Feff/Aeff''' in Jy/K (see Eq.17 in [[attachment:cali_rep.pdf]]) 1. '''Error beams.''' A part of the power pattern is distributed in three error beams (see the analysis of [[attachment:greve_1998.pdf]]). The size of the described Gaussians is unchanged, however the main beam efficiencies have been improved since 1998, lowering the strengths of the error beams. A new paper is in preparation. Astronomers should take the contribution of the error beam into account when converting antenna temperatures to brightness temperatures, especially when mapping extended sources. === Gain elevation curves === Gain elevation curves show the point source sensitivity or aperture efficiency of the telescope versus elevation. Fits to the observations of August 2007, indicate a maximum gain at 49.2deg, as the following image shows. {{attachment:gain-el-aug07.png}} === Efficiencies before 2007 === * [[http://www.iram.es/IRAMES/telescope/telescopeSummary/telescope_summary.html|Efficiencies of 3/2005]], see also the [[http://www.iram.fr/IRAMFR/ARN/aug05/node6.html|IRAM Newsletter 8/05]]. * [[http://www.iram.es/IRAMES/telescope/telescopeSummary/beam_effis.html|Plot of efficiencies against frequency, measured in 2000]], * [[http://www.iram.es/IRAMES/telescope/telescopeSummary/effi_history.html|Compilation of efficiencies obtained in the past till 2001]]. |
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| [http://www.iram.es/IRAMES/mainWiki/TelescopeSystemSummary Back to the IRAM 30m System Summary] | [[#beginOfPage|Back to top]] [[http://www.iram.es/IRAMES/mainWiki/TelescopeSystemSummary|Back to the IRAM 30m System Summary]] |
Contents
Telescope efficiencies and beam widths
Efficiencies measured 8/07 (and 6/08)
Freq
HPBW
Feff
Beff
Aeff
S/TA*
Comments
GHz
arcsec
%
%
%
Jy/K
72
33.4
98
79
65
5.9
estimated
86
28.5
98
78
64
5.9
145
16.9
95
64
53
6.9
210
11.3
94
62
51
7.2
260
9.0
90
53
44
8.0
345
7.0
87
39
32
10.6
estimated
- Measurements were conducted during night time when effects of anomalous refraction and any panel buckling are strongly reduced. In addition, the panel backstructure is heated in a random fashion since 8/05, improving on its thermal balance. (JP, CT, CK 2/09). ABCD receivers were used to observe Uranus and Mars, while small. Receivers were tuned to single sideband. Planetary brightness temperatures Tb from ASTRO/GILDAS:
- Mars: 215K constant with frequency
Uranus: 139K at 86GHz, 116K at 145GHz, 102K at 210GHz, 94.5K at 260GHz, 85.6K at 345GHz following Griffin & Orton 1993
Half power beam width HPBW. The observed HPBWs can be well fitted by HPBW/arcsec=2406/Freq/GHz or HPBW/rad=1.166 Lambda/D, with the wavelength Lambda and the telescope diameter D.
Forward efficiency Feff. The values for Feff were updated after the 12th of December 2000 when a new reflecting ring was put around the secondary mirror. Forward efficiencies are derived from skydips. Values in the table are from measurements in August 2007.
Main beam efficiency Beff. Beff is the ratio of main beam solid angle over the entire antenna pattern solid angle. It is best derived from a source which has a diameter comparable to the size of the main beam. It can be calculated from the peak antenna temperature TA*, the HPBW, the source diameter, and source brightness temperature Tb (see Eq. 18 of cali_rep.pdf). For a source which fills the main beam, Beff=TA* Feff/Jnu(Tb), where Jnu(Tb) is the Rayleigh Jeans brightness temperature at frequency nu. Here, we assumed a pure Gaussian beam, HPBW=1.166Lambda/D, and derived the beam efficiency from Beff=1.21 Aeff (cf. Eq. 5.33 in Baars 2007 "The Parabolical Reflector Antenna in Radio Astronomy and Communication").
Aperture Efficiency Aeff. Aeff can be obtained via pointings on point-like celestial calibrators with a well known flux, like Uranus or Mars, when it is small. Aeff can be computed from 3.906 K TA* Feff / Ssou, where K is the correction factor that considers the coupling of the disk size of the planet to the HPBW, TA* is the peak antenna temperature, and Ssou is the intrinsic flux density of the planet. (see Eq.16 in cali_rep.pdf or spatial_response_framework_v1.8.pdf)
Point source sensitivity S/TA*. S/TA* is expressed as 3.906 Feff/Aeff in Jy/K (see Eq.17 in cali_rep.pdf)
Error beams. A part of the power pattern is distributed in three error beams (see the analysis of greve_1998.pdf). The size of the described Gaussians is unchanged, however the main beam efficiencies have been improved since 1998, lowering the strengths of the error beams. A new paper is in preparation. Astronomers should take the contribution of the error beam into account when converting antenna temperatures to brightness temperatures, especially when mapping extended sources.
Gain elevation curves
Gain elevation curves show the point source sensitivity or aperture efficiency of the telescope versus elevation. Fits to the observations of August 2007, indicate a maximum gain at 49.2deg, as the following image shows.
Efficiencies before 2007
Efficiencies of 3/2005, see also the IRAM Newsletter 8/05.