Contents

  1. Telescope efficiencies and beam widths
    1. Telescope efficiencies after painting the surface (valid from September 2024, updated on March 2026)
      1. Notes about the data
      2. Values for deriving the Efficiency using the Ruze formula
      3. Beam Widths
    2. Telescope efficiencies after painting the surface (valid from September 2024)
      1. Notes about the data
      2. Values for deriving the Efficiency using the Ruze formula
    3. Update on telescope efficiencies and errorbeam parameters (November 2016)
    4. Parameters describing the beam of the 30m telescope: HPBW, Feff, Beff, Aeff, point source sensitivity, Errorbeams
    5. Gain elevation curves
    6. Gain variation with wobbler throw
    7. Past efficiencies
      1. Efficiencies measured with EMIR in 2009
      2. Efficiencies measured with ABCD receivers in 8/07 (and 6/08)
      3. Efficiencies before 2007

Telescope efficiencies and beam widths

Telescope efficiencies after painting the surface (valid from September 2024, updated on March 2026)

icon-new.gif

JSG, 30-Jul-2026. Computations using all the specific observing sessions from 2024-Aug to 2025-Aug.

Freq (GHz)

Ap. eff

err

Beff

err

S/TA*

Feff

84.25

0.62

0.01

0.75

0.03

5.9

0.95

98.25

0.59

0.01

0.75

0.02

6.2

0.95

100.25

0.58

0.01

0.75

0.02

6.4

0.95

143.25

0.47

0.02

0.60

0.02

7.7

0.93

157.25

0.43

0.02

0.56

0.02

8.4

0.93

159.25

0.43

0.02

0.57

0.02

8.4

0.93

215.75

0.45

0.02

0.52

0.02

8.0

0.92

229.75

0.42

0.02

0.52

0.02

8.5

0.92

231.75

0.43

0.02

0.52

0.02

8.3

0.92

252.57

0.36

0.02

0.43

0.02

9.9

 0.92

268.57

0.34

0.02

0.41

0.02

10.6

0.92

270.25

0.33

0.02

0.39

0.03

11.0

0.92

339.75

0.16

0.02

0.25

0.01

20.0

0.82

341.75

0.17

0.02

0.23

0.03

19.0

0.82

Notes about the data

Values for deriving the Efficiency using the Ruze formula

/!\ The efficiencies from the combination of E0 and E2 bands are systematically higher than those derived from the combination E1 and E3. The reason is not well known, but it is preferred to use two separate curves, with parameters given as:

  1. Ap.eff E0&E2: Ilum.eff: 0.65 (+/- 0.01), roughness: 71 (+/- 2) microns

  2. Ap.eff E1&E3: Ilum.eff: 0.57 (+/- 0.01), roughness: 78 (+/- 2) microns

attachment:Aeff_Ruze.png

We can also fit Beff in a Ruze-like formula, again with independent fittings for E0&E2 and E1&E3:

  1. Beff E0&E2: Beff(0): 0.82 (+/- 0.01), equiv. roughness: 74 (+/- 1) microns

  2. Beff E1&E3: Beff(0): 0.72 (+/- 0.01), equiv. roughness: 73 (+/- 1) microns

attachment:Beff_Ruze.png

Beam Widths

The HPBW as a function of the frequency found from 39-59 degrees elevation range data is; HPBW(arcsec) = 2430/Frec(GHz) for E0, E1, and E2 bands (only slightly smaller, <2%, than the historic value of 2460/Frec(GHz)), and 2730/Frec(GHz)" for E3 band.

Telescope efficiencies after painting the surface (valid from September 2024)

MSP, 01-Dec-2025. Computations done by JSG.

Freq (GHz)

ap. eff

err

Beff

S/TA*

Feff

84.25

0.62

0.01

0.82

5.9

0.95

98.25

0.59

0.01

0.78

6.2

0.95

100.25

0.58

0.01

0.76

6.4

0.95

143.25

0.47

0.02

0.62

7.7

0.93

157.25

0.43

0.02

0.57

8.4

0.93

159.25

0.43

0.02

0.56

8.4

0.93

215.75

0.45

0.02

0.59

8.0

0.92

229.75

0.42

0.02

0.56

8.5

0.92

231.75

0.43

0.02

0.57

8.3

0.92

252.57

0.36

0.02

0.47

9.9

 0.92

268.57

0.34

0.02

0.44

10.6

0.92

270.25

0.33

0.02

0.43

11.0

0.92

339.75

0.16

0.02

0.21

20.0

0.82

341.75

0.17

0.02

0.22

19.0

0.82

Notes about the data

  • All data have been derived from Uranus observations, using ASTRO fluxes as from GILDAS Feb22.
  • Each session consists of dozens of pointings for several band combinations, at different elevations, always including the optimal elevation range (around 52º). Gain-Elevation correction has been applied using the CLASS procedure. Each season's values are the median of all the pointing scans that passed a quality filter.

  • Main Beam Efficiency (Beff) in the table is supposed for the optimal elevation and computed as Beff = 1.31*ApEff.

  • Feff values are the defaults used by Pako. Feff values from skytips were derived too, being only slightly different at high frequencies, but close to the current ones.

Values for deriving the Efficiency using the Ruze formula

/!\ The efficiencies from the combination of E0 and E2 bands are systematically higher than those derived from the combination E1 and E3. The reason is not well known, but it is preferred to use two separate curves, with parameters given as:

  1. E0&E2: Ilum.eff: 0.65 (+/- 0.01), roughness: 71 (+/- 2) microns

  2. E1&E3: Ilum.eff: 0.57 (+/- 0.01), roughness: 78 (+/- 2) microns

Update on telescope efficiencies and errorbeam parameters (November 2016)

The following table is taken from the report on "Improvement of the IRAM 30m telescope pattern" of 26-August 2013 which is available here. It gives the strengths (in percent) of the main beam, the three errorbeams, and the forward efficiency, as a function of observing frequency.

  • Freq

    Beff

    P1'

    P2'

    P3'

    SumP

    Feff

    eta_fss

    86

    81

    0

    7

    6

    12

    95

    2

    115

    78

    1

    8

    6

    14

    94

    2

    145

    73

    2

    9

    6

    17

    93

    2

    210

    63

    4

    11

    9

    24

    94

    6

    230

    59

    4

    11

    11

    25

    92

    8

    280

    49

    3

    11

    15

    29

    87

    9

    340

    35

    2

    11

    14

    28

    81

    19

    345

    34

    2

    11

    14

    28

    80

    18

See the report for explanations on the errorbeam parameters P1', P2', P3', SumP. The half power beamwidths (HPBW) of the main beam are described to a good accuracy by HPBW(arcsec) = 2460/Freq(GHz). For the aperture efficiencies and point source sensitivities see previous observations listed below. A fit of the Ruze formula to these main beam efficiencies results in a beam efficiency in the low frequency limit of Beff0 = 0.863 and a total surface rms of 66 micrometer: beff-jp-02nov2016.png. This includes the contribution of all mirrors between primary and the EMIR horns.

Lower frequencies have been made available in December 2015, with the upgrade of the E090 band. Beam properties are described in the commissioning report here.

Parameters describing the beam of the 30m telescope: HPBW, Feff, Beff, Aeff, point source sensitivity, Errorbeams

  1. Half power beam width HPBW. The observed HPBWs can be well fitted by HPBW/arcsec=2460/Freq/GHz or HPBW/rad=1.166 Lambda/D, with the wavelength Lambda and the telescope diameter D.

  2. 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.

  3. 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. When using p.59, Eq.4.13, Eq.5.33 of Baars (2007, The Paraboloidal Reflector Antenna in Radio Astronomy and Communication), we find that the observed relation, HPBW=2460/nu with HPBW in arcsec and nu in GHz, is consistent with an edge taper of -16.2dB, HPBW=1.19 lambda/D in radian, and Beff=1.27Aeff (cf. te.greg, CK, 8-May-2015). Previously, we had sometimes assumed, HPBW=1.17Lambda/D, corresponding to HPBW=2405/nu, and to an canonical edge taper of -13dB, leading to Beff=1.21 Aeff.

  4. 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)

  5. Point source sensitivity S/TA*. S/TA* is expressed as 3.906 Feff/Aeff in Jy/K (see Eq.17 in cali_rep.pdf)

  6. 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 report by Kramer, Penalver, Greve of August 2013 is available online here. 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

The point source sensitivity or aperture efficiency drops for large and for low elevations above/below the optimum of about ~50deg. This effect becomes more pronounced with increasing frequency. At 210GHz, the aperture efficiency drops to 80% of its optimum value at an elevation of 20deg or 80deg (cf. Report of April-2012 by J.Penalver where we also offer a CLASS script to observers to correct for the gain elevation curve).

Gain variation with wobbler throw

The point source sensitivity or aperture efficiency also drops with increasing wobbler throw. This effect becomes more pronounced with increasing frequency. At about 230GHz, the point source sensitivity drops to 80% of its optimum value for a wobbler throw of +-2' (cf. Figure 6 in Greve et al. 1996).

Past efficiencies

Efficiencies measured with EMIR in 2009

  • Freq

    HPBW

    Feff

    Beff

    Aeff

    S/TA*

    Date

    Comments

    Beff/Aeff

    Beff with Beff=1.28Aeff

    GHz

    arcsec

    %

    %

    %

    Jy/K

    86

    29

    95

    81

    63

    5.9

    4.4.2009

    1.29

    80.6

    115

    78

    predicted

    (1)

    145

    16

    93

    74

    57

    6.4

    4.4.2009

    1.30

    73.0

    210

    11

    94

    63

    49

    7.5

    29.3.2009

    1.29

    62.7

    230

    10.7

    92

    58

    46

    14.11.2012

    (2)

    1.26

    58.9

    260

    9

    88

    53

    41

    8.4

    29.3.2009

    1.29

    52.5

    330

    340

    7.5

    81

    35

    29

    10.9

    24.11.2009

    1.21

    37.1

Comments: (1) The beam efficiency at 115GHz is predicted from the measured beam efficiency at adjacent frequencies, using the Ruze formula. <CK, 15-Jan-2013> See also the EMIR Users Manual and the EMIR Commissioning Report. (2) See report by JP.

Efficiencies measured with ABCD receivers in 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

Efficiencies before 2007

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