Beams LFI

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Wish List[edit]

list of information to be inserted in the explanatory supplements

- Description of LFI FOV.

- Description of various telescope models as reported in the beam paper.

- Format of beam data

- Definition of various coordinate frames for beams


LFI is observing the sky with 11 pairs of beams associated with the 22 pseudo-correlation radiometers. Each beam of the radiometer pair (Radiometer Chain Assembly - RCA) is named as LFIXXM or LFIXXS. XX is the RCA number ranging from 18 to 28; M and S are the two polarization namely main-arm and side-arm of the Orthomode transducers #darcangelo2009b (see also LFI naming convention).

Figure 1. A sketch of the Planck LFI field of view in the (u,v) plane is shown. The polarization direction on the sky are highlighted by the colored arrows. The M-polarization is shown in green and the S-polarization in red. Main beam shapes are shown for completness and they are not representative of flight beams.

Main Beams and Focal Plane calibration[edit]

As the focal plane calibration we refer to the determination of the beam pointing parameters in the nominal Line of Sight (LOS) frame through main beam measurments using Jupiter transits. the parametes that characterise the beam pointing are the following:

  • THETA_UV ($\theta_{uv}$)
  • PHI_UV ($\phi_{uv}$)

They are calculated starting from u,v coordinates derived form the beam reconstruction algorithm as

$\theta_{uv} = \arcsin(u^2+v^2)$

$\phi_{uv} = \arctan(v/u)$

Three additional angles are used to characterize the beams in the RIMO:

  • TILT
  • PSI_UV ($\psi_{uv}$)
  • PSI_POL ($\psi_{pol}$)

the Tilt angle is the angle between the major axis of the gaussian fitting and the U-axis CHECK THIS

$\psi_{uv}$ and $\psi_{pol}$ are not derived from measurements but they are extimated form optical simulations. They are the quantities that represent the polarization direction of each beam, in the following approximation: the M- and S- beams of the same RCA point at the same direction on the sky

Effective beams[edit]


Window Functions[edit]



There is no direct measurements of sidelobes for LFI. The sidelobe pattern is estimated by simulations taking into account the geometry of the telescope and the satellite structure. In figure


<biblio force=false>

  1. References


(Planck) Low Frequency Instrument


LFI Radiometer Chain Assembly

[LFI meaning]: absolute calibration refers to the 0th order calibration for each channel, 1 single number, while the relative calibration refers to the component of the calibration that varies pointing period by pointing period.

Line Of Sight

reduced IMO