At 30, 44, and 70 GHz, each detector is a linearly polarized radiometer, and there are two orthogonally polarized radiometers behind each horn. Each radiometer has two diodes, both switched at high frequency between the sky and a blackbody load at ~4.5 K (Mennella et al. 2011). At 100 GHz and above, each detector is a bolometer (Planck HFI Core Team 2011a). Most of the bolometers are sensitive to polarization, in which case there are two orthogonally polarized detectors behind each horn. Some of the detectors are spider-web bolometers (one per horn) sensitive to the total incident power. Two of the bolometers, one each at 143 and 545 GHz, are heavily affected by random telegraphic signals (RTS; Planck HFI Core Team 2011a) and are not used. Three other bolometers (two at 217 GHz and one at 857 GHz) exhibit short periods of RTS that are discarded.

Effective (LFI) or Nominal (HFI) centre frequency of the N detectors at each frequency.

Mean scanning-beam properties of the N detectors at each frequency. FWHM ≡ FWHM of a circular Gaussian with the same volume. Ellipticity gives the major-to-minor axis ratio for a best-fit elliptical Gaussian. In the case of HFI, the mean values quoted are the result of averaging the values of total-power and polarization-sensitive bolometers, weighted by the number of channels (not including those affected by RTS). The actual point spread function of an unresolved object on the sky depends not only on the optical properties of the beam, but also on sampling and time domain filtering in signal processing, and the way the sky is scanned.

The noise level reached in 1 s integration for the array of N detectors, given the noise and integration time in the released maps, in both Rayleigh-Jeans and thermodynamic CMB temperature units for 30 to 353 GHz, and in Rayleigh-Jeans and surface brightness units (M Jy sr^-1 s^1/2) for 545 and 857 GHz. We note that for LFI the white noise level is within 1–2% of these values.