Beam response maps for the 30 GHz 27S radiometer. Top: scanning beam (or main beam) in local telescope coordinates, i.e., the instantaneous spatial sensitivity to a point source centered at the beam maximum. Bottom: corresponding 4π beam map, oriented such that the main beam is located on the north pole. The main Planck far sidelobes are caused by spillover from (i.e., diffraction around) the primary and secondary mirrors. The beams are normalized such that their combined integral over the full sky equals unity.