A dual output polarimeter devoted to the study of the Cosmic Microwave Background

We have developed a correlation radiometer at 33 GHz devoted to the search for the residual polarization of the Cosmic Microwave Background (CMB). The two instrument’s outputs are a linear combination of two Stokes parameters (Q and U, or U and V). The instrument is therefore directly sensitive to the polarized component of the radiation (respectively linear and circular). The radiometer has a beam-width of 7 or 14 deg, but it can be coupled to a telescope increasing the resolution. The expected CMB polarization is at most a part per milion. The polarimeter has been designed to be sensitive to this faint signal, and it has been optimized to improve its long term stability, observing from the ground. In this contribution the performances of the instrument are presented, together with the preliminary tests and observations.