Beam characterization for the QUIET Q-Band instrument using polarized and unpolarized astronomical sources

Beam characterization is of critical importance when analyzing and interpreting data from Cosmic Microwave Background (CMB) experiments. In this paper we present scanning strategies, data analysis methods and results of the 44 GHz (Q-Band) beam characterization for the Q/U Imaging ExperimenT (QUIET) Phase-I, using the Crab nebula (Tau A) and Jupiter as polarized and unpolarized point sources, respectively. The beams are modeled as a sum of gaussian terms multiplied by orthogonal polynomials after symmetrization using observations taken at different rotation angles about the optical axis. The l-space window function calculation procedure is explained and applied, along with the corresponding propagation of parameter uncertainty. These window functions encode the effect of the finite resolution of the instrument on its ability to measure the angular power spectrum, as a function of multipole l. Additionally, the instrumental polarization is characterized in terms of two-dimensional Mueller fields which describe the coupling of the Stokes parameters. The data presented in this work were collected during the first season of QUIET observations that started in October 2008.