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 . 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.
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