  We present an analytic approach to the estimation of beam asymmetry effects
in CMB temperature and linear polarization anisotropy experiments. We derive
via perturbative expansions simple and accurate results for the case of an
elliptical Gaussian window. Our results are applied to investigate the effect
of beam ellipticity in the estimation of full-sky polarization correlation
functions and the covariance matrix of power spectra. The relevance of this
effect is also discussed by forecasting errors including beam asymmetry for
current and future CMB experiments.
