Left: beam window functions computed using GRASP beams (blue curve), elliptical Gaussian beams (with the same descriptive parameters of the GRASP beams, green curve), and circular Gaussian beams (with the same FWHM of the GRASP beams, red curve). Right: per cent difference between the window function computed using GRASP beams and circular Gaussian beams (blue curve). The same ratio using elliptical Gaussian beams instead of GRASP beams is also shown (green curve).