Optical aberrations for the final beams of the horns located at different places within the focal plane (corresponding locations x and y chosen according to upper left figure and the respective z values over each horn, in the focal plane localization). The focus of the telescope is placed at δ = −15° and has a beam that is devoid of aberrations while the aberrations are increasingly large, but less than ~10 dB, as we move away from the center of the focal plane.