The aperture blockage by feed, stalls, and subreflector generally causes degradation of gain and raising of crosspolarisation and sidelobe levels. Consequently, to attend recent recommendations for sidelobe envelope, the design of earth station antennas has employed offset-fed configurations to eliminate blocking effects. Several dual offset designs have been presented employing sections of confocal conic or shaped reflectors. A possible disadvantage of these designs is that their main reflector does not show circular symmetry and thus connot be manufactured by spinning. The use of spherical main reflector is particularly interesting from the point of view of fabrication process for mass production. This work extends the investigation of the design of dual offset antennas with a spherical main reflector. The phase correcting subreflector is shaped using Geometrical Optics meanings. A diffractive analysis based on Physical Optics approximations is used to predict the radiation pattern, the efficiency and the crosspolaristion.