The diffraction theory of large-aperture spherical reflector antennas

The field along the axis of a spherical reflector is determined from the geometry of the system rather than from each term of the aberration taken separately. The procedure shows how the field distribution changes from the case of small aberration, where there is a well-defined focus, to the geometric optics limit. A spherical reflector becomes an efficient antenna when a set of feed elements is located along the axis to reduce the effects of spherical aberration. The number and position of these elements is dictated by the size and curvature of the reflector and the allowable distortion of the wavefront.