A method of calculating the secondary pattern of a reflector illuminated by a feed array is developed. Geometrical optics is used to determine the incident field via a coordinate transformation approach. The incident field from each element is superimposed to form the total field used in finding the surface currents of the physical optics radiation integral. The technique allows each element to be arbitrarily excited, positioned and oriented. The element patterns may be different allowing mutual coupling to be included. / M.S.