The electromagnetic effect of edges on the radiation pattern of horn and reflector type antennas is investigated. An attempt is made to control the radiation pattern by changing the edge geometry. Both theoretical and experimental results are given. Edge diffraction methods are discussed in detail and form the basis of the theoretical analysis. Comparisons are made with other methods where applicable. The particular antennas considered are pyramidal horns, sectoral horns, and circularly symmetric paraboloidal reflectors illuminated by a source at the focus. Radiation from the horns is investigated only in those principal planes reducible to a two-dimensional problem. Scattering from the reflectors is considered as a three-dimensional problem.