Study and extension of the validity range of the G.T.D. in Rayleigh's zone of a circular aperture

The paper presents the study and extension of the validity range of the geometrical theory of diffraction (GTD) in the Rayleigh's zone of a circular aperture. The divergence near the shadow boundary is supressed by using Kouyoumjian's diffraction coefficient instead of Keller's It is noted that a caustic correcting factor is insufficient in the Rayleigh zone, and a new method of calculation is proposed. The exactness of the results given by the geometrical theory of diffraction in Rayleigh's zone is shown to be dependent on the illumination law of an aperture.