Radiation by a circular open ended waveguide including near field and far out side lobes

An asymptotic formulation for predicting the radiation from (coupling into) open ended waveguide is introduced, which is based on the Incremental Theory of Diffraction. For the sake of simplicity, in this paper the formulation is explicitly developed for the scalar case. The analysis is concentrated to exploiting the capabilities of the ITD to describe small aperture radii and the field below the aperture plane. Preliminary results are presented and compared with the Wiener-Hopf exact solution in the far field limit.