ITD approach for predicting near field radiation by a circular horn

Incremental diffraction coefficients at the edge of a circular horn (CH) are derived on the basis of the incremental theory of diffraction (ITD). These distributed diffracted field contributions are used to predict mode radiation in the near zone, as well as to study the reciprocal problem of EM coupling of a spherical wave into the CH. To preserve accuracy at aspects below the aperture plane, second order incremental diffraction contributions are also included. For the sake of simplicity, the analysis is restricted to the scalar case, with hard boundary conditions on the walls. This provides guidelines for the more general EM case.