Abstract
It is shown that the diffracted field in certain parts of both the near and far field of a slit aperture formed by two non-planar screens satisfy the variational principle. Microwave measurements of the axial electric field intensity for a slit aperture with various angles of inclination of the non-planar screens are presented, and compared with the results of the variational principle, with Kirchhoff's approximation theory and with the results of an asymptotic solution of the integral equation.