The tangential electric fields vanish at the walls of the two-dimensional horn in the H-plane. This affects the GO field and produces the following equation for them:

Equation (1) includes the phasing term and square-root spreading factor of a two-dimensional field. The horn walls tilt from the centerline by the angle α. Figure 2-28 plots the GO field and shows that it vanishes at the walls. We do not expect edge diffraction because the field vanishes at the edges, but Figure 1 shows diffraction patterns that peak in the direction of the walls.

We call this new term slope diffraction. This new type requires another set of coefficients not identical to the edge (or wedge) diffraction coefficients. While the amplitude of the edge diffraction is proportion to the field incident on the edge, the amplitude of slope diffraction is proportional to the derivative of the field in the direction normal to the edge. We figure the same geometric factors for both edge and slope diffraction but now must calculate the normal derivative of the incident electric field. Figure 2 plots the H-plane pattern of the horn. The pattern fails to predict a pattern behind it. The E-plane diffraction produces a back hemisphere pattern for a real horn, but our two-dimensional model does not include the E-plane.