Reflection from the aperture of a longE-plane sectoral horn

The complex reflection coefficient of a long
E
-plane sectoral horn is derived using the geometrical theory of diffraction. Single diffraction alone is shown to be sufficient to describe the contribution from the
E
(widely separated) edges, while singly and doubly diffracted fields from the
H
edges are included by using an open waveguide result derived elsewhere. A relatively uncomplicated expression is obtained for the complex reflection coefficient of the horn which agrees well with experiment for horns with slant wall lengths greater than about
3\frac{1}{2}
guide wavelengths.