A note on diffraction theory and polarization

The plane-wave method of calculating the field radiated from an aperture has two forms depending on whether the source is taken as the tangential electric or magnetic field. The Huygens¿Kirchhoff method is intermediate between them. There is an apparent inconsistency in the predicted polarization of the distant fields; this is shown to depend on aperture-field terms usually neglected, and measured values of the polarization of the field due to a small horn are given.