Diffraction of a linearly polarised radiation field by a narrow slit in a plane conducting reflector

The diffraction of the radiation field of a linearly polarized feed with a circularly symmetrical gain pattern by a narrow slit in a perfectly conducting screen of infinite extent and zero thickness is investigated. Using known results for plane-wave diffraction by a narrow slit, the field in the slit may be calculated. Expressions are given for the field components in the far field. Cross-polarization and gain characteristics of the total field have been calculated. Some numerical results are presented for slit widths less than 1 mm at 20 GHz. The influence on cross-polarization and gain turns out to be small.