Radiation from wide flare-angle corrugated conical horns

A study of the crosspolarisation behaviour of corrugated conical horns with arbitrary flare angles and constant slot depth is presented. Copolar and crosspolar radiation from the horn is obtained as spherical wave expansions of closed-form terms. Generation of higher-order modes, both at the throat and along the horn, is studied in detail. It is concluded that in a dominant-mode wide flare-angle horn (with a semiflare angle ¿¿1, greater than about 30¿¿) the higher-order EH12 mode generated at the throat is far more important than the mode converted along the horn. The reverse is true for narrow flare horns (¿¿1, < 20¿¿). It is shown, both theoretically and experimentally, that the overall level of crosspolar radiation from a 30¿¿ horn of aperture diameter about 5 wavelengths is less than ¿¿ 45 dB below the on-axis copolar radiation level, over more than a 20% bandwidth.