The corrugations present a capacitive reactance to the passing wave. When a corrugated surface is inductive, it will support surface waves. The depth of corrugations must be between λ/4 and λ/2. Less than λ/4 or greater than λ/2, it is inductive. Between 3λ/2 and λ it will be capacitive again, but this second passband is seldom used. A quarter-wavelength corrugation depth balances the two modes and gives the best results. The corrugations need be only λ /4 at the aperture. Before the aperture we find it better to deepen the slots. Quarter-wavelength deep corrugations mismatch the horn in the transition region, where the TM11 mode is generated the TE11 mode and depths approaching λ /2 have the least effect on match.-The corrugations present a capacitive reactance to the passing wave. When a corrugated surface is inductive, it will support surface waves. The depth of corrugations must be between λ/4 and λ/2. Less than λ/4 or greater than λ/2, it is inductive. Between 3λ/2 and λ it will be capacitive again, but this second passband is seldom used. A quarter-wavelength corrugation depth balances the two modes and gives the best results. The corrugations need be only λ /4 at the aperture. Before the aperture we find it better to deepen the slots. Quarter-wavelength deep corrugations mismatch the horn in the transition region, where the TM11 mode is generated　the TE11 mode and depths approaching λ /2 have the least effect on match.