TE/11/-to-HE/11/ mode converters for small angle corrugated horns

A theoretical and experimental study of mode conversion from the transverse electric TE/11/ mode in a circular waveguide to the HE/11/ hybrid mode in a small angle conical corrugated horn is given. Mode conversion is achieved through a transition section where the slots are either ring-loaded or are conventional slots of varying depth. Using varying depth slots the optimum design gives a return loss exceeding 30 dB over a 1.45 bandwidth ratio, with the low frequency limit determined by the deterioration in return loss, and the upper frequency limit determined by the excitation of excessive levels of the unwanted EH/12/ hybrid mode. Using ring-loaded slots a bandwidth ratio of 1.55 is possible, increasing to at least 2.0, if the small amount of EH/12/ mode generated is acceptable.