Improvements of mode converters for low-power excitation of gyrotron-type modes

To test quasi-optical mode converters for gyrotrons, efficient low-power generators for rotating high-order modes of high purity are necessary. Based on previous designs consisting of a coaxial cavity with a perforated wall and a quasi-optical mirror, the paper shows a more rigorous synthesis and analysis procedure, leading to an efficiency enhancement (in some cases from 2% to 22%) and to a significantly higher mode purity. Designs of 140GHz generators for the TE22,6 and TE76,2 modes are presented. Experimental results on the TE22,6 mode exciter are discussed.