BROAD-BAND LINEARLY POLARIZED BEAT-WAVE TE(M1) TE(11) MODE CONVERTERS/

Broadband linearly polarized waveguide mode converters have been devel oped to transform the high-order cylindrical TE(m1) output wave from h armonic gyrotron amplifiers into the more useful TE(11) fundamental wa veguide mode. The converter's corrugation period is equal to the beat between the two waves and the bandwidth is predicted to be inversely p roportional to the number of periods. Four-period TE(31)/TE(11) and TE (41)/TE(11) converters with an azimuthal perturbation of m(c) = 4 and m(c) = 5, respectively, have yielded a peak conversion efficiency of 9 8% with a bandwidth greater than 3% and a one-period beat-wave convert er has been designed to yield 12% bandwidth. However, it has been obse rved in measurements that the strong coupling in a short converter can lead to a shift of the center-frequency with an accompanying reductio n of the efficiency and bandwidth. A two-period TE(41)/TE(11) converte r with 5% bandwidth displayed a 5% frequency shift and a conversion ef ficiency of only 86%.