Broadband linearly polarized beat-wave TE(m1)/TE(11 ) mode converters

• Published in: IEEE transactions on microwave theory and techniques Vol. 44; no. 2; pp. 311 - 317
• Main Authors: McDermott, D B, Pretterebner, J, Chong, C K, Kinney, C F, Razeghi, M M, Luhmann, N C
• Format: Journal Article
• Language: English
• Published: 01-02-1996
• ISSN: 0018-9480
• DOI: 10.1109/22.481581

Broadband linearly polarized waveguide mode converters have been developed to transform the high-order cylindrical TE(m1) output wave from harmonic gyrotron amplifiers into the more useful TE(11 ) fundamental waveguide mode. The converter's corrugation period is equal to the beat between the two waves and the bandwidth is predicted to be inversely proportional 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 98% with a bandwidth greater than 3% and a one-period beat-wave converter has been designed to yield 12% bandwidth. However, it has been observed in measurements that the strong coupling in a short converter can lead to a shift of the center-frequency with an accompanying reduction of the efficiency and bandwidth. A two-period TE(41)/TE(11) converter with 5% bandwidth displayed a 5% frequency shift and a conversion efficiency of only 86%