A Lossy Dielectric-Ring Loaded Waveguide With Suppressed Periodicity for Gyro-TWTs Applications

• Published in: IEEE transactions on electron devices Vol. 56; no. 10; pp. 2335 - 2342
• Main Authors: DU, Chao-Hai, LIU, Pu-Kun
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.10.2009; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amplifiers; Applied sciences; Attenuation; Circuit properties; Circuits; Data mining; Devices; Dielectric losses; Dielectrics; Electric, optical and optoelectronic circuits; Electronic circuits; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronic tubes, masers; Electronics; Exact sciences and technology; Gyrotron-traveling-wave-tube amplifier (gyro-TWT); Harmonic analysis; Harmonics; lossy dielectric; modal transition; Oscillations; Phase velocity; Wave propagation; Waveguide components; Waveguides; Harmonic; Dielectric loss; Gyrotron-traveling-wave-tube amplifier (gyro-TWT); modal transition; Travelling wave amplifier; Microwave; Operating mode; Travelling wave tube; Gyrotron; Waveguide; Periodic structure; Dielectric waveguides; Dielectric function; Millimetric wave; Phase velocity; lossy dielectric; Periodic system
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2009.2028384

A dielectric-loaded (DL) waveguide is an attractive possibility for interaction circuits with high-power sources in the millimeter-wave regime down to tenths of millimeters, particularly for gyrotron-traveling-wave-tube amplifiers (gyro-TWTs). We present results on a systematic investigation of the influence of the periodically loaded lossy dielectric on the propagation characteristics of the operating modes, which reveals that a complex mode in the periodic system can be mapped to a corresponding mode in an empty waveguide or a uniform DL waveguide. Dielectric losses not only induce modal transitions between different modes with similar field structures and close phase velocities in the uniform system but also unify the discrete mode spectrum into a continuous spectrum in the periodic system. Since the lossy dielectric functions as a power sink, the higher order Bloch harmonic components arising from the structural periodicity are suppressed, and the mode spectrum of the lossy periodic system degenerates into that of an empty waveguide. This alleviates the potential danger of spurious oscillations induced by the higher order harmonic components, making the periodic lossy DL waveguide promising in a high-power millimeter-wave gyro-TWT.