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Modal Transition and Reduction in a Lossy Dielectric-Coated Waveguide for Gyrotron-Traveling-Wave Tube Amplifier Applications

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4 Author(s)
Chao-Hai Du ; Key Lab. of High Power Microwave Sources & Technol., Chinese Acad. of Sci., Beijing ; Qian-Zhong Xue ; Pu-Kun Liu ; Ming-Hong Wang

A metal cylindrical waveguide coated with an inside layer of lossy dielectric which affects the propagation characteristics of a guided electromagnetic mode is investigated for gyrotron-traveling-wave tube (gyro-TWT) amplifier applications. This paper reveals a series of novel phenomena. The dispersion curve of a higher order mode has a turning point during its evolvement from the fast wave region to the slow wave region. An electromagnetic mode in the lossy dielectric-coated waveguide exhibits a transverse partial-standing-wave distribution. The dielectric loss induces modal transition which results in the dispersion curves of a pair of nearby modes crossing each other and interchanging mode structures. Modal reduction caused by strong dielectric loss merges a pair of nearby modes into one. In this one merged mode, the dielectric-coated waveguide is equivalent to a conventional cylindrical waveguide with imperfect conducting wall. This improved understanding of lossy dielectric-coated metal cylindrical waveguide is of value and usefulness for application toward gyro-TWTs capable of high-power and wide bandwidth.

Published in:

IEEE Transactions on Electron Devices  (Volume:56 ,  Issue: 5 )