Hybrid-mode helix-loading effects on gyro-travelling-wave tubes

Abstract

A hybrid-mode hot dispersion relation for a gyro-TWT, employing a cylindrical waveguide loaded with a helix supported from the inner wall of the waveguide by a dielectric, has been derived. The dispersion relation is interpreted to obtain the conventional TWT-type gain equation in the Pierce form, including the effect of the circuit loss. This is used to study the gain-frequency response of the device for an initial search of the operating and structure loading parameters, for an enhanced performance in terms of the gain and bandwidth. It is found that a helix-loaded gyro-TWT, while exhibiting a 3dB bandwidth almost similar to an ordinary gyroTWT, gives a large gain both in the cyclotron fundamental and second harmonic operations in the hybrid mode. The relative permittivity of the helix dielectricsupport, and the location of the helix with respect to the envelope are found to have a greater effect than the helix pitch angle on the cold dispersion characteristics of the device. The distributed circuit loss is identified as another handy parameter to shape the gain-frequency response of the device. © 1997 Taylor and Francis Group, LLC.