Analysis of an anisotropically loaded helix in the fast-wave regime for gyro-traveling-wave amplifiers

Abstract

The dielectric-supported helix enclosed in an anisotropic metal envelope made of a metal cylindrical waveguide provided with a large number of thin metal vanes projecting radially inward from its wall is field analyzed to study its characteristics in the fast-wave regime. The tape-helix, instead of a simpler sheath-helix model, is used to consider the space-harmonic effects. Care is taken to account for the finite helix wire/tape thickness by considering a free-space gap between the mean and the outer radii. The nonuniformity of the radial propagation constant over the various cross-sectional regions of the structure is also taken into consideration in the analysis. The dispersion relation developed as a special case passes on to that obtained elsewhere for a vaneless, dielectric-absent structure as well as for a vaneless dielectric-present, structure. It is found that the parameters of the anisotropic envelope play a more dominant role in controlling the dispersion characteristics of the structure than the helix parameters. Furthermore, the effect of the controlling parameters is found to be less as the helix is brought closer to the waveguide wall. The analysis presented can be used in the design of a helix-loaded cylindrical waveguide interaction structure for a wideband fast-wave, gyro-traveling-wave amplifier. © 1997 John Wiley & Sons, Inc.