Tape Analysis of an Inhomogeneously-Loaded Helical Slow-Wave Structure for Broad-Band Traveling-Wave Tubes

Theoretical simulation of the dispersion and interaction impedance characteristics of an inhomogeneously-loaded helical slow-wave structure is validated. The structure is supported by double-curve-shaped rods which are smoothed out into a number of dielectric tubes with their respective effective permittivity values. The effects of the helix thickness are taken into account by considering a free-space gap equal to the difference between the mean helix radius and the outer helix radius. Moreover, the helix tape model is used instead of the simpler sheath-helix model. The theoretical predictions are compared with those of MAFIA simulation. The dispersion error is found to be within 3–6 percent and the impedance characteristic is in great agreement with that of MAFIA simulation. At last, for the sake of comparison, the cold-test characteristics under sheath-helix model are also provided.