Computation for dispersion of gyro-TWT with a helical waveguide by MAFIA

This paper provides a simple technique to design and optimize the spiral waveguide of Gyro-TWT. The dispersion characteristics of helical waveguide was given out. The structure of waveguide was modeled by CAD and it′s dispersion curve was calculated by MAFIA using quasi-periodic boundary condition. The modes were calculated alternation 30° phaseshift from -180° to 180°. This method leads to a good agreement with the result of dispersion equation over 8.3~10.6 GHz, and the maximum relative deviation is below 0.5%. For a rather broad frequency band around the point where the longitudinal wavenumber is equal to zero, the slope of the dispersion curve trends to a positive constant. As a micro-wave amplifier, Gyro-TWT using spiral waveguide has a good potential in improving its effectivenes