Backward-Wave Suppression for Broadband Helix Traveling-Wave Tubes Using the Phase Velocity Variation of Output Circuit

Based upon the principle of suppression of backward-wave oscillation (BWO) using the phase velocity variation of output circuit in broadband helix traveling-wave tubes (TWTs), four kinds of nonuniform output circuit models have been presented. Two-wave theory has been used to calculate the backward-wave gain of two-section and three-section output circuits. This method breaks through the limits of equal-length section and weak tapering change in the two-wave theory. By calculating the backward-wave gain, the authors obtained the relationship between the oscillation-start current of backward wave and the tapering position and strength for these four kinds of output circuits, which develops the two-wave theory. These results provide the theoretical support for the suppression of BWO in broadband helix TWTs.