Second harmonic suppression for miniature high efficiency TWT

The second harmonic suppression for miniature high efficiency TWT, based on Rowe large signal theory, is simulated using two-section helix output circuit with a positive step and a negative step in this paper. The locations and pitches of two steps are investigated in detail for high efficiency. The saturation output power with and without steps are compared schematically in order to display the benefits of this kind of circuit structure. The simulation and test results indicate that the second harmonic is suppressed greatly and the forward fundamental output power is increased obviously at the lower frequency band. The saturated power output is smoothed over the entire bandwidth ranging from 6 to 18 GHz using this optimized circuit.