The Second Harmonic Reduction in Helix Travelling Wave Tubes

Wide band traveling wave tubes (TWTs) are widely used as amplifiers in communications and electronic counter -measure systems. The harmonic waves, especially the second harmonic waves, in the TWTs often cause its fundamental wave power output and efficiency reduction. So far many efforts are still making to reduce this harmful effect. The harmonic wave injection was used to reduce the harmonic waves. But harmonic wave injection will ask other microwave souse to work with TWT together. It is not very convenient for TWT applications. Dionne pointed out that the phase velocity and the axial beam coupling impedance of the fundamental space harmonic waves associated with the circuit structure. These characteristics are dependent upon both the physical dimensions of the structure and the electrical influence of the requisite mechanical support structure (backwall and dielectric loading). This paper describes our research on the reduction of the harmonic wave in wide band TWTs by changing the slow wave circuit structure.