Analysis of helical slow-wave structures for space TWTs using 3-D electromagnetic simulators

This paper presents a detailed analysis of traveling wave tube (TWT) helical slow-wave structures (SWSs) using three-dimensional (3-D) electromagnetic simulators. The main advantages of this approach are its capability to take into account the real 3-D geometry of this complex structure, and consequently to eliminate the approximations used in the analytical approach. In addition, it provides higher accuracy than experimental results. Two different methods have been applied (finite elements and finite integration) to predict the cold parameters (phase velocity, coupling impedance, and attenuation) at a level of accuracy higher than the usual practice. An extended analysis has been performed to guarantee the stability and accuracy of the results, as well as to study the sensitivity of the results to the discretization. This paper has shown that both methods, as implemented in two commercially available simulators, are perfectly suitable for the accurate modeling of such complex geometries.