Harmonic suppression in a helix TWT using SUNRAY-3D code

Summary form only given. Because of the inherently wide bandwidth of the helical slow-wave structure (SWS) and nonlinearity in the electron beam at large signal levels, second and higher order harmonics of the input RF signal(s) are also generated significantly near the output, at the cost of the growth of the input (fundamental) RF signal. This reduces the TWT efficiency. Therefore, the helix SWS is to be designed in such a fashion that the harmonic levels can be suppressed near the tube output to enhance the growth of the fundamental RF signal. This requires an accurate multi-signal large-signal model for analysis of the beam-wave interaction along the helix SWS. The SUNRAY-3D program (V Srivastava, IETE Journal of Research, vol.49, no.4, p.239-246, 2003) was used for determination of the generation of second harmonic power along with output power of the fundamental (input) RF signal, after checking convergence of simulated results for different numbers of discs per wavelength and for different number of rings per disc, for a broadband TWT. Harmonic power is given along with the output power of the fundamental (input) RF signal.