Simulation of RF coupler of a multi-section TWT with matched sever-loss

A methodology for the simulation of coaxial RF coupler of a helix traveling-wave tube was developed including the effects of helix-to-coupler discontinuity and the RF match at the taper-profiled sever-loss region. The attenuator at the sever-loss was modeled by considering the carbon-coated helix-support rods as lossy dielectric rods having finite conductivity as a step function corresponding to the circuit attenuation constant along the taper-profiled loss in the sever-loss region. The methodology for incorporating the sever-loss in the simulation and typical simulation results for an X-Ku band RF coupler are presented.