Three-Dimensional Electromagnetic Analysis of Attenuator-Coated Helix Support Rods of a Traveling-Wave Tube

Attenuator-coated helix support rods in a helical slow-wave structure (SWS) were modeled by considering them to be made up of lossy dielectric material having equivalent bulk conductivity varied along the length following the loss of the coating. The same conductivity values were used in 3-D modeling of the helical SWS having the helix supported by three such support rods inside a metal envelope, and the attenuation constant of the structure was found. The approach was used for characterizing the attenuation constants in the sever regions of two typical SWSs, one operating in the X-Ku-band and the other in K-Ka-band. The method is general and would be useful for analyzing sever loss in any type of helical SWS having different geometries as well.