Analysis of some periodic structures of microwave tubes: part II: analysis of disc-loaded fast-wave circular waveguide structures for gyro-travelling-wave tubes

In part I of the present paper, we analysed helical slow-wave structures of travelling-wave tubes (TWTs) taking into account the space harmonic effects arising from the axial periodicity of helix turns as well as azimuthal periodicity of the dielectric helix-supports and metal vanes of the envelope of the structure. Here, in part II of the paper, we extended the analysis to the fast-wave regime to study a disc-loaded circular waveguide interaction structure of a gyro-TWT taking into account the space harmonic effects arising from the axial periodicity of the annular discs. Four variants of the structure were studied. Two of these variants use thin and thick metal discs, respectively. The third variant has inherently two interwoven metal disc-loaded structures, and the fourth variant has dielectric discs interposed between consecutive metal discs. We studied the effect of tapering the disc parameters and predicted the optimized parameters for the wideband and high-gain gyro-TWT performance. The analyses presented in parts I and II of the paper should prove to be very useful in the design of wideband TWTs and gyro-TWTs, respectively.