An Estimate of the Interaction Impedance of a Vane-Loaded Helix Using Equivalent-Circuit Analysis (Short Paper)

The expression for the interaction impedance of a broad-band vane-loaded helical slow-wave structure has been found using Pierce's simple theory for a helix in free space, and the results of the equivalent-circuit analysis of the loaded structure. The interaction impedance has been found to be of the order of half the characteristic impedance in a typical loaded structure. The dependence of the small-signal gain on the thickness of the helix wire, the size of the vanes, and the location of the metal envelope has been predicted.