Coupling impedance of circular waveguide comb slow wave structure

In this paper the coupling impedance of circular comb slow wave structure is investigated in detail. Some problems in the computer simulation for interaction impedance are investigated, and a new method for the calculation of interaction impedance is proposed. The study leads to the conclusion that the circular comb slow wave structure has an impedance over 1 W at its fundamental mode within a relatively wide band and may interact with the beam effectively. Besides, the inner radius of the structure is 1/4~1/3 times the wavelength, and 5 times larger than that of a helix, implying 25 times of beam current and 25 times of average power compared to a helix. Calculation of interaction shows that a traveling wave tube in Ka band with maximum power of 170 kW may be realized using this kind