A simple method for estimating the quality factor of cylindrical re-entrant cavity of Klystrons

A simple method for estimation of the unloaded quality factor of single and double re-entrant cylindrical cavities was developed based on Wheeler’s incremental inductance rule. The proposed approach was benchmarked for a Ka-band re-entrant cavity against 3D electromagnetic simulation using CST Studio and also with measurements. The analysis is general and unlike the approach of Fujisawa, it could be extended to analyze the re-entrant cavity comprising dissimilar materials. The effect of surface roughness on the quality factor of the cavity also could be estimated using the present analysis.