Analytical method for determining characteristic parameters of reentrant cavities

For reentrant and pillbox cavities widely used in klystrons, on the premise of omitting the thickness of the drift tube, we have deduced the characteristic equation for predicting the resonant frequency of these cavities accurately. Moreover, the analytical formulae for the characteristic impedance and intrinsic quality factor of cavities are found. For a concrete structure, the characteristic parameters of cavities are calculated by the formulae and the program SUPERFISH separately, and good agreement between the results is noticed.