Measurement of Circuit Impedance of Periodically Loaded Structures by Frequency Perturbation

A method is described for determining the circuit impedance of a slow-wave structure from experimental measurements of the perturbation in the resonant frequencies caused by passing small beads through the interaction region. From these measurements the gain parameter C of such a structure, when used as a traveling-wave tube, can be determined. The results agree with measured experimental gains as well as with theoretical calculations. The method is limited to periodic structures which can be short-circuited and hence made resonant. The principles involved are not new, but their adaptation to traveling-wave tubes is not generally known.