Transverse-wave tubes as high-efficiency microwave amplifiers

The theory of microwave tubes using cyclotron- and synchronous-wave interactions is reviewed, and an analysis is presented of the energy exchange mechanism and the axial-beam velocity spread induced by the RF interactions in transverse-wave traveling-wave tubes. The analysis of the energy spread in a realistic model of the beam shows that the maximum efficiency attainable (with collector depression) is limited by the nonzero size of the beam and the nonzero space-charge density. Considering practical limitations of the beam parameters and the saturation characteristics, possible design parameters for high-efficiency, transverse-wave tubes operating at moderate power levels have been obtained. The attainment of such goals with reasonable circuit length appears possible but difficult, mainly due to relatively low interaction impedance available for transverse-wave interactions.