The ridge-loaded ring-plane traveling wave tube (TWT) is an important type of high power broad band microwave amplifier.Making use of field matching method

combining with the variational method

the dispersion equation of the ridge-loaded ring-plane slow wave structure and small signal gain of this type of TWT are presented in this paper.The influences of all geometrical dimensions on the propagation characteristics

and the effects of the electron parameters on the gain are discussed

respectively.A large signal numerical calculation has also been done to investigate the nonlinear phenomena in this kind of TWT.In order to get higher power in broader operating bandwidth for this kind of TWT

the optimum opening angle

a smaller radius of the loaded ridge

and appropriate electron parameters must be chosen.This paper provides the theoretical basis for design of the ridge loaded TWT.