A broadband transverse field interaction continuous beam amplifier device mprised of an elongated continuous cathode modulating grid structure, an elongated continuous demodulating grid-collector structure, first or input waveguide transmission line means including the modulating grid for propagating an input RF wave transversely to an electron beam traveling from the cathode-grid structure to the output-collector structure where the electrons are bunched or modulated by the process of transverse wave interaction, and second or output waveguide transmission line means including the demodulating grid for propagating an induced amplified RF output wave resulting from prebunched electrons traversing the demodulator grid. Both input and output transmission line means include slow wave structures which are implemented in the grid structures.