Analysis of the Small Signal Gain of a Sheet Beam BWO With a Partially Dielectric-Loaded Nonuniform Grating

A partially dielectric-loaded (PDL) nonuniform grating with lower ohmic losses for a sheet beam backward wave oscillator (BWO) and a clinotron is proposed in this paper. The expressions of the electromagnetic fields for the PDL nonuniform-grating-based slow-wave structure (SWS) are derived by using Maxwell's equations and Floquet's theorem. The dispersion equation is derived using the field-matching method and is verified by simulation. The expression of the Pierce small signal gain of a BWO with a PDL nonuniform grating is obtained by using the electromagnetic field expressions and the small signal gain theory. The effects of different parameters on the gain of a BWO with a nondielectric-loaded (NDL) nonuniform grating and those of a BWO with a PDL nonuniform grating are discussed, and the mode competition of this kind of BWO is analyzed in terms of gain. The oscillation frequencies obtained from the mode competition analysis are verified by a particle-in-cell (PIC) simulation, confirming the validity of the analysis.