Theory and Simulation of Arbitrarily Shaped Groove Staggered Double Grating Array Waveguide

A theoretical model for the arbitrarily shaped groove staggered double grating array waveguide (SDGAW) slow-wave structure is proposed in this paper. The boundary of the groove was approximately replaced by a series of steps and the formulas of dispersion and interaction impedance were obtained utilizing the field matching method combined with the continuity of transverse admittance. Considering the traditional single mode approximation (SMA) model is not so accurate for describing the high frequency (HF) characteristics, a multiple modes approximation (MMA) model is established, which takes account for the higher order terms in the grooves, thus greatly improves the accuracy of the numerical calculations. As an example, the HF characteristics of a cosine groove SDGAW for a 0.22-THz traveling wave tube were calculated utilizing the SMA model, the MMA model, and HFSS code, the results were compared and discussed. Comparison of the HF characteristics among several kinds of groove shaped SDGAWs has been made by numerical calculation.