Double Square Ring Metamaterial based Backward Wave Oscillator for Microwave Generator

This paper presents, an all-metal double square rings (DSR) metamaterial (MTM) based slow wave structure (SWS). The design of modified MTM is used as an array of SWSs for backward-wave oscillator (BWO) operating in S-band. Negative dispersion is obtained for the single unit cell (UC) near the operating frequency, using the eigenmode solver. Also, the effective material parameter are determined by using S-parameter retrieval approach. The proposed DSR-MTM oscillator comprises of 11 axially periodic SWSs that are placed into a square waveguide. The large signal characteristics are analyzed for the proposed electromagnetic (EM) structure in the presence of sheet beam, using particle-in-cell (PIC) solver in CST Microwave Studio (MWS). The simulation results shows that the modified DSR-MTM based BWO is capable of generating a maximum power of 5.4 MW, achieving over 56.25% of electronic efficiency operating at the frequency of 3.5 GHz. Hence, the proposed design find its potential application in high performance microwave vacuum electron devices (VEDs).