Backward-Wave Oscillation Suppression in Folded Waveguide Traveling-Wave Tube With Metamaterial Absorber.

A D-band folded waveguide (FWG) traveling-wave tube (TWT) with metamaterial absorber (MMA) is proposed, where the MMA is designed to suppress the backward oscillation in this FWG-TWT. The MMA consists of single splitter rings (SRs) with silica layer that adheres to the inner surface of a metallic waveguide. The absorption frequency of this MMA is well designed to cover the backward frequency of FWG slow wave structure (SWS). Therefore, this MMA achieves the transmission of forward wave and the attenuation of backward wave, which improves the performance of FWG-TWT. Simulation results show that 66.1 W saturated output power driven by 5 mW 150GHz input signal, with a corresponding gain of 41.2 dB, and a bandwidth of 18 GHz with output power greater than 40 W can be achieved with 90 periods SWS. The proposed FWG-TWT with MMA may provide a high gain for high frequency amplifier, where it is helpful to design an FWG-TWT with low input power.