A Ka -Band Folded Waveguide Traveling Wave Tube With Lumped Resistance Metamaterial Absorber

A Ka-band, folded waveguide traveling wave tube (FWG-TWT) composed of a folded waveguide (FWG) slow wave structure (SWS) and a compact lumped resistance metamaterial absorber (LR-MMA) as a sever load is proposed in this article. The LR-MMA consists of five resonant rings with a metallic ground plane and a separating silica layer. Lumped resistances are used and concentrated resistances are added at the opening of the resonant ring to match the surface impedance of the LR-MMA with that of the metallic waveguide. Simulation results show that the proposed LR-MMA has an absorption bandwidth of 3 GHz at 34-GHz center frequency with absorption exceeding 90%. A FWG-TWT using this LR-MMA is simulated; the output power of this traveling wave tube (TWT) is 112.5 W at 34 GHz, corresponding to a gain of 51.5 dB. The performance of the FWG-SWS using the LR-MMA is similar to that of the FWG-SWS using a wedge sever (WS). For this FWG-SWS, the sever load length of the proposed metamaterial attenuator (MMA) is 0.5 mm, which is much shorter than 9.4 mm of the traditional WS. The LR-MMA is suitable for microfabrication technology and it can be easily assembled with a FWG-SWS, which is helpful for achieving an integrated SWS for the TWT.