Graphene Metasurface Absorber for Traveling Wave Tube Backward Wave Oscillation Suppression

To address the issue of backward wave-induced instability in traveling-wave tubes (TWTs), this letter proposes a graphene metasurface absorber (GMA) for backward wave absorption. The beam-wave interaction simulation results show that the U-shaped meander-line slow wave structure (ML-SWS) with a central operating frequency of 80 GHz, generates pronounced backward waves at 119.7 GHz and 233.7 GHz. The GMA exhibits frequency-selective absorption characteristics, achieving an absorption rate exceeding 78% for the aforementioned backward waves. When integrated beneath the U-shaped ML-SWS, further particle-in-cell (PIC) simulations demonstrate a significant suppression of the backward waves, resulting in enhanced operational stability. We prepared microstrip line samples loaded with GMA that can be excited by probe pad. The measured results show that the absorption rate of the GMA at 90 GHz is 86.8%. This design provides a new way to improve the stability of TWTs.