Enhanced RF performance in multi-tunnel backward-wave oscillators

We propose an efficient beam-wave interaction circuit employing a multi-tunnel, slow-wave structure for W-band backward-wave oscillators. The tunnel is disposed one of above and below the beam tunnel, which enhances RF characteristics. The interaction circuit is prepared using a deep-reactive ion etched (DRIE), multi-level microfabrication on silicon wafers. The return loss shows strong resonances predicted by finite-element method (FEM) simulations. The multi-tunnel interaction circuit demonstrates almost similar aspect in return loss to the circuit without beam tunnel. A 1.6 times increase in RF output power is estimated from the particle-in-cell calculation, when compared to the case without multi-tunnel structure. Therefore, we conclude that the multi-tunnel, slow-wave structure successfully improves RF performance.