Compact coupling technologies for the metamaterial based backward wave oscillators

Metamaterials (MTMs) as a kind of artificial subwavelength structures exhibit exotic electromagnetic behaviors such as the reversed Cherenkov radiation [1]. The property provides a novel approach to achieve the compact vacuum electron devices (VEDs), in which MTMs are used to construct the compact high frequency structures [2]. However, as we know, to further promote the miniaturization of MTM-based VEDs, we need compact output structures, compact magnetic focusing system besides compact high frequency structures.