Recent advances in metamaterial klystrons

As a kind of artificially structured media, electromagnetic metamaterials (MTMs) have exotic electromagnetic properties that are not found or difficult to achieve in natural materials. This class of metal/dielectric-structured artificial media has attracted great attention during the past two decades and made important breakthroughs. A variety of passive and active devices based on MTMs have been developed rapidly. Especially MTM klystrons, which show very remarkable advantages, including miniaturization, high gain, and high efficiency in the microwave band. MTM extended interaction klystrons creatively combine the advantages of MTMs, extended interaction technology, and klystrons. It provides a new design idea for the development of brand-new klystrons with high performance. In this review paper, we report the recent advances in MTM klystrons including MTM extended interaction oscillator and MTM extended interaction klystron amplifier. Furthermore, the prospects and challenges of MTM klystrons are discussed. Finally, the development trend is concluded.