Review

Research progress in metamaterial-inspired klystrons

National Key Laboratory of Science and Technology on Vacuum Electronics, School of Electronic Science and Engineering, University of Electronic Science and Technology of China (UESTC), Chengdu 611731, PR China

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Received: 12 October 2025
Accepted: 12 November 2025
Published online: 23 January 2026

Abstract

Metamaterials are a class of artificial subwavelength structures exhibiting novel electromagnetic properties that are absent or difficult to achieve in natural materials. These novel properties include negative refractive, reversed Doppler effect, reversed Cherenkov radiation, and anomalous radiation pressure, and are primarily determined by the shape, dimensions, and arrangement of their unit cells. Loading metamaterials into klystrons can leverage their subwavelength characteristics to achieve device miniaturization. Based on coherent transition radiation and the subwavelength characteristics of metamaterials, a series of significantly miniaturized and high-efficiency klystrons has been developed. Notably, the first S-band metamaterial-inspired klystron features a high-frequency structure volume approximately 0.44 times that of a conventional klystron, achieving a measured electron efficiency of 57.4%. Compared to conventional klystrons, the first P-band metamaterial-inspired klystron exhibits a 66% reduction in high-frequency structure volume and a 32% reduction in weight, with a measured electron efficiency exceeding 48%. These experimental results validate the miniaturization and high-efficiency advantages of metamaterial-inspired klystrons, which hold significant application prospects in large scientific facilities, radar, communications, medical imaging, microwave heating, and other fields.