Quasi-Optical Mode Converter Based on All-Dielectric Metamaterial for High-Order Mode Vacuum Electronics Devices

metamaterials (ADMs) have recently attracted much attention due to their ability to achieve wavefront control with high power capability. In this article, an investigation on quasi-optical mode converter (QOC) based on ADM for high-order vacuum electronics devices (VEDs) is presented. Specifically, four ADM QOCs are designed to convert the cylindrical waveguide TE01, TE21, TE31, and TM01 modes into linear polarized Gaussian beams at 35 GHz. Electromagnetic simulations show that the Gaussian mode contents of the output waves from four mode converters are all over 94% with high polarization contents. Furthermore, a Ka-band ADM mode converter with the input mode of circular waveguide TE01 mode is fabricated and measured. Experimental results show that the output fields with scalar Gaussian content over 90% can be obtained at 30-38.85 GHz, corresponding to a relative bandwidth of 25.3% around 35 GHz. The maximum scalar Gaussian mode content of 99.18% is observed at 34.56 GHz in the experiment. The investigation opens new avenues toward high-order mode conversion technology based on ADM.