Theoretical designs and experiments on dual-band input coupler for gyrotron traveling wave tube

Abstract

In this paper, a novel K/Ka dual-band input coupler for the gyrotron traveling wave tube is theoretically and experimentally investigated. This input coupler mainly consists of three modules, a Y-type power division coupler, a coaxial cavity coupler, and a Bragg reflector. When the dual-band coupler operates in K-band, the Y-type coupler couples out the TE11 mode, and simulation results show the −1 dB bandwidth is 3.3 GHz in the frequency range of 17.9–21.2 GHz. In Ka-band, the TE21 mode coupled out by the coaxial cavity coupler, the −1 dB bandwidth is 3.5 GHz within 33.7–37.2 GHz, and the reflection coefficient keeps a pretty low level. The prototype was fabricated and measured to further verify the designed dual-band input coupler's performance. The back-to-back cold test results show that the −3 dB bandwidth of the K-band is about 2.5 GHz, and the −3 dB bandwidth of the Ka-band is 2.44 GHz.