Design and Measurement of a Broadband Sidewall Coupler for a W-Band Gyro-TWA

The input coupler is an important component for a microwave amplifier. In this paper, a sidewall single-hole input coupler for a W-band gyrotron traveling-wave amplifier that operates at the frequency range of 90-100 GHz was designed and measured. Instead of using a cutoff waveguide, a broadband Bragg-type reflector with a small spread in phase was optimized for use as part of the input coupler. The minimum radius of the reflector was two times the size of a cutoff waveguide, which reduced the possibility for some of the beam electrons being collected in this section and lost to the amplifier interaction region.