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

Abstract

The input coupler is an important component for a microwave amplifier. In this paper, a side-wall single-hole input coupler for a W-band gyrotron travelling wave amplifier (gyro-TWA) 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.

Bandwidth Study of the Microwave Reflectors with Rectangular Corrugations

“…A larger phase spread of the reflector will result in a smaller bandwidth of the input coupler [27]. To optimize a reflector for amplifiers, the goal functions need to take the phase response into account.…”

A multiple-hole input coupler for a 372 GHz gyro-travelling wave amplifier

“…The efficient coupling of the microwave radiation is important to the overall performance of the device, not only to reduce the cost of the high frequency source, but also minimize the possibility of oscillation in the system. A side-wall coupler [6] has been developed for a W-band gyro-TWA, and the simulated and measured results show that a good transmission coefficient can be achieved by using a rectangular-to-circular T-junction and a broadband reflector [7]. The W-band design can be scaled to higher frequencies, but the tolerance studies show that the bandwidth is sensitive to the dimensions of the rectangular hole.…”

Input coupling systems for mm-wave amplifiers

“…An input coupler for the W-band gyro-TWA has been designed and measured [9]. It contains a pillbox-type microwave window and a T-junction side-wall coupler.…”