Reflection Monitor for an Oversized Circular Waveguide

A new set-up to determine the power relation between transmitted and reflected waves propagating in a highly oversized cylindrical waveguide is presented. This system is up to now the only known possibility of a high directivity measurement in a highly oversized waveguide, where arbitrary modes in broad range are propagated alternatively or even simultaneously. The function of a bidirectional coupler is achieved from the free space radiation of a linear array of holes in the wall of the waveguide. The radiated electromagnetic field is sampled by two receiving antennas placed at opposite locations. The present application is the reflection monitor used at the output of high-power gyrotrons in the 130 - 160 GHz frequency range.