Further considerations of overmoded rectangular waveguide for high-power transmission

In a previous paper, suggestions were advanced for using a large-size rectangular waveguide, whose transverse dimensions are just less than ¿×2¿, to increase the continuous-wave power-handling capability of a waveguide run. In the present paper, it is shown that, over a certain frequency range, the power handling can be further increased by operating the ¿/2¿ waveguide with the electric field directed parallel to the narrow face rather than the broad face, as previously. Trapped-mode resonance effects in such a system are investigated experimentally, and it is shown to be possible to suppress them using a long-slot directional coupler, which acts as a mode-selective attenuator.