Low-loss broadband multimode corrugated waveguide performance

A 30-m-long waveguide run using circular corrugated waveguide (i.d.=6.35 cm) with a corrugated period and depth of 254 μm (0.01 in.) has been fabricated and installed on TFTR (Tokamak Fusion Test Reactor) for use in electron cyclotron emission measurements, and is the first large scale application of this type of waveguide. It is designed for low-loss (<0.01 dB/m) multimode operation between 75 and 575 GHz, and includes three E-plane and four H-plane miter bends. Single-mode measurements at 140 GHz and multimode measurements at 250 GHz indicate that both ohmic losses as well as loss due to mode conversion are negligible with this type of transmission line.