Wideband polarizers, switches and waveguide for overmoded corrugated transmission lines

Overmoded corrugated waveguide is efficient at transmitting power over a large frequency bandwidth. This operational flexibility becomes important in multi-frequency systems. For 50-mm diameter aluminum corrugated waveguide nominally designed for the ITER 170 GHz ECH system, the theoretical ohmic loss of the HE11mode is around 0.3e-3 dB/m. In a possible dual-frequency system at ITER, the theoretical loss in the same waveguide increases to a manageable 0.8e-3 dB/m at 104 GHz. As examples of other wideband components, General Atomics has built several pairs of 63.5-mm diameter waveguide polarizers for the TCV tokamak's ECH transmission line that are designed to operate for 1 MW at frequencies ranging from 82.6 to 118 GHz. In addition, polarizers have been designed for ITER's 50-mm diameter transmission line. A computer code that calculates both the required mirror rotation angles and the ohmic losses predicts that these polarizers will function effectively at both 170 GHz and 104 GHz. A new class of wideband waveguide switches with rotary actuators have been supplied for the 82.6–126 GHz transmission lines at TCV, further emphasizing the broadband capabilities of corrugated waveguide components.