For ECH in the large helical device, we are carrying out R&D of millimeter transnission line of the mirror relay system and corrugated waveguide system. For many higher modes to propagate in the waveguide transmission, identification of mode and measurement of mode-conversion coefficients are important for the design of system. As the method of mode-identification, multihole k-spectrometer and measurement of radiation pattern have been used. Though the former can be applied to the waveguide with the smooth wall, it seems to be difficult to measure the propagation mode directly in the corrugated waveguide and is necessary to calibrate sensitivity of mode.
K. Ohkubo, K. Ohkubo,
"Development of FFT mode conversion detector", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15767P (4 December 2017); doi: 10.1117/12.2297990; https://doi.org/10.1117/12.2297990