AbstractPolarizers with non-rectangular grooves are studied in high power millimeter wave transmission lines for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) of fusion plasmas. The groove shape is important for determining the polarization parameters and avoiding arc breakdown in the system. A low-power measurement has been carried out for several polarizers with different groove depths. The polarization characteristics experimentally measured are in good agreement with numerical results in which the actual groove shape is taken into account. The polarizers are designed and applied to different frequencies of ECH/ECCD systems. Favorable results have been obtained in high-power transmission up to 500 kW, 0.2 s.