Performance of a remote steering antenna for ECRH/ECCD applications in ITER using a four-wall corrugated square waveguide

For the upper electron cyclotron wave launcher on the international thermonuclear experimental reactor (ITER), the use of a 'remote steering antenna' based on the imaging properties of square waveguides is planned. To characterize launchers of this type, low-power experiments on a four-side corrugated square waveguide, with a scanning mirror at the input of the waveguide, were performed in the frequency range 140-160 GHz. It is shown that elliptical polarization, which is necessary for the electron cyclotron current drive (ECCD), can be transmitted without depolarization and that the usable steering range of the antenna is at least 20degrees. Low-power measurements demonstrate that mitre bends can be integrated into the waveguide, practically without extra loss. Detailed calorimetric measurements for this set-up confirm this statement for the polarization perpendicular to the scanning plane, whereas excess loss is measured for the parallel polarization. Various modifications of mitre bends are investigated and results are discussed.