Dual-function circular polarization converter for microwave/plasma processing systems

Generation of a uniform density plasma has been a key consideration in the design of microwave/plasma processing systems. A circularly polarized wave can generate a plasma with good azimuthal uniformity as well as provide str ong resonant interaction with the plasma electrons. In this article, we rep ort the development of a three-port polarization converter which efficientl y converts the TE10 wave of a standard rectangular waveguide into a circula rly polarized TE11 wave of a cylindrical waveguide. Employing the same prin ciple for mode conversion, the converter is also made to function as a prot ective device of the high power microwave source by providing a separate po rt for the return and damping of the reflected wave. Such a converter has b een analyzed, constructed, and tested. At the operating frequency of 2.45 G Hz, test results indicate a 25 dB return loss, 97% end-to-end polarization conversion efficiency, and better than 20 dB rejection of the reflected wav e. The structural simplicity of the device allows high power operation as w ell as easy construction for system research and applications. (C) 1999 Ame rican Institute of Physics. [S0034-6748(99)01402-1].