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

Abstract

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 strong resonant interaction with the plasma electrons. In this article, we report the development of a three-port polarization converter which efficiently converts the TE10 wave of a standard rectangular waveguide into a circularly polarized TE11 wave of a cylindrical waveguide. Employing the same principle for mode conversion, the converter is also made to function as a protective device of the high power microwave source by providing a separate port for the return and damping of the reflected wave. Such a converter has been analyzed, constructed, and tested. At the operating frequency of 2.45 GHz, test results indicate a 25 dB return loss, 97% end-to-end polarization conversion efficiency, and better than 20 dB rejection of the reflected wave. The structural simplicity of the device allows high power operation as well as easy construction for system research and applications.