Experimental study of a high power coupler for a tunable cavity formed by a vane-type structure

In this study, a high power coupler designed for a tunable planar cavity is experimentally tested. The cavity consists of a periodical vane-type structure, of which the height of the vane can be mechanically adjusted so that the resonance frequency can be fine tuned. The cavity is designed to be operated at pi mode and resonant at 2.45 GHz. The high power coupler is composed of a rectangular waveguide and a cylindrical ceramic rod with tapered ends. One end of the ceramic rod is intruded into the gap between two vanes of the cavity. Through this coupler, the TE10 mode of the rectangular waveguide is converted into the TE11 mode of the ceramic rod and then couples to the TEM mode in the gap between vanes of the cavity. Experimental results show that a microwave power up to 5 kW can be effectively transmitted to excite the pi mode of the cavity. This cavity can be used to excite large area plasmas.