A compact and broadband feeding structure for in-situ plasma probe measurements

A compact and broadband symmetrization for in-situ plasma diagnostics is presented in this paper. Based on the maximum dimensions of the applied multipole resonance probe (MRP), a 5.8 mm by 33 mm stepped tapered balun is integrated into the holder of the probe. It possesses a return loss better than 30 dB and an insertion loss below 0.25 dB in conjunction with a high symmetry from 0.2 to 6 GHz. Hence, an undisturbed resonance behavior can be evaluated to calculate internal plasma parameters by one reflection measurement. The balun is investigated by detailed simulations in CST Microwave Studio and by measurements of a back-to-back transition. Additional measurements within an argon-oxygen plasma prove the suitability of the integrated balun.