Modeling Microwave Resonance of Curling Probe for Density Measurements in Reactive Plasmas

A compact new type of microwave resonator probe called curling probe is proposed for electron density measurements in reactive plasmas, where a spiral slot is excited by a monopole antenna. The resonance characteristic of the curling probe is simulated by the finite-difference time-domain (FDTD) method. The frequency dependence of power reflection coefficient and the electromagnetic field structures revealed two types of resonance at the same density: the high-frequency volume wave resonance along a spiral slot and the low-frequency surface wave resonance in an aperture of the probe. The analytical formulae of resonance frequencies as a function of electron density are derived.