Plasma-Enabled Tuning of a Resonant RF Circuit

A concept of plasma-enabled tuning of radio frequency systems is introduced and experimentally verified in this paper. Specifically, a commercial gas discharge tube (GDT) is employed as a plasma cell integrated in an inductor-capacitor (LC) resonator. The principal factor affecting the characteristics of the LC circuit with the embedded GDT, studied for the first time in this paper, is the decrease in the cathode sheath thickness and thus increase in the capacitance of the plasma cell with increasing current in the abnormal glow discharge regime. The reduction of plasma cell resistance is an additional factor. The sample LC resonator demonstrates frequency tunability by 55% in the range of 240-372 MHz, while the discharge current increases up to 90 mA, at the expense of reduction in quality factor from 62 to 5 as a result of ohmic losses. Theoretical estimates based on the fundamental principles of glow discharges supplemented by circuit simulations show good agreement with measurements. The local minimum in frequency behavior of the resonator's quality factor is shown to be related to frequency-dependent plasma parameters. The results of this paper indicate that plasma tuning techniques could be a viable alternative for emerging applications.