Analytical Estimation of the Efficiency of Surface-Wave-Excited Plasma Monopole Antennas

In this communication, the propagation equations of the electromagnetic waves in an inhomogeneous plasma column are solved, and the analytical estimation of the efficiency of the plasma antenna is presented. To validate the analytical results, an experimental prototype of a plasma monopole antenna is implemented while it is simulated using a commercial full-wave electromagnetic simulator. The implemented antenna can be excited by two different RF signals, at 450 and 1500 MHz, with a controllable power level between 1 and 50 W to adjust the effective length of the antenna. The proposed configuration allows both communication and excitation waves to be applied to a single coupling sleeve on the plasma column using a diplexer. Based on the measurement of the phase difference of two different positions along the column, using a phase difference detector microchip, the plasma density is estimated along the column. Good agreement between the results validates the proposed analytical method. The results show that the efficiency of a surface-wave-excited antenna strongly depends on the gas pressure, the excitation frequency, and the thickness of the tube. Therefore, for an optimized plasma antenna, all these parameters have to be properly used.