Analytical Study on the Resonance Frequency of Tunable Surface-Wave-Excited Plasma Antennas

In this article, an accurate analytical model for the calculation of the resonant length of a surface-wave-excited plasma antenna based on the distribution of the plasma density along the column is presented. In the proposed method, the propagation and attenuation constants for a surface-wave-excited plasma column are derived by solving the surface wave propagation problem on a three-layer tube, and as a result, the distribution of the plasma density along the column is investigated. Specifically, it is shown that a plasma column acts as a slow wave medium. Therefore, the resonant length of a plasma antenna is less than the resonant length of its metallic counterpart. For the experimental validation of the presented model, an efficient coupling structure for feeding the excitation wave to the plasma antenna is proposed that allows frequency tunability and reconfigurability of the antenna. A prototype of the proposed structure has been designed and fabricated. Good agreement between the analytical, numerical, and measurement results validates the proposed model.