Analytical formulation for radiation characteristics of a surface wave sustained plasma antenna

Abstract

This paper reports the analytical formulation of a surface wave sustained plasma antenna based on the antenna theory and the theory for a surface wave sustained plasma. The antenna (tube) structure is a basic quarter-wavelength monopole antenna, comparable to a wavelength of a surface wave. The theory for a surface wave sustained plasma in a semi-infinitely long tube is extended to a finite length plasma. The electron density distribution is calculated based on the extended theory, and antenna characteristics are obtained from the electron density distribution. The analytical results obtained from the formulation show good agreement with the numerical results. The electron density in the finite length tube depends on the existence of the interference between forward- and backward-traveling waves and the boundary condition at the tube end. The electron density distribution is determined based on the balance between the forward- and backward-traveling waves. In the case that the plasma does not reach the tube end, which is equivalent to the case of a semi-infinitely long tube, the antenna gain is constant at a low value due to high plasma resistance and low radiation resistance, without the propagation of the backward-traveling wave. Once the plasma reaches the tube end, due to the coexistence of the forward- and backward-traveling waves with their interference, the electron density is elevated fairly beyond the critical density for sustaining surface wave propagation. Consequently, the antenna gain increases with the synergistic effect of the decrease in plasma resistance and the increase in radiation resistance, and the surface wave sustained plasma works as an antenna.