The efficiency of the transformation of the surface wave energy of a longitudinally inhomogeneous cylindrical plasma column into radiation is investigated. Plasma is limited by a dielectric shell. The analysis was carried out by the method of spectral decomposition of the field by a complete set of functions, including surface and spatial waves of the plasma column. A system of integro-differential equations for coefficients of decomposition is derived. These coefficients determine the amplitudes of the transmitted, reflected and scattered waves, as well as radiation patterns. The system of equations is solved for an arbitrary longitudinal change in the density of the plasma. The dependences of the transformation coefficients of the surface wave energy on the plasma density gradient, the electric length of the plasma inhomogeneity section, the electric radius of the plasma cylinder, the dielectric constant and the dielectric thickness are calculated. Examples are given where the part of the energy of a surface wave, which is transformed into a radiation at sharp angles, is 35%. The padiation patterns are pointed and have one beam. The maximum of radiation is formed at an angle, that equal several degrees relative to the direction of propagation of the surface wave. The width of the beam decreases, and its position shifts to zero, when the density gradient of the plasma increases. The influence of dielectric properties on the radiation characteristics is investigated.
Ключові слова: Cylindrical plasma antenna, spectral decomposition method, radiation, surface waves