Plasma antenna applications have been developed in the past decade. In these cases, it is enough to know a somewhat estimation of the plasma densities. Microwave interferometry is known to be a suitable method to measure average plasma and collision frequencies. In this paper, an improvement of this technique on a cylindrical tube is investigated in three steps. First, the transmission and reflection coefficients are calculated by considering the radial nonuniformity of electron density, and then, the relation between attenuation and phase change with plasma parameters is derived. Second, the reflections caused by plasma and dielectric which are significant for lower measurement frequencies are added. Furthermore, the microwave scattering method is presented as a novel diagnostic technique by performing backward and forward scattering analysis. Finally, the measurement setup in X-band using the vector network analyzer is utilized to validate the implementation of the theory, which results in the approval of the modifications. © 2018 IEEE.
