The influence of anisotropic conductivity of composite materials used in the manufacture of antennas on the parameters of antenna-feeder microwave devices has been considered. To test experimentally the possibility of such an effect, horn antennas of the L– and C– frequency bands were created from carbon-composite materials of various structures with a graphene-containing epoxy-binding substance. The study of the polarization characteristics of these antennas showed that the presence of anisotropic conductivity of the walls of the waveguide part of horn antennas made of composite materials leads to a change in the parameters of the antennas, which is more noticeable for high –frequency C-band antennas.