[en] There are many factors which lead to attenuation factors related to physical and geometrical properties of the metal from which wave guides are made. When considering the physical properties of the inner medium, it is found that average transmitted power increases with the increasing of air pressure or vacuumizing it or by replacing it with a highly ionized gas. This fact has created the suggestion that electromagnetic field leads to ionizing the air under average pressure and temperature making plasma medium which causes the field attenuation. Starting from the fluid equations describing cold plasma and using Maxwell's equations of electromagnetic field, we calculated the permittivity tensor of the plasma .(8 tabs., 30 refs.)