The electromagnetic fields in air from a horizontal electric dipole over a perfect conductor covered with a plasma layer are studied. The total field includes the direct wave, the ideal reflected wave, the lateral-wave, and the trapped surface wave. The refractive index of plasma is a complex function of frequency, so the solutions of the pole equations which are used for the computation of the trapped surface wave are also a function of frequency. The influences of the frequency to the pole equations and the solutions are investigated.