Excitation of ion cyclotron resonance frequency (ICRF) waves in tokamak plasmas by using the waveguide antenna is investigated. To obtain the surface impedance of the plasma, the wave propagation equation for the fast wave is solved. The reflection/transmission coefficient is calculated for the parallel plates launcher that simulates the ridged waveguide. Dependence of the transmission coefficient on geometrical and plasma parameters is studied. It is found that the transmission coefficient can be of the order of 10%, comparable to that of the loop antenna. Non-plasma loss of the launcher is also discussed.