The three-dimensional structure of ICRF (Ion Cyclotron Range of Frequency) waves in a tokamak plasma is investigated. In a two-ion-species plasma (majority deuterium and minority hydrogen) with radial density inhomogeneity, the wave equation is solved numerically by employing a cold-plasma approximation. The plasma is immersed in a toroidal magnetic field with a gradient and is surrounded by the vacuum region and the conducting wall. Waves are launched by a Faraday-shielded poloidal-current antenna of finite extent in toroidal and poloidal directions. The wave field and the energy deposition profile are obtained by introducing a simple model for the collision. The wave accessibility condition is examined for plasma parameters and density profiles. In a cold-fluid approximation, two mechanisms of power absorption, i.e. two-ion hybrid resonance and cavity resonance, are found, and the differences between them are studied. The antenna loading impedance is also calculated for each case. High-and low-field-side excitations are compared. Non-plasma losses at the wall are considered in obtaining the coupling efficiency. Good coupling conditions and desirable antenna designs are also discussed. It is found that efficient coupling is expected in a wide range of plasma parameters.