An extensive numerical investigation of the waveguide-plasma coupling, in the lower hybrid range of frequencies, is presented. The role of a sharp density gradient at the plasma edge is investigated. It is found that, in the case of a very sharp gradient, the accessibility condition |n||| > nc = (1–ω2/ωiωe)−½ is violated and an appreciable fraction of the total energy is launched in the range |n||| < nc. The case of one, two and four waveguides is considered, and it is found that the general pattern of the energy spectrum is very similar for the three antennas.