The classical experiment of the microwave transmission through an axially magnetized semiconductor sample filling a waveguide is analyzed in terms of modal analysis, with a direct use of the guided helicon modes and of their adjoint modes. The validity of the numerical results is established by directly checking the continuity of the transverse components of the electromagnetic field through the vacuum semiconductor junctions. The calculation predicts satellite dimensional resonances, due to the higher helicon modes. These satellite resonances disappear if sufficient inhomogeneities, i.e., carrier density fluctuation of about 10%, are introduced in the mathematical model of the sample.