The resonant mode field expansion technique presented in previous papers to analyse one- or two-port microstrip structures of different geometrical shapes is now applied to multiport radial lines. In particular, a radial-line n-way power divider is considered. This device allows, under certain hypotheses, an equiphase and equiamplitude splitting of an input signal. The Z matrix formulation has been derived and utilized to obtain the scattering parameters for the circuit. The numerical results are in good agreement with both experimental and theoretical data presented in the literature. The low number of resonant modes required to obtain satisfactory numerical convergence allows a substantial reduction of the computing time with respect to other more complicated approaches.