Free software for microstrip dispersion problem

Hi everybody,
Has anyone used free software (freefem, pdnmesh, meep etc.) for the full-wave solution to dispersive propagation constant and frequency-related (not static) characteristic impedance of microstrip (or any other inhomogeneous transmission line)? I know other software which does static analysis (ATLC, MMTL), but i need dispersive parameters. Thank you in advance