frequency-dependent RLGC model

hi

how can i calculate the Ri, Li, Gi, Ci parameters for a frequency dependent unit-cell RLGC model? example 1st order or up to 3rd order Debye model.
are there any equations?

i would like to make frequency dependednt spice models (not w-element model, since its not compatible with most of the spices, like ngspice...) from arbitrary power planes, with RLGC grid.