Reference data for reproducing in the future.

microstrip-long-rogers.s2p is a Sonnet EM solver simulation of a ~8 inch long microstrip on RO4350B using default ABS point spacing from 0.01 to 40 GHz. The resulting s2p has 200 MHz sample spacing which leads to huge differences in phase from one line to the next.

microstrip-long-rogers-interpolated.s2p uses a Sonnet netlist project to resample the source data to 5 MHz per line. This looks much nicer when doing channel emulation.

microstrip-long-rogers.s2p.txt
microstrip-long-rogers-interpolated.s2p.txt

See https://experts.syr.edu/en/publications/interpolation-and-extrapolation-of-s-parameter-data-of-a-microwav for possible algorithm.