Plots of real (blue) and imaginary (red) parts of the refractive index of water in the microwave wavelength regime. I went through old papers to dig up the experimental data (circles) to compare to a fit to the theory (dashed lines).
https://files.mastodon.social/media_attachments/files/113/068/973/633/827/019/original/73875d5fa6144877.jpg