Hello,
I'm not sure how to do this exactly, but we have these examples for studying the dispersion relation of SPR that might be helpful:
https://optics.ansys.com/hc/en-us/articles/360042160673
https://optics.ansys.com/hc/en-us/articles/360042160633
https://optics.ansys.com/hc/en-us/articles/360041686774