Need help with matlab coding for complex permittivity

My final year project is about getting the dielectric constant of a liquid based substance in a frequency band of (75-110) GHz. I am using a A Quasi-Optical Free-Space Method for Dielectric Constant measurement. I have to implement a code in matlab to get the dielectric constant from the S21 parameters (transmission coefficients). As far as what I have researched I have to get the complex permittivity by computing the measured S11, S21 using Genetic algorithm
(GA). I have attached a thesis paper that is similar to my project. Please help me, even if it is just a small suggestion!

i guess u deal with plasma materials :D
just look at maxwell equations and you will find out that you can include imaginary part as conductivity :P