Determination of effective dielectric constant out of multilayered substrate

Good day, ALL!

I would like to determine effective dielectric constant out of multilayered substrate to calculate the dimensions and the parameters of patch antenna at THz. I have multilayered substrate, and nothing else. I am stucked. I have read a lot of papers, but most of them for X-band, but effective diel.constant changes as frequency gets higher. I am using CST to design this antenna.

Please, could you help me to find out somehow?

Looking forward your feedback.

Jukenaikam