Optimal substrate thickness(Fr4) for microstrip antenna

Hello everyone. I'm designing a microstrip antenna in cst mws, subs - fr4, freq. - 2 ghz, using inset feed, 50 hom.
Can anyone help me to define the optimal substrate thickness for my structure to achieve the best results in simulating.
I've already read specifications for fr4, but i can't define the very optimal thickness. How do i do that?

hi, you need a substrate FR4 epoxy with .8 or 1.6 thickness

Hi,
I think, that is given by the manufacturer and you must choose one of several thicknesses.

But I find thist formula: BW = 4f2(t/0,794) [MHz] - this is the approximate width of the frequency band microstrip antenna. (f - frequency in [GHz], t - thicknes in [mm]).

But if you have CST MWS, there is nothing better than to try it ;)