Effect of FR4 mathematical relation between length & thi

Hi to all! I know that the FR4 substrate thikness has a big effect on the design of a planar antennas. Does anyone know the mathematical relation between length and thikness?

thanks

Mathematical relation can be found in Balanis book (2nd ed): chapter 14.2

Hi. May I know where to find this Balanis book?

Thank you.

Just go to Book Upload part of this site and search for this book.