The role of dielectric permitivity in antenna design ?

What is the role of dielectric permitivity in antenna design. FOr example what is different between when epslon is 2.3 , 2.3 and 2.5 . WHy we choose 2.2 instead of 2.5.

In which case we will think of changing the permitivity of substrate when the design of antenna is fail ( not as expected ) -by your experience

Thank you for reading this topic

Radiation factor (Qr) and Bandwidth of the microstrip (or patch) antenna are affected by substrate permittivity Er.

The gain of an antenna will increase if we decrease the dielectric constant.

Increase the dieclectric constant, decrease the size.
But it is not the main factor to decide which dielectric constant is choosen, If you design antenna in 5.8 Ghz, which dielectric you will chosse, 2.2 or 2.5 ? What is different between them