Square Antenna Array for THz communications

Hello!

I am designing a planar antenna rod array. I have tried differents designs with different base length and elements number and get differents results.
And I am trying to understand why the slightest change of the length of the base of a sigle element has on the overall gain of the array system.
Can anyboody help me in simple words how to figure out the relation between single elements spacing, the number of elements and the overall gain for a planar dielectric rod array antenna?

Thanks