I suggest using the transmission line solver to look at an individual patch, then using the periodic solver to look at the patch in an infinite array. Then, if you need to, model edge elements using 6 by 6 or 5 by 5 arrays in the transmission line solver. Elements 2 from the edge will be very similar to the infinite array, and the ones next to the edge may not be very different either, but the ones at the edge will have a different impedance, and the ones at the corners. This will also show the effects of any ground plane edge.

Modelling 16 by 16 is a big problem and your machine may not be big enough or fast enough for CST to do it.

For X-band phased array design in CST, use the Time Domain Solver for the single element to quickly obtain broadband S11 and radiation patterns, and apply the Frequency Domain Solver with Floquet ports in a unit-cell setup to analyze embedded element impedance and scan performance for the full 16×16 array, direct EM simulation is extremely heavy, so the practical approach is to extract embedded element patterns and synthesize the array response, while full-array runs should only be attempted with the Integral Equation (IE/MLFMM) solver for metallic-dominant structures or the Time Domain solver on high-performance hardware.

Steps given by Cem Guler are practically works and results are consistent, matching with simulation. we have also used same steps.