how to design patch antenna array

What frequency?
What array spacing? (lambda/2?)
What sort of feed arrangement did you have in mind for the patches? (probe/aperture coupled/edge fed?)
Any phase shifts between the driven elements for beam steering?

While all of the above are essential to know from an implementation viewpoint, fundamentally the design of a 1x2 phased array is pretty simple: split your RF input(output) into two and drive each antenna separately [from equal length feed lines] as if it were its own single antenna system.

Generally a 50:50 (3dB) splitting ratio is used, often performed via a Wilkinson or similar architecture since the splitter bandwidth [generally] exceeds the bandwidth of the radiating element.

Try this file, hope that it's useful for you.