I stuck with some questions about 3x3 patch array. It's said that patch antenna frequently is 200 Ohm. Is it always? Ain't that change with antenna design parameters such as length? Do I have to consider each patch is 200 Ohm and design the feed lines in respect to 200 Ohm and at the end of the antenna, transform it to 50 Ohm which's I wanna feed the antenna with?
A patch antenna is not always 200 ohms. In the case of an antenna array, you have two options: either you ignore the array affect, or you take it into account.
Ignoring it could still perform okay if you have a little coupling between patches. The fact that a patch is directional helps you somewhat here.
If you don't, then you have to take it into account, but I would say that requires some form of EM simulator. It depends on how far the patches are separated from each other. If you do, you will have 3 different impedances: The center patch will experience the most coupling (and thus the biggest shift in impedance), as it is surrounded by other patches. The corner patches have the least coupling (as they are only coupling on two edges) and thus will have the smallest shift in impedance. The edge patches will sit somewhere in the middle.
How you deal with this is a whole other question in and of itself, and will depend on what kind of structure you are working, how you are exciting the patches, etc.