I would agree with Michel answer above, it definitely can be done using CST. Take a look at the following links that contains articles on how to design phased array antenna using CST. Note that you can find more articles from CST site regarding the design of phased array antenna using CST. Just do a search on CST site using the keyword "Phased Array Antenna Design" and you will get a lot of articles including the below ones that I found interesting: