simulating a patch antenna without ground plane in CST

Hi, everyone,

It seems that most versions of CST Microwave Studio can not correctly simulate a patch antenna without a ground plane. I am recently working on a fish-bone patch without a ground plane for wireless capsule endoscopy applications, however, CST gives terrible simulation result. The statement at the beginning is the answer from my teacher and I am just wondering have anybody ever confronted a similar problem? Could you please share me with your solutions?

Thank you very much,
Tim