CST vs HFSS

Hi,
I'm just wondering if anyone has encountered this same problem that I'm facing. I have simulated an antenna structure in CST, and have gotten some results, and due to some unexpected behaviour, I'm trying to verify the same behaviour in HFSS. The behaviour is somewhat consistent (3 resonance, the bandwidth ratio...), however, it is sooo much shifted in terms of frequency! (up to 3-4 GHz).
Can anyone help!

Dear mimi-wan,
With so little info, the discrepancy could be due to many things, including the mesh setting. Please provide us with more details. How about uploading the simulation files or at least images of the models in CST and HFSS?