HFSS 9.0 Unrealistic Simulation Results

I try to make Surface MRı coil. In order to achieve to this aim, I made one model and took measurements. In HFSS 9.0, I simulate this model but my results are very interesting.Because Magnitude of S11 parameter is bigger than 1 and I didn't explain this results. I have some predictions for this problem but I didn't have any explanations. First of all, I try to use capacitor and my definition for Lumped RLC may not be true.Then, My solution type is modal and this may cause problem. Another prediction My sweep is Fast and this can be problem. I don't know which of them cause problem.Therefore, I put my design and results here. Please help me.
Thanks for help.

I have basic problem with capacitor definition. I have to define 3 pf capacitance in my design.However, when I define a cylinder Lumped RLC with height is 1.53 mm , which is in the substrate with its height is 1.53 mm too, then my measurements of S11 paramaters are bigger than 1. Obviously, this is unrealistic result.If anyone can help me to define right capacitor value in HFSS, I am really grateful.