Center frequency of strip antenna design in HFSS

i have done our final project in HFSS software,i planned to design a compact antenna which operates for multiband by inserting slots in the patch.i designed 10mmx10mmx1.6mm antenna.But i not aware of the center frequency of this design.i have a doubt that when we do process in HFSS software we have a step that 'add solution setup' in that step we inneed to give the center frequency,in the sweep also we mention the start and stop frequency it should covers the center frequency.i have a doubt that if we not correctly mention the centerfrequency in the anlaysis setup if the result is accurate or not.in my design i obtained the result at 1.5GHz having -23.2dB return loss,in theoritical case this dimensions frequency was around 10GHz to 14GHz.

please clarify this doubt.... with regards
bagya

I dont think you are getting the right results. I can't be completely sure without the details. These dimensions should result in a resonance at a high frequency as you have mentioned. what about the radiation pattern? does it radiate well at 1.5 ghz ? If you are in doubt specify a high center frequency, lower freq results will still be accurate.