IE3D /HFSS

hi frens,

I did simulate the same set of antennas using IE3D and HFSS but did end up with different results.Did feed wid the same probe feed...how come the result be different..the resonance frequencies are real different in both cases.. Have you come across the same??

P.S. I did check one of a paper they had given the result from both the simulators have similarities...