Gain result difference in IE3D AND HFSS Design>>>please Help me

Hi
I have simulated two dipoles,
the Design have 2 port and s parameters result are same in HFSS and IE3D
Gain using HFSS is 3.6 dB BUT using IE3D is 5.8 dB
could any body help me please, its urgent
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i've attached design file
------------------------------antenna alone.rar
any comment is could be helpful
thanks

so interesting , no comment at all!
by the way i solved it by myself
port type in hfss should be terminal and some difference seems logical because there is tho kind of different methods(MOM and FEM)
cheers