difference in simulated result 4 2 element dipole using feko

Hi
I have simulated 2 dipole above finite ground as given in that paper. in that paper they didnt mention abt type of ground , i used PEC as ground.I didnt give proper radius to dipole as given in paper. From my simulated result i could c 20 db difference between mine and paper result. Can anyone give me the reason 4 it. will ground plane and dipole radius make this difference in result?

They are using a 50 to 200 Ohm balun. So in FEKO, maybe try a 200 Ohm characteristic impedance for the S-parameter calculation.