Problem In Retriving Negative Index of Refraction From SRR With Wire

I am new to HFSS and after much struggle i had able to re do the structure proposed in D.R Smith paper but in the process of retrieving index of refraction my result is some how different w.r.t D.R Smith paper.My magnitude,phase and impedance response is same as paper.I had attached my simulated index of refraction and the result shown in paper n_Simulated.bmpn_SmithPapper.bmp. I tried hard but could not able to get the result.Help me ...........It is urgent.

Thanks