momentum antenna

i am using ADS momentum in my antenna design working at 2.45GHz.when i plot the S11(dB)-rectangular plot i get a very good return loss of -22dB.when i plot the S11 in smith,i obtained the following,
S11=0.075/-156.019
impedance=43.487-j2.677

When i plot the rectangular for real(Zo) i obtained 50.006 and the imag(Z0) i obtained 0.016.my question is why the result doesnt match with the impedance in S11 smith chart i plotted which is 43.487-j2.677.

Hi, I have the same Doubt. I guess, the smith chart is not calibrated to 50 Ohms as our neetwor analysers are calibrated