how to locate 50 ohm impedance

hi,

am designing a dual rectangular patch antenna. plz tell me hoe to find 50 ohm impedance in smith chart..am using ie3d for designing

assuming that you are looking for spatial points of 50ohm then:

if you have access to the E and H fields of you simulation data then the 50ohm point(s) will be the point(s) at which the ratio of the E and H fields corresponding to 50ohm (of course scaled by some factors. also the E and H field must be in phase if you are looking for real 50ohm).