how to get the dispersion diagram using HFSS simulating the metamaterial antennas

Can anyone explain how to get the dispersion diagram(phase constant) using HFSS simulating the metamaterial antennas(for example leaky wave antenna)

For metamaterials, it is possible to get the dispersion diagram by this way:
Simulate the HFSS model, and get the S pameters
Then program in the matlab using the S parameters.
But for metamaterial-based antennas with only one feeding port, how to get the dispersion diagram. Thanks:

I need to know the equation of Dispersion, or if you have the program in matlab for that purpose, could you share it :) (I need it for a transmission line model using HFSS)

i have a same problem. How can I get dispersion relation of a transverse slot leaky wave antenna on microwave cst....basically i need beeta/Ko verses frequency. any one can also send detailed report on er.neel.gupta@gmail.com......