hfss unit cell

Hello,
I'm currenlty trying to implement an EBG ground plane on my microstrip antenna design. I'd would like to characterize the EBG unit cell by plotting the "Reflected Phase" of an incident plane wave, as a function of frequency.

I'm would like to use HFSSv11 to do this. My geometry uses a Master/Slave boundry conditions on each side of the EBG structure, and an Absorbing Air box at the top.

I'm using and incident plane wave to excite the structure, but I'm unable to figure out how to plot the "Reflected Phase" of this plane wave as a function of freq.

Does anyone have any ideas?

THanx