How to calculate single-ended S-parameter from differential s-parameter?

Dear all,

I am designing a deferential feeding antenna.
A wide band 180 deg power divider is used to transform a single-ended signal to two deferential signals which are anti-phase with each other.
and the two deferential signals are fed into the antenna via two coaxial ports.

I used HFSS to get deferential S-paramenters of the two coaxial port.
Regardless the effect of power divider,
can anyone tell me how I can calculate the single ended s-parameter from the deferential s-parameter?

If you have the solved HFSS model...simple look at the terminal S Parameters rather than the Differential S Parameters. Just by using Differential S Parameters in HFSS does not mean that the Single Ended S Parameters are unavailable.

Have Fun.