How to use Differential Port Setting in CST 2009?

I working on a project and it need to feed the signal by using differential port so that the phase shift is out of phase by 180 degree.
It's not the simultaneous excitation method which select in "Excitation Selection" in Transient Solver Parameters.
Anyone can help?
Thanks!

*bump
Anyone can help?

I have the same problem did you find a solution for it? if you found it please help me.

If you do not wish to use the simultaneous excitation feature, then the alternative would be to use 'Combine 3D Results' post-processing template.