CST Circularly Polarized Plane Wave + Plus Scattering Parameters

I'm trying to learn how to setup circular polarization in CST 2009 Microwave Studio for a plane wave. Assume a very simple dipole atten. Ground plane with feed (waveguide port over this feed), dielectric slab, dipole and then waveguide port 2 in front of the attn. How could I send a plane wave circularly polarized from port 2 in the negative z direction. Please look at the diagram. And obtain scattering parameters?

Thank you

Did you solve this problem? If you did, can you please post your solution. Thanks.