[Moved]CST spiral antenna design help

Hi,
I am designing a spiral antenna in CST (without Antenna Magus, unfortunately!) and am wondering how to use the port excitation? I have used EMPIRE previously and in this you can simply define a discrete port between the two arms of the spiral and the simulator works fine. However, I have no idea how to do this in CST.
Thanks

Hi,
I have the same problem, I need some help :/ My antenna is a spiral one with many layers, I couldn't do the design but I made it in a format of a ring,can it give the correct results? I want to use the port excitation but I get errors in simulation. It doesn't work event when I change meshing.
Thanks