balun coaxial feed in spiral antenna

Hi freinds

I want to know how to design balun coaxial feed in CST MWS to feed two archimedean spiral antenna. I need some information about balun coaxial feed.
Plz help me to design baluns coaxial feed in CST.

thank you

Regards
kaanee

I would also be happy if someone can provide information about the procedure to embed a balun coaxial feed in CST for feeding. Did anyone have experience about it before using CST?