how to set exponential curve in CST

Hi,
i am trying to design the vivaldi antenna for rcs applications.To construct exponential curve i tried 2D curve options in cst...but it is not working...how to make a curve in cst..I am using spline to construct it. but it is not working .....
somebody pl help me out...
thanks...

You could use scripting and "plot" your own curve. Just create some points and then combine then to a curve.