HOow to create taper in vivaldi a0Macors->Curve->Creat 2D curve analytically (xy-UV)

How to create taper in vivaldi antenna of rate 0.3/cm.
I crated by using Macors->Curve->Creat 2D curve analytically (xy-UV), but what is the equation that want to put in the edit history list like yyy=exp(0.3xxx). please tell me the correct equation