Vivaldi antenna Exponential taper equations in HFSS

Hello,
We are designing and fabricating a micostrip fed Vivaldi antenna in the frequency range of 1GHz-3GHz. We are most likely to use FR4-Epoxy as the substrate. However, we are not certain about implementing the equation for the exponential taper of the Vivaldi antenna in HFSS. Request your help in this regard.