make vivaldi antenna with resistive loading

substrate height 0.8 or 1.6
frequency response 0.5 -3.5 ghz
substrate maximum size 70*70 or 60*70
using software cst mws 5
problem is how to i resistive load in software by using lumped element & how to put wire ?

figure

I have same problem in antenna design , I need to use resistive load in the edges of the antenna but I don't Know how? please help me? thanks