Realization LB antenna CST

Good working,

I have a real low band antenna (20-520MHz) that works as a monopole and I am realizing it with CST (computer simulation technology). I do not know which type of port I can use (Discrete or waveguide port) and how I can choose the port dimensions in order to measure the VSWR and the farfield. How can I do it?

Thanks who Will help me :)