When building Line's it's unavoidable that you will encounter at some point an Un-Removable object such as an Antenna. There are multiple ways to avoid these and some are more effective than others. Here are a few examples:

Going Around

Going around is a simple and efficient way as long as the line is not too wide and the turns aren't too short. These are best only used in Side Lines.

Going under

Going under is just as simple. Dig 2 hole's and place tunnels. Of course tunnels can't be signaled so for busy line's Multiple tunnels for every track could be required.