Doing a proper radar was one of the many things that I considered in the past, but I have plenty of scripts WIP. What else are you actually planning to implement once you have a script that does the LOS bit? A graphical display, I assume, because if not, you'll not be happy with my attached script (since it deals with the finding as well as LOS of the aircraft)?
On your request, I've thrown a script together which deals with terrain LOS, but it doesn't take into account buildings and other features (it could, but the speed cost would most probably be prohibitive assuming you have more than a couple of aircraft or are using anything like a reasonable range). I think I'd like to alter the logic a bit after doing some more research into how radar work though, before I'll consider it finished.