You seem quite resourceful so you might enjoy MetaMath[1]. This is, in my opinion, literally learning mathematics from first principles. Well, it's not really learning mathematics (insofar that lot of the concepts won't be particularly novel), but it's really showing you the "first principles" of mathematics, and how you can build that up into other stuff.
If you feel like MetaMath is your kinda thing, do visit the FAQ; it's quite good (and virtually required reading if you're going to do this alone).
Admittedly, it's not going to give you the tools suited for solving problems of antenna designs, or enlighten you about electromagnetism, but if you're into just pure recreational mathematics, it's worth a look.