If you want some in-depth technical details on how VORs work, I found this video very helpful. It goes into many of the details of the analog radio engineering:
You can also compare and contrast how VOR/DME and TACAN works, to see two different solutions to one problem (polar coordinate measurement in 3D space.)
The mechanical differences are quite obvious when you look at a VOR, a TACAN, and a VORTAC, but the engineering behind them is interesting.
[1] https://news.ycombinator.com/item?id=40400619