You can say that again, for example please check this excellent references by ARRL for radio communications [1].
[1] ARRL Handbook for Radio Communications 100th Edition Six-Volume Set:
https://home.arrl.org/action/Store/Product-Details/productId...
I disagree, it's much more that, far too much to discuss here. A starting point would be to check the ARRL and RSGB handbooks which provide a reasonably comprehensive overview of AR. (Google each for more info.)
There are many more specialist books if you want even more in-depth information.