Hello aspirant. The major subjects in ece would be mathematics, physics,  networks analysis , electro mechanics, semiconductors, analog communications, data structures,signals and systems,  waves, instruments and measurements related to electricals,  digital electronics. More or less everything would be covered in these only.

Coming to subjects related to mathematics, every subject will have a part of mathematics in it. If exclusively to be said, then it would be computational techniques, theory of computation.

Hope this helps

Regards

Nikhitha