HOW to learn Advanced EM theory?

Oh yes...Advices hmm...
Okay I am not a master of Advanced EM theory at all..but what I learnt from my experience is that you should be very strong in the Mathematics needed for EM theory at basic level.
There are some good books about the topic Intermediate Maths for EM theory,learn all the mathematical & engineering functions which are there in EM like Green,henkel etc etc in EM context.
Good to start asap.

thanks!
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