I found online a downloadable, free book on electromagnetic field theory, more from an electrodynamics standpoint (physics).  So far I have only skimmed through but it gives treatment of spectral analysis of an arbitrary source, radiation problems, relativistic electrodynamics, etc.  Even more important, is that it is an ongoing project — people are welcome (infact, highly encouraged) to submit ideas/work to be included in the book or to find errors in it’s current form.  This provides the benefit of at least some sort of checks and balances on what is in the book, in terms of people reading it and submitting feedback, and also it is a collaborative effort to provide a completely free source for this knowledge, which they remind us should be free always.