As someone who is actually working in the EW and ELINT field(My firm designs antennas for military and space applications), I can assure you that EW101/102/103/104 are the best and most easy to understand academic material on the subject. Since one can rarely afford such costly books, I used to sit in my department library during my intern days and now have 250 pages of short notes on virtually every EW/ELINT subject, be it antenna, scan patterns, emitter location, receiver type, jamming, decoys etc.