One of my favorite antenna books is available on eBay for another week or so, at the very reasonable price of $65. Optimisation of Wire Antennas by Landstorfer and Sacher does a beautiful job showing how energy flow streamlines aid not only in understanding how antennas work, but also as design tools for thin wire antennas. I presented a few of their insights in The Art and Science of Ultrawideband Antennas, but you’ll find many more clever technical ideas if you go straight to the source. If you’ve missed the eBay opportunity, you may have luck finding a copy on Amazon.