Re our conversation on patch antennas and circular polarization, I found
this document which (in part) explains how to get circular polarization
with a single feedpoint. Fascinating!
http://orbanmicrowave.com/wp-content/uploads/2014/12/Orban-Patch-Antennas-2009-rev.pdf
To my disappointment none of my books were useful on this point. I remember
reading a detailed explanation of them somewhere, but I'm not finding it
now. This link seems like a pretty good start though.