Volakis, John (2007). Antenna Engineering Handbook, Fourth Edition. McGraw-Hill. Sec. 26.1. ISBN9780071475747: Note: in contrast with other authors, this source initially defines ellipticity reciprocally, as the minor-to-major-axis ratio, but then goes on to say that "Although [it] is less than unity, when expressing ellipticity in decibels, the minus sign is frequently omitted for convenience", which essentially reverts to the definition adopted by other authors.{{cite book}}: CS1 maint: postscript (link)
Sletten, Mark A.; Mc Laughlin, David J. (2005-04-15). "Radar Polarimetry". In Chang, Kai (ed.). Encyclopedia of RF and Microwave Engineering. John Wiley & Sons, Inc. doi:10.1002/0471654507.eme343. ISBN978-0-471-65450-6.