What is axial ratio in antenna design?

i am new to antenna design. i would like to wat they do mean by axial ratio why its so important?

Hi,

A circular polarized wave radiates energy in both the horizontal and vertical planes and all planes in between. The difference, if any, between the maximum and the minimum peaks as the antenna is rotated through all angles, is called the axial ratio or ellipticity and is usually specified in decibels (dB). If the axial ratio is near 0 dB, the antenna is said to be circular polarized. If the axial ratio is greater than 1-2 dB, the polarization is often referred to as elliptical.

the above is from the following website
http://www.astronwireless.com/polarization.html

BR
Adel_48