Axial ratio bandwidth measurement

hello everyone,i have obtained the curve of axial ratio Vs frequency for circularly polarized micro strip antenna..but with the help of this curve how to measure the exact axial ratio bandwidth...do i take reference at 3 dB?
suggestions are welcome......

thanks,
sonia

From definition: The axial ratio bandwidth is related to the polarization bandwidth.

hi sonia can you please tell me how did you measure axial ratio of antenna?which machine?have you measured axial ratio versus frequency?