To obtain the axial ratio bandwidth

Hi

I have designed an antenna look like bird nest works on circular polarization. But I need to find the Impedance bandwidth and axial ratio bandwidth.When I plot the axial ratio, the minimum point is obtained at 5dB and no points below the 3 dB. So that I can't find the axial ratio bandwidth. Also my graph contain a high peak at 4.5GHz.So what will I do to obtain the axial ratio bandwith? pls help me to solve this problem...Here the plot at theta=30 and phi=0