bird nest antenna axial ratio plot

[Blesvin]

hi

I almost obtained the reflection coeff graph with bw of 30% even the paper contains 40%. But I didnt get the axial ratio plot with points below 3dB. what parameter in antenna has to be changed to obtain this graph? my antenna contains the probe at the center of circular ground plane and 8 inclined dielectric slabs around it. pls help me to solve this problem....

 

[Blesvin]

how to get desired axial ratio bandwidth for a circularly polarized bird nest antenna

hi sir

I have to design a antenna look like bird nest with probe feeding. The axial ratio bandwidth at 3dB in the paper is 54% when theta=30 and phi=0. But I didn't got any point below 3dB at this angle.I almost obtain points around 7dB. What will I do to obtain bandwidth at 3dB for axial ratio plot?
pls help me.. Thank u in advance...