From RL plot we can see that some portion of 10dB impedance BW (from 8 to 8.76GHz) is outside the C-band.
So to bring it inside the C-band, we decreased the height of the DR continuously and for H=3.575, we got 10dB impedance
BW inside the C-band. Here 99.3% rad.
efficiency and 20.35% BW is (1.49GHz) achieved as shown in the plot below: