Figure 6 Snapshots of the fabricated fractal array showing (a) Fractal radiators (b) Ground view (c) Testing of reflection coefficient on VNA
RETURN LOSS (S11/S22 (DB)) CHARACTERISTICS AND VOLTAGE STANDING WAVE RATIO (VSWR)
Return loss is used to estimate the power absorbed by the antenna from the transmission line. VSWR is defined as the ratio of peak voltage to the minimum voltage in the standing wave pattern that sets up in the transmission line due to impedance mismatches. The value of VSWR should lie between 1 and 2 for the maximum transfer of power from the feedline to the antenna. Equation 13 shows the relationship between return loss and VSWR [14].
\(\text{Return\ loss\ }\left(\text{dB}\right)=\ -20\text{Log}_{10}(\frac{VSWR-1}{VSWR+1})\)(13)
Figure 7 shows the variation of simulated and measured reflection coefficient (S11/S22 (dB)) as the function of frequency. The proposed fractal array covers a simulated operational band from 4.395-10.184 GHz (79.4% fractional bandwidth) and peak S11/S22 (dB) of -54.5 dB at 9.4 GHz frequency. The measured results on a VNA show a frequency band from 4.6-10.45 GHz (port-1, S11) and 4.55-10.32 GHz (port-2, S22) with fractional bandwidths of 77.7% GHz and 77.6 % respectively. The simulated and measured S11/S22 (dB) responses show an acceptable similitude of 95% match at the lower frequency band and a 97% match at the higher frequency band.