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.