# High-Gain Multi-Band Koch Fractal FSS Antenna for Sub-6 GHz Applications
## 3 Results and Discussion
### Parametric Investigations
#### 3.1.4 FSS Loading for Frequency Tunability and Gain Enhancement
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multirow{2}{*}{**FSS Loading**} & **Gap (H) between Substrates** & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } & **S\({}_{\mathbf{11}}\) (GHz)** & \multirow{2}{*}{\
\begin{tabular}{} \end{tabular} } & **S\({}_{\mathbf{11}}\) (GHz)** & \multirow{2}{*}{
\begin{tabular}{} \end{tabular} } & **Gain at 3.5 GHz (dBi)** \\ \hline Parent antenna with FSS below & & 3.38 & \(-\)31.32 & 2.84–4.36 & 10.29 (6.20–8.78) & \multirow{2}{*}{10.46} \\ the radiator (distance between radiator and FSS = 3.0 mm) & & 11.78 & \(-\)12.43 & 10.93–12.48 & 8.39 & \\ \hline Parent antenna with FSS below & & 3.44 & \(-\)30.36 & 2.85–4.47 & 8.43 (6.28–8.99) & \multirow{2}{*}{8.31} \\ the radiator (distance between radiator and FSS = 4.6 mm) & & 8.0 & \(-\)20.52 & 6.28–8.99 & 8.59 (6.40) & \\ \hline Primary antenna with FSS below & & **3.50** & \(-\)**27.85** & **2.86–4.53** & **7.14** (6.51–8.74)** & **7.14** (6.53)** & **7.14** (6.53)** \\ \hline Primary antenna with FSS below & & **11.18** & \(-\)**10.44** & **10.78–11.56** & **6.53** & \\ \hline Primary antenna with FSS below & & 3.56 & \(-\)27.49 & 2.87–4.58 & 6.93 (6.62–8.71) & \multirow{2}{*}{7.08} \\ the radiator (distance between radiator and FSS = 6.2 mm) & & 7.70 & \(-\)16.26 & 6.62–8.71 & 8.53 & \\ \hline Primary antenna with FSS below & & 3.56 & \(-\)29.15 & 2.86–4.58 & 7.93 (6.71–8.77) & \multirow{2}{*}{7.87} \\ the radiator (distance between radiator and FSS = 7.0 mm) & & 10.76 & \(-\)10.66 & 10.22–11.25 & 7.91 & \\ \hline Primary antenna with FSS below & & 3.56 & \(-\)32.11 & 2.89–4.61 & 8.12 (6.89–8.77) & \multirow{2}{*}{8.03} \\ the radiator (distance between radiator and FSS = 7.8 mm) & & 10.82 & \(-\)10.51 & 10.56–11.04 & 8.0 & \\ \hline Primary antenna with FSS below & & **3.62** & \(-\)**32.29** & **2.87–4.62** & **11.37** (6.99–8.81)** & **14.02** (6.62–8.71) & \multirow{2}{*}{**(Gain Enhan.)**} \\ \cline{1-1} \cline{5-5}
**primary antenna with FSS below & & **10.58** & \(-\)**10.90** & **10.22–10.92** & **7.20** & \\ \hline Parent antenna with FSS below & & 3.62 & \(-\)33.74 & 2.88–4.64 & 8.27 (6.27–8.89) & \multirow{2}{*}{8.49} \\ the radiator (distance between radiator and FSS = 9.4 mm) & & 7.88 & \(-\)13.04 & 7.04–8.63 & 8.08 (6.40–8.63) & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Frequency tunning using FSS loading. Figure 11: FSS loading effect on miniaturized [PERSON] fractal antenna: (**a**) frequency tuning and gain enhancement and (**b**) effect of air gap on resonance frequency and cumulative effective permittivity. 3.1.5. Proposed Antenna with SRR Loading  
The effect of the SRR loading effect on the miniaturized circular [PERSON] fractal antenna is represented in Figure 12 in terms of their reflection coefficient curve comparisons, and these cases are showcased in Table 6. The miniaturized antenna, when loaded with an SRR, results in a reduced gain value from 13.38 dBi to 9.37 dBi. The advantage of loading the SRR is that it significantly improves the reflection coefficient below \(-10\) dB and converts the single wide band (without SRR) into two narrow bands; this will help to reduce the application interference. The decreased value of the gain is maintained by placing an FSS layer beneath the antenna ground at a 7.0 mm distance. This helps to improve the bandwidth in the first two bands and enhances the gain from 9.37 dBi to 14.02 dBi at the design frequency.