# Wideband Ring-Monopole Flexible Antenna with Stub for WLAN/C-Band/X-Band Applications
## 3 Antenna Fabrication and Analysis
### Bending Characteristics  
Figure 15 is a photograph of when the proposed antenna was bent in the horizontal and vertical directions by hand, and it can be seen that the antenna was bent without any problem. If the antenna is bent by hand, the exact degree of bending is unknown. However, if the antenna is bent with a cylindrical Styrofoam, as in Figure 16, the bending degree of the antenna can be quantified by the radius. Styrofoam was used for measurement because it is commonly available at low cost and is a material that does not have much effect on the antenna.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ref. No.** & \begin{tabular}{c} **Dimension** \\ **(mm\({}^{2}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Bandwidth** \\ **(GHz)** \\ \end{tabular} &
\begin{tabular}{c} **Peak Gain** \\ **(dBi)** \\ \end{tabular} & **Application** \\ \hline
[11] &
\begin{tabular}{c} \(34.9\times 48\) \\ (0.116 \(\lambda\times 0.16\)\(\lambda\)) \\ \end{tabular} & 1–8 & 3.1 & UWB \\ \hline
[12] &
\begin{tabular}{c} \(71\times 98.35\) \\ (0.568 \(\lambda\times 0.787\)\(\lambda\)) \\ \end{tabular} & 2.4–2.45 & 6.85 & 5G/WLAN \\ \hline
[13] &
\begin{tabular}{c} \(20\times 32\) \\ (0.155 \(\lambda\times 0.249\)\(\lambda\)) \\ \end{tabular} & 3.24–3.91 & 4.03 & WiMAX/WLAN/5G \\ \hline
[14] &
\begin{tabular}{c} \(32.6\times 52\) \\ (0.152 \(\lambda\times 0.243\)\(\lambda\)) \\ \end{tabular} & 1.4–16.4 & 5.19 & UWB \\ \hline
[15] &
\begin{tabular}{c} \(40\times 50\) \\ (0.294 \(\lambda\times 0.367\)\(\lambda\)) \\ \end{tabular} & 2.2–25 & 4.5 & UWB \\ \hline
[16] &
\begin{tabular}{c} \(40\times 55\) \\ (0.267 \(\lambda\times 0.355\)\(\lambda\)) \\ \end{tabular} & 2–20 & 6.36 & UWB \\ \hline
[17] & \
\begin{tabular}{c} \(36\times 30\) \\ (0.375 \(\lambda\times 0.312\)\(\lambda\)) \\ \end{tabular} & 3.97–6.24 & 6.3 & WiMAX/UWB \\ \hline Proposed antenna &
\begin{tabular}{c} \(32\times 40\) \\ (0.256 \(\lambda\times 0.32\)\(\lambda\)) \\ \end{tabular} & 2.36–2.87 & 5.63 & WLAN/C-band/X-band \\ \hline \hline \end{tabular}
\end{table}
Table 2: Parameter comparison with references.  
Figure 14: Gain of proposed antenna.  
Figure 17 shows the S-parameter results measured when bent both horizontally and vertically round a cylindrical Styrofoam with radii of 25 mm and 30 mm. Radii of 25 mm and 30 mm correspond to the bending angles of 73 and 61 degrees, respectively, when bent horizontally, and 92 and 76 degrees, respectively, when bent vertically.  
Figure 16: Photo of the antenna bent using a styrofoam cylinder.  
Figure 17: _Cont._  
Figure 15: Photo of the antenna when bent. (**a**) Antenna bent horizontally; (**b**) antenna bent vertically.  
When the antenna was bent, the S-parameter of the antenna changed. As a result of measuring the S-parameter according to the degree of horizontal and vertical bending of the proposed antenna, the S-parameter changed slightly. It is seen that the proposed antenna is suitable as a flexible antenna. This is because the resonant frequency and bandwidth do not change significantly compared to the flat antenna depending on the degree of bending or the direction of bending.