## 2 Clothing Components in Wearable Textile Antennas
### Buttons
#### 2.1.1 Buttons
A unique button-like antenna with circular polarization operating at 5 GHz for wireless body area network (WBAN) applications has been described in [38]. The antenna yields a characteristic omnidirectional pattern with circular polarization (CP) that is appropriate for on-body communication. The 3 dB AR ranges between 5.79-5.9 GHz. This is the first button antenna that combines omnidirectional radiation with CP. A wide-band button antenna that operates at 2.45 GHz with 0.658 GHz impedance bandwidth and 1.8 dBi gain is presented in [39]. Bandwidth and gain are enhanced by the dielectric loading of the body whilst radiation efficiency is decreased due to losses. The wideband characteristics make the antenna robust to various environmental conditions and enable great manufacturing tolerances. Different positioning above the ground provides different radiation patterns making the antenna suitable for on- and off-body communications depending on location. Conclusively, a button-shaped antenna is inherently low-profile and user-friendly since a button is a typical part of clothes. A button topology presents a simple structure and can be easily integrated into clothing by applying ordinary sewing [15]. These features make a button-shaped antenna a suitable candidate in wearable antenna technology. Based on the recorded research works, it is obvious that the button antenna designs can cover different wireless needs within wearable technology. In Table 1, the button antennas' structural and performance characteristics are summarized. In Figure 1, configurations of button antennas found in the literature are shown revealing the button-adjusted shape design of the antennas. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & \multirow{2}{*}{**Type/Radiation**} & **Dimensions (mm)** & \multirow{2}{*}{**App.**} & \(\mathbf{f_{c}}\) & **BW** & \(\mathbf{e_{rad}}\) & **Gain** \\  & & & **L, W, H** & & **(GHz)** & **(GHz)** & **(\%)** & **(dBi)** \\ \hline
[11] & Top Monopole/ Omnidirectional & 40, 40, 13.39 & ISM/Wi-Fi & 2.45 & 0.13 & N/A & N/A \\ \hline
[13]\({}^{*}\) & Top Monopole/ Omnidirectional & 17, 17, 15.35 & ISM & 4.5 & 0.65 & N/A & 2.2 \\ \hline
[14] & Triangle patch-FSS/ & \multirow{2}{*}{30, 30, 5} & WLAN & 5.25 & 0.6 & 70 & 5.1 \\  & Broadside & & & & & & \\ \hline
[15] & Disc Monopole/ Omnidirectional & 17, 17, 11 & WLAN & 2.4 & 0.147 & N/A & 2.4 \\ \hline
[16] & Disc Monopole/ Omnidirectional & 17, 17, 11 & WLAN & 2.4 & 0.147 & N/A & 2.4 \\  & Omnidirectional & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A performance comparison of button antenna designs found in the literature with respect to antenna type/radiation, dimensions, application (App. ), frequency of operation (\(\mathbf{f_{c}}\)), 10-dB impedance bandwidth (BW), radiation efficiency (\(\mathbf{e_{rad}}\)) and far-field gain (Gain), where available. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref. ** & **Type/Radiation** & **Dimensions (mm)** & **App. ** & **\(\mathbf{f_{c}}\)** & **BW** & **e\({}_{\text{rad}}\)** & **Gain** \\  & **L, W, H** & **App. ** & **(GHz)** & **(GHz)** & **(\%)** & **(dBi)** \\ \hline
[17] & \begin{tabular}{c} Disc Monopole/ \\ Omnidirectional \\ \end{tabular}  & 17, 17, 12.8 & WLAN & 2.4 & 0.159 & N/A & 0–3 \\ \hline
[18] & \begin{tabular}{c} Patch/ \\ Broadside \\ \end{tabular}  & 16.02, 16.02, 4.575 & ISM/WLAN & 2.4 & 0.09 & 91.9 & 1.05 \\
[19] & \begin{tabular}{c} E-shaped PIFA \\ patch/ \\ Omni-Broadside \\ \end{tabular}  & N/A & ISM & 2.45 & 0.1 & N/A & \(-\)0.8 \\
[20] & \begin{tabular}{c} Patch-Monopole/ \\ Omni-Broadside \\ \end{tabular}  & 16.02, 16.02, 4.575 & ISM & 2.4 & 0.09 & 91.6 & 1.05 \\
[21] & \begin{tabular}{c} Disc Monopole/ \\ Omnidirectional \\ \end{tabular}  & 17, 17, 8.9 & WLAN & 2.45 & 0.294 & 87 & 3.4 \\
[22] & \begin{tabular}{c} Monopole/ \\ Omnidirectional \\ \end{tabular}  & 17, 17, 8.9 & WLAN & 2.45 & 0.294 & N/A & 2.2 \\
[22] & \begin{tabular}{c} Monopole/ \\ Omnidirectional \\ \end{tabular}