## 2 Clothing Components in Wearable Textile Antennas
### Zip  
The zip as a clothing component is widely used in jackets and pants. Still, few researchers have examined its potential use in wearable antenna designs. A zip antenna can present a lot of advantages such as low cost, compact size, planar flexible structure, and simple garment integration. Owing to these features, a textile monopole antenna based on a commercial zip fastener is proposed for 2.5 GHz WLAN applications in [49; 50]. The zip antenna achieves an omnidirectional pattern with a realized gain of about 0 dBi. The antenna tunable capability is examined. Furthermore, a handbag metal zipper is presented in [51] to act as an off-body antenna. It is found that the zip antenna can operate at a satisfactory level for both \"user cases\", closed and open. The textile antenna can present multiple resonant frequencies by shifting the feeding point and can generate different radiation directivities by opening or closing the handle of the zipper. At 2.44 GHz, the zip antenna gain is almost 5 dBi. Similar to the handbag zipper, a jacket zipper antenna is presented in [52] demonstrating the natural radiation pattern reconfigurable capabilities  
Figure 3: Textile reconfigurable patch antenna applying different Velcro states: (**a**) on-; (**b**) off-state, respectively.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **Type/** & **Dimensions (mm)** & \multirow{2}{*}{**App.**} & \(\mathbf{f_{c}}\) & **BW** & \(\mathbf{e_{rad}}\) & **Gain** \\  & **Radiation** & & \(\mathbf{L}\)**, \(\mathbf{W}\), \(\mathbf{H}\)** & & **(GHz)** & **(GHz)** & **(\%)** & **(dBi)** \\ \hline
[47] & Patch/ & 49, 57.6, 4.26 & ISM/WLAN & 2.486 & 0.09 & 85.76 & 7.80 \\  & Broadside & (100 \(\times\) 70 GND) & & & & & \\ \hline
[48] & Patch/ & 53, 53, 4.2 & ISM/WLAN & 2.47 (LP) & 0.103 & 77.1 & 6.10 \\  & Broadside & (100.4 \(\times\) 74.2 GND) & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance comparison of Velcro patch 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.  
of a zip antenna. The antenna operates at various frequency bands depending on the feeding position (1.5 GHz and 7.5 GHz or 2.5 GHz). The zipper can efficiently radiate in omnidirectional, multi-lobe, and omni-like modes when the zip is fully closed, half-opened, and opened, respectively. The achieved gain ranges from 0.9 to 8.9 dBi at various frequencies. This work also validates the tunable reconfigurable nature of a zipper, proving the great potential and capabilities of such CC as the main radiator.  
Furthermore, in [48], a textile patch antenna that includes a fully conductive zip (teeth and cloth holding the zip) has been proposed by the authors of this review paper. The zip is embedded into the patch layer to provide polarization and frequency reconfigurability avoiding the use of complex active circuit elements. The zip serves as a polarization actuator. The work has been partly presented in Section 2.2. It should be highlighted that the conductive zip can shift the antenna resonance frequency downwards due to the elongation of the current path on its structure. Furthermore, due to the ohmic losses of the conductive zip, degradation of the antenna radiation efficiency has been noticed. Still, the repeatability measurements showed acceptable performance and stability of the zip patch antenna.