## 2 Clothing Components in Wearable Textile Antennas
### Buttons
#### 2.1.1 Buttons  
Several researchers have successfully proposed button designs as wearable antennas [11; 12]. In [11], a metallic G-shaped cuff button antenna is proposed for Wireless Local Area Network(WLAN)/Bluetooth wearable applications at 2.45 GHz. The antenna achieves satisfactory omnidirectional radiation patterns that are necessary for wireless data transfer with adjacent electronic devices. In [13], commercial jeans buttons have been electrically characterized for possible antenna use in industrial, scientific and medical (ISM) applications. The microstrip-fed buttons resonate at the 4.5 GHz band and present monopole-like radiation properties in terms of radiation pattern and far-field gain. The measured maximum gain is 2.2 dBi. In [14], a miniaturized button-shaped triangular patch antenna has been proposed for WLAN biomedical applications at 5.25 GHz. A frequency selective surface (FSS) has been applied as a superstrate layer to enhance antenna gain. The proposed antenna configuration shows a measured gain of 5.1 dBi over the frequency band of operation. Furthermore, various research works have developed dual-band antennas (2.4 GHz and 5 GHz) [15; 16] for on- [17] and for off-body operation [18; 19; 20] following almost standard jeans-shaped buttons [21]. In [15], a dual-band antenna has been developed for wearable WLAN applications. The total size is practically similar to that of a trouser button. The measured radiation patterns are omnidirectional at both operating frequencies (2.4 GHz and 5.2 GHz) to enable wireless connectivity with body-worn or elevated external devices. The gain is estimated to be close to 2.4 dBi. Similar work has been presented in [16] and in [17] presenting an upgraded antenna button design in terms of size reduction. In [18], a dual-band button antenna has been designed and experimentally validated. The proposed antenna presents a quasi-monopole radiation pattern at 2.45 GHz and a quasi-broadside radiation pattern at 5 GHz to be applied for on- and off-body wireless communication, respectively. The measured antenna gain is 1.05 dBi at 2.45 GHz and 4.5 dBi at 5.2 GHz. High radiation efficiency is, also, achieved accompanied by a small button configuration. Antenna resonance and radiation performance seems to be slightly affected by the presence of the human body due to the large ground plane. Similar work has been presented in [20]. In [19], a dual-band dual-mode E-shaped button antenna has been presented for body-centric applications. An omnidirectional pattern and a broadside pattern are achieved at 2.45 GHz and 5.8 GHz, respectively. Simulated and measured results show that the proposed design is robust under bending conditions and on-body environments. Further, it is easy to be integrated into clothes due to its flexible ground plane. In [22], a dual-band G-shaped antenna cuff button antenna has been designed. The button antenna operates at 2.45 GHz (WLAN/Bluetooth technology) and 5.8 GHz (HiperLAN technology) presenting omnidirectional radiation patterns. It should be noticed that the button shape antennas without a substrate fill [23] are less sensitive to feeding due to the lack of a dielectric layer. Frequency-tuning degradation due to structural deformation or insufficient electrical characterization of the substrate and potential humidity in the substrate is, also, avoided [16]. On the other hand, button designs using a dielectric substrate are reduced in size [24; 25]. Finally, a miniaturized dual-band button antenna has been presented in [26] for wireless body area network applications. The antenna consists of a spiral inverted-F radiating part and a metal flange. In the lower band of 2.45 GHz, the antenna shows an omnidirectional pattern while in the higher band of 5.8 GHz a broadside pattern is achieved. The measured antenna peak gains on tissue phantom are \(-\)0.6 dBi and 4.3 dBi, respectively. A dual-band and dual-polarized button-shaped antennas are proposed in [27]. The antenna operates at 2.45 and 5.8 GHz.