## 3 Manufacturing Techniques for Wearable Antennas
### Flexible Textile Wearable Antennas
#### 3.2.2 Woven or Knitted Conductive Sheets  
This technique requires more time to construct a single antenna but may allow an element of automation for mass production. This can result in a more tolerant and flexible antenna structure compared to using copper tape. We will include woven metallic cloths, in this section. An example of this is Nora Dell which is a textile coated with nickel and silver to from a highly conducting flexible sheet (Figure 4). Figure 3: Textile patch antenna (substrate: felt, conducting sections: copper tape) with partially detached copper tape due to environmental conditions. Many papers considering textile antennas using woven or knitted conductive sheets have been published and will be reviewed in this section. The first compact fabric antenna design for commercial smart clothing was presented in [26]. This compact antenna is a patch antenna using fleece fabric as substrate and knitted copper for the conductive sections. In [27] a nickel plated woven textile, which has a high tolerance against oxidation and corrosion, is stable and has a very good conductivity, was attached on a spacer by using ammonia-based textile glue. The textile glue showed negligible influence on the sheet resistance since the plated textile is densely woven [27]. In [15] two antennas manufactured by using two different methods of attaching conductive Flectron onto Fleece fabric were considered. The layers in the first antenna were attached to each other by using a glue stick and the layers have been additionally stitched together using non-conducting threads to enhance the robustness of the antenna. For the second prototype an adhesive sheet which melts when ironing was used to attach the layers together. The first antenna showed better performance in terms of return loss and bandwidth. It can be assumed that the adhesive sheet melting inserts more losses into the antenna compared to the glue stick. In [28] four different methods were used to attach the conductive woven textile on the non-conductive textile were examined: (i) liquid textile adhesive (golden fix); (ii) point wise application of conductive adhesives; (iii) sewing and (iv) adhesive sheets which melt when ironed. The 4 th attachment method yielded the best results out of the four methods; it barely affected the substrate (felt) thickness which helped the antenna to maintain the geometrical designed dimensions [28], also described the design of woven and knitted conductive textiles, the material selection criteria and the characterization of the material properties (sheet resistance of the conductive textiles and the permittivity, tangent loss of the non-conductive textile). The effect of various wave patterns of conductive cloths in combination with the non-conductive dielectric substrate is presented in [29, 30]. This was studied because not all fabric patterns are symmetric. There are some fabrics with asymmetrical patterns on each side. This means that some conductive fabric patterns have the majority of the conductive threads on one side of the fabric. In these works ([29, 30]), the cases where the side of the fabric (conductive) with the majority of the conductive threads was directly attached onto the dielectric non-conductive substrate yielded less dielectric loss and better conductivity compared to the cases where the side of the fabric (conductive) with the minority of the conductive threads was directly attached on the dielectric non-conductive substrate. Figure 4: [PERSON] conductive cloth. In [31] an aperture coupled patch antenna using two different textiles (fleece and felt) for the substrates was proposed, designed and manufactured. Additionally, two different conductive textiles were used for the patch, ground and the microstrip line. For the patch, Shieldit was selected because it has an additional adhesive layer which made it easier to attach the patch to the substrate. For the ground and the microstrip line Flectron was used because of its smoothness and low surface resistivity.