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A. Mehmann
Mobile phones operate in different frequency bands, for example 900 MHz and 1800 MHz. To design wire antennas that resonate at different frequencies, branched strips of different lengths are employed. The size is reduced by meandering the strips [8]. In smart textiles, monopoles and dipoles are used for wireless communication. In particular, in on-body communication, monopoles are utilized because of their omnidirectional radiation pattern, which makes performance independent of antenna rotation. The polarization of monopole antennas oriented perpendicular to the body surface allows for on-body surface waves, which reduces the path losses [9]. However, monopoles orientated perpendicular to the body surface can be obtrusive and uncomfortable. Examples of monopoles or dipoles in textile are as follows: • A prototype of a wearable meander dipole with different branches of different length for tri-band communication in the frequency ranges of 915, 1575, and 2400 MHz. The dipoles are 118 and 72 mm long. As an alternative to textile integration, silicone encapsulation was employed, with higher losses due to the water content of the material [10]. • A meandered flare dipole on polyester fabric by embroidering silver-coated polymers. The size of the antenna was approximately 190 mm × 25 mm. The antenna was operated at 500 to 600 MHz, and its performance was found to be comparable to a copper antenna of identical shape [11]. • A 26.5-mm-dipole antenna for the 2.45 GHz frequency band. Nickel–copperplated woven polyester was glued onto denim with a relative permittivity of 1.67 and thickness 0.85 mm. The antenna has a bandwidth of 430 MHz [12]. • Textile dipoles with length 57.4 mm for the 2.4 GHz frequency band, see Fig. 7.2. The conductive fabrics are woven silver-plated nylon and embroidered conductive threads. The silver-plated fabric antenna has an average gain of 1.7 dB compared to the embroidered antenna with gain −4.3 dB [13].
Fig. 7.2 Textile dipole antenna of length 57.4 mm from silver fabric (left), two embroidered antennas, and a feeding structure on the right. Courtesy of Kaufmann et al. [13]