# Modeling and Analysis of Wearable Antennas
## 1 Introduction  
Wired communications using coaxial cables and optical fibers, and wireless communications that propagate electromagnetic waves in free space using antennas, are common forms of communications. Wired communications have low propagation loss due to the communication line, and for this reason, they are advantageous for high-speed communications and high security. On the other hand, since wireless communications dramatically improve the working environment by eliminating cables, its application is spreading even for short distance communications. A sheet-like waveguide is a form of communications that incorporates the advantages of both wired and wireless communications. Compared to wireless communications, the loss due to the communication line is small and the security is high. Moreover, since the communication line is sheet-like, it can be used on the floor or the desk so that it can improve the working environment. Notably if you can construct a transmission line with a flexible material, you can wear it in a similar way to clothes, and you can achieve a good affinity with wearable devices through activities such as sensing of biological activity information and its transmission. Various applications may be expected for this technology such as monitoring of medical data and developing multifunction suits for rescue workers. Also, if wired communication with cables is expressed as one-dimensional communication, and wireless communication using antenna radiation is expressed as three-dimensional communication, communication by a sheet-like waveguide can be expressed as two-dimensional communication and can be thought of as a new physical layer of communication. In recent years, wearable technology has developed rapidly. This technology combines electronic technology, biotechnology and medical technology [1; 2]. In order to cope with wireless communication problems between wearable devices, the concept of a body area network (BAN) is proposed [3; 4; 5]. The most basic and most important part of the body area network is the wireless transceiver antenna. Sensor flexibility trend requires that the communication antenna should also have flexible ductility. However, the traditional antenna manufacturing process uses a rigid substrate while using a metal material with good electrical conductivity but no flexibility, resulting in the conventional antenna not having flexibility, while the conventional antenna has deformation occur during stretching, resulting in rapid deterioration of antenna performance, which is difficult to apply in the flexible wearable field. In order to cope with this challenge, some new materials with excellent characteristics have been developed, and the emergence of new materials provides more freedom for antenna design. Currently, flexible antennas are designed in the industry to make antennas using new flexible conductive materials, such as conductive composites [6], metal films [7] or liquid alloys [8; 9] to further enhance the ductile properties of the antennas. The flexibility of the antenna is improved, although the exploration of the flexible ductile antenna structure is less so. It can guarantee the stability of the working bandwidth of the antenna and good impedance matching. This paper also analyzes the effects of stretching in different directions on the performance of the antenna, including the bandwidth, input impedance and the change of the pattern. To achieve a full integration of a wearable system into smart clothing and protective garments, several wearable textile antennas have also been presented [8; 9; 10; 11; 12; 13; 14; 15; 16]; some conventional planar antenna layouts have been implemented by using electrotextiles (embroidered conductive polymer fibers, Shieldit(r), Flectron(r)) and non-conductive textile substrates (fleece fabric, cotton/polyester, felt, flexible pad foam commonly available in protective garments, Cordura layers, etc.).