# Modeling and Analysis of Wearable Antennas
## 2 Sheet-Like Transmission Line  
### Information Transmission by a Sheet-Like Transmission Line  
In millimeter-wave band integrated circuit (MMIC) packages and high-frequency band (RF) modules, those crossing orthogonal lines are called ribbon wire bonding, and as the wavelength becomes shorter like millimeter waves, the size of the intersecting parts can be ignored but their effect on transmission cannot be ignored. As a solution to this problem, a ribbon wire interconnector with proximity coupling of resonators arranged in layers has been proposed [6]. As shown in Figure 1, the ribbon wire interconnector has a two-layer structure, and a microstrip resonator with a ground plane is opposed and a coupling resonator is loaded thereon. The lower layer resonator is excited by the microstrip line and propagates the electromagnetically coupled resonators of the upper and lower layers with low loss. As a result, a gap having a width of g is formed, and it is possible to intersect microstrip lines orthogonal to this gap. This structure is applied not only to the ribbon wire interconnector but also to the power divider [25], the phase shifter (DPS) [26], and the like. Its structure is simple, thus having the advantage that printing technology can be used for its production. In the literature [24], the insertion loss is less than 1.25 dB within the band of 33.1% at 6 GHz. By connecting this structure in cascade, a sheet-like one-dimensional line can be realized. Since this line uses a resonator for the parasitic element, if there is another resonator, that is, an antenna is arranged in the vicinity, strong coupling is obtained and electromagnetic connection with external equipment becomes easy. Furthermore, if the lower layer resonator and the upper layer parasitic element are arranged in a staggered manner, a line having a two-dimensional structure is formed and a sheet-like line is formed. Figure 2 shows the waveguide of one-dimensional structure and its transmission characteristics. It can be seen that the power input from port 1 is efficiently transmitted to port 2. Figure 1: Ribbon wire interconnector. Figure 2: Sheet-like one-dimensional transmission line. (**a**) Waveguide structure, (**b**) Transmission characteristics of the waveguide. Next, the transmission line with the two-dimensionally arranged structure is a structure in which the upper layer parasitic resonator is arranged at the center of the four resonators on the resonator array layer lined with the ground plate as shown in Figure 3[10; 27; 28]. The transmission loss is suppressed by optimizing the dimension of the upper layer parasitic element resonator, and the frequency to be used in the dimension of the lower layer resonator is determined. Although the microstrip resonance length is designed with reference to a half wavelength (\(\lambda/2\)), as the overlapping area of the lower layer resonator and the parasitic element as viewed from above is wider, the coupling strength is stronger and the transmission loss decreases. Consequently, the distance between adjacent resonators is optimized as a parameter. Also, in order to suppress the occurrence of higher order modes, we have a symmetrical structure. Figure 4 shows the transmission characteristics when the lower layer resonator designed at 5 GHz is 4 \(\times\) 4 elements, obtained by simulation using the moment method. In order to clarify the transmission line characteristics, the following is considered:  
* the transmission characteristics of only the waveguide provided with the input/output ports 1 and 2 in the lower layer resonator. * port 1 is connected to the line and the half-wavelength dipole. * characteristics when the ports 1 and 2 are both half-wavelength dipoles installed on the transmission line. * the half-wavelength dipole is arranged in the same way as (c). The above four transmission characteristics are compared when the transmission line is removed.