# Development of Wearable Textile MIMO Antenna for Sub-6 GHz Band New Radio 5G Applications
## 2 Antenna Design Method  
Figure 1 depicts a proposed antenna configuration as its top and back surfaces, respectively. This antenna features an irregular octagonal MIMO patch antenna configuration without any slots. This antenna is built upon an economical jeans substrate and powered through a 50-ohm microstrip line, featuring jeans fabric with an ideal loss tangent of 0.02 and relative permittivity of 1.6, as measured through loss tangent measurement and relative permittivity analysis. The dimensions for the antenna are 40 mm \(\times\) 50 mm, while our investigations also explore the ground plane slotting effects as well as the parasitic strip lines between individual elements of its configuration, utilizing an ANSYS HFSS tool for analysis and fine-tuning purposes. The dimensions of the irregular octagonal patch are approximately equal to a quarter wavelength at operating frequency, i.e., 0.25\(\mathrm{\SIUnitSymbolMicro}\) at 4.6 GHz frequency, as shown in Equation (1), is used to find the resonant frequency and dimensions of the antenna. \[f_{r}\approx\frac{c}{4(P4+P8)\sqrt{\frac{1+\epsilon_{r}}{2}}} \tag{1}\]Here, \(c\) is the speed of light, \(\varepsilon_{r}\) is the relative permittivity, and \(P4\) and \(P8\) are the dimensions of the irregular octagonal patch. A narrow slot is strategically incorporated into the ground plane to optimize antenna performance by altering the electric length of the current density distribution in the partial grounding. The investigation delves into the inter-element interactions, considering the inherent challenges associated with the two-port MIMO antenna design. A parasitic metallic strip line is located between the two irregular octagon-shaped patch antenna elements to mitigate interference and to provide requisite isolation. The antenna elements are strategically distributed with an inter element spacing of approximately 0.24 \(\lambda\) (\(\lambda\) being wavelength related to operating frequency). Table 1 displays the dimensions for the irregular octagon two-port MIMO antenna proposed here. Notably, the proposed textile antenna's dimensions are compact, measuring 40 mm by 50 mm, demonstrating enhanced efficiency. Extending a two-port wearable antenna design to include more ports requires careful consideration of various factors, including coupling, geometry optimization, matching networks implementation, feeding network setup, simulation testing, and comprehensive simulation/testing. Figure 1: Proposed two-port irregular octagon-shaped MIMO antenna. (**a**) Conventional. (**b**) Proposed. An equivalent circuit for a patch antenna provides an accurate representation of its electrical properties in an easily understood form, featuring components like capacitors, inductors, and resistors to model its behavior and understand and analyze its performance, such as impedance matching, radiation pattern, and bandwidth characteristics, without complex electromagnetic simulations. The AWR Design Environment allows users to quickly determine the equivalent circuit parameters of an antenna by selecting its components. The patch antenna with a series inductor with an initial value of 0.01 pF is connected to a parallel RLC patch circuit featuring extracted values \(\mathrm{Rp}=54\ \mathrm{\Omega}\), \(\mathrm{Lp}=8\ \mathrm{nH}\), and \(\mathrm{Cp}=0.33\ \mathrm{pF}\). Additionally, the CLC circuit model for parasitic elements with inductance extracted as \(\mathrm{Ls}=4.42\ \mathrm{nH}\) and \(\mathrm{Cs}=16.85\ \mathrm{pF}\) between antenna elements and the parasitic element [25] is shown in Figure 2a. Differences between both \(\mathrm{S}\)-parameters in the simulation are accepted and reasonable between the simulation and model circuit simulation models in terms of both model \(\mathrm{S}\)-parameter values, as shown in Figure 2b.