# A Compact Wearable Textile Antenna for NB-IoT and ISM Band Patient Tracking Applications
## 2 Antenna Design Methodology
### Evolution of the Antenna  
There are five steps of antenna evolution, as shown in Figure 3. Initially, a denim substrate of the size of 60 mm \(\times\) 60 mm was chosen to design a square monopole patch antenna with microstrip feed and the partial ground plane (after placing it on cotton fabric of 3 mm thickness), as shown in Figure 3a, to reduce the dielectric loading due to high dielectric constant of biological tissues of human body [33]. In step 0 of antenna evolution, the antenna is resonating at 4.8 GHz, as shown in Figure 4 This change shifted the 4.8 GHz resonance to 1.8 GHz, due to increased current path along the width of the antenna, as shown in Figure 5. In the second step (step 1), four rectangular slots of the same width and different length along the width are etched, to create the stepped profile, as shown in Figure 3b. Up to this point, the antenna is resonating in the single frequency band of 1.8 GHz, but the objective is to design a multiband antenna that could support multiple applications. Therefore, in the third step (step 2, Figure 3c), the rectangular slot is etched along the length at the center of the partial ground plane. Due to this, the current vectors split, and multiple frequency bands are created. Next, two L-shaped hook-like slots are created along the width of the partial ground plane that helped to increase the current path. Now, a second resonance at 3.2 GHz is obtained with wide impedance bandwidth and a third resonance at 5.7 GHz with poor impedance matching at 1.8 GHz and 5.7 GHz. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Symbol** & **Value** & **Symbol** & **Value** & **Symbol** & **Value** & **Symbol** & **Value** \\ \hline \(L\) & 60 & \(L_{7}\) & 18 & \(W_{F}\) & 3.6 & X\({}_{1}\) & 18.5 \\ \(L_{P}\) & 50 & \(L_{8}\) & 13 & \(W_{1}\)–\(W_{6}\) & 6  
Next, in the fourth step (step 3, Figure 3d), an asymmetric meandering line is etched from the top of the patch, and two bent metal strips are also connected to each end of the ground plane. It increased the current path and caused a shift in the middle 3.2 GHz resonance to 2.3 GHz and the higher frequency band 5.8 GHz to 5.7 GHz. However, the middle and the high-frequency bands shifted to the lower side, but the lowest frequency band (1.8 GHz) shifted to a slightly higher side (2.1 GHz). One more resonance at 3.4 GHz is also noticed. In this step, a good impedance matching in all the resonating bands is achieved, but the desired bands needed to be tuned. Consequently, in the final step (step 4, Figure 3e), the asymmetric meandering of the top patch is modified, and the width of each positive and negative peak of meandering line slots is increased. Due to the modified meandering slots, a merger of two close resonances (2.45-2.8 GHz) and (5.1-5.8 GHz) is created at the second (2.45 GHz) and third (5.8 GHz) ISM frequency bands, respectively. Finally, resonances at 1.8 GHz NB-IoT band, RFID ISM 2.45 GHz, and 5.8 GHz bands are achieved  
Figure 4: Simulated \({}^{1}\)S\({}_{11}\)1 of design evolution. Figure 5: Current distribution at (**a**) 1.8 GHz, (**b**) 2.45 GHz, (**c**) 5.8 GHz. with impedance bandwidths of 0.31 GHz (1.68-1.97 GHz), 0.96 GHz (2.05-3.01 GHz), and 1.14 GHz (4.96-6.1 GHz), respectively. Current distributions at 1.8 GHz, 2.45 GHz, and 5.8 GHz on the proposed antenna are shown in Figure 5. From Figure 5a it is clear that the antenna's stepped section and ground plane show the highest current intensity at 1.8 GHz. The antenna's top meandering slot and the ground plane's slot created the ISM 2.45 GHz frequency band, which can be verified by high current intensity, as shown in Figure 5b. However, the rectangular ground slot helped to achieve the ISM 5.8 GHz frequency band, as shown in Figure 5c. The coupling between the human body and the wearable device is crucial to enhance antenna performance and minimize adverse effects on the body. Use of high-impedance surfaces can suppress surface waves, reducing the energy that couples into the body [33].