## 2 Antenna Design
### Radiation Modes  
The antenna gives two types of radiations in the lower and upper bands. The lower band is used for on-body communication, whereas the upper band is used for off-body communication. In the lower band, it acts as a monopole antenna with vertical omnidirectional radiation, which has less radiation toward the body. The lower band reduces the shadow fading issue because of its strong diffraction and longer wavelength. However, in the upper band, a higher mode of the meander line is combined with the first mode of the monopole strip to obtain a wide bandwidth and omnidirectional radiation pattern. When the antenna is mounted on-body, the radiation pattern becomes wider with a wide bandwidth due to the lossy tissues. Thus, the power is radiated nearly in all directions and provides an omnidirectional radiation pattern in both bands. Figure 3a shows the \begin{table}
\begin{tabular}{c c} \hline \hline
**Symbols** & **Dimensions (mm)** \\ \hline a & 50.00 \\ \hline b & 37.20 \\ \hline c & 40.20 \\ \hline d & 8.49 \\ \hline e & 0.73 \\ \hline f & 2.38 \\ \hline g & 1.00 \\ \hline h & 14.13 \\ \hline i & 37.20 \\ \hline j & 22.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The dimensions of the proposed meander line monopole antenna. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Characteristics** & **Dual-Band Monopole** & **Meander-Line Antenna (Lower/Upper Band)** \\ \hline
**Antenna Parameters** & **Free-Space** & **On-Chest** & **On-Arm** \\ \hline Simulated S\({}_{11}\) (dB) at the Center Frequency & \(-21.02/-17.00\) & \(-17.73/-17.00\) & \(-25.20/-25.00\) \\ \hline Measured S\({}_{11}\) (dB) at the Center Frequency & \(-21.00/-19.00\) & \(-23.00/-19.00\) & \(-25.00/-20.00\) \\ \hline Simulated and Measured Center & 2.2 and 5.6/3.0 and & & 2.3 and 5.7/3.0 and 6.0 \\ Frequency (GHz) & 5.6-6.0 & & \\ \hline Simulated Bandwidth (MHz) & 1282.4 and 450.5 & 688.9 and 500.9 & 1261.7 and 524.2 \\ \hline Measured Bandwidth (MHz) & 1255.0 and 430.2 & 671.9 and 475.2 & 1243.1 and 501.1 \\ \hline Simulated Gain (dBi) & 3.03/4.85 & 3.80/4.67 & 3.00/4.55 \\ \hline Measured Gain (dBi) & 2.76/3.67 & 3.45/4.25 & 2.76/4.15 \\ \hline Simulated Radiation Efficiency (\%) & Lower (85.34/83.32) & (54.37/53.40) & (60.0/59.51) \\ Upper (63.82/50.57) & (54.27/51.39) & (63.73/62.05) \\ \hline Voltage Standing Wave Ratio (VSWR) & 1.22/1.29 & 1.61/1.21 & 1.06/1.19 \\ \hline Radiation Pattern (O/O) & Omnidirectional & Omnidirectional & Omnidirectional \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of the antenna’s performance measures. current path at the lower band, which follows the path of A-B-C-D (\(l_{1}\)). It demonstrates that the antenna's length at the resonant frequency is half a wavelength. Figure 3b shows the quarter-wavelength resonance mode, where the current follows around the path of A-B-C-E (\(l_{2}\)). It can be observed that there is a small current on the ground plane. Thus, the resonant frequencies depend on the ground plane and the long (\(l_{1}\)) and short (\(l_{2}\)) parts of the meander line monopole antenna. The simulated reflection coefficients (S\({}_{11}\)) of various antennas and their effects of length on the overall reflection coefficient are shown in Figure 4. The length of the top monopole-shaped meander line strip and a truncated ground plane has a great impact on the resonant frequency and impedance bandwidth (BW). Increasing or decreasing the length of the monopole strip (\(l_{1}\)) results in a lower resonant frequency. The length of (\(l_{1}\)) and a ground plane has a great impact on the operating frequency and impedance BW in the lower band, varying the length from 40.20 mm to 36.49 mm shifted the resonant frequency from approximately 2.8 GHz to 3.4 GHz, while there was a minor effect on the upper impedance bandwidth (BW), which shifted from 5.90 to 6.295 GHz. The length of the meander line strip (\(l_{2}\)) also affects the resonant frequency and impedance bandwidth (BW) in the upper band.