## 2 Types of Flexible Wearable Antennas
### Monopole Antennas  
Monopole antennas emit energy in an omnidirectional pattern so that the coverage is achieved horizontally at 360 degrees. They are thus highly appropriate for applications requiring wide and uniform coverage, such as mobile communication, IoT networks, and vehicular systems. Monopole antennas are valued for their simplicity, cost-effectiveness, and ease of deployment; they are often used in scenarios where devices need to communicate with multiple nodes or cover wide areas. In the field of the SAR, monopoles have omnidirectional radiation. The antenna design may change to add slots or wings to deflect radiation from the body or use reflectors and directors to control the radiation. Electromagnetic shielding or low-SAR materials, such as ferrite sheets, can be used to absorb and redirect waves, and substrates with a low dielectric constant can be used to limit tissue energy absorption near the antenna. The SAR can be reduced by changing the antenna power with transmission power or proximity sensor-based adaptive power management. Antennas are placed away from the body or in insensitive areas to reduce the SAR. For fair comparison, Table 4 selects a list of wearable antenna designs, including gain, return loss, dielectric constant, materials, and applications [37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48]. Return loss matches impedance well, with values as low as \(-34\) dB [39]. Gain varies from 1.68 to 4.79 dB. for wearability, which favors textiles and polymers [45], while it uses rigid materials for specific applications. Wavelengths ranging from 42.85 mm at 7 GHz to 122.45 mm at 2.45 GHz [45; 47] help to balance size and performance. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref. No.** & \begin{tabular}{c} **Antenna** \\ **Type** \\ \end{tabular} & **Frequency Range (GHz)** & \
\begin{tabular}{c} **Medical** \\ **Application** \\ \end{tabular} &
\begin{tabular}{c} **Key** \\ **Characteristics** \\ \end{tabular} & **Advantages** \\ \hline
[31] & Patch Antenna & 3–10 (C/X band) &
\begin{tabular}{c} Breast cancer \\ detection \\ \end{tabular} & Compact, low-profile & Low-cost fabrication \\ \hline
[32] & Slot Antenna & 1–6 (S/C band) & \begin{tabular}{c} Brain stroke \\ detection \\ \end{tabular} & \
\begin{tabular}{c} Wideband, linear, \\ or circular slots \\ \end{tabular} &
\begin{tabular}{c} High gain, good \\ directivity \\ \end{tabular} \\ \hline
[33] & \
\begin{tabular}{c} Vivaldi \\ Antenna \\ \end{tabular} & 1–10 (S/C/X band) & Breast tissue imaging &
\begin{tabular}{c} Slot antenna with wide \\ bandwidth \\ \end{tabular} & High sensitivity \\ \hline
[34] & Horn Antenna & 0.3–30 (UHF/L/S band) & \
\begin{tabular}{c} Lung disease \\ diagnosis \\ \end{tabular} & Directional antenna &
\begin{tabular}{c} Deep penetration \\ into tissues \\ \end{tabular} \\ \hline
[35] & Array Antenna & 10–30 (K/Ku band) & \begin{tabular}{c} High-resolution 3D \\ imaging \\ \end{tabular} & \
\begin{tabular}{c} Multiple smaller \\ antennas \\ \end{tabular} &
\begin{tabular}{c} High-resolution \\ imaging \\ \end{tabular} \\ \hline
[36] & \
\begin{tabular}{c} Metamaterial \\ Antenna \\ \end{tabular} & 30–100 & Cancer detection &
\begin{tabular}{c} Advanced control over \\ electromagnetic waves \\ \end{tabular} & Compact and flexible \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Applications of microwave imaging antennas in medical diagnostics.