## 3 Proposed Antenna for On- and Off-Body Conditions
Hence, the antenna must be designed and optimized so that the reflection coefficient, radiation pattern, fidelity, and other parameters mentioned above do not change dramatically with placement. Figure 4 shows that the working BW for on-body conditions does not deviate from the off-body conditions dramatically. However, the working BW is reduced slightly when the antenna touches the body. All the resonances are obtained and minimal shifts in resonance occurred. A vital parameter that should be defined when a wearable antenna concerned is the SAR value. Industry and government standards dictate that it be less than 2 W/Kg for both standards, 1 and 10 g. Table 2 shows that the antenna offers acceptable SARs at different frequencies using both standards. In addition to Table 2, Figure 5 depicts the SAR distribution on-body (breast). To measure the SAR on the body, a layer of skin, breast fat, muscle, and bone are used; the antenna is located near the breast (4 mm distant from the breast) to take the measurement. \begin{table}
\begin{tabular}{c c c c c} \hline
**SAR/\(f_{r}\)** & **3.8 GHz (1 g, 10 g)** & **5.8 GHz (1 g, 10 g)** & **7 GHz (1 g, 10 g)** & **28 GHz (1 g, 10 g)** \\ \hline Values (W/Kg) & 0.25, 0.071 & 0.7, 0.171 & 1.29, 0.520 & 2.04, 0.690 \\ \hline \end{tabular}
\end{table} 
Table 2: Specific absorption rate (SAR) values at different frequencies and standards. Figure 4: The reflection coefficient result of the proposed antenna on-body (on breast) and off-body for simulation (sim) and measurement (meas). When an antenna is designed for the purpose of image reconstruction, having a stable radiation pattern is important. Figure 6 shows the radiation pattern of the antenna at the resonant frequencies and lower-end and higher-end of the working BW. In addition, it shows that the radiation pattern does not change at different frequencies by more 20\({}^{\circ}\). The antenna's robustness in harsh environments and under different bending conditions must be investigated to ensure performance is not affected drastically. Besides, this investigation should be done for the conditions when the wearable antenna must be  
Figure 5: Specific absorption rate (SAR) variation on breast at different frequency and standards (1 g, 10 g). Figure 6: (a) Radiation pattern of the antenna at different frequencies on-body (breast phantom) and off-body (solid line: simulated, dashed line: measured) and (b) radiation measurement setup on breast phantom. bended as it is positioned on a breast or embedded in a bra as wearable imaging device. Therefore, the antenna is bent up to 150\({}^{\circ}\), as presented in Figure 7, to determine whether the reflection coefficient result is disturbed (the bending angle starts from 10\({}^{\circ}\) to 150\({}^{\circ}\) to check different angles of bending because an actual breast does not have a homogenous shape and it requires different bending angles to be considered). Figure 7 shows that the reflection coefficient results were not altered extremely by bending conditions up to 140\({}^{\circ}\). Most of the BW was still attained and the other resonances at 3.8 and 5.7 GHz were obtained as well, apart from a few stopbands occurring in the BW. Simulated and measured results of gain and radiation efficiency for both on- and off-body conditions (on-body: on breast) are presented in Figure 8 and Table 3. It shows that the maximum gain and radiation efficiency are 10.1 dBi  
Figure 7: The antenna’s reflection coefficient results in different bending degrees: (**a**) bended prototype and (**b**) reflection coefficient results. addition, radiation efficiency of more than 82% is obtained for the entire working BW. Once the antenna's radiation characteristics have been investigated and evaluated for on- and off-body conditions, the antenna's capability in image reconstruction of tumours should be assessed. _Proposed Antenna's Capability for Image Reconstruction_  
The operation of the proposed wearable UWB antenna will be shown in both time and frequency domains.