## 3 Proposed Antenna for On- and Off-Body Conditions
Narrowband antennas are usually propagated and described in the frequency domain, and their radiation characteristic are considered constant over a few percent of the working bandwidth. Since the UWB devices are often known as an impulse-based technology, the antenna's property in time-domain is to be investigated when a continuous wave illuminates the transmitter antenna [3; 20]. On the other hand, a two-dimensional vector with two orthogonal polarization components is assumed in frequency domain. However, the transient response of an antenna varies principally with time, along with the angles of departures and polarization. Figure 9 shows the simulation setup and how a UWB pulse is sent and received between every two UWB antennas [20]. Figure 8: Simulated and measured gain and efficiency for both on-body (breast) and off-body (free space) conditions. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Parameters/\(f\),** & **Eff (\%)** & **Gain (dBi)** & **Eff (\%)** & **Gain (dBi)** & **Eff (\%)** & **Gain (dBi)** & **Eff (\%)** & **Gain (dBi)** \\
**(GHz)** & **Sim. On** & **Sim. On** & **Sim. off** & **Sim. off** & **Meas. on** & **Meas. on** & **Meas. off** & **Meas. off** \\ \hline
3.8 & 81.90 & 3.10 & 83.90 & 3.12 & 82.90 & 3.00 & 82.90 & 3.01 \\
5.8 & 84.90 & 5.65 & 85.90 & 5  
Before starting the image construction of a tumour in the breast several vital factors affecting these processes should be investigated and evaluated. Figure 9 shows the simulation setup of four array elements of the proposed wearable antenna around the breast phantom with diameter of 100 mm. The received signals from the distinct arrays should be investigated first. The received signals and the time delay are used in the signal analysis to reconstruct the image of the tumour. The received signals from the different array elements (A2-A4) in both on- and off-body conditions are presented in Figure 10. Array one (A1) transmits and the other arrays receive the signals. It was noticed that the signals' shape did not change when they faced the breast model, while the signal's amplitude differed, and they shifted. Figure 10: Simulated setup of the antenna array elements in on-body conditions (with (uh) and without (h) tumour). Figure 9: Simulated setup of the antenna array elements in on-body conditions, A1: antenna array 1; A2: antenna array 2; A3: antenna array 3; A4: antenna array 4  
Figure 11 shows the transmission coefficient results of the arrays arranged around the breast model as shown in Figure 4:0 Figure 11 illustrates that a perfect isolation and low mutual coupling is observed: the transmission coefficient level is less than \(-25\) dB for all arrays, in situations both with and without tumours. The fidelity factor is a parameter that plays important role in imaging. It shows the similarity among the received signals from different arrays in different angles. In addition, it shows by how much a signal is distorted when it transmits from the transmitter and is received by the other arrays. Figure 12 shows high fidelity among the received signals from different arrays for on-body conditions (with and without the presence of tumours). After the proposed antenna's characteristics were investigated and evaluated in both on- and off-body conditions (and with and without tumours), the antenna's capability  
Figure 4:1 Simulated setup of the antenna array elements in on-body conditions (with (uh) and without (h) tumour). Figure 4:2 Simulated setup of the antenna array elements in on-body conditions (with tumour (T) and without tumour (N/T)). in image reconstruction of tumours in the breast was assessed under various conditions: with a central tumour (with and without skin) and with two and three tumours. Figure 13 shows the reconstructed image using the robust time reversal algorithm presented in [47]. The spherical tumours were perfectly detected under all four conditions. Only very small ignorable clutters were detected in these images.