# Simple Compact UWB Vivaldi Antenna Arrays for Breast Cancer Detection
## 3 Results and Discussion  
Both arrays provide good measured and simulated results, as summarized in Table 5 and illustrated in Figure 13. Arrays 1 and 2 provide good, measured input impedance matching of \(<\)\(-\)10.28 dB (Sim. \(<\)\(-\)10.11 dB) and \(<\)\(-\)10.2 dB (Sim. \(<\)\(-\)10.29 dB) through 3.24-13 GHz (Sim. 3.22-12.85 GHz), respectively, as shown in Figure 13a, which implies the effectiveness of integrating the UWB VTSA [1] and VNSA [28] and UWB 2:1 and 3:1 unequal split NTL WPDs [27] for compactness and gain enhancement. As can be observed from Figure 13a and Table 5, with the 52% size reduction and 6.76% (Sim. 17.96%) BW improvement provided by Array 2, only 5.46% (Sim. 6.26%) of the MG is reduced. This implies the effectiveness of the VNSPA theory [28] for compactness and performance enhancement. Due to the difference in the signal path through the VTSA and VNSA in Array 1 and 2, respectively, there is a slight phase difference, as shown in Figure 13b. Fabrication tolerance, human and lab error, improper soldering of SMA connectors, and the difference between the simulation and actual measurement environment are the causes of the discrepancy between the results from the simulation and the findings from the measurements. It can be noticed from Table 5 and Figure 13c that the MG of the proposed Array 1 and 2 is enhanced by 23.39% (Sim. 25.84%) and 15.11% (Sim. 15.38%) as compared to the VTSA and VNSA single elements, respectively. Also, it can be noticed that the gain for Array 1 and Array 2 after reaching their peak values at around 8.8 GHz (Array 1: 8.61 dBi and Array 2: 8.1 dBi) reduces to 7.9 dBi and 7.8 dBi, respectively, at 9-10 GHz. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameters** & **Calculated** & **Optimized (VNSA [28])** & **Optimized (Array 2)** \\ \hline r & - & 0.17 & \\ \hline \(Wmax\) (mm) & 24.45 & 21.03 & \\ \hline \(L_{T}\) (mm) & 27 & \(L_{N}\) (mm) = 16.75 & \\ \hline \(L_{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text{ \text{ \text{ \text{ \text{  }}}}}}}}}}}}}}}\) (mm) & 6.57 & 5.76 & 5.74 \\ \hline \(W_{min}\) (mm) & - & 0.286 & \\ \hline _radsl_ (mm) & 3.285 & 1.505 & 1.32 \\ \hline _dis_ (mm) & - & 23.8 & 21.8 \\ \hline _sp_ & 52.36 & - & 50 \\ \hline _Wa_ (mm) & 1.819 & 1.25 & 1.34 \\ \hline \(W_{p1}\) (mm) & 1.819 & - & 2.07 \\ \hline \(W_{p2}=W_{p3}\) (mm) & 1.819 & - & 1.7 \\ \hline _Lar_ (mm) & - & - & 44.755 \\ \hline _War_ (mm) & - & - & 81.08 \\ \hline \end{tabular}
\end{table} 
Table 4: Calculated and optimized parameters of Array 2 with its single element (VNSA). Figure 12: Photograph of the fabricated arrays: (**a**) front view and (**b**) back view. These fluctuations mainly result from high-order modes at high frequency. Also, Figure 13d and Table 5 indicate that Arrays 1 and 2 achieve good efficiencies between 68.92% and 81.39% (Sim. 70.98% and 93.52%) and 73.17% and 92.11% (74.75% and 94.77%), respectively, at UWB. The good impedance matching of the proposed arrays can be expressed also in terms of the simulated input impedance, as shown in Figure 13d, where its real and imaginary parts oscillate around 50 \(\Omega\) and 0 \(\Omega\), respectively. A nearly flat group delay within the UWB frequency band is an important feature for UWB applications, to guarantee satisfaction of signal transmission. The measurement setup to obtain the face-to-face (F 2 F) group delay between two samples of Array 1 and Array 2 with R = 400 mm and 800 mm, respectively, are shown in Figure 14a. Figure 14b depicts that the approximate measured flat measured group delay provided by Arrays 1 and 2 are around 3.5 ns (Sim = 2.5 ns) and 2.3 ns (Sim = 1.7 ns). The measured group delay is greater than the simulated one due to the fabrication and measurement tolerance in which the signal will face more losses during its propagation. Figure 13: Simulated and measured (**a**) S\({}_{11}\), (**b**) phase, (**c**) gain, and (**d**) simulated input impedance of the proposed arrays.