# An Ultra-Wideband Vivaldi Antenna System for Long-Distance Electromagnetic Detection
## 2 Antenna Configuration Design and Performance
### Ultra-Wideband Narrow Beam Antenna
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline W & 55 & d5 & 8 \\ L & 82 & l1 & 5 \\ a & 4 & l2 & 8 \\ b & 8 & l3 & 23 \\ R & 4 & R1 & 6 \\ d1 & 9 & w & 1 \\ d2 & 7.5 & C1 & 20.6 \\ d3 & 1.5 & C2 & 16 \\ d4 & 2.5 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Final optimization results of the parameters of Vivaldi narrow-beam antenna (mm). Meanwhile, the minimum beam width is 59.4\({}^{\circ}\). What's more, Figure 5b show the gain of the proposed antenna, which is greater than 4.54 dBi and the directivity consistency is good. According to the characteristics, the proposed antenna can be an excellent candidate for the array element of the receiving antenna in an ultra-wideband Vivaldi antenna system. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref. No.**} & \multirow{2}{*}{\
\begin{tabular}{c} **Dimension** \\ **(mm2)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Operating** \\ **Frequency** \\ \end{tabular} } & \multicolumn{6}{c}{**HPBW**} \\ \cline{3-10}  & & & **2 GHz** & **3 GHz** & **4 GHz** & **5 GHz** & **6 GHz** & **7 GHz** & **8 GHz** \\ \hline
[24] & 120 \(\times\) 90 & 2–5 GHz & 130 & - & 75 & 65 & - & - & - \\
[19] & 200 \(\times\) 80 & 3–14 GHz & - & 85\({}^{\circ}\) & - & - & - & 50\({}^{\circ}\) & - \\
[25] & 297 \(\times\) 190 & 0.6–3.2 GHz & 51.4\({}^{\circ}\) & 55\({}^{\circ}\) & - & - & - & - & - \\
[26] & 258 \(\times\) 150 & 0.5–6 GHz & 48.7\({}^{\circ}\) & 45.1\({}^{\circ}\) & 54.3\({}^{\circ}\) & 71.1\({}^{\circ}\) & 58.6\({}^{\circ}\) & - & - \\
[27] & 274 \(\times\) 282 & 0.4–9.8 GHz & - & 74\({}^{\circ}\) & - & - & - & - & 74\({}^{\circ}\) \\
[28] & 100 \(\times\) 90 & 3–6 GHz & - & 55\({}^{\circ}\) & - & 55\({}^{\circ}\) & - & - \\ proposed & 82 \(\times\) 55 & 2.5–8.5 GHz & 65.9\({}^{\circ}\) & 65.2\({}^{\circ}\) & 59.4\({}^{\circ}\) & 55.4\({}^{\circ}\) & 44\({}^{\circ}\) & 46.7\({}^{\circ}\) & 66.2\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison between proposed antenna and literature. Figure 5: (a) Return loss of the simulated narrow beam Vivaldi antenna. (b) The gain of the simulated narrow beam Vivaldi antenna. Figure 6: E-plane pattern of narrow beam Vivaldi antenna with structure at **(a)** 2 GHz; **(b)** 3 GHz; and **(c)** 4 GHz; **(d)** 5 GHz; **(e)** 6 GHz **(f)** 7 GHz; **(g)** 8 GHz. To strengthen the directional radiation capability of the antenna and meet the requirement that the beam width has to be less than \(10^{\circ}\), the Vivaldi antennae with improved beam width were arranged into an 8-element array. To reduce the feed ports, a power divider was used to feed the antenna array. The antenna array model is shown in Figure 7 and the array antenna parameters are shown in Table 5.  
The single element is 82 mm long and 55 mm wide. The power divider is a microstrip T-branch power divider which is enlarged in the Figure 7. The length below the T-shaped knot is 16 mm, which is about \(\lambda/4\), and the width is 3.2 mm. The width on both sides is 1 mm, and the width of the antenna unit feeder is also 1 mm. The distance between the last-level power divider line and the leftmost side of the antenna array is 239 mm, and the other levels of power divider are distributed in a symmetrical structure. The length of each level of power division microstrip line is 16 mm and the width is 1 mm. Three positioning points were marked, and a hole with an inner diameter of 6 mm was drilled so that the antenna array can be assembled on the turntable support. The final model of the designed narrow-beam eight-element antenna array was simulated and measured, and the simulated and measured E-plane radiation patterns of the antenna at different frequencies were obtained as shown in Figure 8. As shown in Figure 9a, the original Vivaldi antenna works in the frequency range from 2.5 to 4 GHz. The return