# A Versatile Shared-Aperture Antenna for Vehicle Communications
## 4 Discussion
the characteristic of direction selection in the horizontal direction, and its maximum gain is 5.3 dBi. Additionally, the beam switching time of a reconfigurable antenna is also an important indicator affecting communication quality. Based on the performance of PIN diodes, the beam switching time is approximately 1.25 \(\upmu\)s, which is sufficient to enable tracking communication between vehicles. To highlight the advantages of this antenna, a comparison with existing vehicle-mounted antennas is shown in Table 4. Through comparison, it can be found that this design has a high port density. In addition, compared with previous designs [3; 19; 22; 30], this design has the ability to scan, and compared with the direct array scanning of [31], this design achieves lower scanning costs and does not require multi-channel control of the antenna phase. At the same time, the worst isolation of this design is 25 dB, which is better than that of past studies [3; 19; 31]. In addition, the radiation efficiencies of this design are relatively high, all above 80%. Our future work will focus on the design of radome protection and back-end RF circuits. For the application scenario, requiring automotive on-board installation, we should also fully consider the waterproof performance, protective performance, impact \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Work**} & **Freq.** & **Band-Width** & **Number** & **Sannable** & **Port Density** & **Isolation** & **Gain** & **Radiation** \\  & **(GHz)** & **Width** & **of Functions** & **Scannable** & **(\(\mathbf{\lambda_{2}^{3}}\))** & **Isolation** & **(\(\mathbf{\mathbf{\mathrm{G}}}\)Bi)** & **Efficiency** \\ \hline
[3] & 1.8/2.4/ & 10\%; 11.4\% & & & & & 20 dB; 40 dB; & 4.2; 4.1 & 66\%; 62\% \\  & 3.5/5.8 & 7.5\%; 7.6\% & 3 & No & 4 & 18 dB; 20 dB & 3.7; 2.9 & 71\%; 61\% \\ \hline
[19] & 5.9/28 & 41.6\% 6.7\% & 2 & No & 7.15 & 20 dB; 35 dB & 5.5; 8.5 & 83\%; 96.9\% \\ \hline
[22] & 5.9/28 & 1.6\% 2.5\% & 2 & No & 1.73 & 55 dB; 38 dB & 10; 11.9 & 86\%; 96\% \\ \hline
[30] & 5.9/28 & 3.7\%/10.9\% & 2 & No & 0.67 & 45 dB; 50 dB & 10.8; 13.7 & 88.7\%; 92.3\% \\ \hline
[31] & 5.9/26 & 15.44\%/11.4\% & 2 & Yes & 2 & 17 dB; N.A. & 4; 12.5 & 61\%; N.A. \\ \hline This Work & 1.575/3 & 6.3\%/53.3\%/ & 3 & Yes & 9 & 25 dB; 30 dB; & 7; 8.3; 5.3 & 81\%; 90\%; 85\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison with the state-of-the-art proposed shared-aperture antenna. Figure 20: **(a)** The schematic diagram of antenna installation on a car. **(b)** Horizontal radiation pattern of pattern reconfigurable antenna. **(c)** Vertical radiation pattern of pattern reconfigurable antenna. resistance performance, and wind resistance performance of the antenna. Therefore, in response to the requirements of the above scenarios, we will conduct more in-depth research on low wind resistance and low loss antenna covers. We will also design more frequency and higher port density shared-aperture antennas, optimize their performance, and pay more attention to the switching time of reconfigurable antennas, using better PIN diodes to achieve rapid switching of directional patterns. In addition, a complete three-band RF channel will be designed to demonstrate the performance of the design in conjunction with actual communication demonstrations in cars.