# A Review on 5G Sub-6 GHz Base Station Antenna Design Challenges
## 4 Future Trends in 5G Base Station Antennas  
The foundation of any BSA antenna is the radiating elements in the arrays. Therefore, it is important to select wideband radiating elements with stable radiation patterns. Table 4 contains some of the recent state-of-the-art radiating elements that show wideband performance. Some of the design concepts used in the design of these elements can be used as the basis to develop more improved radiating elements for current and future 5G antennas. Figure 14: (a) Multiband embedded scheme; (b) multi band side-by-side scheme; (c) multiband -up-and-down coaxial scheme [2]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Reference** & **Antenna Element Type** & \
\begin{tabular}{c} **Frequency** \\ **Band (GHz)** \\ \end{tabular} & **Size \({}^{\star}\)** &
\begin{tabular}{c} **Impedance** \\ **Bandwidth** \\ \end{tabular} & **Isolation (dB)** & **HPBW** & **XPD (dB)** & **Gain (dB)** \\ \hline
[20] & Cross-dipole antenna with U-shaped & 1.68-3.23 & 0.38\(\times\) 0.38.8 & 63\% & \textgreater{}32 & \(65\pm 5\)\({}^{\circ}\) & \textless{}16 & 8.5 \\ \hline
[28] & Octagon shape folded dipoles & 1.69-2.71 & 0.50\(\times\) 0.50\(\lambda\) & 46.4\% & \textgreater{}28 & \(66.5^{\circ}\pm 5.5^{\circ}\) & 25 & 9.8 \\ \hline
[29] & Magneto-electric loop antenna & 1.7-2.7 & 0.43\(\times\) 0.43\(\lambda\) & 45.5\% & NG \({}^{\star}\) & \(66.5^{\circ}\pm 3.5^{\circ}\) & \textgreater{}20 & NG \({}^{\star}\) \\ \hline
[3] & Folded Dipole with coplanar stripline & 1.7-2.25 & 0.52\(\times\) 0.52\(\lambda\) & 27.8\% & \textgreater{}25 & \(66.3^{\circ}\pm 2.9^{\circ}\) & \textgreater{}16 & \textgreater{}8 \\ \hline
[16] & Loop radiator, cross shaped feeding with & 1.7-2.9 & 0.56\(\times\) 0.56\(\lambda\) & 52\% & \textgreater{}26 & \(66.2^{\circ}\pm 3.7^{\circ}\) & NG \({}^{\star}\) & 8.5 \\  & loop parasitic element & & & & & & & \\ \hline
[10] & Octagonal shaped loop radiator with Y- & 1.7-2.7 & 0.39\(\times\) 0.39\(\lambda\) & 45\% & \textgreater{}25 & \(68^{\circ}\pm 2^{\circ}\) & NG \({}^{\star}\) & 8.2 \\  & shaped feeding line & & & & & & & \\ \hline
[39] & Slotted patch with shorting strips & 0.82-0.99 & 0.42\(\times\) 0.42\(\lambda\) & 18.7\% & \textgreater{}30 & \(65^{\circ}\pm 10^{\circ}\) & NG \({}^{\star}\) & 9.9 \\ \hline
[38] & Spline Edged bowtie radiator & 1.42-2.9 & 0.50\(\times\) 0.50\(\lambda\) & 68\% & \textgreater{}20 & \(65^{\circ}\pm 11^{\circ}\) & 20 & 8 \\ \hline
[37] & crossed stepped-width loop dipoles & 1.68-294 & 0.41\(\times\) 0.41\(\lambda\) & 54.5\% & \textgreater{}28.5 & \textless{}66.2^{\circ}\pm 3.7^{\circ}\) & NG \({}^{\star}\) & 8.5 \\ \hline
[52] & Square-loop shape dipole & 1.63-295 & 0.36\(\times\) 0.36\(\lambda\) & 58\% & \textgreater{}31 & \(58.1^{\circ}\pm 12^{\circ}\) & \textless{}27 & 8.8 \\ \hline
[1] & Folded dipole & 0.79-1 & 0.44\(\times\) 0.44\(\lambda\) & 23.5\% & \textgreater{}30 & \(69^{\circ}\) & NG \({}^{\star}\) & 7.7 \\ \hline
[15] & Orthogonal dipoles with fan-shaped slots & 2.27-2.53 & 0.49\(\times\) 0.49\(\lambda\) & 52.6\% & \textgreater{}25.4 & \(60^{\circ}\) & NG \({}^{\star}\) & 7.6 \\ \hline
[17] & Leaf cover antenna with round metal & 1.39-2.8 & 0.42\(\times\) 0.42\(\lambda\) & 67\% & 30 & \(65^{\circ}\pm 5^{\circ}\) & NG \({}^{\star}\) & 9 \\ \hline \hline \end{tabular} \({}^{\star}\)size in terms of wavelength(0) at midband frequency, \({}^{\star}\)Not Given.  
\end{table} 
Table 4: Comparison of a selected set of wideband radiating elements used in BSAs. The massive MIMO is one of the most popular topics among the 5G BSA community. Currently, the massive MIMO used in the 5G network is typically standalone, i.e., contains only one frequency band commonly referred to as mid-band (2.6 GHz-4.2 GHz) with 32 or 64 ports (eight dual-polarized columns with two or four rows). No other bands are integrated into those active antennas. The massive MIMO antennas require the radios to be used for each of the ports.