# A Dual-Polarized and Broadband Multiple-Antenna System for 5G Cellular Communications
## 7 Possible Integration of a High-Frequency Antenna  
Beyond the sub-6 GHz spectrum, integrating high-frequency antennas, such as mmWave phased arrays, is crucial for advancing 5G and paving the way for future 6G networks [60]. As proof of concept, a new mmWave phased array antenna has been developed for integration into shared smartphone PCBs. The configuration and design details are shown in Figure 17, featuring eight end-fire loop-dipole antenna elements that are linearly arranged on a compact board with overall dimension W\({}_{\rm X}\) = 36, L\({}_{\rm X}\). The parameter values in millimeters are as follows: W\({}_{\rm X}\) = 36, L\({}_{\rm X}\) = 5, W\({}_{\rm X1}\) = 0.4, L\({}_{\rm X1}\) = 3.25, W\({}_{\rm X2}\) = 0.15, L\({}_{\rm X2}\) = 1.35, W\({}_{\rm X3}\) = 1.5, and L\({}_{\rm X3}\) = 0.15. Figure 18a shows the S-parameters of the array, demonstrating a broad impedance bandwidth of 27-44 GHz, supporting key mmWave frequencies (such as 28, 36, 38, and 45 GHz) with adequate mutual coupling (\(<\)\(-\)13 dB) between elements. Figure 18b compares the maximum gains of a single antenna element and the phased array over the operating frequency band. The individual element achieves gains of 4-5 dBi, while the phased array significantly outperforms this, with gains exceeding 12 dBi.  
Figure 19 further illustrates the 3D beam-steering functionality of the phased array at 30 GHz, showing robust beam-steering capabilities with end-fire radiation patterns and high gain levels. These results underscore the array's potential for enhanced directional communication and connectivity in mmWave 5G and future 6G applications. Figure 20 illustrates the potential placements of the proposed mmWave phased array within the smartphone PCB configuration. Its compact design allows for seamless integration into small areas of the board, demonstrating versatility and adaptability. Further investigation could be considered in future research to fully unlock the potential of high frequency antennas for 5G and 6G technologies.  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Ref.** & **Antenna Type** & **Bandwidth (GHz)** & **Efficiency (\%)** & **Size (mm\({}^{2}\))** & **Isolation (dB)** & **ECC** & **Diversity** \\ \hline \([22]\) & L-shaped strip monopole & 3.4–3.6 (0.2) & 40–70 & 150 \(\times\) 63 & 10 & \(<\)0.1 & No \\ \([23]\) & Folded dipole & 3.45–3.55 (0.1) & 50–70 & 154 \(\times\) 74 & 15 & \(<\)0.1 & No \\ \([24]\) & Inverted-F antenna & 3.3–3.8 (0.5) & 40–75 & 150 \(\times\) 75 & 13 & \(<\)0.06 & No \\ \([25]\) & Corner-cut patch & 4.4–5 (0.6) & 40–80 & 150 \(\times\) 75 & 10 & \(<\)0.1 & No \\ \([26]\) & Square-loop with slot & 3.4–3.8 (0.4) & 55–70 & 150 \(\times\) 75 & 17 & \(<\)0.03 & Yes \\ \([27]\) & E-shaped slot & 3.4–3.6 (0.2) & 40–75 & 150 \(\times\) 75 & 19 & \(<\)0.1 & No \\ \([28]\) & L-shaped slot & 3.6–4.7 (1.1) & 85–95 & 150 \(\times\) 75 & 10 & \(<\)0.08 & No \\ \([29]\) & SCS Patch-Slot & 3.5–3.7 (0.2) & 50–80 & 150 \(\times\) 75 & 16 & \(<\)0.03 & Yes \\ \([30]\) & Coupled-loop monopole & 3.3–5 (1.7) & 40–70 & 150 \(\times\) 75 & 13 & \(<\)0.1 & No \\ \([31]\) & E-shaped slot with F-probe & 3.5/4.7 (0.2/0.2) & 65–70 & 150 \(\times\) 80 & 18 & \(<\)0.1 & Yes (Limited) \\ \([32]\) & PIFA & 3.8/5.4 (0.1/0.1) & 40–85 & 150 \(\times\) 74 & 13 & \(<\)0.01 & No \\ \([33]\) & Monopole with T-slot & 3.5/5.5(0.4/1) & 30–80 & 150 \(\times\) 75 & 14 & \(<\)0.02 & No \\ \([34]\) & Open-loop monopole & 3.5/4.9 (0.2/0.2) & 60–80 & 150 \(\times\) 75 & 10 & \(<\)0.1 & No \\ \([35]\) & Paired Slot & 3.4–3.6 (0.2) & 40–65 & 150 \(\times\) 75 & 18 & \(<\)0.1 & No \\ \(\mathbf{This}\) & **Trapezoid slot with** & **3.2–6 (2.8)** & **65–80** & **150 \(\times\) 75** & **13** & **\(<\)0.005** & **Yes** \\ \(\mathbf{Work}\) & **L-monopole feeding** & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 17: Schematic of the phased array.