# Dual-Circularly Polarized 60 GHz Beam-Steerable Antenna Array with 8 \(\times\) 8 Butler Matrix
## 4 Conclusions  
In this paper, a beam-steerable dual-circularly polarized 60 GHz patch antenna array is proposed. A \(1\times 4\) dual-fed stacked patch antenna array is integrated with an \(8\times 8\) Butler matrix. By utilizing the \(8\times 8\) Butler matrix, the proposed antenna array generates dual-circular polarization with a beam-steering capability. Depending on the excitation status of each input port of the \(8\times 8\) Butler matrix, the main beam of the antenna array can be steered in four directions and the polarization property (RHCP or LHCP) is determined. The reflection coefficient, beam-steering performance, and axial ratio of the antenna were analyzed at 60 GHz. The measured results for the fabricated antenna agreed well with the simulated ones. Thus, the proposed antenna array system could be a good candidate for millimeter-wave 5G applications that require wide beam coverage and polarization diversity.  
Figure 19: Measured axial ratio of the antenna for port 2 model and port 4 model.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & [3] & [4] & [19] & **This Work** \\ \hline \multirow{2}{*}{Configuration} & \(2\times 4\) Patch & \(1\times 4\) Patch & \(1\times 6\) ME Dipole & \(1\times 4\) Patch \\  & (\(8\times 8\) BM) & (\(4\times 4\) BM) & (\(5\times 6\) BM) & (\(8\times 8\) BM) \\ \hline \multirow{2}{*}{Center Frequency [GHz]} & \multirow{2}{*}{60} & \multirow{2}{*}{60} & \multirow{2}{*}{28} & \multirow{2}{*}{60} \\  & & & & \\ \hline \multirow{2}{*}{10 dB Return Loss Bandwidth [GHz]} & \multirow{2}{*}{7} & \multirow{2}{*}{5.3} & \multirow{2}{*}{1} & \multirow{2}{*}{9.6} \\  & & & & \\ \hline \multirow{2}{*}{Dimensions [mm \(\times\) mm \(\times\) mm \(\times\) mm]} & \(27\times 40\times 0.254\) & \(9.75\times 13.1\times 0.127\) & \(65\times 95\times 2.032\) & \(25.7\times 32\times 0.254\) \\  & (\(5.4\lambda_{0}\times 8\)0.3 \(\times\) & (\(2\lambda_{0}\times 2.6\lambda_{0}\times\) & (\(6\lambda_{0}\times 8.8\lambda_{0}\times\) & (\(5.1\lambda_{0}\times 6.5\lambda_{0}\times\) \\  & \(0.05\lambda_{0}\)) & \(0.03\lambda_{0}\)) & \(0.19\lambda_{0}\)) & \(0.05\lambda_{0}\)) \\ \hline Peak Gain [dBi] sim./meas. & 12.1/12.3 & N/A/8.9 & 13.7/11.7 & 10.67/10.18 \\ \hline BM Insertion Loss [dB] & 11 & 7.5 & 8.5 & 10.5 \\ \hline \multirow{2}{*}{BM Phase Error [deg]} & N/A & \(\pm 10\) & \(\pm 10\) & \(\pm 29\) \\  & 8 & 4 & 5 & 4 \\ \multirow{2}{*}{Number of Scanning Beams} & \multirow{2}{*}{(2-D scanning)} & \multirow{2}{*}{(\(\pm 14^{\circ}\)/\(\pm 40^{\circ}\))} & \multirow{2}{*}{(\(0^{\circ}\)/\(\pm 20^{\circ}\)/\(\pm 40^{\circ}\))} & \multirow{2}{*}{(\(\pm 11^{\circ}\)/\(\pm 40^{\circ}\))} \\ \hline Polarization Diversity & No & No & No & Yes \\ \hline Polarization Type & Linear & Linear & Circular & Dual-Circular \\ \hline \end{tabular} BM: Butler matrix.  
\end{table}
Table 3: Comparison of various antenna array systems integrated with a Butler matrix.  
**Author Contributions:** The presented work was carried out in collaboration between all the authors. [PERSON] wrote the paper. [PERSON] participated in the conception. [PERSON] supervised the research. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government(MSIT) (2018-0-00732, Fundamental research for solving the bottleneck technology of millimeter wave 5G cellular array antenna).  
**Conflicts of Interest:** The authors declare no conflict of interest.