# Dual-Circularly Polarized 60 GHz Beam-Steerable Antenna Array with 8 \(\times\) 8 Butler Matrix
## 3 Performance of the Proposed Antenna Array System
### Experimental Results  
To account for the effect of using an actual connector on the antenna performances, a simulation including the connector was carried out using the Ansys HFSS [22] and CST Microwave Studio [23]. The connector model was based on the datasheet from Southwest for a 1.85 mm end-launch connector. Figure 14 shows the modified antenna array system with the connector model for when port 2 and port 4 of the proposed antenna are excited. The transition part was added to properly mount the connector to the antenna array system. Figure 15 shows the comparison between the antenna array systems with and without the connector model on the reflection coefficient and the radiation pattern in the \(xz\)-plane. The simulated \(-\)10 dB reflection coefficient bandwidths of the modified antenna array system with the connector model for port 2 and port 4 are 8.67 GHz (55.15 GHz-63.82 GHz) and 7.07 GHz (56.71 GHz-63.78 GHz), respectively. The radiation patterns of the modified antenna array system with the connector models agree well with those of the original antenna array system without the connector models. Figure 16 shows the fabricated prototypes of the antenna with connector for port 2 and port 4. Figure 17 shows a photograph of the fabricated antenna and measurement setup. The fabricated antenna with a V-band connector is connected to a waveguide-to-coax adapter and a waveguide feed. The simulated and measured reflection coefficients of the antenna are shown in Figure 18a,c. The measured \(-\)10 dB S\({}_{11}\) bandwidths of the antenna for port 2 model and port 4 model are 9.61 GHz (52.41 GHz-62.02 GHz) and 6.63 GHz (54.60 GHz-61.23 GHz), respectively. The simulated and measured normalized far-field radiation patterns at 60 GHz are shown in Figure 18b,d. For the port 2 model, the main beam points to the \(-\)35\({}^{\circ}\) with a gain of 8.94 dBi. The direction of the main beam switches to \(-\)9\({}^{\circ}\) with a gain of 10.18 dBi for the port 4 model. There is some discrepancy between the measured and simulated results, which is related to the fabrication tolerances realized in the alignment process and the effect of the glue for stacking the two substrates. Further, the output amplitude imbalance of the Butler matrix degrades the antenna gain. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Input Port** &
\begin{tabular}{c} **Beam-Steering Angle \(\mathbf{\Theta}\)** \\ **(xz-plane, \(\mathbf{\phi}=\) 0\({}^{\circ}\))** \\ \end{tabular} & **Polarization** \\ \hline Port 1 & \(+\)11\({}^{\circ}\) & RHCP \\ Port 2 & \(-\)38\({}^{\circ}\) & RHCP \\ Port 3 & \(+\)40\({}^{\circ}\) & RHCP \\ Port 4 & \(-\)11\({}^{\circ}\) & RHCP \\ Port 5 & \(+\)11\({}^{\circ}\) & LHCP \\ Port 6 & \(-\)39\({}^{\circ}\) & LHCP \\ Port 7 & \(+\)39\({}^{\circ}\) & LHCP \\ Port 8 & \(-\)11\({}^{\circ}\) & LHCP \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Phases associated with the selected port of the \(8\times 8\) Butler matrix. Figure 14: Modified connector model of the proposed antenna: (**a**) port 2 model and (**b**) port 4 model. Figure 16: Fabricated prototypes of the antenna: (**a**) port 2 model and (**b**) port 4 model. Figure 15: Comparison of the simulated results between the original model and modified model: (**a**) reflection coefficient for port 2 model, (**b**) radiation pattern for port 2 model, (**c**) reflection coefficient for port 4 model, and (**d**) radiation pattern for port 4 model. Figure 19 shows the measured axial ratio of the antenna for the port 2 model and port 4 model. Due to the losses induced by the connector and microstrip line-to-stripline transition part, the measured and simulated axial ratios differ slightly from the results of the original antenna array system without  
Figure 17: Fabricated antenna and measurement setup.