# Novel Beam Scan Method of Fabry-Perot Cavity (FPC) Antennas
## 3 Results  
To prove the proposed beam-scan method in an FPC antenna, we fabricated and measured a prototype antenna for a scanned beam at \(\theta=30^{\circ}\)and \(\phi=0^{\circ}\), which is presented in Figure 9. The total volume of the antenna excluding the four acrylic supports measures 380 mm \(\times\) 300 mm \(\times\) 53.04 mm. Here, we could not help but fabricate the \(y\)-axis length shorter than that of the \(x\)-axis due to the limited fabrication facilities. However, it does not matter for proving our idea because the antenna is designed to scan the beam on the \(xz\)-plane (\(\phi=0^{\circ}\)) where the \(x\)-axis length plays a crucial role rather than that of the \(y\)-axis. Figure 8: Reflection and transmission coefficients of (**a**) the PRS and (**b**) the AMC cell. All characteristics are obtained at the design frequency. Figure 9: (**a**) The fabricated FPC antenna that consists of the PRS superstrate and the AMC ground plane with four acrylic supports and (**b**) its measurement environment. Impedance matching results for different scan angles are plotted in Figure 10. To confirm that our idea is still valid for other beam-scan directions but \(\theta_{t}=30^{\circ}\), we have conducted additional simulations for \(\theta_{t}=0^{\circ}\), \(\theta_{t}=15^{\circ}\), and \(\theta_{t}=45^{\circ}\). As shown in Figure 10, the \(-10\) dB bandwidths are well maintained for the most cases. However, we can find that the impedance matching is slightly deteriorated for \(\theta_{t}=45^{\circ}\). This is owing to the large variation of reflection phases of AMC cells compared to the other cases, which needs to be further improved in future works. A little discrepancy between the simulated and the measured results for \(\theta_{t}=30^{\circ}\) is caused by the limited fabrication tolerance, which is significantly influential for our antenna. Three-dimensional radiation patterns of the proposed antenna for each target direction are also shown in Figure 11. As we can see, the FPC antenna can scan the main beam well by properly adjusting the AMC configurations. To show the beam-scan performance more clearly, we plotted the contours of the radiation patterns on both the H- and E-plane for each scanning case in Figure 12. The specific performances of the proposed antenna at the design frequency are summarized in Table 2. As is described, the antenna can scan the main beam in the target direction with well-maintained high gain and a relatively narrow half-power beamwidth (HPBW). Good agreement between expected and experimental results verifies the validity of our design approach. Figure 10: Input reflection coefficients (S11) according to the frequency for each scanned beam case. Figure 11: Simulated 3D radiation patterns for each scanned beam at the designed frequency. All target directions are on the \(xz\)-plane (\(\phi=0^{\circ}\)): (**a**) \(\theta_{t}=0^{\circ}\), (**b**) \(\theta_{t}=15^{\circ}\), (**c**) \(\theta_{t}=30^{\circ}\), and (**d**) \(\theta_{t}=45^{\circ}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Beam Scanning Angle**} & \multirow{2}{*}{**Realized Gain**} & \multicolumn{2}{c}{**Sidelobe Level**} & \multicolumn{2}{c}{**Half-Power Beamwidth**} \\  & & \multicolumn{2}{c}{**[dB]**} & \multicolumn{2}{c}{**[\({}^{\circ}\)]**} \\ \cline{3-6} \cline{5-6}  & & **E-Plane** & **H-Plane** & **E-Plane** & **H-Plane** \\ \hline \(0^{\circ}\) & \(11.8\) & \(-14.1\) & \(-19.2\) & \(45\) & \(36\) \\ \(15^{\circ}\) & \(11.4\) & \(-13.1\) & \(-18.3\) & \(43\) & \(36\) \\ \(30^{\circ}\) & \(13\) & \(-18.1\) & \(-12.8\) & \(34\) & \(34\) \\ \(41^{\circ}\) & \(10.6\) & \(-8\) & \(-7.1\) & \(23\) & \(40\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulated performance parameters of the proposed antenna. Figure 12: Radiation patterns for different target directions \(\theta_{t}=0^{\circ}\), \(15^{\circ}\), \(30^{\circ}\) and \(45^{\circ}\) on the (**a**) H-plane and (**b**) E-plane. All results are obtained at the design frequency.