# Design of a Flat-Panel Metasurface Reflectarray C-Band Antenna
## 3 Reflectarray Antenna Measurement
### Flat-Panel Metasurface Reflectarray Antenna  
The designed flat panel reflectarray antenna was printed on an FR4 PCB board. The air gap between the dual square ring metasurface and the GND plane was maintained by cylindrical PCB spacers made of polyester. The source horn antenna was tied to a wooden pole to keep a distance of 200 mm from the metasurface reflector, as shown in Figure 5 (F/D = 0.35). The far-field response of the fabricated flat panel metasurface reflectarray antenna was measured in an anechoic chamber. The measured far-field co-pol and cross-pole gain patterns are shown in Figure 7. The results show good agreement between the measurement and simulation. The measured peak co-pol gain value was 20-22.2 dBi, the cross-pol gain value was \(-\)3.6\(\sim\)\(-\)0.6 dBi, and the side-lobe level was 16-18 dB. There was less than 1 dB of difference between the simulated and measured co-pol peak gain values. The measured radiation directions of the reflected waves were 12-14\({}^{\circ}\), which were very close to the designed radiation direction of 14-16\({}^{\circ}\). The small discrepancy of 1-3\({}^{\circ}\) in the reflection angle can be considered as fabrication error such as misalignment of the mounted source horn antenna. The measured 1-dB and 3-dB beamwidth values are 5\({}^{\circ}\) and 10\({}^{\circ}\), respectively. Figure 7 shows 1-dB and 3-dB bandwidth of the proposed reflectarray antenna. The 1-dB and 3-dB bandwidth are 500 MHz (5.6-6.1 GHz, 8.5 %) and 860 MHz (5.4-6.26 GHz, 14.8%), respectively. The aperture efficiency (\(\varepsilon_{A}\)) can be calculated from the measurement data because \(\varepsilon_{A}=A_{e}/A_{p}=\lambda_{0}{}^{2}G/\left(4\pi A_{p}\right)\) where \(Ae\) is effective area of antenna, \(Ap\) is physical area of antenna, \(\lambda_{0}\) is a wavelength and \(G\) is antenna gain [14]. The measured aperture efficiency of the proposed antenna is 21.1%. The performance comparison table is shown in Tables 2 and 3. Those reported reflectarray antennas at the C-band have multi band or tunable capability, but they also have relatively high loss due to active components, such as varactors or PIN diodes. The proposed reflectantenna features high gain and a low-profile.  
Figure 6: Designed circular horn antenna: (**a**) \(S\)-parameter and (**b**) antenna gain.  
Figure 7: Measured gain patterns of the designed reflectarray antenna: (**a**) 5.6 GHz, (**b**) 5.7 GHz, (**c**) 5.8 GHz, (**d**) 5.9 GHz and (**e**) 6.0 GHz.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Co-pol Gain (dBi)**} & \multicolumn{2}{c}{**Cross-pol Gain (dBi)**} & \multicolumn{2}{c}{**Radiation Angle (\(\theta\), \({}^{\circ}\))**} \\ \cline{2-7}  & **Sim.** & **Mea.** & **Sim.** & **Mea.** & **Sim.** & **Mea.** \\ \hline
5.6 GHz & 21.3 & 20.0 & \(-\)6.0 & \(-\)2.7 & 16 & 14 \\ \hline
5.7 GHz & 21.9 & 21.3 & \(-\)7.0 & \(-\)3.5 & 16 & 13 \\ \hline
5.8 GHz & 22.2 & 22.0 & \(-\)14.0 & \(-\)1.9 & 14 & 13 \\ \hline
5.9 GHz & 22.0 & 22.4 & \(-\)14.0 & \(-\)0.6 & 14 & 13 \\ \hline
6.0 GHz & 21.8 & 22.2 & \(-\)17.0 & \(-\)3.6 & 14 & 12 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulation and Measurement Data.