# Digitized Reconfigurable Metal Reflectarray Surfaces for Millimeter-Wave Beam-Engineering
## 4 Experimental Results and Discussion  
Figure 7 is a picture of the reflectarray antenna measurement configuration in a near-field scanning probe chamber, and the inset shows the three-dimensional modeling of the designed antenna and a feeder. In order to measure the beam steering angle of the beam-steered antenna, a curved feeding part is manufactured. The experimental results of the fabricated antennas are compensated for the loss in the straight and curved waveguide.  
Figure 8 shows experimental and simulated far-field radiation patterns of bore-sight and \(-\)20\({}^{\circ}\)-beam reflectarray antennas for H-plane for a two-bit quantized phase. For the comparison, the experimental (solid) and simulated results (dashed) are shown in the same figure. The experiment was conducted in a near-field measurement system. The used feeder is a W-band rectangular pyramidal horn with 14.7 dB which has the minimum  
Figure 6: Simulated far-field patterns in H-plane of digitized reflectarray antennas when the re-radiation field is directed at \(\theta\) = 20\({}^{\circ}\).  
Figure 7: A picture of the reflectarray antenna measurement configuration and the three-dimensional modeling of the designed antenna and a feeder.  
reflection at antenna frequency. The constructed antenna was manufactured using a typical machining process with a vertical resolution of 30 \(\upmu\)m. The maximum gain are 31.91 and 31.73 dB and a half-power beam width are 2.61\({}^{\circ}\) and 3.15\({}^{\circ}\) for bore-sight and \(-20^{\circ}\)-aimed antennas in H-plane, respectively.  
The experimental results are similar to the simulated results. Between two results, the side lobe and measured gain have some differences due to the interference from the feeder support bar and the scattering fields at the edge of the conductor cells. In the case of a \(-20^{\circ}\)-aimed antenna, the radiated filed is very similar to that of a bore-sight antenna. By these results, we can anticipate that wide angle tunning of a digitized metal reflectarray antenna is possible. The far-field radiation characteristics of measured and simulated results of reconfigurable metal reflectarray in H-plane are summarized in Table 1. The measured gain is lower than a simulated one under 0.7 dB due to the blockage by feeder flanges and struts.  
The measured \(-20^{\circ}\)-aimed antenna gain and return loss for the frequency range of 80\(\sim\)110 GHz with the simulation results is shown in Figure 9. The measured gain below 95 GHz shows a good agreement with the simulated one, but the difference is increased at the higher frequency range due to the phase error of a blockage and a diffraction caused by the waveguide flange and the supporting strut. Nevertheless, the 1-dB gain bandwidths of a designed metal reflectarray antenna from experimental and simulated results are about 6.2 % (92.3\(\sim\)98.2 GHz) and 5.3 % (92.7\(\sim\)97.7 GHz), respectively and return loss was less than about -10 dB in 80\(\sim\)110 GHz.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Angle (deg)**} & \multicolumn{1}{c}{**Gain (dB)**} & \multicolumn{1}{c}{**HPBW (deg)**} & \multicolumn{1}{c}{**Side Lobe Level (dB)**} \\ \hline \multirow{2}{*}{0\({}^{\circ}\)} & Sim. & 32.39 & 2.42 & \(-18.47\) \\  & Exp. & 31.91 & 2.61 & \(-11.15\) \\ \multirow{2}{*}{\(-20^{\circ}\)} & Sim. & 32.44 & 2.45 & \(-20.46\) \\  & Exp. & 31.73 & 3.15 & \(-11.91\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Measured and simulated radiation performances of two-bit digitized reconfigurable metal reflectarray antennas in the H-plane.  
Figure 8: Experimental (solid) and simulated (dashed) far-field radiation patterns of proposed two-bit digitized reconfigurable reflectarray antennas when two different observation angles are applied. (**a**) \(\theta=-20^{\circ}\); (**b**) \(\theta=0^{\circ}\).