# Beam Scanning Capabilities of a 3D-Printed Perforated Dielectric Transmitarray
## 4 Prototype Manufacturing and Experimental Characterization
The ratio between the main scanning beam direction and the feed offset angle can be defined as the Beam Deviation Factor (BDF), i.e., \(\text{BDF}=\theta_{b}/\theta_{f}\). For a very large scanning angle range, this parameter has to be optimized to obtain the desired performances. In the case of the designed TA, the values of the BDF are reported in the 7 th row of Table 1: since it is equal to 0.9, it means that the achieved range of variation for \(\theta_{b}\) is of 54\({}^{\circ}\). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \(\theta_{f}\) & \(0^{\circ}\) & \(\pm 10^{\circ}\) & \(\pm 20^{\circ}\) & \(\pm 30^{\circ}\) \\ \hline
**Gain** & 29.97 dBi & 29.30 dBi & 27.96 dBi & 27.07 dBi \\
**Ap. Eff. (30 GHz)** & 35.1\% & 30.1\% & 22.2\% & 18.1\% \\
**HPBW\({}_{E}\) (30 GHz)** & 3.8\({}^{\circ}\) & 3.9\({}^{\circ}\) & 4.1\({}^{\circ}\) & 4.3\({}^{\circ}\) \\
**HPBW\({}_{H}\) (30 GHz)** & 3.9\({}^{\circ}\) & 3.9\({}^{\circ}\) & 4.1\({}^{\circ}\) & 4.8\({}^{\circ}\) \\
**SLL\({}_{E}\) (30 GHz)** & \(-\)22.6 dB & \(-\)20.4 dB & \(-\)16.0 dB & \(-\)11.1 dB \\
**SLL\({}_{H}\) (30 GHz)** & \(-\)22.6 dB & \(-\)22.4 dB & \(-\)20.1 dB & \(-\)15.5 dB \\
**BDF** & 1 & 0.9 & 0.9 & 0.9 \\
**X-pol (30 GHz)** & \(-\)40.4 dB & \(-\)39.6 dB & \(-\)38.5 dB & \(-\)36.3 dB \\
**1-dB BW** & 23.5\% & 24.5\% & 23.3\% & 24\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Transmitarray performances for different scanning angles. Figure 8: Simulated and measured co-polar radiation pattern in the E-plane at 30 GHz for different scanning angles. Figure 9 shows the measured radiation patterns in H-plane, with a blow-up of the region close to the maximum in the inset. Apart from the reduction of the maximum gain, the radiation patterns are almost unchanged for \(-20^{\circ}\leq\theta_{f}\leq 20^{\circ}\), and also for \(\theta_{f}=\pm 30^{\circ}\) the most significant effect is just a contained increase of the side lobes. In both Figures 8 and 9, only the co-polar component of the radiated field is shown, to not make the plot incomprehensible, but the values of the cross-pol measured at 30 GHz for each considered pointing angle are reported in Table 1: in all cases, it stays very low, reaching a maximum value of about \(-36\) dB. In Figure 10, the frequency variation of the gain for the different scanning angles is plotted, while the values of the 1-dB bandwidth are reported in the last row of Table 1. For the different values of \(\theta_{f}\), the 1-dB bandwidth remains larger than 23% and this represents an advantageous feature with respect to other transmitarray configurations implemented with metallic-dielectric elements, which have in most cases a narrow band and it decreases furthermore when the direction of maximum radiation changes. In Figure 11, the behavior of the measured and simulated gain at the design frequency as a function of the scanning angle is finally shown: the flatness of the curves is a further proof of the excellent scanning capabilities of the designed antenna; moreover, it is worth noticing the good agreement between the simulated and measured results. Figure 9: Measured co-polar radiation pattern in the H-plane at 30 GHz for different scanning angles. Figure 11: Comparison between the simulated and measured variation of the gain as a function of \(\theta_{f}\). Figure 10: Measured frequency behaviour of the gain for different scanning angles.