# Beam Scanning Capabilities of a 3D-Printed Perforated Dielectric Transmitarray
## 4 Prototype Manufacturing and Experimental Characterization  
The performances of the TA have first been numerically analyzed using CST MW Studio; then, a prototype has been manufactured and experimentally characterized in an anechoic chamber. The prototype has been fabricated using the 3D-printer Object30 by Stratasys(r) that exploits Polyjet technology and allows for achieving a nominal resolution of 100 \(\upmu\)m. In addition, the support connecting the feed to the TA and allowing its movement in the E-plane has been manufactured through a 3D-printing technique and, in particular, an FDM (Fused Deposition Modelling)-based 3D-printer has been exploited to realize it. A photo of the entire antenna and its measurement setup in the anechoic chamber is shown in Figure 7.  
Note that, to simplify the antenna assembly, the beam steering mechanism illustrated in Figure 6a is implemented in a slightly different way, as appears from Figure 7a more clearly from the sketch in Figure 6b: it is the TA that rotates around an axis in the horizontal plane, namely the \(x\)-axis in the reference coordinate system adopted in Figure 6, passing through the junctions that connect it to the supports; if this rotation is such that the angle between the \(y\)- and the \(y^{\prime}\)-axis in the sketches of Figure 6b is equal to \(\theta_{f}\), the field radiated by the field impinges on the TA surface with an angle that is actually \(\theta_{f}\); in other words, it is sufficient to make a rotation of the coordinate system to overlap the drawing in Figure 6a to that in Figure 6b and this proves that they are equivalent. In the anechoic chamber, the measurement of the radiation pattern is done performing a 3D scanning in \((\theta,\phi)\), where \(\theta\) and \(\phi\) are the angles used in the spherical coordinate system; when the measurement in the E-plane (i.e., the \(yz\)-plane in Figure 6) is performed, the radiation pattern as a function of \(\theta\) is obtained. Therefore, \(\theta_{b}\) is immediately found in the correspondence of the direction of maximum radiation and operating a translation proportional to the rotation applied to the Transmitarray, i.e., the angle \(\theta_{f}\). The measured value of the main parameters characterizing the antenna radiation performances for the different \(\theta_{f}\) are summarized in Table 1. In the first column, the value of these quantities for broadside radiation, where the gain is maximum, are listed. In the considered range for \(\theta_{f}\), the gain decreases less than 3 dB, from a maximum of 29.97 dB at 0\({}^{\circ}\) to 27.07 dB for \(\theta_{f}=\pm 30^{\circ}\). This corresponds to an enlargement of the main beam, that is, however, never larger than \(1^{\circ}\) in both planes (see 4 th and 5 th rows of the table). The decrease of the gain also affects the aperture efficiency, which reduces to 18% at the extremes of the scanning coverage. For what concerns the Side Lobe Levels (SLLs), their increase is more noticeable in the E-plane, where the beam is squinted, as also appears from the measured and simulated co-polarized radiation patterns at the frequency \(f_{0}\) plotted in Figure 8, for several values of the angle \(\theta_{f}\). These patterns confirm the good scanning capabilities of the designed antenna, since they  
Figure 7: Beam scanning TA mounted in the anechoic chamber: (**a**) manufactured prototype and its support structure; (**b**) measurement setup including the open-ended waveguide probe. stay almost unchanged for scanning angles between -20\({}^{\circ}\) and 20\({}^{\circ}\), but also, when \(\theta_{f}=30^{\circ}\), they do not degrade significantly. Note that the maximum of the different plotted patterns occurs for angles \(\theta_{b}\) that are slightly different from the corresponding angles \(\theta_{f}\). In fact, even if theoretically \(\theta_{b}=\theta_{f}\), in practice, this condition is not verified especially when these angles increase and what happens is that \(\theta_{f}\) is typically less than \(\theta_{b}\)[28].