## 5 Experimental Validation  
The proposed planar dielectric lens made up of 576 square prism cells was manufactured and measured at the facilities at the University of Oviedo. The lens was manufactured with a 3D printing technique using the printer Ultimaker 3 and measured in a planar acquisition range. The setup in the planar range is depicted in Figure 12. A vector network analyzer PNA-X from Keysight was connected to the feeding horn, a standard gain horn  
Figure 11: S parameters of the three horn antennas (**a**) \(s_{11}\), \(s_{22}\), and \(s_{33}\) and (**b**) \(s_{21}\), \(s_{31}\), and \(s_{32}\) according to the port definition given in Figure 10.  
Figure 10: Setup to simulate the S parameters of the three horn antennas operating at the same frequency carrier. of 15 dBi (Flann 22240-15), and a second port was connected to an open-ended Ka-band wave-guide used as a near-field probe. Due to the limitations of the facilities, only one horn was used in the measurements. However, the structure bearing the horn antenna enables moving the feed into an arc of radius 100 mm, thus placing the horn antenna on the different positions of the cluster. The measurements were performed at three different feed positions (\(\theta=0^{\circ},15^{\circ},20^{\circ}\)) in a bandwidth of 4 GHz, from 26 to 30 GHz, evaluating the electric field on the horizontal plane _xoz_. The copolar component \(\hat{y}\) of the electric field through the propagation direction \(\hat{z}\) and \(x=y=0\) is measured and compared with the simulations in Figure 13. The simulations and measurements highly agree at the maximum position and the field decay within the measured area, obtaining a similar depth-of-focus considering a 3 dB decay of the electric field. In Figure 14, the electric field in the plane _xoz_ at three different positions (\(\theta=0^{\circ},15^{\circ}\) and \(20^{\circ}\)) is shown, and Table 2 outlines a comparison between the simulated and measured focusing performances. Due to the antenna symmetry, only the three positions shown in Figure 12 were measured. These results confirm that a displacement of the feed according to (1) moves the near-field spot, while the focusing characteristics remain practically unchanged. For the central spot, both the maximum location and depth-of-focus, highly agree with simulations. The agreement for the middle spot (\(\theta=15^{\circ}\)) is also significantly good, highlighting that the depth-of-focus is not only close to the simulations, but also to the central spot. At the widest position (\(\theta=20^{\circ}\)), an angular shift of the spot starts to appear, and the position of the maximum is compressed. These effects are a consequence of the phase aberrations due to the off-focus feeding. Figure 12: Setup used to measure the near-field radiated by the prototype in the planar acquisition range as the University of Oviedo. Figure 13: Comparison between the simulations and measurements of the normalized amplitude (dB) of the electric field along the propagation direction and \(x=y=0\) at 28 GHz with the feed \(\theta=0^{\circ}\). The in-band response is analyzed from 26 to 30 GHz. In Figure 15, the normalized electric field amplitude through the propagation direction and \(x=y=0\) is shown for the central spot and different frequencies. The measurements presented an extremely stable behavior from 27.5 to 29 GHz, keeping a similar depth-of-focus, and the maximum barely shifted it position. At the frequencies out of this range, the maximum of the field was displaced, whilst the depth-of-focus was enlarged or shortened, regarding the frequency. These results show a great in-band response compared with transmitarrays based on resonant elements. In Table 3, different published works of antennas with scanning or multi-focusing capabilities are compared with this work. These solutions are typically used in far-field (FF) applications, while only a few published works may be found on near-field (NF) ones.