## 4 Measurement Results and Performance Analysis  
The antenna array was integrated into the ABDP for testing of the full system in an anechoic chamber. Each of the antennas was connected to one of the 16 ADC channels of the ZCU216 board, and the system was placed in the anechoic chamber as demonstrated in Figure 14. The antenna array was mounted on a foam platform facing the transmission antenna (WBH2-18S from Q-Par Angus, Leominster, UK) and the ABDP covered in panels that absorb RF waves. Additionally, the DAC to which the output of the beamforming is being routed to, was connected to PORT2 of the Vector Network Analyzer (VNA). Figure 13: Planar array reference frame. The azimuth plane radiation patterns of the array were first obtained for four directions at two different planes. The planes tested were \(\varphi=0^{\circ}\)and \(\varphi=45^{\circ}\), where the main beam was pointed towards \(\theta=0^{\circ}\) (broadside), \(\theta=340^{\circ}\), \(\theta=45^{\circ}\), and \(\theta=300^{\circ}\). The same radiation pattern was simulated in CST, and the results are presented in Figures 15 and 16. There is a great agreement between the measured and simulated patterns. In terms of the main lobes, it was possible to point the beam at the desired positions, with a noticeable deviation at higher \(\theta\) values, such as in the \(\theta=60^{\circ}\) and \(\theta=300^{\circ}\), which was expected as discussed previously. Nevertheless, the measurements and the simulations present the same limitations of the system. There is a slight difference in the side lobes and the nulls between the two planes. In the \(\varphi=45^{\circ}\) plane, there is a slightly larger null and side lobe relative to the simulations. This can be due to mutual coupling between antenna elements that is not reproduced by the simulations, due to material imperfections, or small misalignments in the measurement setup and the array itself. It is not possible to compare the absolute gain values of the measurement with the simulation because the analog signal measured by the VNA is generated by the DAC of the ZCU216, as previously discussed. Moreover, these results are normalized to the value at \(\varphi=0^{\circ}\) and \(\theta=0^{\circ}\), separately for the two planes. In addition to the single-beam tests, a multibeam radiation pattern was also simulated and measured. The three beams were pointed towards \(\theta=0^{\circ}\), \(\theta=45^{\circ}\), and \(\theta=330^{\circ}\). The azimuth plane radiation patterns are presented in Figure 17. It is possible to observe that the proposed system successfully produced a radiation pattern with the three proposed beams. The measured multibeam radiation pattern greatly matches the predicted one. As can be seen, the maxima were pointed towards the desired \(\theta=0^{\circ}\) and \(\theta=45^{\circ}\) directions, while the beam towards \(\theta=330^{\circ}\) was slightly shifted towards \(\theta=315^{\circ}\). Since this was predicted by the simulation, it is possible to conclude that this was due to the array's resolution limitation. This could potentially be improved with the use of arrays with more elements. In the direction of \(\theta=330^{\circ}\), it is noticeable that the measured gain deviates slightly from  
Figure 14: Antenna array and ZCU216-based ABDP inside the anechoic chamber for radiation pattern measurement. the theoretical value. This can be explained by the measurement setup demonstrated in Figure 14. When pointing towards \(\theta=330^{\circ}\), the array starts to turn towards the box containing the ABDP and the cables, which interferes with the ideally anechoic environment of the anechoic chamber, leading to a reduction in the received power. Figure 16: Measured and simulated single-beam azimuth radiation patterns at \(\varphi=45^{\circ}\) with the main beam pointing towards: (**A**) \(\theta=0^{\circ}\), (**B**) \(\theta=340^{\circ}\), (**C**) \(\theta=300^{\circ}\) and (**D**) \(\theta=45^{\circ}\).