# Enhanced Efficiency and Reduced Side Lobe Level Convex Conformal Reflectarray
## 5 Optimized CRA: Numerical and Experimental Characterization  
Once the feed horn performance was assessed, the whole CRA system was assembled and it was numerically and experimentally characterized. Figure 7 shows the entire CRA antenna mounted on the outdoor test range at Politecnico di Torino. The relative position between the feed and the convex reflector was kept the same as the configuration in [20]. In addition, in this case, the simulations were carried out with CST Microwave Studio. The computed and measured radiation patterns at \(29,30\) and \(31\) GHz are shown in Figures 8-10. In each figure, the simulated co-polar patterns in the E (vertical) and H (horizontal) planes are plotted; moreover, both the measured co-polar and cross-polar components are represented. From the plots, it can be seen that there is very good agreement between the simulated and measured results. Figure 6: Designed horn: simulated frequency behavior of its reflection coefficient magnitude \(|S_{11}|\), simulated and measured cross-polarization level. Figure 7: Photo of the entire CRA system mounted on the outdoor test range at Politecnico di Torino. As far as the system performance is concerned, it must be noticed that it is very good also in the vertical plane, it is the most affected by the CRA curvature, and it remains almost constant over the considered band. The cross-polarization reaches a maximum value of \(-25\,\)dB in the H-plane at the frequency of \(31\,\)GHz, while in the E plane, it is always fully below \(-30\,\)dB; this is also thanks to the performance of the designed feed. The values of the maximum SLL are reported in columns 2 and 4 of Table 1 for the E and H planes, respectively. In the same table, the SLL in the two planes for the configuration introduced in [20] is also shown (column 3 and column 5) for the sake of comparison: the optimized configuration proposed here exhibits side lobes that are lower at least \(2\,\)dB in the E-plane and from \(3\,\)dB to \(5\,\)dB in the H-plane than those for the antennae in [20]. Note that in the case of the \(2\,\)dB in the E-plane, the \(2\,\)dB in the H-plane is not a good indicator of the \(2\,\)dB in the E-plane. Figure 8: Radiation patterns in the E (**left**) and H (**right**) planes at \(29\,\)GHz. Figure 10: Radiation patterns in the E (**left**) and H (**right**) planes at \(31\,\)GHz. Figure 9: Radiation patterns in the E (**left**) and H (**right**) planes at \(30\,\)GHz. addition to \(f_{0}\), in Table 1, the frequencies of 29.2 GHz and 30.8 GHz are considered since those are the values limiting the bandwidth for the configuration in [20]. In fact, as it emerges from Figure 11, where the frequency behavior of the simulated and measured gain of the CRA considered here and of the measured one for the configuration in [20] are shown, for frequencies beyond 30.8 GHz, the gain of the latter strongly decreases. The curves in Figure 11 show the good agreement between the numerical and experimental results and the improvement of the performance obtained with the optimized configuration; the gain is greater by almost 3 dB in the 1-dB bandwidth than that of the antenna in [20] (see also columns 6 and 7 in Table 1); the bandwidth on its turn is increased from 7 % to 11 %. The increase in the gain is also responsible for a significant improvement in the antenna efficiency that is more than twice at all the three frequencies, as it emerges also from columns 8 and 9 of Table 1.  
To further prove the effectiveness of the proposed technique, a comparison with the performance of the CRA illuminated with a feed designed for optimizing the antenna system efficiency is also carried out. As reported in [1; 4], similar to what is commonly done for reflectors, in case of RAs, the aperture efficiency can be evaluated as the product of several terms, the most significant of which is the illumination efficiency and the spillover efficiency, which can be evaluated numerically (see, for example, [4]).