## 3 Array System Overview
### Single Element of SA Array  
The single antenna element of the SA consists of a slotted-patch antenna, as in [29], integrated with a semi-cylindrical metallic superstrate closed on the upper side, as illustrated in Figure 3. The configuration of the slotted-patch antenna consists of a single metallic layer mounted on a dielectric substrate, which dimension-matches the ground plane beneath it. The substrate material exhibits a relative permittivity of 3 and a dielectric loss tangent of 0.0017, with a thickness of 1.5 mm. The metallic layer consists of a circular patch with a thickness of 35 \(\upmu\)m. The patch incorporates two identical, narrow square-shaped slots of equal side length, symmetrically distributed along its perimeter. It is excited by two coaxial probes positioned in planes inclined at \(45^{\circ}\) with respect to the principal axes and located 90 mm from the patch center. The slot geometry, together with the placement of the coaxial feeding points, is optimized to excite two orthogonal  
Figure 2: Schematic view of SA mounting position and scan capabilities. modes in quadrature, thereby enabling the generation of Circularly Polarized (CP) radiation. The presence of two independent feeding points also enables dual circular polarization; as illustrated in Figure 3, Port A is designated for RHCP, while Port B handles LHCP. Also shown in Figure 3, the slotted patch antenna is then connected to the cylindrical metallic superstrate by four supports, which create an air gap separating the antenna from the superstrate. The superstrate consists of a circular aluminum sheet with 1 mm thickness and radius \(C\), positioned approximately at a distance of \(\lambda/7\) above the slotted-patch antenna. Surrounding the disk, a cylindrical crown is integrated to minimize electromagnetic leakage in unwanted directions and reduce mutual coupling between adjacent elements in array configurations. The overall structure functions as a Fabry-Perot Cavity (FPC) antenna, where constructive interference between direct and reflected waves enhances radiation gain. In standard FPC designs, this condition is achieved with a cavity height of approximately \(\lambda/2\)[30]. Our configuration compensates for the reduced height through the phase-shifting effect introduced by the curved metallic rim. This geometry alters the boundary conditions and the reflection phase at the superstrate, allowing constructive interference to occur at a much lower cavity height. Although this compact structure does not reach the theoretical directivity of a full-height FPC, it achieves a gain improvement of approximately 5 dBi while maintaining circular polarization and bandwidth performance. This solution offers a favorable trade-off between size, fabrication simplicity, and electromagnetic efficiency while also avoiding the performance degradation typically associated with ultra-thin dielectric superstrates [31]. The key dimensional parameters and their corresponding values for the SA are reported in Table 1. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Symbol** & **Value** & **Quantity [mm]** \\ \hline \(d\) & metallic patch radius & 120 \\ \(D\) & dielectric substrate radius & 170 \\ \(x\) & slot length in the x-direction & 25 \\ \(y\) & slot length in the y-direction & 3.5 \\ \(L\) & cavity dimension & 45 \\ \(C\) & superstrate radius & 115 \\ \(H\) & cavity height & 110 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dimensional parameters and their values. Figure 3: The geometry of the SA element: on the left, the front view of the slotted patch antenna element located at the base of the SA; on the right, the side view of the antenna element with the metallic superstrate. The reflection coefficient of the overall SA element structure, shown in Figure 4, exhibits a magnitude below \(-10\) dB over a \(10\) MHz bandwidth centered at \(412\) MHz. Measurement results are provided for both ports, corresponding to RHCP and LHCP excitations.