## 3 Array System Overview
### SA Feeding Network  
The SA system consists of three main components, as predictable from Figure 8.  
The first is the SA array of dual-CP slotted-patch antennas with cavity-based metallic superstate. The second component currently consists of analog feeding networks, one for each polarization, which combine signals from the SA elements. These networks should enable phase shifting and amplitude tapering to facilitate electronic scanning and beam shaping in the elevation plane. However, in our case, the feeding networks are prototypes intended to validate the general operation of the antenna system, primarily in the broadside direction. They are not yet configured to perform full beamforming functionality or dynamic beam steering.  
Finally, a dedicated circuit manages the DC power supply and controls the beamforming networks. This unit handles power distribution and enables communication with external systems for SA control.  
The SA comprises 19 radiating elements, each featuring two RF connectors, one for each polarization. The connectors are directly routed to two separate beamforming boards located beneath the ground plane: one dedicated to RHCP, the other to LHCP. The overall dimensions of a single feeding network are approximately 470 mm per 300 mm. Figure 9, on the right, illustrates the layout of the network, showing the individual transmission lines  
Figure 8: SA block diagram.  
Figure 7: The radiation pattern of the SA element for the LHCP port.  
of the power division structure, which have been miniaturized to fit within the available space. The circuit is implemented on a 0.8 mm thick dielectric layer made of ASTRA MT-77, the same material used for the slotted patch antenna substrate. Amplitude tapering across individual channels can be implemented by introducing controlled impedance mismatches at the corresponding ports. In the same figure, on the left, the physical placement of the networks is also shown.  
The feeding network is a corporate combining network with 19 input ports and a single output port, providing equal power distribution with a 1/19 split at each input port. This uniform power division can be verified through the scattering parameters of the network, representing the transmission from each input port to the output port. In this context, port 1 denotes the output (or sum) port, while ports x corresponds to the index of the 19 input ports. To ensure equal contribution from each input, the scattering coefficient, \(S_{1x}\), is defined as \(\left|S_{1x}\right|_{dB}=20 log_{10}\big{(}\sqrt{1/19}\big{)}\), which corresponds to an amplitude attenuation of approximately \(-12.79\) dB. The simulated scattering parameters for one of the network configurations are reported in Figure 10, showing a maximum variation of 1 dB among different paths. The corresponding parameters for the dual network are identical, as expected from the inherent duality of the two architectures.  
Each network guarantees the phase alignment of the signals at all input ports within \(\pm 2.0^{\circ}\) as shown in Figure 11; to support this requirement, all 38 RG142 coaxial cables (19 per polarization) connecting the antenna ports to the beamforming boards are precisely  
Figure 10: Amplitude of scattering \(S_{1x}\) parameter.  
Figure 9: Photographs showing the layout and physical placement of the two feeding networks.  
matched to a length of 1 m, with a tolerance of \(\pm\)2.8 mm, thereby ensuring phase coherence across the entire SA array.