# Design of Dual Circularly Polarized Sequentially-Fed Patch Antennas for Satellite Applications
## 4 Array Prototype Fabrication and Measurements  
A prototype of the 2-by-2 array operating in the higher UHF band (\(f=2.2\) GHz) is shown in Figure 5(a). The gain of such an antenna is reported in Figure 5(b), in which a fair agreement between simulated and measured co-polar gain patterns can be found in the elevation angle range \(\theta\in[-30,30]\). Moreover, the array presents a very low cross-polar component (\(<\)\(-25\) dB), as it can be inferred from the simulated traces with filled triangle markers. It is worth noting that, to ensure the dual-CP antenna performances, the CP radiation pattern should be measured by feeding alternatively both RHCP and LHCP input ports. However, by considering that the radiated gain pattern does not differ significantly if the input port is switched, for the sake of brevity, in Figure 5(b) only the co-polar and cross-polar gain patterns radiated by the array are provided at the central frequency \(f=2.2\) GHz, when the RHCP input port is fed. Such results allow the array to be used as a primary feeder for reflector systems for S-band satellite applications. The feeding scheme that guarantees the proper \(120^{\circ}\) phase shifts between the three pins used to feed array patches (already presented in Figure 2a), and thus CP, was scaled and replicated for each element of the array. Finally, the four RHCP (LHCP) ports were connected to two standard RHCP (LHCP) \(\Sigma-\Delta\) networks [31] to obtain the RHCP (LHCP) sum and difference patterns required for satellite tracking, as schematically shown in Figure 7. The two \(\Sigma-\Delta\) feeding networks were realized on a separate board in microstrip technology. On the other hand, the scaled networks used to feed each array element, schematically shown in Figure 2a, are printed on their back. The four feeding networks were fabricated by using a ROGERS TMM4 substrate, with different thickness \(h_{d}=2.54\) mm, due to the frequency scaling at \(f=2.2\) GHz. The \(\Sigma-\Delta\) feeding network was fabricated as shown in Figure 7(a), whereas in Figure 7(b) the circuit layout is presented, in which all network ports are labeled from P1 to P8. According to [31], the network is able to synthesize the sum (\(\Sigma\)) and the difference (\(\Delta_{az}\), \(\Delta_{el}\)) patterns required for satellite azimuthal and elevation tracking. In particular, the RHCP (LHCP) \(\Sigma-\Delta\) networks were connected through the ports labeled by A, B, C and D to the four RHCP (LHCP) array input ports. The sum pattern (A+B+C+D signal) is obtained at port P1. The two difference patterns, i.e., \(\Delta_{az}\) and \(\Delta_{el}\), are instead obtained by synthesizing the signals A+B-C-D and A+C-B-D at ports P4 and P2, respectively. Moreover, In Figure 7(c) the simulated reflection coefficients at network ports \(S_{jj}\) (\(j=5,6,7,8\)), which are directly connected to the array RHCP/LHCP ports, are shown. For the sake of simplicity, in Figure 7(d) the simulated the insertion loss \(IL=-\log_{10}|S_{j1}|\) (\(j=5,6,7,8\)) between network output (A, B, C and D) and input \(\Sigma\) (P1) ports is also presented. As it is apparent, good reflection coefficients and satisfactory insertion loss occur. In Figure 7(e) the simulated relative phases between network output (A, B, C and D) and input \(\Sigma\) (P1) ports is also provided. Such a result clearly shows that all the output signals of \(\Sigma-\Delta\)  
Figure 5: Simulated RHCP (\(G_{R}\)) and LHCP (\(G_{L}\)) gain patterns versus elevation angle with (filled markers) and without (empty markers) monopoles around the 2-by-2 array, for the cut-planes at (**a**) \(\phi=0^{\circ}\) and at (**b**) \(\phi=90^{\circ}\). The results are provided at the central frequency \(f=2.2\) GHz. networks, used to feed the 2-by-2 array (Figure 7), are in phase over all the considered bandwidth, as required.