## 4 Antenna Farm Based on Two Dual-Band Dual Reflectarray Configurations
Figure 11 shows the phase distributions implemented in the subreflectarray at 19.7 GHz and 29.5 GHz in one LP; note that the phase distributions in the orthogonal LP show the opposite phase variation at each frequency to deviate the orthogonal LP beam in the opposite direction. Then, the main parabolic reflectarray only converts the dual-LP incident field into dual-CP, so their cells have been designed to introduce a phase difference of 90\({}^{\circ}\) between the two orthogonal components of each incident LP [22]. The design of the subreflectarray and the main parabolic reflectarray has been carried out separately. The radiation patterns of the designed subreflectarray (without the main reflectarray) have been simulated and the results have been compared with those obtained considering ideal reflectarray cells (providing the required phase distributions without any phase errors and zero dielectric losses). As an example, Figure 12a shows the comparison between the ideal and realized patterns in the azimuth plane (\(\varphi\) = 90\({}^{\circ}\)) for the subreflectarray in H polarization at 19.7 and 29.5 GHz. Note that the patterns in Figure 12a show a wide main lobe since the subreflectarray does not focus the beam radiated by the feed (the parabolic surface of the main reflectarray will focus the beam). In the same way, the simulated radiation patterns of the designed polarizing main reflectarray (without the  
Figure 10: Dual reflectarray system proposed to operate simultaneously in Tx and Rx. (**a**) Operating principle of the dual-configuration, (**b**) functional scheme of the proposed antenna on the satellite. subreflectarray, so that the main reflectarray is illuminated from the virtual focus of the dual system) have been computed and compared with the simulations performed with ideal cells. Figure 12b shows the comparison between the ideal and realized patterns in the azimuth plane at 19.7 and 29.5 GHz for the polarizing main reflectarray in RHCP (obtained from the H polarization radiated by the feed). The patterns in Figure 12 show a satisfactory agreement between the designed and ideal performances of both reflectarrays. The dual system configuration results in relatively large incidence angles from the feed on the subreflectarray, which complicates the design of the elements of the subreflectarray. As a result, the simulated patterns of the designed subreflectarray show a slightly lower gain and higher cross-polar levels than in the ideal case (see Figure 12a). On the other hand, the simulated results of the designed main reflectarray show an excellent performance, which is practically identical to the ideal behavior (see Figure 12b). Finally, the dual antenna configuration is illuminated by the cluster of 27 feeds shown in Figure 3 rotated 90\({}^{\circ}\) in the x\({}_{l}\)y\({}_{l}\)-plane. The simulations of the complete dual reflectarray have considered 15 of the 27 feeds (an array of 3 \(\times\) 5 feeds, plotted with solid lines in  
Figure 11: Required phase distributions of the 0.65 m flat subreflectarray at the (**a**) lower and (**b**) upper operating frequencies for the same linear polarization (LP). Figure 12: Simulated radiation patterns at 19.7 and 29.5 GHz in the azimuth plane of the ideal and realized antenna components. (**a**) Subreflectarray for H polarization, (**b**) main reflectarray for right-handed circular polarizations (RHCP). Figure 3), since the beams produced by the remaining feeds are expected to have similar behavior. The simulated pattern contours of the 30 beams generated by the designed dual reflectarray simultaneously at 19.7 GHz and 29.5 GHz are depicted in Figure 13 at the EOC levels of the beams (between 45 and 46 dBi). The simulated beams match with the required spot distribution, where there is room for the beams that would be generated by a second dual reflectarray operating at slightly different frequencies to form the complete four-color multispot coverage in Tx and Rx.