## 5 Isolated S-Band Antenna Results  
Following the design of both the QM and the FM models, individual measurements were conducted to validate the simulated model in the electromagnetic software CST Microwave Studio 2023. Measurements of the S-parameters and radiation characteristics, including gain patterns and axial ratio, were conducted for the frequencies of interest in both models. These measurements were carried out in the compact range chamber at INTA facilities (see Figure 9). As demonstrated in Figure 10, the S-parameter simulation exhibited a high degree of correlation with the actual measurements, thereby validating the design. Furthermore, the excellent reproducibility observed in the manufacturing, assembly, and measurement processes resulted in two S Band Antenna models demonstrating identical functionality, both in terms of S-parameter measurement and radiation measurement. Consequently, these antennas are to be qualified for space mounting on dummies, with the understanding that QM and FM models will be subjected to divergent qualification and acceptance test levels. The following measurements versus simulations of the axial ratio at the two frequencies of interest (uplink and downlink) are presented below, as well as the comparison of the gain in the copolar and cross-polar components for both left-hand and right-hand polarization. As the comparison between measurements and simulations of the QM antenna shows high coincidence, the designed model is validated. As demonstrated in Figure 11, the comparison between measurements (solid line) and simulations (dashed line) of the co-polar and cross-polar gain for both principal cuts of each polarization and for the uplink and downlink frequencies is shown. It is evident that the gain difference between simulations and measurements is minimal. Figure 9: Measurement setup of the QM antenna in INTA’s compact range chamber. The gain values demonstrate notable stability across theta, with peak gain ranging from [6.5; 7; 6] dBi. Additionally, the back radiation exhibits minimal interference, contributing to the prevention of disruption in the inter-satellite link. Concerning the axial ratio (AR), the objective is to preserve dual circular polarization over a substantial frequency bandwidth and over the widest possible angular range of theta from both ports. This ensures uninterrupted communication with the ground station even in the event of satellite rotation. As demonstrated in Figures 12 and 13, the AR remains below the requisite 4 dB level within the designated angular range [\(\pm 50^{\circ}\)], thereby ensuring uninterrupted ground communication. As with the gain outcomes, the dashed lines represent simulations,  
Figure 11: Gain measurement vs. simulation of isolated antenna; (**a**) f = 2.03 GHz—Port 1; (**b**) f = 2.03 GHz—Port 2; (**c**) f = 2.205 GHz—Port 1; (**d**) f = 2.205 GHz—Port 2. Figure 10: Measurements vs. simulations of S—parameters amplitude of QM S Band Antenna. while the solid lines represent measurements. The close agreement between these lines substantiates the efficacy of the designed antenna model. Figure 14 compares the AR bandwidth as a function of frequency (boresight direction) between simulated and measured results when the antenna is isolated, demonstrating that the antenna meets the AR bandwidth requirements of 8%. The dashed lines represent simulations, the solid lines represent measurements, and the green dotted lines represent the margins in which AR must meet the requirement of <4 dB. Finally, as presented in Table 3, a comparison is made between the proposed design in this article and other designs mentioned in the references. While the text cites numerous references to antennas deployed on satellites, the comparison is specifically limited to those  
Figure 14: AR measurement vs. simulation of isolated antenna varying with frequency. (**a**) Port1; (**b**) Port 2. Figure 12: AR measurement vs. simulation isolated antenna, \(\text{f}=2.03\) GHz: (**a**) Port 1; (**b**) Port 2.