## 6 Fabrication and Measurement  
To verify whether the actual performance of the antenna matches the simulation results, an antenna sample was fabricated and tested. The MTS and the feed network are printed on two separate dielectric substrates, as illustrated in Figure 11a,b, respectively. After printing, these two substrates were precisely aligned and tightly bonded together to form the complete antenna. Figure 10: Simulated values of the axial ratio for different r\({}_{2}\). The reflection coefficient of the antenna was measured using a PNA3769 vector network analyzer sourced from Puna Technology Company, which is located in Nanjing, China. The results indicate that the IBW of the antenna is 4.92-7.37 GHz (39.5%), as shown in Figure 12a. The measured results are basically in line with the simulated ones. The axial ratio test outcomes for the antenna are depicted in Figure 12b. As observed, the antenna's ARBW spans from 5.25 GHz to 7.33 GHz, accounting for a 33.1% bandwidth. The frequency-dependent variations in both the simulated and measured AR curves align closely. Notably, the antenna demonstrates two minima in its axial ratio at 5.4 GHz and 7.1 GHz, where the axial ratios decrease to 1.6 and 1.1, respectively. This indicates that the antenna possesses good CP performance. Figure 13 presents the frequency-dependent characteristics of the antenna's gain and radiation efficiency. Within the CP operational bandwidth, the gain of the antenna exhibits a range from 7 dBic up to 9.4 dBic. Meanwhile, its radiation efficiency shows a fluctuation range between 80% and 94%. Specifically, at the frequency of 6.9 GHz, the antenna reaches its peak gain of 9.4 dBic. The gain fluctuation arises from multiple factors. On one hand, there is an inherent trade-off between improving gain and reducing axial ratio when adjusting the physical dimensions of antenna elements. For instance, modifying the size or spacing of radiating patches to enhance gain might disrupt the delicate balance required for achieving the desired axial ratio across the CP bandwidth, leading to inconsistent gain performance. On the other hand, at higher-order resonances within the CP bandwidth, the antenna's radiation pattern degrades, causing non-optimal radiation and thus gain variations [12]. Figure 11: Fabricated sample of the proposed antenna. (**a**) Top view; (**b**) bottom view. Figure 12: Comparisons of the measurement and simulation. (**a**) \(\mathrm{S}_{11}\); (**b**) AR. The far-field radiation patterns of the antenna are depicted in Figure 14. Specifically, Figure 14a,b presents the radiation patterns in the E-plane and H-plane, respectively, at 5.4 GHz, while Figure 14c,d show the radiation patterns in the E-plane and H-plane, respectively, at 7.1 GHz. The measured radiation patterns are basically consistent with the simulated ones. At 5.4 GHz, the cross-polarization ratio is less than \(-20\) dB; at 7.1 GHz, it is less than \(-15\) dB, indicating that the antenna exhibits distinct left-hand circular polarization characteristics. To elucidate the spatial radiation characteristics of the antenna more clearly, Figure 15a displays 3D gain distribution at 5.4 GHz. It can be observed that the antenna features a unidirectional radiation beam and low back radiation, indicating high mode excitation efficiency. Figure 15b presents the 3D radiation pattern at 7.1 GHz, demonstrating stable directional radiation characteristics within the upper hemisphere. Despite the presence of  
Figure 14: Radiation patterns of the proposed antenna. (**a**) 5.4 GHz, E-plane; (**b**) 5.4 GHz, H-plane; (**c**) 7.1 GHz, E-plane; (**d**) 7.1 GHz, H-plane. Figure 13: Comparisons of the measurement and simulation. (**a**) Gain; (**b**) efficiency. minor sidelobes, a peak gain of 9.36 dBic is achieved. A comprehensive analysis of both the 2D and 3D radiation patterns reveals that the antenna exhibits good properties, including high directivity, angular stability, and symmetric beam shape.