## 2 Antenna Design
From another perspective, the proposed radiator can be considered integrated, as two identical bow-tie dipole antennas are placed on the x and y axes and with a 90\({}^{\circ}\) phase difference between the feedings of them. Therefore, a circularly polarized wave is produced that has an electric field vector that revolves on the x-y plane. Since the triangular patch elements are identical,  
\[\left|\tilde{E}_{x}\right|=\left|\tilde{E}_{y}\right|, \tag{1}\]  
and the obtained RHCP wave can be expressed as  
\[\tilde{E}(z,t)=\tilde{E}_{x}{\cos(wt-kz)}+\tilde{E}_{y}{\cos(wt-kz+\frac{\pi} {2})}. \tag{2}\]  
Figure 3: Comparison of the simulated results: (**a**) S\({}_{11}\); (**b**) Axial Ratio. Figure 2: Simplified antenna structure archetype. Thus, the RHCP wave is achieved with an onboard solution using just a single-feed. Therefore, the proposed antenna design does not need any extra hybrid couplers or any complex feed network, which adversely affects the reliability of the antenna performance in the space environment. On the other hand, even if the greater part of the RHCP wave is reflected by the ground plane, diffracted waves can still propagate across the plane and increase the back lobe of the radiation pattern [17]. Therefore, it is aimed to weaken the diffracted waves by changing the boundary conditions with a relatively thick dielectric cavity frame placed perpendicular to the reflective ground plane. In order to observe this effect of DCF on back lobe radiation, the proposed antenna structure with DCF is simulated without DCF for the starting and ending frequencies of the operational frequency band, and the radiation pattern results are compared, as shown in Figure 4. It is observed that the use of DCF in the proposed antenna design prevents the constructive effect of the diffracted waves on the back lobe by scattering and helps to weaken them, while increasing the vibration and thermal resistance. The antenna structure is designed and optimized by utilizing ANSYS HFSS. The designed antenna is presented in Figure 5, including details such as mounting apparatus, DCF, radiator, and radome to make the simulation conditions as close as possible to the measurement conditions. Thus, all possible factors that are presumed to affect antenna performance are fully simulated and optimized before the fabrication and measurement stage. The initial values for the optimization of the designed antenna are determined by experience gained from the simulation and measurement results of the preliminary prototypes of this study, previously presented in [20; 21; 22]. The ultimate values of the optimized GNSS antenna design parameters are determined by taking the fabrication precision and capabilities into account. The manufacturable ones are evaluated as the final design parameter values of the proposed antenna structure. The final production parameters determined for the presented space vehicle compatible antenna structure are given in Table 1.  
The radius of the ground plane is limited by the radius of the radiator substrate (R\({}_{\text{sub}}\)) and, hence, the length of triangular patches (L). In order to achieve a compact antenna design, the radius of the antenna structure should be as close as possible to the radiator width, dominantly determined by the L value, which is directly dependent on the operating frequency. Figure 4: Comparison of the gain pattern results: (**a**) 1.16 GHz; (**b**) 1.61 GHz.