## 2 Antenna Design  
The proposed antenna design is composed of four main parts as radiator, conducting ground plane, DCF, and radome. In order to utilize the design efficiently in space applications, the radiator part should be protected by a low-loss radome that is also resistant to temperature changes. Additionally, the radiator needs to be supported by a lightweight structure around the edge so as not to reduce the ground plane effect and to withstand the vibration caused by the launch process. Accordingly, a dielectric cavity support structure and radome are designed by using Ketron 1000 PEEK (\(\epsilon_{\tau}\) = 3.2, tan\(\delta\) = 0.002) material considering its distinguishing features for space applications such as high robustness, lightweight, low dielectric loss, and low outgassing. In addition, the thermal resistance of selected material is quite satisfactory enough to meet the need for the structural integrity of the antenna to remain stable during highly variable thermal conditions in the space environment. Moreover, the DCF and radome are also mounted to each other with screws specially fabricated from PEEK in order to increase structural strength and prevent possible structural integrity deterioration that may arise from the difference in thermal expansion of the used materials. The radiator part is built on a RO4003C (\(\epsilon_{\tau}\) = 3.38, tan\(\delta\) = 0.0021) substrate with 0.813 mm thickness. Its design consists of two bow-tie dipole antennas (in other words, four triangular patch elements). Two of the patch elements placed as perpendicular to each other on the top surface of the substrate are shown in Figure 1a with design parameters. The other two elements of the radiator part are placed on the bottom surface as a mirror image symmetric of their counterparts on the top surface, as given in Figure 1b. The planar base surface of the antenna structure is a conductor that acts as a ground plane. A metallic hollow mast is physically used to stabilize the clearance between the radiator part and the ground surface in a vibration-proof manner, as shown in Figure 2. In addition, a 50 \(\Omega\) coaxial cable, which is utilized to feed the triangular patch elements on the radiator part, also passes through the metallic mast. In addition, the outer conductor of the coaxial cable is connected to both this metallic mast and the patch elements on the bottom surface, while the inner conductor is connected to the central feed point of the patch elements on the top surface. Another important issue to be examined in antenna designs fed by a coaxial cable is the feeding efficiency losses that may arise from the unbalanced phase nature of the coaxial cable and the possible impedance mismatch between the radiator and the coaxial cable. In the antenna design in this study, the unbalance and mismatch effects of the 50 \(\Omega\) coaxial feed are analyzed with an ideal delta-gap feeding (Lumped Port in HFSS or Discrete Port in CST Studio) assigned between the central feed points of the patch elements on the top and bottom surface of the substrate. Thus, the radiator part of the antenna is fed by an  
Figure 1: Design parameters of the radiator part: (**a**) Top-view; (**b**) Bottom-view. ideal feed by eliminating the effect of the coaxial cable, and the reflection coefficient and axial ratio results are compared with the practically applied coaxial feed case, as given in Figure 3. The comparative results show that the proposed antenna design is quite suitable for coaxial feeding. In order to generate an RHCP, the vertically placed patch elements on the top and bottom surface are respectively fed by the inner and outer conductor of the coaxial cable, which inherently have a 180\({}^{\circ}\) phase difference between of them. The horizontally placed patch elements on each surface are connected to vertically placed counterparts by ring-shaped delay lines that provide two additional 90\({}^{\circ}\) phase delays.