# Compact UHF Circularly Polarized Multi-Band Quadrifilar Antenna for CubeSat
## 3 Prototype Measurement Results  
The proposed concept is manufactured and assembled using two FR4 dual-layer substrates (\(\epsilon_{r}\) = 4.4 and tan \(\delta\) = 0.02). A ceramic ring is used to fix the structure. From EM simulation, it was possible to predict that the ceramic ring will not have any impact on the radiofrequency performance of the structure. Twelve 0.8 mm diameter vertical pins are soldered to connect the two substrates. This structure ensures solid mechanical properties to reduce any risk of vibration during launch vehicle takeoff. Four holes are etched into the top substrate to screw the antenna on the CubeSat structure. In Figure 9, the top and side views of the prototype are shown. The radio frequency performance of the proposed design is measured without and with the 3U structure composed of a 10 \(\times\) 10 \(\times\) 30 mm aluminum frame in the experiments.  
The measured reflection coefficients of the antenna without and with the structure are presented in Figure 10. An \(S_{11}\) lower than \(-\)10 dB is obtained in the 860-930 MHz band, which shows good agreement with the simulated results. The radiating characteristics are performed in an anechoic chamber. The measured broadside gain versus frequency is shown in Figure 10. A right-hand circular polarization with an axial ratio lower than 3 dB is obtained from 860 MHz to 930 MHz. As anticipated from the 3D EM modeling, the broadside gain in the prototype mounted on the CubeSat structure is relatively lower than that in the antenna-only case.  
Figure 10: (a) S parameter measurement and (b) realized gain measurement of the antenna with and without structure.  
Figure 9: Picture of the prototype with: top view of the prototype; side view in hybrid coupler orientation; side view of the prototype in balun orientation.  
For the antenna alone, the radiation patterns of the real gain at 870 MHz and 920 MHz are shown in Figure 11. According to this report, a good agreement is obtained with the simulated results. An RHCP 122\({}^{\circ}\) beamwidth pattern is measured with peak gains of 2.3 dBic and 1.1 dBic at 870 MHz and 920 MHz, respectively. In the case where the proposed antenna is integrated with the structure, the realized gain radiation patterns at 870 MHz and 920 MHz are shown in Figure 12. Similarly to the simulation results, the gain is decreased due to the contribution of the vertical currents flowing on the 3U structure. The 3 dB beamwidth is wider, with 132\({}^{\circ}\) and 129\({}^{\circ}\) at 870 MHz and 920 MHz, respectively. The axial ratio level versus theta for different configurations is also computed and shown in Figure 13. An axial ratio level lower than 3 dB can be observed over a 120\({}^{\circ}\) aperture beamwidth for both configurations. Some asymmetry in the axial ratio results can be observed.  
These measurement results validate the performance of the proposed structure for the targeted application.  
Figure 11: Measured gain radiation pattern of the antenna without structure, with RHCP in blue and LHCP in red, plain trace for phi = 0\({}^{\circ}\), and dashed trace for phi = 90\({}^{\circ}\).  
Figure 12: Measured gain radiation pattern of the antenna with structure, with RHCP in blue and LHCP in red, plain trace for phi = 0\({}^{\circ}\), and dashed trace for phi = 90\({}^{\circ}\).