# Exploring CP Array Antenna Characteristics and Its Applications to a Deployable Structure
## 2 Design and Experimental Results
### Circularly Polarized Antenna Design
#### 2.2.2 Array Antenna Characteristics for Various Mounting Scenarios
Please note that the radiation patterns in \(\phi=90^{\circ}\) are not provided in the measurement results due to the symmetric structure of the proposed CP antenna design. In addition, all radiation patterns presented in this study are normalized to the peak gain values at each frequency to compare the radiation characteristics such as sidelobe level and axial ratio with ease. These experimental results given in Figures 6 and 7 can be a reference of the transmitting antenna for WPT application in our study, and it corresponds to the first mounting configuration. The first mounting configuration of the proposed CP antenna, designed with a large panel, is divided into four units and each unit contains a 4 \(\times\) 4 CP array antenna with a separate feed point. The fabricated four units of the CP antenna are shown in Figure 8a, where the units are seamlessly combined to form a large panel which is of identical size with the one from the first configuration. To effectively measure the radiation pattern in the anechoic chamber, an additional 1:4 power divider was designed and fabricated to feed the four input ports using a coaxial cable. This power divider is attached to the rear side of the four units, as depicted in Figure 8b, with its detailed design provided in Figure 8c. This configuration corresponds to the second mounting configuration described in Figure 1, demonstrating that the proposed CP array antenna can be implemented regardless of the interface between the PA modules and the transmitting antenna. In other words, we would like to verify that the proposed CP antenna design, with four separate feed lines, can replace a single large-panel antenna design when WPT system specifications such as efficiency, output power level, or the number of PA modules vary to meet different application requirements. Furthermore, this second mounting configuration is applicable to 27U CubeSats, where multiple separate PA modules interface with the antenna using four coaxial cables, as shown in Figure 8d as an example. Figure 8e-i present the measured CP antenna performance, including return loss, gain, axial ratio, and radiation patterns. For more details, the return loss of the fabricated four-unit CP antenna remains below \(-20\) dB at the center frequency of 5.8 GHz, even when measured using a 1:4 power divider along with  
Figure 6: Comparison of the simulation and measurement results, (a) S\({}_{11}\) and (b) axial ratio and gain. four pairs of additional SMP connectors and bullets. These SMP connectors and bullets are commercially available from Amphenol (SMP-MSLD series). The radiation characteristics of the fabricated CP antenna, including the gain variation trend with frequency, excellent axial ratio (AR), half-power beamwidth, and sidelobe level, closely resemble those of the CP array antenna designed on a large single panel. These results confirm that the proposed antenna design effectively maintains its radiation performance as a transmitting antenna in the WPT system, regardless of the interface between the PA modules and the transmitting antenna. To investigate the radiation characteristics of the transmitting antenna in the third mounting configuration, two large panels are connected using deployable hinges allowing for stowed or deployed configurations. This mechanical operation is feasible because the input SMA connectors for each panel are placed in the same plane when the panels are fully deployed, as illustrated in Figure 9a. In an anechoic chamber, the input signal from a signal generator is fed into the fabricated antenna through a T-junction and two identical coaxial cables, as depicted in the inset of Figure 9b. Simulation results indicate that in the \(\phi=0^{\circ}\) plane, the gain increases by 3 dB, and the beamwidth is reduced by half, while the beamwidth in the other plane remains unchanged. It should be noted that the radiation pattern for the third configuration is plotted only at the center frequency of interest, as this frequency is of primary importance for the applicable WPT system.