# Exploring CP Array Antenna Characteristics and Its Applications to a Deployable Structure
## 4 Conclusions  
We propose an 8 \(\times\) 8 circularly polarized (CP) array antenna design constructed using circular-shaped microstrip patches. A single radiating element, designed to operate at 5.8 GHz, generates CP radiation characteristics through coupling between the feed line and the patch via a cross-shaped slot. Three possible mounting configurations of the transmitting antenna, as part of a wireless power transmission (WPT) system likely operating in space with a 27U CubeSat, are considered. The proposed CP array antennas are fabricated, and their performance is evaluated. Measurement results indicate that the CP antenna on a single large panel achieves a return loss of less than \(-10\) dB, an antenna gain exceeding 20 dB, and an excellent axial ratio of less than 0.5 dB at the center frequency with a half-power beamwidth of approximately 8\({}^{\circ}\). Furthermore, it is confirmed that the radiation characteristics remain consistent even when the large panel is divided into four units. To assess performance under different mounting configurations, two large panels are connected using deployable hinges. Measurement results demonstrate that the axial ratio and gain characteristics remain comparable across different configurations. To prevent undesired gain reduction or asymmetrical sidelobe levels, the phase response of the input signals to the CP antennas forming the transmitting antenna must be carefully managed. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \begin{tabular}{c} **No. Radiating** \\ **Elements** \\ \end{tabular} & \begin{tabular}{c} **Center** \\ **Frequency, \(f_{0}\)** \\ **[GHz]** \\ \end{tabular} & **Antenna Size** & **Peak Gain at \(f_{0}\)** & \
\begin{tabular}{c} **Measured** \\ **Impedance BW** \\ **[GHz]** \\ \end{tabular} &
\begin{tabular}{c} **Measured** \\ **Axial Ratio BW** \\ **[GHz]** \\ \end{tabular} \\ \hline
[6] & 2 \(\times\) 2 & 3.5 & \
\begin{tabular}{c} 2.41 \(\times\) 2.41 \(\times\) \\ 0.062 [\(\lambda^{3}\)] \\ \end{tabular} & 16.3 dBic & 2.7–4.1 &
\begin{tabular}{c} 2.82–3.88 \\ (31.6\%) \\ \end{tabular} \\ \hline
[7] & 4 \(\times\) 4 & 66 &
\begin{tabular}{c} 4.42 \(\times\) 8.48 \(\times\) \\ 0.51 [\(\lambda^{3}\)] \\ \end{tabular} & 20.5 dBic & 55.83–71.48 & 57–73 (23.8\%) \\ \hline
[8] & 4 \(\times\) 4 & 60 &
\begin{tabular}{c} 5.46 \(\times\) 5.48 \(\times\) \\ 0.51 [\(\lambda^{3}\)] \\ \end{tabular} & 19.3 dBic & 54.6–67.3 & 57–67 (21.5\%) \\ \hline
[9] & 1 \(\times\) 4 & 4.7 &
\begin{tabular}{c} 0.99 \(\times\) 0.42 \(\times\) \\ 0.3 [\(\lambda^{3}\)] \\ \end{tabular} & 14 dBic & 3.4–6.5 & 4–6 (42.0\%) \\ \hline
[10] & 2 \(\times\) 2 & 5.8 & \begin{tabular}{c} 1.82 \(\times\) 1.87 [\(\lambda^{2}\)] \\ 0.13 [\(\lambda^{3}\)] \\ \end{tabular} & 10.24 dBic & 5.078–6.080 & 5.08–6.08 (18\%) \\ \hline This work & 8 \(\times\) 8 & 5.8 & \begin{tabular}{c} 10.89 \(\times\) 10.89 \(\times\) \\ 0.13 [\(\lambda^{3}\)] \\ \end{tabular} & 22.65 dBic & 4.0–7.47 & \begin{tabular}{c} 3.80–7.95 \\ (71.6\%) \\ \end{tabular} \\ \hline This work & 8 \(\times\) 8 & 5.8 & \begin{tabular}{c} 10.89 \(\times\) 10.89 \(\times\) \\ 0.13 [\(\lambda^{3}\)] \\ \end{tabular} & 21.06 dBic & 4.01–7.25 & \
\begin{tabular}{c} 4.30–8.85 \\ (78.4\%) \\ \end{tabular} \\ \hline This work & 8 \(\times\) 16 & 5.8 &
\begin{tabular}{c} 10.89 \(\times\) 22.28 \(\times\) \\ 0.13 [\(\lambda^{3}\)] \\ \end{tabular} & 19.10 dBic & 4.06–7.47 & 4.4–7.4 (51.7\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison table. **Author Contributions:** Conceptualization, T.-H.L. ; software, T.-H.L. ; validation, T.-H.L. ; writing--original draft preparation, T.-H.L. and W.L. ; writing--review and editing, K.-J.L., W.L. and S.-H.Y. ; supervision, T.-H.L. and S.-H.Y. ; funding acquisition, S.-H.Y. All authors have read and agreed to the published version of the manuscript.