# A Multi-Band Circularly Polarized-Shared Aperture Antenna for Space Applications at S and X Bands
## 3 Results
### Simulated Results  
Figure 3 shows the simulated performance of the S-band patch for the proposed shared aperture antenna. The S\({}_{\rm 11}<-10\) dB bandwidth of the S-band patch is 30 MHz (from 2013 MHz to 2043 MHz, 1.5%). The Axial Ratio (AR) of the proposed antenna is measured in the boresight (+z axis in Figure 1) direction. The simulated AR \(<\) 3 dB bandwidth starts from 2013 MHz to 2020 MHz (7 MHz, 0.35%), as shown in Figure 3b. It has a minimum AR value of 1.9 dB at 2016 MHz. Figure 3c,d show the polar plots of the RHCP and LHCP radiation patterns for the patch in the \(\varphi\) = 0\({}^{\circ}\) and \(\varphi\) = 90\({}^{\circ}\) planes, respectively. It is clear in the plot that the RHCP is more dominant, and the maximum RHCP gain is 7.7 dBic at 2016 MHz. From the radiation patterns of the S-band antenna, it is evident that the antenna has a peak RHCP gain at the boresight. Due to the partial reflective surface, the antenna has a slightly higher gain compared to conventional S-band patch antennas.  
Figure 4 depicts the simulated results of the X-band patch of the proposed antenna. The S\({}_{\rm 11}<-10\) dB bandwidth of the proposed X-band FPRA starts from 8320 MHz and ends at 8530 MHz (210 MHz, 2.5%). It has an AR \(<\) 3 dB bandwidth that ranges from 8433 MHz to 8500 MHz (67 MHz, 0.8%), as shown in Figure 4b, measured in the boresight (+z axis in Figure 1) direction. A simulated maximum RHCP gain of 12.8 dBic was achieved from the single X-band patch antenna. This increased gain from a single radiating patch is close to the gain achieved for a 4-element antenna array [25]. The minimum AR = 0.9 dB of the X-band patch occurred at 8460 MHz. Figure 4c,d show the RHCP and LHCP gain patterns of the proposed antenna in the \(\varphi\) = 0\({}^{\circ}\) and \(\varphi\) = 90\({}^{\circ}\) planes, respectively. These patterns occurred at the frequency 8460 MHz, where the Axial Ratio is the lowest (0.9 dB). The RHCP beam of the X-band patch antenna was more direct due to the PRS being placed at an approximate 0.5\(\lambda_{\rm x}\) (\(\lambda_{\rm x}\) being the free-space wavelength at X-band frequency) distance away from the X-band patch. From the simulated results, it can be concluded that the proposed dual-band shared aperture antenna is an excellent option to replace two antenna systems of a CubeSat and to cover two bands. The S-band patch has a narrow bandwidth, but it is sufficient to perform as the uplink/downlink antenna for TT&C due to the fact that the data speed required to send/receive commands to the CubeSat is not that high. The X-band patch shows a high RHCP gain, which is desirable for establishing a fast downlink connection. The 67 MHz Axial Ratio bandwidth of the proposed antenna can establish Megabits per second (Mbps) and a speed communication link with a ground station.  
\begin{table}
\begin{tabular}{l l c c} \hline \hline
**Antenna Parts** & **Parameters** & **Symbol** & **Value (mm)** \\ \hline \multirow{8}{*}{S-band Patch} & Square Ring antenna length & L\({}_{\rm 1}\) & 41.7 mm \\ \cline{2-4}  & Square Ring antenna slot length & L\({}_{\rm 2}\) & 13.8 mm \\ \cline{2-4}  & Square Ring patch corner & \multirow{2}{*}{\(\rm P_{c}\)} & \multirow{2}{*}{2.2 mm} \\  & perturbation length & & \\ \cline{2-4}  & Distance between slots & d & 7.05 mm \\ \cline{2-4}  & Square Ring antenna feed location & (\(\rm X_{s}\), \(\rm Y_{s}\)) & (5.7, 0) mm \\ \hline \multirow{8}{*}{X-band Patch} & X-band square patch length & L\({}_{\rm 3}\) & 10.8 mm \\ \cline{2-4}  & X-band square patch corner & \multirow{2}{*}{\(\rm q_{c}\)} & \multirow{2}{*}{1 mm} \\ \cline{1-1}  & perturbation length & & \\ \cline{1-1} \cline{2-4}  & X-band patch feed location & (\(\rm X_{p}\), \(\rm Y_{p}\)) & (12.3, \(-\)10.4) mm \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._