## 4 Evaluation
### Simulation on the Components of AcpAS  
#### 4.1.1 Simulation on the Septum Polarizer  
The septum polarizer was simulated and optimized using ANSYS HFSS EM simulation software. Moreover, polarizers designed for operating frequencies of 19.6 GHz-21.6 GHz and 29.2 GHz-31.2 GHz were developed. Figure 8 shows the structure of the polarizer, and Table 2 provides the specific length parameters of K-band and Ka-band, where \(a\) is the width of the square waveguide, \(L\) is the length of the waveguide, \(d\) is the thickness of the septum, \(l_{0}\)-\(l_{5}\) are the lengths of each step, and \(a_{0}\)-\(a_{5}\) are the heights of each step.  
Figures 9 and 10, respectively, show the distribution of the electric field vector at the output port of the septum polarizer at 20.6 GHz over one time period T, when Port 1 is fed and Port 2 is matched, and when Port 2 is fed and Port 1 is matched. It can be observed that when only Port 1 is fed, the septum polarizer generates RHCP waves, and when only Port 2 is fed, the septum polarizer generates LHCP waves.  
Figures 11 and 12, respectively, show the simulation results of the VSWR, port isolation, phase difference between the two modes, and amplitude difference between the two modes for the designed K-band and Ka-band septum polarizers. It can be seen that for the K-band septum polarizer, within its operating frequency band, VSWR \(\leq\) 1.6, port isolation \(\leq\) 14 dB, the phase difference between the two modes is \(\geq\)86.3\({}^{\circ}\), and the amplitude difference \(\leq\) 0.1 dB; for the Ka-band septum polarizer, within its operating frequency band, VSWR \(\leq\) 1.6, port isolation \(\leq\) 14 dB, the phase difference between the two modes \(\geq\)83.1\({}^{\circ}\), and the amplitude difference \(\leq\) 0.4 dB. Both septum polarizers exhibit good performance and meet the feed requirements of dual-CP antennas.  
Figure 8: Schematic diagram of the septum polarizer structure. (**a**) Side view of septum circular polarizer. (**b**) Front view of septum circular polarizer.  
Figure 7: Photograph of the fabricated prototype of the proposed antennas.  
Figure 11: Simulation results of the VSWR, port isolation, phase difference, and amplitude difference for the K-band septum polarizer. (**a**) VSWR and isolation. (**b**) Phase difference and amplitude difference.  
Figure 12: Simulation results of the VSWR, port isolation, phase difference, and amplitude difference for the Ka-band septum polarizer. (**a**) VSWR and isolation. (**b**) Phase difference and amplitude difference.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Length Para.** & \(a\) & \(d\) & \(L\) & \(l_{0}\) & \(l_{1}\) & \(l_{2}\) & \(l_{3}\) & \(l_{4}\) & \(l_{5}\) & \(a_{1}\) & \(a_{2}\) & \(a_{3}\) & \(a_{4}\) & \(a_{5}\) \\ \hline K-band & 8.5 & 1 & 34.82 & 16.02 & 1.51 & 2.29 & 2.65 & 2.38 & 1.05 & 7.14 & 4 & 2.22 & 2.01 & 0.24 \\ Ka-band & 6.3576 & 0.5 & 22.8 & 7.86 & 1.19 & 2.06 & 2.58 & 2.25 & 1.86 & 5.06 & 2.99 & 2.23 & 1.12 & 0.62 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Length Parameters of the K/Ka-band septum polarizer (mm).  
Figure 10: Diagram of LHCP electric field vector. (**a**) \(t=0\). (**b**) \(t=T/4\). (**c**) \(t=T/2\). (**d**) \(t=3T/4\).  
Figure 9: Diagram of RHCP electric field vector. (**a**) \(t=0\). (**b**) \(t=T/4\). (**c**) \(t=T/2\). (**d**) \(t=3T/4\).