## 5 Performance Discussion
### Scattering Performance  
To the authors' best knowledge, the scattering performance of CPFTA is studied for the first time in this paper. In order to make a comparison, the RCS of the same size metallic board is simulated and measured. Due to the limitation of experimental conditions, RCS at X-band was measured, as shown in Figure 18(a). For the detection wave in the broadside direction, the NCPFTA presents the effect of diffuse scattering, as shown in Figure 1. The total RCS of the NCPFTA and GCPFTA in normal direction are shown in Figure 18(b),c. Both under x-polarized and y-polarized detection waves, the NCPFTA has lower RCS in broad  
Figure 18: (a) The measured S11 of antennas. (b) The measured realized gain of antennas. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline Ref. & Type & Pol. & Feed & Feed & \multirow{2}{*}{H/D} & \multirow{2}{*}{Center Fre.} & \multirow{2}{*}{Peak Gain} & \multirow{2}{*}{S11} & \multirow{2}{*}{3-dB} & \multirow{2}{*}{3-dB} & \multirow{2}{*}{RCS} \\  & & Type & & Integration & & & & & & & \\ \hline
[11] & FTA & LP & horn & NO & 0.3 & 27.5 & 25.2 & 21.6 & \multirow{2}{*}{\(\sim\)} & 18 & NO \\
[12] & FTA & LP & horn & NO & 0.33 & 21 & 21.9 & \(>\)9.5 & \multirow{2}{*}{\(\sim\)} & 6.7 & NO \\
[16] & FTA & CP & Microstrip & YES & 0.16 & 10.3 & 21.8 & 16.3 & 23.2 & 11.6 & NO \\
[29] & FRT & CP & Array & YES & 0.29 & 5.3 & 22.8 & 15.1 & \(>\)11.3 & 13 & NO \\ GCPFTA & FTA & CP & Microstrip & YES & 0.15 & 9.5 & 21.4 & 21.1 & 6.5 & 15.7 & YES \\ NCPFTA & FTA & CP & Microstrip & YES & 0.15 & 9.5 & 22.4 & 21.1 & 23.6 & 16.5 & YES \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison between the proposed CPFTA and some literature. band. For \(y\)-polarized detection waves, the NCPFTA shows obvious RCS reduction at 7.7-12.7 GHz. Compared with GCPFTA, the maximum RCS reduction is 12.9 dB at 9.4 GHz. In order to further explore the reasons for RCS reduction, the cell of transmitarray is simulated under \(x\)-polarized and \(y\)-polarized detection waves. The amplitudes of reflection and transmission are shown in Figure 20. The transmitarray cells of GCPFTA are uniformly arranged, as shown in Figure 11a. In addition, the cell shows different electromagnetic responses to \(x\)-polarized and \(y\)-polarized detection waves, as shown in Figure 20. Hence, the total RCS of the GCPFTA is different obviously under the different polarized detection waves, as shown in Figure 19b,c. However, because of the sequential rotation technique of the NCPFTA, the cell arrangement of transmitarray is similar along the \(x\)-axis and \(y\)-axis, as seen in Figure 14a. Therefore, the total RCS of the NCPFTA is similar under \(x\)-polarized and \(y\)-polarized detection waves, as shown in Figure 19b,c. For the GCPFTA, the frequency of high transmission amplitude is basically consistent with the frequency of small RCS, as shown in Figures 19 and 20. Compared with metallic board, the reason for the RCS reduction is the transmission of detection waves. After penetrating the transmitarray, the detection waves are converted into cross-polarized waves by the reflectarray. Then, the waves are reflected many times in the air cavity between the transmitarray and reflectarray, and are dispersed to multiple directions. For the NCPFTA, there are two reasons for RCS reduction. One is the transmission of detection waves. The other is the reflected phase cancellation of transmitarray. Figure 20 shows large reflection components. The anisotropic patches of transmitarray with different rotation directions will possess different reflection performances. The reflected waves can  
Figure 19: (**a**) The RCS measurement in microwaves anechoic chamber. The simulated and measured total RCS of the NCPFTA and the GCPFTA under (**b**) \(x\)-polarized and (**c**) \(y\)-polarized detection waves. Figure 20: The amplitudes of co-polarized reflection, cross-polarized reflection, co-polarized transmission and cross-polarized transmission under (**a**) \(x\)-polarized and (**b**) \(y\)-polarized detection waves.