## 3 Simulation and Experiment  
### Simulation and Analysis of Matrix-Type Coding Metasurfaces  
The frequency domain solver in EM simulation software of CST MICROWAVE STUDIO is used to perform the numerical simulation. As shown in Figure 5a, the numerical results of coding \(a\) to \(f\) are depicted to explore the RCS reduction characteristics of different ratio combinations. The coding 0 presents the RCS reduction of coding 0 or 1, the numerical value is essentially zero in the frequency  
Figure 4: Far-field scattering results of: (**a**) metal plate; (**b**) coding 0 or 1, and matrix-type random coding MS; (**c**) coding \(a\); (**d**) coding \(b\); (**e**) coding \(c\); (**f**) coding \(d\); (**g**) coding \(e\); and (**h**) coding/ at 9.5 GHz.  
Figure 3: Arrangements of six matrix-type random coding MS: (**a,b**) coding \(a\) and \(b\) with the ratio \(\alpha=m_{0}/m_{1}=1/1\); (**c,d**) coding \(c\) and \(d\) with the ratio \(\alpha=m_{0}/m_{1}=5/4\); and (**e,f**) coding \(e\) and \(f\) with the ratio \(\alpha=m_{0}/m_{1}=2/1\).  
range of 5-16 GHz, which means the single coding MS cannot reduce the RCS. The coding \(a\) and \(b\) are the MSs with the ratio \(\alpha=m_{0}/m_{1}=1/1\); the coding \(c\) and \(d\) present the ratio \(\alpha=m_{0}/m_{1}=5/4\); and the coding \(e\) and \(f\) present the ratio \(\alpha=m_{0}/m_{1}=2/1\). It can be seen clearly that the RCS reduction curves of different coding sequences with fixed ratio \(\alpha\) are basically consistent. The RCS reduction will increase with decrease of the numerical value of \(\alpha\) in the whole interested frequency range. The optimal RCS reduction result is presented at \(\alpha=m_{0}/m_{1}=1/1\); these results verify the above theoretical assumptions.  
As shown in Figure 5b, the RCS reduction curves of coding \(a\) are basically consistent at \(x\)- and \(y\)-polarized wave incidence, which indicates a polarization-insensitive property of the proposed MSs. In addition, the RCS reduction of coding \(a\) is greater than 8 dB in the whole frequency range of 5.5-15 GHz, and the RCS reduction reaches a maximum of 21 dB at 9.5 GHz.  
To further discuss the energy scattering characteristic of matrix-type random coding MS, the scattering patterns of coding \(a\) under normal incidence are studied, as shown in Figure 6a-f. Here is a comparison of coding \(a\) and metal plate with the same size 300 \(\times\) 300 mm\({}^{2}\) at 5, 8, 9.5, 10, 13, and 16 GHz. According to \"energy conservation law\", the main lobe energy can be suppressed by enhancing the scattering EM energy of side lobe, so an effective RCS reduction can be achieved under normal incidence. The metal plate has a strong main lobe in whole interested frequency range. As shown in Figure 6a,f, the MS has almost no inhibitory effect on main lobe at 5 and 16 GHz. Figure 6b,e shows that the main lobe energy of MS has a certain suppression compared with the metal plate at 8 and 13 GHz. The scattering EM energy is scattered to all around, as shown in Figure 6c,d, which indicates the MS has a significant inhibitory effect on main lobe at 9.5 GHz and 10 GHz, respectively. Generally, the closer it is to the center frequency of the basic unit, the better the effect of reducing RCS can be achieved. Thus, the matrix-type random coding MS allows a wideband and high efficient RCS reduction by adjusting the scattered field simply compared with works proposed before [15; 16].  
Figure 5: (**a**) RCS reduction of matrix-type random coding MS with different ratio combinations of “0” and “1” units; and (**b**) RCS reduction of coding \(a\) at \(x\)- and \(y\)-polarized wave incidence.