# Design of a Polarization-Insensitive and Wide-Angle Triple-Band Metamaterial Absorber
## 3 Analysis and Discussion
The top and bottom metal surfaces are separated by a dielectric, which can be equivalently modeled as capacitance C6. In addition, resistors R1, R2, and R3 are placed in each branch to represent the energy dissipation caused by electromagnetic resonance within the absorber when it is excited by the incident electromagnetic wave. The equivalent circuit was simulated using ADS software, and the two-port \(S_{11}\) results were compared to the full-wave simulation \(S_{11}\) results from CST, as shown in Figure 9. It can be seen that, except for the relatively large deviation at the third absorption peak, the results from both methods show a high level of agreement in the other frequency bands. This fully demonstrates the feasibility of using ADS for equivalent circuit analysis. Furthermore, considering that the equivalent circuit theory of frequency-selective surfaces is essentially an adaptation of antenna theory, the deviation observed at the third absorption peak remains within an acceptable range. Next, we analyze the polarization sensitivity of the MMA and the impact of different incidence angles on its absorption performance. Figure 10a shows the absorption spectra under a normal incidence of a plane wave as the polarization angle changes. The polarization angle increases from 0 degrees to 90 degrees, with an amplitude of 15 degrees. It can be observed that the MMA's absorption performance remains almost unchanged for incident waves with different polarizations. This phenomenon occurs because the designed MMA has a high degree of geometric symmetry, as shown in Figure 11. This high symmetry ensures that the energy loss caused by electromagnetic resonance and the magnetic response within the MMA remains consistent for incident waves with varying polarizations, indicating that the MMA is polarization-insensitive [71]. Figures 10b and 10c show the absorption spectra for TE and TM incident waves at different incidence angles, respectively. For TM waves, the incident wave retains all magnetic field components. As the incidence angle increases from 0\({}^{\circ}\) to 80\({}^{\circ}\) in 10\({}^{\circ}\) increments, all three absorption peaks remain clearly visible. As shown in Figure 10c and Table 2, when the incidence angle increases from 0\({}^{\circ}\) to 70\({}^{\circ}\), the absorption efficiency of the three peaks remains above 90%, maintaining a high level. Only when the incidence angle reaches 80\({}^{\circ}\) does the absorption efficiency at around 4.3 GHz and 7.5 GHz drop to 72.6% and 82.2%, respectively, while the absorption efficiency at 14.8 GHz remains largely unchanged, staying above 97%. On the other hand, as the incidence angle exceeds 30\({}^{\circ}\), two new absorption peaks emerge between the second and third absorption peaks. The absorption efficiency of these new peaks increases with the incidence angle, reaching over 90% and 60% when the angle reaches 80\({}^{\circ}\). The appearance of these new peaks can be attributed to additional electromagnetic resonances occurring at other frequencies between the electromagnetic wave and the fixed MMA structure under oblique incidence, resulting in secondary absorption peaks. For TE waves, as shown in Figure 10b and Table 3, the situation is similar to that of TM waves. The difference is that when the incident angle of TM waves reaches 80\({}^{\circ}\), the absorption efficiency of the first two absorption peaks drops to below 90%, while when the incident angle of TE waves changes to 60\({}^{\circ}\), the absorption efficiency of the three absorption peaks has greatly attenuated, dropping to below 90%. When the incident angle increases to 80\({}^{\circ}\), the absorption efficiency of the three absorption peaks is further reduced to 46.7%, 72.4%, and 57.1%. Compared to the TM wave, the absorption efficiency of the first and third absorption peaks decreased by more than 50%.