## 5 Numerical Results and Discussion
The material properties and the material layer thicknesses are the same as in Figure 2. As shown in Figure 6a,b, the RCS level for single-layer loading increases almost monotonically with an increase of \(kb\), while for multi-layer loading, the RCS is reduced with an increase in the number of layers over the entire frequency range. As for Figure 6c with \(\theta_{0}=60^{\circ}\), the RCS value does not reduce even with an increase of the number of material layers and shows complicated features over the entire frequency range. This is because, for larger incidence angles, multiple reflections occur inside the waveguide leading to resonance phenomena. Finally, let us discuss differences in the backscattering characteristics between H- and E-polarizations. From the angular dependences in Figure 7a for \(kb=3.14\) (low frequencies), the backscatter characteristics of the two polarizations are completely different from each other. It is also seen that H-polarization shows better RCS reduction characteristics than E-polarization at low frequencies. On the other hand, we observe from Figure 7b for \(kb=62.8\) (high frequencies) that the RCS characteristics for both polarizations become close to each other. Figure 8 shows a comparison of the frequency dependences between the two polarizations. It is interesting to note that there are great differences in the RCS characteristics, and in particular, the RCS oscillates more rapidly in the E-polarization than in H-polarization. This clearly shows that the resonance effect in the waveguide is stronger in the E-polarization. Figure 2: Monostatic RCS [dB] versus incidence angle \(\theta_{0}\) for \(L_{1}/2b=0.5,\ kt=1.57\). one-layer material loading (regions II\(-\)V: vacuum). two\(-\)layer material loading (regions III\(-\)V: vacuum). three\(-\)layer material loading (regions IV\(-\)V: vacuum). four\(-\)layer material loading (region V: vacuum). five\(-\)layer material loading. (a) \(kb=1.57\). (b) \(kb=3.14\). (c) \(kb=15.7\). (d) \(kb=31.4\). (e) \(kb=47.1\). (f) \(kb=62.8\). Figure 3: Monostatic RCS [dB] versus incidence angle \(\theta_{0}\) for \(L_{1}/2b=1.0,\ kt=1.57\). Other particulars are the same as in Figure 2. (**a**) \(kb=1.57\). (**b**) \(kb=3.14\). (**c**) \(kb=15.7\). (**d**) \(kb=31.4\). (**e**) \(kb=47.1\). (**f**) \(kb=62.8\). Figure 4: Monostatic RCS [dB] versus incidence angle \(\theta_{0}\) for \(L_{1}/2b=3.0\), \(kt=1.57\). Other particulars are the same as in Figure 2. (**a**) \(kb=1.57\). (**b**) \(kb=3.14\). (**c**) \(kb=15.7\). (**d**) \(kb=31.4\). (**e**) \(kb=47.1\). (**f**) \(kb=62.8\). Figure 5: Monostatic RCS [dB] versus incidence angle \(\theta_{0}\) for \(L_{1}/2b=5.0,\ kt=1.57\). Other particulars are the same as in Figure 2. (**a**) \(kb=1.57\). (**b**) \(kb=3.14\). (**c**) \(kb=15.7\). (**d**) \(kb=31.4\). (**e**) \(kb=47.1\). (**f**) \(kb=62.8\). \[\sigma=\frac{\lambda}{2}\left|U_{(+)}(-k\cos\theta)\pm V_{(+)}(-k\cos\theta) \right|^{2} \tag{90}\]0 Monostatic RCS [dB] versus normalized frequency \(kb\) for \(\theta_{0}=0^{\circ}\), \(30^{\circ}\), and \(60^{\circ}\), \(L_{1}/2b=1.0\), \(kt=1.57\). Other particulars are the same as in \[\sigma=\frac{\lambda}{2}\left|U_{(+)}(-k\cos\theta)\pm V_{(+)}(-k\cos\theta) \right|^{2} \tag{90}\]1 (**a**) \(\theta_{0}=0^{\circ}\). (**b**) \(\theta_{0}=30^{\circ}\). (**c**) \(\theta_{0}=60^{\circ}\). \[\sigma=\frac{\lambda}{2}\left|U_{(+)}(-k\cos\theta)\pm V_{(+)}(-k\cos\theta) \right|^{2} \tag{90}\]2 Comparison of the monostatic RCS [dB] versus normalized frequency \(kb\) between E- [46] and H-polarizations (this paper), \(L_{1}/2b=1.0,\ kt=1.57\). (**a**) \(\theta_{0}=0^{\circ}\). (**b**) \(\theta_{0}=60^{\circ}\). \[\sigma=\frac{\lambda}{2}\left|U_{(+)}(-k\cos\theta)\pm V_{(+)}(-k\cos\theta) \right|^{2} \tag{90}\]3 Comparison of the monostatic RCS [dB] versus incidence angle \(\theta_{0}\) between E- [46] and H-polarizations (this paper), \(L_{1}/2b=1.0,\ kt=1.57\). (**a**) \(kb=3.14\). (**b**) \(kb=62.8\).