# Oblique Wide-Angle Multi-Sector Metamaterial Absorber for Space Applications
## 3 Measurement
### Measurement Results  
The sectorial absorber A+B was measured for angles 35\({}^{\circ}\), 45\({}^{\circ}\), 55\({}^{\circ}\) and 65\({}^{\circ}\). For the sake of comparison, two other measurements corresponding to sector A + A and sector B + B were also conducted. The overall dimensions of sector A+B, A+A and B+B are the same. The measurement results are compared with each other and also against full-wave simulations (uniform infinite array, CST A and CST B) for each angle in Figure 10.  
Figure 10: _Cont._  
Figure 9: Picture of the measurement setup. At 35\({}^{\circ}\) (Figure 10a,b), the dips are well marked and the result of sector A + B is very close to the one of the uniform sector A + A. As desired, sector A exhibits a better absorption than sector B for this angle. For TE, the frequency positions of the dips are in good agreement with simulations for both uniform absorbers. For TM, the absorption levels are well respected between simulation and measurement but the measurements are more selective and there is a frequency shift of approximately 100 Hz. Figure 10: Bistatic measurement of the sectorial absorber for TE polarization at 35\({}^{\circ}\) (**a**), 45\({}^{\circ}\) (**c**), 55\({}^{\circ}\) (**e**) and 65\({}^{\circ}\) (**g**) and TM polarization at 35\({}^{\circ}\) (**b**), 45\({}^{\circ}\) (**d**), 55\({}^{\circ}\) (**f**) and 65\({}^{\circ}\) (**h**). The measurements of sectorial absorber A + B is compared against uniform absorbers A + A and B + B and also with the simulation of uniform infinite absorbers A and B. 250 MHz for uniform absorber A + A. The absorption band remains well positioned relatively to the [2 GHz, 2.3 GHz] objective. At 45\({}^{\circ}\) (Figure 10c,d), the curves are smoother than for other measurements, which could be explained by the fact that the reflection point is located in the middle of the panel, relatively far from wedges and from the transition between the two panels (see Figure 8). Like before, the curve of sector A + B is very close to sector A + A and sector A exhibits a higher absorption than sector B for both polarizations. The measurements show more selective dips than the simulations. For TE, there is an acceptable agreement between measurement and simulation for uniform sector A despite a frequency shift of approximately 300 MHz. Sector B measurements are degraded compared to simulations. For TM, a shift of approximately \(-\)300 MHz is observed for sector A + A and sector A + B. At 55\({}^{\circ}\) (Figure 10e,f), the reflection point corresponds exactly to the transition between the two panels. For sector A + B, the backscattered signal is the complex average between the A and B contributions. For comparison, the average between reflection coefficients measured for sectors A + A and B + B (\(\varGamma_{A+A}+\varGamma_{B+B}\)/2) is also reported with the dotted black lines in the graph. For TE, there is a very good agreement between the average and the measurement of sector A + B. For TM, we also observe a good agreement between the average and the measured sector A + B. In this case, A and B are out of phase (\(\Delta\varphi=260^{\circ}\) between A and B at 2.4 GHz from measurements) which contributes to shift the dip of A + B compared to either A or B. Note that this kind of destructive interference between the backscattered field from adjacent pavings has been exploited in recent years to design metallic-only absorbers [22]. For TE, the comparison between measurement and simulation is acceptable despite a deviation in the level of the reflection coefficient for both sectors A and B. For TM, we also observe a discrepancy concerning the level, but the resonant frequencies are well respected. At 65\({}^{\circ}\) (Figure 10g,h), it is observed that, contrarily to 35\({}^{\circ}\) and 45\({}^{\circ}\), the sector A + B becomes very close to B + B for both polarizations. As expected from the design, the sector B shows higher absorption than sector A at this angle.