Geometry- and angle-dependent monostatic scattering of microwave absorbers

The scattering behavior of microwave absorbers is an essential indicator of their quality and suitability for use in anechoic chambers. Current research activities deal with the revision of the IEEE Std. 1128 on the practice recommended for absorber characterization. In this context, the angle-dependent backscattering of microwave absorbers was studied experimentally with respect to their different geometric shapes at otherwise similar material properties. The dielectric permittivity of pyramidal and flat absorbers was measured between 1 GHz and 10 GHz, followed by systematic monostatic reflectivity measurements. The radar cross-section method was applied to derive the reflectivity with respect to different illumination angles for vertical and horizontal polarization. The measured results agree well with electromagnetic simulations of the reflectivity; they conform with the supplier specifications for normal incidence but provide additional information for oblique angles of incidence. A comparison with a metallic reference plate shows that the reflectivity patterns of the absorbers are dominated by their geometric shape, while the material properties resulted in a quantitative offset. These findings lead to a better understanding of the physical origin of the scattering phenomena of microwave absorbers in general and help to further improve the accuracy of absorber reflectivity measurements.