Performance comparison of finite size ultra thin microwave absorbers by means of bistatic scattering cross section and absorption efficiency

This paper proposes a method to evaluate the performance of microwave absorbers in free space environment based on the bi-static scattering cross section and the absorption efficiency. Evaluation based only on reflection at boresight is not sufficient since information concerning wave scattering on the sphere surrounding the absorber is unknown. To illustrate the method, we design an ultra-thin absorber (12 × 12 cells with total area of 10 cm × 10 cm) for the X-band and compare it in terms of the proposed parameters with a commercial laminate absorber `Eccosorb DSF-10´ of similar surface area. Performance evaluation is done for several incidence angles. It is shown that the Eccosorb DSF-10 has slightly better absorption efficiency at low incidence angles. However at incoming angles ≥ 45° the ultra-thin absorber shows better absorption efficiency. To evaluate the scattering intensity in the specular direction, we use the ratio of the bi-scattering cross section in that direction to the total scattering cross section. At lower incoming angles, the Eccosorb DSF-10 has lower ratios (i.e. better performance) while at higher incoming angles (≥ 60°), the ultra-thin absorber has lower scattering in the specular direction.