A Hierarchical Impedance Matching Approach for Ultrawideband Absorbers With Wide Angular Stability

In this article, a novel approach for ultrawideband absorbers with angular stability is proposed. The hierarchical impedance matching (HIM) method is employed to reversely calculate the surface admittance based on the impedance-matching conditions. A specific portion of the overall structure is treated as a black-box model, deriving from the frequency-dependent characteristics of the surface admittance. The angle-dependent factor is incorporated to ensure impedance matching at oblique incidences, while a hierarchical layer-by-layer approach streamlines the design process for multilayer absorbers. Simulation outcomes for three absorbers employing generic units validated the effectiveness. An ultrawideband absorber with wide angular stability is fabricated and measured informed by the capacitive response at low frequencies and inductive response at high frequencies, as calculated based on impedance-matching conditions. Under normal incidence, the prototype with a thickness of
$0.09~\lambda _{L}$
exhibits a −10-dB absorption bandwidth of 171.4% from 1.46 to 19.0 GHz. Moreover, it maintains measured angular stability within a 50° incident angle for dual polarizations in such a ultrawideband. This synthesis approach intuitively unveils the relationship between absorption performance and the characteristic of the surface, promising enhanced angular stability for ultrawideband dual-polarized absorbers.