Impedance Well Effect From Circuit Analysis and New Design Concepts for Ultrabroadband Passive Absorber

The limitation in enhancing the absorption bandwidth of a microwave absorber with a thin thickness in the ultrahigh-frequency (UHF) band has become an important challenge in the electromagnetic scattering field. Therefore, in this study, a new design concept of a single-layer impedance-well (IW) passive absorber is put forward for the first time, which exhibits enhanced absorption bandwidth and effectively approaches the Rozanov thickness limit for passive absorbers. The design concept proposed in this study is explained by using the transmission line theory and circuit analysis. Furthermore, the input impedance and electric field distribution of the IW absorber are systematically analyzed to demonstrate the existence of the IW effect and the predicted functionalities of the IW absorber. The simulated and measured results reveal that the designed absorber with the IW effect can obtain an absorption band over 0.45–2.34 GHz range with a bandwidth ratio (BWR) of 5.2 (135.5%) at a minimum reflectivity reduction of −10 dB under normal incidence. In addition, the thickness is reduced to $0.069 \lambda _{{\mathrm {L}}}$ , which $\lambda _{{\mathrm {L}}}$ is the wavelength at the lowest operating frequency.