An Ultrathin Digital-Coding Absorber/Reflector Based on Active Frequency Selective Surface

In this paper, an ultrathin digital-coding absorber/ reflector based on active frequency selective surface (AFSS) has been proposed. The AFSS incorporates a switchable layer and metal ground. Additionally, the bias network of PIN diodes is considered and designed. Manipulating the states of the PIN diodes, four different operating states of the AFSS can be adjusted. Simulation results demonstrate that the proposed AFSS, operating as an absorber, exhibits outstanding absorptivity exceeding 90% within the frequency range of 9.43-16.51 GHz. Additionally, within this frequency range, adjusting the state of the PIN diode allows this AFSS to achieve good reflection performance as well. Remarkably, the thickness of the AFSS is only 0.072
$\lambda_{L}$
. An equivalent circuit model is also presented.