An Active Metamaterial Absorber With Ultrawideband Continuous Tunability

In this paper, an active metamaterial (MM) absorber loaded with PIN diodes is proposed. By adjusting the bias currents of PIN diodes to change the value of the introduced equivalent resistance, the Q factors of multiple resonances of the whole structure are altered. Therefore, multiple broadband absorption states with moderate absorption performance at different frequencies are obtained. These states cover continuously tunable absorption frequencies in an ultrabroad frequency band. Bias circuits for PIN diodes are also specially designed to obtain polarization-insensitive absorption performance. Optimizing works were carried out by analyzing the operating mechanism based on the simulated field distribution and power loss distribution. The presented absorber covers an ultrawideband absorption bandwidth with a reflection coefficient below -10 dB from 0.78 GHz to 4.62 GHz (142.2% in relative bandwidth) by adjusting the PIN diodes. It is worth noting that the absorption bandwidth of the low-resistance state reaches 21.0% in the P band, which greatly improves performance in the low-frequency regime. The absorber also shows good angular stability under oblique incident angles from 0° to 30°. In addition, the total thickness of the absorber is only 1/16 of the wavelength at the lowest operating frequency with an areal density of 2.06 kg/m
²
.