Ultrawideband Dual-Polarized Frequency-Selective Absorber With Tunable Reflective Notch

An ultrawideband dual-polarized frequency-selective absorber (FSA) with a tunable reflective notch is proposed in this communication. The structure is constructed by combining a broadband FSA as well as a tunable lossless frequency-selective surface (FSS). The FSA consists of a lossy layer and an air spacer, which is backed with a metal plane. Varactors are employed in the lossless FSS and a dc bias is applied to adjust the frequency of the reflective notch. An equivalent circuit model (ECM) of the notch-tunable FSA is established to explain the operating principle, and the impedance condition of the ultrawide absorptive band is discussed. The ECM results agree well with the frequency-domain simulation results. The absorption band with a reflection coefficient below -10 dB extends from 2 to 8 GHz. It is worth mentioning that the reflective notch with nearly perfect reflection is demonstrated to be tuned from 2.24 to 4.56 GHz. A prototype of the structure is fabricated and measured to validate the design concept. Its measured absorption band from 2.5 to 8 GHz is in favorable agreement with the simulated results. These findings will be useful for designing intelligent antenna reflector systems with out-of-band radar cross section (RCS) reduction.