Multifunctional Frequency Selective Rasorber With Dual Mode and Continuous Tunability

This article introduces a multifunctional polarization insensitive frequency selective rasorber (MF-FSR) comprised of periodic metallic patterns printed on two dielectric substrates and separated by an air-spacer. The novelty of the proposed MF-FSR lies in its combined feature of mode switching and frequency tuning characteristics. This uniquely offers a real-time and multifunctional capability to switch from "rasorber mode (FSA-T)" into an "absorber with notch band (FSA-N)" mode where both modes support continuous tunability of their "transmission" or "notch" band. By controlling the reverse bias voltage of the embedded varactor, the transmission band in FSA-T mode can be tuned from 3.76 to 4.26 GHz with a very low insertion loss in the range of 0.62-0.95 dB. In complementary FSA-N mode, the notch band is also tunable from 4.17 to 4.71 GHz. Moreover, the same varactor set can control the tuning of transmission or the notch band depending upon MF-FSR's basic state of operation which is further independently controllable by the p-i-n diode. Equivalent circuit models are also thoroughly examined. Finally, a prototype is fabricated and experimentally tested, showing a good agreement with the predicted results.