A Multifunctional Reconfigurable Frequency-Selective Surface With Simultaneous Switching and Tuning Capability

This article presents a multifunctional reconfigurable frequency-selective surface (MRFSS) that can switch between important electromagnetic (EM) operations (reflection, transmission, and absorption), while offering simultaneous frequency tunability. The proposed design involves metallic patterns imprinted on both sides of a single-layer FR4 substrate, with varactors placed on the top side and p-i-n diodes on both the top and bottom sides to achieve the desired switching and tuning characteristics. By articulately controlling the bias conditions of the p-i-n diodes, the novel MRFSS structure can exhibit multiple functions under different working states, whereas the frequency tunability is attained in each state by adjusting the reverse bias voltage of the varactor diode. Under the OFF (top side)-OFF (bottom side) state of the p-i-n diodes, the MRFSS exhibits a bandpass transmission response tuning from 1.68 to 2.56 GHz having an insertion loss of around 1.8–2.9 dB. The OFF-ON state depicts a narrowband absorption behavior regulating between 1.84 and 2.85 GHz with corresponding absorptivity values from 84.3% to 96.5%. The on-on state exhibits the reflection mode, having a reflection coefficient (S11) of −1.5 dB, tuning in the range of 2.55–4.62 GHz. The fourth mode (on-off) also exhibits a selective-reflection behavior between 2.48 and 4.43 GHz. A detailed analysis including the step-by-step design methodology, equivalent circuit modeling, and oblique incidence response has been presented. A prototype has been fabricated and characterized using the free space measurement technique, showing similar behaviors as those of the simulated responses. Overall, the proposed MRFSS structure with multiple switching and tuning characteristics holds great potential for various EM applications.