An improved dual-polarized multifunctional active frequency selective surface (MAFSS) with parallel-feeding configuration is proposed in this paper. The designed structure is composed of two metallic layers separated by a thin dielectric layer. Three independent and controllable functions of electromagnetic switching, polarization selection and frequency tuning are integrated together into the proposed structure via introducing PIN diodes and varactor diodes. To reduce the negative effects of extra feed lines, FSS elements themselves play a significant role in connecting the active components and allowing the direct currents to flow through. A special biasing configuration is designed to provide parallel bias voltages for the two different types of active devices. Finally, an FSS prototype is fabricated and measured, and the measurement results as well as the simulation results both demonstrate great performance of the MAFSS structure. In addition, the proposed structure also perform well under circumstances of oblique incidence and different polarization.

This paper proposes a 2-b multifunctional active frequency selective surface (MAFSS) whose structure is made up of two metallic layers printed on both sides of an F4BME substrate, measuring $320 \times 320 \times 0.8$ mm ³ . The PIN diodes, embedded on two metallic layers, are controlled through two independent sets of external dc bias network. No additional feeder lines are considered necessary within the MAFSS array, which weakens the bias network's negative impact on the transmission characteristics of the MAFSS. Using an innovative and effective diode switching technique, two functions (electromagnetic switch and polarization selection) and thus four working states (dual-polarized bandpass for code “00,” dual-polarized shielding for code “11,” TE wave selection for code “10,” and TM wave selection for code “01”) have been realized. The equivalent circuit method and the surface current analysis have been used for a better understanding of the physical principles of the design. A prototype of the proposed structure has been fabricated and measured. The measurements have shown a good agreement between the simulated and the measured results, demonstrating thereby that the proposed structure can give excellent performance. Using the results of extensive numerical and experimental studies, the proposed structure has also been proved to give stable performance, with respect to different incident angles and wave polarizations around LTE-2.1 GHz.

A wideband and polarization-insensitive absorber/reflector with multifunctional characteristics is proposed in this paper. The designed structure comprises a switchable layer, an air spacer and a metal ground. The switchable layer contains active resonant elements, whose switching properties are realized by controlling PIN diodes. Bias networks for the PIN diodes are integrated into the structures and no dedicated bias lines are required. Thus, the negative effect of extra bias lines can be alleviated. In order to achieve switchable and polarization-insensitive properties simultaneously, a super-element configuration is developed by combining four similar unitary elements. One unique feature of the designed device lies in its real-time and multifunctional capability to switch among multiple working states. In addition, the switchable bandwidth of the proposed structure covers a much wider frequency band compared to previous switchable absorber/reflector designs. Distributions of electric field and surface current as well as an equivalent circuit model are presented to gain the necessary physical insight into the working mechanism of the switchable structure. Finally, a prototype of the proposed design is fabricated and measured for validation.

In this communication, a switchable active metasurface (SA-MS), with functions for absorption and polarization conversion, is proposed. The metasurface comprises rotated cross loops that are loaded with four sets of parallel-connected lumped resistors and PIN diodes on each arm. When the PIN diodes are in the OFF state, the proposed structure performs broadband absorption functions from 3.7 to 10.7 GHz. When the PIN diodes are in the ON state, those parallel lumped resistors are shorted and the structure transforms into a rectangular loop that converts the x(y)- to a y(x)-polarized one from 5.9 to 9.6 GHz. Furthermore, the proposed SA-MS and its mirror symmetry structure are used as the meta-atoms in the chessboard array. Such implementation can achieve backward radar cross-section (RCS) reduction based on the phase cancellation principle in the conversion mode without any impact on the absorption function. Moreover, the scattering pattern of the checkerboard structure in the transition mode is more varied than that in the absorption mode. The two different modes provide flexibility for the RCS reduction and enable it to cope with complex electronic reconnaissance. Finally, a chessboard and uniform arrays sample printed on the FR4 dielectric layer have been fabricated and measured. The experimental results are consistent with the simulated results.

In this paper, a 2.5-D approach has been used to design 2.5-D miniaturized multifunctional active frequency-selective surfaces (2.5-D MMAFSSs). The unitary element, based on the via-connected metal strips and metallic parallel plates, can be miniaturized to 0.063λ ₀ , where λ ₀ is the free-space wavelength. To achieve the relative polarization symmetry, four similar subcells based on the unitary element are combined together to constitute a 2.5-D MMAFSS unit cell. The novelty of the proposed design lies in four independent operating states that can be realized by actively changing the on-off states of p-i-n diodes. In addition, the miniaturized configuration is beneficial for the easy realization of multiple electromagnetic states with great angle stability and polarization insensitivity. For a better understanding of the physical principle, the analyses of both surface current and electric field distributions are conducted at resonance frequencies. Also, the equivalent circuit models are established to further clarify the working mechanism of the structure. Finally, a prototype of the 2.5-D MMAFSS operating at 1.9 GHz is fabricated and measured to validate the proposed concept, and the experimental results are in satisfactory agreement with the simulated ones.

A frequency selective surface (FSS) absorber with a biasing control system is presented in this letter. The absorber consists of the top-layer FSS structure, the bottom-layer metal sheet, and an air spacer in between. The biasing circuit is controlled by a single-chip microcomputer with constant current outputs and each output port is connected to one p-i-n diode, which is employed to realize different absorption bands by controlling the induced current distribution. Both simulated and measured results demonstrate that fast switching function can be realized within certain frequency ranges (3.62-5.35 GHz and 7.92-9.27 GHz) with the absorption depth below -10 dB.