This paper presents a frequency selective surface (FSS) with a wideband second-order bandpass response in the dual-band of microwave and millimeter wave. The overall structure consists of three layers of metal pattern and two layers of thin dielectric substrate. The top and bottom metal layers have capacitive patches with integrated curled Jerusalem cross slot resonators, while the intermediate metal layer has an inductive grid structure with cross-shaped slot resonators. The incorporated slot resonators play a pivotal role in achieving the desired transmission poles or zeros, which enable a wideband second-order filtering response in the dual-band and a quick roll-off at the passband edges, increasing the efficacy of electromagnetic shielding. To fully investigate the structure's frequency response, an equivalent circuit model of the structure is created, spanning the complete frequency range of 5–50 GHz. Physical samples are created and measured to confirm the suggested approach’s efficacy. The passband center frequencies of the FSS are found at f₁ = 19.42 GHz and f₂ = 42.78 GHz, and the − 3 dB bandwidth is 4.34 GHz (17.25–21.59 GHz) and 8.54 GHz (38.51–47.05 GHz), respectively. The simulation results align well with the experimental data. The transmission response rapidly transitions from the passband to the stopband at the passband boundaries.

This work proposes a frequency selective metasurface (FSM) with two transmission windows within the wideband RCS reduction band. First, to achieve dual transmission windows, dual-band and triple-band artificial magnetic conductors (AMCs) are introduced as the two elements of the FSM. Second, the input reactance conditions of the two elements under the reduction condition are derived, and the circuit parameters are optimized to meet these conditions. Furthermore, the transmission and RCS reduction performance after arraying are analyzed based on array theory. Third, based on the corresponding equivalent circuit models, two dual-layer structural elements are designed and arranged in a checkerboard pattern. Finally, a metasurface prototype is fabricated and experimented with. The experimental results demonstrate that the proposed FSM exhibits a -10 dB RCS reduction from 4.2 to 13.9 GHz and transmission windows with insertion losses of -1.45 dB at 7.3 GHz and -1.52 dB at 12.6 GHz.

This paper presents an ultra-wideband dual bandpass frequency selective surface (FSS) that exhibits outstanding transmission characteristics and a miniaturization feature in the required frequency band. In order to obtain a dual-band filtering response, initially, a specific topological structure of a dual-band bandpass microwave filter is theoretically investigated and using periodic structures with capacitive, inductive, or resonant-type surface impedances synthesizes its components. Subsequently, employing a compact cascaded hybrid resonant element to construct the FSS, which is composed of convoluted strip grids (CSG), convoluted square rings (CSR), and square rings arranged on different layers. In addition, an accurate equivalent circuit model (ECM) is constructed to analyze the working mechanism of the proposed FSS. Finally, the designed FSS is made and measured. The results indicate that the designed FSS achieved -3 dB bandwidths of 105.4% from 1.01 to 3.26 GHz and 47.8% from 3.75 to 6.10 GHz, respectively. At the center frequency of the first passband, the FSS's size is as compact as 0.056λ ₀ × 0.056λ ₀ . The test results obtained are in good agreement with the results of the full-wave simulation and show excellent resonant stability with respect to different polarizations and incident angles up to 45°.

This work proposes a metasurface capable of achieving a -20dB radar cross section reduction (RCSR) with a relative bandwidth of 123.6%. First, the RCSR performance achieved by introducing phase cancellation and absorption mechanisms within the same frequency band. The focus is on deriving the relationship between the number of non-planar metal ground units and the reduction bandwidth. Second, a circuit analog absorber (CAA) structure is designed to achieve broadband absorption functionality. Additionally, the RCSR performance of the non-planar metal ground with randomly arranged units is analyzed. Finally, by replacing the ground of the CAA with a non-planar metal ground, enhanced scattering performance is achieved. A metasurface prototype is fabricated, assembled, and measured for its reflection performance. The experimental results align well with the simulation results, showing a reduction of more than -20dB from 3.4 to 14.4GHz.

Developing a metamaterial absorber (MA) with both flexibility and temperature insensitivity continues to be a challenge in the field of radar stealth. In this paper, we propose a compensation method for designing flexible and temperature-insensitive MA. This method is revealed through the relationship between the square resistance of the resistive film, the permittivity of the substrate, and the temperature. Importantly, the compensation method is applicable to both the MA in the plane state and the bending state. By utilizing the benefits of the compensation mechanism and the flexible designability of the bilayer cross-shaped structure, the flexible MA proposed in this paper can achieve temperature-insensitive absorption across a broad frequency range. Experimental results indicate that the absorption peaks achieve an absorptivity greater than 90% within the frequency of 7.2–9.4 GHz, exhibiting excellent temperature stability from 25 °C to 300 °C. In comparison to previous studies on flexible MAs, this design offers a distinct advantage in high-temperature environments and provides valuable guidelines for the design of integrated multi-functional absorbers in practical applications.

In this article, a dual-passband reconfigurable frequency-selective surface (DRFSS) with continuous and connected passband tuning ranges is proposed. First, an equivalent circuit analysis of the DRFSS is conducted to evaluate the impact of design parameters on the two passbands’ transmission performance. In addition, the influence of varactor diodes on the tunable bandwidth is analyzed. Second, based on the analysis, a design method is proposed. Third, a composite unit cell structure is developed, incorporating two parallel groups of identical varactors for simultaneous dual-passband tunability, with an isolated bias network ensuring polarization-independent performance. Finally, prototypes for parallel-plate waveguide (PPW) and free-space measurements are fabricated and measured. Experimental results agree well with simulations, verifying the superior performance and feasibility of the proposed DRFSS. Key features include a tunable relative bandwidth (RBW) of up to 119.0%, high-transmission efficiency within the passbands, and the distinctive characteristic of connected tunable passbands. In addition, the design can be adapted for independently tunable passbands as needed.