In this article, a broadband radar cross section (RCS) reduction metasurface with a reconfigurable high-selectivity passband is proposed. Based on the equivalent circuit analysis, the feasibility of achieving the high-selective passband with multimode working state and RCS reduction near the passband through the combination of the checkerboard metasurface and the switchable bandpass frequency selective structure (FSS) is verified. The switchable FSS in the bottom layer can realize the function of wave transmittance/reflection by controlling the on/off states of the p-i-n-diodes, and a novel staggered patch structure is introduced to realize the fast conversion between different working modes without using complex feeding networks. The checkerboard metasurface in the upper layer not only realizes the RCS reduction function through scattering cancellation but also improves the passband selectivity of the switchable FSS under different working modes. Finally, a prototype of the proposed structure is fabricated and measured. The measured results show that the proposed structure can be flexibly switched between the three working modes. In different working modes, the structure has a wide RCS reduction bandwidth and a high-selective passband.

In this work, an ultra-thin frequency selective surface is developed with a square unit cell loaded with three ring slot pairs. The outer ring slot pair is loaded with metal shorts It achieves one polarization-insensitive passband with sharp transition at Ka-band. The design is verified with full-wave simulated results, as well as the measured results. The fabricated FSS has a flat passband and its measured 3-dB bandwidth is from 33 GHz to 37.5 GHz. A complete angular stability study of the FSS has been conducted. Meanwhile, it can directly attach to the aperture of the horn antenna to lower the whole profile of FSS-antenna configuration. Working as a radome, this FSS can be a good candidate for radar communications and radar cross section reduction in radar stealth research area at Ka-band.

A dual-absorptive-bands frequency selective rasorber with Minkowski loop arrays is proposed in this letter, which has a passband and two absorptive bands on either side of the passband. In our design, this structure consists of a lossy layer and a frequency selective surface (FSS) layer. These two layers are isolated by air. The lossy layer is composed of Minkowski loop arrays with branches and resistors loaded on the loop, and the FSS layer is a metallic array composed of grids and square loops. Based on the equivalent circuit model and the surface current distribution, the electromagnetic characteristics of the frequency selective rasorber (FSR) are studied, and the simulation results show that the structure has a passband with an insertion loss of 0.36 dB at 7.65 GHz. Additionally, the fractional bandwidth of $-$ 10 dB reflection reaches up to 119.3% under normal incidence and has good stability under oblique incidence. Furthermore, the FSR is fabricated and measured to verify our design and demonstrates good agreement with the simulations.

A miniaturized dual-bandstop frequency selective surface (FSS) using convoluted structures is proposed. The working central frequencies of the proposed FSS are 2.66 GHz and 5GHz with -0.5dB bandwidths of 0.6 GHz and 0.5 GHz respectively. The size of the unit cell is 6.88mm which is about 5.9% of the wavelength at the first working frequency. The equivalent circuit and current distributions are introduced to explain the FSS frequency performance. A prototype of the proposed FSS is fabricated and measured. The simulation and measured results show that the working frequencies, the bandwidths of the passband and two stopbands of the the proposed FSS have excellent stabilities under different polarizations and incidence angles. This FSS is a good candidate to isolate the wireless networks.

In this letter, a hybrid multiorder wide bandpass frequency selective surface (FSS) with high selectivity and low insertion loss is achieved by combining the two-dimensional (2-D) FSS structure and the 3-D vertical structure. The 3-D periodic vertical printed circuit board pieces (PVPCB) are used as the dielectric layer in the unit cell to achieve a proper band flatness without introducing great insertion loss. The multiorder response of the proposed FSS is achieved using a series of 3-D PVPCB instead of stacking the 2-D FSS layers. The proposed FSS unit cell is constructed by combining the full-wave and equivalent circuit simulations, since the physical structures have a good one-to-one correspondence with the circuit elements. The module design method is used to accelerate the design procedure, and the simulation result proves the effectiveness of this design method. Finally, the prototype is fabricated and measured to prove the effectiveness of the proposed FSS. The measured relative bandwidth and rectangle coefficient achieved is 130.4% and 0.76, respectively. The measured maximum insertion loss over the whole passband is 0.7 dB. Because of its strong capability of out-of-band rejection, the proposed FSS structure is a good candidate to enhance high-frequency electromagnetic pulse protection of wideband radar systems.

In this letter, an frequency selective surface(FSS) structure by combining parallel LC resonators is proposed to achieve wideband performance. The metal vias are used to connect top layer and bottom layer so that the equivalent element in the circuit can be enlarged or minished. The metal vias minimize the unit size greatly which achieves 0.0624 $\lambda$ . The bandpass performances of TE and TM polarizations are achieved by different parts- $S_{TE}$ and $S_{TM}$ and the structure is further miniaturized by making cross with $S_{TE}$ and $S_{TM}$ . The FSS has steep roll-offs at the edges of the passband according to the simulated results.The prototype of the proposed FSS is manufactured and tested. The measured -3dB bandwidth is from 1.3GHz and 4GHz, its relative bandwidth can achieve 110%. The thickness of the proposed FSS is 0.254mm. The measured results show the proposed FSS has better polarization and incident angle stabilities compared with other FSSs. This FSS is a good candidate to strengthen the detectivity performance of S-band active radar and isolate communication system.