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.

This letter presents a frequency selective absorber (FSR) with a passband and two wide absorption bands. The structure is composed of a resistive layer and a bandpass frequency selective surface (FSS) layer. The resistive layer is a combination of metal lines with loaded resistors and rectangular spiral resonators, which generate parallel resonances. Square slots are designed in the bandpass FSS to produce parallel resonance inside the passband and perform as a metal plane outside the passband. A nearly transparent window can be obtained by adjusting the parallel resonant frequencies of two layers to be consistent. The simulation results show that the 3 dB transmission band ranges from 6.5 to 7.76 GHz, and the minimum insertion loss is 0.05 dB at 7.09 GHz. The dual-polarized FSR presents stable operating characteristics and realizes two absorption bands on both sides of the passband, and the fractional bandwidth of the reflection coefficient lower than −10 dB is up to 127%, which ranges from 2.69 to 12.04 GHz. In addition, the FSR is manufactured and measured, and the measurement results are consistent with the simulation results.

This paper presents a novel dual-polarized frequency selective rasorber (FSR) with two transmission bands and two absorption bands. The FSR has a 2-D structure composed of a lossy and a lossless frequency selective surface (FSS) layer. The unit cells of the lossy and FSS layer are both arranged to hexagonal periodic structures. The unit cell of the lossy layer is a combination of a loop with loaded resistors and three folded loops. The loop with resistors is located in the center of the unit cell, and surrounded by three folded loops. The equivalent circuit model shows that the two transmission poles are generated by two parallel LC circuits. The two absorption bands located at the lower side of the first transmission pole and between the two transmission poles are generated by series resonances. The FSR realizes two transmission poles at 6.1 GHz and 10.1 GHz, respectively. The reflection coefficient lower than -10 dB ranges from 3.24 to 10.5 GHz. The lower and higher absorption bands with absorption rates greater than 80% range from 3.3 to 4.97 GHz and 7.42 to 9.03 GHz, respectively. A prototype is fabricated and measured to validate our design and the measurement results match well with the simulation results.