This paper presents a frequency-selective rasorber whose transmission window locates at the higher frequency of absorption band. The accomplished rasorber is composed of dipole-like and slot arrays, and has realized the transmissive/absorptive performance. In every unit cell, each pair of dipole-like elements connected by vias is printed on the two sides of the substrate, and the coupling between long and short dipoles is suppressed by this structure. A guiding circuit is studied based on the analysis of the current path, and the insertion loss of transmission window is significantly reduced by the surface current at the pass-band that is hindered to pass through lossy elements. The presented rasorber acts as an absorber at the low frequencies, while providing a high transmittance window at 5.6 GHz. This design is elaborately optimized to achieve low reflection and angle-insensitive performance. Finally, the presented structure is validated by numerical simulations and experimental measurements. This rasorber could be used for secrecy communications among stealth facilities while providing stable broad-band absorptive properties.

In this Letter, a new frequency-selective absorber (FSA) is presented that has wide-band transmission/absorption/reflection reduction responses. The presented absorber is completed by lossy cross-dog bone and lossless second-order frequency-selective surfaces (FSSs). The modal interaction pole generated by the lossy array is employed to achieve a wide-band transmission. Three absorption bands are combined to realize a continuous stop-band with high absorptivity. Furthermore, the improved absorber structure is investigated to reduce the strong reflection between the absorption and transmission bands. The 10 dB reflection reduction is obtained with a fractional bandwidth of 126.4%. Meanwhile, the - 3 dB fractional pass-band width is 41.3% with minimum insertion loss (IL) of 0.37 dB. The absorption bandwidth of 91.5% is provided with at least 90% absorptivity. The distance between the lossy and lossless layers is only 0.08 $\lambda_L$ L at the lowest operating frequency. Finally, the proposed design is validated by a good agreement between the numerical simulations and experimental measurements.

In this Letter, an active second-order frequency-selective surface (AFSS) that features a switchable wide pass-band is proposed. Compared to other multi-layer feeding structures, only one layer of FSS is elaborately reconfigured in this design, whose full planar symmetry structure is not destroyed, to achieve the desired all-polarized controlled behavior. The presented design provides good responses under different incident angles and polarizations. The fulfilled structure is composed of three FSS layers and is controlled by semiconductor switches. When the switches are in OFF-state, the proposed design acts as a high-transmittance second-order filter with a low ripple level, whose -0.5 dB passband width is over 24.4% and minimum insertion loss is only 0.1 dB. By switching the semiconductors to ON-state, the unit cells of the top FSS layer are short-connected, which leads to an ultra-wideband shielding behavior from 0 to 10 GHz. Moreover, the proposed structure presents consistent responses under 0°-90° rotation polarizations. Both filter and shielding responses can be obtained up to the 60° incidence. Finally, a prototype is fabricated and measured, and the desired wideband, high-efficiency, wide-angle, and polarization-insensitive switchable performances are obtained through equivalent-circuit calculations, numerical simulations, and experimental measurements.

In this article, a novel multifunctional reconfigurable wideband frequency-selective surface is proposed. Compared with the conventional structures that can only realize two switchable states of transmission and reflection, this design could independently manipulate the TE and TM waves through four modes. Second-order equivalent circuits based on two polarizations are studied to solve the impedance mismatch caused by the asymmetric structure and biasing system, by using compensation capacitors. With different biasing voltages, the passband and stopband can be achieved by second-order filter and multireflection responses, respectively. Each mode does not affect the others, while their transmission or reflection performances in the corresponding modes are almost the same. From 0° to 45° incidences, in the transmission state, high-transmittance windows (the minimum insertion loss is 0.1 dB) with a −3 dB fractional bandwidth of 43.2% are realized. When this design operates in the shielding state, it can prevent the incident energy from penetrating the structure with extremely stable oblique incident performances from lower frequencies to 11 GHz. Finally, a prototype is fabricated for measurements, and the proposed design is validated by the calculated, simulated, and measured results.