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 novel design for radiation pattern-reconfigurable antenna is described in this letter. The design is based on a wideband Vivaldi antenna structure. Two different radiation patterns are achieved by switching the feeding paths to obtain two antennas operation modes, monopole mode and Vivaldi mode. The reconfigurable antenna can adjust the radiation patterns by controlling the bias voltage of pin-diodes. Therefore, by combining the two radiation patterns, a broad coverage of reconfigurable pattern is generated. In addition, the pattern reconfigurable antenna can operate at a wide frequency band from 2.7 to 12GHz. Details of the simulated and experimented results for the pattern-reconfigurable antenna are shown.

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, 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.