The simultaneous improvement in radiation and scattering performance of an antenna is normally considered as contradictory. In this paper, wideband gain enhancement and radar cross-section (RCS) reduction of Fabry-Perot (FP) resonator antenna are both achieved by using chessboard arranged metamaterial superstrate (CAMS). The CAMS is formed by two kinds of frequency selective surfaces (FSSs). The upper surface of CAMS is designed to reduce RCS based on phase cancellation principle, and the bottom surface is used to enhance antenna gain on the basis of FP resonator cavity theory. Both simulated and measured results indicate that, compared with primary antenna, the gain of the proposed FP resonator antenna is enhanced by 4.9 dB at 10.8 GHz and the 3-dB gain bandwidth is from 9.4 to 11.1 GHz (16.58%). Meanwhile, the RCS of the proposed FP resonator antenna is reduced from 8.0 to 18.0 GHz, with peak reduction of 39.4 dB. The 10-dB RCS reduction is obtained almost from 9.6 to 16.9 GHz (55.09%) for arbitrary polarizations. Moreover, the in-band RCS is greatly reduced, owing to the combined effect of CAMS and FP resonator cavity.

This paper proposes a dual-polarized dual-band frequency selective rasorber (FSR) with low insertion loss, which is a two-tier structure. At the top layer, two interdigital resonators with different length, which are adopted to achieve two transmission bands, are inserted into the center of the lumped-resistor-loaded metallic dipole. At the bottom, the bandpass FSS consists of two square slots with different size, and its resonance frequencies are the same as the top layer. Thusly electromagnetic waves can transmit through the FSR with low insertion loss. Full-wave simulation results show that the proposed FSR achieves two transmission bands at 8.5GHz and 10.8GHz with 0.15dB and 0.31dB insertion loss respectively. To validate the performance, the proposed FSR is manufactured and measured, the measured results tally well with the simulated results. Compared with the reported dual-band FSR previously, the proposed FSR is dual-polarized, the insertion loss at two transmission bands is highly improved, and the absorption performance besides transmission band at high frequency is realized.

In this article, the frequency-selective rasorber (FSR) built on multilayer resistive sheets, which achieves a broad absorption band, was proposed. First, the detailed analysis of the absorption and transmission performance for FSR with the single-layer/multilayer resistive sheets based on the equivalent circuit model (ECM) was demonstrated, which proved that the FSR with the multilayer resistive sheets can obtain a broader absorption band. Second, the multilayer resonator (MR) of a smaller size and higher design freedom compared with single-layer resonator was proposed. Then, the FSR on the basis of multilayer resistive sheets using MR was designed. It consists of the three-layered metallic structures and separated by an air spacer. For the top and middle layers, the lumped-resistor-loaded metallic dipole with the MR inserted into the center was applied to generate a wide absorption band and transparent window, respectively. For the bottom layer, the square-slot frequency-selective surface was optimized to match the transmission band of the resistive sheet. Simulated and measured results show that the broad absorption band and transmission band with low insertion loss have been realized, and the proposed FSR yields the widest relative bandwidth $\vert S_{11}\vert \le -10$ dB of 145.2%.

A double-layer complementary metasurface (MS) with ultra-wideband polarization conversion is presented. Then, we propose two application cases by applying the polarization conversion structures to aperture coupling patch antenna (ACPA). Due to the existence of air-filled gap of ACPA, air substrate and dielectric substrate are used to construct the double-layer MS. The polarization conversion bandwidth is broadened toward low-frequency range. Subsequently, two application cases of antenna are proposed and investigated. The simultaneous improvement of radiation and scattering performance of antenna is normally considered as a contradiction. Gratifyingly, the contradiction is addressed in these two application cases. According to different mechanism of scattering suppression (i.e., polarization conversion and phase cancellation), the polarization conversion structures are utilized to construct uniform and orthogonal arrangement configurations. And then, the configurations are integrated into ACPA and two different kinds of metasurface-based (MS-based) ACPA are formed. Radiation properties of the two MS-based ACPAs are improved by optimizing the uniform and orthogonal arrangement configurations. The measured results suggest that ultra-wideband polarization conversion properties of the MS are achieved and radiation enhancement and scattering suppression of the two MS-based ACPAs are obtained. These results demonstrate that we provide novel approach to design high-performance polarization conversion MS and MS-based devices.

This paper aims to achieve a high-transmittance varactor-tunable frequency selective surface (FSS). First, the impedance condition for the high-transmittance FSS is deduced. Next, a square-slot FSS loaded with varactors, owns the empirical formulas for equivalent circuit parameter extraction, is selected to demonstrate the proposed method for realizing a high-transmittance varactor-tunable FSS. Several conclusions are deduced and verified through the full-wave simulation. To illustrate the effectiveness of the proposed method, two FSSs operating at the same frequency are designed. The simulation and measurement results show that the FSS with the higher transmission rate follows the deduced conclusions. Note that the transmission rate of the varactor-tunable FSS is more than 77.8% (S21 = 1.09dB) from 4.84 to 5.9GHz when the bias voltage applied to the varactors is tuned from 5 to 20V. Compared to the reported tunable FSSs, the varactor-tunable FSS achieved in this paper obtains the highest transmission rate over the tunable transmission band.