This paper presents a miniaturized frequency selective rasorber (FSR) that has a wide transmission band with low insertion loss (IL) and a wide absorption band below the transmission band. The FSR is composed of a resistive sheet and a bandpass FSS. The unit cell of the resistive sheet is a resistorloaded hexagonal metallic loop (HML), each side of which is inserted with a circular spiral resonator (CSR) in the center. The CSR is equivalent to a parallel LC circuit that has a high inductance and low parasitic capacitance. At high frequency of 10 GHz, the CSR resonates to be an infinite impedance, around which a 0.5-dB-transmission band of 8.68-11.34 GHz is produced. The bandpass FSS is a triple-layer FSS in which two layers of identical hexagonal patches are coupled through a layer of hexagonal aperture; it has a fast roll-off 0.5-dB-transmission band of 8.2- 11.33 GHz, which almost coincide with that of the resistive sheet. The 1-dB-transmission band of the FSR by placing the resistive sheet on the bandpass FSS is 8.3-11.07 GHz. At low frequency, the FSR performs as an absorber, and the 10-dB-absorption band is 2.4-7.1 GHz. Besides, due to its tiny physical sizes of only 1.2mm×1.6 mm, the CSR can be viewed as a lumped element circuit with a high inductance, in which the parallel resonance is almost independent to incident angle. The transmission performance of the FSR has a good independence of and polarizations and incident angles. A prototype of the proposed FSR is fabricated and measured to validate the design.

In this paper, we propose a method for designing checkerboard surfaces using strategically placed artificial magnetic conductors (AMCs) for wideband radar cross section (RCS) reduction. The theoretical analysis shows that the reflection phases of the two AMCs should be linear. The cancelation conditions of checkerboard structure are analytically derived using an equivalent transmission line model, and the ideal impedance conditions of the two AMCs are obtained, which serve as guidance to select patterns of two AMCs unit. A planar checkerboard surface with two kinds of AMC elements is designed for wideband RCS reduction. A 10 dB RCS reduction is observed for approximately 91.5% of the relative bandwidth (3.77-10.14 GHz) under normal incidence. A prototype of the proposed checkerboard surface is fabricated, and the measurements results show good coincidence with the synthetic studies. The bistatic RCS of the checkerboard surface is considered for both transverse electric and transverse magnetic polarizations under oblique incidence.

A novel frequency-selective rasorber (FSR) with dual-band transmission and wideband absorption property is proposed in this letter. The FSR is a two-layer structure composed of a lossy resistive sheet at the top and a lossless bandpass frequency selective surface (FSS) at the bottom, separated by an air spacer. The element of the resistive sheet is a lumped-resistor-loaded metallic dipole with a dual-resonance structure inserted in the center. The dual-resonance structure is realized by three different series LC structures in parallel, based on the Foster reactance theorem. There are two impedance poles between the three impedance zeros of the series LCs, where two transparent windows can be obtained for the lossy resistive sheet. The bandpass FSS is a simple dual-band FSS by etching two slots with different shapes and dimensions in a metallic plane. The FSR has realized two transmission bands at 7.7 GHz and 12.6 GHz, and the band with $\rm \vert S11\vert < -10 dB$ is 3.7-11.1 GHz. The design has been validated by full-wave simulation and experimental measurement.

This paper proposes a wide transmission band frequency selective rasorber (FSR) based on convoluted resonator (CR). The FSR consists of a two-layered metallic structure with an air gap in the middle. At the top layer, the lumped-resistor-loaded metallic dipole with a CR inserted into the center is applied to generate wide absorption and transmission bands. At the bottom layer, the wideband FSS is realized by a triple-layer metallic structure in which two layers of identical square patches are coupled through a layer of the square aperture. The full-wave simulation results show that the wide transmission band with low insertion loss and wide absorption band are realized. To validate the performance of the proposed FSR, the prototypes are fabricated and measured, and reasonable agreement between the simulated and measured results is obtained. The measured results show that the transmission band with insertion loss less than 1dB is covered from 9.00GHz-12.63GHz with 33.5% relative bandwidth. Compared with the previous FSRs with wide transmission band, the proposed FSR yields the widest relative bandwidth, better oblique performance, simpler design.

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%.