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To break through the limitation of harmonic loss on transmission bandwidth, a multilayer frequency‐selective rasorber (FSR) for wideband transmission is present in this letter. First, the principle of harmonic suppression implemented by a lossy layer is described and analyzed in detail. Second, based on this lossy layer, an absorption–transmission (A–T) rasorber with harmonic suppression, which can generate a wide passband above the lower absorption band, is achieved. And then, by combining with a transmission–absorption (T–A) rasorber, an absorption–transmission–absorption (A–T–A) FSR with a wide and low insertion loss (IL) passband can be obtained. The simulation result shows that the −1‐dB passband ranges from 7.1 to 17.49 GHz with 84.5% relative bandwidth. Finally, a prototype is fabricated and measured to validate the design. [ABSTRACT FROM AUTHOR]

A single‐sheet structure‐based switchable broadband FSR/absorber is proposed. The lossy layers I, II, and the FSS are printed along the direction of electromagnetic (EM) wave propagation (z‐direction) at the top, middle, and bottom positions of the substrate, respectively. A PIN diode is used in the lossy layer II and the FSS to switch their operating states. By activating or deactivating the PIN diodes, the design can operate as either an FSR or absorber. The FSR achieves a passband with an insertion loss of 0.64 dB at 3.9 GHz, and two absorption bands with fractional bandwidth of 87.6% and 20.8%, respectively. The absorber has a wide absorption band from 1.6 to 5.4 GHz (109%). It is transparent to EM waves of orthogonal polarization. The measured and simulated results are in close agreement, which exhibits stable performance under 30° of oblique incidence in both the xz‐ and yz‐planes. [ABSTRACT FROM AUTHOR]

A polarization‐insensitive frequency‐selective rasorber (FSR) with a high‐transmission passband and two wide absorption bands is proposed. The proposed FSR consists of an absorptive layer and a frequency selective surface (FSS) layer. The absorptive layer employs a four‐arm square spiral resonator with four fork shape resonators connected by lumped resistances to form broadband transmission and absorption. The FSS layer is formed by three metallic patches and two dielectric substrates, which are applied to generate a wide passband. The simulated results demonstrate that the 1‐dB transmission passband enables to obtain of 40.2% fractional bandwidth (FBW) from 9 GHz to 13.53 GHz, and the minimum in‐band insertion loss (IL) is 0.07 dB. Besides, the reflection bandwidth below −10 dB can reach 135% from 3.29 GHz to 16.90 GHz. Finally, the FSR's prototype is fabricated and measured. The results of measurement are fitted well with the simulated ones, which means that the proposed FSS can achieve broadband transmission and absorption. [ABSTRACT FROM AUTHOR]

A hybrid frequency‐selective rasorber (HFSR) with low‐frequency absorption and high‐frequency polarization conversion based on rectangular spiral resonator (RSR) is designed, which implements a broad transmission band in the middle band, simultaneously. The HFSR is made up of three components, which are separated by two air gaps. A bandpass frequency‐selective surface (FSS) is employed to realize a broad transmission window at the bottom layer, serving as a metal background of the top layer. The middle lossy layer is composed of the RSR and T‐type metallic strips with four resistors, which is used to absorb the electromagnetic waves (EMWs) in the low‐frequency band and provide a broadband transmission band. The top layer is formed by a pair of arrows to achieve the linear polarization conversion at the high‐frequency band. A four‐port equivalent circuit model (FP‐ECM) with absorbing function is established to explain the physical principle of the proposed HFSR. The simulation results reveal that the 1 dB transmission band is obtained in 7.67–12.06 GHz with a 44.5% fractional bandwidth (FBW). Besides, the co‐polarized reflection coefficients (S11 < −10 dB) are achieved in 4.51–15.81 GHz with a 111.2% FBW. Moreover, the HFSR has a stable oblique incident angle of 30° under TE‐ and TM‐polarized waves. In addition, the radar cross‐section (RCS) of the HFSR can be reduced from 3.0 to 16.0 GHz, which has a 136.8% FBW. Finally, the archetype of the designed HFSR is fabricated and tested to validate the reliability of the simulation results. [ABSTRACT FROM AUTHOR]

In this letter, a parallel‐plate waveguide (PPW)‐type transverse electromagnetic (TEM) transmission chamber covering 2–14 GHz is designed, analyzed, and fabricated, which consists of a feed structure and two metal cover plates. The feeding structure is made of a structure similar to a monoconical antenna, with a good impedance bandwidth. To reduce the edge radiation of the PPW structure, the TEM wave cell (TEM cell) is surrounded by absorbing foam. Moreover, to verify the testing effect of the designed TEM cell, a simple square frequency‐selective surface was tested in the TEM cell. The test results are in good agreement with the simulation results. It has been shown that the designed TEM cell can be used as an effective supplement to the transmission reflection test method for periodic structures. [ABSTRACT FROM AUTHOR]

Frequency-selective rasorbers (FSRs), which have absorptive and transmissive properties at different frequencies, are crucial in a wide range of applications in communication and radar engineering. However, the FSRs currently available usually exhibit a single high-performance transmission band, which cannot meet the rising demands for modern multiband communication/radar systems. In this article, we propose a dual-band frequency-selective rasorber that utilizes a cascaded metasurface and is designed with an equivalent circuit model and parameter optimization. In addition, a prototype dual-band frequency-selective rasorber is fabricated and characterized. Microwave measurements present two highly transparent peaks located near 11.5 and 17.5 GHz with an insertion loss of around 0.5 dB. Also, there are two absorption bands with absorptivities higher than 80% at 3.9–10.2 GHz and 13–15 GHz. Such low insertion loss for both transparent bands is achieved by optimizing the position of resistors through mode analysis. Our approach facilitates the manufacture of high-performance multi-band frequency-selective rasorbers for use in multi-band communication systems.

n this study, we propose a rasorber in the Ka-band as a means of reducing the radar cross section (RCS) and compare its character- istics and performance with those of state-of-the-art studies. A rasorber is a combination of a radome and an absorber. It implements the radome function while absorbing external electromagnetic waves. Frequency-dependent frequency-selective rasorber (FSR) is the most commonly used type of rasorber. An FSR, comprising lossy and lossless resonators, is designed in this study to have an electromagnetic transmission characteristic at 35 GHz through a parallel LC tank circuit. The lossy resonator located in front of the losselss resonator exhibits a broadband electromagnetic absorption characteristic due to an additional series RLC circuit. The center frequency of the trans- mission band is tuned by adjusting the resonant frequency of the LC tank circuit. Additionally, the proposed FSR is designed with a transmission band located at the end of the absorption band. It has a transmission frequency of 35 GHz with an absorption rate of 80 % or more at 7.8～28.5 GHz including the X, Ku, and K-bands. [ABSTRACT FROM AUTHOR]

This study proposes a dual-polarized frequency-selective rasorber (FSR) with a switchable wide passband. The FSR is made up of two layers: the first is a lossy frequency-selective surface (FSS), which is made up of meander lines and lumped resistors that absorb energy. The position of the lumped resistors can be determined via characteristic mode analysis. Another layer is a lossless FSS with PIN diodes for the reconfigurable function. The lossless FSS is made up of three layers for a wide passband. When PIN diodes are turned off, the absorption bands in the lower band vary from 2.73 to 3.76GHz, while the upper band ranges from 6.07 to 7.94 GHz. Meanwhile, the reflect band with a value greater than −3 dB spans the frequency range from 4.21 to 5.88 GHz. When the PIN diodes are turned on, the passband with insertion loss less than −1 dB extends from 3.82 to 5.3 GHz. At the same time, the absorption band ranges from 5.9 to 7 GHz. Due to the nonlinearity of PIN diodes, there is a certain difference between the simulated and the measured results. Also, we analyzed the influence of the inductance value of PIN diodes on the whole structure.

This paper presents an absorptive/transmissive frequency selective structure based on fiber-reinforced composite materials with adequate mechanical stability for naval ships, aircrafts, and other modes of applications. The proposed design achieved mechanical and electromagnetic stability with a) a fractal-loop-based resistive sheet that realizes broadband absorption characteristics, b) a four-legged element frequency selective surface (FSS) with bandpass-type characteristics, and c) a foam-core sandwich type e-glass /epoxy laminate. Despite the fact that the eleven-layer absorptive/transmissive FSS (AFSS) structure was associated with several performance degrading factors, such as dielectric layer losses, and losses arising from the use of multiple lumped elements (i.e., tolerance, solder joint effects), the performance of proposed design was confirmed via simulations that it had a low-transmission compound loss of 1.2 dB at the passband of 7.78 GHz and an absorption performance of 90% in the frequency range of 1.77-5.59 GHz. Following its fabrication and based on experimental measurement, it was verified that its response was very similar to the design outcome.

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.

Abstract A polarization-independent frequency selective rasorber (FSR) with a transmission band at high frequency and a broadened absorption band at low frequency is designed and analyzed in this paper. The FSR consists of a resistive sheet and a bandpass frequency selective surface (FSS). A strip-type micro resonator (MR) is developed and applied in the resistive element. The MR is equivalent to a parallel LC circuit and resonates at the transmission band. The induced surface current distributions on the resistive element at different frequencies can be controlled as expected using the MRs, so that a high in-band transmission at high frequency and an absorption band at low frequency can be obtained, which are almost independent to each other. The absorption bandwidth can be broadened by cascading more MRs with several resistor-loaded metallic strips. Besides, due to the tiny dimensions of the MRs, polarization-independent absorptive/transmissive performances can be achieved by printing two orthogonal arrays of resistive elements on different surfaces of a dielectric substrate. The performance of the FSR is verified by both numerical simulation and experimental measurement. [ABSTRACT FROM AUTHOR]

A novel dual-polarized transmissive/absorptive frequency-selective rasorber (FSR) with an ultrawide absorption spectrum covering both the X- and Ku-bands is proposed in this paper. The FSR is constructed from a bottom lossless transmission layer and a top lossy absorption layer, in which a resistor-loaded incurved square loop strip line structure is utilized to obtain an ultrawide absorption band. To quantitatively analyze its operation principle, an accurate equivalent circuit model of the proposed FSR was developed. A 2D prototype was designed, assembled, fabricated, and measured. The FSR exhibits an absorption band that ranges from 8.1 to 19.1 GHz (81%) under normal incidence, whereas the passband insertion loss at 4.5 GHz is less than 0.45 dB. The total thickness of the FSR is only 5.1 mm, which keeps low profile characteristics. The simulation agrees well with the measured results. [ABSTRACT FROM AUTHOR]

A frequency‐selective rasorber (FSR) with two low insertion loss transmission bands is proposed. The FSR is composed of the resistive sheet layer at the top and bandpass FSS layer at the bottom, and separated by air spacer. Full‐wave simulation results show that the FSR realize two transmission bands at frequencies 8.5 GHz and 10.8 GHz with 0.45 dB and 0.77 dB insertion loss. Meanwhile, the band with |S11| < −10 dB is over 4.2‐8.8 GHz and 9.2‐17.4 GHz. Compared with the reported FSR with two transmission bands, the proposed FSR in this article achieves two transmission bands with lower insertion loss and wide absorption band at high frequencies. To validate the performance of the proposed FSR, the samples are fabricated and measured, reasonable agreement between simulated and measured results is achieved. [ABSTRACT FROM AUTHOR]