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In this paper, a fast response and miniaturized phase shifter is proposed based on liquid crystals (LCs). The proposed phase shifter is implemented utilizing a slot line-based loaded line structure. The high characteristic impedance of the slot line effectively enhances the phase-shifting capability per wavelength, facilitating the miniaturized design. A cascaded ABCD matrix is employed to analyze the electromagnetic characteristics of the periodic unit, guiding the phase shifter design. In addition, a high-impedance bias network is adopted to apply DC bias. The experimental validation illustrates that the proposed phase shifter achieves a phase shift of 225 degrees per wavelength at 14.125 GHz. The reflection coefficient vertical bar S-11 vertical bar remains below -10 dB across the 13 GHz to 15 GHz, and the figure of merit (FoM) reaches 118.7 degrees/dB at 14.125 GHz. Furthermore, the millisecond-level response time provides additional competitive advantages for high-frequency applications, particularly in potential uses for satellite communications and radar systems.

A dual-passband single-polarized converter based on the band-stop frequency selective surface (FSS) with a low radar cross-section (RCS) is designed in this article. The unit cell of the proposed converter is formed by a polarization layer attached to the band-stop frequency selective surface. The simulation results reveal that the co-polarization reflection coefficients below -10 dB are achieved in 3.82-13.64 GHz with a 112.4% fractional bandwidth (the ratio of the signal bandwidth to the central frequency). Meanwhile, a polarization conversion band is realized from 8.14 GHz to 9.27 GHz with a polarization conversion ratio which is over 80%. Moreover, the 1 dB transmission window is obtained in two non-adjacent bands of 3.42-7.02 GHz and 10.04-13.91 GHz corresponding to the relative bandwidths of 68.9% and 32.3%, respectively. Furthermore, the radar cross-section of the designed structure can be reduced in the wideband from 2.28 GHz to 14 GHz, and the 10 dB RCS reduction in the range of 4.10-13.35 GHz is achieved. In addition, the equivalent circuit model of this converter is established, and the simulation results of the Advanced Design System (ADS) match well with those of CST Microwave Studio (CST). The archetype of the designed converter is manufactured and measured. The experiment results match the simulation results well, which proves the reliability of the simulation results.

In this letter, a novel ultra-compact spoof surface plasmon polaritons (SSPPs) low-pass filter which shows a high-efficiency transmission and an excellent out-of-band suppression is investigated. It consists of a pair of double-layer SSPPs, the top layer using interdigital strip and meander-line, and the bottom layer is metal gratings of fish-bone shape. The vast advantages of the proposed SSPPs structure in lower asymptotic frequency mode compared with traditional SSPPs structure with the same size enables the proposed low-pass filter to be more miniaturized. The dimensions of the miniaturized structure are 0.75 lambda(0) x 0.1 lambda(0) (lambda(0) is the wavelength corresponding to the central operating frequency). The high-efficient mode conversion is achieved by gradient meander-line lengths. Moreover, we also investigate the transmission performance of the proposed structure when it is conformal. To validate the design concept, the prototype of a straight and bend low-pass filter has been manufactured and measured. The experimental results of the fabricated sample agree with the simulation results well, in which the insertion loss is less than 0.5 dB, the reflection coefficient less than -15 dB, and excellent out-of-band rejection of the attenuation is greater than 30 -dB, which proves the design validity. The proposed ultra-compact SSPPs structure may have great potential applications in miniaturized integrated circuits in the microwave and terahertz (THz) frequencies.

A novel bandpass filter (BPF) based on spoof surface plasmon polaritons (SSPPs) using a compact folded slotline structure is proposed and experimentally demonstrated. The proposed novel SSPPs structure compared with a conventional plasmonic waveguide with slot line SSPPs unit structure at the same size, the considerable advantages in much lower asymptotic frequency with tight field confinement, which enable the proposed filter to be more miniaturization. A high-efficient mode conversion structure is designed to transition from TE-mode to SSPPs-mode by gradient slotline lengths. The low-frequency stop-band can be committed with microstrip to slotline evolution on both sides of the dielectric, while the high-frequency cutoff band is realized by the proposed SSPPs structure. The influence of dispersion relation, electric field distribution, surface current, and structural parameters on the transmission characteristics of the proposed BPF are analyzed by finite difference time domain (FDTD). To validate the design concept, the prototype of the miniaturized SSPPs BPF has been manufactured and measured. The experimental results show high performance of the fabricated sample, in which the working in a range of 0.9 GHz-5.2 GHz with the relative bandwidth is 142%, the insertion loss less than 0.5 dB, the reflection coefficient less than -10 dB, and the group delay is less than one ns. This works provides a mirror for realizing the miniaturization of waveguides, and the application and development of high-confinement SSPPs functional devices in the microwave and THz regimes.

In this paper, a frequency selective rasorber with lowpass and wide absorption band using graphene-loaded lossy layers and capacitive metasurface lowpass layer is presented. Two lossy layer structure is adopted to broaden the absorption band, and graphene-based omnidirection resistive film is introduced in both lossy layers to enhance the absorption band. Besides, a capacitive metasurface rather than a bandpass FSS is introduced as the bottom lowpass layer, which avoids the harmonic resonance and thus benefits to realize the wideband response. Finally, a lowpass response below 1GHz with 1 dB insertion loss and a wideband absorption around 3.6-14GHz.

An ultra-miniaturized narrow-band metamaterial absorber for L-band is presented in this paper. The proposed design operates at 1.21 GHz with reflective coefficient of -22.3 dB. The unit cell is miniaturized to $0.02 \lambda_{0}$, where $\lambda_{0}$ is the free-space wavelength at center operating frequency. The miniaturization scheme is by using meander-line and plated vias in absorber. Several parts of the metal ground are dug out to avoid connecting with vias. The structure is polarization insensitive as there are plated vias on two opposite sides only. On the upper surface of the medium, meander-lines extend from the sides with vias toward the center of the cell, and the meander-lines are connected by two short vias and a strip in the medium. To explain the mechanism of the proposed absorber, we present an analysis of the current and electric field distribution at the operating frequency. Further, the unit cell is also simulated under various polarization angles $(\varphi)$ and incident angles $(\theta)$. The results show that the proposed absorber exhibits a good oblique incident angular stability of up to 50 degree, as well as a polarization insensitivity of up to 40 degree. The fractional bandwidth is 1.65% centered at 1.21GHz. The high absorptivity for a narrow-band makes the proposed absorber a useful candidate to defense against strong radiation attacks and electromagnetic interface in various electronic circuits in satellite and radar applications. The ultra-miniaturized elements and 2.5D design make it stable at large incident angles.

采用贴片谐振型与网栅感性型单元级联组合的方法,设计了一款二阶宽带带通频率选择表面(FSS),在0°～45°入射角范围内,通带为8.0～12.6 GHz,覆盖X波段,平均插入损耗小于1dB.该结构由两层贴片型单元阵列和一层感性金属网栅级联组成,优化确定的FSS单元尺寸为0.136 λ×0.136 λ(λ为工作波长).设计的FSS单元为小型化对称结构,采用等效电路法和全波电磁仿真,对该FSS结构的工作机理和TE/TM极化波在不同入射角的传输频率响应进行分析.研究结果表明在0°～60°入射角范围内传输频响具有较好的角度稳定性和极化一致性,所设计的单元级联结构的层间耦合小,弱化了单元对齐的影响,其对带通曲面天线罩设计具有应用价值.

In this paper, an angle- and polarization-insensitive ultrathin absorber working in the P-band based on is proposed and designed. The absorber is composed of a periodically arranged fan-shaped resistance sheet, a magnetic substrate and a metal back plate. The high permittivity frequency dispersive magnetic materials (FDMM) is used to reduce the thickness of the absorber. A solution of this thickness-bandwidth dilemma was presented by using resistive fan-shaped resonators and FDMM in substrate. The absorptivity of the absorber is calculated by the finite-difference time-domain (FDTD) method and the absorbing bandwidth is optimized. The results shows that an absorption more than 90% was achieved in the frequency range of 0.2-1 GHz for all polarization angles at normal incidence and the relative bandwidth is 133%. Under oblique incidence, the absorber shows a stable response a wide range of incidence angle varied from 0° to 50° for both transverse electric (TE) and transverse magnetic (TM) mode. The overall thickness of this proposed absorber is only about 1/83 of the center wavelength. This work providing new ways for ultrathin high-performance absorbing materials of wider bandwidth and stronger absorption.

In this paper, a graphene-based rasorber with a wide transmission band and a narrow transitional band is proposed. The type of the rasorber is TA which means it has an absorption band above the transmission band. Concretely, the transmission band is located in the X band which is ranged from 9.36GHz to 11.8GHz under 1dB insertion loss, the absorption band is located in the Ku band which is ranged from 13.2GHz to 18GHz under −10dB reflection. The absorption band is mainly realized by the top layer of the model, with a graphene ohmic sheet configured Jerusalem cross. To realize the wide transmission band, a second-order bandpass FSS(frequency selective surface) is used as the bottom layer. Through introducing a transmission zero at the upper side of the transmission band of FSS, the transitional band is reduced.

Based on graphene integrated dual-mode microstrip resonators, two dual-band tunable filtering attenuators with similar performance but different structures and theories are designed in this paper. The field distribution and resonance frequencies of dual-mode microstrip resonator are analyzed, so that the influence of graphene on different resonant modes can be confirmed. Then, two dynamically tunable dual-band filtering attenuators are designed. By using different design concepts and selecting appropriate loading positions of graphene, two different filtering attenuators which can achieve controllable attenuation from 1.5 dB to 7.1 dB and 1.7 dB to 7.6 dB at the first or the second band can be obtained. Last but not least, the attenuations of this two passband can be controlled independently.

A 3-D artificial electromagnetic structure based on square coaxial structure is proposed for meeting the stealth aircraft radome's requirements to realize the high-transmission and reduce the radar cross section (RCS) of antennas. This structure is implemented by synthetically utilizing the two-dimensional anisotropic design method and various modes of microwave resonance. Simulating calculation indicate the proposed structure has less-than 1.1dB insertion loss in the range of 9.0GHz-11.0GHz and more-than 10.0dB mean-reflectivity in the range of 1.0GHz-8.0GHz and 12.0GHz-20.0GHz, while keeping incident-angle stability and polarization consistency. The proposed artificial electromagnetic structure has important application values of engineering.

In this paper, we propose a vector-fitting-based method to extract the equivalent circuit of the one-port-loaded resonator from the simulated S-parameter data. Once the circuit element values are extracted, the resonant frequency, external Q-factor, and unloaded Q-factor can be calculated accordingly. For verification, a parallel resonant circuit model and two simulation models are used to test the method, the extracted parameters agree well with the preset or simulated one. Compared with other methods, this method is simpler and faster.

A low-profile filtering antenna with a wide stopband based on substrate integrated waveguide (SIW) is presented in this article. First, a five-pole bandpass filter using a cul-de-sac topology scheme with two finite-transmission zeros (FTZs) is proposed. The SIW filter which consists of three single-mode cavities using TE101 mode and a dual-mode cavity using TE201 and TE103 mode achieves a wide stopband due to the suppression of TE102, TE202, and TE104 mode. Then a cavity-backed slot antenna is designed so that its bandwidth is narrower than that of the filter, thus making it behave as a last-order resonator. With a center frequency of 10 GHz and a fractional bandwidth of 4.03%, the antenna has good stopband performance and achieves a gain of 7.8 dB in terms of a flat gain profile.

In this paper, a novel equivalent circuit analysis method of frequency selective surfaces(FSS) utilizing full-connected neural networks(FNN) is proposed which can feedback circuit parameters within very short time(less than 1s) once the structure parameters are given. To validate our idea, the equivalent circuit model of hexagon ring FSS is analyzed. And then the equivalent circuit parameters are obtained by simulation and curve fitting. A dataset of the structure parameters labeled with circuit parameters is constructed and used to train our FNN. Finally, the favorable effect of the FNN is showed which proof the efficiency of our method.

In this article, a beam switchable pattern-reconfigurable antenna (PRA) using the adjustable impedance property of graphene is presented. The PRA consists of two dipoles and a Vivaldi antenna with the feed line on the other side of the substrate. To realize dynamical manipulation of radiation beam, three graphene pads are set on the feed line. By electrically controlling the graphene nanoplates, the beam can be switched to three directions: −90°, 0° and +90°. The results show that the PRA antenna operates at 5.8GHz with gain of 2.15dB, 5.73dB and 1.37 dB in three directions respectively. Moreover, the state at the 0° covers a wide band of 5.1-9.3GHz.

In this paper, the equivalent circuit analysis of frequency selection surface (FSS) based on transition matrix method is proposed. The equivalent circuit topology of FSS can be obtained by the electric field distribution, and the mapping relationship between equivalent circuit parameters and 3D structure parameters can be setup. Firstly, a full-wave simulation by HFSS (High Frequency Structure Simulator) and curve-fitting by MWO (Microwave Office) with different structure parameters of FSS is conducted, and a discrete database including the 3D structure parameters and the equivalent circuit parameters can be obtained. Then, a transition matrix relationship is established to map the relationship between 3D structure parameters and the equivalent circuit parameters. The objective function can be constructed and the least square method is used to complete the space mapping, each value in the transition matrix is a continuous function. Finally, a software is developed to verify this method, which can calculate the S parameters of more than ten types of single-layer FSS at different incident angles, permittivity and thickness.

A method for designing a dual-polarized wideband absorber with low profile by using dual-resistor-loaded metallic strips is proposed in this paper. Each unit cell consists of a resistive sheet with dual-resistor-loaded metallic strips and an underlying conducting plate. Two-dimensional arrays of two unequal metallic strips are printed on the dielectric substrate, and two resistors are embedded in the metallic strips. By properly designing the resonant frequencies of these metallic strips, a wide absorption band with three resonances is obtained. An equivalent circuit model is introduced, and the current distributions are examined to understand the physical mechanism of the proposed absorber. An example of the absorber is fabricated and measured to verify our designed concept. The measured results show that the wideband absorption performance with a fractional bandwidth of 129% under the normal incidence and the stable angular response are achieved. In addition, the proposed absorber has a low profile with 0.08λL, where λL is the wavelength at the lowest operating frequency.

Miniaturized element frequency selective surface (MEFSS) design technology is one of the research hotspots in recent years, the application space of frequency selective surface (FSS) has been expanded, especially in low-frequency applications, surface shaping applications and other fields. In this paper, we provide a design of MEFSS unit and loaded on the dual screen FSS. Compared with the original dual screen FSS, the simulation results shows that the hybrid structure with loading MEFSS present a wider bandwidth, giving faster roll off in sidebands, and the cut-off is obviously improved, it also can ensure insensitivity to incident angle variation and polarization.

In this paper, an absorptive frequency selective surface with a wide high selective passband and two absorption bands is proposed. The absorptive frequency selective surface, is formed by generating two absorption bands besides the broadband transmission bands. The resistive layer and FSS layer consist of a wideband absorber and frequency selective surface respectively. It is shown by full-wave simulation that the structure has a 3dB transmission window from 7.8 to 12 GHz with a 42.4% fractional pass-bandwidth. And from 4 to 16.5GHz, the reflection coefficient can be reduced to -10dB.