This paper presents a low-pass frequency selective surface (FSS) based on two band-stop FSS layer separated by an air spacer. By arranging three transmission zeros in an staggered sequence, a wide stopband below −10 dB is achieved from 4.3 GHz to 18.4 GHz (124.2%). Meanwhile a transmission pole is introduced below the stopband to realize a passband from 0 to 3.5 GHz, with maximum passband insertion loss of 0.65dB. The proposed FSS exhibits good performance and simple structure, making it suitable for microwave communication applications.

Conventional tensor holographic impedance metasurfaces provide flexible control over beam direction and polarization but usually suffer from limited aperture efficiency due to the restricted impedance tuning range of anisotropic unit cells. To address this issue, a scalar-tensor composite holographic impedance metasurface is proposed by introducing an isotropic scalar structure into a tensor holographic framework. The additional scalar component increases the average surface impedance while largely preserving the anisotropic impedance contrast required for polarization manipulation, thereby enhancing the leakage rate of the surface wave and improving the radiation efficiency. Full-wave simulations confirm a significantly enhanced leakage rate and improved overall aperture efficiency. This composite architecture provides a simple, effective means of improving the radiation efficiency of holographic leaky-wave antennas without adding structural complexity.

This paper proposes a novel low-pass frequency selective surface (FSS) with high-frequency rejection. Through theoretical derivation of the equivalent circuit model (ECM), an additional transmission pole can be generated below the transmission zeros by cascading two band-stop FSSs incorporated with an air spacer, therefore enhancing the low-pass performance. Based on the above findings, a compact and simple FSS is designed, which consists of two dual band-stop FSS with an air spacer. The staggered distribution of the four transmission zeros substantially broadens the stopband. The full-wave simulation result shows that the proposed FSS has an ultra-wide out-of-band rejection with transmission coefficient under −10 dB from 4.42 GHz to 27 GHz (143%), while maintaining a relatively good low-pass characteristic under 4.42 GHz with a maximum insertion loss of 1.36 dB. The full-wave simulation result matches closely with the ECM result.

Vortex beams carrying orbital angular momentum (OAM) have garnered considerable interest for their unique helical phase fronts and mode orthogonality, which offer promising prospects in modern wireless communications and detection. However, their inherent divergence poses a fundamental challenge for long-range applications. To overcome this limitation, we propose a low-profile, low-divergence vortex beam emitter utilizing spoof surface plasmon polariton (SSPP) waveguides, capitalizing on their tunable dispersion and structural adaptability. The emitter incorporates 16 sub-emitters configured into a uniform concentric circular array (UCCA) to effectively reduce beam divergence angle, suppress sidelobes, and simplify the feeding network. Each sub-emitter is implemented using a double-sided comb-shaped widened (DSCSW) SSPP waveguide, which not only enables efficient circularly polarized radiation via leaky-wave mechanisms but also concurrently serves as a reflective surface, thereby obviating the need for additional reflectors and achieving a minimal profile with low metal coverage. Simulations and measurements confirm that the proposed design features a simple feeding network, an ultra-thin profile of 0.0672 (2 is free-space wavelength at 10.1 GHz), and generates vortex beams with a notably low divergence angle of 3 degrees and a gain of 16 dBic.

This paper presents a dual-mode fixed-frequency leaky-wave antenna (LWA) array utilizing joint amplitude–phase control and a dedicated decoupling structure. The 38-element array is based on reconfigurable unit cells capable of 2-bit phase modulation through the combination of geometric and transmission phases, along with 1-bit amplitude modulation based on a reflection-cancellation mechanism. An amplitude–phase synthesis algorithm is developed to independently steer the main beam and reshape the sidelobe distribution, enabling precise manipulation of sidelobe positions while maintaining a stationary main beam direction. To overcome the performance degradation caused by practical mutual coupling, a dedicated decoupling structure is implemented to minimize excitation errors and restore modulation accuracy. Simulation results at a fixed frequency confirm that the decoupling structure contributes to a 3.8 dB gain enhancement and a 6 dB sidelobe level (SLL) reduction. The prototype demonstrates versatile dual-mode configurability: in the high-gain mode, it achieves a peak realized gain of 13.4 dBi; in the optimized low-SLL mode, it maintains a measured SLL below −14.0 dB across a scanning range of ±45°. With an overall beam-steering coverage exceeding 120°, the proposed LWA offers a robust and high-performance solution for advanced interference-sensitive communication systems.

In this paper, a novel method based on bias-integrated multi-resonant arrays is proposed for multifunctional metamaterials. In contrast to conventional active designs with a single active band, the proposed metamaterial could independently manipulate the in-band and out-of-band functions by providing frequency-shiftable and function-reconfigurable responses, respectively, through changing its electrical biasing voltage and physical rotation (or incident polarization) angle. Under each manipulation mode, the proposed multi-resonant structure provides destructive interference windows with different paths for the in-band, and by changing the biasing voltage of the loaded active semiconductor components, the resonance can be switched among these paths, thereby shifting the in-band operating frequency from 4.7 GHz to 5 GHz. After rotating the physical angle of the structure, the proposed design not only switches the out-of-band function from co-polarized reflection to polarization conversion, but also provides cross-polarized and circularly polarized outputs for the lower (around 4.2 GHz) and higher (around 5.4 GHz) out-of-bands, respectively. Additionally, owing to the proposed bias-integrated architecture and frequency compensation strategy, the in-band and out-of-band reconfigurable functions are nearly independent and exhibit negligible mutual influence. It is noted that, due to the developed quasi-symmetrical structure, similar frequency-switchable and function-reconfigurable responses could be achieved under the two orthogonal polarized incidences (TE/TM and -45°/45°). Finally, a prototype was fabricated and measured, and the effectiveness of our approach was validated through theoretical analyses, numerical simulations, and experimental measurements.

This article presents a novel absorptive multifunctional metamaterial with switchable high-efficiency and wideband in-band response while providing stable out-of-band shielding performance. Distinct from conventional cascaded rasorber-based designs requiring resonant bands alignment between lossy/lossless arrays, an innovative filtering cavity, which could confine and manipulate the incident energy within it, is developed to achieve exceptional bandwidth and efficiency behaviors. The polarization-selection and ohmic-loss characteristics of each cavity’s spectrum-distinct array could be independently controlled, and with an appropriate biasing strategy, three distinct mechanisms of second-order filter, wideband absorption, and multireflective shielding can be obtained and switched through one structure. These functionalities are realized through four polarization-independent and three all-polarized control modes, and each state presents nearly identical performance in its corresponding mode. Therefore, high-transmittance windows with the minimum insertion loss of 0.1 dB are realized in the filter mode with the 95% fractional bandwidth of 40%. When switching to the absorption mode, the incident energies within the passband can be efficiently absorbed by the structure (the bandwidth of 95% absorption rate is 30%). In the reflection mode, the metamaterial acts as a perfect multireflector throughout the operating band. It is worth noting that, attributing to the quasi-symmetric structure, the proposed method not only independently provides the aforementioned performance under both TE and TM incidences without degrading the performance of other modes, but also enables all-polarized functions of filter, absorber, and reflector. Finally, a prototype is fabricated for measurements, and the calculated, simulated, and measured results validate the proposed design.

This letter presents a stealth two-dimensional leaky-wave antenna (2-D LWA) with integrated radar-absorbing properties. Substrate-integrated image guide is employed to construct the LWA. The use of patch-type radiating elements without direct metal connections allows the antenna to perform in-band beam scanning while also enabling control over its out-of-band reflection properties. To this end, the patches are loaded with a metal-based resistive ink to maintain the reflection and absorption characteristics, ultimately enabling the antenna to combine beam scanning with out-of-band absorption. Moreover, the low-profile, integrated design reduces the spatial requirements for a radar system incorporating a radome. A proof-of-concept prototype is fabricated and measured, which demonstrated frequency-controlled beam scanning from -40 degrees to 0 degrees and a wide absorption bandwidth from 7 GHz to 11 GHz. Owing to its beam-scanning capability, absorbing properties, low profile, and low cost, this LWA is a promising candidate for radar systems requiring stealth, scanning, and detection functionalities.

In this letter, a novel multi-functional frequency selective rasorber (FSR) with switchable transmissive/reflective in-band is presented. Owing to the proposed design strategy, three distinct operating mechanisms are integrated into our structure, thereby enabling a tri-state response in one system. The in-band window can be switched between transmission and shielding states, while high-efficiency absorption bands are realized at the both sides of the in-band. By employing two identical and orthogonally arranged lossless coplanar layers, the polarization-independent (P. I.) controlled performance could be realized within the active band. A miniaturized lossy hybrid resonator, whose periodic dimensions and operating frequencies are matched to those of the lossless array, has been developed to achieved the aforementioned functionalities upon integration with the lossless one. The desired three-state functions could not only be obtained and controlled under TE and TM polarizations, but also extended to arbitrary polarizations. Finally, the effectiveness of the design is validated through the good agreement among equivalent-circuit calculations, numerical simulations and experimental measurements.

In this letter, a novel multifunctional frequency-selective rasorber (FSR) with switchable transmissive/reflective in-band is presented. Owing to the proposed design strategy, three distinct operating mechanisms are integrated into our structure, thereby enabling a tri-state response in one system. The in-band window can be switched between transmission and shielding states, while high-efficiency absorption bands are realized at both sides of the in-band. By employing two identical and orthogonally arranged lossless coplanar layers, the polarization-independent controlled performance could be realized within the active band. A miniaturized lossy hybrid resonator, whose periodic dimensions and operating frequencies are matched to those of the lossless array, has been developed to achieve the aforementioned functionalities upon integration with the lossless one. The desired three-state functions could not only be obtained and controlled under TE and TM polarizations, but also extended to arbitrary polarizations. Finally, the effectiveness of the design is validated through the good agreement among equivalent-circuit calculations, numerical simulations, and experimental measurements.

An electrically tunable wide-beam-scanning metagratings leaky-wave antenna (MGs LWA) based on liquid crystal (LC) is proposed. Two-dimensional (2D) periodic slotted MGs with capacitive and inductive behaviors are etched on the bottom layer of the substrate and backed by a ground plane with an LWA framework. Two different slotted MG elements are adopted to suppress the open-stopband effects. A theoretical analysis is conducted to provide a conceptual framework for the equivalent electromagnetic fields generated by slotted MGs. Using LC, tunable beam scanning is achieved at a fixed frequency. The LC is placed between the inverted MGs LWA radiating metal and the ground plane to control the LC molecules’ orientation angle by applying a DC voltage across them, thereby adjusting the LC permittivity. Using the results obtained, the proposed antenna can be tuned up to 40° at a fixed frequency by applying a biased DC voltage ranging from 0 V to 10 V. The actual operating bandwidth is 40% for continuous beam scanning of 71°, with a scanned sensitivity of 8.35°/GHz at the zero voltage (V = 0 V), and beam scanning of 61°, with a scanned sensitivity of 7.17°/GHz at the saturation voltage (V = 10 V). The proposed MGs LWA has a realized gain of up to 13.84 dBi. Finally, the proposed antenna has excellent performance due to its potential to achieve wide tunable beam scanning with a narrow beamwidth compared to traditional LWAs’ limitation of radiation angle, depending on the excitation frequency, which makes the proposed antenna suitable in terms of range and sensing calibration for operation at a specific frequency in sensing communication and radar applications.

A method for generating dual high-order orbital angular momentum (OAM) modes by integrating spoof surface plasmon polariton (SSPPs) and spoof localized surface plasmon (SLSPs) is proposed. The proposed design consists of N rotationally arranged SSPP waveguides periodically loaded with SLSP patches, which enables broadband circularly polarized (CP) radiation and introduces a dynamic phase. Unlike conventional approaches that rely on excitation phase control and complex feeding networks, the proposed method utilizes dynamic and geometric phases to synthesize the required phase distribution for high-order OAM modes, thereby eliminating the need for phase-shifting networks. Moreover, exploiting the leaky-wave theory, dual high-order OAM modes with l = -N + 1 and l = N + 1 are generated by varying the frequency to alter the dynamic phase. The experimental results confirm that the proposed device is capable of generating high-order l = -7 and l = +9 OAM modes at 9.7 and 13.0 GHz, with gains (divergence angles) of 8.4 dBic (33 degrees) and 5.6 dBic (23 degrees), respectively. This work provides a phase-network-free solution for dual high-order OAM generation with frequency-controlled mode switching, demonstrating potential for applications in sensing, radar detection, and mode-division multiplexing systems for wireless communications.

Discretized metasurfaces offer freeform flexibility in electromagnetic response manipulation, but higher structural resolution causes random generation to produce fragmented pixelated geometries that are hard to fabricate and degrade performance. We propose an inverse design framework centered on a Fourier-based metasurface generator that uses 2D Fourier series to maintain geometric diversity while suppressing structural fragmentation. The Kramers–Kronig relation is embedded as a physical prior in the spectrum prediction network to shorten training while preserving accuracy, and a boundary detection mechanism is incorporated into the genetic algorithm to maintain geometric continuity during optimization. The framework is validated on linear-to-circular and linear-to-elliptical polarization conversion tasks, with agreement between simulations and measurements confirming the effectiveness of the proposed approach.

To satisfy the low-frequency transmission and high-frequency out-of-band suppression demands of spacecraft communication systems, this paper presents a low-pass frequency selective surface (FSS) based on a single dielectric substrate with resonant metal layers on both sides. The proposed structure achieves a passband from 100 to 400 MHz and a stopband with rejection below −10 dB across the 1–18 GHz range. Two resonant units generate distinct strong resonances near 2.85 GHz and 10 GHz, effectively broadening the stopband. An equivalent circuit model is established, and the transmission mechanism is analyzed through full-wave simulations, and the electric-field distributions at the two resonances confirm the dual-resonance mechanism. The structure further maintains stable transmission under transverse-electric (TE) and transverse-magnetic (TM) polarizations up to 60° oblique incidence, making it well suited for spacecraft electromagnetic compatibility protection and antenna-window applications.

PurposeThe purpose of this paper is to develop a novel design method for reconfigurable liquid crystal holographic antennas (LC-HAs) to suppress electromagnetic (EM) leakage and mutual coupling between radio frequency (RF) channels.Design/methodology/approachThe antenna is composed of tunable liquid crystal (LC) radiators and the feeding waveguide, which are coupled to each other through air slots opened on the upper wall of the waveguide. The slow wave is realized by a broken nail structure mounted on the lower wall of the waveguide. Attributed to the ingenious multimode-resonant antenna element design, the extremely high amplitude tuning efficiency of the antenna element is achieved under the limited LC volume.FindingsAttributed to the ingenious multimode-resonant antenna element design, the extremely high amplitude tuning efficiency of the antenna element is achieved under the limited LC volume, which enables the proposed LC-HA to reach a scanning angle of -60 degrees to + 60 degrees, and the gains of 12.5 dB - 15 dB over the whole scanning angle. Holographic algorithm is used to realize beam scanning. Numerical simulation results are highly consistent with the preset angle of the algorithm, indicating that the working mechanism and design method of the proposed antenna are reasonable and proper. An antenna prototype is fabricated and measured. The experimental results are consistent with the simulation results.Originality/valueThis paper provides a novel design method for reconfigurable LC-HAs fed by a slow-wave rectangular waveguide, which has an advantage over existing microstrip-fed or gap-waveguide-fed LC-HAs in suppressing EM leakage and mutual coupling between RF channels.

This letter presents a rasorber that can tune the passband frequency while exhibiting negligible influence on the cross-polarization performance and out-of-band responses. The key distinction of our work from other reported ones is that the proposed method not only enables independent tuning of the TE/TM transmission windows, but also preserves the out‑of‑band frequencies and absorption performance during in‑band reconfigurability. A separate design for the TE- and TM-controlling resonators is developed with an independent biasing system, and an equivalent-circuit model that includes the feeding networks for both polarizations is established to facilitate the reduction of the feeding-system impact on the polarization-independent performance. Moreover, the lossy hybrid resonator is designed to route the stopband currents through the resistors while bypassing the varactors, whereas the passband currents are directed through the varactors while bypassing the resistors, thereby preventing the tunable window from interfering with the low-reflection band and further improving the transmission efficiency. By employing reconfigurable semiconductor components for lossy and lossless arrays, the reactive characteristics for the two arrays can be independently changed, enabling precise frequency matching in both of them. The proposed structure not only provides stable polarization-independent control up to 40° oblique incidence but also delivers a uniform tunable response across all polarizations under a specific biasing strategy. Finally, a prototype is fabricated for experiments, and the calculated, simulated, and measured results validate the proposed design.

This article presents a multifunctional metamaterial based on an antenna-filter/polarization converting-antenna (A-F/PC-A) module array that could provide ultrawideband transmission (Tx), polarization conversion (PC), and reflection (Rx) responses for two polarizations through six active modes. Reconfigurable receiving and radiating antenna arrays are elaborately designed to enable this system could operate under arbitrarily linear polarized waves. Moreover, to further facilitate the polarization manipulation between the receiving and radiating antenna arrays, while providing a good impedance matching for each operating mode, an improved active filter array with a strong coupling mode, and a PC mode are proposed. Attributing to the proposed second-order structure, high-transmittance windows (the minimum insertion loss is 0.1 dB) with a -3-dB fractional bandwidth of 66.7% are realized in the Tx mode. Within this passband, the polarization characteristics and Tx state of the incident electromagnetic (EM) wave can be flexibly modulated. In the PC mode, the relative bandwidth with a PC rate (PCR) of more than 90% reaches 55.6%. When switching to Rx mode, the structure acts as an effective EM shield with the Tx coefficient below -10 dB throughout the operating band. Finally, a prototype is fabricated for measurements, and the calculated, simulated, and measured results validate the proposed design.

An ultra-wideband high-purity dual-mode circularly polarized (CP) vortex antenna is proposed to generate orbital angular momentum (OAM) vortex beams with modes +/- l. The proposed antenna consists of a uniform circular array (UCA), an in-phase feeding network and a metasurface. Different from traditional OAM multiplexing antennas composed of multiple UCAs arranged in concentric rings, the proposed design only utilizes one UCA to generate two OAM modes. A dual-port ultra-wideband CP antenna is designed using characteristic mode analysis and exploited as the array element. In addition, the feeding phase of each array element is provided by its rotation angle, enabling to have a more compact-size multiplexed structure, a less complex feeding network and to generate two high-purity OAM beams. Moreover, a metasurface is used to increase the isolation between the two ports, and two ultra-wideband 1 x 8 power dividers are also designed as the in-phase feeding network. A proof-of-concept prototype of the proposed antenna is fabricated and measured. The measurement results confirm that the proposed antenna can generate both l = + 1 and -1 modes simultaneously through two ports, with -3 dB axial ratio (AR) bandwidths up to 67.9% and 52.4% respectively, and peak gains of 13.8 dBi and 13.9 dBi respectively. The proposed antenna can provide a new trajectory for OAM multiplexing antenna design in wireless communication systems.

The paper introduces a novel broadband second-order filter characterized by an angularly stable, polarization-independent switchable working window. In contrast to traditional designs limited to dual polarization and a single function, this innovative filter allows independent and continuous tuning or phasing of TE and TM waves. This capability is enabled by adopting a via-hole jump layer structure, facilitating the independent manipulation of TE and TM waves at different frequencies. This resolves challenges related to conflicting electromagnetic waves in co-layer orthogonal polarization directions on a single metasurface. Moreover, the design achieves a structural broadband second-order filter by splitting and layering the middle layer. This approach not only broadens the filter's operational bandwidth but also ensures independent dual-polarization feeding, thereby guaranteeing polarization independence across a wide frequency range. Furthermore, the implementation of a gap capacitor through a single-layer branch plays a crucial role. It effectively shifts the transmission passband frequency to the lower frequency band, resulting in significant miniaturization. As a result, the unit size is reduced to a mere 10.4% the central working wavelength. Overall, these advancements represent a substantial leap forward in filter technology, offering enhanced versatility, polarization independence, angular stability, and compact size. AFSS structures with these capabilities demonstrate significant potential applications in beam space aperture antennas.

By modifying the dimensions of the artificial metasurface patch, this unit can achieve a 360-degree phase coverage. By calculating the phase compensation required for each unit rationally and corresponding to the corresponding unit size, it can obtain OAM beams of the anticipated topological charge in two directions of theta=+/- 30 degrees, phi= 0 degrees. Therefore, our research demonstrates that a single metasurface can generate multiple OAM beams in various directions and support different modes, thereby significantly enhancing the coverage and versatility of OAM-based wireless communication systems.