Jiahui Fu

In this Letter, a low-divergence, low-sidelobe circularly polarized (CP) vortex emitter is proposed to generate a high-gain orbital angular momentum (OAM) beam of mode + l . Its leaky-wave radiation arises from the interaction between a bound surface wave and the spatially varying patches. A direct aperture field synthesis method is developed based on the Hankel transform relation inherent in the topological nature of vortex waves. To manipulate the aperture-field amplitude and phase simultaneously, a nonuniformly modulated metasurface (MTS) is utilized, and the modulation parameters are determined by solving local periodic problems. Modulated MTS emitters with different OAM modes are designed and simulated, all exhibiting low divergence and high sidelobe suppression ratios (SLSRs). To validate the proposed method, an emitter with OAM mode l = +1 is fabricated and tested. Experimental results demonstrate a divergence angle of 4°, an SLSR of 25.6 dB, and a gain of 23.3 dBic at 17 GHz, while the emitter maintains a thickness of 0.043 λ ₀ and an overall profile of 0.663 λ ₀ . The proposed emitter is well suited for vortex imaging.

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.

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.

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°) and 5.6 dBic (23°), 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.

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.

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.

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 (2D LWA) with integrated radar-absorbing properties. Substrate-integrated image guide (SIIG) 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° to 0° and a wide absorption bandwidth from 7 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.