Metasurfaces enable versatile electromagnetic wave manipulation through subwavelength meta-atoms, facilitating compact and multifunctional integration. Current metasurface designs mostly depend on external spatial feed structures, increasing complexity and size. This work proposes a low-profile, guided-wave-driven, liquid-crystal (LC)-based programmable metasurface with dual-band, dual-polarisation capabilities for independently controllable, dynamic beam scanning. It consists of an LC-based programmable layer fabricated by standard LCD processes and a broadband waveguide feed structure with high alignment tolerance. A complementary resonance mechanism allows meta-atoms to retain nearly identical radiating-structure dimensions across both frequency bands, overcoming traditional scaling constraints. By dynamically adjusting the LC molecular orientation, the distribution of radiated electromagnetic energy can be precisely controlled. Experimental validation demonstrates exceptional beam scanning capabilities, achieving up to +/- 75 degrees (150 degrees total) at both frequency bands, surpassing previous designs. In addition, the proposed metasurface achieves controllable near-field focusing by independently programming the aperture amplitude distribution, enabling precise energy localisation at reconfigurable focal positions. The proposed metasurface offers considerable potential for advanced next-generation mobile and satellite communication applications.

Leaky metasurfaces offer a promising route to integrated wavefront control, yet their overall performance is constrained by the intrinsic limitations of constituent meta-atoms. Here, we propose a leaky Fourier metasurface (LFM) based on sinusoidally modulated microstrip lines to circumvent the bandwidth and functionality limitations imposed by meta-atom configurations. By replacing discrete meta-atoms with deterministic, non-resonant Fourier gratings, the LFM enables broadband, diffraction-order-multiplexed beam and focus steering. An analytical framework directly links the sinusoidal modulation parameters to the phase profile, eliminating the need for complex meta-atom optimization. As proof of concept, we demonstrate both far-field beam steering and near-field focus steering across three distinct diffraction orders, with experimental results validating the design. This platform provides a scalable and versatile approach to multifunctional wavefront manipulation, with potential applications in communications, sensing, and radar systems.

Liquid-crystal (LC)-based metasurfaces enable dynamic electromagnetic control with low power consumption, but reducing the LC thickness to improve response speed often causes severe radiation-efficiency degradation. This work introduces a dual-resonant coupling mechanism to address this limitation in thin-layer LC guidedwave metasurfaces. By combining an admittance-equivalent model with temporal coupled-mode theory, we establish a unified framework that reveals an asymptotic cubic scaling of efficiency degradation in thin LC layers and provides an effective route to enhancing radiative coupling through an auxiliary radiating structure. A parasitic patch layer is incorporated above the LC resonator to form a hybrid dual-mode system that enhances radiation while suppressing dissipation. Two 71-element metasurface prototypes were fabricated and experimentally characterized. Measurements show more than 6 dB realized-gain improvement across the operating band and an average enhancement of 8.5 dB at 27.5 GHz, while maintaining beam scanning from - 60 degrees to +60 degrees.

A guided-wave-driven liquid-crystal (LC) holographic metasurface is proposed for reconfigurable circularly polarized beam scanning at 27.5 GHz. The metasurface consists of 61 LC meta-atoms excited by a gap substrate-integrated waveguide. Each meta-atom integrates an LC-tunable resonant subsystem and a chamfered metallic patch to realize tunable radiation amplitude and circular polarization. By holographically controlling the aperture amplitude distribution, beam scanning from −60° to 60° is achieved. Full-wave simulations show good impedance matching, stable realized gain, and an axial ratio below 3 dB over the investigated scanning states. The proposed design provides a compact solution for reconfigurable circularly polarized millimeter-wave antennas.

Perfect vortex (PV) beam, as a novel paradigm to carry orbital angular momentum (OAM), owns constant radius of energy intensity and infinite mode of helical patterns, which overcomes the divergence performances of conventional vortex beam. However, common approaches for PV beam generation require optical cascading systems that should constitute of various lenses and components with bulk volume and high alignment standards, also cannot realize PV customization. Thus, in this paper, we propose a general scheme based on compact platform of geometric metasurface to achieve PV beams generations and deformable wave-front modulations. The adopted unit cell is designed with “ABA”-shaped configuration, which can high-efficiently transform circular polarization incident wave into its cross-polarized state and impose required PV phase patterns. Here, we construct series of metasurface lenses to achieve PVs with eight different OAM modes at operating frequency 10 GHz, and additionally conduct quasi-elliptical energy-ring intensities and fractional modals of PVs by introducing asymmetric periodicity and extra singularities. By exploiting compact metasurface platform, this general scheme for PV beam generation and modulation would provide a theoretical foundation for the electromagnetic waves controlling in modern wireless communication systems.

The advancement of low earth orbit (LEO) satellite communication technology has necessitated the emergence of antenna systems with exceedingly stringent technical requirements, including beam scanning, dual-band orthogonal polarization, low-profile, low-cost, and lightweight. Programmable guided-wave-driven metasurfaces demonstrate dynamic and advanced control of electromagnetic (EM) waves without external spatial feeding, complex power divider and accompanying phase shifter networks, making it a good candidate for LEO satellite communication. Herein, a frequency-multiplexed guided-wave-driven metasurface for independent and dynamic control of dual-band EM waves is proposed to achieve uplink and downlink in LEO satellite communication. Through vias are utilized to connect the meta-atoms and the bottom layer of the substrate integrated waveguide, realizing a guided-wave-driven metasurface in which a complicated feeding network of radiation-type metasurface can be avoided. By modulating the states of the four p-i-n diodes integrated within each meta-atom, dynamic and independent 1-bit phase switching across two distinct, tailored frequency bands is achieved. To validate this concept, the designed metasurface is fabricated and characterized, which exhibits excellent beam-scanning performance at the two operating bands: 10.4 GHz for downlink and 12.5 GHz for uplink. The proposed low-profile, dual-band, and programmable metasurface shows great application potential in further satellitecommunication.

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.

Metasurfaces have attracted extensive attention due to their excellent capabilities in wavefront manipulation. However, chromatic aberration, which is widely present in phase-modulated tuning metadevices, limits their applications in modern communication systems. Far-field achromatism has been explored but only considered for single-order diffraction. With increasing demands and studies on multibeam diffraction, including, but not limited to, phase-modulated metasurfaces and metagratings, most of them are not suitable for dispersion manipulation. In this article, we analyze the achromatic mechanism of the diffraction field and propose a feasible solution to coherently control the dispersion on multiorder diffractions simultaneously. The chiral phase is introduced in the meta-atom to engineer the dispersion characteristics. In addition, an achromatic dispersion metasurface is designed for dual-beam generation as proof of concept. The two beams with propagation direction -35 degrees and +35 degrees show good angle stability at the targeted frequencies of 7, 10, and 13 GHz. Moreover, the limitations on beam direction accuracy and metasurface aperture are also discussed. An improvement method that can greatly enhance the accuracy of diffraction angle is further proposed, where the deviation between actual beam angles and expected ones is reduced to below 0.8 degrees, with a 73% enhancement. The proposed work builds up a major advance for diffraction management and shows great potential in wireless communications and radar detection.

This paper proposes a high-efficiency linear to circular (LTC) polarization conversion metamaterial based on a multi-mode electromagnetically induced transparency-like (EIT-like) effect in the microwave band. The EIT-like transmission windows of bright-bright (B-B) and bright-dark (B-D) modes are constructed by generating multi-path excitation through an asymmetric structure. Then, the frequency shift and phase differences of the TE- and TM-polarized EIT-like windows are achieved by the perturbation method, which attributes to an LTC polarization conversion response with a high efficiency of 99.8%. The perturbation method also contributes to the insensitive performance for both EIT-like and LTC windows, corresponding to polarization angles of 240° and 120°, respectively. Finally, the proposed structure is fabricated and measured, and the simulation and experimental results are in good agreement.

In this study, a novel holographic reconfigurable antenna featuring a compact-cell design for wide-angle scanning in liquid crystal technologies is proposed. The antenna's radiating structure is ingeniously crafted to activate the complementary resonance mechanism, which is realised by an inductance equivalently formed by the slot in the ground layer and a tunable capacitor made by the combination of the metal strip, ground, and liquid crystals. This mechanism effectively mitigates challenges related to the limitations of resonant length in antenna unit design, thus facilitating a compact unit with a length less than 0.121 lambda. Additionally, the influence of the feed line width on the radiation characteristics of the antenna element was investigated, discovering that widths below 0.03 mm exert minimal influence, a dimension readily achievable with current manufacturing technologies. The designed antenna element achieves a return loss of less than -10 dB and an axial ratio exceeding 30 dB. The response time of the designed liquid crystal antenna is investigated. An array comprising 61 compact units was designed, incorporating a feeding structure compatible with LCD manufacturing standards. The measurement result confirmed that the array could effectively scan beams between -76 degrees and +78 degrees, consistently maintaining excellent matching properties.

This study presents an innovative dual approach design for a circularly polarized (CP) multiple-input--multiple-output (MIMO) antenna specifically tailored for millimeter-wave (mm-wave) internet-of-things (IoT) applications. The MIMO-CP antenna comprises four rectangular slatted radiators, a hexagonal nested neutralization line (HN-NL), and a circular segmented defected ground (CS-DG). The effective decoupling compact antenna dimensions are 30 mm x 30 mm x 0.508 mm (2.80 lambda(0) x 2.80 lambda(0) x 0.0457 lambda(0)) while lambda(0) is the free-space wavelength at 28 GHz. The integration of HN-NL and CS-DG among the MIMO radiators facilitates a decoupling strategy that improves the axial ratio (AR) bandwidth (BW), and isolation. The antenna achieves a 3 dB ARBW from 27.21 GHz to 32.83 GHz (20.67%), a mutual coupling of no more than -28 dB, a reflection coefficient of <=-10 dB from 25.12 GHz to 34.5 GHz (30.96%), and a peak gain of 7.25 dBi at lower frequencies and 8.13 dBi at higher frequencies. The efficient MIMO characteristics of the compact, low-profile antenna provide them an attractive choice for IoT mm-wave applications.

In this article, a novel nine-mode absorption-transmission/absorption/reflection-absorption (A-T/A/R-A) active frequency-selective rasorber (AFSR) is proposed. It consists of a lossy array-I and a lossless array-II (and array-III) that could control the energy loss intensity and transmission state of electromagnetic (EM) wave, respectively. The lossy layer-I is constructed with an active-hybrid resonator, which realizes multiple current paths to contribute to in-band switchable lossy/lossless states while providing a stable out-of-band absorptive performance. Meanwhile, the lossless structure, composed of a double-layer active frequency-selective surface (AFSS) with symmetric and noncoupling characteristics, is employed for an ultrathin and switchable bandpass filter. Furthermore, attributed to the elaborately designed polarization-isolation bias system for both the lossy and lossless layers, all polarization-insensitive and polarization-independent functions could be realized in modes 1-3 and 4-9, respectively. As a result, this AFSR can independently provide ultrawideband (UWB-A), A-T-A (AFSR-T), and A-R-A (AFSR-R) modes, for both TE and TM incidences. In UWB-A mode, it achieves a -10-dB absorptive band from 2.6 to 9.7 GHz. When the operating mode switches, in AFSR-T and AFSR-R modes, the transmission or reflection band can be generated at the same frequency of 7.4 GHz with low energy losses of less than 0.1 dB. Finally, a prototype is manufactured, and the measured results are in good agreement with the CST simulation and circuit calculation results.

Reconfigurable intelligent surfaces (RISs) are considered as one of the potential technologies for the sixth generation (6 G) wireless communication systems. Research on RIS channels is crucial for future RIS-assisted communication systems. However, current RIS channel measurements are only conducted when the receiver (Rx) is stationary, lacking moving channel measurements. In this paper, RIS is used as the transmitter (Tx) antenna in a hall environment to measure the 28 GHz RIS channel. We use near-field coding and far-field coding to measure the RIS channel during the movement process, respectively. The channel characteristics, including path loss, delay spread (DS), Ricean K-factor (KF), temporal autocorrelation function (TACF), and channel capacity are analyzed. It is found that in the hall environment, the coding mode of RIS exerted significant influences on path loss and channel capacity, whereas their impacts on DS, KF, and TACF were relatively minor.

This paper provides a comprehensive review of ultra-wideband (UWB) high-efficiency power amplifier (PA) design based on gallium nitride (GaN) technology. It covers key challenges and advancements in three major architectures: reactive matching power amplifiers (RMPAs), distributed power amplifiers (DPAs), and load-modulated balanced amplifiers (LMBAs). The study highlights the trade-offs between bandwidth, efficiency, output power, and gain, which are critical in UWB PA design. Techniques such as reactive impedance matching, load modulation, and continuous-mode operation are discussed in detail, along with innovative methods like the nested-mode PA, sequential load-pull technique, and quasi-MMIC designs. This paper also explores recent developments in DPAs and LMBAs that address limitations in efficiency at power back-off, output power, and gain. Future research directions emphasize miniaturization, integration, and enhanced performance for UWB applications in communication, military, and satellite systems. The insights presented aim to guide researchers in achieving optimal PA designs by balancing conflicting performance metrics.

Terahertz (THz) communication has emerged as one of the key technologies for sixth-generation (6G) wireless networks. Nevertheless, the transition to higher operational frequencies poses various challenges including high-speed digital-to-analog conversion (DACs) and analog-to-digital conversion (ADCs), heterogeneous integration of optoelectronic devices, resulting in an urgent need for solutions. In this paper, we demonstrate a groundbreaking THz analog differential operator driven by diffractive neural networks (DNN), implementing ultra-fast and high-throughput analog domain differential operations. The designed multilayer all-optical DNN composed of compact dielectric metasurfaces is trained with trigonometric functions to perform analog differential computing of complex input signals by approximating the differentiation of finite decompositions of time-domain function based on the Fourier transform theory, significantly improving integration, throughput, and processing speed. Our design has been experimentally validated to successfully implement single-direction differential operation on one-(1D) and two-dimensional (2D) signals with superior structural similarity index measure (SSIM) and peak signal-to-noise ratio (PSNR), providing a promising path for the development of integrated and ultrafast THz communication systems.

Recently, the metasurface, with full control of electromagnetic wave properties over a deep-subwavelength thin surface, has been widely exploited in radar and communication systems, and is important for next-generation wireless power transfer systems, 6G communications, and other technologies. In these contexts, there are high demands for active metasurface devices with a simple feeding structure, high gain, and full-space beamforming. Here, a multifunctional leaky Fourier surface (LFS) based on a metasurface is proposed to achieve complete control of leaky electromagnetic waves through Fourier engineering. Such LFS directly maps the on-demand electromagnetic functionalities into the profile of a microstrip line with sinusoidal bends by customizing the Fourier components of the leaky surface. In doing so, we have shown several complicated and advanced functionalities, including wideband beam scanning, multiple beam generation with arbitrary gain ratios, omnidirectional scanning, and dual-beam full-space scanning. Our LFS architecture with superior beamforming capabilities is important for next-generation wireless energy, information, and communications systems.

This research introduces an innovative hybrid approach for developing a circularly polarized (CP) multiple-input multiple-output (MIMO) antenna designed for millimeter-wave (mm-wave) band applications. The proposed CP-MIMO antenna consists of four orthogonal rectangular slotted radiators, a hexagonal ring hybrid coupler-shaped parasitic element (HRHCP), and a rear Jerusalem cross-shaped decoupling ground (JCDG). A small antenna measuring 35 × 35 × 0.508 mm 3 (3.15λ 0 × 3.15λ 0 × 0.0457λ 0 ) is realized by multiple techniques, including slots in the radiator, dielectric guiding, and parasitic elements, with λ 0 denoting the free space wavelength at 27 GHz. The decoupled arrangement effectively minimizes the distance between the two radiators to 0.212λ 0 . The integration of a JCDG and HRHCP component among the MIMO antenna radiators enables the implementation of an effective decoupling technique aimed at mitigating the effects of mutual coupling (MC). The simulated outcomes of the proposed antenna with decoupling exhibit improved S-parameters, with |S 11 | < -10 dB throughout the frequency range of 24.23 to 29.02 GHz. The MIMO antenna has a low MC of |S 12 | at -29 dB and a 3-dB axial ratio (AR) spanning from 26.1 to 28.5 GHz. The proposed antenna demonstrates a maximum gain of 7.0 dBi in the lower frequency range and 7.5 dBi in the higher frequency band. An equivalent circuit model (ECM) is created for both single and MIMO layouts, providing a more detailed analytical insight. The experimental data are appropriately compared with the simulated data. The proposed architecture is optimal for 5G, satellite, and mm-wave applications, where compactness, low MC, and enhanced AR bandwidth are critical.