ABSTRACT A compact two‐port Omega Loop Annular Fusion (OLAF) MIMO antenna operating at 5.8 GHz is developed for Industrial Internet of Things (IIoT) sensing and short‐range wearable body‐centric wireless applications in controlled environments. The antenna is built on a 25.9 × 29.7 × 1.8 mm polyethylene substrate ( = 2.25, tan δ = 0.001). The proposed design employs an omega‐shaped radiating element integrated with an outer annular ring to achieve effective impedance matching. Additionally, a simple inclined slotted decoupling strip is introduced to mitigate coupling between the antenna radiators and improve port isolation without altering the ground plane. The fabricated antenna achieves a measured return loss bandwidth of 5.80–5.84 GHz, high isolation of 43.55 dB, a peak gain of 6.8 dBi, and a radiation efficiency of 96%. Furthermore, the antenna exhibits excellent MIMO performance with low envelope correlation, ideal diversity gain, negligible spectral capacity loss, and optimal active reflection characteristics. The measured and simulated results validate the proposed design, demonstrating its suitability for compact, reliable, and high‐performance dedicated wireless links in the 5.8 GHz ISM band for Industrial IoT sensing and wearable body‐centric wireless applications in controlled environments.
ABSTRACT Antenna structures usually involve many strongly coupled geometric parameters. Directly embedding full‐wave simulations into swarm‐intelligence optimization leads to high computational cost and slow convergence, while making it difficult to balance conflicting objectives such as impedance bandwidth, circular‐polarization axial ratio, and gain. To address this issue, this paper proposes a surrogate‐model‐assisted improved multi‐objective grey wolf optimization framework. The framework takes “structural parameters + frequency” as inputs to rapidly predict the swept‐frequency responses of |S11|, axial ratio (AR), and realized gain (Gain). By adaptively updating the convergence factor and introducing probabilistic mutation perturbations after position updates to enhance global exploration and avoid premature convergence, an improved grey wolf optimization strategy (IGWO) is constructed. On this basis, the method is extended to a multi‐objective framework by introducing an external archive to store non‐dominated solutions and combining grid crowding with a leader‐selection mechanism to maintain diversity, thereby obtaining a more evenly distributed Pareto‐optimal solution set. Using a millimeter‐wave circularly polarized magnetoelectric dipole antenna element as an example, the proposed method significantly reduces the number of full‐wave simulations while improving impedance bandwidth and axial ratio bandwidth, achieving comprehensive optimization of high gain, demonstrating the effectiveness and practical applicability of the framework.
ABSTRACT Designing broadband filtering power dividers with simultaneous wide bandwidth, low insertion loss, and compact size remains a significant challenge. This paper presents a novel solution using a three‐conductor broadside coupled line (TCBCL) structure, implemented on a low‐loss multilayer substrate integrated suspended line (SISL) platform. The proposed design features an air‐gap quasi‐metallic configuration between conductors to minimize dielectric loss. Input power is coupled directly from the center conductor to two side conductors, achieving equal power division ratio with an inherent broadband bandpass response. The output ports isolation is enhanced by vertically connecting two surface mounted resistors between the top and bottom conductors. For validation, a prototype was fabricated and measured, exhibiting an ultra‐compact core circuit size of only 4.11 mm × 1.08 mm × 3.25 mm. Measured results show an insertion loss below 0.57 dB across 7.7–18.1 GHz, corresponding to a fractional bandwidth (FBW) of 80.62%. This work demonstrates an effective and miniaturized design approach for high‐performance, highly integrated RF front‐ends and passive devices.
ABSTRACT This article introduces a design strategy for a class of broadband high efficiency power amplifier (PA) utilizing a novel bandpass filtering transformer. For fundamental impedance matching, the novel bandpass filtering transformer consisting of a triple‐mode cross‐shaped resonator is used to achieve high selectivity and harmonic suppression. With the advantage of the filtering characteristic, the second harmonic impedance can be controlled at the edge of the Smith chart, placing it within the high‐efficiency region of PA. This approach not only provides small‐signal gain response with sharp rejection characteristic but also achieves high efficiency in large‐signal simulation. For verification, a wideband filtering PA operating at 3–4 GHz is implemented and measured. The measured drain efficiency (DE), output power, and gain of the fabricated PA are 68.6%–81.2%, 40–40.1 dBm, and 11.1–12 dB, respectively.
ABSTRACT This letter presents a novel dual‐level compressive sensing (CS) scheme to accelerate the new accurate subentire‐domain (ASED) basis function method for electromagnetic scattering problems of finite periodic arrays. On level one, a multiple measurement vectors (MMV)‐CS model is employed to reconstruct the whole basis functions in a subarray with very few measurements, which greatly reduces both the computation time and the number of basis functions after singular value decomposition. On level two, the overdetermined sparse representation based on the MMV‐CS or single measurement vector (SMV)‐CS model is constructed to solve the induced currents for monostatic or bistatic scattering problems, respectively. With either the MMV‐CS or SMV‐CS model, only very few rows of the impedance matrix need to be calculated, and the time‐consuming construction of the reduced matrix equation is replaced by the CS equation, which can be more efficiently solved. Numerical simulations indicate that the proposed framework attains a substantial acceleration over the new ASED basis function method while preserving comparable accuracy for both discrete and electrically connected arrays.
ABSTRACT This letter proposes a frequency‐dependent subcell technique for simulating general dispersive layers within the finite‐difference time‐domain (FDTD) method using weighted Laguerre polynomials (WLPs). By reformulating the Maxwell–Ampère equations in integral form, we derive spatially resolved update equations to precisely model the electric field in subcells containing general dispersive materials. This approach significantly reduces computation time and memory consumption for multi‐scale structured electromagnetic (EM) devices. Two numerical examples verify the method's advantages. In contrast to the conventional ADE‐WLP‐FDTD approach, it accelerates computations and lowers memory usage while maintaining comparable accuracy levels.
ABSTRACT A compact quad‐band power divider based on short‐circuited coupled lines is proposed. Two‐section parallel coupled lines are employed for impedance transformation, while stepped‐impedance short‐circuited coupled lines are introduced to compensate for the dispersion effects caused by the unequal phase velocities of the even and odd modes, thereby improving impedance matching and multiband performance. Explicit closed‐form synthesis equations and a systematic design procedure are derived through a complete theoretical analysis. To validate the proposed method, a quad‐band power divider operating at 0.9, 1.9, 3.1, and 4.1 GHz is designed, fabricated, and measured. The measured results agree well with the theoretical predictions and simulations, demonstrating satisfactory power division, impedance matching, and isolation performance at all four operating frequencies. Owing to its compact size, low insertion loss, and explicit synthesis capability, the proposed divider is a promising candidate for multistandard RF front‐end applications, including cellular communications, Internet of Things (IoT), broadband wireless systems, and satellite communications.
ABSTRACT An all‐optical automatic gain‐controlled (AGC) erbium‐doped fiber amplifier (EDFA) is proposed and experimentally demonstrated for suppressing optical signal power fluctuations in terrestrial free‐space optical communication (FSOC) systems. The proposed AGC EDFA employs a simple optical feedback loop consisting of two optical couplers, an optical bandpass filter and a conventional EDFA, eliminating the need for electronic feedback circuitry. The operating characteristics of the amplifier were investigated by measuring the gain and amplified spontaneous emission (ASE) spectra under different feedback ASE peak power levels. Stable AGC operation with gain saturation was achieved when the feedback ASE peak power exceeded approximately −15 dBm, whereas excessive ASE feedback resulted in pump power depletion and reduced amplifier gain. Optical signal fluctuations emulating atmospheric turbulence were generated using an acousto‐optic modulator (AOM), and the fluctuation suppression performance was evaluated under sinusoidal, randomly varying, and square‐wave driving conditions. The proposed AGC EDFA effectively suppressed optical signal fluctuations over an AOM driving frequency range from 1 Hz to 10 kHz and reduced both the peak‐to‐peak signal variation and the scintillation index under randomly varying input conditions. Dynamic response measurements further revealed that the transient response depends strongly on the magnitude of the input optical power fluctuation because of the ASE lasing buildup dynamics and pump power depletion. These results demonstrate that the proposed all‐optical AGC EDFA provides a simple, cost‐effective, and practical approach for mitigating turbulence‐induced optical power fluctuations while offering useful design guidelines for optimizing the dynamic performance of AGC EDFAs in terrestrial FSOC systems.
ABSTRACT A dual parametric sensing structure of anti‐resonant fiber (ARF) based on surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) is presented in this paper. Gold film and gold nanoparticles are deposited inside two large anti‐resonant tubes of the cladding to excite the SPR and LSPR effects. Numerical simulations based on the finite element method (FEM) are performed to evaluate the sensing performance. The results show that there are two resonance loss peaks, peaks 1 and 2, caused by SPR and LSPR effects, respectively. When the refractive index (RI) of analyte 1 changes, both peaks 1 and 2 shift, with sensitivities of 7250 nm/RIU and 10000 nm/RIU, and the linearities are 0.978 and 0.995. When the RI of analyte 2 changes, only peak 1 shifts, with a sensitivity of 4625 nm/RIU, and the linearity is 0.991, while peak 2 remains constant. The cross‐sensitivity problem can be resolved by the dual wavelength matrix method. This dual parametric sensing structure has potential applications and development prospects in various fields such as environmental monitoring and biomedical detection.
ABSTRACT Most traditional reconfigurable antennas use electronic switch components to achieve reconfiguration characteristics, requiring complex feeding networks that are susceptible to electromagnetic interference and insertion losses. And reconfiguration is discrete and has a limited range. In response to these issues, a design scheme for frequency and pattern composite reconfigurable antennas based on compliant mechanisms is proposed in this paper. The influence of the decisive parameters in the scheme on the antenna reconfiguration characteristics is analyzed, and a novel composite reconfigurable antenna is designed based on this scheme. The performance of the antenna is measured using a vector analyzer and an OTA darkroom and compared with simulation analysis. It is proved that the antenna has low loss, large bandwidth, high gain, and wide range continuous reconfiguration performance, verifying the feasibility of the proposed composite reconfigurable antenna design scheme in this paper.
ABSTRACT Laser‐induced breakdown spectroscopy is a versatile analytical technique for rapid multi‐element detection; however, its sensitivity is often limited due to low emission intensity and high detection limit for trace elements. In this work, the enhancement of LIBS performance is systematically studied with magnetic field confinement combined with machine learning‐based analysis for trace elements in Aluminum alloys. A magnetic field of 0.5 T is applied to confine the plasma, and its effect on emission characteristics and analytical sensitivity is evaluated in comparison with unconfined (0 T) conditions. Six certified Al alloys were used to collect the emission spectra with and without magnetic field confinement. A significant enhancement in emission intensity is observed under magnetic field confinement, indicating effective plasma plume confinement. This improvement led to enhanced plasma excitation conditions and improved LIBS detection sensitivity. Furthermore, the limit of detection (LOD) of trace elements is evaluated using the calibration curve method to establish the relationship between spectral emission and elemental concentrations. The results demonstrate that the magnetic field confinement significantly reduced the LOD values in all selected trace elements. The LOD values of Mg (II) 279.55 nm and Fe (II) 288.25 nm were significantly reduced from 0.0645 to 0.0446 and from 0.0829 to 0.0673, respectively, under magnetic field confinement. The reduction of LOD under magnetic field confinement is attributed to the plasma confinement, resulting in more uniform radiation. Furthermore, to assess the quality and reliability of the LIBS signal, three machine learning models, namely Partial Least Squares Regression (PLSR), Support Vector Regression (SVR), and Gaussian Process Regression (GPR), were used. The comparison between the actual and predicted concentrations in regression plots revealed improved agreement in the presence of magnetic field confinement, as evidenced by increased values. Additionally, among the applied regression models, GPR achieved the superior predictive performance based on the evaluation parameters, RMSEP, ARE, and , owing to its strong capability to model nonlinear relationships and reduce prediction uncertainty. The proposed technique, integrating magnetic field‐assisted plasma enhancement with machine learning, provides an effective approach for improving the detection capability of LIBS and offers strong potential for high‐sensitivity trace element analysis.
ABSTRACT A broadband monopulse antenna based on aperture coupled stacked patch antenna is presented. The microstrip feed line is applied in such a way that the antenna has slant polarization. So, the antenna's orientation relative to the target has no influence on the angle estimation. A reduced size meander‐line rat‐race coupler was used to design comparator network. Four meander‐line rat‐race was used to allowing tracking in both azimuth and elevation plane. Antenna dimension is 1.51.5 × 0.2 at minimum frequency. All PCB antenna components, including monopulse comparator and radiation element was fabricated and is mechanically fastened using multiple screws to ensure a rigid integration. The bandwidth (VSWR < 2) is 12%, and the operating frequency is 3.1–3.5 GHz. The Sum and difference pattern measured in anechoic chamber shows high stability and null depth better than −30 dB.
ABSTRACT An innovative wideband microstrip bandpass filter (WM‐BPF) is proposed for FR1 5 G communication. The designed filter has a compact size of 11 × 13 mm 2 (0.45 λg × 0.53 λg), where λg refers to the guided wavelength of the resonant frequency. Its structure consist of a central resonator, inspired by traditional Moroccan Zellij patterns, positioned between two symmetrical rectangular sections. The proposed filter is optimized through a parametric study to acheive the desired performance characteristics. The modeling and analysis of the proposed BPF have been carried out using HFSS (High Frequency Structure Simulator) simulation tool, while the corresponding equivalent circuit has been created using the ADS (Advanced Design System). A prototype of the proposed WM‐BPF is fabricated using an FR4 substrate with a thick of 0.8 mm and measured using a ZVA 67 VNA instrument. The fabricated filter exibits a resonant frequency at 6.16 GHz and a bandwidth of 3.72 GHz, ranging from 4.60 GHz to 8.32 GHz. The maximum value of S 11 is equal to −33.9 dB, and the fractional bandwidth is around 60.39%. The novelty of the proposed BPF lies in its ability to achieve a wide passband operation with high performance specifications while maintaining a very small size. These characteristics underscore the filter's relevance for 5 G deployment in nations such as the United States (4.94–4.99 GHz, 5.9–7.1 GHz), Canada (5.9–7.1 GHz), the U.K., Germany, France, Italy (5.9–6.4 GHz), China (4.8–5 GHz), Japan (4.5–4.9 GHz, 5.9–6.4 GHz), South Korea (4.72–4.82 GHz, 5.9–7.1 GHz), and Australia (5.9–6.4 GHz) by supporting 5 G FR1 New Radio (NR) bands including n96 (5.925–7.125 GHz), n102 (5.925–6.425 GHz), n104 (6.425–7.125 GHz).
ABSTRACT In this paper, an ultra‐wideband (UWB) notch antenna for wearable applications is proposed, and the operating frequency of the antenna is 3.04 to 14.4 GHz. On the basis of the monopole UWB antenna, five notch bands from 3.87 to 4.27 GHz, 5.23 to 6.26 GHz, 8.4 to 8.56 GHz, 9.48 to 11 GHz, and 11.45 to 12.69 GHz are realized. The antenna uses Rogers 5880 material as the dielectric substrate and is only 0.45 mm thick. Due to the use of flexible materials and the low‐profile nature of the antenna, the antenna can be slightly curved, which allows it to be applied in the wearable field. Five‐notch bands are achieved by adding a notched structure on both sides of the microstrip line, inside the rectangular patch, and at the bottom of the substrate. By adding a metal through hole inside the substrate, an electric current is introduced into the notch structure at the bottom of the substrate to achieve a better notch effect. The overall antenna size is 30 × 25 × 0.45 mm 3 , which meets the design requirements of miniaturized antennas. By simulating the S 11 curved antenna and the Specific Absorption Rate (SAR) value of the human hand, the antenna is suitable for wearable applications.
ABSTRACT This paper presents an extremely high isolation of a Multiple‐Input Multiple‐Output (MIMO) antenna incorporating a parasitic element on a U‐slot Defected Ground Structure (DGS) for 5G Vehicle‐to‐Everything (V2X) communication. MIMO antenna was designed using a Rogers RT5880 substrate with a low‐profile 1.49 λ ×1.49 λ × 0.031 λ. The antenna operates at 5.9 GHz and exhibits superior isolation characteristics, achieving a mutual coupling level of as low as −48 dB. The design also achieves a high gain of 8.5 dBi, a high bandwidth (5.8–6.08 GHz) of 4.74% and an exceptional radiation efficiency of 98%. The novelty of this work lies in the combined use of a parasitic strip line structure and a U‐slot DGS arranged strategically to suppress mutual coupling without increasing the antenna footprint. Both simulated and measured results confirm the proposed antenna's suitability for next‐generation 5G V2X systems.
ABSTRACT Wideband balun and balanced bandpass filters (BPFs) are proposed with a differential coupled structure mainly made up of a center‐shorted coupled three‐line in this letter. By feeding two half‐wavelength ( λ g /2) open‐circuited lines from opposite terminals and symmetrically coupling their electric fields to a quarter‐wavelength ( λ g /4) short‐circuited output line, the balun achieves wideband differential‐mode (DM) conversion and common‐mode (CM) rejection. The conditions for realizing out‐of‐phase signals with equal amplitude are derived from the impedance matrix of a general six‐port coupled three‐line structure. A high‐selectivity balun BPF is then designed and implemented by extending two differential feeding lines with short‐circuited stubs on a two‐layer back‐to‐back microstrip structure with a coupling slot etched in the common ground. Furthermore, a compact balanced BPF with wideband CM suppression is synthesized based on a symmetrical shot‐circuited stepped impedance resonator fed by two pairs of differential structures and implemented using broadside coupled stripline. For demonstration, both designed BPFs are fabricated and tested. Results show that both proposed balun and balanced BPFs have compact sizes and nice balance performances.
ABSTRACT This study focuses on the design of an ultra‐wideband power amplifier targeting high performance, high output power, and low cost. In contrast to conventional 50 Ω internally‐matched schemes relying on expensive custom metal‐ceramic packages, this letter presents a 2–6 GHz 100 W ultra‐wideband gallium nitride (GaN) power amplifier using a hybrid integration approach. Specifically, an in‐package pre‐matching network within a standard commercial package transforms the low output impedance of the bare die to an intermediate real impedance, while an external Klopfenstein taper on the printed circuit board is utilized to achieve impedance matching from this intermediate impedance to 50 Ω with a compact footprint over an ultra‐wide bandwidth. Measurement results demonstrate that the realized power amplifier delivers 50–51 dBm output power, 42%–65% drain efficiency at saturation, and 7.5–11.9 dB gain at 50 dBm output power across the entire 2–6 GHz band under continuous‐wave (CW) excitation.
ABSTRACT A novel Class E/F power amplifier (PA) with wide bandwidth is presented in this paper. The proposed approach is used to realize a high‐efficiency PA. By introducing an additional shunt capacitance into the original circuit, a harmonic control network is obtained, which satisfies the load impedance requirements of Class E/F PA at odd and even harmonics, while simultaneously matching the fundamental impedances to a 50 Ω load. Experimental verification shows that the fabricated PA achieves a measured drain efficiency (DE) of 67.2%–79.2% in the range of 1.9–3.0 GHz, with an output power of 40.2–43.0 dBm.
ABSTRACT This study presents an antenna for global short‐message communication systems, operating in the B2b (1197–1217 MHz) and Lf4 (1610–1630 MHz) bands. To achieve excellent impedance matching within the target frequency ranges, the antenna employs a rhombic cross‐dipole with a central open circular slot, integrated with a top‐loaded circular patch technique. Dual‐circular polarization (Dual‐CP) is realized via a dual‐stub network combined with orthogonal baluns, while the feed network incorporates built‐in high‐pass and low‐pass filters to ensure high port isolation. Additionally, eight equidistantly arranged passive monopole fences are placed around the radiating element to enhance antenna gain at low elevation angles. Experimental results indicate the antenna exhibits a compact form factor (110 mm diameter × 48 mm height) and lightweight design (300 g), with Dual‐CP port isolation exceeding 54 dB. These superior performance metrics make the proposed antenna well‐suited for lightweight satellite systems, demonstrating significant application potential in global satellite short‐message communication scenarios.
ABSTRACT This paper presents a compact dual‐band leaky‐wave antenna (LWA) based on a periodically loaded microstrip line incorporating two non‐identical stepped‐impedance resonator (SIR) stubs per unit cell. The dual SIR configuration excites two independent leaky modes within the same aperture, enabling frequency‐controlled beam scanning in both sub‐6 GHz and upper 7 GHz ranges, suitable for V2X and future 6G applications, respectively. The designed structure exhibits continuous beam steering from approximately to in the lower band (5.6–5.9 GHz) and from to in the upper band (7.1–7.7 GHz). The antenna is realized on an FR‐4 substrate (), achieving measured impedance bandwidths of and in the two bands, with peak realized gains of 3.23 and 3.03 dBi, respectively. A periodic dispersion analysis and an equivalent lumped‐element model are developed to verify the leaky‐wave mechanism. Simulated and measured results show good agreement, confirming that the dual SIR loading within a single aperture can effectively produce distinct leaky‐wave radiation bands while maintaining compactness and low fabrication cost.
