Wiley: Microwave and Optical Technology Letters: Table of Contents

A Metasurface‐Based Circularly Polarized Magneto‐Electric Dipole Antenna Arrays With Wide Bandwidth for Ku Band

Ting Wu, Min Yao Wang, Zhuo Yue Bai — Mon, 08 Jun 2026 02:48:27 -0700

ABSTRACT

This letter proposes a novel broadband circularly polarized magnetoelectric dipole antenna array loaded with metasurfaces (MS). To further improve the gain and expand the axial-ratio (AR) bandwidth, a beveled 4 × 4 MS structure was loaded on the top layer of the magnetoelectric dipole antenna element. Subsequently, a 4 × 4 antenna array was designed through sequential rotation (SR) technology. A prototype of the antenna array was fabricated and the design was verified. The test results show that within the operating frequency band, the impedance bandwidth of the device is 40% (12–18 GHz), and the gain bandwidth of 3 dB is 32.37% (12–16.64 GHz). The 3 dB AR bandwidth of 32.11% (12–16.59 GHz) and a peak gain of 18.5dBic were simultaneously recorded. Therefore, the antenna proposed in this letter demonstrates strong applicability to Ku-band (12–18 GHz) communication.

Quantitative Analysis of the Delay Fiber Length Requirement for Accurate Laser Linewidth Measurement in Self‐Heterodyne Method

Hailang Zhou, Haoyi Han, Kan Chen, Xuan She, Ran Bi, Xiaowu Shu — Sun, 07 Jun 2026 05:59:44 -0700

ABSTRACT

The delayed self-heterodyne method (DSHI) is a standard technique for measuring laser linewidth. A widely adopted empirical criterion suggests that the delay fiber length must exceed 6 times the laser's coherence length; however, the theoretical basis for this factor is rarely detailed. Based on the fundamental theory of DSHI, this paper elucidates the measurement mechanism and quantitatively analyzes the impact of delay fiber length on measurement accuracy. We investigate the physical origin of spectral broadening and propose three criteria—algebraic, peak-to-peak ripple, and systematic error—to determine the optimal fiber length. Comprehensive analysis demonstrates that the delay fiber length should be at least 6.22 times the laser's coherence length to maintain a systematic measurement error below 1%.

An Analog Linearizer for Doherty Amplifiers Based on Impedance Modulation

Minxian Song, Songbai He, Fei You, Haiqian Tang, Chuan Li, Peng Hao — Fri, 05 Jun 2026 04:24:29 -0700

ABSTRACT

This paper presents an analog linearizer for Doherty amplifiers (DPAs) to accurately compensate for gain curves with multiple inflection points. The linearizer consists of a hybrid coupler and two Schottky diode nonlinear networks, one of which is used to achieve a gain trend with a single point of inflection, while the other further increases the number of inflection points through impedance modulation between branches. By sweeping its bias voltages, the proposed linearizer has a flexible tunable gain range and a low phase variation. Excited by a single carrier 64-QAM signal with a bandwidth of 20 MHz, the test results show that the proposed linearizer is able to effectively compensate the AM−AM of DPA at 3.5 GHz without deterioration of AM−PM. The output adjacent channel leakage ratio (ACLR) of the example DPA is improved by 5 dB, from −32.8/−32.6 to −40.8/−41.1 dBc, and the error vector magnitude (EVM) is improved from −29.4 dB to −37.9 dB.

Design of A Triple‐Band Filtering Power Divider With Unequal Power Division Ratios

Fri, 05 Jun 2026 00:37:03 -0700

ABSTRACT

In this paper, a novel triple-band unequal filtering power divider with favorable selectivity and isolation is proposed. Through the utilization of one bandpass resonator (BPR) and two bandstop resonators (BSR), a triple-band bandpass filtering response is achieved. The external coupling of two output ports are set to different values to achieve an unequal power division ratio. A comprehensive analysis is provided to guide the design, and subsequently, a triple-band FPD prototype is designed, fabricated, and measured for validation. The measured results are found to be in good agreement with the simulated ones, indicating that the designed FPD operates at 1.8 GHz/2.2 GHz/2.48 GHz with the 3-dB fractional bandwidth (FBW) of 6.4%/5.7%/3.2%, with the unequal power distribution of k = 2.

A Broadband Multifunctional Reconfigurable Reflective Metasurface Element

Yuchen Liu, Shaobin Liu, Zhichao Sun, Jian Lou, Junyin Wang — Thu, 04 Jun 2026 03:59:27 -0700

ABSTRACT

This letter presents a broadband multifunctional reconfigurable reflective metasurface element (RRME) operating in the X-band. Unlike conventional reconfigurable metasurface elements that typically offer limited functionality and polarization flexibility, the proposed element integrates broadband 1-bit phase modulation, continuous reflection-amplitude tuning, and polarization-dependent control. By exploiting the switching and attenuating characteristics of PIN diodes and a compact DC-bias network, the reflection response is controlled through the PIN-diode pair aligned with the polarization of the incident wave. Under this polarization-selective biasing scheme, broadband 1-bit phase modulation with a phase difference of 180° ± 30° is achieved over the 9.65–11.7 GHz band, and the reflection amplitude can be continuously tuned from near-unity reflection to below −10 dB over 9–11.5 GHz, without increasing structural complexity. A prototype is fabricated and measured with a rectangular waveguide, and good agreement between simulations and measurements validates the effectiveness of the proposed design.

Miniaturized Self‐Diplexing Antenna Design With Dual‐Mode Operation in Each Band and Based on a Double‐Layered Open Cavity

Yipei Liu, Yun‐Sheng Xu, Chang Chen, Xiang Zhang, Weidong Chen — Thu, 04 Jun 2026 00:48:47 -0700

ABSTRACT

This paper presents a miniaturized self-diplexing antenna with dual-mode operation in each band. The design is based on a single open cavity of the substrate integrated waveguide type, which contains double substrate layers and double patches. The cavity may generate modes in pairs with four magnetic side walls, similar field patterns in the horizontal substrate plane, and near resonant frequencies. By selecting the lowest order paired TE₁₀₀ and TEM₀₀₁ modes as working modes, not only double-resonance points in each frequency band but also significant miniaturization can be achieved. It offers excellent independent frequency tuning compared with stacked microstrip patch antennas. The antenna has a very compact size of 0.48 × 0.41 × 0.03λ ³, where λ is the dielectric wavelength at the center frequency of the lower band. To validate the proposed design, a prototype of the antenna is fabricated and tested. The measured bandwidths are 3.04% and 3.12%, and realized gains 6.27 and 6.56 dBi for the lower and higher bands, respectively. The measured isolation between the two input ports is less than −30 and −28 dB for the two bands, respectively. The designed antenna demonstrates excellent performance, with a simple design process supported by fundamental analysis.

High Selectivity and Wide Stopband Limiting Filter With Dual‐Path Resonators and Quasi‐Lumped Topology

Kun Feng, Hao‐Ran Zhu — Wed, 03 Jun 2026 22:21:04 -0700

ABSTRACT

In this paper, a high selectivity and wide stopband limiting filter with dual-path resonators and quasi-lumped topology is presented. Dual-path resonators (DPRs) are employed to realize a bandpass cell with multiple transmission zeros (TZs) on both sides of the passband for skirt selectivity enhancement, which is further improved by stepped-impedance open stubs (SIOSs). To achieve a wide upper stopband without increasing the circuit size, a quasi-lumped topology incorporating limiting diodes is designed to introduce additional TZs in the upper stopband for controllable spurious-response suppression. A prototype of the proposed limiting filter is fabricated with a center frequency f ₀ of 3.55 GHz. Measurement results show that the stopband is extended up to 5.27f ₀ with a minimum rejection level of 21.4 dB. The selectivity factor, defined as the ratio of the 15-dB bandwidth (BW) to the 3-dB bandwidth, is 1.44. Good agreement between simulated and measured results is observed.

Interpretable Hardness Classification of Alloy Steels Using LIBS With CARS and SHAP

Changjin Che, Qiang Yao, Shuaiqi Xu, Zengyan Wang, Yunzhong Gao — Wed, 03 Jun 2026 01:37:09 -0700

ABSTRACT

With the development of modern industry, the requirements for metallic materials are becoming increasingly stringent. Hardness, as one of the core indicators for evaluating material properties, holds significant importance in industrial applications. Therefore, rapid and real-time hardness detection should be carried out to further eliminate unqualified products. This study combines laser-induced breakdown spectroscopy (LIBS) and classification models. The method identifies metals of different hardness levels quickly. The investigated samples were divided into low, medium, medium-high, and high hardness groups, and multiple classification models were selected for comparison. Competitive adaptive reweighted sampling (CARS) was employed for feature extraction, and the extracted features were used as input data for model construction. Among the models, the convolutional neural network (CNN) achieved the best performance, with accuracy and F1-score reaching 0.99. The results demonstrate that the combination of LIBS and classification models can be effectively applied to the detection and classification of metal hardness. Finally, SHapley Additive exPlanations (SHAP) was adopted to further analyze the contribution of features. The top-10 elements in terms of contribution also validated the effectiveness of feature extraction and the classification model.

A Compact Low‐Cost Reconfigurable Intelligent Surface for Wide‐Angle Beam Steering

Goundla Sricharani, Patinavalasa Megh Sainadh, Saptarshi Ghosh — Wed, 03 Jun 2026 01:31:10 -0700

ABSTRACT

This letter presents a 2-bit reconfigurable intelligent surface (RIS) implemented on a low-cost FR4 substrate for wide-angle beam steering applications in 5G and beyond. The proposed RIS employs a varactor diode-based unit cell design combined with an air spacer that achieves four discrete reflection states (−165°, −75°, 15°, and 105°) over an aperture size of 4.4λ ₀ × 4.4λ ₀, λ ₀ being the wavelength at 4 GHz. With the dynamic regulation of reflection phases, the design exhibits the beam steering operation covering an angular range of −50° to +50° under normal incidence, further extending to ±70° for an incident angle of ±60°. A detailed analysis is carried out to illustrate the steering operation, which is further confirmed by experimental measurements conducted in both indoor and outdoor environment. A comparative analysis with existing designs reveals significant improvements in the beam steering performance, thereby demonstrating the potential of the proposed RIS in advanced wireless communication systems.

Four‐Port Orthogonal MIMO Antenna Using Meander‐Line Elements for ISM Band and Wireless Applications

Ajay Kumar Maddirala, Bappadittya Roy — Tue, 02 Jun 2026 05:38:44 -0700

ABSTRACT

This letter presents a compact wideband four-port multiple-input multiple-output (MIMO) antenna designed for ISM band and wireless communication applications. The primary design challenges addressed include achieving wide impedance bandwidth, maintaining high inter-element isolation, and ensuring compactness within a limited substrate area. To mitigate mutual coupling, four meander-line monopole radiators are arranged in an orthogonal configuration, while a circular ring integrated with symmetric stubs is employed to enhance impedance matching and decoupling. Additional ground stubs and defected ground structures are introduced to further suppress surface current coupling. The proposed antenna operates over a wide frequency range from 2.37 to 5.27 GHz and occupies a compact footprint of 0.428 λ × 0.428 λ × 0.013 λ $0.428\lambda \times 0.428\lambda \times 0.013\lambda $, where λ $\lambda $ corresponds to the free-space wavelength at 2.47 GHz. Fabricated on an FR4 substrate, the antenna is experimentally validated in an anechoic chamber. Measured results demonstrate isolation better than − 18 $-18$ dB across the operating band. Key MIMO performance metrics indicate excellent diversity behavior, with an envelope correlation coefficient (ECC) of 0.038, diversity gain (DG) of 9.998, channel capacity loss (CCL) below 0.27 bits/s/Hz, and mean effective gain (MEG) below − 3 $-3$ dB. The close agreement between simulated and measured results confirms the suitability of the proposed antenna for compact MIMO-based wireless systems.

Study on Thermally Induced Spot Drift Effect in Yb3+‐Doped N × N Square‐Array Multicore Fibers

Wenshi Liu, Jianyong Ding, Haohao Gao, Xiao Shen — Tue, 02 Jun 2026 00:37:58 -0700

ABSTRACT

Multicore fibers have found significant applications in laser coherent beam combining systems, but thermally induced spot drift (TISD) compromises the coherent combining efficiency. This paper, based on thermo-optic effects and heat conduction theory, employs numerical simulation and parametric methods to establish a model of a 5 × 5 square array of ytterbium-doped multicore fibers. It analyzes the characteristics of spot drift caused by thermal refractive index gradients and the degradation patterns of system performance. By investigating how fiber structural parameters affect thermal effects and analyzing the temperature distribution characteristics, we find that reducing the core size, increasing the core spacing, increasing the core–cladding refractive index difference, and adopting a distributed pumping strategy can effectively suppress the detrimental effects of thermal nonlinearity on beam quality. This study provides theoretical support for the thermal management design and structural optimization of high-power fiber lasers, ensuring stable operation within an appropriate temperature range. It offers strategic guidance for performance breakthroughs in related applications.

On‐Chip High‐Selectivity Substrate Integrated Waveguide Bandpass Filter Based on Through Glass via Technology

Mon, 01 Jun 2026 03:02:50 -0700

ABSTRACT

This letter presents a high-selectivity fourth-order W-band Substrate Integrated Waveguide (SIW) bandpass filter, realized using wafer-level Through Glass Via (TGV) technology. To achieve steep out-of-band rejection, extracted-pole resonator and singlet resonator technologies are adopted to generate two asymmetric transmission zeros (TZs) flanking the passband, significantly enhancing frequency selectivity. Furthermore, a novel micro-hole array structure is introduced on the metallization layers to effectively mitigate thermal stress, a common challenge in large-area glass processing. The fabricated prototype, centered at 86.9 GHz, demonstrates a passband from 84.3 to 89.1 GHz with an insertion loss of less than 2.6 dB. The excellent agreement between measured and simulated results validates the design methodology, offering a highly competitive filtering solution for integrated W-band communication and radar systems.

Optically Transparent Ka‐Band Absorber With Multi‐Fractal Rings and a Metal Mesh Ground Plane

Mon, 01 Jun 2026 00:00:00 -0700

ABSTRACT

An optically transparent absorber based on multi-fractal ring resonators and a metal mesh ground plane is presented for Ka-band applications. By merging multiple resonances, the proposed absorber maintains an absorption bandwidth from 25.8 to 31.1 GHz. The metal mesh ground plane provides 89% optical transparency while exhibiting only a 0.11-dB difference in the referenced reflection loss compared to a continuous metal ground at 28.0 GHz. Measured results confirm good agreement with simulations and demonstrate angularly stable absorption under oblique incidence. This proposed structure can be integrated onto glass surfaces to suppress window-induced reflections in dense millimeter-wave propagation environments.

Low Insertion‐Loss High Power X‐Band SPDT Transmit/Receive Switches in 250 nm GaN HEMT

Tae‐Hoon Kim, Mun‐Kyo Lee, Soonyoung Hong, Jung‐Dong Park — Sun, 31 May 2026 07:15:53 -0700

ABSTRACT

We present three X-band transmit/receive (T/R) switches utilizing single-pole double-throw (SPDT) structures in 250 nm GaN HEMT technology. The first T/R switch was designed to achieve low insertion loss by constructing the SPDT structure with a series λ/4 transmission line (T-line) and meticulously selected two HEMT switches in parallel for each transmit and receive path. Based on the proposed low-loss architecture, the second T/R switch integrated 2^nd and 3^rd harmonic rejection notches to suppress harmonic distortions effectively. The third T/R switch was implemented to operate with a positive control voltage, achieved by employing a positive bias voltage at the source of the HEMT with AC coupling capacitors at the drain and source of the normally-on HEMT. Measurements demonstrated that the fabricated three T/R switches achieved insertion losses of 0.44 , 0.54 , and 0.66 dB, corresponding IP_0.2dB of 44 , 44 , and 43 dBm, respectively. With a compact die size of 5.4 mm², the three T/R switches exhibited excellent RF performance, surpassing the recently reported novel X-band SPDT switches in 250 nm GaN HEMT.

Analysis and Design of Full‐Band Reflectionless Printed Log‐Periodic Dipole Antenna With Dual Absorptive Notched Bands

Sun, 31 May 2026 07:14:26 -0700

ABSTRACT

In this letter, the analysis and design of a full-band reflectionless printed log-periodic dipole antenna (PLPDA) with dual absorptive notched bands is proposed. Resistive loading units (RLUs) are applied to the PLPDA, thereby achieving flexible notched bands through energy absorption rather than reflection. Resistors are loaded at the end of the feeding line to absorb nonradiated low frequency components, achieving full-band reflectionless characteristic. The reflection coefficient is maintained below −10 dB from DC to 12 GHz, while the realized gain exhibits over 15 dB suppression at 2.45 and 5.8 GHz. Therefore, the proposed antenna is suitable for ultra-wideband (UWB) systems requiring suppression of low frequency and targeted band interference.

A Wideband Horn Array Ridge Waveguide Antenna for Millimeter Automotive Radar Applications

Xinwei Chen, Quan Xue, Wenquan Che, Yuehui Cui — Sun, 31 May 2026 07:10:11 -0700

ABSTRACT

A wideband horn array ridge waveguide antenna is presented for millimeter automotive radar applications. This antenna is a slotted waveguide antenna loaded with a horn layer. After introducing a pair of ridges to the waveguide cavity, the antenna operates in modes quasi TEM₁₈₀, quasi TEM₁₉₀, and quasi TEM₁₋₁₀₋₀. By combing the three modes together, the ridge waveguide antenna obtains a wide band. A horn layer has been employed to narrow the half-power beamwidth of the slotted waveguide antenna, thereby enabling a 3.5-dB gain enhancement. The horn elements of the horn layer are not uniformly arranged and are interconnected in order to reduce sidelobe levels. The impedance matching is also obviously improved by the horn layer. The proposed antenna has been fabricated and measured. The results confirm that the ridge waveguide antenna has a wide bandwidth of 68.7–87.6 GHz with a gain of 17.5 dBi. A Stable fan-beam radiation pattern is realized and the SLLs are around−20 dB.

A Wideband Magnetic Dipole Antenna With an Artificial Magnetic Conductor Reflector and Its Wide‐Angle Scanning Phased Array

Honglin Zhang, Jiarong Wang, Zhijian Li, Zhijian Chen, Shaowei Liao — Sun, 31 May 2026 03:25:16 -0700

ABSTRACT

Wideband and compact phased arrays are widely used in communication systems because of their wide-angle scanning capabilities. This paper presents a wideband wide-angle scanning phased array composed of eight compact magnetic dipoles and an artificial magnetic conductor (AMC) reflector. The magnetic dipoles, fed by tapered L-probes, achieve a fractional bandwidth of 45.3% (1.76–2.79 GHz) while maintaining a compact size of 0.188λ ₀ × 0.188λ ₀ at 2.25 GHz. The AMC reflector improves the front-to-back ratio (FBR) by 10 dB because it suppresses the backward radiation. The phased array is constructed with an element spacing of 0.42λ ₀ to suppress grating lobes. Measured results demonstrate a maximum scanning range of ± 65° within a 34.8% fractional bandwidth (1.85–2.63 GHz), with a gain fluctuation less than 3 dB and a peak gain up to 13.2 dBi. The performance and compactness of the array ensure its suitability for wide-angle scanning applications.

Wideband n‐Way Power Dividers Using Transformers for HF/VHF Applications

Da‐Hai Ni, Lei Liu, Jie Chen, Zheng‐Bin Wang — Fri, 29 May 2026 06:06:35 -0700

ABSTRACT

In this letter, an n-way power divider based on ferrite transformers is presented for high-frequency (HF) and very-high-frequency (VHF) applications, where a novel circuit topology is proposed to realize wideband impedance matching. And a radial isolation network constructed by n resistors is introduced to improve the isolation, thereby avoid jumper resistors between output ports. The even-odd-mode analysis method is adopted to explore the mechanism of the proposed topology. Then, a wideband five-way power divider is designed to verify the validity of the proposed method and topology. The measured results demonstrate that this design exhibits excellent performance in the frequency band of 0.01-450 MHz. The return loss of the input port is better than 20 dB, the isolation between output ports is more than 23 dB, and the amplitude and phase imbalances are less than 0.2 dB and 1.7°, respectively.

Enhanced Frequency‐Beam Scan by a Metamaterial ULWA With Multiple Lorentz Resonances

Fri, 29 May 2026 06:04:08 -0700

ABSTRACT

Uniform or quasi-uniform leaky wave antennas (ULWAs) can realize fast beam scanning in space by varying the operating frequency. This scheme is enabled by the dispersive spectrum of the master waveguide (MWG). The dispersion of the MWG is crucial in determining the antenna's frequency beam scanning rate (FBSR), which is commonly low. To enhance the FBSR of a ULWA, we propose a metamaterial waveguide with double Lorentz resonances. We demonstrate that enhanced spectral dispersion of the MWG is formed between two distinct Lorentz oscillations through a superposition effect. By shifting either of the Lorentz oscillations, we can tune the MWG's spectral dispersion. As a result, the ULWA based on this highly dispersive MWG shows a controllable FBSR. We designed and fabricated a ULWA prototype in experiments. The measured FBSR of the ULWA can reach up to 19.8°/%, which is much higher than any previous designs. The proposed ULWA with enhanced FBSR can be used to promote novel applications, including fast target sensing, tracking, and imaging.

A 1–12 GHz Ultra‐Wide Band Bidirectional Amplifier Featuring Enhanced Loop Stability

Rui Diao, Yu Ai, Tiedi Zhang, Chao Fan — Fri, 29 May 2026 03:37:13 -0700

ABSTRACT

Bidirectional amplifiers (BDAs) are key components in RF communication systems, enabling efficient two-way signal transmission over shared paths. Enhancing their performance is essential for improving signal integrity, reduce power loss, and increase overall system efficiency, particularly in compact and high-frequency wireless applications. In this study, we report the design and fabrication of an ultra-wideband BDA operating at 1–12 GHz using the GaAs 0.25 μm PHEMT process. we introduce a new common-leg topology, which significantly improves the switching speed between transmit and receive (T/R) modes. We incorporate RLC negative feedback and peaking inductor techniques to ensure consistent gain flatness across the operating band of the developed amplifier and provide positive gain slope compensation. Moreover, we analyze the high-frequency stability in the bidirectional signal paths by proposing a design methodology based on the loop stability model to guarantee unconditional stability. Our findings demonstrate a small-signal gain exceeding 13 dB in both T/R modes over the full 1–12 GHz band of the amplifier, with input and output return losses better than 10 dB. The noise figure remains below 4 dB, and the output 1 dB compression point (OP-1dB) is better than 14 dBm. Additionally, the amplifier exhibits stable performance across varying temperature conditions, indicating robust thermal reliability.

A Novel Microstrip‐Valley Photonic Topological Waveguide for Robust Microwave Transmission

Yiyang Chen — Fri, 29 May 2026 00:46:49 -0700

ABSTRACT

Topological insulators exhibit considerable immunity to path defects, and their lightweight advantage makes them easier to integrate compared to metallic waveguides and coaxial cables, offering a novel approach to support scattering-resistant transmission and transmission along bent paths. By adjusting the unit cell morphology of valley photonic crystals, this paper designs a C ₃-symmetric microstrip valley photonic lattice based on a sector-shaped structure, which opens the degeneracy at the K(K′) points in the Brillouin zone and forms a topologically nontrivial photonic bandgap. Simulations and experiments demonstrate that this waveguide exhibits excellent filtering selectivity within the frequency range of 10.5–11.5 GHz, enabling unidirectional transmission and low-insertion-loss transmission of electromagnetic waves in the communication band. Compared with traditional metallic rectangular waveguides, the insertion loss variation caused by introducing a Z-shaped bending path is minimal, indicating remarkable robustness against path defects.

Wideband Microstrip Fed Slot Antenna Featuring Mode Conversion and Coordinated Radiation

Honglin Zhang, Wenxin Ke, Zhijian Chen, Zhijian Li, Shaowei Liao — Fri, 29 May 2026 00:38:28 -0700

ABSTRACT

Wireless communication systems need broadband antennas with small backward radiation antennas for large throughput and low interference. This letter presents the design of a microstrip fed slot wideband antenna featuring mode conversion between heterogeneous transmission lines and coordinated radiation of multiple slots, which ensure the antenna achieve an average gain of 5.17 dBi in a bandwidth ranging from 0.75 to 2.24 GHz. Aiming at reducing backward radiation, electro-magnetic wave is redirected to the upper hemisphere through four rectangular slots that were placed in the ground plane. Measured results show the antenna's max gain of 6.12 dBi and a variation of ±0.95 dB in a fraction bandwidth of 99.7%, which verifies the design as they agree well with the simulated ones. The average gain increment from original antenna to proposed antenna is 8.6 dB and the average backward radiation reduction from original antenna to proposed antenna is 16.03 dB. The wide bandwidth, small backward radiation and gain variation make the antenna suitable for wideband communication systems.

A Compact Pattern‐ and Polarization‐Reconfigurable Dielectric Resonator Antenna

Kunlong Zhao, Shiwen Lei, Menglong Chen, Xiaotong Sun, Wei Yang — Fri, 29 May 2026 00:34:15 -0700

ABSTRACT

In this letter, a compact pattern- and polarization-reconfigurable dielectric resonator antenna (DRA) based on complementary source is proposed. The antenna consists of a dielectric resonator (DR), four metallic rods, and two input ports. The DR operates in TE 111 ${\text{TE}}_{111}$ mode, acting as a magnetic dipole, while the metallic rods function as electric dipoles, forming different complementary sources. By switching the excited modes of input ports and ON/OFF states of four p-i-n diodes, the antenna generates eight modes. These modes include broadside modes ( θ = 0 ∘ $\theta ={0}^{\circ }$) with linear polarization at φ = 0 ∘ ∕ 4 5 ∘ ∕ 9 0 ∘ ∕ 13 5 ∘ $\varphi ={0}^{\circ }\unicode{x02215}4{5}^{\circ }\unicode{x02215}9{0}^{\circ }\unicode{x02215}13{5}^{\circ }$, and tilted modes ( θ = 3 8 ∘ $\theta =3{8}^{\circ }$) at φ = 0 ∘ ∕ 9 0 ∘ ∕ 18 0 ∘ ∕ 27 0 ∘ $\varphi ={0}^{\circ }\unicode{x02215}9{0}^{\circ }\unicode{x02215}18{0}^{\circ }\unicode{x02215}27{0}^{\circ }$, respectively. Thus, the antenna realizes reconfigurable pattern and polarization. A prototype is fabricated and verified. The fabricated antenna features a compact size of 0.39 λ 0 × 0.39 λ 0 × 0.15 λ 0 $0.39{\lambda }_{0}\times 0.39{\lambda }_{0}\times 0.15{\lambda }_{0}$ ( λ 0 ${\lambda }_{0}$ represents the free-space wavelength at 3.55 GHz). The measured overlapped ∣ S 11 ∣ $| {S}_{11}| $ under −10 dB is 3.28–3.84 GHz (15.7%), covering the 5G-N78 band.

Graphene‐Au‐Cu‐MXene Multilayer Metamaterial Plasmonic Biosensor With Machine Learning‐Assisted Optimization for Label‐Free THz Detection of Waterborne Bacterial Pathogens

Fri, 29 May 2026 00:00:00 -0700

ABSTRACT

Detection of waterborne bacterial pathogens such as Escherichia coli, Salmonella typhimurium, and Vibrio cholerae requires methods that operate with high sensitivity and can be deployed outside laboratory settings. This study describes a multilayer metamaterial plasmonic biosensor operating in the terahertz frequency range for label-free refractive index sensing. The device uses a 4 × 4 periodic array of vertically stacked resonant nanostructures on a silicon substrate. The structure combines a gold Y-shaped nanoresonator, a copper circular cavity, a MXene square-ring resonator, and a graphene circular disc. This configuration supports strong field confinement, electrical tunability through graphene, and reduced reliance on noble metals.Finite element simulations in COMSOL Multiphysics quantify the dependence of absorption on incidence angle, graphene chemical potential, and resonator geometry. The optimized configuration uses a copper circular resonator diameter of 5500 nm, a MXene square-ring outer dimension of 2000 nm, and a gold Y-resonator arm width of 600 nm. Within a refractive index range of n = 1.33 to n = 1.3921, the device achieves a peak sensitivity of 0.751 THz/RIU and a figure of merit of 1.140 RIU⁻¹. The frequency response shows a linear relation with refractive index, with R ² = 0.93337 across the evaluated material configurations. A regression-based surrogate model trained on the simulation dataset predicts device response with R ² above 0.9992 and mean absolute percentage error below 0.2%. This model reduces the need for repeated full-wave simulations during design iterations. The results support the use of the proposed structure for label-free THz sensing of waterborne pathogens over relevant refractive index ranges.

Design of a Dual‐Band Reconfigurable Doherty Power Amplifier Based on Dual‐Mode and Dual‐State Optimization

Thu, 28 May 2026 01:21:09 -0700

ABSTRACT

This paper presents a reconfigurable dual-band Doherty power amplifier (DPA) that uses a dual-mode and dual-state optimization method to meet the requirements of different operating frequency bands. First, load-pull simulations are performed for both frequency bands in saturation and back-off power states. Then, the on/off states of PIN diodes are switched to change the carrier output matching network (OMN) and the phase of the DPA. When the PIN diodes are off, the DPA operates in Mode 1 (2.6–2.8 GHz), while it operates in Mode 2 (3.4–3.7 GHz) when the PIN diodes are on. To ensure high efficiency in different modes, the carrier OMN is optimized using an adaptive particle swarm optimization algorithm by targeting a dual-mode and dual-state impedance objective function, meeting the impedance requirements for both saturation and back-off power states under Mode 1 and Mode 2. For validation, a dual-band reconfigurable DPA operating at 2.6–2.8 GHz and 3.4–3.7 GHz is designed and fabricated. Measurement results show that for Mode 1 and Mode 2, the saturated efficiency exceeds 52.7%, the 6 dB back-off efficiency exceeds 42.5%, and the saturated power exceeds 43 dBm.

Broadband Gain Enhancement and Frequency Scanning of Fabry–Perot Antenna With Non‐Uniform Partially Reflecting Surface

Xinyu Zhu, Xing Zhao, Minghao Hu, Haoming Ying, Qishen Huang, Bingying Li — Thu, 28 May 2026 01:18:57 -0700

ABSTRACT

This paper presents a Fabry–Perot (FP) antenna with broadband gain enhancement and frequency scanning characteristics. Three types of partially reflecting surface (PRS) units with large reflection amplitudes in a wideband make up a non-uniform PRS. Though the PRS with only the first type of units can broadly improve the antenna's gain, one steep gain stopband exists, dividing the 3 dB gain bandwidth. Therefore, some units are adjusted to the other two types of units to remove the gain stopband and realize wideband gain enhancement. Moreover, the FP antenna also realizes frequency scanning due to the phase difference of the incident waves to PRS that varies with frequencies. The measured results show that the FP antenna has a 10 dB impedance bandwidth of 6.7–14.7 GHz (74.8%) and a 3 dB gain bandwidth of 6.5–12.9 GHz (66%) with a peak gain of 11.6 dBi at 8.5 GHz. The antenna also has a large gain-bandwidth product per unit area (GBP/A) of about 640 with a compact structure. In 6.5–12.9 GHz, the FP antenna offers a relatively large unidirectional beam scanning range from 5° to 44°.

Multiobjective Optimization Design of Transmitting Antenna for Microwave Wireless Power Transmission

Yijing Hu, Qinghe Zhang, Lei Zhang, Zhaoyang Shen, Han Liu — Thu, 28 May 2026 01:17:56 -0700

ABSTRACT

Microwave wireless power transmission is a technology that achieves wireless power transmission through microwaves, widely used in fields such as wireless charging and space solar power plants. Its core performance indicators include beam collection efficiency, peak radiation level, and aperture power coefficient. This paper proposes a multiobjective antenna optimization design method for wireless power transmission that integrates surrogate models to address the issue of insufficient consideration of these performance metrics and inefficient optimization in existing research. First, Bernstein polynomial basis functions are used to reduce the dimensionality of the antenna design decision space and the number of decision variables, Multiobjective optimization functions are analyzed and designed, a surrogate model based on Gaussian processes is constructed, and the efficiency of antenna optimization design is improved; Finally, the multiobjective optimization design of reflector antenna aperture illumination is achieved using the covariance matrix adaptive evolutionary multiobjective optimization algorithm. The numerical and comparative results have verified the effectiveness of the proposed method, providing new insights for the design of microwave wireless power transmission systems.

Novel Filtering Antenna Based on Modified Closed Ring Resonator for 6G Applications

Dilip Kumar Choudhary — Thu, 28 May 2026 01:16:48 -0700

ABSTRACT

This work examines a small-scaled filtering antenna using a modified closed-ring rectangular resonator with increased gain, low profile, and wide bandwidth. The two resonators, made up of a modified closed rectangular ring and a U-shaped ring having a mutual coupling effect between them, are used to design a wideband bandpass filter. The rectangular radiator has been used instead of the one resonator at the intended filter's load side in the proposed antenna with filtering characteristics. Further, the defected ground has provided wider bandwidth with improved gain. The filtering antenna has undergone a comprehensive study. With a center frequency of 5.95 GHz, the design provides a 10-dB bandwidth for impedance of 57.8% between 4.25 and 7.65 GHz. It has a flat gain of almost 3.0 dB in the working range and a reflection coefficient of over 25 dB at the center frequency. The results are compared with the simulated values once the proposed structure is fabricated. The 6G frequency range would be a good fit for the suggested filtering antenna.

A Novel Millimeter‐Wave Circularly‐Polarized SIW Slot Antenna Array

Thu, 28 May 2026 01:16:19 -0700

ABSTRACT

Millimeter-wave circularly-polarized substrate integrated waveguide (SIW) slot antennas using novel resonant modes are proposed in this paper. Unlike conventional circularly polarized SIW slot antennas, the proposed circularly polarized slot antenna employs two novel SIW TE₁₀₁ and TE₀₁₁ cavity modes, with the electric field oriented parallel to the metal plane. The resonant frequencies of TE₁₀₁ and TE₀₁₁ modes in SIW cavity are mainly determined by the cavity height. Consequently, they have high resonant frequencies, demonstrating good feasibility for designing millimeter-wave circularly-polarized slot antennas. Additionally, the radiation slots on the top metal plane are excited by the electric field of the cavity modes, which eliminates the need of power dividing network for feeding the array elements, thereby simplifying the antenna feeding structure. A 4×4 millimeter-wave circularly polarized SIW slot array is then designed and analyzed. The final results show that the proposed antenna can achieve 3.24% operation bandwidth, 12.19 dBic peak gain, and higher than 90% total efficiency.

Broadband Circularly Polarized Antenna Employing Cascaded Water Dipole and Helix

Thu, 28 May 2026 01:13:15 -0700

ABSTRACT

This article presents a compact directional circularly polarized (DCP) antenna employing cascaded water dipole and helix. It consists of five half-wavelength water cylinders as vertical dipoles for generating vertical electric component and six half-wavelength open helices for horizontal electric component. The dipoles and helices are connected in series and the central dipole is splitted for a differential feed. Owing to the 90° phase difference between the vertical and horizontal fields and an asymmetric distribution of the dipole radiators, a relative broadband unidirectional CP radiation is achieved by only using a single radiator with compact size. A prototype is fabricated employing 3D printing technology, reducing the difficulty of practical realization of the antenna. Measured results show that a matching bandwidth of 30% and an axial ratio bandwidth of 10.1% are achieved. This antenna features a broadband DCP radiation while having a simple, compact, and highly transparent structure, which is potentially useful for CP wireless communications.

Spectral Characteristics of AlO Molecules in 1064 nm Nanosecond Laser‐Induced Aluminum Plasma

Xuefeng Chu, Qiuyun Wang, Hailong Yu, Xun Gao — Thu, 28 May 2026 01:11:58 -0700

ABSTRACT

As the plasma plume generated by nanosecond laser ablation of aluminum expands in ambient air, AlO molecules are formed through reactions between aluminum species in the plasma and oxygen-containing species in the surrounding atmosphere. In this work, the emission characteristics of AlO molecules in 1064 nm nanosecond laser-induced aluminum plasma were systematically investigated by time-resolved optical emission spectroscopy. The influence of laser energy on the temporal evolution of AlO molecules was analyzed, and the plasma electron temperature was determined. At a fixed laser energy, the intensity of atomic Al emission decreases gradually with delay time, whereas the AlO molecular emission first increases and then decreases, reaching a maximum at about 20 μs. When the laser energy is increased from 30 to 70 mJ, the AlO molecules peak shifts to later delay times and the emission duration becomes longer. Meanwhile, the plasma electron temperature rises from about 4000 K to 5500 K. These findings show that the formation and evolution of AlO molecules are closely related to the thermal state and cooling process of the plasma, and provide useful insight into molecular formation and related plasma chemical reactions in laser-induced plasma.

A Single‐Layer Miniaturized Endfire Filtering Antenna With Radiation Pattern Reconfigurability

Ming Xiang, Chun Liang, Xiao Liu, Hao‐Lan Zhou, Dajiang Li, Kun‐Zhi Hu — Thu, 28 May 2026 00:59:38 -0700

ABSTRACT

This letter presents the design and implementation of a single-layer pattern-reconfigurable endfire filtering antenna. Based on a microstrip quasi-Yagi structure, the antenna achieves controllable reversal of the end-fire radiation pattern between the +Z and -Z directions by integrating PIN diodes into the radiation enhancement strips. A pair of U-shaped parasitic strips is placed near the driven element, introducing two additional resonances within the passband to extend the impedance bandwidth and generating a radiation null in the upper stopband to enhance filtering capability. Additionally, a pair of bent parasitic strips is incorporated to create a radiation null in the lower stopband, thereby enhancing out-of-band suppression. Measured results demonstrate that the antenna achieves a −10 dB impedance bandwidth of at least 18.1% in both the endfire directions, exhibiting advantages such as single‑layer structure, miniaturized size, favorable radiation performance, and good agreement between simulation and measurement.

Highly‐Integrated Active Reconfigurable Broadband Van Atta Retrodirective Antenna Array

Dinglun He, Shufang Li, Li Deng — Thu, 28 May 2026 00:00:00 -0700

ABSTRACT

The currently available Van Atta retrodirective antenna arrays are confined to having single and fixed functions, low integration, narrow bandwidth, and a high profile. These limitations hinder their integration with other systems and confine their applications. In this letter, we incorporate surface mount technology (SMT) and radio frequency (RF) chip technology into the Van Atta retrodirective antenna array. Consequently, we develop a low-profile, highly integrated active reconfigurable broadband retrodirective antenna array. This array can operate within the 5–6.2 GHz bandwidth, achieving a relative bandwidth of 21%. It offers an adjustable radar cross section (RCS) range of −41 ~ 20 dB. When the gain is between 0 and 10 dB, within the ±40° range, the radar RCS fluctuation doesn't exceed 3 dB, and the profile height is under 4 mm. Owing to its outstanding retrodirective performance, high-level integration, flexible reconfigurability, and broadband characteristics, this array is highly adaptable to fields such as radar simulation, target deception, and Internet of Things (IoT) communication.

A Wideband Angularly Stable Cross‐Polarization Converter With High Efficiency and RCS Reduction

Riya Malia, Archana Rajput — Thu, 28 May 2026 00:00:00 -0700

ABSTRACT

A low-profile, compact, and wideband reflective cross-polarization converter (CPC) metasurface is proposed. The unit cell, consisting of an l-shaped metallic strip and a diagonally shifted square patch, has a periodicity of 0.168 λ L $0.168{\lambda }_{L}$, where λ L ${\lambda }_{L}$ is the wavelength at the lowest operating frequency. The structure is printed on a thin FR-4 dielectric layer of thickness 0.005 λ L $0.005{\lambda }_{L}$ and incorporates a 4.5 mm air gap ( 0.094 λ L $0.094{\lambda }_{L}$), backed by a copper ground plane, resulting in a total thickness of 0.099 λ L $0.099{\lambda }_{L}$. The proposed design achieves an average polarization conversion ratio (PCR) above 90% over a wide fractional bandwidth of 91.14% (7.29–19.52 GHz). Under oblique incidence, the average PCR remains above 93% up to 4 5 ∘ $4{5}^{\circ }$. The wideband polarization conversion mechanism is explained through surface current analysis and an equivalent circuit model for both co- and cross-polarized reflection coefficients. A planar checkerboard configuration, formed by arranging the CPC unit cell and its mirror-symmetric counterpart, achieves more than 10 dB monostatic RCS reduction over 7.04–18.58 GHz (90.1% fractional bandwidth) for normal incidence, with an average reduction of 17.71 dB compared to a copper sheet. Owing to its thin profile, the structure maintains satisfactory conformal performance under bending. A 5 dB RCS reduction is preserved over 6.02–19.12 GHz (104.21%) at 6 0 ∘ $6{0}^{\circ }$ bending with an average reduction of 14.41 dB. For 3 0 ∘ $3{0}^{\circ }$ and 9 0 ∘ $9{0}^{\circ }$ curvature angles, bandwidths of 6.77–19.47 GHz (96.80%) and 7.26–18.64 GHz (87.88%) are achieved, with corresponding average RCS reductions of 10.74 dB and 9.19 dB, respectively. The fabricated prototype demonstrates efficient wideband RCS reduction in both planar and conformal checkerboard configuration states, confirming its suitability for stealth applications.

New Method for Generating Mixed‐Mode OAM Beam With Controllable Energy Proportion by Tensor Holographic Impedance Metasurface

Huifen Huang, Jiajia Jiang — Wed, 27 May 2026 00:14:52 -0700

ABSTRACT

In this paper, a mixed-mode Orbital angular momentum (OAM) beam is generated by tensor holographic impedance metasurface (THIMTS). Different from the conventional impedance superposition principle, this paper proposes a new design method to generate the mixed-OAM modes. As examples, four THIMTSs are designed: (1) Mixed-OAM mode l = ±1 or ±2 with equal mode energy distribution proportion (same weight). (2) Mixed-OAM mode l = ±1 with different mode distribution proportion (different weight) 6:4 or 4:6. The proposed method for generating the mixed-modes can avoid interference between modes, which exists for conventional superposition principle, and the designed THIMTSs have following advantages: high purity (total 98%), a measured peak gain of 21.26 dBi for mixed-mode l = ±1 with equal mode energy at 27 GHz, and arbitrary mode energy proportion. The proposed design method can be used to design THIMTS, which has great application values in many fields such as advanced wireless communication with encoding anti-noise performance or multiplexing high capacity, OAM beam long-range communication, radar detection and imaging.

Issue information

Wed, 27 May 2026 00:12:09 -0700

Microwave and Optical Technology Letters, Volume 68, Issue 6, June 2026.

Multi‐Pixel Photon Counter Enabled High‐Sensitivity Detecting for Underwater Wireless Optical Communication

GuangSheng Huang, JieWen Lei, Qingjie Lu, SiYuan Zhao, KaiBin Lin — Wed, 27 May 2026 00:00:00 -0700

ABSTRACT

This paper presents a robust Underwater Wireless Optical Communication (UWOC) system designed to achieve long-range transmission by overcoming the limitations of conventional receivers in turbid and high-attenuation channels. The system features a novel architecture that synergizes high-order 16-Quadrature Amplitude Modulation (16-QAM) modulation with a high-sensitivity Multi-Pixel Photon Counter (MPPC) receiver. To enable reliable data recovery from ultra-weak signals (−40 dBm) typical of long-distance links. This paper implemented a specialized FPGA-based digital signal processing unit featuring carrier synchronization and Gardner timing recovery to suppress stochastic noise. Experimental results demonstrate that the system achieves a data rate of 16 Mbit/s and successfully maintains a Bit Error Rate (BER) below the 7% hard decision forward error correction(HD-FEC) limit even at a received optical power as low as −40 dBm. This performance significantly extends the dynamic range of UWOC links, validating the system's capability for reliable long-range transmission under extreme signal attenuation.