This paper presents a compact dual-band RF energy harvesting rectifier designed for operation at 2.45 GHz and 5.2 GHz Industrial, Scientific, and Medical (ISM) bands. The rectifier employs a voltage-doubler topology integrated with a dual-band impedance matching network (MN) composed of a coupled-line section and a microstrip transmission line. The analytical design of the MN is established using the ABCD-matrix formulation to determine the initial modal impedances and electrical lengths, which are subsequently refined through full-wave electromagnetic optimization in ADS. The proposed approach achieves accurate dual-frequency impedance transformation using only two matching segments, significantly simplifying the structure compared with conventional multi-section designs. The prototype, fabricated on a low-cost FR-4 substrate, occupies a compact area of 34×25 mm². Measurements show high power conversion efficiencies of 75% and 55% at 2.45 GHz and 5.2 GHz, respectively, under a 0 dBm input power and a 1 kΩ load, in close agreement with simulations. The results confirm that the proposed design provides an effective and low-cost solution for ambient RF energy harvesting and low-power IoT applications.

Cables are the main coupling path of electromagnetic interference, and the electromagnetic interference generated by cable conduction and radiation can interfere with the motor position encoder signal. Cable grounding can reduce the impact of this interference on the encoder signal. Therefore, this article first obtains the shielding mechanism of single end grounding and double end grounding of cables through theoretical analysis. Then, under two interference modes of plane wave radiation and adjacent cable radiation, the voltage frequency response and interference voltage peak and amplitude of single end grounding and double end grounding of the cable were compared. The results showed that the double end grounding of the cable shielding layer had better anti-electromagnetic interference effect. In addition, based on the double end grounding, comparing the interference voltages of different grounding resistances, cable lengths, shield thicknesses, and load conditions, some conclusions about the changes in interference voltage have been obtained.

Underwater electromagnetic communication is severely limited by the high permittivity and conductivity of water, which cause strong attenuation at higher frequencies. To overcome this challenge, a compact dual-polarized hexagonal loop antenna is proposed and experimentally validated for low-frequency underwater communication at 40-45 MHz. The antenna, fabricated on FR-4 and sealed with epoxy resin, eliminates bulky waterproof housings while ensuring stable impedance performance with a measured return loss better than -10 dB. Experiments conducted in freshwater confirm the effectiveness of polarization diversity, achieving an average received-power improvement of 4.59 dB under maximal-ratio combining. These results demonstrate, for the first time, the feasibility of a practical dual-polarized hexagonal loop design for robust, low-frequency underwater communication systems and future MIMO-like implementations.

In this paper, we present a dual-mode, dual-polarized orbital angular momentum (OAM) antenna, implemented as a four-element uniform circular array (UCA) with a series-fed network on a single-layer substrate. The novelty of the antenna lies in its ability to generate four orthogonal states simultaneously in a single transmission channel - two from l = ±1 OAM states and two from vertical/horizontal polarizations - without requiring multilayer feeds or complex phase-shifting networks. Full-wave simulations and experimental measurements have been used to validate the antenna's performance within the 5.85-6.1 GHz band. Far-field radiation patterns exhibit the characteristic vortex-beam profile, featuring a conical shape with a central null, while phase distributions reconstructed via FFT-based holography confirm the generation of distinct OAM modes. The antenna has four feed ports; of these, activating Ports 1 and 4 yields the highest OAM modal purity at 6 and 6.1 GHz, while Ports 2 and 3 peak in purity at 6.1 GHz. Owing to its compact, reconfigurable architecture, the designed and tested antenna is well-suited for integration into space- and power-constrained platforms such as UAVs, IoT devices, and full-duplex MIMO systems.

With the increasing demand for high-capacity communication systems, vortex beams endowed with orbital angular momentum (OAM) have emerged as a promising candidate for enhancing channel capacity of communication systems. Persistent limitations of conventional OAM generators, such as narrow bandwidth, single-mode constraints, and decreased purity in high-order OAM modes are addressed. In this work, by combining Pancharatnam-Berry (PB) phase theory and equivalent circuit, we design a metasurface unit with gradient phase compensation. The metasurface unit overcomes the bandwidth limits of the resonant structures, achieving 360˚ linear phase modulation over 8-20 GHz (85.7% relative bandwidth) and allowing vortex waves with multiple OAM modes and high order mode purity. Quantitative assessment of modal purity via OAM spectral decomposition demonstrates exceptional agreement between experimental measurements and full-wave simulations, thereby corroborating the theoretical framework and underscoring the methodology's potential for practical implementation.

To mitigate unbalanced vibration caused by rotor eccentricity in composite cage rotor bearingless induction motors (CCR-BIM), this paper proposes an enhanced hybrid control strategy integrating a rotor-speed adaptive second-order generalized integrator (RA-SOGI) harmonic observer with dual-channel compensation. A variable step-size adaptive LMS (VSS-ALMS) algorithm is introduced to optimize RA-SOGI, enabling real-time extraction of fundamental vibration components with reduced computational burden and improved convergence. In the feedback channel, an adaptive PID controller with variable learning rates and residual feedforward correction is designed, achieving a superior balance between transient response and steady-state precision. Lyapunov-based analysis establishes the global asymptotic stability of the proposed scheme under practical step-size constraints. Experimental validations demonstrate that the proposed method significantly outperforms conventional PID and feedforward control, achieving faster convergence, higher vibration attenuation, and enhanced trajectory stability in high-speed CCR-BIM operation.

A wide band, high gain 1 × 2 array Vivaldi shaped slot Substrate Integrated Waveguide (SIW) Multiple Input Multiple Output (MIMO) antenna with square shaped periodic Artificial Magnetic Conductor (AMC) placed beneath the antenna for applications in X band is presented. A two-port MIMO antenna backed by AMC patches is designed and realized for enhanced gain and bandwidth. The single antenna 1 × 2 array has electrical dimensions of 1.57λ_r × 1.13λ_r × 0.027λ_r. The designed antenna structure has bandwidth of 1.39 GHz (8.79 GHz-10.18 GHz) with a percentage bandwidth of 14.65% and Gain of 11.67 dBi. The edge to edge distance between the MIMO antenna elements is 5 mm (λ_r/4). The periodic AMC patches improve vital MIMO antenna performance metrics like Isolation, Envelope Correlation Coefficient (ECC), Diversity Gain (DG), Channel Capacity Loss (CCL) and radiation pattern. The unit cell analysis of periodic square AMC patch and a polynomial regression model to find the best goodness of fit for Gain-Bandwidth product versus square AMC patch size is studied. Antenna gain variation seen over the complete bandwidth is < 1 dBi which makes it a flat gain response antenna. The proposed high-gain, wide-band 1 × 2 Vivaldi-slot SIW MIMO antenna with AMC is suitable for X-band radar, point-to-point high-throughput wireless links, and compact platform communication systems requiring robust diversity performance.

In this paper, a new method is proposed for failure diagnosis of programmable metasurfaces, which jointly uses the single-point measurement strategy and Bernoulli-Gaussian (BG) prior. Specifically, leveraging the dynamic tuning property of programmable metasurfaces, the radiated fields is measured with a single fixed probe, therefore reducing the time and error of the measurement process. Moreover, the BG prior inherent in the programmable metasurface under test is exploited during the reconstruction process in order to perform the diagnosis with a small number of measurements without resorting to prior knowledge of the radiation pattern of the failure-free programmable metasurface. The accuracy, efficiency and robustness of the proposed method are verified through a set of representative numerical experiments, where the results are compared with those from existing diagnostic methods.

This paper presents a medical ethanol concentration sensor based on the principles of liquid-coupling loss, which enables rapid and accurate measurement and classification of medical ethanol concentrations. The sensor system consists of integrated circuits for liquid-coupling loss, amplitude detection, signal processing, and visualization. It utilizes variations in RF signal amplitude to determine the concentration. Theoretical analysis, grounded in the Bruggeman model, quantitatively correlates the dielectric constant of medical ethanol with its concentration, thereby establishing a robust theoretical foundation for the sensor design. Experimental validation demonstrates the sensor's ability to precisely differentiate among medical ethanol concentrations of 95%, 75%, and 50% at test frequencies of 1 GHz, 2 GHz, and 3 GHz. The agreement between empirical data and theoretical predictions confirms the sensor's efficacy and reliability. Key advantages include user-friendly operation, cost efficiency, and intuitively presented results, rendering the sensor highly suitable for broad medical applications.

This paper presents a 2.45 GHz/5.8 GHz circularly polarized RFID reader antenna based on an Artificial Magnetic Conductor (AMC) for detecting tagged objects in IoT applications. An efficient reader antenna is proposed to increase the interrogation distance and reduce the uncertainty in tag detection. The antenna consists of two dipole pairs printed on both sides of the substrate to operate at 2.45 GHz and 5.8 GHz, connected via feed delay lines in a cross-dipole configuration. The read range is further enhanced by a 5×5 AMC surface placed 0.042λ₀ below the printed antenna, where λ₀ is the wavelength at the lower resonant frequency. The AMC backing results in a gain of 7.1 dBi at 2.45 GHz and 9.41 dBi at 5.8 GHz, improving the read range of the reader. Impedance bandwidth is also enhanced to 2.25-2.91 GHz for the 2.45 GHz band and 5.1-6.3 GHz for the 5.8 GHz band, reducing tag detection errors. The axial ratio bandwidth of the antenna is 2.18-2.99 GHz at 2.45 GHz and 5.27-5.88 GHz at 5.8 GHz, ensuring circular polarization over the operating bands.

To enable accurate online observation of permanent-magnet (PM) flux linkage in permanent-magnet synchronous motors (PMSMs), this paper proposes an improved adaptive higher-order square-root cubature kalman filter (IAHSRCKF) flux-linkage observer. Firstly, a nonlinear PMSM model is established to capture complex operating conditions. Secondly, fifth-order cubature integration and an adaptive estimator are embedded into a square-root cubature Kalman framework, yielding an adaptive fifth-order SRCKF observer that tracks PM flux-linkage variations under parameter drift and disturbances. Then, experimental scenarios are created by perturbing key electromagnetic and mechanical parameters and injecting external time-varying disturbances. Finally, simulation and hardware tests benchmark the proposed IAHSRCKF against UKF, CKF, and SRCKF. Results demonstrate that IAHSRCKF achieves the highest flux-estimation accuracy, exhibits low sensitivity to parameter uncertainties, and maintains strong robustness across complex operating conditions, thereby enabling reliable online monitoring of PM flux linkage.

A compact Ultra-Wideband (UWB) Multiple-Input Multiple-Output (MIMO) antenna with a culturally inspired radiating structure is developed in this study. The radiating element is inspired by the traditional gonjong shape of Minangkabau architecture, which resembles upward-curving buffalo horns, forming a distinctive roof-like patch that enhances the impedance characteristics. A 50-ohm microstrip line is used to excite the patch, with a partial ground plane placed beneath the patch. To improve bandwidth and support low-frequency operation, an L-shaped strip is introduced on the ground plane, and the patch is optimized through edge modification and parametric analysis. The antenna achieves a wide measured impedance bandwidth of 2.2-20 GHz (S₁₁ < -10 dB), fully covering and extending beyond the Federal Communications Commission (FCC)-defined UWB range. High isolation is achieved with S₁₂ consistently below -20 dB across the band. Excellent MIMO performance is demonstrated with an envelope correlation coefficient (ECC) below 0.01, diversity gain (DG) above 9.95 dB, channel capacity loss (CCL) lower than 0.4 bit/s/Hz, and Total Active Reflection Coefficient (TARC) below -10 dB. The antenna also exhibits stable radiation patterns and maintains high efficiency throughout the operating band. With overall dimensions of just 30 × 30 mm², the developed antenna is more compact than most recent UWB MIMO designs, making it highly suitable for modern wireless communication systems requiring wide bandwidth and reliable multi-antenna performance.

High frequency communication systems are critical for 5G networks, particularly in the millimeter-wave bands, where ultra-wideband (5G-UWB) performance is essential for high data rates and low latency. In this work, we propose, for the first time to the best of our knowledge, an ultra-wideband 5G MIMO beamforming module covering both the 28 and 60 GHz bands. The proposed design is based on a low-cost, low-profile Rotman Lens (RL) implemented on an FR4 substrate with a thickness of 1.6 mm and a dielectric constant of 4.3. The RL features five beam ports and seven array ports, with additional dummy ports introduced to minimize reflections and enhance adjacent beam port isolation across the full 5G-UWB range. Simulation results demonstrate excellent performance, with isolation and mutual coupling maintained below -25 dB between input beam ports and below -15 dB between array ports across the entire bandwidth. The VSWR remains below 2 for all ports. Although this work presents a single RL-based beamformer, it is envisioned as a building block within a larger hybrid MIMO architecture, where multiple lenses can be interconnected to support parallel data streams and spatial multiplexing. This modular approach enables flexible scaling to full MIMO operation while maintaining low cost and compactness. The proposed design is a strong candidate for 5G and mmWave applications, including hybrid beamforming systems, MIMO architectures, radar, and satellite communications. Comparative analysis with recent literature demonstrates its superior bandwidth and isolation performance.

Circularly polarized (CP) antennas minimize polarization losses and improve signal reliability in ultra-reliable and low-latency satellite communication. Compact design, wide impedance and axial ratio bandwidth (ARBW) are key requirements for circularly polarized antennas utilized for modern automotive wireless applications. In this work, a miniaturized slotted antenna for C-band automotive-oriented wireless applications is proposed. The antenna achieves a wide measured impedance bandwidth of 69.5% (4.0-8.26 GHz, 4.26 GHz) and exhibits an ARBW of 51% (4.96-8.33 GHz, 3.37 GHz). The overall compact size of 25 × 30 × 1.6 mm³ (0.33λ × 0.40λ × 0.02λ at 4 GHz) further underscores its suitability for integration in space-constrained C-band communication systems. The anticipated design is optimized using rigorous parametric analysis to achieve a wide ARBW from θ = -27˚ to +33˚ which is very beneficial for satellite applications. The fabricated prototype demonstrates a measured peak gain of 4.8 dBi and radiation efficiency ranging from 82% to 92% across the radiating band. Measurement results obtained from the fabricated antenna are validated with simulations and show satisfactory agreement. The anticipated design, when compared with existing literature, is found to outperform other designs in terms of size, ARBW, and impedance bandwidth. The achieved resonance in the proposed design can be utilized for satellite communication, medical and automotive applications (tele-operated driving support, high-definition map collecting and sharing, infrastructure-based teleoperated driving), and other applications in C-band.

The increasing deployment of 5G wireless technologies has raised the need for accurate, tissue equivalent phantoms to explore electromagnetic (EM) wave interactions with human body organs. This paper investigates stability and homogeneity of a low-cost, easy-to-fabricate human muscle phantom exposed to radiation exposure from 5G signals at frequencies of 700 MHz, 2.4 GHz, 3.5 GHz and 20 GHz. The phantom was formulated using agar, polyethylene powder, sodium chloride, xanthan gum, sodium dehydro-acetate, and deionized water. Its permittivity and conductivity were measured using a vector network analyzer (VNA) over a 45-day period under low (2-5°C) and room temperature (27°C) storage. The results showed that the phantom was most homogenous at 20 GHz with the standard deviation (SD) of 0.51033 and the relative standard deviation (RSD) of 1.67%. For conductivity, the phantom demonstrated good homogeneity. However, it was not aligning to the corresponding real human muscle conductivity. The most homogenous conductivity was observed at 2.4 GHz with the SD and RSD of 0.06194 and 2.31% respectively. In terms of stability, relative permittivity was most stable at 20 GHz under room temperature conditions, with a maximum deviation of 21%. Stability of conductivity performance, on the other hand, was best maintained at 2.4 GHz under room temperature, where the highest observed deviation was 53%. The findings highlight the potential of using low-cost materials to fabricate phantoms with stable electromagnetic properties suitable for wireless exposure studies, although further optimization is needed for accurate conductivity matching.

This paper presents a passive, structure-based approach for selective signal transmission and crosstalk suppression in dense radio frequency identification (RFID) tag environments. The proposed method employs a mechanically reconfigurable double-layer tag design based on the mirror-antenna principle, which enables dynamic switching between transmission and shielding modes by adjusting the interlayer spacing. Simulation results demonstrate pronounced differences in the reflection characteristics and radiation intensity of the tag under the two operating modes at 915 MHz. Experimental validation further confirms the effectiveness of the system in mitigating interference and ensuring reliable tag identification in multi-tag scenarios. The design is compact, energy-efficient, and cost-effective, supporting scalable applications in smart retail and automated inventory management.

Based on the current trends in wireless communication systems, a novel high-isolation dual-notch ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna is proposed, measuring 46 mm × 46 mm × 0.8 mm. The antenna is printed on an RO4350 substrate and consists of two identical antennas placed orthogonally. The antenna unit features a third-order stepped rectangular structure and employs microstrip feeding, incorporating inverted U-shaped and M-shaped grooves etched onto the antenna unit to achieve dual-notch functionality, thereby addressing electromagnetic interference issues in wireless local area networks (WLAN) operating at 5.15-5.85 GHz and 7.25-7.75 GHz. To address the issue of mutual coupling in MIMO antennas, this paper presents an innovative decoupling method known as the RMS-ZINC approach. This technique involves excavating a T-shaped groove on the rear of the dielectric substrate, symmetrically aligned with the diagonal, and filling it with a dielectric material primarily composed of zinc. This material substitution effectively manipulates the coupling current paths, achieving a high isolation level of -20 dB. The experimental results show that the operating bandwidth of the antenna ranges from 2.89 to 10.19 GHz, with a peak gain of approximately 5 dB (7.15 dBi) and a maximum radiation efficiency of up to 92%. The measured results are essentially consistent with the simulated ones, indicating the practical application value of the proposed MIMO antenna with notch functionality.

This paper presents the design, fabrication, and analysis of a wideband circularly polarized wearable antenna operating in the frequency range of 2.6 GHz to 4.7 GHz. The antenna is designed on a jeans substrate with dimensions of 25 × 30 × 1.4 mm³, having a dielectric constant of 1.7 and a loss tangent of 0.085. The proposed antenna demonstrates a gain of 2.8-3.4 dB across the operating frequency band and exhibits circular polarization in the frequency range of 3.2 GHz to 3.9 GHz. To achieve wideband performance and circular polarization, the antenna design incorporates an octagonal ring patch with a hybrid slot and stub in the partial ground plane, along with four slots in the ring patch. The antenna is fabricated and its performance is validated through Vector Network Analyzer and anechoic chamber measurements, showing good correlation with simulated results. Specific Absorption Rate (SAR) analysis and on-body simulations are conducted to evaluate its suitability for wearable applications.

To address the engineering challenges of conformal frequency diverse array (FDA) on complex curved surfaces and beamforming optimization, and leveraging the fact that the surface of a streamlined platform can be approximated by an elliptical arc, an elliptical-arc conformal FDA is taken as a representative example, and a conformal frequency diverse array method based on joint parameter optimization (JO-CFDA) is proposed. First, a polygonal approximation model is employed to achieve conformity between the array and the curved surface; then, the parameter α is introduced to control the non-uniform distribution of inter-element spacing along each edge; finally, the parameter β is used to allocate the frequency-offset exponent in a slope-normalized manner. These two parameters work in concert to jointly optimize beam characteristics in both the spatial layout and frequency-domain distribution. Simulation results demonstrate that the proposed method can significantly reduce sidelobe levels and enhance beam directivity while maintaining mainlobe width and peak gain, thereby validating its effectiveness and superiority.

With the growth of demand for high-rate and high-quality wireless communication services, Unmanned Aerial Vehicle (UAV) communication technology has received a lot of attention. By deploying Reconfigurable Intelligent Surface (RIS) on the UAV, more users can be reached while effectively expanding the signal coverage. The rotational nature of the UAV also provides new degrees of freedom in the design of RIS-assisted millimeter-wave Multiple Input Multiple Output (MIMO) systems. In this paper, using the advantages of UAV and RIS technologies, Aerial Reconfigurable Intelligent Surface (ARIS) is introduced to assist the communication, and the millimeter-wave Vehicle to Infrastructure (V2I) communication scenario based on the ARIS-assisted multi-vehicle beam tracking problem. First, Zero Forcing (ZF) beamforming is employed at the base station to eliminate inter-vehicle interference. On this basis, the vehicle-side beam combining matrix, the RIS-side reflection beamforming matrix, along with the rotation angle of the ARIS, are jointly designed to maximize the number of vehicles and data rates, thereby providing high-quality communication for beam tracking studies. Secondly, an ARIS-assisted multi-vehicle beam tracking model is derived in a MIMO-based 3D communication scenario. Finally, an Extended Kalman Filter (EKF) algorithm based on the angular deviation correction mechanism is proposed to realize the beam tracking of multiple vehicles. Simulation results show that the proposed EKF algorithm can effectively reduce the beam tracking error in multi-vehicle communication scenarios with robust beam tracking capability under the joint design based on beam merging matrix, beamforming matrix and ARIS rotation angle.