To overcome bandwidth-accuracy trade-offs in sensorless surface-mounted permanent magnet synchronous motor (SPMSM) drives, this study addresses the limitations of traditional observers. Conventional first-order sliding-mode observer (SMO) inherently exhibits high-frequency chattering due to discontinuous switching functions. To smooth the estimated back-EMF, a low-pass filter (LPF) is typically appended as a remedy; however, this filtering induces speed-dependent phase lag during medium- and high-speed operations, whereas its impact at low speeds is negligible. Although conventional higher-order model-based SMO (HOSMO) can better attenuate chattering, a lower cutoff frequency inherently compromises dynamic tracking precision due to increased phase lag. To overcome these challenges, the proposed scheme substitutes filter-dependent laws with a second-order super-twisting algorithm (STA), ensuring continuity of the control signal and zero phase lag. Furthermore, a state-dependent adaptive tuning mechanism based on a continuous nonlinear barrier function was developed. This adaptive law dynamically boosts observer gains to suppress transient perturbations and contracts them at a steady state to minimize chattering. Comprehensive simulations and experimental verifications demonstrated that the proposed gain-adaptive super-twisting higher-order SMO (GAST-HOTSMO) significantly reduced harmonic distortion, restricted estimation errors, and accelerated dynamic recovery compared to conventional methods.

This paper presents a low-profile, flexible, and wideband conformal wearable antenna for biomedical and wireless applications, including Internet of Things (IoT). The proposed antenna is based on an edge-truncated and slotted rectangular patch structure (ETSRP) developed on a jeans textile substrate, with compact overall dimensions of 0.163×0.269×0.006³. The antenna offers peak gain of 6.3 dBi with an impedance bandwidth of 2.32 GHz to 8.84 GHz, corresponding to a fractional bandwidth of 116.5%, with a reflection coefficient (S₁₁) of -42.4 dB in the ISM bands. The antenna's performance was evaluated using a human phantom and showed minor frequency detuning across different placement conditions. The specific absorption rate (SAR) was evaluated at 2.45 GHz and 5.8 GHz, with values of 0.7 W/kg and 0.8 W/kg, respectively, which are within accepted safety limits. The measured results were in good agreement with the simulated results in terms of impedance bandwidth, gain, and resonance characteristics. The proposed textile antenna offers wideband operation, low SAR, and compact size, making it suitable for wearable biomedical devices and IoT-based on-body communication systems.

To reduce the cost and improve the accuracy of position estimation for switched reluctance motors (SRMs) at medium to-high speeds, this study proposes a sensorless control strategy based on a dual-stage resonant filter (DSRF) and a feedforward phase-locked loop (FPLL). First, to address issues of weak dc-offset suppression and high-frequency harmonics in the second-order generalized integrator (SOGI) when processing nonlinear flux linkage, a DSRF with ideal band-pass characteristics is proposed. This filter effectively suppresses the dc-offset and higher-order harmonics. Second, the proposed FPLL introduces a feedforward compensation path related to the speed derivative. By adding zeros to broaden the system bandwidth, the dynamic response is accelerated. The tracking accuracy and response speed of the position observer are also enhanced under variable-speed and sudden-load conditions. Finally, the effectiveness of the proposed strategy was verified on a six-phase 12/10 SRM experimental platform. The experimental results show that the proposed sensorless control strategy achieves a fast and highly accurate estimation of the rotor position and speed at medium to-high speeds, particularly during dynamic processes, thereby enhancing system reliability and dynamic performance.

To address the requirements for compact size and low cost of RF signal sources, a novel design method for high-efficiency Class-F power oscillators is proposed. The key contribution of this method is the integrated design of the harmonic-tuning and impedance-matching networks. An asymmetric π-type harmonic tuning network is proposed to simultaneously realize harmonic termination for high-efficiency Class-F operation and fundamental load impedance matching, thereby significantly reducing circuit footprint. The amplifier's output was coupled to a feedback network via a capacitor and returned to the amplifier through a frequency-selective network, enabling a stable self-excited oscillation. To verify the design, a power oscillator is implemented using a low-cost LDMOS transistor and an FR4 substrate. The experimental results show that the fabricated oscillator operates at 918\,MHz with a direct current-to-radio-frequency (DC-RF) efficiency of 68.20% and a maximum output power of 42.90 dBm. Additionally, a low phase noise of -130 dBc/Hz at 1 MHz offset is achieved, robustly validating the effectiveness of this approach.

In‎ this ‎paper, ‎ a low-cost, lightweight open ‎transverse electromagnetic (TEM) ‎cell with an operating bandwidth from DC up to around 1.5 GHz is‎ designed ‎and‎ fabricated‎. Initially, a fully metallic open cell is simulated, and associated TEM modes are exhibited by the spatial electric field distributions. The cell length (L_b), width (W_b), and height (H_b) are respectively 398, 200, and 103.93 mm. In the next step, a printed circuit board (PCB) is used as the septum to reduce the device's overall weight. Moreover, longitudinal slots are cut on both sides of the septum to prevent the transverse currents, which results in the excitation of higher-order modes. For further weight reduction, sub-wavelength slots are cut in the metallic sidewalls without affecting the overall performance. The metal filling factor reduction is of great importance for reaching a portable test facility with reduced cost. Finally, the device's input ports are further manipulated to reduce discontinuity by gradually tapering them. The device is realized by the combination of metal sheet, computer numerical control (CNC) water jet, machining, and PCB technologies. The measured scattering parameters confirm the acceptable performance of the fabricated device.

This paper presents the design and experimental validation of a miniaturized Printed Log-Periodic Dipole Array (PLPDA) antenna operating within the 1.3-6.0 GHz frequency range. The objective of this work was to reduce the antenna's overall footprint while preserving its wideband performance. A sequential miniaturization strategy was adopted, employing m-segment fractal geometry for lateral size reduction and Cross-Entropy (CE) optimization for axial compaction. The reference PLPDA, measuring 255 mm × 116 mm, was progressively refined to a final size of 217 mm × 88 mm, achieving an overall footprint reduction of approximately 34%. The simulated and measured results confirmed excellent impedance matching, with S₁₁ remaining below -10 dB across the entire operating band and an average gain exceeding 7 dB. These results validate that the proposed CE-optimized m-segment PLPDA successfully achieves substantial miniaturization without degrading bandwidth or radiation performance. The presented approach offers a practical framework for developing compact, high-performance wideband antennas.

This paper proposes a model-free direct speed control (MFDC) method based on a second-order ultra-local model to address the speed loop bandwidth issue and difficulty of further improving the dynamic response performance in the speed control of a traditional cascaded permanent magnet synchronous motor drive system. The speed control method based on an accurate mathematical model has poor robustness to unknown disturbances, such as parameter uncertainty and inverter nonlinearity. This method eliminates the double closed-loop cascade structure of the traditional speed outer loop and q-axis current inner loop. By establishing a second-order ultra-local model of the surface-mounted permanent magnet synchronous motor ( SMPMSM ) drive system considering parameter uncertainty and inverter nonlinearity, the mechanical speed of the motor was directly related to the inverter's output voltage, and a model-free direct speed controller integrating speed control and torque current control functions was designed. Simultaneously, a model-free current controller based on the first-order current ultra-local model is used to realize the independent adjustment of the d-axis stator current. In addition, a virtual q-axis current ultra-local model torque limitation method for direct speed control is proposed to realize an effective constraint of electromagnetic torque without a cascade structure. Experimental results demonstrate that the proposed method provides enhanced load-disturbance rejection, particularly under medium- and high-speed conditions. At 500 r/min, load-step speed fluctuation is reduced from 3.6152% to 2.0638%, and recovery time is shortened from 0.0288 s to 0.0080 s. Under the rated-speed step condition, the speed overshoot is reduced from 2.8028% to 2.2136%.

Millimeter-wave (mmWave) radar supports non-contact action sensing without optical imagery, but its sparse point clouds vary with multipath, aspect angle, and detection quality. We address within-protocol recognition with a radar-informed Multi-Stream Gated Transformer (MSG-Transformer). Separate streams encode target-centered geometry, Doppler velocity, radar-reported SNR, and tracker-estimated horizontal-centroid context prior to temporal fusion. Raw trials are split before frame stacking, and augmentation perturbs only centered coordinates, leaving measured Doppler and SNR unchanged. On 820 archived trials from eight anonymized participant identifiers and nine action categories, MSG-Transformer achieved 97.67% development-set macro recall with 1.03 million parameters and a 3.92 MiB FP32 footprint. This single-split result is not subject-independent or cross-environment evidence.

In this article, a triple-band bandstop filter employing coupled tri-section stepped-impedance resonators is proposed. The characteristic impedances of individual stepped-impedance sections are judiciously adjusted to independently allocate the three stopband frequencies. Subsequently, the coupling coefficients between adjacent resonators are meticulously tuned to simultaneously regulate the bandwidth of each stopband and the corresponding suppression level within the rejection bands. Moreover, out-of-band insertion and return losses are optimized by properly selecting the characteristic impedance of half-wavelength transmission lines interconnecting resonators. To experimentally validate the aforementioned design methodology, a triple-band bandstop filter with stopband center frequencies of 1.2 GHz, 3 GHz, and 4.8 GHz is designed, simulated, fabricated, and measured. The measured responses are found in excellent agreement with simulated results, thereby conclusively substantiating the proposed design concept.

This paper presents a compact, funnel-shaped, MIMO antenna for ultra-wideband (UWB) applications. The antenna element consists of a top funnel-shaped patch and a bottom rectangular ground plane. By using an elliptical slot on the patch and a slit at the center of the ground plane, impedance matching is effectively improved, and bandwidth is significantly expanded. Meanwhile, by etching a slot at the center of the ground plane and introducing semicircular and T-shaped parasitic stubs, the mutual coupling between the antenna elements is successfully suppressed. The overall dimension of the antenna is 48 × 27 × 1.6 mm³. The simulated and measured results exhibit excellent agreement, demonstrating that the antenna achieves a continuous impedance bandwidth covering 3.16-16.48 GHz, which corresponds to a fractional bandwidth of 135.64%. Across the entire operating band, the port isolation exceeds 20 dB; the radiation efficiency ranges from 73.4% to 92.6%; the envelope correlation coefficient (ECC) is below 0.0025; and the diversity gain (DG) is better than 9.9982 dB. Combining ultra-wide bandwidth, high isolation, and extremely low channel correlation, the proposed antenna provides a reliable solution for high-performance UWB-MIMO communication systems.

This paper presents an asymmetric dual-band Doherty power amplifier employing a dual-π-shaped phase-compensation network. To realize effective load modulation at two operating frequencies, dual-band phase compensation lines are introduced at both the input and output of the peaking amplifier. Each compensation line is implemented with a dual-π-shaped dual-band structure, which provides the required phase shift and impedance transformation at the two target frequencies, thereby satisfying the phase relationship required for dual-band Doherty load modulation. Meanwhile, transistors with different power levels are used in the carrier and peaking amplifier branches to form an asymmetric Doherty configuration, improving power-combining capability and efficiency in the output power back-off region. Simulation and measurement results show that the designed power amplifier achieves an output power of 47 dBm, a gain higher than 10 dB, and drain efficiencies of 70% and 65% at 2.6 GHz and 3.5 GHz, respectively. At 9-dB output power back-off, the drain efficiencies reach 60% and 54% at the two frequencies, respectively. These results verify that the proposed dual-π-shaped phase compensation method can effectively realize dual-band load modulation in an asymmetric Doherty power amplifier. Compared with conventional dual-band Doherty configurations, the proposed architecture offers improved dual-band load modulation characteristics and is promising for future multiband wireless communication systems.

This work presents the design and analysis of an ultra-compact multiband circularly polarised microstrip antenna for next-generation implantable medical device (IMD) applications. The antenna is constructed using a Rogers RT/Duroid 3010 substrate, characterised by a relative permittivity (ε_r) of 10.1 and a thickness of 0.635 mm. It features ultra-compact dimensions of 15 × 15 × 0.669 mm³. The design allows for multiband operation at frequencies of 2.5 GHz, 5.8 GHz, 6.8 GHz, and 7.5 GHz. This is done by using U-shaped and rectangular slots, circular perturbations, and a modified ground structure. This configuration ensures a reflection coefficient that remains below -10 dB across both the ISM and UWB-H bands. The proposed design achieves a size reduction of approximately 25-40% compared to existing implantable antennas, while accommodating four operating bands, in contrast to conventional single- or dual-band designs. It provides enhanced bandwidth up to 9.54% in the UWB-H region. Circular polarisation is realised at higher frequencies (7.4-7.6 GHz) with an axial ratio below 3 dB, ensuring orientation-independent communication. The gain ranges from -32.2 dB to -23 dB, consistent with implantable antenna performance in lossy tissues. Performance is validated through full-wave simulations and experimental testing using a three-layer (skin-fat-muscle) tissue model. The maximum specific absorption rate (SAR) is 1.489 W/kg, averaged over 1 gram of tissue, at an input power of 1 W, adhering to IEEE safety standards. Overall, this design successfully balances miniaturisation, multiband operation, polarisation performance, and safety, thereby making it suitable for dependable biomedical telemetry applications.

Negative group delay (NGD) circuits are important for signal delay compensation in RF and microwave systems. However, realizing multiple NGD passbands with low insertion loss and compact size remains challenging. This paper proposes a compact lumped-element tri-band bandpass NGD circuit for low-frequency RF applications. The proposed circuit consists of three parallel resonant branches. Theoretical modeling, parameter analysis, circuit simulation, and experimental measurements are carried out to investigate the NGD characteristics. The fabricated prototype exhibits NGD responses at 46 MHz, 90 MHz, and 146 MHz. The measured group delays are -3.35 ns, -2.13 ns, and -1.41 ns, respectively, while the corresponding insertion losses are 1.807 dB, 1.638 dB, and 1.495 dB. The fractional NGD bandwidths reach 36.96%, 18.88%, and 12.90%. The proposed lumped-element topology provides compact size, low insertion loss, and tri-band NGD performance, making it suitable for low-frequency RF delay compensation and multi-band signal-processing applications.

To improve the electromagnetic operating stability and dynamic response of a permanent magnet synchronous motor (PMSM) speed control system under load disturbances and speed variations, an improved particle swarm optimization-based super-twisting active disturbance rejection control (IPSO-ISTA-ADRC) method is proposed. Focusing on the speed control loop, high-order power terms are introduced into the super-twisting control law within the ADRC framework to accelerate error convergence. A dynamic boundary-layer function is employed to smooth the switching terms and reduce chattering. In addition, a sigmoid function is incorporated into the extended state observer to improve disturbance estimation and compensation, while an improved particle swarm optimization algorithm is used to optimize the controller parameters. The proposed method is further applied to a sensorless PMSM speed control system to evaluate its control performance under sensorless operating conditions. Simulation results show that, compared with PI, LADRC, and boundary-layer-based STA-ADRC, the proposed method effectively suppresses speed overshoot and fluctuations and shortens the recovery time under no-load startup, load disturbance, and speed variation conditions, thereby achieving improved disturbance rejection, faster dynamic response, and enhanced robustness.

In spaceborne multi-input multi-output synthetic aperture radar (MIMO SAR) ground moving target indication (GMTI), the unknown radial acceleration of a target induces severe Doppler spectral broadening, while mismatched conventional reconstruction filters lead to significant image defocusing. To address these challenges, this paper proposes a novel focused imaging method that seamlessly integrates radial acceleration estimation with reconstruction filter design. This method first adaptively suppresses static background clutter by utilizing the extended multi-channel clutter suppression interferometer (M-CSI) technique. On this basis, the frequency-domain cross-correlation characteristics of time-domain sub-aperture signals recovered via inverse reconstruction filtering are exploited to estimate the target radial acceleration deeply buried in residual clutter. Furthermore, a ratio factor resistant to amplitude interference is constructed to search for the radial velocity. Finally, a reconstruction filter for maneuvering targets is designed using the obtained motion parameters, completing the unambiguous recovery of the original Doppler spectrum and pulse compression focusing. Simulation results demonstrate that the proposed method can estimate the target maneuvering parameters, thereby thoroughly resolving the defocusing and artifact issues.

Accurate characterization of magnetodielectric materials is required for the development of microwave sensors and high-frequency communication systems. This study proposes a compact planar microwave sensor that uses a single dual-Split-Ring Resonator (SRR) to simultaneously measure permittivity and permeability. The core innovation lies in the spatial segregation of electric-field-dominant and magnetic-field-dominant sensing regions within a unified resonator framework, which effectively suppresses the mutual interference between the dielectric and magnetic sensing channels. Designed to resonate at 4.15 GHz, the sensor's performance was evaluated through full-wave electromagnetic simulations and experimental validation using six different materials under test (MUT) (including Magtrex555 and various Rogers's substrates). Sixty independent measurements were conducted to ensure reliability. The experimental results demonstrate high sensitivity, with 144.2 MHz/ε_r for permittivity and 45.4 MHz/μ_r for permeability. The proposed sensor enables characterization across a measured permittivity range of 2.2-6.5 and a permeability range of 1-6, demonstrating its capability to evaluate both dielectric and magnetic properties within the specified measurement domain. The proposed sensor achieved average characterization accuracies of 96.93% and 98.81% for permittivity and permeability, respectively, with minimum errors as low as 0.03%. These results confirm that dual-SRR architecture provides a robust, repeatable, and non-destructive solution for magnetodielectric material characterization with a highly compact form factor.

Compact multi-port antennas are essential for future 5G millimetre-wave systems because they support high-speed communication, stable signal quality, and multiple data channels within limited device space. This study presents a compact, planar, six-port MIMO antenna for 38-40 GHz 5G millimetre-wave applications. The antenna is designed on a low-loss Rogers RT5880 substrate with an overall size of 40 × 40 × 0.543 mm³. The design follows an S-parameter-guided approach, beginning with a single radiating element and extending to the final six-port MIMO configuration. The proposed structure maintains a simple planar geometry without using decoupling networks, electromagnetic bandgap cells, frequency-selective surfaces, metasurfaces, dielectric lenses, or external reflectors. Simulated and measured results show good impedance matching across 38-40 GHz, with reflection coefficients below -10 dB and resonance near 39.3-39.5 GHz. Inter-port isolation is mostly better than 20 dB, while the measured gain reaches approximately 8.28 dBi near resonance. The antenna also achieves an extremely low ECC of 5 × 10^-4, a diversity gain close to 10 dB, an acceptable TARC, and a balanced MEG. Such results validate its applicability to compact 5G user equipment, small-cell systems, and high-density wireless platforms.

A flexible multifunctional passive metasurface reflector is proposed, which integrates broadband absorption, linear-to-linear polarization conversion, and dual-band linear-to-circular polarization conversion on a single passive platform. The proposed unit cell consists of a circular split-ring resonator and X-shaped metallic patches loaded with lumped resistors. The metallic patterns were fabricated on a flexible polyimide (PI) substrate, followed by a polymethacrylimide (PMI) spacer layer and a metallic ground plane. Without employing any active components, the metasurface achieves an absorptivity higher than 90% over the 4.45-8.46 GHz band. In the 12.1-15.2 GHz frequency range, the polarization conversion ratio exceeds 90%, enabling efficient linear-to-linear polarization conversion. Furthermore, within the frequency bands of 16.5-17.3 GHz and 17.7-18.2 GHz, the proposed metasurface converts incident linearly polarized waves into right-handed circularly polarized (RHCP) and left-handed circularly polarized (LHCP) waves, respectively, while the output handedness can be interchanged by rotating the incident polarization by 90°. Conformal measurements demonstrate that the proposed metasurface maintains stable absorption performance under moderate bending, with only slight degradation in polarization conversion performance and a small frequency shift in the circular polarization conversion bands. Experimental measurements show good agreement with the simulated results, verifying the effectiveness of the proposed design. Owing to its simple configuration, low cost, multifunctional integration, and conformal capability, the proposed metasurface provides a promising solution for multifunctional electromagnetic manipulation in conformal integrated electromagnetic systems.

Random user orientation in indoor visible light communication (VLC) severely degrades the line-of-sight (LoS) channel and limits the gains of non-orthogonal multiple access (NOMA). This paper proposes a robust resource-allocation framework for an optical reconfigurable intelligent surface (ORIS)-assisted multi-cell VLC downlink under random Eulerangle user rotations. We fit truncated probability density functions (PDFs) for the LoS link and four ORIS links received by side-facing photodetectors (PDs) using Monte Carlo samples, maximum-likelihood estimation, and Akaike information criterion (AIC)-based model selection. Using this statistical channelstate information (CSI), we formulate a joint optical-power, user-association, and ORIS-activation problem that maximizes a weighted statistical-CSI rate surrogate under optical-power, eyesafety, quality-of-service, and physical-association constraints. A block-coordinate-descent (BCD) algorithm updates the three variable blocks using fractional programming, successive convex approximation, and semidefinite relaxation, respectively. Simulation results show gains of up to 14% and 56% over the proportional-allocation optimization (PAO) and time-division multiple-access (TDMA) baselines, respectively, at a signal-tonoise ratio (SNR) of 35 dB for the tested sitting-user orientation range σ_θ ≤ 10˚.

Growing demand for conformal, on-body communication systems has driven the development of compact, mechanically flexible, and conformal antennas. However, the reported literature on flexible dielectric resonator antennas with systematic conformal analysis is limited. This research gap has motivated the present investigations. The study aims to assess the comprehensive conformal analysis of a flexible cylindrical dielectric resonator antenna (CDRA) designed for X-band (operating near 10 GHz). The proposed antenna is bent over cylindrical and conical surfaces with radii of 40 mm and 30 mm, respectively. The conformal configurations are analyzed to evaluate performance and subsequently validated through experiments. The planar antenna resonates at 10.5 GHz, with a measured gain of approximately 5.2 dBi and a bandwidth of 450 MHz (10.27-10.72 GHz). The simulated results showed a downward frequency shift for both cylindrical and conical bending environments compared to the planar configuration. At the same time, the prototype measurements demonstrated an upward shift in the frequency of cylindrical bending of the antenna with increasing curvature, due to material-dependent properties. In contrast, the antenna undergoes non-uniform geometric deformation and strain-dependent permittivity behavior during conical bending. This leads to a downward shift in frequency and significant variations in radiation characteristics. Despite deformations, a stable broadside radiation performance and practically viable gain levels were achieved, with an overall bandwidth of 10.26-11.2 GHz. In addition, a specific absorption rate (SAR) analysis confirms the antenna's compliance with general public exposure safety limits, with a maximum SAR peak of 1.26 W/kg for 10 g averaged mass, in accordance with safety standards. The conformal analyses, along with the SAR validation for compact (less than 2 mm) and fully flexible CDRA, substantiate the novelty of the present study. Hence, the proposed antenna maintains a reliable performance under various bending conditions, highlighting its suitability for flexible, conformal, and wearable X-band applications.