To enhance the disturbance rejection capability and robust stability of PMSM under time-varying disturbances, an improved super-twisting higher-order sliding mode active disturbance rejection cascade control strategy is proposed. Firstly, a second-order mathematical model of the PMSM speed-current dual-loop system is established. Secondly, to address the oscillation issues caused by differentiation of the reference speed in conventional linear error feedback control, a composite sliding mode error feedback control law is designed by integrating the fast super-twisting (FST) algorithm and the fast non-singular terminal sliding mode control (FNFTSMC) method. The control law effectively suppresses system chattering and improves dynamic response. Meanwhile, an improved extended state observer (IESO) is constructed based on deviation control theory, which enhances real-time compensation of the cascade controller by optimizing convergence speed and disturbance estimation accuracy. Finally, hardware-in-the-loop (HIL) simulation results on an RT-LAB platform demonstrate that the proposed method outperforms traditional strategies in both dynamic performance and disturbance rejection, providing a viable solution for high-performance PMSM drive applications.

The prospective applications of a rectangular microstrip patch antenna (MPA) in energy harvesting at radio frequencies (EH). The study aims to develop a rectenna that can detect and connect low power wireless devices to long-term evolution (LTE) networks by capturing low-power radio frequency (RF) signals radiated by cell towers, since the Kappa 438 antenna substrate with relative permittivity 4.25 has high 9 dB gain and 83% of measured efficiency. For the 2.5 GHz LTE band, stubs technology is being used for impedance matching and to decrease the overall rectenna size. The captured RF signals were altered into a usable DC voltage via a rectifier circuit in the manufactured rectenna, having the option of storing the voltage in a battery or utilizing it to power wearable, portable Internet of Things (IoT) systems and wireless sensors. The rectifier circuit is reduced in size by utilizing the SMD-Schottky diode type SMS7630 segments approach, further reducing the complexity and bulk of the rectenna. The rectenna obtains an efficiency of 88% when the RF input power is tuned to 0 dBm, while the maximum output DC voltage generated is 1.7 V when the radio waves power supply is 10 dBm. The rectenna with high gain and directivity has the capability to operate in low power environments, capturing weak radio frequency signals and working across -10 to 10 dBm power dynamic range. power dynamic range. These outcomes represent new contribution to our work which is relevant to other studies listed in Table 6 and demonstrated notable improvements.

In this paper, a miniaturized balanced bandpass filter characterized by biaxial symmetry is designed and implemented using four C-section parallel-coupled microstrip lines. As two orthogonal symmetric axes are inherently embedded across the filter layout, a natural geometric constraint is imposed and therefore furnishes two independent input/output port states. Owing to its symmetric topology, the developed filter replicates the same differential- and common-mode responses at each of its two independent input/output port pairs. To further enhance the common-mode suppression without compromising the differential-mode performance, a quarter-wavelength open-circuited stub is introduced onto the junction of one of the C-section parallel-coupled microstrip lines. By utilizing this stub, the common-mode suppression bandwidth is effectively broadened. Moreover, highly compact circuit sizes are achieved for the developed balanced filters, which is regarded as essential for their integration into modern miniaturized microwave communication systems. Finally, the feasibility of the proposed concept is verified through the design and fabrication of two prototypes, and good agreement is observed between the simulated and measured results.

The advancement of wireless communication has led to continuous innovation in antenna technology to satisfy the growing requirement for wireless communication. However, in wireless communication, antennas still face problems and challenges such as high power consumption and low adaptability. To address these issues, this study introduces magneto electric dipoles to optimize broadband millimeter wave patch antennas and uses metasurface optimization patches to ultimately design broadband dual-polarized millimeter wave metasurface antennas. In comparative tests at different temperatures, the gain of the broadband dual-polarization millimeter-wave meta-surface antenna reached a peak of 10.7 dBi at around 35 GHz at -50 ℃. At 0 ℃ and 50 ℃, the gain reached a peak of 10.2 dBi and 8.5 dBi, respectively. The result shows that the designed antenna has high accuracy, gain, and strong stability in wireless communication, and also has certain anti-interference ability in different environments.

This paper presents a design method for circularly polarized metasurface antennas by integrating waveguide-fed metasurfaces with optical holography principles. Two interleaved linear slot elements on the metasurface top layer are excited by a reference wave from the feed, generating a circularly polarized beam. Simply adjusting the position of each slot element steers the beam in the desired direction. To enhance gain, metal vias are added around the antenna perimeter, reducing reference wave leakage. To validate this method, two 24 GHz circularly polarized holographic metasurfaces were simulated and experimentally characterized. Measurements show a 1.23 dB gain enhancement in the metasurface antenna with metal vias. Simulated and measured results validate the antenna's performance. This approach yields compact, low-profile antennas without requiring a separate feed network. Furthermore, the structure can be extended to create reconfigurable circularly polarized antennas, demonstrating significant potential in this field.

This research introduces a compact and highly selective tri-coupled line microstrip bandpass filter. The design features a narrow capacitive gap positioned at the midline to disrupt symmetry and facilitate bandpass functionality, as predicted through an even- and odd-mode image impedance framework. The split at the midline generates two modal capacitances (C_gg, C_gb), which influence Re (Z_i) and, in conjunction with geometric coupling, determine the passband and roll-off characteristics. Closed-form relationships for microstrip design are utilized to compute line widths and electrical lengths. A systematic parametric analysis demonstrates how the gap and interline spacing impact the fractional bandwidth and the steepness of the transition. Additionally, a substrate survey across dielectric constants ranging from 2 to 12.2 quantifies the trade-off between footprint and selectivity, indicating an area reduction of up to approximately 86% at higher dielectric constants. The selectivity is further enhanced by incorporating auxiliary shunt open stubs that introduce transmission zeros near the edges without necessitating additional resonator sections. A prototype fabricated on an FR-4 substrate operating at 2.4 GHz confirms the theoretical model: the measured |S₂₁| exhibits an insertion loss of approximately 0.58 dB, a fractional bandwidth at 3 dB of approximately 37.3%, a shape factor of 1.3, and two prominent TZs near 1.7 GHz and 3.1 GHz with rejection levels of 48-52 dB. Furthermore, the upper stopband maintains |S₂₁| < -35 dB within the frequency range of 3.10 to 3.20 GHz. These findings substantiate that a single TCL section, featuring a central gap and open stubs, can achieve sharp roll-off and low insertion loss while maintaining minimal layout complexity and enabling straightforward tuning on low-cost printed circuit board materials.

As wireless communication technologies evolve, the demand for more efficient and compact antennas has escalated. Fractal antennas, with their unique self-similar design, offer a promising solution to meet these needs. Traditional antenna designs often face limitations in bandwidth and efficiency, especially in complex environments like urban areas, where high-performance antennas are crucial. This paper proposed a novel star-fractal patch integrated with a Sierpinski triangle fractal defective ground structure. This combination creates a double fractal design, which is further enhanced by adding a rectangular split ring resonator (R-SRR) array as a metasurface superstrate to achieve a reasonable bandwidth with improved gain for C-band wireless applications. This novel antenna structure results in improved impedance matching within the 5.22 GHz to 5.78 GHz operating frequency range. Electromagnetic simulations and anechoic chamber measurements validate the performance parameters of the proposed antenna. A proposed compact fabricated antenna achieved a bandwidth of 10.24% with noteworthy improvements in directivity across the operating frequency range compared to a full ground structure. The measured results align closely with the simulated data, demonstrating the reliability of the design approach. The fractal antenna design demonstrated substantial enhancements in performance parameters, confirming its viability as a superior alternative to conventional antenna designs in enhancing wireless network capabilities. These advancements could enable next-gen wireless and IoT applications by solving challenges in miniaturization, integration, and multi-band operation. Future research aims to enhance capabilities with dynamic reconfigurability, wider and selective frequency coverage of metamaterial inspired fractal antennas.

A compact wideband circularly polarized radio frequency identification (RFID) reader antenna with a coupling inner ring is proposed. The antenna consists of a radiating patch, a feeding network, and vertical fences along the sidewalls. The radiating patch incorporates both an outer ring and a coupling inner ring, which significantly broadens the gain bandwidth. Meanwhile, the sidewall-loaded vertical fences effectively extend the surface current path, enabling directional radiation. The overall antenna size is 100 mm × 100 mm × 24.6 mm. Measured results show a -10 dB impedance bandwidth of 663-1191 MHz, a 3 dB axial ratio bandwidth of 710-1085 MHz, a 4.5 dBic gain bandwidth of 885-1150 MHz and a maximum gain of 6.36 dBic. Featuring a compact structure, wide impedance bandwidth, broad axial ratio bandwidth, and enhanced gain performance, the proposed antenna is well suited for ultra high frequency (UHF) RFID applications, particularly in space-constrained environments or in scenarios where tag antennas are susceptible to frequency deviations.

A four-port cross-shaped RDRA multiple-input-multiple-output antenna is proposed for 5G millimeter-wave applications. The present investigation targeted the 5G n257 band (26.5-29.5 GHz) with resonance exactly at 28.5 GHz. The proposed DR MIMO antenna is constructed over roger RT duroid 5880 laminates with the floor area 10.4×10.4×0.254 mm³ with the compact DRA of dimension 7.6×7.6×1.5 mm³. Each element of the DRA is fed by conformal fed microstrip line that generates TE_21∂, TE_41∂, TE_11∂, TM_14∂ and TM_41∂ modes. The symmetricity of the structure is maintained by locating four arms of the DRA at a separation of 90°, that generates omnidirectional radiation pattern and offers good radiation diversity. The proposed antenna offers 14% impedance bandwidth with below -15 dB isolation. Following the thorough simulation procedure, it has been verified that the compact MIMO DRA operates exactly at 28.5 GHz. To validate design, a four-port single element DRA operating at 28.5 GHz was simulated in CST studio suite, fabricated via ceramic material and then measured in anechoic chamber. The proposed antenna shows the peak gain of 8.4 dBi with 74% radiation efficiency. Both simulation and measurement observations are used to examine the MIMO parameters. The Envelope correlation coefficient is reported as 0.0125 and Diversity gain is reported as 9.8 in approximately all the cases. The Total Active Reflection Coefficient is found to be 18% at 28.5 GHz in measurement and 18.5% at 28.5 GHz in simulation.

Ultrashort pulse semiconductor lasers represent a groundbreaking advancement in photonics by simultaneously overcoming the fundamental constraints of temporal duration, spatial confinement, and energy efficiency. These triple breakthroughs enable unprecedented applications in ultrafast spectroscopy, high-density optical storage, optical atomic clocks, photonic computing, and minimally invasive biomedicine, establishing a new paradigm for precision light-matter interaction in both scientific and industrial domains. This paper analyzes the principle and cutting-edge research progress of ultrashort pulse semiconductor lasers, discusses the implementation difficulties and optimization methods in integrated design, and looks forward to the challenges and future development trends.

This paper presents a reconfigurable multilayer graphene antenna for terahertz sensing, machine learning-based frequency and bandwidth estimation. The antenna utilizes the tunable electromagnetic properties of graphene, enabling dynamic reconfiguration of the resonant frequency and bandwidth. By adjusting key physical parameters including chemical potential, relaxation time, and temperatur, the antenna achieves frequency tuning from 1.542 THz to 1.562 THz, with an improved return loss reaching -30.8 dB and a bandwidth range from 91 GHz to 96 GHz. Furthermore, the resonance frequency and bandwidth are predicted using machine learning algorithms, including Random Forest and XGBoost, with results that closely match simulation data. These results highlight the potential of the proposed structure not only for adaptive communication systems but also for terahertz sensing platforms requiring frequency agility and environmental responsiveness.

The annular micro receiving coil (RC) holds promise in the wireless power supply for capsule endoscopy (CE). The equivalent series resistance (R_SR) of the RC plays a critical role in energy transmission efficiency. Calculating the R_SR is challenging because RC typically incorporates an embedded magnetic core. To overcome this challenge, this paper employs Dowell's method and the Bessel's method respectively to calculate R_SR. The analyzed RC consists of an annular core with two grooves and dual windings positioned within the grooves. The influence of the magnetic core on the R_SR is equivalently considered through the winding skin effect and core losses. We compared the simulated, calculated, and measured values of the R_SR, and found that: the error of Dowell's method becomes smaller when the groove spacing D_g > 4 mm, but fails to capture the influence of D_g on the R_SR. Conversely, Bessel's method effectively captures the influence of D_g but exhibits larger errors (2.09%~26.52%). Based on this finding, we propose a novel Bessel-modified Dowell's (BMD) method by integrating the framework of Dowell's method with a proximity-effect correction term from Bessel's method, which reduces the maximum calculation error to within 13.72%, facilitating rapid optimization of annular coils with embedded magnetic cores.

This paper proposes a fast voltage regulation control method based on direct power calculation. To suppress the issues of long bus voltage recovery time and large voltage fluctuation in dual three-phase permanent magnet generator, firstly, in the voltage outer loop, the fast adjusting component of the inner loop power reference is derived through a direct power calculation method. This approach enhances the dynamic response of the bus voltage. Secondly, to mitigate control errors induced by system losses, a capacitor power compensation method is introduced to generate an error compensation component for the power reference, thereby improving the voltage control accuracy. Finally, the feasibility and effectiveness of the proposed control strategy are validated through both software simulations and experimental tests. In comparison with conventional methods, the proposed strategy provides stronger disturbance rejection and a faster dynamic response, enabling high-performance DC bus voltage control for dual three-phase permanent magnet generator systems.

To enhance robustness and dynamic performance of permanent magnet synchronous motor (PMSM) drives at high speeds, a deadbeat predictive current control method based on a predictive disturbance suppression model (DPCC-PDSM) is proposed. First, the mathematical model of the PMSM and the principle of traditional deadbeat predictive current control (DPCC) are presented. Second, to estimate and compensate disturbance effects caused by external uncertainties, a predictive disturbance suppression model is designed by integrating the recursive least squares (RLS) algorithm with an extended state observer (ESO). Furthermore, leading angle flux weakening control strategy is incorporated into the predictive control framework to overcome voltage and current limitations in high-speed operation. Finally, the stability and effectiveness of the proposed method are validated through experiments. The results demonstrate that the DPCC-PDSM significantly improves robustness and ensures stable and reliable performance of PMSM drives in high-speed flux weakening operation.

This paper examines the optimisation of antenna parameters for wire monopole, vertical trapezoidal monopole, and circular disc monopole antennas with the Enhanced Optimizable Neural Network Classifier (EONNC) and Sugeno Fuzzy Inference System (SFIS). This study includes both quantitative and conventional antenna design techniques, offering comprehensive insights into antenna optimisation tactics. An advanced antenna selection algorithm identifies the ideal antenna by a comprehensive examination of performance metrics with the EONNC, hence reinforcing the rigour of our research process. The geometric parameters of the antennas are delineated, with SFIS proficiently ascertaining the appropriate dimensions. The EONNC categorises antennas into three classifications, whereas the SFIS determines optimal parameters for estimating antenna size. Accuracy measures assess the EONNC performance, whereas the SFIS performance is measured using the Mean Squared Error (MSE) and Mean Absolute Percentage Error (MAPE). Our suggested technique demonstrates remarkable precision in parameter prediction and antenna classification, with a mean absolute percentage error (MAPE) of less than 4% and an accuracy exceeding 99.3%. The research examines the circular disc monopole antenna due to limitations in simulation duration for SAR measurements, resulting in SAR values of 0.978 W/kg for arm measurements and 0.985 W/kg for hand measurements. The proposed techniques are very relevant to actual antenna designs, especially for wearable applications.

In this paper, a radiator employing the Cherenkov mechanism for electromagnetic energy transfer from an optically less dense medium into a more dense one is developed and studied using a two-dimensional numerical model. The radiator’s principal components are a dielectric prism and an open dielectric waveguide, where the phase velocity of eigenwaves exceeds that within the prism. For two linear field polarizations in the 24 GHz to 64 GHz range, this radiator exhibits high efficiency (over 93%) and radiation patterns with main lobes that closely coincide in both direction and width. The direction of radiation demonstrates strong agreement with predictions from the Cherenkov wave theory and shows weak dependence on frequency. These characteristics make the developed antenna suitable for directional emission and reception of electromagnetic pulses of various polarizations with spectral bandwidths of up to one octave or more. It is demonstrated that the radiation patterns of such antennas can be electrically controlled by altering the permittivity of the dielectric waveguide using an external control signal. The proposed antenna design avoids expensive fabrication processes and can be scaled to sub-millimeter wave ranges without significant modifications.

A hybrid machine-learning-based optimization method is proposed for quick optimization of antenna shape design. The hybrid optimization method combines self-supervised learning and transfer learning. The application of self-supervised learning avoids the requirement to obtain labeled simulation data for electromagnetic samples, thereby reducing the difficulty of sample construction. The introduction of transfer learning further improves the sample utilization and optimizes efficiency in electromagnetic tasks. The proposed method enables rapid and high-degree-of-freedom optimization of antennas. To validate its effectiveness, a reflectarray antenna design incorporating distinct elements is employed as a case study. Simulation results indicate that the designed antenna exhibits a realized gain of 26.3 dBi and 46% aperture efficiency at the center frequency, and each element has a highly flexible independent structural design. During the optimization process, the proposed hybrid method demonstrates higher optimization efficiency than traditional methods, while significantly reducing sample construction time.

Resonant slot cut microstrip antenna is a single patch solution to achieve circularly polarized response, but it does not offer tunability in the center frequency of axial ratio bandwidth. This paper presents reconfigurable designs of shorting post loaded U-slot cut circular and equilateral triangular microstrip antennas that offer tunable circularly polarized response. Shorting posts positions alter the excitation of resonant modes on the U-slot cut patch that achieves tuning in the circularly polarized frequency. On substrate thickness of ~0.05λ_cAR, using the circular patch, tuning in the center frequency of axial ratio bandwidth by 253 MHz (28.26%) is obtained, whereas equilateral triangular patch design offers 319 MHz (32.68%) of frequency tuning. In both the designs, broadside radiation pattern with a peak gain of larger than 7 dBic is obtained across the axial ratio bandwidth. Design methodology is proposed that yields a similar configuration as per specific wireless application. With the obtained frequency tuning in axial ratio bandwidth, redesigned variations of the proposed configurations can cater to pairs of GPS L-band applications.

This paper introduces a novel method for designing a wideband tunable bandstop filter (BSF) with constant absolute bandwidth (ABW). The design uses a doublet configuration, where two varactor-tuned resonators are symmetrically coupled to a main transmission line. To maintain constant ABW during frequency tuning, a coupling scheme is proposed where coupling strength decreases as the frequency increases, eliminating the need for additional circuits. Theoretical analysis and closed-form equations are provided for designing the BSF with a wide tuning range. A BSF prototype is designed and tested, demonstrating a 10-dB ABW of approximately 190 MHz across a continuous stopband tuning range from 3.3 to 5.1 GHz, with a fractional tuning range of 42.9%.

Smart antennas provide a unique and viable solution to the problem of multipath effects on signal propagation, particularly in the millimetre wave band. Multiple-Input Multiple-Output (MIMO) technology has certain advantages that can prove instrumental in not just eliminating multipath but turning it into an advantage and using it to improve communication link quality. With the use of MIMO and its unique beamforming capabilities, path loss can be significantly reduced, and more efficient use of the communications frequency spectrum can be achieved. MIMO antenna technology consists of a smart antenna array with multiple transmitting inputs and multiple receiving outputs. In this review, we compare some of the latest developments in MIMO technology. It focuses on design techniques, performance parameters, and novel developments. Recent developments include improvements in UWB, multi-band, and smart wear.