In this paper, a 4-port multiple input multiple output (MIMO) antenna with dual-notched bands and high interference rejection features is presented for ultra-wideband and beyond. The total volume of the intended antenna, computed at 2.63 GHz, is 0.52λ × 0.52λ × 0.014λ. The basic radiating element consists of a spatula-shaped patch etched with a U and an inverted U-shaped slots printed on the top of a dielectric substrate, which is backed by defected partial ground plane. With the goal of achieving good polarization diversity and high isolation, four identical basic elements are arranged in orthogonal way to form the MIMO configuration. The inter-element isolation has been improved by a swastik-shaped decoupling structure with its arms extended in the form of meander-lines. As a result, the isolation between diagonal and orthogonal elements is better than 20 dB and 25 dB, respectively with envelope correlation coefficient < 0.012 and diversity gain > 9.94 dB. The suggested antenna attains an impedance bandwidth of 2.63-18.44 GHz with ability to shield interferences from 3.38-3.90 GHz and 4.65-6.45 GHz, specifically targeting frequencies associated with WLAN/ISM and Wi-MAX/LTE bands, respectively. Moreover, it exhibits maximum radiation efficiency and gain of 97.88% and 5.94 dBi, respectively in the working band.

To achieve compact size and high electromagnetic shielding performance in RF systems, a substrate integrated half-coaxial line (SIHCL) structure is proposed. A new approximate synthesis method for the SIHCL is proposed using the equivalent capacitor. Subsequently, two fifth-order Chebyshev low-pass filters (LPFs) with a 0.1 dB ripple factor were designed and fabricated: the first implemented in the SIHCL structure and the second in microstrip technology. A comparison of the measured S-parameters between these two low-pass filters demonstrates that both near-end and far-end crosstalk is suppressed for the proposed SIHCL LPF, which is significant for high-speed and high-density integrated systems.

This paper presents a class of wideband hybrid couplers with enhanced isolation, based on an N-section phase shift filter network integrated into an unequal-split, multi-section branch-line hybrid architecture. The key innovation lies in the incorporation of the N-section phase shift network, which significantly enhances the fractional bandwidth with each increase in section and isolation performance compared to conventional designs. A detailed design methodology applicable for any N is developed and validated through the fabrication and testing of two microstrip prototypes for N = 3 and N = 4 at a center frequency of 1 GHz. Both simulated and measured results confirm consistent tight coupling, insertion loss better than 6 dB, and isolation exceeding 15 dB across all prototypes. Furthermore, N = 3 and N = 4 hybrids shows peak isolation of 87.4 dB, 96.8 dB in simulation and 66.5 dB, 72.7 dB in measurement respectively, at the center frequency of 1 GHz. Notably, the designs demonstrate a progressive improvement in the fractional bandwidth, achieving 73.68% and 91.89% for N = 3 and N = 4, respectively. This scalable and frequency-flexible design approach makes the proposed class of hybrid couplers highly suitable for modern microwave systems such as vector network analyzer (VNA) test set, applications in radar, communication receivers, and phased array antennas.

The low-noise amplifier(LNA) is the most vulnerable device in the front-door coupling path of the wireless communication link. When the electromagnetic pulse(EMP) is injected into the LNA circuit, it first generates the electromagnetic response with peripheral components, and then is transmitted further. This affects the pulse value transmitted to the internal semiconductor device and its degree of damage. The pseudomorphic high electron mobility transistor(pHEMT) type transistors are widely used in modern RF circuits because of their good stability and wide frequency characteristics. However, the frequency-selective characteristics of the front-end system exacerbate the electromagnetic coupling damage of the LNA circuit in some frequency bands. Therefore, in this paper, the vulnerable frequency points of the pHEMT LNA circuit under repetitive pulses are analyzed by injection experiment. It is found that both in-band and out-of-band lead to permanent damage to the LNA. For the more vulnerable 3 GHz frequency point, the electromagnetic response under injection withstand and absorption conditions was measured, determining that the gate external resistance offset follows a power-law relationship with the input power. Furthermore, the energy threshold was obtained, which assesses the energy that, after electromagnetic loss by an external 100 Ω resistor, is transmitted to the gate input and causes permanent damage to the LNA transistor. The breakdown damage mechanism of the gate-source of the LNA transistor is verified by failure analysis.

In order to meet antenna requirements for vehicular communication, a compact multiport MIMO antenna design is proposed for the n261 frequency band in 5G millimeter-wave communication. The 3D size of the antenna is 16 × 16 × 17 mm³. By optimizing the radiation patches and layout, a four-port MIMO antenna is developed, with adjacent antenna elements positioned on both sides of the dielectric substrate to minimize coupling between antenna units. Additionally, optimization is performed to achieve 360° radiation coverage for the multiport MIMO antenna. The simulation and measurement results show that the proposed antenna covers the n261 frequency band with an operational bandwidth. The overall isolation between ports of the multiport MIMO antenna is also relatively high. The 12-port MIMO antenna operates in the frequency range of 27.08 to 28.70 GHz, with a gain of 6.25 dBi, and its radiation pattern demonstrates diversity, providing complete 360 ° coverage in both elevation and azimuth planes. Therefore, the proposed antenna not only has a compact size and simple structure but also supports radiation propagation across multiple planes, reducing multipath propagation losses and enhancing communication quality and reliability. It satisfies the requirements of vehicular communication for 5G millimeter wave MIMO antennas.

In this paper the design of a cavity-backed slot antenna array with wideband operation and low sidelobe levels is introduced. A High gain metallic antenna array is designed using rectangular waveguides in both the feeding network and cavity-back slots, where a 16×16 array antenna is built with 8×8 subarrays. The antenna is fabricated using direct laser sintering (DLS) and computer numerical control (CNC) milling technology on both sides of each layer to guarantee no field leakage between antenna layers. For the sake of achieving a wide bandwidth in such array, a 1-to-64-way corporate feeding network is used to distribute the power in the lower feeding layer to excite the coupling apertures beneath the subarrays. The excited power coefficients through the array aperture are tapered using quasi-Taylor synthesis, with an even phase so the modified uneven power waveguide-splitter is designed to taper the field amplitudes within the feeding network till reaching the radiating slots. The array achieved a 14% bandwidth, a gain of more than 31.25 dBi over 1.85 GHz, sidelobe levels higher than 23 dB, and cross-polarization levels better than -40 dB, according to measured data.

Radar-based hand gestures recognition have played an important role in developing human-computer interaction (HCI). However, when radar-based hand gesture recognition techniques are applied to multi-target scenarios, the challenges mainly involve problems of mutual interference and inaccurate recognition of hand motion when both hands move within the same plane. Here, we propose a dual-hand trajectory perception prototype based on a 60 GHz frequency-modulated continuous-wave (FMCW) multiple-input multiple-output (MIMO) radar sensor platform with an L-shaped virtual antenna array. To address the challenges, the approach involves estimating azimuth and elevation angles separately from the two data components derived from the L-shaped array through multiple signal classification (MUSIC) algorithm, incorporating spatial division techniques combined with digital beam formation (DBF). The dual-hand applications mainly include angle targets at two distinct distances or dual-angle targets at the same distance. Therefore, the target distances are first determined using range fast fourier transform (range FFT). If a single target distance is identified, we proceed to solve for the angles of two targets. Alternatively, if two distinct target distances are distinguished, we individually solve for the single-angle target corresponding to each distance. Furthermore, to mitigate noise inherent in the raw data of visualization, a frame point removal and smoothing algorithm is devised to refine the trajectories. Experimental verifications prove that the proposed multi-target motion perception algorithm by using a MIMO FMCW radar sensor platform can realize accurate recognition of air-writing gestures and enable tracking the trajectories of both single-handed and dual-handed targets in three-dimensional space. It also gives a new option for controlling the HCI.

This article presents a compact, triple-band half mode substrate integrated waveguide (HMSIW) based self-multiplexing antenna (SMA) designed for various X-/Ku- band applications. The proposed SMA comprises a compact HMSIW with slots of unequal widths excited with three different ports resembling the anatomy of an arrow. These three slots are driven by a 50 Ω microstrip line feed, facilitating radiations at 10.82, 12.28, and 13.95 GHz with good isolation between the ports. Independent functioning at three different frequency bands is made possible by the remarkable versatility of the proposed SMA design method. With the isolation of nearly 20 dB between ports and gains of 3.97, 4.62, and 7.55 dBi at ports resonating at three distinct frequencies, the SMA-HMSIW element's total arrangement allows for a small antenna size of 0.44λ_g² at the lowest frequency of operation. The proposed SMA structure has been fabricated, and the results are measured which show good agreement with simulated ones.

This paper proposes a four-port ultra-wideband (UWB) MIMO antenna with high isolation and three notch bands. A cross-shaped decoupling structure (CSDS) is synergistically integrated with an improved L-shaped ground plane to achieve high port isolation. Composite resonant slots (CRSs) are introduced on the radiating patch, and two L-shaped slots are etched on the feed line to suppress interferences from WiMAX (3.19 GHz), C-band (4.45 GHz), and X-band (7.95 GHz). Simulation and measurement results verify that the Voltage Standing Wave Ratio (VSWR) at the center frequencies of the notched bands is greater than 6.8, 8.1, and 4.3, respectively. In the operating frequency band of 2.7-12 GHz (excluding the notched bands), the isolation is > 24.3 dB, envelope correlation coefficient (ECC) < 0.0045, diversity gain (DG) > 9.9990 dB, total active reflection coefficient (TARC) < -10 dB, and channel capacity loss (CCL) < 0.4 bps/Hz. It fully meets the requirements of high-performance MIMO systems for channel independence and transmission efficiency. Compared with similar studies, this work has significant advantages in core indicators such as bandwidth, number of notched bands, and isolation, providing new ideas for the design of UWB-MIMO systems in complex electromagnetic environments.

Unmanned aerial FPV systems demand ultra-low latency, high-reliability communication. At high speeds and in cluttered environments, Doppler shifts and rapid multipath changes significantly increase packet error rates (PER). This paper introduces a novel solution: real-time geometry tuning of a circularly polarized helical antenna array to mitigate these effects in ExpressLRS (ELRS) long-range FPV control links. Using full-wave simulations (Ansys HFSS) and blind field trials, we validate system performance. A new analytical framework integrates Doppler-induced frequency offset into the antenna's radiation pattern and PER model. The adaptive array autonomously adjusts coil pitch and diameter based on velocity and attitude, reducing PER by 20% at speeds over 150 mph. It also maintains near-unity VSWR, preventing reflection spikes, and halves RSSI variation, indicating improved link stability. These results demonstrate that tunable helical antennas can effectively mitigate Doppler and multipath impairments in high-mobility UAV environments, informing future antenna designs and supporting the development of AI-integrated, adaptive RF systems for drone racing and autonomous swarms.

This work explores the data-driven approaches for breast tumor detection and analysis of different breast tissues by using microwave sensing technique. Microwave sensing offers a promising trade-off in tissue penetration depth and is prominent dielectric disparity between healthy and tumorous tissues at microwave frequencies. Tumor cells exhibit unique properties, such as increased water content and different ionic composition, which create distinct dielectric traits compared to healthy tissue. This frequently shows variations in loss characteristics compared to normal tissue and can exploit those differences for detection. The key parameter used is Specific Absorption Rate for the determination of tumor location. The differential absorption between healthy and tumor tissue is potentially aided in identifying the presence of lesion. The five sets of reflection characteristics are recorded with the system comprising UWB antenna with breast phantom by using VNA with a gap of 4-5 days. Further, the dimensionality reduction technique is applied to extract the features using PCA and tSNE. In order to enhance the detection accuracy, dimensionality reduction techniques are used in tandem with the supervised machine learning approach. Among the four supervised algorithms, including SVM, KNN, RF and MLP, the random forest was found to be the most optimal for the data with an auc score of 99.97%.

Nowadays, microelectronic integrated circuit (IC) design constitutes the biggest challenge of negative group delay (NGD) electronic engineering research. Bandpass (BP) type NGD circuits are generally designed with resonant and not-integrable inductive large size network-based topology. However, BP-NGD circuit integrability is delimited by the inductor design. A design solution for fully resistive-capacitive (RC) network-based BP-type IC in 130-nm CMOS technology is the purpose of the present research work. The theory expressing the design equations of RC-network based BP-NGD circuit is developed. The design feasibility is verified with a proof-of-concept (POC) represented by a 130-nm CMOS RC-network passive IC with 0.68 mm × 0.72 mm physical size simulated by Cadence®. The obtained results of S-parameters confirm the BP-NGD behavior of the CMOS IC POC with 21.9-MHz NGD center frequency and -0.99-ns NGD value over 68-MHz NGD bandwidth. The BP-NGD characterization results are in excellent agreement with the theoretical model. The robustness of 130-nm CMOS BP-NGD RC passive IC is explored by 2000 trials Monte Carlo statistical analysis with respect to the uncertainty of component parameters.

Flux-reversing machines (FRMs) have the advantages of high torque density and wide speed range. However, their disadvantage is the low utilization rate of permanent magnets (PMs). To enhance PM utilization, a novel dual-PM FRM (DPFRM) with Halbach arrays is proposed in this paper. Halbach arrays are applied to both the stator interlayer and half of the rotor teeth, forming a consequent-pole structure together with iron cores. This layout significantly reduces the number of rotor magnets used. With the use of Halbach arrays, this design effectively reduces magnetic flux leakage. It also achieves higher torque density under low current conditions, demonstrating enhanced electromagnetic performance. To achieve better overall performance, both the conventional FRM and the proposed DPFRM are globally optimized. Their no-load and load performances are evaluated through finite element analysis (FEA). The analysis verifies that the DPFRM achieves higher back electromotive force (Back-EMF) and torque density, and also exhibits lower torque ripple. Therefore, the proposed design significantly improves PM utilization, effectively mitigating the primary limitation of conventional FRMs.

This paper presents a miniaturized broadband port-reuse microstrip circuit to address the challenges of bulky volume, excessive insertion loss, and parameter deviation superposition caused by discrete port design and discrete circuit design in the interconnection between active phased array antennas and T/R components. Based on an integrated design methodology, the circuit achieves bandpass filtering, bidirectional power coupling output, DC power supply port functionality, and RF/DC isolation through a single-port interconnection. Experimental results demonstrate that the implemented circuit in Ku-band exhibits 13.5-15.18 GHz bandpass filtering characteristics, bidirectional signal power monitoring capability, 0-12 V/2.5 A DC power supply functionality, and effective RF/DC signal isolation. The measured results align well with theoretical predictions. This architecture demonstrates exceptional adaptability and seamless integration capability, showing significant potential for large-scale deployment in various transceiver architectures such as satellite communication systems.

To improve the current and torque regulation performance of the traditional deadbeat predictive current control (DPCC) for switched reluctance motors under model parameter mismatch, this article proposes an improved DPCC method based on the sliding mode strategy. First, a dedicated torque-current converter is formulated to achieve precise transformation of electromagnetic torque into corresponding q-axis current references. Second, a unified anti-disturbance sliding mode control compensation scheme is introduced into both the torque-current converter and the deadbeat controller to mitigate the negative effects of model parameter mismatch on current and torque control. This integration achieves indirect torque control through phase current modulation, effectively reducing torque ripple. Furthermore, the stability of the controller under model parameter mismatch conditions is rigorously demonstrated through Lyapunov stability analysis. Finally, the effectiveness of the proposed control method is demonstrated through simulation results, and its significant superiority in current control performance and torque ripple suppression is shown.

This paper presents the design, simulation, and experimental validation of a 1-bit reconfigurable reflectarray. Each unit cell is equipped with a single PIN diode, enabling binary phase control (0˚ and 180˚) for dynamic beam steering. The reflectarray employs a compact and cost-effective architecture, with digitally reconfigurable elements that allow real-time control of the reflected wavefront. The integration of PIN diodes ensures fast switching and low power consumption while maintaining good reflection efficiency and phase performance. Without limiting the applicability of the method, a reflectarray antenna consisting of 9×9 element array operating at 5.8 GHz was designed. Full-wave electromagnetic simulations and measurements demonstrate beam steering capability up to ±15˚, with minimal gain degradation and acceptable side-lobe levels. The proposed reflectarray design is a promising solution for low-complexity, reconfigurable antenna systems in applications such as wireless communications, radar, and IoT systems operating in the 5.8 GHz ISM band.

This paper presents the development of a low-frequency dual-port microwave sensor designed for permittivity detection in both solid and biological materials. The sensor integrates a circular split-ring resonator (CSRR) with an electric field coupled (ELC) structure on a planar dielectric substrate, resulting in a compact and simple architecture that supports ease of fabrication and low-cost implementation. Operating at a resonant frequency of 0.86 GHz, the sensor is particularly suitable for characterising biological samples such as meat, fish, squid, and chicken, as lower frequencies offer deeper penetration and better interaction with high-loss biological tissues. Validation through full-wave simulation and experimental measurement confirms the sensor's capability to detect permittivity variations across a wide range of materials. A polynomial fitting model is employed to extract permittivity values based on resonance frequency shifts, achieving accurate results with a maximum error below 7% and overall accuracy exceeding 93%. The device demonstrates reliable performance in estimating permittivity values from ε_r = 1-9.8, including unknown biological samples with normalized sensitivity of 0.02% and frequency detection resolution 0.019 GHz. Measurements show clear frequency shifts that correlate with dielectric changes, and the experimental results align closely with the simulation data. The simple structure of the sensor also supports straightforward integration with common measurement instruments such as vector network analysers, making it practical for real-time monitoring and portable applications. The low operating frequency combined with the straightforward design provides an effective solution for applications requiring permittivity detection of lossy, heterogeneous, or biological materials. This work contributes a feasible and efficient sensor platform for use in medical diagnostics, food quality inspection, and other industrial contexts where reliable, low-cost dielectric sensing is essential.

In this paper, a compact microstrip line (MSL)-to-circular waveguide (CWG) transition using a rectangular patch is introduced. As the rectangular patch is placed 2.68 mm (0.043 λg) away from the short-circuited plane of the CWG, the transition is very compact. By truncating the rectangular patch of the compact MSL-to-CWG transition, a compact MSL-fed CWG polarizer using the corner-truncated patch is proposed. The proposed polarizer has a compact size and a phase difference of -90.97° at 9.65 GHz. The axial ratio is within ±1 dB from 8.5 GHz to 10 GHz. The reflection coefficient is smaller than -10 dB from 9.03 GHz to 10.5 GHz. In addition, as the corner-truncated patch is adopted, the proposed polarizer does not require a complex manufacturing process on the waveguide. Moreover, as the microstrip line feeds the polarizer, it can be easily integrated with other planar circuits. To verify the simulation results, the MSL-fed CWG polarizer using the corner-truncated patch is fabricated and measured. The simulation and measurement results are in good agreement.

This article presents a compact and flexible ultra-wideband (UWB) antenna with a defected ground structure (DGS) for IoT applications. The antenna is fabricated on a 0.7 mm thick jeans substrate to ensure high flexibility and take advantage of its universal availability. Machine learning techniques are applied to optimize the antenna's performance. A ring-shaped patch with DGS and C-type stubs is used to achieve a large bandwidth and reduce size. The total dimension of the proposed flexible antenna is 38 × 26 × 1.7 mm³. The primary aim of this article is to design a flexible UWB antenna with a remarkable impedance bandwidth of 131.45%, which covers frequencies from 2.56 GHz to 12.38 GHz. It operates at 3, 8, and 11.32 GHz frequencies with 99%, 98.30%, and 96.71% radiation efficiencies, respectively. The realized gain is 2.51, 3.70, and 5.46 dBi at frequencies 3, 8, and 11.32 GHz, respectively, with a peak gain of 5.46 dBi at 11.32 GHz. Specific absorption rate (SAR) values were tested using a human phantom and met FCC limits, confirming suitability for wearable and flexible IoT applications. The design was optimized using machine learning (ML), with KNN performing best, achieving 99.5% accuracy in S-parameter prediction. The measured and simulated results are correlated with each other for flat and bent antennas.

Microwave-based object localization system is a noninvasive technique that uses microwave signals to detect, map, and analyze the properties of materials. This approach provides information about hidden objects within materials. However, the localization process can be complex, requiring sophisticated algorithms to interpret the signals accurately. This study proposes a new technique for microwave-based object localization system using Radio Frequency (RF) Codes to perform spatial detection with four pairs of RF Code sensors representing bits of ``111,'' ``110,'' ``101,'' and ``011.'' The system incorporates four identical RF Code paths arranged symmetrically around a circular container, improving spatial coverage and enabling accurate detection of hidden objects located at eight different spatial positions. Steel is used as the hidden object, while Stone serves as Material X in this system. The system achieved an average detection accuracy of 70% and a detection efficiency close to 100% across all spatial positions. Additionally, the RF Code performance chart is designed to interpret the detection accuracy results, making the analysis more accessible and practical. The proposed system has potential applications in nondestructive testing, material analysis, industrial inspection, and security systems, offering a reliable and efficient solution for detecting hidden or embedded objects.