Search Results (7,448)

Reliable and fast radiation pattern prediction is critical for large-scale tightly coupled linear antenna arrays. Strong mutual coupling and finite-array edge effects limit the accuracy of conventional array factor methods, while full-wave simulations become computationally prohibitive for large arrays. To address this issue, a fast and efficient radiation pattern prediction method (FERPP) is proposed. For central elements, the far-field response is obtained from a calibrated reference array and extended through position-dependent phase compensation. For edge elements, responses are extracted from independent local full-wave simulations. All element responses are assembled into a global far-field response matrix, enabling direct radiation pattern synthesis using the extended method of maximum power transmission efficiency. Simulation results obtained with a 1024-element linear microstrip patch antenna array operating at 3.5 GHz, with small inter-element spacing, demonstrate close agreement with full-wave simulations. For a broadside single-beam case, the predicted peak gain is 29.10 dBi, compared with 29.02 dBi from full-wave simulation. For a scanned beam at 30°, the predicted peak gain is 28.22 dBi, while the full-wave result is 28.99 dBi. For an equal-weight three-beam configuration at −30°, 0°, and 30°, the proposed method yields a peak gain of 23.87 dBi, compared with 24.21 dBi from full-wave simulation. In terms of computational efficiency, the proposed method requires only about 1.8% of the computational time required for a full-wave simulation. These results demonstrate that the proposed FERPP method provides a practical and efficient solution for radiation pattern prediction and beamforming analysis of large-scale tightly coupled linear antenna arrays. Full article

The purpose of this research is to determine which factors contribute to extending the read range of transponders equipped with different coupling-circuit topologies operating within selected RFID frequency bands. The analysis covered transponders that varied in both the configuration of their coupling circuits and their geometric dimensions. To accomplish this, transponder models were created using the EMCoS Studio electromagnetic simulation environment. Each model was subjected to simulations that yielded the mutual inductance and the voltage induced at the chip terminals. This study examines how the impedance of the embroidered antenna, the impedance of the chip’s coupling circuit, and the magnetic flux density affect the resulting chip voltage. In several of the investigated configurations, the peak chip voltage appeared outside the frequency range normally associated with RFID systems. The frequency at which this maximum occurred was dependent on the mutual inductance value. Understanding how individual parameters influence mutual inductance makes it possible to shift the voltage peak into a target operating band. Numerical simulation results, combined with the transponder’s mathematical model, enabled the calculation of the mutual inductance and the terminal voltage—quantities that directly determine the achievable read range. This study focuses on factors such as the resonant frequencies of the antenna and coupling circuit, their impedances, and the characteristics of the magnetic field. The findings show that tuning these parameters can affect not only the location of the voltage maximum, but also its amplitude. This effect introduces additional complexity in designing and selecting suitable transponder configurations. Full article

This work introduces a wideband four-element multiple-input multiple-output (MIMO) antenna system with four rectangular patches arranged in a sequentially rotated configuration. Wideband frequency operation is realized by exploiting the TM₁₀, TM₀₁ and TM_11δ modes through the utilization of a slot and metallized vias in the patch design. Another group of metallized vias are used to control coupling between the antenna elements, achieving an isolation level of over 17 dB. A prototype is fabricated and measured, demonstrating −6 dB impedance bandwidth ranging from 4.23 GHz to 5.96 GHz, enabling coverage of the N79 (4.4–5 GHz), V2X (5.905–5.925 GHz) and Wi-Fi 5/6 (5.150–5.850 GHz) frequency bands. The MIMO antenna features an efficiency of over 45% and a low envelope correlation coefficient (ECC) lower than 0.25. Owing to its broad bandwidth, compact geometry, and good isolation, the proposed MIMO antenna provides an efficient and practical solution for 5G MIMO applications integrated within mobile terminal back covers. Full article

Nymphaea candida Presl is a rare and endangered waterlily species, and cultivating robust seedlings suitable for artificial propagation has become a critical issue for the conservation of this species. In this study, Aspergillus sp., an endophytic fungus isolated from the roots of N. candida, showed the capability of solubilizing phosphate and potassium and producing siderophores. The application of Aspergillus sp. significantly increased leaf length, leaf width, leaf number, and root length of N. candida seedlings by 97.83%, 131.37%, 94.12%, and 171.25%, respectively. Meanwhile, Aspergillus sp. application significantly enhanced soil organic matter content, alkali-hydrolyzable nitrogen content, sucrase activity, and peroxidase activity by 6.57%, 31.62%, 23.26%, and 7.53%, respectively. Moreover, Aspergillus sp. enriched beneficial microorganisms including Cyanobium, Aquicella, and Cryptomycota to form a more stable rhizosphere soil microenvironment. Additionally, Aspergillus sp. upregulated genes involved in photosynthesis and photosynthesis–antenna protein pathways in N. candida leaves, with the expression levels of psbA, petG, and psbH significantly increasing by 2.17, 4.48, and 0.28-fold, respectively. Therefore, the endophytic fungus Aspergillus sp. might be a reliable tool for the propagation of N. candida seedlings, which would be helpful for the conservation of this rare and endangered aquatic plant species. Full article

In this paper, a multi-feed transmitarray with high-gain, wide-angle beam-scanning, and low-cost features is presented. A novel hybrid phase distribution (HPD) method is proposed to improve the beam-scanning range by combining the single-focal and bifocal principles according to the actual feed illumination area. By using the proposed method, the phase distribution of the transmitarray for different scanning angles can be obtained more accurately, thereby reducing the phase error between the actual and ideal phase distributions. To construct the transmitarray, a three-layer polarization conversion unit cell, consisting of two orthogonal polarizers in the outermost layers and a polarization rotating patch in the middle layer, is designed to provide high-efficiency transmission and full 360° phase coverage. Based on the HPD method, a single-polarized transmitarray antenna with a focal diameter ratio of 0.28 is designed and simulated. The simulated results show that the enhancement of the beam-scanning range is successfully realized. This design can perform a discrete ±60° beam-scanning range with a peak gain of 24 dBi. The gain losses of 0.7 dB at ±30° and 4.7 dB at ±60° are achieved. The cross-polarization levels are about 44 dB and 35 dB at 0° and −60° scanning angles, indicating low cross-polarization of the proposed solution. A five-beam prototype is fabricated and measured for experimental verification purposes. The measured results demonstrate good consistency with the simulations in the main lobe, with slight deviations due to practical fabrication and measurement constraints. The proposed design has advantages such as low-cost, wide beam-scanning angle, high-gain, low-profile and easy fabrication. Full article

Continuous introduction of advanced optimization algorithms promotes the development of electromagnetic (EM) technology in radar and communication systems. Wideband antenna design within a given space and wideband array pattern synthesis, especially in the scenario of strong mutual coupling, are two typical challenging electromagnetic problems. In this paper, a nature-inspired algorithm, i.e., the water cycle algorithm (WCA), is introduced to resolve the above two EM problems. Two typical wideband antennas, i.e., the dual-band E-shaped microstrip antenna and the typical magnetoelectric (ME) dipole antenna, are designed on the basis of the established WCA-based antenna design scheme. Compared with the well-known algorithms that have been introduced in antenna design, including the differential evolution (DE) algorithm and the gray wolf optimizer (GWO), better results can be achieved with WCA. In the sequel, a WCA-based low peak sidelobe level (PSLL) pattern synthesis is implemented based on a uniformly spaced 27-element folded fractal ME dipole array antenna with mutual coupling as high as −10 dB, the results of which further validate the superiority of WCA in array pattern synthesis and demonstrate the value of this application innovation. Full article

Background/Objectives: Accurate intraoperative tumour localisation remains challenging in minimally invasive colorectal surgery, where conventional tattooing methods suffer from marker migration, tissue diffusion, and potential allergic reactions. Radio frequency identification (RFID) technology offers a promising alternative through implantable passive transponders detectable via electromagnetic coupling, eliminating ionising radiation exposure. Methods: This preclinical feasibility study evaluated three RFID frequency bands for surgical tumour marking: 134 kHz (low frequency, LF), 13.56 MHz (high frequency, HF), and 868 MHz (ultra-high frequency, UHF). Finite element electromagnetic simulations characterised antenna field distributions, while experimental validation employed glass-encapsulated transponders in air and tissue-simulating saline (0.9% NaCl, σ ≈ 1.5 S/m). Detection ranges were measured across 28 angular configurations with expanded measurement uncertainty (k = 2) ranging from ±0.9 to ±3.2 mm. Results: Maximum detection distances in air were 25.0 ± 0.9 mm (LF), 23.0 ± 1.1 mm (HF), and 68.0 ± 2.3 mm (UHF). In saline, ranges decreased to 22.5 ± 1.0 mm, 20.7 ± 1.2 mm, and 18.0 ± 1.4 mm, respectively, demonstrating tissue attenuation of 10% at LF/HF vs. 74% at UHF. Angular characterisation revealed 64–70% range reduction at orthogonal orientation for LF/HF systems. Computational–experimental correlation yielded r² = 0.975 across 154 paired observations. Conclusions: The 13.56 MHz HF band emerges as the optimal candidate for clinical translation, offering adequate tissue penetration (20.7 mm), superior antenna miniaturisation potential (5 mm diameter), established biocompatibility pathways, and mature near-field communication ecosystem support. Future development should address angular sensitivity through multi-axis antenna configurations and validation in anatomically realistic tissue phantoms. This study establishes the electromagnetic evidence base for clinical system development; translation to clinical practice requires sequential preclinical and clinical evaluation. Full article

A broadband low-RCS circularly polarized (CP) antenna based on a bi-functional, single-layer polarization conversion metasurface (PCM) is proposed in this manuscript. The designed bi-functional PCM unit cell achieves a polarization conversion ratio (PCR) exceeding 90% across an ultra-wideband from 15.8 GHz to 31.2 GHz. According to the principle of phase cancellation, they are configured as a checkerboard array to reduce the monostatic RCS. A co-design strategy was employed for the design of the feeding structure. Analysis reveals that the slot has a significant impact on the subarray PCR, leading to multiple zeros that affect the RCS reduction. Notably, further analysis indicates that an appropriate feed structure can compensate for the zeros caused by the slot, achieving a balance between radiation performance and scattering performance. The array exhibits an RCS reduction exceeding 6 dB over a wide frequency band from 15.9 to 31.3 GHz and realizes a circularly polarized far-field pattern with an axial ratio (AR) below 0.5 from 16.3 to 17 GHz and a maximum gain of 10.38 dBi. Measured results of the antenna prototype match the simulations well. The proposed integrated design offers a viable solution for stealth platforms. Full article

Radio network planning is critical for 5G deployments, particularly for temporary installations in rural areas where terrain and vegetation significantly impact signal propagation. While empirical path loss (PL) models characterize propagation environments through scenario-specific parameters—leading to inherently noisy predictions at individual sites—machine learning (ML) approaches can predict site-specific path loss from multiple features simultaneously. This study conducts a systematic literature review of rural path loss prediction methods and introduces a novel dataset collected via a 5G nomadic measurement platform in a vineyard environment, capturing real-world propagation characteristics. We present a comprehensive comparison of machine learning and interpretable machine learning techniques, demonstrating that vegetation dynamics (quantified through the Normalized Difference Vegetation Index, NDVI) is an important driver of path loss variability when combining data across seasonal campaigns—though not within individual campaigns, where distance dominates. Cross-campaign NDVI transfer, however, is sensitive to satellite resolution, which appears to conflate vine canopy with seasonally managed inter-row ground cover. In cross-campaign transfer, XGBoost proves substantially less susceptible to NDVI-induced degradation than Explainable Boosting Machines (EBM), and a hybrid Log-Normal Shadowing (LNS) and XGBoost model confirms that NDVI captures seasonal variability more effectively than empirical path loss parameters alone. Still, the data captured the expected seasonal trend between April and June 2025, from which our interpretable models derived useful propagation insights. Tree-based models like Random Forest and XGBoost achieved the highest prediction accuracy ($R^2$ up to 0.924 on individual campaigns, 0.891 on combined data, and up to 0.945 (individual) and 0.907 (combined) with antenna pattern-corrected path loss), while explainable boosting machines achieved near-parity ($R^2$ up to 0.919; 0.876 on combined data) with the advantage of interpretability. Among individual campaigns, June—with densest canopy cover—yielded the highest $R^2$ values. These findings provide actionable insights for optimizing temporary 5G networks in precision agriculture and other rural applications. Full article

This work presents a spiral-loop sequential-phase (SLSP)-fed radial-sector patch circularly polarized (CP) antenna for S-band CubeSat platforms. The architecture stacks three RO4003C substrates in an aluminum enclosure: a lower layer with tapered-blade parasitic elements, a middle layer with the SLSP feed and four radial-sector patches, and an upper tilted hexagonal metasurface superstrate separated by an air-gap. Characteristic mode analysis is used to realize an orthogonal modal pair. A prototype integrated on a CubeSat structure was measured in an anechoic chamber and validated under vibration and thermal-vacuum testing per ECSS/NASA practices. The antenna achieves a measured return loss bandwidth of 2–2.34 GHz, an axial ratio bandwidth of 2.04–2.25 GHz, and a maximum gain of 7.24 dBic at 2.18 GHz. The metasurface and parasitic elements enhance bandwidth while maintaining boresight CP. The novelty lies in the integration of SLSP-fed radial-sector patches with a tilted hexagonal metasurface superstrate and tapered-blade parasitic elements within a compact stacked configuration, making the proposed antenna well suited for CubeSat S-band applications. Full article

We propose a terahertz (THz) antenna-coupled wire-channel field-effect transistor—modified EdgeFET (m-EdgeFET), formed by combining single-gate FinFET and dual-side-gate EdgeFET concepts, which is used for THz detection. The proposed hybrid design was implemented on AlGaN/GaN high-electron-mobility transistor (HEMT) structures, demonstrating distinct response characteristics under 150 GHz and 300 GHz radiation at room temperature. The responsivity dependence on the channel length was determined, revealing that the peak responsivity reached up to 6.5 V/W at a gate voltage of −3 V, i.e., at a gate bias that is an order lower in magnitude than that required for EdgeFET to reach the maximum response. Meanwhile, the gate leakage current decreased by an order of magnitude (to about 1 nA) compared to a FinFET with similar geometry. The proposed geometry was shown to operate in two regimes: source-drain coupling (SD) and gate coupling (GG) of THz radiation with the transistor wire channel. The results confirm that the m-EdgeFET design is suitable for electrically controlled and fast THz detection. Full article

Millimeter-wave (mmWave) unmanned aerial vehicle (UAV) networks are a promising solution for rapidly deployable backhaul systems in urban disaster scenarios, where terrestrial infrastructure may become unavailable. Although mmWave bands provide wide bandwidth for high-capacity transmission, their strong susceptibility to blockage and beam misalignment poses significant challenges in dense urban environments, particularly under UAV positional fluctuations caused by wind. This study investigates the optimization of multi-hop mmWave UAV backhaul networks with the objective of maximizing the bottleneck link capacity. A three-dimensional urban model of the Shinjuku area in Tokyo is employed, and radio propagation is evaluated using a ray-tracing-based approach considering line-of-sight (LoS) constraints and inter-link interference. Particle Swarm Optimization (PSO) is used to determine optimal UAV placements for two- to four-hop configurations. Numerical results demonstrate that multi-hop relaying combined with directional 2 × 2 patch antennas significantly improves the minimum link capacity, enabling the target backhaul capacity of approximately 9 Gbps per link under static conditions. However, capacity degradation is observed when UAV jitter is introduced due to LoS blockage and beam misalignment. To address this issue, a jitter-aware optimization method incorporating an expanded Fresnel-zone constraint is proposed. The proposed method substantially mitigates capacity degradation under realistic positional fluctuations, resulting in more robust backhaul performance. These findings demonstrate that jitter-aware placement design is essential for realizing reliable high-capacity mmWave UAV backhaul networks in dense urban disaster environments. Full article

The demand for hardware-efficient interference suppression algorithms is growing with the increasing density in wireless communication networks. In this paper, a robust position-only null steering method for linear antenna arrays is proposed based on Honey Formation Optimization with Single Component (HFOSC), a metaheuristic algorithm founded on the ripening process of honey in beehives. By optimizing only the element locations, the proposed method avoids the use of phase shifters and attenuators, thus reducing implementation complexity while maintaining flexibility in pattern control. A 30-element linear array with Chebyshev excitation is used to test the technique under representative interference scenarios such as single-null, multiple-null, and wide-sector nulling cases, as well as constrained practical designs. The simulation results demonstrate that the proposed approach can realize strong interference suppression across different cases while maintaining the main-beam shape and acceptable sidelobe performance. In idealized discrete-interference cases, nulls below −90 dB are achieved, while in a practical constrained design with a minimum inter-element spacing of 0.5λ and a position resolution of 0.1λ, a null depth of −72.89 dB is still achieved, confirming the practical applicability of the method. Moreover, comparative results with GA, PSO, and DE over 100 independent runs illustrate that HFOSC achieves the lowest optimization cost and the smallest standard deviation, along with a favorable overall trade-off between beam preservation and null suppression, with statistically significant superiority in optimization performance. The proposed method does not require phase shifters and attenuators, providing a simple, hardware-friendly, and robust solution for adaptive interference cancellation in wireless communication systems. Full article

This article concerns the issue of contactless estimation of the complex electrical permittivity of masonry materials by means of a microwave technique in the frequency domain. The main aim of the study was to develop a method enabling the determination of the real part of relative permittivity and the electrical conductivity of ceramic building materials using microwave reflection measurements, as well as to assess the applicability of the proposed approach for moisture diagnostics in porous media. The research was performed using a reflection-mode measuring setup comprising a vector network analyser and a broadband horn antenna, while measurements were carried out in the frequency range from 1 to 6 GHz on samples of solid ceramic brick with six gravimetric moisture levels. A one-dimensional model of electromagnetic wave propagation in the material was developed, considering complex permittivity, impedance transformation, and a calibration procedure compensating for the influence of the antenna and free-space propagation. Based on the fitting of the magnitude and phase characteristics of the reflection coefficient, the electrical parameters of the tested samples were estimated. The results obtained showed an increase in both permittivity and conductivity with increasing moisture content and revealed very good agreement with the reference values determined using the time-domain method. It can be concluded that the frequency-domain microwave approach may be effectively applied for contactless and non-destructive diagnostics and estimation of the dielectric properties and moisture content in ceramic materials. Full article

River levees in Taiwan are exposed to typhoons, earthquakes, and long-term erosion and scour, which often cause subsurface voids of varying severity within the levee body. This study conducted a quantitative physical analysis of 0.15 m-thick concrete specimens containing voids of different dimensions (widths of 0.10–0.40 m and sizes of 0.06–0.15 m). The specimens were scanned using ground-penetrating radar (GPR) antennas with center frequencies ranging from 750 MHz to 2.3 GHz. Variations in electromagnetic-wave reflection amplitude within the material were used to determine void size along the X-axis, whereas the depths corresponding to the reflection points were quantified along the Y-axis. The void area was then estimated based on the X-Y coverage. The results showed that absolute amplitude differentiation provided distinct quantitative features that reflected the presence of voids of various sizes. The proposed method was further validated using an actual river-levee scour case. The findings of this study offer a practical reference for the inspection, maintenance, and repair of river levees. Full article