Very High Frequency (VHF) communication systems historically rely on line-of-sight (LOS) propagation for effective signal transmission between the receive and transmit antenna(s) for link viability. Traditionally, LOS between transmit and receive locations has been improved by increasing antenna height, moving transmission and receiving points to higher locations, and installing repeaters to boost and repeat the signal. However, these options are not always feasible due to the prohibitive cost of tower construction, cost and/or availability of moving to a new location, and inaccessible geography. This paper explores the potential of atmospheric superrefraction and ducting phenomena to extend VHF communication and propagation beyond typical LOS distance limitations, particularly in maritime environments. We present a model and simulation of a VHF communication link between two sites, where superrefraction/ducting atmospheric phenomena are present, with the ocean as the primary geographic barrier to LOS communication, to determine the optimal VHF antenna configuration. The study aims to determine optimal VHF antenna configurations based on the two sites’ tower height constraints, transmit power, and link distance. A comparative analysis of the optimized parameters and a previous link setup is conducted to evaluate potential improvements and the consistency of received signal strength and overall link reliability, accounting for atmospheric superrefraction and ducting. This research contributes to the growing body of knowledge on adaptive communication strategies in challenging geographical settings and provides practical simulations to enhance long-distance VHF communications in coastal and maritime domains by leveraging atmospheric phenomena.
This work presents the design, analysis, of a floral ultra‐wideband (UWB) monopole patch antenna for wireless communication applications. The antenna is fabricated on an FR4 substrate with a dielectric constant of 4.4 and a thickness of 1.6 mm. Its wedge‐shaped ground plane structure features three floral radiator elements, with a V‐slot in the center region of the middle radiator having an 8‐mm radius and the two side radiators each having a 5‐mm radius. Comprehensive simulation studies reveal that the designed antenna exhibits an operational bandwidth of 2.37–13.96 GHz, resulting in a percentage bandwidth of 142% for S 11 < −10 dB. Additionally, the antenna achieves a peak gain of 5.23 dB, indicating excellent impedance matching and power transfer efficiency. The introduction of this innovative floral monopole UWB antenna represents a novel contribution in UWB antenna design, making it a promising candidate for a wide range of high‐speed wireless communication applications that require exceptional bandwidth, gain, and impedance matching characteristics.
This work introduces a dual-polarized metamaterial absorber with a wide transmission window located between two absorption bands. The structure is designed to achieve strong out-of-band absorption while maintaining broad in-band transmission. The top resonator includes four modified split-ring resonators with lumped resistors to achieve broad out-of-band absorption on both sides of the transmission window. The lower layer consists of a rectangular slot that operates as a parallel LC resonator, forming a band-pass frequency-selective surface (FSS) that provides a broad in-band transmission window while simultaneously serving as a defected ground plane to enhance out-of-band absorption. With an overall thickness of 0.075 λL, the proposed design achieves a 120% fractional bandwidth and maintains absorptivity greater than 80% over the 2.5–10.0 GHz frequency range, while exhibiting a low insertion loss of 1.0 dB at the center frequency of 5.98 GHz. The proposed rasorber demonstrates excellent overall performance by combining a wide out-of-band absorption, a broad in-band transmission, a high fractional bandwidth, low electrical thickness, angular stability, dual-polarization characteristics, and a simple, cost-effective fabrication approach. Equivalent circuit modeling, parametric analysis, polarization analysis, and surface current distribution studies are performed to investigate the operating mechanism and validate the performance of the proposed rasorber. The measured results of the fabricated prototype are in close agreement with the simulated results. The proposed rasorber exhibits significant potential for deployment in radomes, high-data-rate multiband communication systems, and other RCS-sensitive platforms.
This paper presents a compact dual circularly polarized (CP) stacked-patch antenna and a corresponding sequentially rotated 4×4 array for S-band satellite communication applications. The driven patch is excited through two orthogonal H-shaped slots that couple energy from the feedline, while a parasitic patch placed above the driven patch and separated by an airfoam spacer enhances the impedance bandwidth and radiation performance. A planar branch-line hybrid coupler provides quadrature-phase excitation to the aperture slots, enabling LHCP or RHCP operation through selective port excitation. The fabricated antenna exhibits measured −10 dB impedance bandwidths of 26.95% and 23.26% for Port 1 and Port 2, respectively, with a 3 dB axial-ratio bandwidth spanning 1.90–2.40 GHz and a peak realized gain of 7.0 dBic, covering both the S-band downlink (1.98–2.01 GHz) and uplink (2.17–2.20 GHz) frequency bands. The corresponding dual-CP 4×4 array maintains active reflection coefficients below −10 dB at broadside and during beam scanning up to 30°, while preserving stable circular polarization, low sidelobe levels, and high realized gain. These results demonstrate a compact, array-compatible dual-CP antenna solution offering wide bandwidth, high polarization purity, and reliable beam-scanning performance for modern S-band satellite communication systems.
In this paper, a phase-only beampattern optimization algorithm is proposed for a frequency diverse array (FDA) radar to achieve a low probability of intercept (LPI). To avoid the high hardware complexity of joint amplitude–phase optimization and performance loss caused by simple phase truncation, we formulate a fractional quadratic optimization framework constrained by per-antenna constant modulus, which minimizes the radiated power at hostile interception positions while maximizing the echo energy at the local receiver. To solve the resulting nonconvex fractional programming objective problem under phase-only constraint, we construct a manifold optimization framework on the complex circle manifold. By defining the tangent space, normal space, Riemannian gradient, orthogonal projection, and retraction mapping, an alternating Riemannian manifold algorithm is further deduced, which enables low-complexity iterative phase updating without amplitude adjustment. Simulation results demonstrate that the developed manifold-based phase-only optimization algorithm effectively suppresses beam energy in the interception region and reduces the detection probability of hostile electronic support measure (ESM) receivers.
Electromagnetic (EM) simulation tools play a vital role in antenna and microwave engineering by enabling accurate modeling, optimization, and validation before fabrication. Among the most widely used commercial EM simulation platforms are CST Studio Suite and Ansys HFSS, both of which are recognized for their advanced solver architectures and broad application capabilities. This paper presents a comparative analysis of CST and HFSS in terms of numerical accuracy, computational efficiency, and practical usability. A benchmark case study based on a 3.5-GHz rectangular microstrip patch antenna is investigated under identical simulation conditions in both platforms to ensure a fair comparison framework. The comparative results indicate that HFSS achieves improved numerical accuracy, demonstrating approximately 38.46% and 28.00% lower resonance and gain errors, respectively, whereas CST provides superior computational efficiency with approximately 38.89% lower simulation time and 24.21% lower memory consumption. In addition, the simulated S11 responses obtained from both solvers show good agreement with only a slight resonance frequency shift. To further strengthen the comparative framework, the study also discusses mesh convergence and repeatability analysis, UWB and SAR-oriented applications, and high-Q resonator structures. Rather than identifying a universally superior EM solver, this work highlights the practical trade-offs between numerical accuracy and computational efficiency to provide useful guidance for selecting suitable EM simulation platforms according to specific antenna and microwave engineering requirements. The presented analysis offers practical insights for students, academic researchers, and industry practitioners working in modern EM design applications.
Finite element time domain (FETD) method has been widely applied in ground penetrating radar (GPR) simulation based on the second-order electromagnetic equation due to its advantages of high flexibility of mesh discretization, few solving wavefield component, and high precision. The complex frequency shifted perfectly matched layer (CFS-PML) boundary condition markedly improves wave absorption, particularly for evanescent and low-frequency waves. However, the CFS-PML implementation, which is typically employed in finite difference time domain (FDTD) methods that solve first-order electromagnetic equations, cannot be directly adapted for FETD simulations. This paper proposes a novel framework that constructs auxiliary differential equations (ADE) to avoid the computationally intensive field splitting and convolution in electromagnetic simulations. This framework enables a rigorous derivation of the second-order wave equation for GPR and its FETD discretization within the ADE-CFS-PML boundary. To solve the derived variational form of the ADE-CFS-PML equations, the FETD is employing an unstructured triangular mesh for spatial discretization. In addition, the time discretization of CFS-PML implementation is modified by using the Newmark difference scheme to ensure the stable and accurate time-marching process. The validity of the proposed ADE-CFS-PML implementation is first certified by benchmarking its performance against conventional PML and uniaxial-PML (UPML) boundary condition, in a homogeneous elongated model, with the reference solution confirming the accuracy. Further, comparison of FETD simulation results for a complex model with different mesh discretization types confirms the superiority and practicality of the triangular mesh, which achieves higher simulation accuracy with comparable mesh sizes to square meshes.
This paper presents the design, implementation and optimization of a broadband monopole whip antenna integrated on an electrically small (at the lower frequency, i.e., 30 MHz) handset ground plane, targeting long-distance handheld radio communication. The proposed antenna covers a broad frequency range from 30 to 520 MHz, with functional operation extending up to 600 MHz. In order to counter the effects of the compact ground plane and to ensure optimum impedance matching, the design incorporated three RL trap circuits placed strategically on the radiator. A parametric analysis was carried out to analyse the effect of each element in the trap circuits on the performance of the antenna. In addition to the parametric analysis, the Genetic Algorithm was used to optimize the parameters to ensure the least voltage standing wave ratio in the desired frequencies. The design was tested and analysed, and the results showed a VSWR as specified in the requirement with similar radiation patterns in all directions, even with the compact ground plane of the handheld radio device. In comparison to other designs in the current state of the art, the proposed design provides substantial size reduction without compromising the efficiency of the broadband design.
Vision‐based unmanned aerial vehicle (UAV) tracking technology faces severe challenges in dynamic and complex air‐to‐air scenarios, manifested specifically as occlusion interference, abrupt changes in light intensity, and feature motion blur caused by high‐speed target maneuvering. Traditional tracking methods are limited by static template strategies and fail to effectively model the temporal correlation of motion cues, which easily leads to trajectory drift and even target loss. To address the above bottlenecks, this paper proposes a real‐time UAV target tracking algorithm optimized based on the dual memory template‐motion correction (DMT‐MC) strategy. The algorithm adopts a dual memory template strategy to balance the long‐term stability and short‐term dynamic adaptability of target features. Meanwhile, it introduces adaptive Kalman filtering guided by matching scores for motion correction, fusing spatiotemporal cues to improve the tracking stability of the target in scenarios such as fast movement and occlusion, and avoiding trajectory jumps caused by single‐frame feature noise. To verify the algorithm performance, this paper constructs A2A‐UAV‐Tracking, the first benchmark dataset for air‐to‐air UAV tracking in highly adversarial environments. Comprehensive experimental results demonstrate that the target tracking algorithm optimized by the DMT‐MC strategy significantly outperforms other mainstream lightweight trackers used for comparison, fully proving its effectiveness and robustness in complex dynamic scenarios. The constructed dataset has been made available for download at https://github.com/KingArthurYu/A2A-UAV-Tracking .
This study presents a miniaturized filter based on half-mode substrate-integrated waveguide (HMSIW) resonant cavities, a bent-line resonator, and a composite right/left-handed (CRLH) resonator. The filter employs two HMSIW resonant cavities, which effectively reduce its size and prevent the propagation of higher-order modes TE120 and TE220 within the resonant cavities. The bent-line resonator and CRLH resonator are etched between the two HMSIW cavities, forming four transmission poles in the passband. By utilizing the opposite phase transmission characteristics of the bent-line resonator and the CRLH resonator, finite transmission zeros (FTZs) can be generated on both sides of the filter’s passband, resulting in a high-frequency selective quasielliptic filter response. The filter was fabricated and measured, and the simulation and measurement results are in good agreement. Compared with other SIW filters, the proposed filter features a compact size, improved selectivity, and the ability to suppress higher-order modes, making it valuable for certain applications.
This study proposes measurement results of shadowing loss in a four-story office building. Shadowing loss includes building entry, exit, indoor, and diffraction losses. Data were collected by adopting a local averaging stage loaded with an elevated work platform for up to two stories. The main body of the building was composed of concrete and metal, and glass windows were placed on the building. A straight corridor was placed between two sides of an office. The investigated frequencies were 3 and 7 GHz. The 50% shadowing losses for the frequencies were 36.2 and 37.4 dB, respectively. These values were similar to or lower than those of the corridor. This is thought to be a reflection of other outer buildings. An additional experiment with a directive horn antenna confirmed that the antenna toward the edge of the building received more power than that toward the wall (or window) of the building. This can be utilized for small-cell planning in 5G or 6G communication services.
Combining wearable sensing technologies with intelligent classification algorithms opens new possibilities for tracking human activities and postures, with applications in healthcare, rehabilitation, and human-computer interaction. In the present scenario of wearable-based human activity monitoring, body-worn equipment can facilitate real-time observation by integrating sensing systems onto the human body. The extensive focus of this research is to develop and implement an on-body ultra-wideband antenna based on FR4 and jeans substrate tailored for activity recognition applications and to demonstrate its feasibility to be used for a human body posture recognition and classification system. This research work reports the development of compact body-worn UWB antennas integrated with intelligent machine learning algorithms to achieve reliable and high-accuracy human posture and activity recognition. The antennas are optimized for stable on-body performance, ensuring reliable signal acquisition during dynamic movements. Key scattering parameters (S11 and S21) are used as features for classification. The compact wearable transmitting and receiving antennas are designed and implemented to capture datasets of on-body antenna characteristics, including reflection and transmission parameters, voltage standing wave ratio (VSWR), reflected power, and mismatch loss associated with various human body postures, performed by different subjects. The comparative performance exploration of various machine learning classifiers, such as random forests (RFs), decision trees (DTs), support vector machines (SVMs), Gaussian Na & iuml;ve Bayes (GNB), K-nearest neighbors (KNNs), extreme gradient boosting (XGB), and neural networks for processing, analyzing, and classification purposes, is performed based on datasets observed for different body postures. Enhanced classification performance is achieved with the GNB and DT classification algorithms. Experimental results showcase high classification accuracy and clear distinguishability across posture states. These findings establish the potential of UWB wearable antennas combined with AI-driven models for intelligent healthcare monitoring and activity-aware applications.
This paper presents a high-rejection filtering antenna based on nonuniform metasurface (MTS). The antenna consists of three metal layers and two substrate layers. The upper metal layer is nonperiodic MTS patches with removed units. The MTS is fed by a T-shaped microstrip line at the bottom through by a pair of disconnected bow-tie slots etched on the middle ground plane. The proposed MTS is analyzed using characteristic mode analysis (CMA). The maximum current distribution of the characteristic modes which resonate at about 6.58 GHz is located at the edge patches rather than in the center. Therefore, the bow-tie slots etched at the center of the ground plane cannot effectively excite these modes, which leads to a radiation null at the upper band. A shorting probe is embedded in the bottom substrate to create a radiation null at the lower band. A preliminary filtering response is formed. And then, by loading two groups of split-ring resonators (SRRs) on both sides of the feedline, radiation nulls are generated at 3.68 GHz, 7.15 GHz, and 7.7 GHz, effectively enhancing the out-of-band rejection level, especially at the upper band. The simulated and experiment results show that the proposed antenna achieves impedance bandwidth (|S11| <= -10 dB) over the frequency range of 5.7-6.1 GHz, with a peak gain of 8.7 dBi. Particularly, the out-of-band rejection level exceeds 22.4 dB and 24 dB, at the upper and lower band, respectively. Compared with some reported filtering antennas, the proposed antenna achieves a higher rejection. Moreover, the proposed antenna is simple in structure and easy to manufacture.
This letter proposes the design and measurement of a periodic metasurface that achieves anomalous reflection with reduced RCS in a given parasitic direction. A previous study proposed a semianalytical model to predict the RCS behaviour of such a metasurface. However, this first study did not include any experimental exploration to verify the theoretical results. To complete this study, this work presents an experimental validation of the proposed design, with a focus on manufacturing and measurement issues. The synthesis, design specifications, fabrication method and experimental setup are presented and discussed. Measurement results are also examined in detail, highlighting some limitations in metasurface RCS measurements. The proposed metasurface effectively achieves the predicted RCS level reduction in the considered parasitic direction. The agreement between simulation and experimental results demonstrates the accuracy of the modelling and the efficiency of the optimisation procedure.
Vision-based unmanned aerial vehicle (UAV) tracking technology faces severe challenges in dynamic and complex air-to-air scenarios, manifested specifically as occlusion interference, abrupt changes in light intensity, and feature motion blur caused by high-speed target maneuvering. Traditional tracking methods are limited by static template strategies and fail to effectively model the temporal correlation of motion cues, which easily leads to trajectory drift and even target loss. To address the above bottlenecks, this paper proposes a real-time UAV target tracking algorithm optimized based on the dual memory template-motion correction (DMT-MC) strategy. The algorithm adopts a dual memory template strategy to balance the long-term stability and short-term dynamic adaptability of target features. Meanwhile, it introduces adaptive Kalman filtering guided by matching scores for motion correction, fusing spatiotemporal cues to improve the tracking stability of the target in scenarios such as fast movement and occlusion, and avoiding trajectory jumps caused by single-frame feature noise. To verify the algorithm performance, this paper constructs A2A-UAV-Tracking, the first benchmark dataset for air-to-air UAV tracking in highly adversarial environments. Comprehensive experimental results demonstrate that the target tracking algorithm optimized by the DMT-MC strategy significantly outperforms other mainstream lightweight trackers used for comparison, fully proving its effectiveness and robustness in complex dynamic scenarios. The constructed dataset has been made available for download at .
Microwave breast imaging has become a significant area of research due to the high incidence of breast cancer in women and the limitations of conventional detection methods. In recent years, this field has gained momentum as it offers improved detection rates and several advantages like it is nonionizing and safe, cost-effective, portable and flexible, has real-time imaging potential, etc. A crucial element in microwave breast imaging systems is the use of well-designed antennas, often organized in arrays. These antennas must meet important criteria such as wide bandwidth, compact size, manageable design complexity, and cost-effectiveness. While numerous studies have introduced antennas that meet these criteria, there is still no comprehensive classification and evaluation of these designs specifically for microwave breast imaging applications. This paper addresses the gap by presenting a comprehensive study of conventional methods of breast imaging and several antenna and antenna array configurations that have been proposed for microwave breast imaging. The investigation examines the suggested antenna elements for these systems, categorized by antenna type and the enhancements related to operational bandwidth, antenna size, radiation characteristics, and the techniques used to achieve these improvements. At the conclusion of the study, a qualitative assessment of the antenna designs is provided, facilitating a comparison between them. This evaluation determines whether a particular design is suitable for the implementation of microwave breast imaging, based on its performance. In addition, the research provides an evaluation of the studied antenna configurations, highlighting the merits and limitations of each.
Wearable antenna arrays play a critical role in enabling reliable wireless connectivity for Internet of Things (IoT) applications in smart-city environments. However, achieving stable electromagnetic performance, low specific absorption rate (SAR), and mechanical robustness using low-cost textile materials remains a challenge. In this work, a single-layer 1 & times; 2 rectangular microstrip patch antenna array operating at 2.45 GHz is designed, fabricated, and experimentally evaluated using three textile substrates (felt, denim, and polyester) and two conductive materials (copper tape and conductive fabric). The antennas are characterized in terms of impedance matching, gain, radiation pattern, bending-induced detuning, and SAR compliance. The results demonstrate that material selection has a dominant influence on antenna performance, with the denim-conductive fabric configuration providing the most balanced trade-off between gain (2.04 dBi), impedance stability, and mechanical flexibility. SAR analysis shows values of 0.005 W/kg (1 g) and 0.015 W/kg (10 g) at 2.45 GHz, which are significantly below international safety limits and achieved without the use of artificial magnetic conductors or electromagnetic bandgap structures. Bending analysis reveals a predictable frequency-shift behavior, enabling design-level compensation for wearable operation. The proposed antenna array offers a low-profile, cost-effective, and safe solution for smart-city-wearable IoT applications.
Half impulse radiating antenna (HIRA) is commonly used in high-power ultrawideband (UWB) systems. These systems come under the class of Intentional Electromagnetic Interference (IEMI) systems, which are intended to generate intense electric fields (similar to 10 kV/m and above) in a far field range. Conventionally, coplanar transverse electromagnetic (TEM) feed is used as feed for HIRA. In this paper, a novel feed mechanism utilizing exponentially tapered half TEM horn for HIRA antenna is suggested, resulting in higher radiated peak electric field values. Time-domain simulations of HIRA with new feed antenna confirm that higher electric field values observed are due to the gain improvement throughout the frequency range of interest. A detailed analysis of field illumination pattern at reflector shows that gain improvement observed is due to uniform distribution of electric field at the aperture of reflector. The presented new feed mechanism results in peak electric field enhancement by similar to 60%. For a high-power UWB radiator, this results in significant improvement of Figure of Merit (FOM) by a factor of 1.6. The proposed feed mechanism is very useful in cases where the input pulse in UWB is having significant low frequency content. Initial experimental results for the new antenna and standard feed HIRA antenna with the UWB pulse generator system are also compared.
A compact four-element mmWave MIMO antenna designed using characteristics mode analysis (CMA) with wideband performance and high isolation is presented. The antenna is realized on a 0.254-mm Rogers RO5880 substrate with meandered conductive strips arranged in a window-shaped configuration and a partially truncated ground-plane notch. CMA is employed to observe the modal behavior of the structure, revealing that Mode 1 is the dominant radiating mode, while Modes 2 and 3 contribute to resonance formation and bandwidth enhancement. The single antenna element occupies a compact size of 12 & times; 14 mm2 (0.1305 lambda 0 & times; 0.1119 lambda 0, where lambda 0 is the wavelength at 28 GHz), whereas the four-port MIMO configuration measures 24 & times; 32 mm2 (0.224 lambda 0 & times; 0.229 lambda 0). A decoupling structure is introduced to suppress mutual coupling, achieving interelement isolation better than 20 dB. The proposed MIMO antenna operates over a wide impedance bandwidth from 24.5 to 33.5 GHz and exhibits a peak realized gain of 6.2 dBi. Due to its symmetric layout, the design is inherently scalable to higher order MIMO systems. Experimental results obtained from a fabricated prototype show good agreement with simulations, validating key MIMO performance metrics, including ECC, MEG, CCL, and DG, confirming the suitability of the proposed antenna for mmWave RF applications.
Next-generation Wi-Fi 7 (IEEE 802.11be) and Wi-Fi 8 (IEEE 802.11bn) demand compact multielement antennas offering wide bandwidth, high isolation, and stable radiation within limited device space. Conventional MIMO designs often face strong coupling, narrow bandwidth, or low efficiency, restricting high-throughput multilink performance. This work presents a Hilbert curve fractal (HCF) four-port MIMO slot antenna that leverages fractal self-similarity to extend the surface current path and excite multiple resonant modes within a compact size. The HCF slot supports TE20 and TE40 modes-TE20 excites the lower 5-GHz band (5150-5945 MHz), while TE40 generates a higher-order resonance in the 6-GHz band (6150-7150 MHz). Merging both bands allows for broadband dual-band operation. A defective ground structure reduces surface waves and improves isolation, while a genetic algorithm optimizes geometric parameters for wideband impedance matching across all four ports. The improved design has a measured bandwidth of 2125 MHz (5.0-7.125 GHz), a peak gain up to 6.51 dBi, radiation efficiency greater than 82%, and isolation up to -32 dB. The low ECC (< 0.005) and 10-dB diversity gain make it suitable for durable, high-capacity Wi-Fi 7, Wi-Fi 8, and future sub-6-GHz communication systems.
