This investigation presents a wideband, flexible, and ultraminiaturized square ring multiple-input multiple-output (MIMO) antenna made for sub-6 GHz applications. The design incorporates a semicircular ground plane with a neutralization line and two orthogonally positioned feed ports, together with two square ring radiating elements connected by four short strips, to enhance isolation between the two ports. To enhance isolation and MIMO performance, a 50 Ω microstrip line positioned orthogonally feeds each ring. The antenna achieves a wideband resonant with a center frequency of 4.2 GHz, maintains the S11 under -10 dB, and achieves port isolation of up to 18 dB across the frequency span from 3.2 to 5.8 GHz and a fractional bandwidth of 61.9% with maximum peak gain of 3.21 dBi. Detailed evaluations of the radiation patterns, surface current distributions, and S-parameters of the antenna are provided. Built on a flexible PDMS substrate, the antenna's observed findings closely match estimates, proving its efficiency. This design method consequently provides a dependable solution and has significant potential for 5G sub-6 GHz MIMO systems.
A wideband and low-profile folded transmitarray antenna (FTA) is proposed for K-band application in this paper. To ensure high gain and reduce the profile of antenna system simultaneously, both the transmissive metasurface and reflective metasurface with polarization conversion function are employed to construct multiple reflection paths for near-field electromagnetic waves, and a conventional widebeam open-ended waveguide is adopted as the feed source. The phase compensation of the transmissive surface is optimized using the Genetic Algorithm to reduce the quantization error caused by the state discreteness of the transmission unit, thus widening the gain bandwidth. For the fabricated prototype, the upper transmissive metasurface consists of 27×27 units and the lower reflective metasurface consists of 24×24 units. The antenna profile is 1.5λ0, and the height-to-diameter ratio is only 0.19. Measurement results show that the 3-dB gain bandwidth is 36.4% (18.8–27 GHz) and the peak gain is 23.3 dBi. The proposed FTA is a promising candidate for future wireless communication systems.
A thin film antenna inspired by stripline structure with a broad bandwidth is proposed. Integrated with a grounded coplanar waveguide (GCPW) as the feeding line of the stripline, this antenna features double asymmetric slots etched in the top and bottom ground planes of the stripline in order to transform a conventional stripline into a highly efficient antenna. The proposed antenna has compact dimensions of 28 mm × 6 mm (equivalent to 0.28λ₀ where λ₀ is the wavelength in free space corresponding to the lowest operational frequency) comprising five layers with a total thickness of 0.149 mm. The measured results show that the antenna could cover the frequency range of from 2.98 GHz to 5.14 GHz (fractional bandwidth of 53.2%) with high gain, efficiency and omnidirectional radiation pattern which can be a potential candidate applied for the private LTE (long-term evolution) and sub-6 GHz 5G and communication systems.
In this paper, a hybrid multilayer frequency selective surfaces (FSS) radome capable of maintaining a stable passband over a wide frequency range is proposed. The radome is composed of two FSS arrays embedded within the dielectric layers of a C-sandwich structure, enabling it to operate over a wide passband and maintain a stable frequency response with respect to different incident angles and polarizations. The design procedure employs curve fitting based on the equivalent circuit method (ECM), which is used to determine the initial structural dimensions of the FSS. For verification, a prototype was fabricated. The measured frequency response agreed well with the numerical results of the ECM and full-wave simulations, exhibiting flat-top characteristics at 4–12 GHz and remaining stable at an incident angle of 50° for TE and TM polarizations.
Electromagnetic (EM) noise from a gigawatt-level pulse-forming-network (PFN) Marx generator in a high-power microwave (HPM) system is investigated through both simulation and experiment. Using CST Studio Suite, EM noise was analyzed in terms of emission locations and spectral characteristics. The results show that noise is primarily generated within the PFN-Marx generator and transmission line, and radiates externally through insulator plates. Frequency spectrum analysis indicates distinct peaks below 1.5 GHz, with field strengths on the order of tens of V/m at a distance of 1 m. Experimental measurements conducted on the same model exhibited good agreement with the CST simulations, confirming the reliability of the modeling approach. In addition, simple metallic shields applied to the model suppressed the dominant low-frequency peaks, leaving weaker high-frequency components around 12.8 GHz with magnitudes of several tens of mV/m as residual emission. This work provides one of the few experimental validations of CST-based EM noise modeling for PFN-Marx generators and demonstrates that a validated, geometry-based simulation approach can serve as a practical tool for evaluating electromagnetic interference characteristics and shielding effectiveness in HPM system design.
This paper presents an enhanced eigenvector-correlation-based mode tracking method with two core parts. In Part Ⅰ, two redundant-mode-eliminating filters eliminate numerous unexcitable modes and limit correlation computations to localized mode pairs, significantly reducing computational complexity. In Part II, a correlation classification and a multicriteria approach (including eigenvalue difference criteria, energy operator criteria, and least-squares trajectory fitting criteria) address mode swapping and degeneracy. This method ensures tracking accuracy, reduces time consumption, and is insensitive to mesh refinement and frequency step size, making it suitable for wideband tracking.
This paper presents a compact broadband circularly polarized antenna based on a metasurface. The antenna is designed to minimize transmission losses in microwave power transfer (MPT) systems while ensuring a stable flat-top radiation pattern for efficient energy transmission. The proposed structure is composed of aperture-coupled feeding and a metasurface in which four-unit cells are sequentially eliminated to enhance the antenna’s circular polarization (CP) characteristic s. The antenna is fabricated and experimentally validated in this work, with measurements indicating strong agreement with the simulation results. Moreover, the antenna demonstrates excellent impedance matching across a wide bandwidth of 22.65% (4.46–5.85 GHz) and broadband CP characteristics with an axial ratio (AR) less than 3 dB over the 4.66–5.88 GHz range. The proposed antenna also maintains a stable flat-top (1-dB) radiation pattern throughout its operational frequency range. At 4.8 GHz, the flat-top beamwidths for the E-plane and H-plane are 58% and 60%, respectively, with a realized gain of 7.5 dBi. At 5.8 GHz, the flat-top beamwidths are higher than 56% in both planes, with a realized gain of 8.2 dBi. The proposed antenna offers superior performance in terms of compactness, a broadband flat-top beam, and broadband CP compared to those developed in previous studies.
Short-range three-dimensional (3D) synthetic aperture radar (SAR) imaging has drawn significant attention across various domains, including security surveillance, non-destructive testing, and medical diagnostics. This paper introduces a fast adaptive alternative direction method of multipliers (FA-ADMM) framework designed to enhance both efficiency and accuracy in SAR image reconstruction. Our approach addresses two key challenges in the single holographic frequency ADMM (SFH-ADMM) model: image degradation from fast Fourier transform operations and slow convergence due to fixed ADMM penalty parameters. To overcome these issues, we refine the augmented Lagrangian formulation to ensure stable convergence and introduce an adaptive tuning mechanism that dynamically adjusts penalty parameters based on the connection between relaxed ADMM and relaxed Douglas–Rachford splitting. Additionally, we seamlessly integrate denoising convolutional neural network and autoencoder architectures into the iterative process to enhance noise suppression and image fidelity, respectively. The synergy of these innovations within a unified framework significantly accelerates convergence and improves reconstruction quality, making it well suited for real-world short-range 3D SAR applications.
In this paper, a multibeam antenna without a phase shifter is designed for railway communications in the upper 5G band (28 GHz). Railway turning angles can reach up to-20 degrees to 20 degrees depending on line geometry and train speed. Based on the curvature of railway tracks in realistic scenarios, the required beam deflection range spans-30 degrees to 30 degrees. This limited beam deflection range makes the Rotman lens a suitable replacement for phase shifters in beam steering, thereby significantly reducing system cost. Depending on the choice of antenna element, the antenna can create either linear or circular polarization. The measurement results demonstrate that the linearly and circularly polarized antennas achieved maximum directivities of 10.8 dBi and 11.2 dBi, respectively. The antenna bandwidth under linear (circular) polarization reached 2 GHz (1.8 GHz), which is sufficient to support the high data-rate requirements of the 5G communications. In addition, the antenna size was minimized to fit into a shark-fin cover mounted on the vehicle.
This paper presents a dual linearly polarized planar antenna element optimized for private 5G applications in the 4.6–4.9 GHz frequency band, targeting Korea’s 4.7 GHz allocation. Wide beamwidth antenna elements are increasingly critical in private 5G (P5G) networks to simplify base station architecture and enable efficient MIMO implementation without sectorization, making them a cost-effective solution. Nevertheless, simultaneous improvement in both beamwidth and bandwidth for dual-polarized planar antennas has rarely been demonstrated, due to technical challenges associated with antenna volume, fabrication complexity, and cost constraints. To achieve wide angular coverage while addressing these design challenges, a dielectric grid layer (DGL) is integrated into the dual-polarization antenna design. The DGL refracts the radiated energy outward through angular phase transformation, effectively enhancing the half-power beamwidth (HPBW). The proposed antenna achieves an HPBW exceeding 131°, enabling single-element sector coverage well-suited for compact and high-performance deployments. The design offers high polarization purity, with cross-polarization discrimination greater than 25.2 dB and port-to-port isolation exceeding 28.6 dB, facilitating reliable dual-polarized MIMO operation. The peak realized gain surpasses 2.5 dBi across the operational band. Simulation results are validated through measurements, showing good agreement in radiation patterns, beamwidth, and polarization characteristics. With its broad angular coverage, dual linear polarization, and high isolation, the proposed antenna provides a cost-effective, compact, and fabrication-friendly solution for next-generation P5G-MIMO platforms, ensuring practical and efficient deployment.
In this paper, statistical inference is used to predict a practical linear equation for determining signal loss rates over distance in a suburban over-rooftop path under both line-of-sight (LoS) and non-line-of-sight (NLoS) conditions. Unlike existing prediction equations, the proposed model provides an 80% confidence interval with the same slope as a regression equation and an appropriate intercept based on distance. Additionally, the proposed Gaussian mixture model clustering algorithm can classify unlabeled real-time measurements as either LoS or NLoS with high accuracy, significantly improving the convenience of signal measurement.
This paper presents a method of introducing novel bar shaped multiple patches to enhance the gain of the often-ignored North Atlantic Treaty Organization (NATO) radio frequencies E-band, that is from 2–3 GHz while maintaining high gain through the entire bandwidth of the antenna. The patches are introduced in the vicinity of the antenna flares. The length of the patches increases subsequently in the end fire direction to cater for different frequency fields. This approach improves the gain and directivity by field coupling, without getting a tradeoff with the absolute bandwidth of the antenna. This new antenna prototype has dimensions of 100 mm × 90 mm × 1.5 mm with measured gain from 3.8–7.8 dBi from 2–10 GHz and for NATO E-band the gain ranges from 3.8–5 dBi which is better than the previous designs with respective antenna size.
This paper proposes a method for analyzing propagation environments using terrain information and for predicting the communication coverage between a control tower and airborne platforms. This method involves collecting terrain data and implementing it in a Wireless InSite simulator. Digital elevation model data are used to model a communication environment, and mounting analysis allows the antenna pattern of an airborne platform to be generated. The analysis assumes flight scenarios in which the airborne platform follows a given trajectory at various altitudes. At altitudes of 600 m, 1,200 m, and 1,800 m, communication coverage increases with altitude, and communication is possible for 44.91%, 81.99%, and 95.45% of the total communication time in the predefined flight scenario, respectively. A dust particle attenuation coefficient model is used to observe changes in communication coverage due to weather conditions at the Ku-band. At altitudes of 600 m, 1,200 m, and 1,800 m, when dust particles are present, communication is possible for 37.48%, 61.91%, and 62.52%, respectively. A rainfall case is also evaluated using an ITU-R model-based rain attenuation calculation at 30 mm/hr. With rain, communication is possible for 29.72%, 40.16%, and 34.47% at 600 m, 1,200 m, and 1,800 m, respectively. These results demonstrate that terrain and weather conditions should be considered when analyzing the communication coverage between a control tower and airborne platforms.
This work introduces a simulation-driven framework for reliably reproducing experimental trends pertaining to two-dimensional thin films, thus rendering advanced heterostructure research feasible for facilities without sophisticated equipments. Zhang and his colleagues fabricated a molybdenum disulfide (MoS2) device in a ground-signal-ground (G-S-G) configuration and derived its equivalent electrical circuit. This research simulates a MoS2-graphene based coplanar transmission line (CPTL) in a G-S-G configuration using Ansys HFSS. Thereafter an accurate equivalent electrical model circuit was designed and calculated for its hetero-junction device using Advance Design System simulator. For validation the characteristic curves of the simulated and modeled devices are compared with the measurements obtained for the metallic MoS2 proposed by Zhang and his colleagues, which are used in this study for validation purposes rather than as a foundation for the proposed model. The validation results confirms that the proposed simulation method can consistently replicate experimental trends. Furthermore, the effect of the combined properties of MoS2 and graphene on performance is evaluated based on S-parameters, and its high-frequency behavior is assessed through scattering parameter analysis (S11, S21), particularly at 5.9 GHz. Among the four different configurations assessed in this study, the one with the graphene monolayer positioned on the source side of the MoS2 signal line exhibited improved high-frequency performance in terms of I–V and C–V characteristics, as well as a low parasitic effect. Therefore, it can potentially be utilized in future devices and next-generation Wi-Fi spectra.
This work presents a generative machine learning model that predicts upper graphene element configurations for a multilayer flexible electromagnetic absorber. The model uses the lower graphene layer as input and S-parameters as conditional input. It is increasingly difficult to fabricate multilayer absorbers using the conventional design process, which introduces performance and efficiency issues. With advances in machine learning algorithms and corresponding hardware, it is becoming easier to design multilayer absorbers using machine learning approaches. A conditional variational autoencoder—a type of generative machine learning model—was used to train our model. We integrated a residual network into our encoder portion to enable better feature extraction capabilities for our proposed model. We prepared the dataset using the High Frequency Structure Simulator, an electromagnetic simulation software program developed by Ansys. We reconstructed the upper and lower graphene structures from the dataset and predicted the upper graphene structure using the given S-parameters and the lower graphene structure of the absorber. Satisfactory agreement between the predicted and actual structures was observed.
This paper presents a real-vehicle electromagnetic compatibility (EMC) evaluation method for dual-mode vehicle-to-everything (V2X) systems supporting WAVE and LTE-V2X. Unlike conventional EMC tests that are limited to assessing regulatory compliance, the proposed method quantifies the effects of electromagnetic interference on communication quality based on packet error rate (PER), latency, and throughput. A dual-mode V2X module comprising an 8-layer printed circuit board and a software stack was tested under DSRC, C-V2X, and GNSS conditions in accordance with EN 301 standards. The results confirm full compliance with emission limits and robust immunity, maintaining 0% PER and stable performance even at 30 V/m. Compared with single-mode systems, the proposed dual-mode design demonstrates superior resilience, offering a performance-centric framework for EMC validation of future autonomous and cooperative driving applications.
The measurement of unintended electromagnetic emissions from vehicles is both costly and time-consuming, making real data acquisition challenging. In addition, the inherent complexity of vehicle modeling significantly affects the accuracy of simulations. Given this context, this letter proposes modeling the emission spectrum as a Gaussian process and examines the accuracy of spectrum fluctuation estimations by comparing experimental data with data generated from relatively simple simulations.
This study presents a method for detecting kidney tumors using a wearable rectangular microstrip antenna based on the first peak phase and amplitude of the o21(t) signal obtained at the receiving antenna. The study is conducted in four stages. First, a rectangular microstrip patch antenna operating at 2.4 GHz is designed and implemented. Its reflection coefficient (S11) is measured using a vector network analyzer, and its radiation pattern is measured in an anechoic chamber. In the second stage, computer simulation technology (CST Studio Suite) is employed to create a kidney system model containing elliptical tumors with x-radius of 2 mm, y-radius of 1 mm, and height of 6 mm, positioned at a depth of 10.2 mm below the kidney surface while maintaining a distance of 122.84 mm from the antenna. In the third stage, a SARcompliant antenna system placement is determined by performing a distance sweep at 25, 50, 75, 87.84, and 100 mm at an input power of 0.5 W. Ultimately, 87.84 mm was selected as the most suitable placement (accepted power, approximately 0.492 W; maximum 10 g SAR, approximately 1.71 W/kg; total SAR, approximately 1.22 W/kg). Finally, in the fourth stage, tumor detection is performed using only the first local maximum of the o21(t) signal. The phase of the signal Aal) which is the phase difference between two signals at tumor number transitions has also been observed as an important parameter in tumor detection. The number of tumors is detected based on the increase in amplitude AA (%) and phase change of the signals. The CST results for the tumor-free and single-tumor cases presented a distinct difference Aal) approximately 125 degrees and AA approximately 15% while the 1 -> 2 and 2 -> 3 transitions exhibited additional phase steps of approximately 99 degrees and approximately 81 degrees, respectively, along with approximately 11%-16% increase in amplitude. Meanwhile, an important detection threshold was observed for the transition pertaining to 1-3 tumors: when the tumor dimensions were reduced to x = 1.9 mm, y = 0.9 mm, and z = 5 mm, the received o21(t) signal became indistinguishable from the tumor-free case. Therefore, it was confirmed that the proposed system reliably detects tumors of size less than or equal to 2 mm & times; 1 mm & times; 6 mm. Overall, the proposed method enables fast, non-ionizing, and low-cost tumor detection based on a single receiving-port observation and the first peak.
In this paper, we classify human arm movements using point clouds obtained from a millimeter-wave multiple-input multiple-output (MIMO) radar integrated with radar–camera cross-learning. When a radar receives signals reflected by the entire human body, delineating the specific details of arm movements is challenging. Our approach involves skeletonization of human point clouds measured by a MIMO radar and then processing them using diverse deep learning models. To enhance the skeletonization of the point cloud model, cross-learning between radar and camera systems is implemented. The point clouds obtained from the radar are trained on camera data, since they offer a higher resolution. Two training methods are investigated in this study. The first method utilizes a two-dimensional convolutional neural network (2D-CNN) regression model to extract the arm angles of the skeleton model for determining the class of arm motion. The second method employs an autoencoder (AE) along with data augmentation, performed using a stable diffusion model, to enhance the robustness of feature extraction. The feasibility of the proposed feature extraction methods is validated through experimentation based on six distinct arm motions, resulting in arm motion classification accuracies of 95.23% for the 2D-CNN method and 98.1% for the AE-based method. These outcomes underscore the efficacy of the proposed techniques, which show significant promise for application in detailed human motion classification using radar.
Modern radars with active electronically scanned array (AESA) are capable of performing multi-functions, such as search, acquisition, and track for multiple targets. In the case of airborne AESA radar, interleaving of air-to-air and air-to-surface operation is also possible. To allocate sufficient radar resources to tasks of high priority (such as tracking targets with high threat), the time allocated to search task should be reduced, which can be accomplished by controlling search frame time. The search frame time can be reduced either by broadening beamwidth, reducing dwell time, or increasing beam spacing. In this paper, the detection range performance is analyzed for reduced search frame time by tuning either of the three parameters (beamwidth, dwell time, and beam spacing). In particular, two-dimensional multi-step interlaced scanning (MIS) is applied when beam spacing is changed, and it is shown that increasing beam spacing with MIS minimizes the degradation of the detection range performance as the search frame time is reduced.
