ABSTRACT Radar electromagnetic phantoms aim to deceive radar systems by introducing virtual targets—entities that do not physically exist—into radar imagery, thereby inducing erroneous recognition. Information metasurfaces, functioning as digitally reconfigurable electromagnetic reflectors, offer unprecedented capabilities in multidimensional radar target signatures control. Nevertheless, existing space‐coding‐based techniques are constrained by static phantom image templates, limiting their ability to generate dynamically reconfigurable radar phantoms. Temporal modulation strategies are susceptible to synchronization errors under non‐cooperative scenarios. To address these challenges, this paper proposes a novel method for generating image‐level, dynamically stable, and reconfigurable radar electromagnetic phantoms via information metasurfaces. The proposed approach leverages the geometric theory of diffraction (GTD) to extract characteristic parameters oftargets. These parameters subsequently guide the design of asynchronous frequency‐modulated sequences implemented on the metasurface. A 1‐bit information metasurface prototype was developed and experimentally validated. The results demonstrate its capability to generate a variety of reconfigurable radar phantoms in high‐resolution range profiles (HRRPs) in real time. Furthermore, both human radar image interpretation and artificial neural network (ANN)‐based classification exhibit high confidence in identifying the modulated imagery as authentic targets, thereby confirming the effectiveness of deception. The developed metasurface and its associated modulation strategy hold significant promise for critical target protection in electronic warfare scenarios.

A uniform geometrical theory of diffraction (UTD) solution was developed earlier for radiation from sources on an analytically defined conducting convex surface. However, its application to meshed surfaces is challenging since it requires geodesic ray tracing and geometry based parameter extraction needed by UTD. The geodesic ray tracing algorithm, and the closed-form expressions and algorithms for geometry-based parameter extraction, which were developed previously for the UTD solution for mutual coupling, are modified accordingly for the application of the UTD solution for radiation to predict near and far fields from a source on a triangulated convex surface. Values for the geometry based parameters extracted from a triangulated circular cylinder and a triangulated sphere are compared with their actual values for validation. Although the proposed approach is applicable to triangulated arbitrary conducting convex surfaces, near and far field results obtained by applying the UTD solution to the analytically defined circular cylinder and sphere are respectively used to validate the results for the triangulated surfaces for these geometries. UTD is the only asymptotic method that includes creeping rays. Hence, the proposed approach is critically important for applications where creeping rays provide a significant contribution to fields radiated into or near shadow regions.

Moiré metalens is attractive for imaging applications due to their compact form factor and high zoom ratio. Here, we propose a novel Moiré zoom metalens system that achieves a continuous 10× zoom over a focal length range of 2.2–22 mm at 1,064 nm, while extending the full field of view up to 93°. A variable aperture, capable of axial translation, is introduced to jointly suppress aberrations and maintain a large aperture size with f-numbers ranging from 2.5 to 7.5. The system delivers near-diffraction–limited imaging resolution across the entire zoom and field-of-view range, with Strehl ratios exceeding 0.9. This level of performance is comparable to commercial optics and is rarely reported in metalens-based zoom systems. Remarkably, the total optical volume is only ∼4.2 × 32 mm, underscoring its potential for miniaturized imaging. Furthermore, we establish an integrated design and validation pipeline that strategically combines geometric optics, scalar diffraction, and vectorial electromagnetic theory. This multi-theory approach provides an efficient and generalizable pathway for the development of high-performance metalens systems.

Multiband fusion (MF) technology can generate an ultra-wideband echo (UWBE) from multiple sub-band echoes (SBEs), thereby improving radar range resolution and enhancing target recognition capabilities. However, current MF methods generally do not account for the incoherence introduced by fluctuations in the scattering characteristics of scattering centers (SCs) across different frequency bands. This oversight can lead to degraded fusion performance. To address this limitation, a novel MF method that explicitly considers the fluctuation of SC characteristics between sub-bands is proposed in this paper. Firstly, a theoretical analysis of the additional incoherent phase term introduced by these fluctuations is conducted, which demonstrates its impact on fusion accuracy. Based on this analysis, scattering centers are extracted from SBEs based on the geometrical theory of diffraction (GTD) model, and then categorized into two distinct types: intrinsic scattering centers (ISCs) and unique scattering centers (USCs). Subsequently, a new incoherent phase estimation and compensation method is proposed, leveraging this categorization to effectively mitigate the inter-sub-band incoherence. The two types of SCs are then processed through either fusion or super-resolution to generate individual UWBEs, which are finally combined to form the final UWBE. The effectiveness of the proposed method is validated using both simulated electromagnetic scattering data and static measured data. Numerical results demonstrate that the proposed method achieves significantly greater fusion accuracy compared to traditional MF approaches, confirming the practical benefits of incorporating SC fluctuation modeling into the fusion process.

In cellular networks, coverage estimation is critical for network planning and optimization. Traditional ray tracing models the propagation of radio waves but faces limitations in large-scale applications due to high computational cost. Deep learning-based methods also accurately predict signal propagation, but are limited in large-scale applications due to the data requirements. In this study, large-scale synthetic datasets are created with Uniform Theory of Diffraction (UTD) based ray tracing simulations to overcome this problem. The proposed method generates 2D coverage maps by analyzing direct, reflected and diffracted electromagnetic propagation paths in 3D digital terrain maps. The developed “Multi-Branch Coverage Estimation Network” aims to estimate the signal propagation accurately and efficiently. Experimental results show that the proposed model provides high accuracy in coverage estimation and works more efficiently than conventional methods. Thus, high quality coverage estimation without the need for real measurements is an important step in wireless network planning.

Conventional pulse-echo ultrasonic inspection uses the ratio of the signal from a crack-like defect to the signal from a reference reflector as one factor which determines whether the flaw merits reporting, further sizing, and, possibly, removal. As these defects are smooth, on the scale of an ultrasonic wavelength, and generally flat, and also large relative to the wavelength, they can be successfully modelled using the geometrical theory of diffraction (GTD). GTD is a rapid method for evaluating the ultrasonic signal from a defect. The signal from the reference reflector is easy to calculate if the reflector is a side-drilled hole whose axis is normal to the ultrasonic beam axis and provided it is in the far field of the transducer. If the reference reflector is a flat-bottomed hole then prediction of the signal for non-normal angles of incidence is more difficult since the signal arises from the curved edge at the intersection of the flat bottom of the hole and its cylindrical side face.

This study introduces new approach which combines the geometrical theory of diffraction (GTD) and the ray tracing (RT) method to analyze the produced scattering pattern due to a striking plane wave on a rough surface with random attributes regarding electromagnetic and statistical properties. The Fresnel equation-based model is utilized to determine the distribution of scattered power for both reflection from the region above the surface and transmission into the region beneath the surface. The polarization (direction of electric field) of the incident optical wave is also considered. The proposed algorithm addresses multi-bounce of striking ray, making it an advanced higher-order GTD-RT approach. The precision of the findings is validated by comparing them with scattering pattern data from empirical observations produced by a Radiant beam striking paper sheets with different roughness properties and different probabilistic characteristics. This study’s numerical results explore how the scattering pattern is influenced by surface degree of granularity, incidence angle, and light refraction coefficient of the rough surface. Additionally, first and second order scattering are calculated and compared. The second-order GTD-RT method provides slightly improved accuracy over the first-order method, especially for highly rough surfaces, but the enhancement remains marginal. Given its low average error (< 2.5%) and significantly lower computational cost, the first-order GTD-RT method offers a more practical and efficient solution for optical scattering analysis in rough surface scenarios. To validate the accuracy and reliability of the proposed model, a subset of the numerical results obtained in this study has been systematically compared with previously published findings derived using alternative analytical approaches, specifically the Geometrical Optics (GO) method and the second-order Kirchhoff approximation. These comparisons serve to highlight the consistency of the presented approach with established theoretical models and underscore its capability to accurately characterize the scattering behavior from rough surfaces under similar conditions.

A new ray-tracing acceleration technique is presented for electromagnetic simulation problems using the Uniform Theory of Diffraction and meshes of planar facets. The innovation involves using relational databases to accurately store spatial information, enabling spatial indexing through space partitioning with R-trees. This technique effectively reduces the computational cost of several critical phases, including the shadowing test. Additionally, there are multiple advantages to utilizing this technology, such as automated memory and disk management along with a query planner that organizes the instructions automatically. Direct rays, multiple reflections, multiple transmissions, simple diffraction, and combinations of these effects have been implemented in PostgreSQL and its spatial library PostGIS. Compared to traditional techniques that employ Angular Z-Buffer acceleration and store information solely in RAM using a low-level language, this approach decreases memory usage by more than 90% in complex scenarios. It also shows a decrease in execution time by more than half when the scenario is sufficiently complex.

Mathematical study of the phenomenon of wave focusing during reflection from 2D-curvilinear reflectors is carried out within the framework of the geometric theory of diffraction based on the Kirchhoff physical theory of diffraction. An explicit form of the leading term of the pressure expansion in the reflected acoustic wave is obtained. In the work, using the example of a concave elliptical reflector, it is established that in the case of a certain mutual arrangement of the source and the receiver, singular focusing effects appear, which lead to the fact that the amplitude of the reflected wave can have a different order of growth with increasing frequency. In each of the established cases, the leading terms of the asymptotic expansions of the pressure in the reflected wave are obtained in explicit form. The obtained asymptotic results are compared with the results of direct numerical calculations of the diffraction integrals.

This study explores the application of Chebyshev ridge structures in the optimization of absorbing materials within microwave anechoic chambers, aiming to enhance absorption performance and improve antenna testing accuracy by integrating Fresnel zone theory. The research employs geometric diffraction theory to analyze electromagnetic wave reflection behavior at different frequencies and optimizes the layout of absorbing materials within the chamber. Simulation results indicate that the introduction of Chebyshev ridge structures significantly reduces the reflection level in the quiet zone, with a decrease of over 10 dB across all frequency bands. The measured reflection levels and tapering in the quiet zone of the chamber constructed with this optimized design meet the requirements for far-field antenna testing. Compared to traditional designs, this optimization effectively minimizes reflection interference and reduces material costs. The findings provide a theoretical foundation and practical reference for the design and engineering application of absorbing materials in microwave anechoic chambers.

Inverse Synthetic Aperture Radar (ISAR) images are extensively used in Radar Automatic Target Recognition (RATR) for non-cooperative targets. However, acquiring training samples for all target categories is challenging. Recognizing target classes without training samples is called Zero-Shot Learning (ZSL). When ZSL involves multiple modalities, it becomes Multi-modal Zero-Shot Learning (MZSL). To achieve MZSL, a framework is proposed for generating ISAR images with optical image aiding. The process begins by extracting edges from optical images to capture the structure of ship targets. These extracted edges are used to estimate the potential locations of the target’s scattering centers. Using the Geometric Theory of Diffraction (GTD)-based scattering center model, the edges’ ISAR images are generated from the scattering centers. Next, a mapping is established between the edges’ ISAR images and the actual ISAR images. Neighbor-Adapted Local Linear Embedding (NALLE) generates pseudo-ISAR images for the unseen classes by combining the edges’ ISAR images with the actual ISAR images from the seen classes. Finally, these pseudo-ISAR images serve as training samples, enabling the recognition of test samples. In contrast to the network-based approaches, this method requires only a limited number of training samples. Experiments based on simulated and measured data validate the effectiveness.

Unmanned aerial vehicles (UAVs) significantly shape the evolution of 5G and 6G technologies in India, particularly in reconfiguring communication networks. Through their deployment as base stations or relays, these aerial vehicles substantially enhance communication performance and extend network coverage in areas characterized by high demand and challenging topographies. Accurate modelling of the UAV-to-ground channel is imperative for gaining valuable insights into UAV-assisted communication systems, particularly within India’s rapidly expanding metropolitan cities and their diverse topographical complexities. This study proposes an approach to model low-altitude channels in urban areas, offering specific scenarios and tailored solutions to facilitate radio frequency (RF) planning for Indian metropolitan cities. The proposed model leverages the International Telecommunication Union recommendation (ITU-R) for city mapping and utilizes frequency ranges from 1.8 to 6 GHz and altitudes up to 500 m to comprehensively model both line-of-sight (LoS) and non-line-of-sight (NLoS) communications. It employs the uniform theory of diffraction to calculate the additional path loss for non-line-of-sight (NLoS) communication for both vertical and horizontal polarizations. The normal distribution for additional shadowing loss is discerned from simulation results. This study outlined the approach to derive a comprehensive statistical channel model based on the elevation angle and evaluate model parameters at various frequencies and altitudes for both vertical and horizontal polarization. The model was subsequently compared with existing models for validation, showing close alignment. The ease of implementation and practical application of this proposed model render it an invaluable tool for planning and simulating mobile networks in urban areas, thus facilitating the seamless integration of advanced communication technologies in India.

The diffraction of anisotropic impedance wedges plays a key role in radar detection, electromagnetic (EM) wave propagation, and high-frequency antenna design. Existing numerical methods are limited by their complexity and high resource demands, restricting their practical engineering applications. This study presents a numerical matching approach grounded in high-frequency EM theory, deriving a simplified expression for the Maliuzhinets wedge special function and constructing an effective diffraction spectrum through enhanced boundary condition constraints. The method significantly broadens the scope of the Uniform Theory of Diffraction (UTD), overcoming challenges associated with large-angle deviations from normal or grazing incidence. Numerical results confirm the method's accuracy and efficiency in solving diffraction fields for anisotropic impedance wedges at arbitrary wedge and skew incident angles.

This article introduces a uniform theory of diffraction–physical optics (UTD–PO) formulation for analyzing radiowave multiple diffraction emanating from trees and buildings in green urban areas, considering illumination from a low transmitter and assuming spherical-wave incidence. Based on Babinet’s principle, this solution models buildings as rectangular sections and accounts for the influence of tree crowns (assuming these rise above the average rooftop height) by incorporating appropriate attenuation factors/phasors into the diffraction phenomena of buildings. The validation of the formulation is achieved through measurements made at the 39 GHz 6G mmWave frequency on a scale model of a green urban environment comprising bonsai trees and bricks. The main advantage of the proposed solution is that the calculations only include single diffractions due to recursion, circumventing the need to use higher-order diffraction terms in the diffraction coefficients, thus reducing the computation time and power. Our results may be beneficial for the design of mobile communication systems, including 6G networks, situated in green urban areas and with transmission source positioned lower than the surrounding infrastructure.

Modeling stochastic elastic wave diffraction by the tips of randomly rough defects

This paper presents a 3D ray-tracing model using geometrical optics and the uniform theory of diffraction in radio channel characterizations of macrocellular environments. On the basis of the environmental information obtained from a digitized map, the model is effectively applied. A technique considering multiple reflections and diffractions through the ray path classification is utilized in this model. Ray paths belonging to each ray category are determined using different methods. The proposed model is justified (the prediction accuracy of the model is better than 6.5 dB) with measurement data for the two scenarios and can provide reliable theory as a basis for radio wave propagation prediction and network planning in urban macrocellular environments.

Sound power, a standard metric used to quantify product noise, is determined through the vibration-based sound power (VBSP) method. This method involves measuring surface velocities and utilizing an acoustic radiation resistance matrix, R, dependent on the structure's geometry. While R matrix expressions have been established for baffled flat plates, fully closed cylinders, and fully closed spheres, this work presents the first analytical expression tailored for baffled simply curved plates with uniform curvature. This development, based on eigenfunction expansion and the uniform theory of diffraction, extends the VBSP method's capabilities for accurate sound power assessment from these structures. Experimental validation involved testing three plates of varying curvature in a reverberation chamber, comparing the VBSP method with the ISO 3741 pressure-based standard. One of the curved plates underwent additional testing in an anechoic chamber following the ISO 3745 standard, confirming the VBSP method's accurate sound power measurements down to the 160 Hz one-third octave band. The same plate was tested in uncontrolled acoustic environments — a busy hallway and an outdoor location. The VBSP results showed strong agreement with ISO 3741, affirming the method's robustness for measuring sound power from baffled simply curved plates in acoustically challenging real-world conditions. This underscores the practicality of the VBSP method, enabling accurate sound power measurements of baffled curved plates in the presence of substantial background noise and environmental variability.

SummaryIn this paper, for the first time, the capability of a compact low‐cost wideband omnidirectional circularly polarized (CP) antenna to suppress multipath fading characteristics in a typical indoor propagation channel for 2.4 GHz applications is investigated. A ray tracing method based on the geometrical optics and uniform theory of diffraction is applied to analyze an indoor propagation channel using the measured radiation patterns of the proposed antenna. The design uses a conventional monopole antenna with a circular ground plane to generate a vertically polarized electric field. Sequentially flag‐shaped stubs are then added to the ground plane to produce horizontally polarized electric field and to improve the impedance bandwidth of the proposed antenna. The antenna is designed for 2.4 GHz WLAN application with 10 dB impedance bandwidth of 25.5% and 3 dB axial ratio (AR) bandwidth of 24.5%. The polarization can be readily changed between the left‐hand circular polarization (LHCP) and right‐hand circular polarization (RHCP) by altering the direction of the coaxial probe (monopole) or varying the orientation of the printed bended stubs. Both the LHCP and RHCP prototypes of the proposed antenna are designed, fabricated, and tested, and the similar results are obtained.

A ray tracing framework based on the utilization of multiple Huygens surfaces is introduced and evaluated. As such, complex propagation environments are divided into smaller subdomains, thereby restricting rays to traverse within a smaller, simpler space. The subdomains are surrounded by the Huygens surfaces and equivalent Huygens sources interconnect the ray based field representations in neighboring subdomains. Compared to conventional shooting and bouncing rays (SBR) based ray tracing simulations, which detect relevant ray hits at receivers via small reception spheres, this approach distributes the wave representation over many rays and collects their overall influence via Huygens surface integrations. By a smart choice of the Huygens surfaces, the ray coverage in complex environments can be increased considerably. Concerning diffraction computations, which rely conventionally on the uniform theory of diffraction (UTD), the flexibility of choosing Huygens surfaces allows to distribute diffraction edges over different subdomains, thus, eliminating the need for consecutive UTD evaluations and the corresponding problems in finding correct multiple diffraction paths. Together with smart ray launching strategies and quickly converging integration methods, the presented approach allows many successive diffraction evaluations with reasonable accuracy and efficiency. The implementation is based on graphics processing units (GPUs), enabling massively parallelized simulations.

Subject and Purpose. The directivity characteristics of a dipole antenna when it is placed above and parallel to a perfectly conducting screen of rectangular shape are considered, aiming to theoretically study dipole antennas with sector-shaped radiation patterns (RP) formed by choosing the optimal electrical dimensions of the screen and the distance between the dipole and the screen. Methods and Methodology. The problem of the dipole radiation field diffraction by the edges of a rectangular screen is solved by the method of the uniform geometric theory of diffraction. The diffracted fields developed at the screen edges are calculated using the uniform asymptotics obtained from the rigorous solution of the model problem of the dipole field diffraction by the edge of a perfectly conducting half-plane. Results. The algorithms and calculation programs developed allow studying the electrodynamic characteristics of the antenna over a wide range of screen electrical dimensions and distances between the dipole and the screen. Radiation patterns, directivity in a path normal to the screen and in directions of maximum radiation, radiation resistance, and protective ratio have been calculated across a broad range of screen dimensions and distances between the dipole and the screen. It has been observed that the antenna of the kind forms sector-shaped radiation patterns when the distance between the dipole and the screen is 0.30 to 0.45 of the resonant wavelength of the dipole. The obtained results have been confirmed by the calculations using the FEKO program. Conclusions. It has been shown that the considered dipole antenna forms sector-shaped radiation patterns when the distance between the dipole and the screen is 0.30 to 0.45 of the dipole resonant wavelength depending on the screen dimensions. The obtained calculation results for the maximum achievable electrodynamic characteristics allow us to find optimal geometric parameters of the antenna with a sector-shaped pattern for a particular application.