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In this paper, a fluted E‐shaped antipodal Vivaldi antenna (AVA) loaded with rectangular‐shaped strips is proposed for ground‐penetrating radar (GPR) application. The corrugation method is implemented by introducing multiple slots in the uppermost and lowermost arms of the antenna, followed by adding additional 10 strips to broaden and stabilize the impedance bandwidth. The electrical dimension of the antenna is 1.07λ × 1.8λ × 0.004λ. The proposed modified AVA (MAVA) exhibits a high fractional bandwidth of 144.8% over an ultrawideband of 1.6–10 GHz. The peak gain achieved by the antenna is 8.97 dBi. The proposed antenna offers a stable unidirectional radiation pattern along E‐ and H‐plane throughout the spectrum with maximum radiation efficiency of 96%. A prototype of the proposed antenna has been fabricated and tested where the measured results bear close resemblance with the simulated results. The pertinence of proposed antenna for GPR subsurface scanning was examined through a field test where scanned result signifies its aptness for such submissions. [ABSTRACT FROM AUTHOR]

This paper introduces an ultrathin, polarization-insensitive, wide angular stable microwave absorber characterized by a high-Quality (Q) factor. The absorber consists of elliptical metallic rings with a thickness of 0.035 mm on the top of Roger’s RT 5880 substrate with a thickness of 0.51 mm and a metallic ground plane with a thickness of 0.035 mm at the bottom. The proposed structure is fourfold symmetric which makes it polarization insensitive. The structure offers angular stability till 60° for the angle of incidence for both Transverse Electric (TE) and Transverse Magnetic (TM) modes under oblique incidence. The structure provides a high-quality factor of 155 at an operating frequency of 7.75 GHz. Also, the structure provides reconfigurability with a change in the axis ratio of the elliptical structure from 7.30 to 9.48 GHz when the axis ratio changes from 0.26 to 0.36 without any change in the unit cell size. The unit cell dimension is 1.07 λg x 1.07 λg x 0.022 λg. With its high Q-factor, thin size, structural simplicity, insensitivity to polarization, and incident angle stability suggested prototype is apt for microwave sensors and antennas to reduce Radar cross-section and X-band satellite communication. [ABSTRACT FROM AUTHOR]

A high-gain transmitarray antenna with low radar cross section (RCS) properties is presented in this paper. Compared with conventional high-profile multilayer designs, we introduce a transmit-reflect selective metasurface integrated with high-gain transmission and random scattering functions, achieving a reduced thickness of 0.13 λ 0 (where λ 0 is the wavelength at the center frequency). For the meta-atom design, we combine geometric rotation and dimension optimization to realize 1-bit independent transmit and reflection phase modulation, respectively. Moreover, in metasurface coding strategy, we employ an initial phase optimization method and a simulated annealing algorithm to determine the optimal coding matrices. The experimental results demonstrate high-performance radiation characterized by the peak gain of 23.6 dB, maximum aperture efficiency of 28.5%, and 3 dB gain bandwidth of 18.4%. For x -polarization, measured 10 dB RCS reduction bandwidth under transverse magnetic (TM) 0°-45° and transverse electric (TE) 0°-20° incidence are 9.02–11.36 GHz. For y -polarization, 10 dB RCS reduction bandwidth under TM 0–60° and TE 0–30° incidence is 8.82–10.96 GHz. [ABSTRACT FROM AUTHOR]

The development of radar systems requires extensive testing. However, field experiments are costly and time-consuming. Sea clutter simulation is of great significance for evaluating radar system detection performance. Traditional clutter simulation methods are unable to achieve clutter simulation based on the description of environmental parameters, which leads to a certain gap from practical applications. Therefore, this paper proposes a sea clutter simulation method based on the deep cognition of characteristic parameters. Firstly, the proposed method innovatively constructs a shared multi-task neural network, which compensates for the lack of integrated prediction of multi-dimensional characteristic parameters of sea clutter. Furthermore, based on the predicted clutter characteristic parameters combined with the spatial–temporal correlated K-distribution clutter simulation method, and considering the modulation of radar antenna patterns, the whole process of end-to-end simulation from measurement condition parameters to clutter data is accomplished for the first time. Finally, four metrics are cited for a comprehensive evaluation of the simulated clutter data. Based on the experimental results using measured data, the data simulated by this method have a correlation of over 93% in statistical characteristics with the measured data. The results demonstrate that this method can achieve the accurate simulation of sea clutter data based on measured condition parameters. [ABSTRACT FROM AUTHOR]

The direction‐of‐arrival (DoA) estimation methods based on coprime array (CA) largely rely on having a sufficient number of snapshots. However, under single‐snapshot conditions typical of vehicle‐mounted imaging radar, CA‐based DoA estimation often suffers from ambiguity leakage, resulting in significant degradation in performance. This paper thoroughly analyses the mechanism of ambiguity leakage in CA by re‐deriving the covariance matrix model under single‐snapshot conditions. To suppress the ambiguity leakage, a triple extended coprime array composed of three pairwise coprime sub‐arrays enhanced coprime constraint is designed. Building on this design, a DoA estimation algorithm based on an iterative adaptive approach is proposed. By leveraging the power spectrum distribution from iterative adaptive approach, a reduced‐noise signal is constructed by retaining only the high‐energy components. Next, the noise subspace using a multi‐stage Wiener filter, and finally, achieve super‐resolution DoA estimation through multiple signal classification spectrum analysis. [ABSTRACT FROM AUTHOR]

The authors analyse the sequential lobing radar (SLR) resistance against the scan rate modulation (SRM) jamming technique. Unlike previous studies, the authors analyse SLRs with sinc antenna patterns, enabling investigation of the sidelobe region's vulnerability. By incorporating second‐order angular tracking loops (SOATLs), the first analysis of break‐lock probability for SLRs under SRM jamming is introduced. The analysis reveals the influence of SOATL parameters (damping ratio and natural frequency) on both angular root‐mean‐square‐error at low jamming‐to‐signal‐ratio (JSR) region and break‐lock probability at high JSR region. Additionally, the impact of squint angle on SLR resistance to SRM jamming is examined. Furthermore, the optimal duty cycle as a function of JSR, which maximises break‐lock probability is presented. Significantly, the theoretical results support the 20 dB JSR requirement for SRM effectiveness, often cited experimentally in literature, and extend the theoretical analysis of the SRM technique carried out for the main lobe region of SLRs. This finding bridges the gap between theoretical analysis and practical observations. [ABSTRACT FROM AUTHOR]

Radar polarimetry is a technique that can be used to enhance target detection, identification and classification; however, the quality of these measurements can be significantly influenced by the characteristics of the radar antenna. For an accurate and reliable system, the calibration of the antenna is vitally important to mitigate these effects. This study presents a methodology to calibrate Ultra-Wideband (UWB) dual-polarised antennas in the near-field using a thin elongated metallic cylinder as the calibration object. The calibration process involves measuring the scattering matrix of the metallic cylinder as it is rotated, in this case producing 100 distinct scattering matrices from which the calibration parameters are derived, facilitating a robust and stable solution. The calibration procedure was tested and validated using a Vector Network Analyser (VNA) and two quad-ridged antennas, which presented different performance levels. The calibration methodology demonstrated notable improvements, aligning the performance of both functioning and under-performing antennas to equivalent specifications. Mid-band validation measurements indicated minimal co-polar channel imbalance (<0.3 dB), low phase error (<0.8°) and improved cross-polar isolation (≈48 dB). [ABSTRACT FROM AUTHOR]

Coal–rock interface recognition is one of the key challenges in advancing unmanned rapid tunneling systems. To address this, a method based on variations in ground-penetrating radar (GPR) reflection wave amplitude is proposed for identifying coal-rock interfaces in soft coal seams. A mathematical model derived from Maxwell's equations calculates the coal seam area based on the reflected wave amplitude. Experiments using a 400 MHz radar antenna show that the method achieves identification errors of 3.58 cm, 3.74 cm, and 4.23 cm for coal-to-rock ratios of 1:2, 1:1, and 2:1, respectively. In practical applications within a coal mine excavation face, the identification error is 6.64 cm. This method provides crucial data for drum height adjustment and cutting arm speed regulation in unmanned tunneling systems. [ABSTRACT FROM AUTHOR]

This paper proposes a design method for thinned array-based aperture-sharing antenna for S/C-band applications. The operating frequencies of the proposed antenna are 3~3.2 GHz in the S band and 6~6.4 GHz in the C band. The single element design uses two RF-35 substrates and achieves a reflection coefficient below −10 dB in the aforementioned operating bands. The measured antenna gains are 6.64 and 6.65 dBi in S and C bands, respectively. To realize aperture sharing for the designed S/C-band single-radiating element, a thinned array-based aperture-sharing array antenna is proposed using the binary genetic learning particle swarm optimization (GLPSO) algorithm. The S-band array antenna of the transmitter shows a half-power beamwidth (HPBW) of 9°, and the sidelobe level of the C-band array antenna of the receiver is −20 dB. [ABSTRACT FROM AUTHOR]

A simple technique for generating single and multiple beams from antenna arrays is presented. The approach is based on the multistage sequential rotation technique. A new feature in using multistage sequential rotation is provided. It is demonstrated that by applying a controlled second sequential rotation, circularly polarized antenna arrays operating alternately in a single-beam mode M1 and multi-beam mode M2 in the same frequency band can be designed. Proof-of-concept is provided mathematically and through numerical simulations in light of case studies. The approach can not only be applied to large antenna arrays following a modular principle adapted to the array size and needed applications without loss of generality, but also paves the way for the manufacture of circularly polarized antennas operating alternately or simultaneously in both modes in the same frequency band. In addition, antennas designed using the proposed approach may have a wide range of applications ranging from monopulse radar to antennas for the compensation of interference and blockage in dynamic communication environments. [ABSTRACT FROM AUTHOR]

This paper proposes a circularly-polarized (CP) metasurface antenna with ultra-wideband radar cross section (RCS) reduction. Initially, the relationship between RCS reduction and phase difference with different reflection amplitudes is analyzed theoretically. Inspired by the shared-aperture principle, a high-frequency resistive layer is introduced into the antenna element to further fulfill ultra-wideband RCS reduction and low-profile requirements. Numerical simulations demonstrate that the inserted layer has no effect on the radiation performance of the antenna array. Then, the proposed element and its orthogonal unit are arranged in a checkerboard pattern for good CP radiation. In this configuration, the proposed metasurface array antenna has a maximum gain of 16.7 dBi with 72.1% aperture efficiency. The bandwidth of 5 dB RCS reduction with x- and y-polarized incidences is 7.10–17.95 GHz and 7.34–17.85 GHz, respectively. The proposed design is verified by the fabrication of prototype antennas and measurements. [ABSTRACT FROM AUTHOR]

This paper analyzes broadband antennas, with a special focus on Vivaldi antennas, for their suitability for through-wall radar applications. It assesses various antenna designs, emphasizing high gain, wide impedance bandwidth, and effective wall penetration capabilities. Vivaldi antennas are superior due to their broad bandwidth, high gain, and directional radiation patterns. This study further explores structural optimizations, feeding techniques, and performance enhancement strategies to refine Vivaldi antenna designs for through-wall radar systems. Through a comparative analysis and technical evaluation, this paper highlights Vivaldi antennas' potential for improving through-wall radar systems' imaging and sensing capabilities. This presents a pathway for future ultra-wideband advancements. [ABSTRACT FROM AUTHOR]

We present a technique for the detection of vertebrate skeletons buried at shallow depths through the use of a ground-penetrating radar (GPR). The technique is based on the acquisition of high-resolution data by medium-to-high frequency GPR antennas and the analysis of the radar profiles by a new forward modelling method that is applied on a set of representative traces. This approach allows us to obtain synthetic traces that can be used to build detailed reflectivity diagrams that plot spikes with a distinct amplitude and polarity for each reflector in the ground. The method was tested in a controlled experiment performed at the top of Cerro Los Quesos, one of the most fossiliferous localities in the Ica Desert of Peru. We acquired GPR data at the location of a partially buried fossil skeleton of a large whale and analyzed the reflections associated with the bones using the new technique, determining the possible signature of vertebrae, ribs, the cranium (including the rostrum), and mandibles. Our results show that the technique is effective in the mapping of buried structures, particularly in the detection of tiny features, even below the classical (Ricker and Rayleigh) estimates of the vertical resolution of the antenna in civil engineering and forensic applications. [ABSTRACT FROM AUTHOR]

Array antennas have an interesting role in the radio astronomy field. The array antennas allow astronomers to obtain high-resolution signals with high sensitivity to weak signals. This paper estimates the meteors' positions entering the Earth's atmosphere and develops a simulation for array antenna radar to analyze the meteor's echoes. The GNU radio software was used to process the echoes, which is a free open-source software development toolkit that provides signal processing blocks to implement in radio projects. Then, the simulation determines the azimuth and elevation of the meteors. An improved Multiple Signal Classification (MUSIC) algorithm has been suggested to analyze these echoes. The detected power of each meteor echo has a Doppler frequency shift due to the high speed of the meteors, which impacts the accuracy of the Direction of Arrival (DOA) estimation. The Doppler shift was considered in this simulation, and the results showed that the suggested method has low complexity and high resolution and can estimate the meteors' position with the minimum error. [ABSTRACT FROM AUTHOR]

In this paper, the cloaked slot antennas (CSAs) in a circular conducting cylinder have been proposed, numerically studied, and fundamentally characterized with respect to the pulsed radar aspects. The two cylindrically slotted antennas have been introduced, namely the axially slotted cloaked antenna and the circumferentially slotted cloaked antenna (CSCA). These two cloaked slot antennas have been parametrically studied to explore the antenna's resonant characteristics together with their cloaking performance. The resonant frequency of the antennas is controlled by the parameters of the aperture of the slot such as width and length, while independently cloaking the CSAs at the cloaking frequency controlled by the parameters of the coated metasurface. The characteristics of the dual-mode operation at resonant and cloaking frequencies have been intensively studied by pulsed radar signal processing. The modulated Gaussian pulse with the modulation frequency being either resonant or cloaking frequency is used as an excitation source. Several scenarios have been proposed and studied to characterize the cloaking performance and communication capacity of the cloaked slot antennas. The radiating pulse from the CSAs has been numerically characterized by a pulse radar signal processing with an interval of 22.5° in terms of the theta and phi polarizations. These two CSAs have directive and omnidirectional characteristics in the theta- and phi-polarization, respectively. [ABSTRACT FROM AUTHOR]

Combining multiple data sources, Digital Earth is an integrated observation platform based on air–space–ground–sea monitoring systems. Among these data sources, the Inverse Synthetic Aperture Radar (ISAR) is a crucial observation method. ISAR is typically utilized to monitor both military and civilian ships due to its all-day and all-weather superiority. However, in complex scenarios, multiple targets may exist within the same radar antenna beam, resulting in severe defocusing due to different motion conditions. Therefore, this paper proposes a multiple-target ISAR imaging method with the removal of micro-motion connections based on the integration of joint constraints. The fully motion-compensated targets exhibit low rank and local similarity in the high-resolution range profile (HRRP) domain, while the micro-motion components possess sparsity. Additionally, targets display sparsity in the image domain. Inspired by this, we formulate a novel optimization by promoting the low-rank, the Laplacian, and the sparsity constraints of targets and the sparsity constraints of the micro-motion components. This optimization problem is solved by the linearized alternative direction method with adaptive penalty (LADMAP). Furthermore, the different motions of various targets degrade their inherent characteristics. Therefore, we integrate motion compensation transformation into the optimization, accordingly achieving the separation of rigid bodies and the micro-motion components of different targets. Experiments based on simulated data demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The radar of the Yagi-Uda antenna array offers useful traits for the detection of stealth targets. It employs the Very High Frequency (VHF) band, which has the advantage of counteracting stealth technology, as the shape of the target and the absorbing materials used for absorbing radar signals are less efficient against VHF. Moreover, the meter wavelength enables the radar to detect targets at distances exceeding those accessible to millimeter- and centimeter-wave radars. Nevertheless, the range of detection of this type of radar remains constrained and requires further development. The majority of current research is concentrated on the signal processing aspect, with less focus being placed on the antenna array. The antenna elements represent a crucial component of the radar station. This article presents a novel development of the traditional 16-element Yagi-Uda antenna array, which is commonly used in surveillance radar systems operating at a meter frequency band. The development is achieved through a modification of the previously mentioned antenna, which aims to increase the directivity of the antenna array, with a minimum cost and the same signal processing as the original antenna array platform. An additional two-row Yagi-Uda antenna array is proposed, comprising 14 elements in each row and an associated power unit. This modification is designed to enhance the pattern characteristics of the array. Simulation and measurement results for the pattern of the antenna indicate that the achieved gain for the proposed modification is more than 3 dB in compression compared to that of the traditional 16-element array. [ABSTRACT FROM AUTHOR]

Achieving a compact-size, high-performance antenna covering the K-Ka bands is not an easy task. A Multi-Input Multi-Ooutput (MIMO) funnel-shaped wideband antenna for RADAR applications is introduced in this paper. One of the flaws of the MIMO antenna is its size. In modern communications, the space given for an antenna is minimal due to the compact size of the communication devices. In the present work, by keeping space occupancy in mind, two element compact antennas, with 76x34x1.6 mm3 size, operating bandwidth of 24.7 GHz, isolation greater than 18.9 dB, and gain of 9.26 dB, were designed. The designed funnel shape patches and defective ground structure provide better gain and isolation, therefore allowing for larger bandwidth. Furthermore, the simulated and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

Samples with compositions of Sr2Sn1−xMnxO4(SSM) with 0 ≤ x ≤ 0.10 are prepared by conventional ceramic route via heat treatment at 1350 °C. Phase and crystal structure analysis is studied using X‐ray diffraction and Rietveld refinement to confirm the crystallization of samples in the tetragonal structure under space group I4/mmm. The size‐strain plot method is employed to identify the role of Mn on crystallite size/microstrain/dislocation density. The scanning electron microscope and energy‐dispersive X‐ray spectroscopy analysis confirm a significant change in the grain size and compositional homogeneity of all samples with Mn‐doping. Dielectric properties of samples are explained in terms of interfacial and orientation polarization of dipoles SnSn4+2+″−VO⋅⋅;2Mn2Mn3+2+′−VO⋅⋅$S n_{\left(\text{Sn}\right)^{4 &amp;amp;amp;amp;amp;plus;}}^{2 &amp;amp;amp;amp;amp;plus;} ^{&amp;amp;amp;amp;amp;aposx; &amp;amp;amp;amp;amp;aposx;} - V_{O}^{\cdot \cdot} ; 2 M n_{2 \left(\text{Mn}\right)^{3 &amp;amp;amp;amp;amp;plus;}}^{2 &amp;amp;amp;amp;amp;plus;} ^{&amp;amp;amp;amp;amp;aposx;} - V_{\text{O}}^{\cdot \cdot}$. Modulus studies show the exclusion of electrode contribution from the electrical properties. The single‐segment circular dielectric resonator antenna is designed with the help of experimental dielectric parameters and showed two major resonant frequencies at 3.6 and 6.7 GHz. The reduction in the S11 parameter and −10 dB reflection coefficient bandwidth with Mn‐doping observed due to overlapping of the E‐field line suggests the application in patch array antenna for radar and satellite communication applications. This study also enables to explore Sr2SnO4‐based Ruddlesden Popper oxide for antenna and mm‐wave communication applications. [ABSTRACT FROM AUTHOR]

The authors propose a novel dual coprime frequency diverse array (FDA) multiple input multiple output (DCFDA‐MIMO) radar network design, empowered by cognitive capabilities, aimed at target discrimination and mitigation of interference present in the standalone radar systems. That is, the proposed DCFDA‐MIMO design capitalises on the complementary advantages of FDAs for target discrimination and coprime arrays for enhanced resolution, resulting in superior performance. Additionally, the proposed DCFDA‐MIMO network employs a 2D multiple signal classification algorithm to achieve high‐resolution target localisation. By incorporating cognitive techniques based on the action‐perception cycle, the proposed approach demonstrates notable improvements in multiple target detection and tracking accuracy with fewer number of antenna elements as compared to existing techniques. Furthermore, it enhances individual radar beamforming performance for interference suppression and true target detection without prior information. [ABSTRACT FROM AUTHOR]

Industrial radar applications like tank level measurement is an important research and application area in radar technology. Radar level measurement is a safe solution even under extreme process conditions (pressure, temperature) and vapors. Special antennas are required to meet electromagnetic requirements such as high gain, low sidelobe level and high bandwidth. The small side-beam level and narrow main beam primarily minimize reflections from the side of the tank, while the bandwidth determines the distance resolution of the measurement system. Another requirement is a small size and good manufacturability of the antenna. The main promising solutions are the use of microstrip, horn or dielectric lens antennas for tank level measurement systems. After several tests, we have concluded that the optimal choice for tank level radar measurement task, in terms of integrability and antenna parameters, is a dielectric antenna. The dielectric antenna has many other applications in modern mobile systems as 5 and 6 G systems where these antennas are elements of antenna arrays of beamforming or MIMO systems. In this paper, a special dielectric lens antenna is presented, satisfying main requirements, namely a circular antenna cross section, high antenna aperture efficiency and low sidelobe level. The center frequency of the antenna is 26 GHz with a bandwidth of 1 GHz. The paper presents the analytic investigation and design of the dielectric lens antenna and the circular waveguide transition in detail. The electromagnetic design of the antenna was carried out using CST Microwave Studio 3D software. [ABSTRACT FROM AUTHOR]

Splendid Unmanned Aerial Vehicle (UAV) applications upshot its enormous use in densely inhabited areas, which is a matter of concern. In such areas, a proper tracking system is required to track an unauthorized/invader drone to ensure safety. With the flexibility of reaching inaccessible places, an Unmanned Aerial Vehicle Mounted Adaptable Radar Antenna Array (UAVMARAA) could be used. In this regard, a Hybrid Unscented Kalman-Continuous Ant Colony Filter (HUK-CACF) is proposed to estimate the position of the invader drone efficiently. Simulation results demonstrate the efficiency and robustness of the proposed filter for tracking system compared to the existing filters in terms of success rate. Further, for various Adaptable Radar Antenna Array (ARAA) patterns such as Uniform Linear Array (ULA), Uniform Rectangular Array (URA), and Uniform Circular Array (UCA), analysis is done for pertaining actual tracking effect for various parameters such as bearing, Doppler shift, ranging, and Radar Cross Section (RCS) by considering wobbling and mutual coupling (MC) effect. The result shows that the proposed filter outperforms in all the scenarios. Among the various ARAA, URA performs better than the other configurations. • The UAVMARAA patrols to track invading drones precisely while smartly navigating its surroundings. • ULA, URA, and UCA configurations are considered for ARAA, which re-tunes itself for better invader drone information, accounting for wobbling and MC effects. • A new filter is proposed to reduce tracking error, analyzed for various parameters including bearing. [ABSTRACT FROM AUTHOR]

This article introduces a novel microstrip slot antenna array (SAA) configuration for radar applications. The proposed antenna is specifically designed for operation in the K-band, spanning from 23 to 24.3 GHz. The antenna structure comprises two substrates: the feed network and ground plane are on the bottom substrate, and the radiating slots are on the top layer of the first substrate. The incorporation of a unique grid feed configuration, featuring 50 Ohm center excitation for the first time, improves the feed mechanism of the microstrip SAA. This innovation contributes to achieving a compact size and high gain. To enhance the side lobe level, the design incorporates a substrate-integrated waveguide-backed cavity, which significantly reduces surface waves. The SAA consists of 25 radiating elements with a gain of 14 dBi. In the elevation and azimuth planes, the half-power beamwidths are measured at 12.1° and 69.1°, respectively. The proposed antenna array's measured impedance bandwidth ranges from 23.15 to 24.75 GHz, guaranteeing a reflection coefficient (S11) of less than − 10 dB. The suggested antenna's applicability for automotive multi-input multi-output radar has been validated. [ABSTRACT FROM AUTHOR]

In this study, a millimeter-wave far-field range antenna measurement system is proposed for W-band monopulse antenna measurements. Since the W-band monopulse antenna installed in radar systems has many input/output ports, multiple calculations are required to measure all the ports. We propose a system structure capable of the simultaneous measurement of multiple channels to quickly and accurately measure the performance of a monopulse antenna. The proposed measurement system includes a multi-channel rotary joint, a pair of diplexers, and multiple vector network analyzer extenders. In addition, an RF sub-system is implemented to reliably measure the phase of the W-band radiation pattern. It utilizes a shared local oscillator source and external power amplifiers for the transmit and receive paths. Employing the proposed multi-channel antenna measurement system, the sum/difference channels of a monopulse antenna were simultaneously measured according to the azimuth angle. In addition, a comparison of the far-field measurements provided by the proposed system and the near-field measurements was conducted. [ABSTRACT FROM AUTHOR]

In view of the nonlinear self interference coupling problem between the transmitting and receiving antennas of radar jammer, a nonlinear self interference cancellation method based on spline interpolation is studied. The method combines spline interpolation and adaptive filtering, and establishes the spline-based Wiener model and the spline-based Wiener model respectively. By introducing the robust arctangent (ARC) function as the cost function, the adaptive learning rules of the spline control points and filter coefficients under the two models are obtained, and the influence of the number of spline control points on the performance of the self-interference cancelation i analyzed. Simulation experiments show that for signals with a bandwidth of 60 MHz, the proposed ARC-based parameter learning method achieves about 4 dB improvement in the interference cancelation ratio compared with the traditional least mean square parameter learning methods, and the convergence speed can be improved by a factor of one. In addition, the method has good tracking performance and low steady-stale error for the scenario of sudden channel change. When non-Gaussian pulse interference exists in the background noise, the proposed method can effectively cope with the interference in the impulse noise environment. [ABSTRACT FROM AUTHOR]

The evolution of charge structure involved in lightning discharge of a thunderstorm over the central Tibetan Plateau is investigated for the first time, based on the data from very high frequency interferometer, radar and sounding. During the developing‐mature stage, the TP thunderstorm exhibited a tripolar charge structure evolved from an initial inverted dipole. At the mature stage, a bottom‐heavy tripole charge structure is clearly presented, with a strong lower positive charge center (LPCC) at temperatures above −10°C, a middle negative charge region between −30°C and −15°C, and an upper positive charge region at T < −30°C. As the LPCC was depleted, the charge structure evolved into a normal tripole with a pocket LPCC. The merging between different convective cells resulted in the formation of two adjacent negative charge regions located directly and obliquely above the LPCC, and horizontally arranged different charge regions were simultaneously involved in the same lightning discharge. Plain Language Summary: Tibetan Plateau thunderstorms usually exhibit special convective structures. Using the data from the accurate lightning VHF interferometer, electric field mill, fast/slow antenna and C‐band radar, the evolution of the charge structure of thunderstorms and their influence on lightning discharges are investigated. Our observation for the first time revealed the charge structure evolution of the central‐TP thunderstorm which involved in the lightning discharge, exhibiting a bottom heavy tripole charge structure with a large LPCC in the mature stage evolved from an initial inverted dipole and the usual tripole in the dissipating stage of the thunderstorm. Under different magnitudes of the LPCC, different types of lightning discharges including ‐IC, +IC and ‐CG flashes were generated, indicating the crucial effects of LPCC on the lightning discharge types. Key Points: The charge structure of the TP thunderstorm evolves from an initial inverted dipole to a mature stage tripole with a strong LPCCHorizontally distributed negative charge zones from cell merger are simultaneously involved in the discharge of a single lightning flashDifferences in the relative magnitude of LPCC leads to various types of lightning discharges [ABSTRACT FROM AUTHOR]

A graphene-based tunable polarization conversion metasurface (PCM) was designed and analyzed for the purpose of reducing the radar cross-section (RCS) of array antennas. The metasurface comprises periodic shuttle-shaped metal patches, square-patterned graphene, and inclined grating-patterned graphene. By adjusting the Fermi energy levels of the upper (μ1) and lower (μ2) graphene layers, different states were achieved. In State 1, with μ1 = 0 eV and μ2 = 0.5 eV, the polarization conversion ratio (PCR) exceeded 0.9 in the bandwidths of 1.65–2.19 THz and 2.29–2.45 THz. In State 2, with μ1 = μ2 = 0.5 eV, the PCR was greater than 0.9 in the 1.23–1.85 THz and 2.24–2.60 THz bands. In State 3, with μ1 = μ2 = 1 eV, the PCR exceeded 0.9 in the 2.56–2.75 THz and 3.73–4.05 THz bands. By integrating the PCM with the array antenna, tunable RCS reduction was obtained without affecting the basic radiation functionality of the antenna. In State 1, RCS reduction was greater than 10 dB in the 1.60–2.43 THz and 3.63–3.72 THz frequency ranges. In State 2, the RCS reduction exceeded 10 dB in the 2.07–2.53 THz, 2.78–2.98 THz, and 3.70–3.81 THz bands. In State 3, RCS reduction was greater than 10 dB in the 1.32–1.43 THz, 2.51–2.76 THz, and 3.76–4.13 THz frequency ranges. This polarization conversion metasurface shows significant potential for applications in switchable and tunable antenna RCS reduction. [ABSTRACT FROM AUTHOR]

In recent years, the significance of millimeter wave sensors has achieved a paramount role, especially in the non-invasive and ubiquitous analysis of various materials and objects. This paper introduces a novel IoT-based fake currency detection using millimeter wave (mmWave) that leverages machine and deep learning algorithms for the detection of fake and genuine currency based on their distinct sensor reflections. To gather these reflections or signatures from different currency notes, we utilize multiple receiving (RX) antennae of the radar sensor module. Our proposed framework encompasses three different approaches for genuine and fake currency detection, Convolutional Neural Network (CNN), k-nearest Neighbor (k-NN), and Transfer Learning Technique (TLT). After extensive experiments, the proposed framework exhibits impressive accuracy and obtained classification accuracy of 96%, 94%, and 98% for CNN, k-NN, and TLT in distinguishing 10 different currency notes using radar signals. [ABSTRACT FROM AUTHOR]

Modern fighter aircraft increasingly need to conjugate aerodynamic performance and low observability. In this paper, we showcase a methodology for a gradient-based bidisciplinary aero-stealth optimization. The shape of the aircraft is parameterized with the help of a CAD modeler, and we optimize it with the SLSQP algorithm. The drag, computed with the help of a RANS method, is used as the aerodynamic criterion. For the stealth criterion, a function is derived from the radar cross-section in a given cone of directions and weighed with a function whose goal is to cancel the electromagnetic intensity in a given direction. Stealth is achieved passively by scattering back the electromagnetic energy away from the radar antenna, and no energy is absorbed by the aircraft, which is considered as a perfect conductor. A Pareto front is identified by varying the weights of the aerodynamic and stealth criteria. The Pareto front allows for an easy identification of the CAD model corresponding to a chosen aero-stealth trade-off. [ABSTRACT FROM AUTHOR]

Electronic warfare equipment estimates the azimuth and elevation of an unknown target by processing radar echoes received from monopulse or array antennas and interrupts radar sensing by transmitting jamming signals to the target. However, state-of-the-art targets maneuver at low altitudes in a sea surface environment to deliberately produce interference through multi-path, which poses a significant challenge for accurately estimating the estimation of the elevation angle. In this study, we propose an algorithm to accurately estimate the elevation angle of a low-altitude target despite the presence of a few arrays. Assuming that the sampled complex echoes are obtained after down-converging from the X-band (i.e., 10 GHz) to the base band, the proposed method demodulates the unknown linear frequency modulation using particle swarm optimization (PSO) and estimates the elevation angle by exploiting the new Fourier relationship between the wavelength and elevation angle. The simulation results suggest that our proposed method can successfully estimate the elevation angle for low-altitude maneuvering targets in a sea-surface environment. [ABSTRACT FROM AUTHOR]

Abstract The author reveals that the power pattern for a particular selected rotating spherical electric current density profile exhibits the following two properties simultaneously: (a) fully omnidirectional in three dimensions (3‐D) and (b) invariant with regards to radio frequency (RF). Specifically, most known antenna designs exhibit either nodal lines or planes for at least some RF frequencies. In contrast, the primary innovation of the subject rotating electric current sphere is that it generates a power pattern that is characterised by no nodal lines nor nodal planes for any RF frequency. In the present analysis, the electro‐magnetic (EM) fields are calculated as an exact solution of Maxwell's equations for the subject electric current density that rotates azimuthally on a spherical surface. As expected, the spatial structure of the resulting EM fields also rotates azimuthally. More surprisingly, this rotating electric current density generates pure magnetic dipole radiation exactly, with the absence of any higher order multipole moments. This proposed antenna concept could offer utility in various applications, including communications beaconing and radar surveillance.

In a software-defined radar (SDR) system, most of the signal processing usually implemented in hardware is implemented by software, thus allowing for higher flexibility and modularity compared to conventional radar systems. However, the majority of SDR demonstrators and proofs of concept reported in the open literature so far have been based on simple antenna systems. As a result, the full potentialities of an SDR approach have not been completely exploited yet. In this work, we propose a flexible antenna module to be integrated into an active electronically scanning array (AESA) with controlled sidelobe level over a wide angular range, exhibiting polarization reconfigurability with a low cross-polarization level and high isolation. For this purpose, analytical and numerically efficient techniques for the synthesis of the aperture distribution and the correct evaluation of the radiating features (e.g., beamwidth, pointing angle, sidelobe levels, etc.) are presented in order to grant real-time control of the digital beamforming network. A sub-array module demonstrator is fabricated and measured to corroborate the concept. [ABSTRACT FROM AUTHOR]

High-frequency radars (HFRs) provide remote information on ocean surface velocity in extended coastal areas at high resolutions in space (O (km)) and time (O (h)). They directly produce radial velocities (in the radar antenna's direction) combined to provide total vector velocities in areas covered by at least two radars. HFRs are a key element in ocean observing systems, with several important environmental applications. Here, we provide an assessment of the HFR-TirLig network in the NW Mediterranean Sea, including results from the gap-filling open-boundary modal analysis (OMA) using in situ velocity data from drifters. While the network consists of three radars, only two were active during the assessment experiment, so the test also includes an area where the radial velocities from only one radar system were available. The results, including several metrics, both Eulerian and Lagrangian, and configurations, show that the network performance is very satisfactory and compares well with the previous results in the literature in terms of both the radial and total combined vector velocities where the coverage is adequate, i.e., in the area sampled by two radars. Regarding the OMA results, not only do they perform equally well in the area sampled by the two radars but they also provide results in the area covered by one radar only. Even though obviously deteriorated with respect to the case of adequate coverage, the OMA results can still provide information regarding the velocity structure and speed as well as virtual trajectories, which can be of some use in practical applications. A general discussion on the implications of the results for the potential of remote sensing velocity estimation in terms of HFR network configurations and complementing gap-filling analysis is provided. [ABSTRACT FROM AUTHOR]

This article introduces a comprehensive Mode-S radar simulation, designed to evaluate interrogation and reply signal functionality in various uplink formats (UFs) and downlink formats (DFs). Mode-S radar, crucial in modern aviation, facilitates communication between aircraft and ground systems, thereby enhancing aircraft tracking, situational awareness, and air traffic safety. Our simulation focuses on optimizing interrogation and reply sequences in the 1030- and 1090-MHz channels, respectively. It provides a practical solution for testing complex air flight scenarios, which may be impractical or costly in real life, by replicating challenging conditions in a computerized environment. This approach aids in developing advanced radar signaling algorithms for air traffic control. The simulator’s user-friendly interface displays real-time aircraft data, demonstrating its realworld applicability. Its successful operation underscores its potential to advance Mode-S radar technology and its value for research in the field. [ABSTRACT FROM AUTHOR]

Over 9 years of hourly surface current data from high‐frequency radar (HFR) off the US West Coast are analyzed using a Bayesian least‐squares fit for tidal components. The spatial resolution and geographic extent of HFR data allow us to assess the spatial structure of the non‐phase‐locked component of the tide. In the frequency domain, the record length and sampling rate allow resolution of discrete tidal lines corresponding to well‐known constituents and the near‐tidal broadband elevated continuum resulting from amplitude and phase modulation of the tides, known as cusps. The FES2014 tide model is used to remove the barotropic component of tidal surface currents in order to evaluate its contribution to the phase‐locked variance and spatial structure. The mean time scale of modulation is 243 days for the M2 constituent and 181 days for S2, with overlap in their range of values. These constituents' modulated amplitudes are significantly correlated in several regions, suggesting shared forcing mechanisms. Within the frequency band M2 ± 5 cycles per year, an average of 48% of energy is not at the phase‐locked frequency. When we remove the barotropic model, this increases to 64%. In both cases there is substantial regional variability. This indicates that a large fraction of tidal energy is not easily predicted (e.g., for satellite altimeter applications). The spatial autocorrelation of the non‐phase‐locked variance fraction drops to zero over a distance of 150 km, a scale that is comparable to the swath width of the Surface Water and Ocean Topography altimeter. Plain Language Summary: Tides in the ocean encompass both the highly predictable daily changes in sea level seen from the shore as well as a less predictable component that changes over time depending on seasonal conditions and wind. Tidal signals are detectable at the ocean surface, for example, via satellite or land‐based radar antenna. The time‐evolving tide signals interact with other processes in the ocean, like currents, and can become harder to predict and describe. Many studies have examined this aspect of tides. In this work, we use land‐based radar observations of ocean currents off the US West Coast to examine this process with high detail, using mathematical techniques to separate the tides from everything else and then evaluating how much the tide has been altered by other processes. This is useful because ocean‐observing satellites can observe a single part of the ocean only when the satellite passes overhead, approximately every 10–20 days, while the data we analyze are sampled hourly and thus more easily allow us to draw conclusions about how tides behave. Key Points: In the California Current System, High‐Frequency Radar resolves stationary and non‐stationary tidesBroadband cusps occur at tidal constituent frequencies, with M2 exhibiting annual modulationWe analyze the tidal modulation to assess physics governing non‐stationary tidal variability [ABSTRACT FROM AUTHOR]

It is necessary to have a reconfigurable antenna for multi-function radar. The same antenna can be used for search, tracking, and imaging applications across a wide range of frequencies. The monopole antenna is suitably etched in its patch to achieve ultra-wideband (UWB) performance, while the modification of the partial ground to have an electromagnetic band gap (EBG) structure and rectangle slots improves the operational bandwidth that extends between 2.7 GHz and 12 GHz. The inclusion of a stub in the microstrip feed along with partial ground brings size miniaturization up to 63%. The perturbation of "L"-shaped slots at the corners of the rectangular patch and loading of left-hand metamaterial (LHM) into the monopole antenna realize circular polarization and also increase the gain of the antenna to 5.68 dBi. The inclusion of a filter across the feedline of the proposed antenna modifies the antenna's frequency/bandwidth in some desirable fashion, which provides bandwidth reconfiguration. The proposed antenna uses a step feed that offers better impedance matching over the wide operating bandwidth. [ABSTRACT FROM AUTHOR]

Integration of sensing and communication (ISAC) is pivotal for realizing the full spectrum of 6G networks, where aerial networks composed of unmanned aerial vehicles (UAVs) emerge as significant enhancers by establishing line-of-sight connections and increasing the coverage of terrestrial networks. Although network slicing can cater to diverse ISAC applications, strategies specifically for ISAC remain unexplored. This article proposes a lightweight scheme for network slicing in an aerial network with ISAC capability to maximize the service-level agreement (SLA) satisfaction ratio (SSR) by jointly optimizing the 3D placement and bandwidth resource allocation of UAVs. The scheme determines the 3D positions of the UAVs based on the locations of users served by high-priority slices and the SSRs of all slice requests. Then the scheme uses a minimum-weight matching algorithm for energy-efficient UAV path planning. Extensive simulations reveal our proposed scheme’s efficiencies in terms of resource allocation, cost savings, and energy savings. [ABSTRACT FROM AUTHOR]

Weight-size optimization is the main challenge of high-power antenna design. This paper presents a low-profile, metasurface-based wideband antenna. The proposed antenna comprises an N-type-to-waveguide transition to excite the metasurfaces and handle high-power excitations. A metasurface array of 4x4-unit cells is integrated into the waveguide. The proposed waveguide is 3D printed, and its internal faces are covered by copper tape to maintain a low weight (less than 200 g). The prototype is experimentally tested, and the results confirm the prototype's functionality from 2.1 GHz to 3.6 GHz with a bandwidth of 52.6% and a peak gain of 8.5 dBi. Furthermore, the high-power handling capability of the proposed design has been experimentally confirmed by exciting it with a 7 kV pulsed source. These results demonstrate the applicability of the proposed antenna in radar applications and wireless communication between Unmanned Aerial Vehicles (UAVs). [ABSTRACT FROM AUTHOR]

This study focused on the detection of water inrush in tunnels excavated by full-section hard rock tunnel boring machines (TBMs) and employed ground penetrating radar methods for conducting research on radar signal processing algorithms. The research demonstrates that conventional techniques are inadequate for eliminating the interference of TBM equipment on radar signal propagation. This study employs a radar antenna array method for signal transmission, utilizing a wavelet double-threshold filtering algorithm and wave propagation theory to suppress clutter. These methods exhibit strong signal reception capabilities and are effective in eliminating 13.1% of the direct wave components. The adoption of a novel, efficient radar signal imaging algorithm simplifies the imaging process. Results of verification indicate that the synthetic aperture algorithm, enhanced with cross-correlation calculation, yields the optimal imaging effect. This investigation, which was conducted in conjunction with the construction of a diversion tunnel in a specific region, has confirmed the applicability of the ground penetrating radar method for the detection of water inrush in TBM tunnels by conducting a comparative analysis of the direct wave removal algorithm and the integration of the optimal imaging algorithm. The innovative application of ground penetrating radar within TBM tunnels, along with a targeted technology to mitigate signal interference from metal equipment, has led to the selection of an appropriate algorithm for both signal processing and imaging. This approach offers a novel solution for the detection of water source disasters in TBM tunnels. [ABSTRACT FROM AUTHOR]

The author reveals that the power pattern for a particular selected rotating spherical electric current density profile exhibits the following two properties simultaneously: (a) fully omnidirectional in three dimensions (3‐D) and (b) invariant with regards to radio frequency (RF). Specifically, most known antenna designs exhibit either nodal lines or planes for at least some RF frequencies. In contrast, the primary innovation of the subject rotating electric current sphere is that it generates a power pattern that is characterised by no nodal lines nor nodal planes for any RF frequency. In the present analysis, the electro‐magnetic (EM) fields are calculated as an exact solution of Maxwell's equations for the subject electric current density that rotates azimuthally on a spherical surface. As expected, the spatial structure of the resulting EM fields also rotates azimuthally. More surprisingly, this rotating electric current density generates pure magnetic dipole radiation exactly, with the absence of any higher order multipole moments. This proposed antenna concept could offer utility in various applications, including communications beaconing and radar surveillance. [ABSTRACT FROM AUTHOR]

This paper presents the design of a 60 GHz millimeter-wave (MMW) slot array horn antenna based on the substrate-integrated waveguide (SIW) structure. The novelty of this device resides in the achievement of a broad impedance bandwidth and high gain performance by meticulously engineering the radiation band structure and slot array. The antenna demonstrates an impressive impedance bandwidth of 14.96 GHz (24.93%), accompanied by a remarkable maximum reflection coefficient of −39.47 dB. Furthermore, the antenna boasts a gain of 10.01 dBi, showcasing its outstanding performance as a high-frequency antenna with a wide bandwidth and high gain. To validate its capabilities, we fabricated and experimentally characterized a prototype of the antenna using a probe test structure. The measurement results closely align with the simulation results, affirming the suitability of the designed antenna for radar sensing applications in future global industrial scenarios. [ABSTRACT FROM AUTHOR]

A frequency-tunable patch antenna with reduced radar cross section (RCS) based on absorbing metamaterial is proposed. By controlling the external voltage of the varactor diodes, the working frequency of the patch can be adjusted. Through an investigation of the composite structure of the patch and absorbing metamaterial, RCS reduction is achieved over the entire wide tunable frequency range of the antenna. Measured results illustrate that the proposed patch antenna can dynamically operate in the range from 2.28 to 3.6 GHz with a gain variation of 7.1–8.7 dBi. Meanwhile, the RCS can be reduced by at least 7 dB and up to 20 dB in a fractional bandwidth of 44.9% of the antenna under a normal incidence. In comparison to conventional RCS-reduced antennas, the proposed one features a broader frequency tuning range and has potential value in wideband radar systems under complex electromagnetic interference environments. [ABSTRACT FROM AUTHOR]

Pulse repetition interval modulation (PRIM) is integral to radar identification in modern electronic support measure (ESM) and electronic intelligence (ELINT) systems. Various distortions, including missing pulses, spurious pulses, unintended jitters, and noise from radar antenna scans, often hinder the accurate recognition of PRIM. This research introduces a novel three-stage approach for PRIM recognition, emphasizing the innovative use of PRI sound. A transfer learning-aided deep convolutional neural network (DCNN) is initially used for feature extraction. This is followed by an extreme learning machine (ELM) for real-time PRIM classification. Finally, a gray wolf optimizer (GWO) refines the network's robustness. To evaluate the proposed method, we develop a real experimental dataset consisting of sound of six common PRI patterns. We utilized eight pre-trained DCNN architectures for evaluation, with VGG16 and ResNet50V2 notably achieving recognition accuracies of 97.53% and 96.92%. Integrating ELM and GWO further optimized the accuracy rates to 98.80% and 97.58. This research advances radar identification by offering an enhanced method for PRIM recognition, emphasizing the potential of PRI sound to address real-world distortions in ESM and ELINT systems. [ABSTRACT FROM AUTHOR]

Purpose. Development of a new approach to improving the accuracy of orientation based on radar reflections from local objects and a digital terrain model. Methodology. The research is based on the theory of radiation, reflection and reception of radar signals. Statistical analysis of a large volume of recorded signals establishes causal relationships between the appearance of “false” reflections formed by the back lobe of the radiation pattern and to develop a computational algorithm for their suppression. Findings. A method and software that allows detecting and suppressing “false” reflections formed by the rear lobe of the antenna pattern without distorting the reflections created by the main lobe. For this purpose, a criterion has been developed, determined by the ratio of the amplitude of the signal received by the front lobe to the amplitude of the signal recorded by the rear lobe. The criterion allows eliminating the “false” signals without having a priori information about the real radiation pattern using a regulator for the reduction of phantom reflections to an average noise level. Originality. For the first time, suppression has been carried out of “false” reflections without having a priori information about the real radiation pattern of the radar station antenna, as well as elimination of the loss of informativeness of the real reflection formed by the main lobe. Practical value. A method is suggested of radar immunity of radar stations is noise immunity due to “false” reflections. The potential of the method and the capabilities of the developed computer program determines the relevance of their capabilities for use by all radar stations at various frequencies, azimuths, ranges and terrain features. [ABSTRACT FROM AUTHOR]

In this paper, a double-layer patterned graphene-based frequency-selective absorber (DGFSA) is proposed as a means of reducing an antenna's radar cross-section (RCS) while simultaneously increasing its gain. The antenna consists of a patch antenna with Multi-Graphene Frequency Selective Absorber (MGFSA) mounted on top. The DGFSA consists of double-layer patterned graphene and a band-pass frequency selective surface (FSS). Two patterned graphene lossy layers with different square resistances are used, which broaden the electromagnetic (EM) wave absorption bandwidth of the DGFSA, thus greatly reducing the out-band monostatic RCSs of the patch antenna. Meanwhile, due to the quasi-Fabry-Perot (F-P) effect, the gain of the proposed antenna is enhanced by 2.4 dB. Additionally, the low-RCS antenna reduces the monostatic RCS from 1.32 to 17 GHz under y-polarization and from 1.4 to 16.8 GHz under x-polarization, respectively. Furthermore, a decrease in the bistatic RCS is accomplished. Results from simulations and measurements match up nicely, which means the antenna we proposed has a good application on the stealth platform. [ABSTRACT FROM AUTHOR]