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For the research on real-time accurate testing technology for the explosion point spatial coordinate of munitions, its currently commonly used methods such as acoustic–electric detection or high-speed imaging are limited by the field conditions, response rate, cost, and other factors. In this paper, a method of spatial coordinate testing for the explosion point based on a 2D PSD (position-sensitive detector) intersection is proposed, which has the advantages of a faster response, better real-time performance, and a lower cost. Firstly, a mathematical model of the spatial coordinate testing system was constructed, and an error propagation model for structural parameters was developed. The influence of the position of the optical axes' intersection as well as the azimuth angle and pitch angle on the test accuracy of the system was simulated and analyzed, thus obtaining the distribution and variation trend of the overall error propagation coefficient of the system. Finally, experiments were designed to obtain the test error of the system for validation. The results show that the system test accuracy is high when the azimuth angle is 20°–50°, the overall error propagation coefficient does not exceed 48.80, and the average test error is 56.17 mm. When the pitch angle is −2.5°–2.5°, the system has a higher test accuracy, with the overall error propagation coefficient not exceeding 44.82, and the average test error is 41.87 mm. The test accuracy of the system is higher when the position of the optical axes' intersection is chosen to make sure that explosion points fall in the region of the negative half-axis of the Z w -axis of the world coordinate system, with an overall error propagation coefficient of less than 44.78 and an average test error of 73.38 mm. It is shown that a reasonable selection of system structure parameters can significantly improve the system test accuracy and optimize the system deployment mode under the long-distance field conditions so as to improve the deployment efficiency. [ABSTRACT FROM AUTHOR]

Synthetic aperture radar (SAR) inter-pulse parameter agility technology involves dynamically adjusting parameters such as the pulse width, chirp rate, carrier frequency, and pulse repetition interval within a certain range; this effectively increases the complexity and uncertainty of radar waveforms, thereby countering active deceptive interference signals from multiple dimensions. With the development of active deceptive interference technology, single-parameter agility can no longer meet the requirements, making multi-parameter joint agility one of the main research directions. However, inter-pulse carrier frequency agility can cause azimuth Doppler chirp rate variation, making azimuth compression difficult and compensation computationally intensive, thus hindering imaging. Additionally, pulse repetition interval (PRI) agility leads to non-uniform azimuth sampling, severely deteriorating image quality. To address these issues, this paper proposes a multi-parameter agile SAR imaging scheme based on traditional frequency domain imaging algorithms. This scheme can handle joint agility of pulse width, chirp rate polarity, carrier frequency, and PRI, with relatively low computational complexity, making it feasible for engineering implementation. By inverting SAR images, the echoes with multi-parameter joint agility are obtained, and active deceptive interference signals are added for processing. The interference-suppressed imaging results verify the effectiveness of the proposed method. Furthermore, simulation results of point targets with multiple parameters under the proposed processing algorithm show that the peak sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) are improved by 12 dB and 10 dB, respectively, compared to the traditional fixed waveform scheme. [ABSTRACT FROM AUTHOR]

The transmit/receive-receive (T/R-R) synergetic High Frequency Surface Wave Radar (HFSWR) has increasingly attracted attention due to its high localization accuracy, but multi-target pairing needs to be performed before localization in multi-target scenarios. However, existing multi-target parameter matching methods have primarily focused on track association, which falls under the category of information-level fusion techniques, with few methods based on detected points. In this paper, we propose a multi-target pairing method with high computational efficiency based on angle information for T/R-R synergetic HFSWR. To be more specific, a dual-receiving array signal model under long baseline condition is firstly constructed. Then, the amplitude and phase differences of the same target reaching two subarrays are calculated to establish the cross-correlation matrix. Subsequently, in order to extract the rotation factor matrices containing pairing information and improve angle estimation performance, we utilize the conjugate symmetry properties of the uniform linear array (ULA) manifold matrix for generalized virtual aperture extension. Ultimately, azimuths estimation and multi-target pairing are accomplished by combining the propagator method (PM) and the ESPRIT algorithm. The proposed method relies solely on angle information for multi-target pairing and leverages the rotational invariance property of Vandermonde matrices to avoid peak searching or iterations, making it computationally efficient. Furthermore, the proposed method maintains superb performance regardless of whether the spatial angles are widely separated or very close. Simulation results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

High-resolution wide-swath (HRWS) imaging has emerged as a focal point in synthetic aperture radar (SAR) research. However, conventional SAR systems face challenges in achieving both high azimuth resolution and wide swath simultaneously due to the minimum antenna area constraint. In this paper, we propose a HRWS imaging method based on multifrequency pulse diversity (MFPD) and azimuth multichannel (AMC) technique, capable of resolving range and Doppler ambiguities concurrently. In MFPD mode, range ambiguous echoes can be separated by matched filters in the range frequency domain, as multifrequency pulses are transmitted by a single channel in the transmitter. To further enhance the ambiguity resolution ability of the system and address azimuth incoherence, a novel scheme applying the MFPD to AMC system is proposed, categorized into two distinct scenarios. 1) Uniform Sampling: This scenario satisfies the displaced phase centre antenna condition. Under this condition, high range resolution imaging can be achieved through spectrum splicing in range frequency domain, simultaneously resolving Doppler ambiguity. 2) Non-uniform Sampling: In this scenario, the ambiguous echoes are processed by spatial digital beamforming and spectrum splicing in two-dimensional frequency domain. Finally, the HRWS imaging can be obtained by performing the traditional SAR algorithm. Furthermore, the proposed method can synthesize a wideband signal from multifrequency signals, thereby enhancing the feasibility of super-high-resolution imaging. Simulation results demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The stratum can be modelled as a horizontal transversely isotropic medium when a single set of vertically parallel fractures embedded in an isotropic background medium, which facilitates efficient study for fractured reservoirs. Elastic parameters and fracture weaknesses are important parameters to describe the characteristics of fractured reservoirs, and seismic inversion plays a significant role in parameters estimation. The commonly used deterministic inversion methods do not fully utilize the prior information and fails to present the uncertainty analysis of inversion results. To address these shortcomings, we propose a Bayesian linearized amplitude variation with offset and azimuth inversion method tailored for horizontal transversely isotropic media, enabling a more robust analysis of uncertainty. Within the framework of Bayesian inversion, the proposed method successfully derives analytical expressions for the posterior mean and covariance of both elastic parameters and fracture weaknesses. The response characteristics of the anisotropic reflection coefficient are analysed, and it is found that the perturbations of elastic parameters have a greater effect on reflection coefficient compared to fracture weaknesses. Synthetic data examples confirm that the accuracy of estimated P‐ and S‐wave velocities and density surpasses that of fracture weaknesses, and the proposed method still performs well for the case of moderate noise. A field data example demonstrates that the inverted profiles agree well with the logging curve, and the estimated fracture weaknesses display significantly high values in the reservoir area. The estimated reservoir parameters not only contribute to a more accurate representation of the fractured gas‐bearing reservoir but also provide insights into the target gas reservoir through its posterior distribution. Both synthetic and field data examples demonstrate the stability and reliability of the proposed method in characterizing fractured reservoirs. We determine that the proposed method provides an available tool for nuanced evaluation of uncertainty for the inversion results, and it is helpful for the fine description of fractured hydrocarbon‐bearing reservoirs. [ABSTRACT FROM AUTHOR]

The shipborne High-Frequency Hybrid Sky-Surface Wave Radar integrates a sky-wave transmitting channel and a ground-wave receiving channel on a shipborne platform. This hybrid radar system combines a skywave source with the added flexibility of a far-away shipborne radar. Ionospheric stratification and height uncertainty introduce uncertainties in the sky-wave channel, resulting in multiple measurements of one target. Additionally, the shipborne platform position is affected by sea state, causing errors in azimuth accuracy setting and subsequently reducing target tracking precision. In this paper, we propose for the first time a target tracking method that combines ionospheric variations with the motion of a shipborne platform. It introduces the variational Bayesian method into the multiple detection mode, which solves the effects of ionospheric altitude error and orientation error of shipborne platforms due to different sea states on target tracking. Simulation experiments validate the effectiveness of the proposed method. Therefore, the proposed method promises advancements in shipborne radar systems for maritime surveillance applications. [ABSTRACT FROM AUTHOR]

The Eccentric Connectivity Index (ECI) and Eccentric Distance Sum (EDS) are two important topological indices with wide applications in biology and chemistry. The Vicsek Fractal (VF) is a notable structure in both polymer physics and network science, and is also known as a regular hyperbranched polymer in the academic realm. In this study, the ECI and EDS of the VF are evaluated analytically by exploring the self-similarity of the structure. First, we derive the recurrence formulas for the ECI and EDS with respect to the generation t of the VF. Then, exact results for the ECI and EDS of the VF are obtained by solving the recurrence relations. The results indicate that the ECI and EDS of the VF scale with a network size of Nt are ECI ∼ Nt1+logp+13 and EDS ∼ Nt2+2logp+13, respectively. The results obtained not only reveal the biological activity and physical properties of the VF but also shed light on the control of the beamwidth in the azimuth plane and the design of the maglev centrifugal blood pump. [ABSTRACT FROM AUTHOR]

A snapshot multi-wavelength birefringence imaging measurement method was proposed in this study. The RGB-LEDs at wavelengths 463 nm, 533 nm, and 629 nm were illuminated with circularly polarized light after passing through a circular polarizer. The transmitted light through the birefringent sample was captured by a color polarization camera. A single imaging process captured light intensity in four polarization directions (0°, 45°, 90°, and 135°) for each of the three RGB spectral wavelength channels, and subsequently measured the first three elements of Stokes vectors (S0, S1, and S2) after the sample. The birefringence retardance and fast-axis azimuthal angle were determined simultaneously. An experimental setup was constructed, and polarization response matrices were calibrated for each spectral wavelength channel to ensure the accurate detection of Stokes vectors. A polymer true zero-order quarter-wave plate was employed to validate measurement accuracy and repeatability. Additionally, stress-induced birefringence in a PMMA arch-shaped workpiece was measured both before and after the application of force. Experimental results revealed that the repeatability of birefringence retardance and fast-axis azimuthal angle was better than 0.67 nm and 0.08°, respectively. This approach enables multispectral wavelength, high-speed, high-precision, and high-repeatability birefringence imaging measurements through a single imaging session. [ABSTRACT FROM AUTHOR]

Navigation system performance degrades significantly in complex environments. It is important to analyze satellite visibility through 3D terrain modelling and separate the satellite signals propagated by NLOS to suppress the NLOS error. However, the traditional 3D terrain modelling visibility analysis method based on the pure terrain cover angle is only suitable for determining the visibility of GNSS satellites and may incorrectly separate LOS propagate measurement signals from members with low relative ranges and elevation angles under air–ground swarm conditions. To this end, this paper proposes a belief-propagating cooperative navigation method based on air–ground visibility analysis, which avoids mistakenly separating close-range LOS cooperative navigation signals by simultaneously considering the distances, elevation angles, and azimuths of the signal sources relative to the air–ground swarm members. The simulation shows that the cooperative navigation NLOS identification method based on air–ground visibility analysis proposed in this paper can more accurately realize the separation of NLOS signals under cooperative conditions than the traditional pure angular 3D terrain modelling visibility analysis method can, and the localization error of the members to be assisted is significantly reduced. [ABSTRACT FROM AUTHOR]

A low-profile multi-port dual-band antenna with pattern and polarization diversity is presented for 2.45 and 5.8 GHz bands. The antenna consists of a monopolar patch for vertically polarized (VP) omnidirectional radiation and four combining printed-dipole and tapered-slot elements arranged in a circular shape for horizontally polarized (HP) multibeam radiation, and consequently, both pattern and polarization diversities are achieved in the full azimuth plane. The monopolar patch employs four vias and a square-ring slot to excite T M 01 and T M 02 modes at 2.45 and 5.8 GHz, respectively. Each HP element utilizes printed-dipole and tapered-slot modes for the lower and upper bands, respectively. The VP and HP elements are collocated with a common ground plane, which not only allows a low profile but also broadens the lower band of the monopolar mode. The final design with 0.03 λ 2.45 - G H z height yields a measured 10-dB return loss bandwidth of 8.6% and 6.7% at 2.45 and 5.8 GHz, respectively, and an isolation ≥ 20 dB among all the ports. Its pattern and polarization diversities are validated by far-field measurements. [ABSTRACT FROM AUTHOR]

Wind resistance performance research on the influence of the exterior features of high-rise buildings is an essential part of structure design. In this paper, the wind resistance tests of three high-rise building models with different concavity shapes on the horizontal plane were investigated using the wind tunnel experiment. The CAARC (Commonwealth Advisory Aeronautical Research Council) standard high-rise model was adopted as the background model (BG model for short), and the other two comparison groups with different planar configurations were designed, one with concave corners around the building (T1 model) and the other with concavity in the middle of the long side of the building (T2 model). The distribution laws of the average wind pressure coefficients of the building facades and roofs under the whole wind azimuths were analyzed comprehensively. The results show that the external shape plays a certain role in wind pressure distribution. Among the three high-rise building models, the most unfavorable positive wind pressure coefficient on the facades occurs in the T2 model (a 4.7% increment compared with the BG model), while the most unfavorable negative wind pressure coefficient appears in the T1 model (a 25% increment compared with BG model). Furthermore, it is noted that the architectural appearance of the T1 model makes the flow field around the building more streamlined, reflecting more favorable wind-resistance performance, including a maximum reduction of 47.2% in the least stresses per unit area on the roof. The research in this paper can provide some references for the design of different exterior features of high-rise buildings. [ABSTRACT FROM AUTHOR]

The satellite–ground bistatic configuration, which uses geosynchronous synthetic aperture radar (GEO SAR) for illumination and ground equipment for reception, can achieve wide coverage, high revisit, and continuous illumination of interest areas. Based on the analysis of the signal characteristics of GEO satellite–ground bistatic SAR (GEO SG-BiSAR), it is found that the bistatic echo signal has problems of azimuth spectrum aliasing and 2-D spatial variability. Therefore, to overcome those problems, a novel SAR imaging method for a GEO SG-BiSAR system with severe azimuth spectrum aliasing and 2-D spatial variability is proposed. Firstly, based on the geometric configuration of the GEO SG-BiSAR system, the time-domain and frequency-domain expressions of the signal are derived in detail. Secondly, in order to avoid the increasing cost caused by traditional multi-channel reception technology and the processing burden caused by inter-channel errors, the azimuth deramping is executed to solve the azimuth spectrum aliasing of the signal under the special geometric structure of GEO SG-BiSAR. Thirdly, based on the investigation of azimuth and range spatial variability characteristics of GEO SG-BiSAR in the Range Doppler (RD) domain, the azimuth spatial variability correction strategy is proposed. The signal corrected by the correction strategy has the same migration characteristics as monostatic radar. Therefore, the traditional chirp scaling function (CSF) is also modified to solve the range spatial variability of the signal. Finally, the two-dimensional spectrum of GEO SG-BiSAR with modified chirp scaling processing is derived, followed by the SPECAN operation to obtain the focused SAR image. Furthermore, the completed flowchart is also given to display the main composed parts for GEO SG-BiSAR imaging. Both azimuth spectrum aliasing and 2-D spatial variability are taken into account in the imaging method. The simulated data and the real data obtained by the Beidou navigation satellite are used to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The measurement of the target azimuth angle using forward-looking radar (FLR) is widely applied in unmanned systems, such as obstacle avoidance and tracking applications. This paper proposes a semi-supervised support vector regression (SVR) method to solve the problem of small sample learning of the target angle with FLR. This method utilizes function approximation to solve the problem of estimating the target angle. First, SVR is used to construct the function mapping relationship between the echo and the target angle in beamspace. Next, by adding manifold constraints to the loss function, supervised learning is extended to semi-supervised learning, aiming to improve the small sample adaptation ability. This framework supports updating the angle estimating function with continuously increasing unlabeled samples during the FLR scanning process. The numerical simulation results show that the new technology has better performance than model-based methods and fully supervised methods, especially under limited conditions such as signal-to-noise ratio and number of training samples. [ABSTRACT FROM AUTHOR]

Semianalytical design approach to a triple‐mode resonant, wideband null frequency scanning sectorial monopole antenna is proposed. As is demonstrated, TE3/5,1, TE9/5,1, and TE3,1 mode within a 150°, circumferentially resonant sectorial monopole are simultaneously excited to realize null frequency scanning functionality. The prototype antenna exhibits a wide impedance bandwidth of 75.3%, ranging from 1.40 to 3.09 GHz. Within the frequency band of 1.55–2.70 GHz, the radiation null linearly scans from θ = +90° to +8° with a null frequency scanning sensitivity of 12.9 MHz/°. Moreover, the antenna possesses maximum gain of 2.5 dBi in the backfire, ‐x‐direction, which indicates that it should exhibit quasi‐unidirectional radiation pattern in the azimuth plane. [ABSTRACT FROM AUTHOR]

With the development of virtual reality, the projection design of the head-mounted display (HMD) requires improvement as well. The surface relief grating (SRG) is one of the popular diffraction elements to achieve light guiding through the waveguide. Using the SRG as the coupler, incoming information light can be coupled into the waveguide by the 1-order diffraction. To increase possible design options for the HMD, SRG with complex geometry has been designed to fit more diffraction conditions. In this paper, a 2D SRG is proposed to form by periodically arranging slanted glass pillars on the surface of a glass waveguide, just like a photonic crystal. The structure can suppress all the other diffraction orders except the 0-order and the [1, 0] order. The best diffraction efficiency of the [1, 0] order can be obtained when the incident light is incident with not only an incident angle but also an azimuth angle. The geometric parameters of the pillars are investigated and optimized with the diffraction efficiency by the finite element method, and the relationship between the incident angles and the diffraction efficiency will also be discussed. The proposed structure has the potential in both the in-coupler and the out-coupler, respectively, for integrating light coming from different azimuth angles or for outputting light to different azimuth angles. [ABSTRACT FROM AUTHOR]

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This study investigated a frequency-selective surface (FSS) that is used to suppress harmonics affecting the performance and accuracy of radar systems. One side of the FSS features a metal grid structure, and when converted into an equivalent circuit model, it exhibits the characteristics of a band-pass filter with an L and C parallel structure. The other side of the FSS features a metallic loop structure and when represented as an equivalent circuit model, it exhibits the characteristics of a band-stop filter with an L and C series structure. The reflection coefficient ( S 11 ) and transmission coefficient ( S 21 ) of the FSS designed based on theory are compared using a CST studio suite and Keysight's Advanced Design System. In addition, the transmission coefficients are verified through actual measurements, wherein the measured transmission coefficient is −0.1 dB at 3.0 GHz and approximately −50 dB at the harmonic frequency of 6.0 GHz. The designed FSS is attached to an actual radar system, and the 2D radiation pattern and maximum gain are measured during steering in boresight, azimuth ( 30 ∘ ) and elevation ( 30 ∘ ) directions. At 3.0 GHz, the maximum gain in boresight is 17.25 dB without the FSS and 17.12 dB with the FSS. At 6.0 GHz, the maximum gain is 12.79 dB without the FSS and 2.69 dB with the FSS. At 3.0 GHz, the maximum gain during azimuth steering is 16.13 dB without the FSS and 16.68 dB with the FSS, and the maximum gain during elevation steering is 15.74 dB without the FSS and 15.90 dB with the FSS. [ABSTRACT FROM AUTHOR]

Near-space high-altitude balloon-based platforms have a series of advantages and provide superior conditions for optical observation. In order to ensure the stability of the optical axis of the optical detection load and stable tracking of the target, a near-space high-altitude balloon-based high-precision pointing and tracking system was designed, which can compensate for changes in the pitch angle and azimuth angle of the platform during flight. The system includes a primary platform stable pointing system and a secondary precise tracking system. In the finished flight experiment, the primary platform pointing system and secondary precise tracking system on the balloon-based observation platform worked normally, providing a guarantee for the coronagraph's stable tracking and detection of the sun. The primary platform pointing system can realize ±1° pointing accuracy, and the simulated accuracy of the secondary precise tracking system is 4″, which guaranteed that the coronagraph obtained more than 20,000 images. In subsequent works, we will upgrade and optimize the whole system and conduct our next flight experiment in the future. [ABSTRACT FROM AUTHOR]

Inverse synthetic aperture radar (ISAR) imaging techniques are frequently used in target classification and recognition applications, due to its capability to produce high-resolution images for moving targets. In order to meet the demand of ISAR imaging for electromagnetic calculation with high efficiency and accuracy, a novel accelerated shooting and bouncing ray (SBR) method is presented by combining a Graphics Processing Unit (GPU) and Bounding Volume Hierarchies (BVH) tree structure. To overcome the problem of unfocused images by a Fourier-based ISAR procedure under wide-angle and wide-bandwidth conditions, an efficient parallel back projection (BP) imaging algorithm is developed by utilizing the GPU acceleration technique. The presented GPU-accelerated SBR is validated by comparison with the RL-GO method in commercial software FEKO v2020. For ISAR images, it is clearly indicated that strong scattering centers as well as target profiles can be observed under large observation azimuth angles, Δ φ = 90 ° , and wide bandwidths, 3 GHz. It is also indicated that ISAR imaging is heavily sensitive to observation angles. In addition, obvious sidelobes can be observed, due to the phase history of the electromagnetic wave being distorted resulting from multipole scattering. Simulation results confirm the feasibility and efficiency of our scheme by combining GPU-accelerated SBR with the BP algorithm for fast ISAR imaging simulation under wide-angle and wide-bandwidth conditions. [ABSTRACT FROM AUTHOR]

In modern warship, coordinated combat strategies require missiles hit targets simultaneously, sometimes even require angle constraints, which is difficult to replicate in three-dimensional (3-D) models. This paper proposes a novel 3-D sliding mode guidance law with multiple constraints. First, the 3-D no-thrust guidance model is derived in the coordinate system with Y -axis upward. Second, a novel guidance strategy is proposed. In pitch direction, a fast nonsingular sliding mode surface algorithm is proposed to satisfy the desired line-of-sight elevation angle. In yaw direction, based on the guidance conditions, a special sliding mode surface is proposed, which can achieve desired line-of-sight azimuth angle and desired impact time when reaching the sliding surface. Finally, simulations and comparisons verify the good performance. [ABSTRACT FROM AUTHOR]

Point cloud completion aims to restore full shapes of objects from their partial views obtained by 3D optical scanners. In order to make point cloud completion become more robust to azimuthal rotations and more adaptive to real-world scenarios, we propose a novel network for simultaneous rotation invariant and equivariant completion with no need of data augmentation, while other existing approaches require separately trained models for different completion types. Our method includes several main steps: First, Density Compensation Mapping (DCM) as well as Aggregative Gaussian Gridding (AGG) modules are introduced to transfer partial point clouds to spherical signals and avoid unbalanced sampling. Second, an encoder based on group correlation is designed to extract rotation invariant global features and equivariant azimuthal features from spherical signals. Third, parallel groups of decoders are proposed to realize rotation invariant completion based on feature fusion. Finally, a feature remapping module as well as Pose Voting Alignment (PVA) algorithm are proposed to unify feature space and realize rotation equivariant completion. Based on these modules, we find that the application of group correlation can be extended to the domain of shape completion; equivariant and invariant completions can be unified in one pipeline, and our inherent rotation equivariant and invariant framework can achieve competitive performances when comparing with existing representative methods. [ABSTRACT FROM AUTHOR]

In solar forecasting, it is common practice for solar data (be it irradiance or photovoltaic power) to be converted into a stationary index (e.g., clear-sky or clearness index) before being used as inputs for solar-forecasting models. However, its actual impact is rarely quantified. Thus, this paper aims to study the impact of including this processing step in the modeling workflow within the scope of very-short-term spatio-temporal forecasting. Several forecasting models are considered, and the observed impact is shown to be model-dependent. Persistence does not benefit from this for such short timescales; however, the statistical models achieve an additional 0.5 to 2.5 percentual points (PPs) in terms of the forecasting skill. Machine-learning (ML) models achieve 0.9 to 1.9 more PPs compared to a linear regression, indicating that stationarization reveals non-linear patterns in the data. The exception is Random Forest, which underperforms in comparison with the other models. Lastly, the inclusion of solar elevation and azimuth angles as inputs is tested since these are easy to compute and can inform the model on time-dependent patterns. Only the cases where the input is not made stationary, or the underperforming Random Forest model, seem to benefit from this. This indicates that the apparent Sun position data can compensate for the lack of stationarization in the solar inputs and can help the models to differentiate the daily and seasonal variability from the shorter-term, weather-driven variability. [ABSTRACT FROM AUTHOR]

Distributed Inverse Synthetic Aperture Radar (ISAR) systems employ multiple spatially separated radars to observe a target, with the potential to enhance radar imaging azimuth resolution and gather more target information. Due to the existence of gaps in the observation angles of each radars, the coherence between pulses of radar echo is disrupted during fusion imaging, making it challenging for the Range-Doppler (RD) algorithm to achieve well-focused images. This paper proposes an imaging method based on sparse signal recovery (SSR), using the reweighted ${l_1}$ l 1 norm with convolution and total variation as regularization terms. This approach not only yields well-focused ISAR images but also better preserves the overall target information compared to other methods, while also exhibiting excellent noise resistance. In addition, the alternating direction method of multipliers (ADMM) algorithm is utilized for the solution to reduce computational complexity. Simulation and measured data verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Azimuth multi-channel synthetic aperture radar (SAR) has always been an important technical means to achieve high-resolution wide-swath (HRWS) SAR imaging. However, in the space-borne azimuth multi-channel SAR system, random phase noise will be produced during the operation of each channel receiver. The phase noise of each channel is superimposed on the SAR echo signal of the corresponding channel, which will cause the phase imbalance between the channels and lead to the generation of false targets. In view of the above problems, this paper proposes a random phase noise compensation method for space-borne azimuth multi-channel SAR. This method performs feature decomposition by calculating the covariance matrix of the echo signal and converts the random phase noise estimation into the optimal solution of the cost function. Considering that the phase noise in the receiver has frequency-dependent and time-varying characteristics, this method calculates the phase noise estimation value corresponding to each range-frequency point in the range direction and obtains the phase noise estimation value by expectation in the azimuth direction. The proposed random phase noise compensation method can suppress false targets well and make the radar present a well-focused SAR image. Finally, the usefulness of the suggested method is verified by simulation experiments. [ABSTRACT FROM AUTHOR]

This letter proposes a novel planar endfire circularly polarized antenna with widened half‐power beamwidth. Widened azimuth beamwidth mechanism of 2D sectorial electric dipole is theoretically revealed, thus it is able to combine with a rectangular magnetic dipole to yield a half‐power beamwidth widened planar endfire circularly polarized antenna. Finally, a prototype planar endfire circularly polarized antenna with sectorial flared angle of α = 270° is fabricated, simulated, and implemented to validate the design approach. As investigated, the antenna exhibits broadened azimuth half‐power beamwidth of 150° over a frequency range of 2.40–2.45 GHz. [ABSTRACT FROM AUTHOR]

In order to address the problems of range ambiguity and azimuth ambiguity in the wide-swath imaging of synthetic aperture radar (SAR), this paper proposes a multi-beam SAR two-dimensional ambiguity suppression method based on azimuth phase coding (APC). The scheme employs an elevation simultaneous multi-beam transmission system with azimuth under-sampling, transmitting different APC waveforms to various range-ambiguous sub-regions. After receiving the echoes, the azimuth digital beamforming (DBF) is used to separate the APC waveform echoes with multi-order Doppler ambiguity, achieving azimuth reconstruction and range ambiguity suppression simultaneously. Finally, the elevation nulling DBF is used to further suppress range ambiguity and obtain the SAR wide-swath image. The superiority of this scheme is reflected in the following aspects: the azimuth DBF simultaneously suppresses azimuth and range ambiguity, the influence of height fluctuations on the ability to suppress range ambiguity is weakened, the use of elevation nulling DBF further enhances the level of range ambiguity suppression, and different range sub-regions can adopt different range resolutions and working modes. The feasibility of this scheme is verified through theoretical analysis and simulation. [ABSTRACT FROM AUTHOR]

Beamforming is an effective way of resolving target direction and anti‐jamming in short wave (SW) radar systems. In conventional beamforming (CBF) at a certain frequency, to get high resolution, the array aperture should be increased, and this is often not allowed in practical applications. A new narrow beam forming (NBF) method for beam sharpening based on the generalised oblique projection (GOP) filter with a flexible parameter is proposed. This method uses a GOP filter bank to form deep nulls in the undesired azimuth range on the pattern and utilises the logic product process to synthesise the GOP filters' outputs and thus obtains a narrow beam. Compared to traditional beamforming methods, the result of NBF has the characteristics of narrower beam width and bigger side lobe suppression ratio (SLSR). Especially, a narrower beam can be obtained in the case of a small array aperture, which is valuable for practical applications. Experimental results of the range‐Doppler spectrum of short wave radar show that this narrow beam forming method can achieve super resolution of targets within a wide beam and greatly suppress clutter. Therefore, NBF can improve the azimuth resolution and achieve interference suppression in a conventional beam. [ABSTRACT FROM AUTHOR]

The algorithm proposed in this study estimates the multipath elevation of targets at low altitudes, including near-zero elevation. Although the double null algorithm is a maximum likelihood elevation estimation algorithm, it diverges when the target elevation is near zero. Addressing this issue, the selective double null algorithm improves the accuracy of multipath elevation at low altitudes by applying previously measured antenna near-field patterns. However, it cannot be applied to active electronically scanned array radars, since antenna beam patterns vary with the steered azimuth and elevation angles. In this paper, the proposed algorithm modifies the double null algorithm to estimate the elevation in the divergence state more accurately. Since it is based on the multipath energy function, the antenna near-field pattern is unnecessary. In addition, to increase the accuracy of elevation estimation, an operation method that selectively uses the estimated elevations according to several conditions is proposed. The proposed algorithm was verified through simulations. [ABSTRACT FROM AUTHOR]

In this paper, a multifunctional transmit-array antenna with beam steering and polarization conversion capabilities for the X-band is presented. The proposed design offers advantages in terms of scalability, faster development and deployment, and ease of maintenance owing to its modular design, which is configured by a receiver, an active circuit, a DC bias control line, and a transmitter. The proposed design is capable of 2D beam scanning of up to ±45° for azimuth and elevation while converting vertical or horizontal polarization by electronic control. To verify its performance, a 16×16 array transmit-array antenna is fabricated and tested using a near-field measurement system. It exhibits a maximum gain of 23.7 dBi, the sidelobe level of 14 dBc, the polarization conversion loss of below 1 dB, and the polarization isolation of above 10 dB. The measurement results agree well with the simulation. [ABSTRACT FROM AUTHOR]

Synthetic aperture radar (SAR) can take images of ship targets at sea all-day and all-weather. However, the azimuth defocus of moving ships in high resolution SAR images has seriously affected the subsequent recognition for ship targets. Due to the non-cooperative nature of ship motion, the defocus characteristics of complex moving ship in SAR images have not been well understood. In this paper, based on the principle of SAR imaging, it has been theoretically deduced that the spatial-variability and time-variability of SAR echo signal phase errors caused by complex ship motion are the decisive factors that lead to the degradation of SAR image quality. On this basis, a SAR imaging simulator for complex moving ship targets is constructed. By simulating SAR imaging of ship point, line, and surface targets at different motion states and synthetic aperture times, the spatial/temporal defocus characteristics of SAR imaging for complex moving ship targets are revealed. Among them, spatial variability can cause non-uniform defocus of ships in SAR images. Time variability causes the ship to transform into an azimuthal energy band in SAR images. Finally, based on the spatial/temporal defocus characteristics, the development direction of future SAR motion ship refocusing technology is discussed. [ABSTRACT FROM AUTHOR]

Radar direction finding is an essential cooperative monitoring method for aircraft, and the directional parameters of the direction finding antenna determine the accuracy of direction finding. A modified amplitude comparison direction finding model is proposed based on the traditional principle of adjacent amplitude comparison direction finding and the error of amplitude comparison direction finding. Based on the correction of amplitude comparison direction finding model, an error correction genetic simulated annealing (COR-GSA) algorithm is proposed to identify unknown directional antenna directionality parameters by determining the antenna directionality parameters that need to be identified. Identification experiments are conducted using a self-designed dual channel direction finding receiver, and 1 000 sets of aircraft real azimuth data are used for verification. The results show that using the COR-GSA algorithm to identify antenna directional parameters has the highest direction finding accuracy. Finally, the identified antenna directionality parameters are used to track the aircraft's azimuth, and the tracking error is reduced by 18. 3% compared to the tracking error without azimuth correction. [ABSTRACT FROM AUTHOR]

A circular antenna array with omnidirectional mode and 360° continuously directional beam-scanning mode operating in 5G indoor communication band is reported. The proposed circular antenna array is composed of 16 subarray elements, and each element consists of two back-to-back E-shaped patch antennas with a differential feeding network. The beam-scanning mode is achieved by controlling the exciting amplitudes and phases of consisting subarray elements, which is optimized by using the extended method of maximum power transmission efficiency, so as to guarantee the maximum possible gain value. The operating frequency of the circular array covers 3.3-3.6 GHz. The omnidirectional gain is about 4.7 dBi, while the directive gain reaches 16 dBi with 360° continuously beam-scanning capability and very slight gain fluctuation in the azimuth plane. The comparison with other state-of-the-art designs shows that the proposed circular array has both higher directional and omnidirectional gain values. [ABSTRACT FROM AUTHOR]

Modern small satellite development represents a new trend, a new design idea, and it can be used as a transmitter to assist helicopter monitoring. The imaging model of the arc array bistatic SAR with a small satellite transmitter is studied. Due to the long resident time of small satellite platform and the wide-area observation capability of arc antenna, it has a wide application prospect in the field of earth detection and remote sensing. However, the motion state of the small satellite and the special scanning mode of the arc antenna have some effects on the SAR imaging results. Therefore, the imaging geometry of the arc array bistatic SAR with a small satellite transmitter is established, and an improved Chirp Scaling imaging algorithm is proposed. Firstly, the motion compensation function is used to compensate the migration caused by the high-speed motion of the small satellite. Then, the two-dimensional spectrum is derived by using standing phase principle and scaling function. Next, the coupling between range and azimuth is compensated by consistent range migration correction and secondary range compression, and residual phase is compensated in azimuth frequency domain. Finally, simulation results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The article is devoted to the improvement of the design of a desalination solar plant for more efficient and economical production of desalinated water due to intensive evaporation of the boiling solution, reduction of energy losses to the external environment and the absence of the need for continuous adjustment of the direction of the light-receiving part of the solar plant. The expedient parameters of the angles of inclination of the optical axis of the lens relative to the azimuth and the incidence vector of solar radiation, which ensure high performance of the solar plant, were experimentally substantiated. The use of a solar collector equipped with an additional heat accumulator will allow water to be supplied for desalination at a temperature of more than 50 °C in sunny weather, and at a temperature of 33–36 °C in variable cloudiness, which will help to increase the efficiency of the desalination solar plant. The presence of a heat accumulator and a layer of thermal insulation under cloudy [ABSTRACT FROM AUTHOR]

Although estimating the azimuth using a geomagnetic sensor is very useful, the estimation error may be very large due to the surrounding geomagnetic disturbance. We proposed a novel method for preprocessing appropriately for geomagnetic and inertial sensor data to be suitable for the proposed Artificial Neural Network model and training method for the model. As a result, the probability of azimuth estimation error within 1 degree is 96.4% with regression estimation. For classification estimation, when the azimuth estimation probability is 90% or more, the probability that the azimuth estimation error is within 1 degree is 100%.

For ultra-high-resolution (UHR) squint spotlight airborne synthetic aperture radar (SAR), the severe range-azimuth coupling caused by squint mode and the spatial and frequency dependence of the motion error brought by ultra-wide bandwidth both make it difficult to obtain satisfactory imaging results. Although some autofocus methods for squint airborne SAR have been presented in the published literature, their practical applicability in UHR situations remains limited. In this article, a new 2D wavenumber domain autofocus method combined with the Omega-K algorithm dedicated to UHR squint spotlight airborne SAR is proposed. First, we analyze the dependence of range envelope shift error (RESE) and range defocus on the squint angle and then propose a new spectrum modification strategy, after which the spectrum transforms into a quasi-side-looking one. The accuracy of estimation and compensation can be improved significantly in this way. Then, the 2D phase error can be calculated with the 1D estimated error by the mapping relationship, and after that the 2D compensation is performed in the wavenumber domain. Furthermore, the image-blocking technique and range-dependent motion error compensation method are embedded to accommodate the spatial-variant motion error for UHR cases. Simulations are carried out to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A broadband single‐layer reflectarray comprising three‐layer concentric split ring elements is proposed. The reflection phase is achieved by changing the flare angle of the inner and outer split rings. The resonance of the element is easily controlled by varying the relative relationships between the homomorphic patches. And the length of the split ring changes in the azimuth direction, which improves the utilization rate of unit space. The middle split ring acts as a parasitic structure with constant size, making the surface current distribution of the element more uniform to improve the element bandwidth. A reflectarray containing 256 elements is designed and tested. The measured results indicate that the peak gain is 25.3 dBi corresponding to the aperture efficiency of 42%. And the 1‐dB gain bandwidth of the reflectarray of 21.7% is achieved. [ABSTRACT FROM AUTHOR]

With the rapid development of terahertz radar technology, the electromagnetic device for terahertz radar cross-section (RCS) reduction is worth investigating. However, the existing research concentrates on the RCS reduction metasurface with fixed performance working in the microwave band. This paper proposes a terahertz dynamic coding metasurface integrated with vanadium dioxide (VO2) for dual-polarized, dual-band, and wide-angle RCS reduction. The simulation result indicates that by switching the state of the VO2 between insulator and metal, the metasurface can realize the effective RCS reduction at 0.18 THz to 0.24 THz and 0.21 THz to 0.39 THz under the left-handed and right-handed circularly polarized incident waves. When the polar and azimuth angles of the incident wave vary from 0° to 40° and 0° to 360° respectively, this metasurface can maintain a 10 dB RCS reduction. This work has potential value in the terahertz stealth field. [ABSTRACT FROM AUTHOR]

High‐resolution gravity field models of the Moon established from Gravity Recovery and Interior Laboratory satellite gravity data have been playing an important role in understanding the interior structure and tectonic evolution of the Moon. Due to the correlations in the high degree and order term coefficients of the gravity field models, the difference between satellite flight orbits, and the random noise of instruments, the high‐resolution gravity anomalies data derived from the models of high degree and order usually present serious multi‐directional striping and random noise, which clearly affect the subsequent interpretation of the data. We provide an omnidirectional filtering method based on the polynomial‐fitting principle to remove multi‐directional striping noise in the lunar satellite gravity anomalies data. A set of azimuth parameters are chosen to suppress all the directions of striping noise. The algorithms of data partitioning and iterative optimization are utilized to make our method suitable and stable for large‐scale data sets. Tests on the synthetic data and the real data from the Moon's Rümker region and globally verified the feasibility of our method with a better destriping effect than the traditional Gaussian filtering or degree‐order‐truncation methods. Plain Language Summary: High‐resolution gravity anomalies derived from gravity field models are often disrupted by interference such as multi‐directional striping and random noise. The omnidirectional filtering method for destriping lunar satellite gravity data can solve this annoying problem by introducing a set of azimuth parameters and the algorithms of data partitioning and iterative optimization. Through theoretical model experiments and high‐precision satellite gravity data tests in the Moon's Rümker region, this study demonstrates our method has a better performance in striping and random noise removal compared to previous methods. This method holds potential for application to satellite gravity data of other planets or other satellite geophysical data. Key Points: The omnidirectional filtering method based on the polynomial‐fitting principle to remove multi‐directional striping noise in the lunar satellite gravity anomalies dataA set of azimuth parameters are chosen to suppress all the directions of striping noiseThe algorithms of data partitioning and iterative optimization are used to make our method suitable and stable for large‐scale data sets [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the trajectory of a hole drilled using a small-dimension drill bit (0.5 mm) in wood-based materials. Computer vision was used to determine the three-dimensional position of the hole. Scans were made to a depth of 5 mm every 0.5 mm (access to subsequent layers was obtained by milling with three three-blade cutter with a diameter of 26 mm). The obtained results allowed us to determine the parameters of the obtained hole, allowing to correlate the quantities, such as deviations (initial, relative, total) and angle of relative azimuth. A good correlation (R2 > 0.75) between total deviation and initial deviation for medium-density boards and hardboards can be found. The initial deviation of the drill determines the direction of the tool into the material and the initial deviation forces a specific direction of further deviation. [ABSTRACT FROM AUTHOR]

This study presents the electromagnetic data, detected in Italy with the Radio Direction Finding system, which preceded the earthquake of 5 April 2024. At 14:23:00 UTC a medium energy earthquake of M4 occurred. .8, in the United States, in New Jersey, Whitehouse station, a few kilometers from New York. The data discussed in this research are the result of continuous 24/7 monitoring and were considered to verify whether the direction of arrival of the electromagnetic signals can be associated with the direction of the future epicentral area, despite the considerable distance between the Rome station and New York. In particular, during the monitoring, low frequencies were recorded with the azimuth coming from the future epicentral area, already ten days before the earthquake occurred. Similar frequencies appeared, respectively, nine and four days before the earthquake. [ABSTRACT FROM AUTHOR]

The study determined optimum roof tilt and building azimuth for rooftop-based distributed photovoltaic (PV) energy generation in Ikeja, Lagos State, Nigeria, as strategic technological input to alternative power generation and new housing development in Metropolitan Lagos. The energy planning & foresight analysis methodology was used. The data were obtained via literature, Global Positioning System (GPS) systems, energy models, and site visits and comprised manual and satellite imagery, dimensions, roof angles, and coordinates of the building structures in the study area (Rows between 0 – 60o, Columns between 0 – 180o ; System sizes: 533 kW, 110 kW, and 0.547 kW). The results showed solar array yield varied from 768,944 kWh per annum for a 500 kVA system to 780 kWh per annum for a 0.5 kVA system. A five-tier rooftop generation template of 245 MWp was consequently developed. The systems ' optimal roof tilt and building azimuth angles were estimated to be 5o and 180o, respectively, though combinations of azimuth and tilt angles not exceeding 30o tilt and 90o azimuth gave acceptable yields. The study concluded that the optimum roof tilt and building azimuth for rooftop-based distributed photovoltaic (PV) energy generation in the study area were strategic policy intelligence inputs for the Federal and Lagos State governments' renewable power generation and new housing development programmes. [ABSTRACT FROM AUTHOR]

The polarization‐independent liquid crystal (LC) phase modulators can greatly improve the efficiency and reduce the complexity of the optical system. However, it is difficult for the LC phase modulator to achieve both good low‐loss modulation and polarization‐independent properties. A LC phase modulator of single layer multi‐microdomain orthogonal twisted (MMOT) structure is proposed which may achieve good polarization independence and low loss in different phase depth. A lightcontrolled azimuth angle (LCAA) process based on the rotation effect of cholesteric liquid crystal (CLC) is developed for the fabrication of the single layer MMOT structure. The measurement results showed that the single layer MMOT LC phase modulator may get very low polarization dependence, about 3.52% under 2Ï€ phase modulation depth, with low loss. The device shows good potential application in optical communication, wearable device, and display. [ABSTRACT FROM AUTHOR]

In current practices of determining continental shelf area, the measured sediment thickness data do not effectively reflect the distribution of sediments across the area due to its dispersed nature. This issue raises potential limitations in unknown optimal survey line layout strategies for maximizing the posterior determination area. This paper adopts the binary search algorithm, relies on existing sediment thickness grid data, and uses geodetic formulas to build an ellipsoidal surface grid distance calculation model. This model quickly screens potential areas for the 1% sediment thickness line candidate points set. By constraining the azimuth parameter values during the construction process of the ellipsoidal point feature buffer zones, efficiently select the candidate points set for the 1% sediment thickness line. Furthermore, by elucidating the essential meanings of points on the formula limit and combining the candidate points set of the foot of the continental slope (FOS)+60 n mile line, the polygon minimal convex hull construction technique and a baseline points optimization algorithm with a length threshold are used to efficiently select points on formula limit. Experimental results demonstrate that this method can effectively assist coastal states in optimizing the determination of continental shelf area to the fullest extent under the length threshold requirements of the United Nations Convention on the Law of the Sea. Experiments have proven that compared to the traditional intersection method, the method presented in this paper can help coastal countries delineate a larger continental shelf area. In typical application scenarios, the gain in area can reach 77,278,427 m2 accounting for 0.51% of the total area. [ABSTRACT FROM AUTHOR]

The shapes of mantle plumes are sensitive to mantle viscosity, density structure, and flow patterns. Increasingly, global tomographic models reveal broad plume conduits in the lower mantle and highly tilting conduits in the mid and upper mantle. Previous studies mostly relied on 2D slices to analyze plume shapes, but fully investigating the complexity of 3D plume structures requires more effective visualization methods. Here, we use immersive headset‐based virtual reality (VR) to visualize the full‐waveform global tomographic models SEMUCB‐WM1 and GLAD‐M25. We develop criteria for the identification of plume conduits based on the relationship between the plume excess temperature and the VS anomaly (δVS). We trace 20 major plume conduits, measure the offsets of the conduits in azimuth and distance with respect to the hotspots, calculate the tilt angle, and evaluate the δVS along all traced conduits. We compare our traced conduits with the conduits predicted by global mantle convection models and vertical conduits. The wavespeed variations along conduits traced from each tomographic model are slower than modeled or vertical conduits, regardless of which tomographic model they are evaluated in. The shapes of traced conduits tend to differ greatly from modeled conduits. Plume ponding and the emergence of secondary plumes, which could result from a combination of compositional variations, phase transitions, small‐scale convection, and variations in viscosity, can contribute to the complex observed plume shapes. The variation of δVS along the traced conduits and complex plume shapes suggest a thermochemical origin of many plumes. Key Points: The variation of shear velocity anomaly along the traced conduits and complex plume shapes suggest a thermochemical origin of many plumesWe identify complex plume shapes (ponding, branching, and merging) that suggest a complex rheological structure of the lower mantleWe provide systematic and quantitative observations of plume shapes that can benefit numerical modeling and geochemical studies of plumes [ABSTRACT FROM AUTHOR]

The mechanisms underlying bat and bird activity peaks (attraction) or losses (avoidance) near wind turbines remain unknown. Yet, understanding them would be a major lever to limit the resulting habitat loss and fatalities. Given that bat activity is strongly related to airflows, we hypothesized that airflow disturbances generated leeward (downwind) of operating wind turbines–via the so-called wake effect–make this area less favorable for bats, due to increased flight costs, decreased maneuverability and possibly lower prey abundance. To test this hypothesis, we quantified Pipistrellus pipistrellus activity acoustically at 361 site-nights in western France in June on a longitudinal distance gradient from the wind turbine and on a circular azimuth gradient of wind incidence angle, calculated from the prevailing wind direction of the night. We show that P. pipistrellus avoid the wake area, as less activity was detected leeward of turbines than windward (upwind) at relatively moderate and high wind speeds. Furthermore, we found that P. pipistrellus response to wind turbine (attraction and avoidance) depended on the angle from the wake area. These findings are consistent with the hypothesis that changes in airflows around operating wind turbines can strongly impact the way bats use habitats up to at least 1500 m from the turbines, and thus should prompt the consideration of prevailing winds in wind energy planning. Based on the evidence we present here, we strongly recommend avoiding configurations involving the installation of a turbine between the origin of prevailing winds and important habitats for bats, such as hedgerows, water or woodlands. [ABSTRACT FROM AUTHOR]