Search

Recent advances in radar seeker technologies have considerably improved missile precision and efficacy during target interception. This is especially concerning in the arenas of protection and safety, where appropriate countermeasures against enemy missiles are required to ensure the protection of naval facilities. In this study, we present a reinforcement-learning-based strategy for deploying decoys to enhance the survival probability of a target ship against a missile threat. Our approach involves the coordinated operation of three decoys, trained using the Multi-Agent Deep Deterministic Policy Gradient (MADDPG) and Multi-Agent Twin Delayed Deep Deterministic Policy Gradient (MATD3) algorithms. The decoys operate in a leader–follower dynamic with a circular formation to ensure effective coordination. We evaluate the strategy across various parameters, including decoy deployment regions, missile launch directions, maximum decoy speeds, and missile speeds. The results indicate that, decoys trained with the MATD3 algorithm demonstrate superior performance compared to those trained with the MADDPG algorithm. Insights suggest that our decoy deployment strategy, particularly when utilizing MATD3-trained decoys, significantly enhances defensive measures against missile threats. [ABSTRACT FROM AUTHOR]

A novel compact microwave metamaterial absorber structure with a wide bandwidth is proposed. The absorber structure is designed on an FR4 substrate with a 2.4 mm thickness. The metamaterial absorber unit cell design consists of a combination of W and S-shaped structures in which splits are incorporated to have the effect of a split ring resonator. The proposed unit cell structure is designed to have a wide absorption band, which includes the X and Ku frequency bands. The optimized dimension of the unit cell is 0.071 λ0 × 0.71 λ0 where λ0 is the wavelength of the center frequency of the absorption band. The WS-shaped structures are oriented to absorb TE and TM waves for a wide range of polarization angles. The simulation results of the unit cell have shown absorption above 95% from 10.48 to 13.28 GHz. In addition, the absorber has an efficiency above 92% for incidence angles from 0° to 60° for fixed polarization. The unit cell structure and array are fabricated, and measurements are performed. The simulation and measured results have shown good agreement. The proposed metamaterial can be used in defense and radar surveillance applications. [ABSTRACT FROM AUTHOR]

Studies commonly assumed that variations in ionospheric conductance were insignificant and proposed that vorticities can be a reliable proxy or diagnostic for ionospheric field‐aligned currents (FACs). We propose a complete method for measuring FACs using data from the Super Dual Auroral Radar Network radar and the Defense Meteorological Satellite Program. In our method, the FACs are determined by three terms. The first term is referred to as magnetospheric‐origin FACs, while the second and third terms are known as ionospheric‐origin FACs. This method incorporates height‐integrated conductances based on observational data, thereby addressing the limitation of assuming uniform conductances. Different from previous works, we can calculate FACs at a low altitude of 250 km and obtain high‐resolution measurements within observable areas. Another advantage of this method lies in its ability to directly calculate and analyze the impact of ionospheric vorticity and conductance on FACs. We apply this method to obtain FACs in the Northern Hemisphere from 2010 to 2016 and analyze the distributions of height‐integrated conductances and total FACs. Our analysis reveals that the average FACs clearly exhibit the large‐scale R1 and R2 FAC systems. We conduct statistical analysis on magnetospheric‐origin FACs and ionospheric‐origin FACs. Our findings show that within the auroral oval, ionospheric‐origin FACs reach a comparable level to magnetospheric‐origin FACs. However, ionospheric‐origin FACs are significantly minor and almost negligible in other regions. This implies that height‐integrated conductance gradients and vorticities play equally significant roles within the auroral oval, whereas vorticities dominate in other regions. Plain Language Summary: Field‐aligned currents (FACs) refer to current sheets that flow parallel or antiparallel to the geomagnetic field lines in the polar region. Typically, the intensity of FACs is estimated using magnetic perturbation measurements, while the current density is determined by the thickness of current sheets. In this study, we propose another method for calculating FACs based on ionospheric plasma vorticities and conductances. This method allows for FAC calculations at lower altitudes compared to previous methods. Additionally, we investigate the significance of vorticities and height‐integrated conductance gradients on FACs. Our findings reveal that both height‐integrated conductance gradients and vorticities significantly influence FACs in auroral emission areas. However, the influence of vorticities is more pronounced in other areas. Key Points: We proposed a complete method for measuring ionospheric field‐aligned currents (FACs)Within the auroral oval, both height‐integrated conductance gradients and vorticities play equally important rolesIn non‐auroral regions, vorticities take on a dominant role in influencing FACs [ABSTRACT FROM AUTHOR]

Ground-based radar systems are critical for physical and dynamical characterization of near-Earth objects (NEOs) and space debris. The operational aspect and applications of radar for planetary defense and space situational/domain awareness (SSA/SDA) are similar, but there are some factors that should be taken into account for an instrument to support both areas: planetary defense is focused on asteroids and comets in heliocentric orbit with perihelion distance <1.3 au. Special attention is given to potentially hazardous objects (PHOs), which are NEOs larger than 140 m that can come within 0.05 au (∼20 lunar distances) of Earth. Radar can quickly and accurately determine NEOs' future trajectory, therefore, the sooner an object can be observed, the safer it is to assess any possible threat. Radar is also useful to help obtaining information about the objects' properties to plan for an impact mitigation mission if needed. For SSA, the focus is artificial objects orbiting Earth. This document presents the radar capabilities of the legacy Arecibo telescope, and explores synergistic future concepts for planetary defense and SSA. • The Arecibo Observatory had the most powerful planetary radar system in the world. • Arecibo supported planetary defense that focuses on near-Earth asteroids and comets. • Ground-based radars are critical for characterization of near-Earth objects. • Space Situational Awareness uses ground-based radar for space debris studies. • Synergistic use of radar system for planetary defense and debris should be explored. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simultaneously developing protective electronics film for multi‐spectra, including the radar, infrared (IR), and visible ranges, for both the military and civilian sectors is extremely challenging. The existing multi‐spectra‐compatible materials mainly concentrate on either the radar/IR or IR/visible bands, trailing the rapid evolution of advanced devices for monitoring electromagnetic signals. Here, it is designed and fabricated an ultra‐thin MXene‐based composite film (20 µm) containing black phosphorus (BP) and Ni chains (M‐B‐M(Ni)) with integrated highly efficient thermal IR stealth, visible light absorption, and electromagnetic wave shielding. M‐B‐M(Ni) exhibits an extremely low IR emissivity of 0.1, decreasing the radiation temperature difference between the surrounding environment and target device. BP offers a high solar absorptance of 80%, which guarantees energy conversion from visible light to heat. Moreover, the absorption proportion of the electromagnetic shielding effectiveness for M‐B‐M(Ni) is 16% higher than that of pure MXene films (68.7%), owing to the improved magnetic loss by decoration with magnetic Ni chains. Due to the combined merits of MXene, BP, and Ni chains, M‐B‐M(Ni) opens an avenue for the construction of advanced multi‐spectra compatible materials for versatile applications in thermal IR stealth, electromagnetic wave shielding, and energy transformation. [ABSTRACT FROM AUTHOR]

Broad beam patterns are essential for typical navigation and target tracking. Significantly, these patterns are helpful for searching radar in defense applications. In this paper, the particle swarm optimization technique-based synthesis of the broad beam pattern of the linear antenna arrays (LAA) is presented. This synthesis technique employs all three design parameters known as the excitation amplitude, inter-element spacing, and the excitation phase to obtain the desired radiation pattern. The objective of this synthesis process involves defining the extent of the effective flat top, ripples through the flat top, and the sidelobe level. Linear array configuration produces desired sector patterns, and the comparisons of these patterns are performed in θ- domain. The consistency of the algorithm is evaluated by extending the study to different LAA lengths. The simulation-based experimentation is carried out in MATLAB, and the results are analyzed using the obtained radiation patterns. [ABSTRACT FROM AUTHOR]

Recently, as global space development and space risk have increased, in Korea, considerable attention has been diverted to the development of space surveillance radar (SSR) capable of wide-area and full-time monitoring. For the efficient development of domestic SSR, which is usually expensive, it is necessary to appropriately derive the requirements for SSR based on analyses of overseas advanced cases. In this study, based on an analysis of the space fence surveillance radar in the USA, the field of view for the search fence was set. By deriving and analyzing the maximum number of observable targets per day and the cumulative distribution of the duration of detection, a method was developed to derive the requirements for the search fence when developing a domestic SSR in the future. [ABSTRACT FROM AUTHOR]

This paper develops the model of the joint phantom track deception and the joint techniques of time-difference of arrival (TDOA) and frequency-difference of arrival (FDOA) localization to deceive air defense radar networks under the condition that an unmanned aerial vehicle (UAV) swarm has no prior knowledge of the radars' precise locations, and related performance experiment and analysis are presented to demonstrate the effectiveness of the proposed method and to clarify the influence factors of phantom track deception. The main contributions of this paper are as follows. Firstly, the model of phantom track deception against a radar network by UAV swarm without prior knowledge of the radars' positions are established. Secondly, TDOA/FDOA are adapted to locate networked enemy radars using UAV swarm, where the Fisher information matrix (FIM) is derived to evaluate the estimation accuracy. Thirdly, the uncertainty analysis consisting of radar location error and UAV position error is deduced. With these efforts, the integrated capability of sensing and jamming is realized. Moreover, the same source testing using space resolution cell (SRC) from the perspective of a radar network is executed to provide guidance for phantom track design. Finally, performance experiment and analysis are given to verify the theoretical analysis with simulation results. [ABSTRACT FROM AUTHOR]

Phage restriction by adenosine deaminase acting on RNA (RADAR) is a process by which bacteria may alter their own transcriptome to resist bacteriophage. In this issue of Cell , Duncan-Lowey and Tal et al. and Gao et al. both show RADAR proteins assemble into massive molecular complexes but present distinct views about how these assemblies obstruct phage. [ABSTRACT FROM AUTHOR]

Choosing a strategy for electronic conflicts in the field of action and situations similar to the problem scenario is a matter of experience and will not necessarily be the best possible choice. Therefore, the importance of providing a reasonable and measurable decision-making method in choosing a strategy in real conditions is quite clear. One of the points that can be deduced from the study of common methods and techniques in electronic warfare is that none of these methods are considered absolute winners and the holder can't consider himself the undisputed winner of the field. Because there is more or less the opposite of any technique. Using a method or tool in a situation may be very effective, but with a change of method or change of tool by the competitor, it becomes a weakness. Therefore, in this battle, the correct and timely use of each technique, and with full knowledge of the opponent and in accordance with the actions performed by him can be considered a factor of success and all useful tools in this field can be used. One of the most useful tools in the field of strategic decision analysis is game theory. With the help of this mathematical tool, the decision-making process between two or more decision-makers can be examined and the results can be analyzed. It is also possible to observe the effect of various parameters involved in the result of the problem, and to plan the result in the desired direction. In this paper, selecting the best response in different stages of the conflict to solve various such problems is achieved and the main purpose is to present a new approach to adopt a strategy and select the radar and disruptive coping technique in case of incomplete information from each other, using a method It is mathematical and algorithmic, so that we have a better performance in the benefit function of the parties. [ABSTRACT FROM AUTHOR]

This paper presents the flight penetration path planning algorithm in a complex environment with Bogie or Bandit (BB) threats for stealth unmanned aerial vehicle (UAV). The emergence of rigorous air defense radar net necessitates efficient flight path planning and replanning for stealth UAV concerning survivability and penetration ability. We propose the improved A-Star algorithm based on the multiple step search approach to deal with this uprising problem. The objective is to achieve rapid penetration path planning for stealth UAV in a complex environment. Firstly, the combination of single-base radar, dual-base radar, and BB threats is adopted to different threat scenarios which are closer to the real combat environment. Besides, the multistep search strategy, the prediction technique, and path planning algorithm are developed for stealth UAV to deal with BB threats and achieve the penetration path replanning in complex scenarios. Moreover, the attitude angle information is integrated into the flight path which can meet real flight requirements for stealth UAV. The theoretical analysis and numerical results prove the validity of our method. [ABSTRACT FROM AUTHOR]

Strong adaptive radar, such as cognitive radar (CNR), can perform various missions while ensuring its own security in electronic warfare, via detecting environments and changing the radar parameters in real time. Unfortunately, most of the current military countermeasures, such as jamming-based electronic countermeasures, have rarely been related to jamming for CNR. Since the behaviours of radar in the traditional design of the jammer-radar scenario are always static, it is easy to create a subjective or local optimal jamming effect. In order to dynamically analyse the execution process of a complete jamming radar mission, this work establishes an equivalent attack-defence game in which the radar is regarded as a defence decision agent, and the jammer is an attack decision agent. The attributes of the game's players, the rules of the game, and the conditions for the end of the game are set clearly by setting reasonable parameters. After searching for antagonism strategies by exhaustive method, it can be found that the survivability of the predictive cognitive jamming is much stronger than that of the normal jamming based on real-time sampling data of radars. This conclusion is demonstrated through a 1 ms simulation of the game process. [ABSTRACT FROM AUTHOR]

With the development of modern weapon techniques, radio frequency integrated technology has attracted widespread attention as a key technology to improve the informationalised level of missiles. Radar and communication are two typical electronic types of equipment, and their integration can support and promote the development of radio frequency integrated technology. In this study, experimental verification of an integrated radar–communication system is carried out. Firstly, the key technologies to achieve radar–communication integration are theoretically analysed. The solutions of the key issues, including signal separation, time synchronisation and frequency synchronisation, are proposed. Furthermore, a radar–communication demo is implemented and the experimental verification is carried out here to verify the feasibility of the proposed methods. [ABSTRACT FROM AUTHOR]

Aiming at the limitation of the coherent accumulation gain of the air defence missile active radar seeker, which is brought by a new generation of manoeuvrable stealth targets, this study proposes a long-time coherent accumulation algorithm based on the blind estimation of relative acceleration between missile and target, which is suitable for the pulse Doppler seeker. By extracting the relative acceleration information carried in the echo signal, the algorithm compensates the original echo signal phase, so that the compensated signal can be refocused in the frequency domain and the seeker detection capability to the large manoeuvring target can be improved. The simulation results show that the seeker sensitivity can be increased by 8 dB when the system false alarm probability is <10−7 and the intercept probability is >0.99. [ABSTRACT FROM AUTHOR]

For moving ship detection in synthetic aperture radar (SAR) images, ship wakes on the sea surface may be detectable, thus leading to interferences in reconnaissance. To address this issue, a wake region detection approach by using multi-feature recombination and area-based morphological analysis is proposed with along-track interferogram-SAR systems. This approach aims to detect the near-ship wake region that is nearby a ship's hull and between two kelvin cusp lines. A novel test is constructed by recombining magnitude, phase, and the local variance of phase in the complex multi-look interferometric SAR image to detect the potential pixels of the ship wakes. Then, with a clustering algorithm based on the proposed test and the pixel spatial distance, the potential wake regions are acquired, and the real ones having sufficiently large areas can be accurately determined. Finally, experimental results on the TerraSAR-X dataset validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article discusses the deficiencies of the European missile defense system proposed by U.S. President George W. Bush to protect the U.S. and Europe from missile threats from the Middle East, particularly Iran. The system would consist of a large X-band radar called the European mid-course radar deployed in the Czech Republic; a forward-based X-band radar would be deployed in an unnamed location near Iran; and a launch site with 10 interceptor missiles would be located in Poland. This system could easily be rendered obsolete through the use of jammers and countermeasures such as lightweight balloons.

Stresses that the radar deployed by the United States in Norway is used in the surveillance of the military movements of Russia. Mistakes committed by the United States government under President Bill Clinton in dealing with Russia; Details on the principal use of the radar in Vardo, Norway; Information on the relay of signals from satellites to military bases.

Considering the blank of standards determining the permissible distance between UHVAC (1000 kV) power transmission lines and ADSR stations, we proposed a method combining the physical optics and a linear-phase-Rao–Wilton–Gisson (LP-RWG) basis function to calculate the scattering field of the UHVAC transmission lines. In the calculation, we use the LP-RWG function to discrete the induced current, and then, acquire the radar cross section (RCS) by calculating the scattering field. Especially we carried out in-field full-scale experiments, and the results verified the accuracy of the proposed RCS calculation method. After further analyzing the impact of incident angles, tower types, and tower numbers on the radar detection loss, we were able to obtain a general estimation of the permissible distance to be 1.9–2.1 km with the RCS as an intermediate parameter. [ABSTRACT FROM AUTHOR]

Many countries including India use the Russian made SAM-3 (Pechora) surface-to-air missile (SAM) weapon systems to protect their strategic and tactical infrastructure. The mathematical computations done in this paper, conclusively proves that SA-125 low-blow tracking radar of Pechora is vulnerable to jamming. A project was undertaken to overcome the jamming vulnerability of Pechora aiming to design and develop an electronic counter counter measure system. This system networked the Pechora tracking radar with a western tracking radar, Flycatcher, developed by HSA Holland. The latter radar works in a MMW band. When jamming (x band) is employed by enemy aircraft the Low blow radar failed to provide target coordinates. But the flycatcher tracking radar which is tracking in Ka band provided the tracking coordinates (after parallax correction) to the command guidance computer. This way the missile guidance is protected until missile warhead in missile blasts near the target. Extensive trials carried out with a number of aircraft sorties proved the success of this developed system against jamming. [ABSTRACT FROM AUTHOR]

This article analyzes the developments in cultural memory in Czech-U.S. relations since the end of the Cold War with a special emphasis on the heated debate about placing a U.S. radar base on Czech soil in 2008. It first describes the abrupt transformation in cultural memory related to the transition from communist rule from the transatlantic perspective. It claims that the debate about the radar base is a clear indication of the shift within cultural memory, which became much more contested, especially when compared with the previous period culminating with the Czech Republic's entry into NATO. As cultural memory is closely linked to dominant historical narratives as well as identity, the findings have serious implications for the future of the transatlantic ties in the region. [ABSTRACT FROM AUTHOR]

Many mountainous regions depend on seasonal snowfall for their water resources. Current methods of predicting the availability of water resources rely on long-term relationships between stream discharge and snowpack monitoring at isolated locations, which are less reliable during abnormal snow years. Ground-penetrating radar (GPR) has been shown to be an effective tool for measuring snow water equivalent (SWE) because of the close relationship between snow density and radar velocity. However, the standard methods of measuring radar velocity can be time-consuming. Here we apply a migration focusing method originally developed for extracting velocity information from diffracted energy observed in zero-offset seismic sections to the problem of estimating radar velocities in seasonal snow from common-offset GPR data. Diffractions are isolated by planewave-destruction (PWD) filtering and the optimal migration velocity is chosen based on the varimax norm of the migrated image. We then use the radar velocity to estimate snow density, depth, and SWE. The GPR-derived SWE estimates are within 6% of manual SWE measurements when the GPR antenna is coupled to the snow surface and 3-21% of the manual measurements when the antenna is mounted on the front of a snowmobile ~0.5m above the snow surface. [ABSTRACT FROM AUTHOR]

Accurate and efficient moving target imaging is an important challenge for targets recognition in current synthetic aperture radar (SAR) combined with a ground moving target indication (GMTI) system. As the key but unknown parameter, the Doppler rates are estimated conventionally by searching any possible values for moving targets imaging. However, this conventional estimation method suffers from low accuracy or low efficiency due to the searching procedure. Focusing on these, we present a method to efficiently image the moving targets without the Doppler rate by Doppler delayed interferometry, and the imaged localization, which is parameterized pseudo-localization, is used to estimate the Doppler rate. In order to improve the estimation accuracy, an improved method based on the Newton method of approximation is proposed by exploiting the unused amplitude information. Compared with the conventional methods, the proposed improved method capable of high accuracy and low computation complexity simultaneously can meet the accurate and efficient requirements in the practical applications. Comparison simulations and real data processing results demonstrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

NCAR/EOL is investigating potential configurations for the next generation airborne phased array radar (APAR) that is capable of retrieving dynamic and microphysical characteristics of clouds and precipitation. The APAR will operate at C-band. The APAR will use the electronic scanning (e-scan) feature to acquire the optimal number of independent samples for recording research quality measurements. Since the airborne radar has only a limited time for collecting measurements over a specified region (moving aircraft platform ~ 100 m/s), beam multiplexing will significantly enhance its ability to collect high-resolution, research quality measurements. Beam multiplexing reduces errors in radar measurements while providing rapid updates of scan volumes. Beamwidth depends on the size of the antenna aperture. Beamwidth and Directivity of elliptical, circular and rectangular antenna apertures are compared and radar sensitivity is evaluated for various polarimetric configurations and transmit/receive elements. In the case of polarimetric measurements, alternate transmit with alternate receive (single channel receiver) and simultaneous reception (dual channel receiver) is compared. From an overall architecture perspective, element level digitization of transmit/receive (T/R) module versus digital sub-array is considered with regard to flexibility in adaptive beamforming, polarimetric performance, calibration, and data quality. Methodologies for calibration of the radar and removing bias in polarimetric measurements are outlined. The above-mentioned engineering options are evaluated for realizing an optimal APAR system suitable for measuring the high temporal and spatial resolutions of Doppler and polarimetric measurements of precipitation and clouds. [ABSTRACT FROM AUTHOR]

In this paper, a joint threshold adjustment and power allocation (JTAPA) algorithm is developed for target tracking in asynchronous radar network (ARN). The basis of the JTAPA strategy is to feed back the target track information from the fusion center to local radar sites to enhance both the target detection capability and the resource utilization efficiency of the ARN. For the detector, we develop a threshold adjustment (TA) algorithm for better detection performance, based on the predicted target location information fed back from the fusion center. For the transmitter, we build an asynchronous power allocation (APA) model based on the perceptual information, and use an optimization technique to control the limited power resource for the next period of time. The goal of the APA scheme is to achieve better target tracking accuracy with a given power budget. The Bayesian Cramér–Rao lower bound is derived, normalized, and subsequently utilized, as the optimization criterion for the APA strategy. The resulting nonconvex optimization problem is solved through relaxation incorporating the spectral projected gradient technique. Simulation results demonstrate that the integration of the TA and APA processes can evidently improve the tracking performance. [ABSTRACT FROM PUBLISHER]