Angular Glint Research Articles

Enhancing the correlation between azimuth and Doppler frequency for speed estimation of nearby tangential targets

With the development of intelligent transportation systems, traffic supervision radar with wide coverage plays a crucial role in traffic management and vehicle-road coordination. The correlation between Doppler frequency and azimuth has been widely validated in wide coverage traffic supervision radar for high-precision velocity measurement. However, angular glint and noise of the nearby targets lead to a decrease in correlation between the azimuth and Doppler frequency, which negatively impacts the accuracy of velocity estimation. Currently, adopting separate filtering strategies for target azimuth and Doppler frequency has limited performance in enhancing correlation. This paper presents a joint observation model for azimuth and Doppler frequency to achieve the extraction of interrelated components from subspaces, which improves the accuracy of velocity measurement. The effectiveness of this approach is validated using data obtained from X-band and Ku-band sensors.

Synthesis of Partially Coherent Geometric Models of Radar Objects Based on Their Incoherent Models

AbstractThe paper considers the transition algorithm from incoherent models to partially coherent ones by the example of the problem of synthesizing a two‐dimensional partially coherent model of a distributed radar object by its five‐point and nine‐point incoherent models. The transition algorithm includes the analytical expressions which allow determining powers and correlation functions of emitting signals for both types of models. The result is confirmed by numerical modeling. The comparison of the precision reflection altimeter formation and correlation function of angular glint provided by equivalent incoherent and partially coherent models is carried out.

Forward-looking Imaging via Doppler Estimates of Sum-difference Measurements in Scanning Monopulse Radar

Monopulse technique is used in scanning radar systems to improve image quality in the forward-looking area. However, monopulse measurements fail to resolve multiple targets in the same resolution cell because of angular glint which often results to image blurring. In response to this, we propose a monopulse forward-looking imaging method utilizing Doppler estimates of sum-difference measurements. First, target multiplicity is resolved by exploiting the different Doppler shifts caused by the relative motion between the platform and the targets at different directions. High azimuthal angle measurement accuracy of the Doppler estimates is then obtained using the Sum-Difference Amplitude-Comparison (SDAC) monopulse technique. Subsequently, the intensity of the sum channel estimates is projected onto the image plane according to the range and angle measurements. To further improve the precision of angle measurements, a Chirp-Z Transform (CZT)-based algorithm is proposed for the reconstruction of the Doppler estimates of the sum-difference channels. Simulation results demonstrate the capability of the proposed methods in resolving multiple targets at high squint angles in a large scanning field. Real data experiments show significant improvement of image profiles using the CZT-based algorithm compared to that of the conventional monopulse imaging method.

Study of Moving Targets Tracking Methods for a Multi-Beam Tracking System in Terahertz Band

This paper studies the methods of moving targets tracking based on a multi-beam tracking system in terahertz (THz) band, which is an initial attempt in this field. Taking the advantage of forming high resolution range profile of THz radar, a target geometric center tracking method is developed at first. However, the tracking performance is deteriorated by the severe angular glint and system disturbance. A further analysis on the experiment data finds a statistical correlation between the angular glint and the normalized amplitude variance, which is exploited to identify and exclude instable scatterers. A non-linear angular discrimination function is also established to deal with the anomalous measurement of the radar. Finally, an instable point exclusion method and a nonlinear angular discrimination method are proposed and combined to develop an improved tracking method, which can suppress angular glint and mitigate measuring perturbation, hence promoting the tracking performance. Proof-of-principle experiments are performed with a multi-beam tracking system working in 0.2 THz band. Tracking results of different targets demonstrate that the improved tracking method can effectively eliminate the tracking failure and significantly promote the tracking accuracy.

Fast Estimated Calculation of Wideband Radar Angular Glint Using Single Frequency Method

In this paper, we proposed a fast and accurately calculated method to estimate the deviation of wideband angular glint based on single frequency or narrow band modeling method of the angular glint. By analyzing the three existing methods of modeling the target angular glint, we show that such methods are consistent when the geometrical optics approximation and linear polarized receiving antenna are assumed. Considering of the tracking system by wideband monopulse radar, the fast calculated method we present can estimate the angular glint in each resolution unit using modeling method of single frequency which is the center one of the whole bandwidth. The mathematical analysis of the unity between the wideband and narrowband modeling method is demonstrated, and the correctness of the new calculated method is well validated by high-frequency electromagnetic simulations based on the physical optics.

Deception Approach to Track-to-Track Radar Fusion Using Noncoherent Dual-Source Jamming

Dual-source jamming is an effective way to prevent monopulse radar systems from performing accurate angle measurements. In this investigation, based on noncoherent dual-source jamming, we propose a cooperative deception approach, which has the benefit of causing persistent and large angular measurement errors to protect a true target and therefore can greatly reduce the discrimination capability of a distributed track-to-track radar fusion system. A scenario involving a single target accompanied by a digital radio frequency memory (DRFM)-based repeater jammer countering two radar systems is illustrated. By controlling the amplitude ratio and time delay in a statistical manner, the active decoy signal and target echo signal can form a noncoherent angular glint effect and result in the deviation of the angle tracking loop of the two radar systems from the true target in opposite directions. The track-to-track association distance related to the retransmission parameters is explicitly derived, and its statistical characteristics are analyzed in detail. Simulations verify the feasibility of the approach. The advantage of the approach lies in its ability to destroy the so-called “common origin” signature of the physical target by injecting false angular information. The direct result is that the true target might not successfully complete the process of track-to-track association, thereby enabling us to realize the desirable effect of “disguise the true target and instead show false decoys”.

Angular glint compensation for seekers based on multicarrier techniques

To solve the problem caused by angular glint in the terminal guidance process, which effects steady target tracking and results in the final miss, the influence of angular glint on the seeker's angle tracking and angular glint compensation methodology using multiple output angle error equation with different detection frequencies at single sensing period to extract the unknown parameters of the target model based on the orthogonal multicarrier technique is proposed here. The method is verified reasonable and feasible through the simulation analysis, the analysis result can be applied to improve the tracking precision of the seeker's terminal guidance process.

Research on pulse compression radar angular glint modelling and suppression

The target angular glint is the main factor restricting the tracking accuracy of radar at close range. There are few researches on angular glint of pulse compression radar. Here, the angular glint model of the large aerodynamic target under pulse compression is proposed. The field measured data verify the validity of the model. Second, a frequency-diversity algorithm based on gating weighting is proposed to suppress angular glint. Simulation results show that its performance is better than the traditional frequency diversity algorithm. Third, the influence of total frequency hopping bandwidth and number of hopping on the frequency diversity algorithm is discussed. Finally, the algorithm proposed here has been applied with the existing experimental prototype. The outfield experiments show that the algorithm can suppress angle glint noise effectively.

Development of a standoff terahertz imaging system for concealed weapon detection

AbstractIn this article, terahertz imaging system based on a single‐channel 360 GHz transceiver front‐end and optical‐machine scanning platform, is studied. The transmitting antenna is irradiated by a wide beam of a small aperture antenna to reduce the “angular glint” effect caused by high frequency electromagnetic radiation. The receiving antenna is of a large aperture to ensure high resolution. Beam scanning is achieved through a fast conical scanning method using a total reflector to achieve fast real‐time imaging.

Angular Glint Error Simulation Using Attributed Scattering Center Models

Angular glints are induced essentially by the superposition of scattering responses from multiple scattering centers and usually fluctuate quickly and widely with the aspect angles for complex targets change. This paper presents angular glint simulation of complex conducting targets using attributed scattering centers. The formulae for linear glint errors (LGEs) are derived based on the parametric models of attributed scattering centers and can be applied for real-time LGE simulation. Our analyses and numerical experiments show that the LGE simulation requires more precise scattering center modeling than the radar imaging simulation does. To ensure the accuracy of the LGE simulation, a forward approach that uses induced currents on conducting targets is used to precisely extract the scattering centers. The numerical results show that the LGE simulation based on the developed scattering center model has high accuracy. More importantly, the scattering center model developed for sparse aspect angles can be used to simulate LGEs for dense aspect angles, as required for complex targets, which leads to high efficiency in simulating LGEs.

ANGULAR GLINT ANALYSIS OF THE 2-D TARGET ABOVE A ROUGH SURFACE BASED ON EXTRACTION OF THE COUPLING CURRENTS

In this paper, angular glint characteristics of a two-dimension (2-D) perfect electric conductor (PEC) target above a PEC rough surface are investigated. The induced surface currents on the target and on the rough surface are obtained by employing the method of moments combining UV matrix decomposition technique (MOM-UV). Based on electromagnetic (EM) theory and the phase- front distortion concept of angular glint, the formulae of angular glint for 2-D target are proposed, and angular glint is calculated precisely by using phase gradient method (PGM). The analysis of the result is implemented by means of numerical extraction of the coupling currents and relationship between the phase front and angular glint, thus revealing the effects of the coupling on the angular glint.

Angular glint calculation and analysis of radar targets via adaptive cross approximation algorithm

Angular glint is a significant electromagnetic (EM) scattering signature of extended radar targets. Based on the adaptive cross approximation (ACA) algorithm accelerated method of moments (MoM) and the plane incident wave assumption, the narrowband, wideband and newly developed high-resolution range profile (HRRP) based angular glint calculation formulations are derived and applied to arbitrarily shaped three-dimensional (3D) perfectly electrically conducting (PEC) objects. In addition, the near-field angular glint is emphasized, which is of great importance for radar-seeker applications. Furthermore, with the HRRP based angular glint, an approach to rigorously determine range resolution cells which own relatively smaller angular glint is provided. Numerical results are presented with new findings to demonstrate the usefulness of the developed formulations.

Inherent Relations among the Three Representations of Radar Target Angular Glint (in English)

Inherent Relations among the Three Representations of Radar Target Angular Glint (in English)

Calculation of angular glint in near field utilizing graphical electromagnetic computing

The angular glint in the near field plays an important role on radar tracking errors.To predict it more efficiently for electrically large targets,a new method based on graphical electromagnetic computing (GRECO) is proposed.With the benefit of the graphic card,the GRECO prediction method is faster and more accurate than other methods.The proposed method at the first time considers the special case that the targets cannot be completely covered by radar beams,which makes the prediction of radar tracking errors more self-contained in practical circumstances.On the other hand,the process of the scattering center extraction is omitted,resulting in possible angular glint prediction in real time.Comparisons between the simulation results and the theoretical ones validate its correctness and value to academic research and engineering applications.

Physical and Statistical Properties of the Complex Monopulse Ratio

Angular glint gives rise to random pointing errors, which can deteriorate the direction-of-arrival (DOA) estimation accuracy. In monopulse radars the glint manifests itself through a complex valued process known as the complex monopulse ratio (CMR). Physical and statistical properties of the glint are considered. It is proposed to use the Poynting vector formalism for the CMR physical interpretation. The complex probability density function (pdf) and correlation function of CMR are derived.

AN ANALYTIC EXPRESSION FOR NEAR-FIELD ANGULAR GLINT PREDICTION OF RADAR SENSOR USING FAR-FIELD SCATTERING CENTERS MODELS

As an important signature of the radar target, the angular glint efiects on radar sensor mainly arise at close distance, especially at target near fleld. However, the current prediction methods of angular glint are mostly based on the far fleld condition. This paper presents a prediction technique of near fleld angular glint based on the scattering center model to solve this problem. Firstly, the near fleld backscattering is represented based on far-fleld scattering center model. Then by solving the derivative of the backscattering phase vs. the position vector of the observer, including incident angles and range, we get the exact expression of angular glint at near fleld. Next, the exact expression is approximated and simplifled in the range of terminal guidance. Finally, the factors afiecting near-fleld angular glint are analyzed using numeric simulation, and the error comparison between the exact and approximate expression is also provided. It is concluded that the expression in (1) is the approximation of ours at far fleld under certain polarization, and the simplifled expression has a well precision in the range of terminal guidance. All these results provide the theoretical basis for the prediction of near fleld angular glint and its signature research.

雷达目标特征信号与运动模式的相关性研究

Aerial and ground targets motion modes have a close relationship with their pose angles, hence with radar signatures. An analysis on target pose angular rates under different motion modes is performed firstly. Expressions of radar signatures are then derived, including radar cross section (RCS), angular glint errors, and high resolution Doppler profile. By taking a two-scatterer simple target as an example, we explore the relationship between the above signatures and target pose angular rates. The relationship between radar signatures and motion modes are then developed. Finally, the simulation results of radar signatures for multiple-scatterer complex target validate the theoretical analysis, and show that it is feasible to identify different motion modes based on radar signatures. The conclusions are significant for the research of motion mode identification, maneuver detection, and maneuvering target tracking and interception using radar signatures.

Angular glint effects generation for false naval target verisimility requirements

A stimulating problem in the generation of coherent countermeasures for high range resolution radar systems is the inclusion of angular glint effects in the preparation of the false target mask. Since angular glint is representative of extended naval targets, this inclusion increases the credibility factor of the decoy playback signal at the adversary radar-operator station. In this paper, the ability of an interferometric inverse synthetic aperture radar (InISAR) simulator to provide a proof of concept towards the clarification of this challenging task is ascertained. The solution consists of three novel vector representations of the generated data, which are proven to behave according to the laws of physics governing the glint phenomenon. The first depiction is the angular glint injection at the target which is followed by the representation of the wavefront distortion at the radar. A value-added time procession integration of the target in pure roll motion provides an expected by ISAR theory side-view image of the naval extended false target. The effectiveness of the proposed approach through verification and validation of the results by using the method of pictorial evidence is established. A final argument is raised on the usage of this software tool for actual obfuscation and deception actions for air defence at sea applications.

Comparison between two concepts of angular glint: general considerations

Angular glint can be interpreted as a distortion of the radar echo signal phase front, or alternatively, atilt of the direction of energy flow from the radial direction. As the complementarities and support of argumentationin our previous work, a general discussion about two concepts of angular glint is made based on electromagnetictheory to demonstrate that these two concepts are equivalent when geometrical optics approximation is used andthe receiving antenna is linearly polarized.

Further comparison between two concepts of radar target angular glint

Two concepts of angular glint are explained as well as the computation methods. A representative target consisting of two combined electric and magnetic dipoles with arbitrary orientation is presented to formulate angular glint linear deviations when the polarizations of the scattered waves and the receiving antenna are considered. Analysis shows that the equivalence between phase gradient method and Poynting vector method exists when geometrical optics approximation is used and the receiving antenna is linearly polarized.