Bistatic Radar Research Articles

차량 탑재 바이스태틱 MIMO 레이다 시스템에서 도플러 전처리 기반 파라미터 추정 기법

In a road environment, the clutter-induced multipath components cause errors in the estimations of the direction of departure (DOD), direction of arrival (DOA), and Doppler frequencies of nearby target vehicles. In this paper, two ESPRIT-based bistatic MIMO radar algorithms are proposed to solve the pairing problem while reducing the computational complexity in a multiobject environment. The first method, named the object subspace algorithm, solves the pairing problem by extracting and processing each object return on an eigenvector basis, but it is shown to exhibit performance degradation. In the second method, named the Doppler preprocessing algorithm, the object return is first separated in the frequency domain and the ESPRIT algorithm is then applied or the object subspace algorithm is reused, if necessary. Finally, the multiobject, multipath environment is simulated to show the parameter estimation (DOD, DOA, Doppler frequency) performances of the two proposed algorithms.

A new target localization method for bistatic FDA radar

Different transmit antenna elements in a frequency diverse array (FDA) radar transmit different frequencies. This makes the transmitted beam to continuously change its orientation, and enables an FDA to scan the space around itself in a simple manner. Furthermore, an FDA can find the range as well as the direction of each target simultaneously. The achievable resolution of direction estimation depends on the receive array geometry. The range resolution can be enhanced by decreasing the width of transmit beam, which depends on the transmit array geometry. The later property makes FDA especially attractive because it is no longer necessary to produce sharp, wideband, and high power pulses to achieve high range resolution. FDA has been studied mostly for collocated transmit and receive array, and a very little has been done on its application in bistatic radar. In this paper we propose a new signal transmission scheme for bistatic FDA radar, and demonstrate how one can detect and localize the targets accurately using a computationally efficient algorithm. The proposed signal transmission scheme is designed to produce the narrowest transmit beam for a given number of transmit antennas. This achieves significantly better detection and localization performance compared to the existing methods. Our estimation approach uses a fast algorithm to produce some initial estimates that can be used to initialize a numerical algorithm for computing the maximum likelihood estimates. We also derive the Cramér Rao bound (CRB) associated with the estimation problem, and demonstrate that the variances of the estimates produced by the proposed method are close to corresponding CRBs.

Microwave Breast Imaging Using Rotational Bistatic Impulse Radar for the Detection of Breast Cancer: Protocol for a Prospective Diagnostic Study.

BackgroundMammography is the standard examination for breast cancer screening; however, it is associated with pain and exposure to ionizing radiation. Microwave breast imaging is a less invasive method for breast cancer surveillance. A bistatic impulse radar–based breast cancer detector has recently been developed.ObjectiveThis study aims to present a protocol for evaluating the diagnostic accuracy of the novel microwave breast imaging device.MethodsThis is a prospective diagnostic study. A total of 120 participants were recruited before treatment administration and divided into 2 cohorts: 100 patients diagnosed with breast cancer and 20 participants with benign breast tumors. The detector will be directly placed on each breast, while the participant is in supine position, without a coupling medium. Confocal images will be created based on the analyzed data, and the presence of breast tumors will be assessed. The primary endpoint will be the diagnostic accuracy, sensitivity, and specificity of the detector for breast cancer and benign tumors. The secondary endpoint will be the safety and detectability of each molecular subtype of breast cancer. For an exploratory endpoint, the influence of breast density and tumor size on tumor detection will be investigated.ResultsRecruitment began in November 2018 and was completed by March 2020. We anticipate the preliminary results to be available by summer 2021.ConclusionsThis study will provide insights on the diagnostic accuracy of microwave breast imaging using a rotational bistatic impulse radar. The collected data will improve the diagnostic algorithm of microwave imaging and lead to enhanced device performance.Trial RegistrationJapan Registry of Clinical Trials jRCTs062180005; https://jrct.niph.go.jp/en-latest-detail/jRCTs062180005International Registered Report Identifier (IRRID)DERR1-10.2196/17524

Moving Target Imaging Using GNSS-Based Passive Bistatic Synthetic Aperture Radar

Current studies of global navigation satellite systems (GNSS)-based bistatic synthetic aperture radar (GNSS-SAR) is focused on static objects on land. However, moving target imaging is also very significant for modern SAR systems. Imaging a moving target has two main problems. One is the unknown range cell migration; the other is the motion parameter estimation, such as the target’s velocity. This paper proposes a moving target imaging formation algorithm for GNSS-SAR. First, an approximate bistatic range history is derived to describe the phase variation of the target signal along the azimuth time. Then, a keystone transform is employed to correct the range cell migration. To address the motion parameter estimation, a chirp rate estimation method based on short-time Fourier transform and random sample consensus is proposed with high processing efficiency and robust estimation errors in low signal-to-noise ratio scenes. The estimated chirp rate can calculate the target’s velocity. Finally, azimuth compression derivation is performed to accomplish GNSS-SAR imaging. A maritime experimental campaign is conducted to validate the effectiveness of the proposed algorithm. The two cargo ships in the SAR images have good accordance with the ground truth in terms of the target-to-receiver vertical distances along the range and the ships’ length along the cross-range.

The Processing Framework and Experimental Verification for the Noninterrupted Synchronization Scheme of LuTan-1

The bistatic synthetic aperture radar (BiSAR) plays an important role in remote sensing. However, the deviation between the two oscillators in BiSAR systems will cause a residual modulation of the echo signal. Therefore, the phase synchronization is an important issue that must be addressed in the BiSAR system. An advanced noninterrupted phase synchronization scheme is used for LuTan-1. The synchronization pulses are exchanged immediately after the ending time of the radar echo receiving window and before the starting time of the next pulse repetition interval, which will not interrupt the normal SAR operation. In order to evaluate the accuracy of the phase synchronization scheme, the model of phase synchronization is introduced at first. The hardware design and processing flow of LuTan-1 are introduced in detail. An innovative internal calibration strategy is also described. Then, the test data acquired by the ground validation system are analyzed to verify the effectiveness of the phase synchronization scheme. The signal-to-noise ratio (SNR) and the synchronization rate are the two most important factors to influence the accuracy in phase synchronization. The conclusions have guiding significance for the synchronization module design of LuTan-1 and the future BiSAR system.

A 3-D Novel Fast Back-Projection Imaging Algorithm for Stratified Media Based on Near-Field Monostatic and Bistatic SAR

A fast back-projection (FBP) imaging algorithm is proposed to generate 3-D uniformly balanced images of an object embedded in a layered structure based on a combined near-field monostatic and bistatic synthetic aperture radar (SAR) system. The spectral layered Green's function is used in the FBP algorithm. Like conventional real-time imaging algorithms, the complexity of the imaging function is reduced via the stationary phase method, and the fast Fourier transform is implemented to accelerate the computation. Unlike conventional real-time imaging algorithms, the singularity problem associated with Green's function and antenna pattern is solved in this proposed algorithm by using a point spread function (PSF). For a real-time imaging system, besides fast image generation, an efficient data acquisition is needed. A combined monostatic and bistatic SAR configuration is used here to decrease the data collection time. The performance of this proposed FBP method is demonstrated by measurements of a stratified environment.

Double‐adaptive chirplet transform for radar signature extraction

This study presents a novel method for time-frequency (TF) signal analysis and chirp rate estimation dedicated for electromagnetic spectrum sensing, electronic warfare, electronic intelligence and/or passive bistatic radar purposes in which frequency modulated signals occur. The approach is based on the double-adaptive chirplet transform, providing optimal analysis window parameters, which is a crucial problem during TF processing. The presented methodology is based on a Gaussian window with two degrees of freedom, which results in a strong concentration of energy on the TF plane around the main component, even if the initial window parameters were mismatched. As an example of the method's usefulness, different types of real-life radar pulses were processed: firstly, two types of non-linear frequency-modulated waveforms were examined as a suitable illustration of the changeability of the analysis window parameters. Secondly, the linear frequency modulated signals were analysed in the presence of strong interference and multipath propagation. The waveforms were processed and compared, creating individual radar signatures, which may allow transmitter classification and signal reconstruction to be carried out in further processing. Moreover, the estimation limitations were compared to the Cramer-Rao lower bound, and an appendix organising mathematical fundamentals for the analysed methods is provided.

Bistatic Scattering From Anisotropic Rough Surfaces via a Closed-Form Two-Scale Model

Bistatic radars have been a topic of increasing interest in recent years, thanks to the introduction of new bistatic (and multistatic) configurations, including those based on the opportunistic exploitation of global navigation satellite systems (GNSSs). The research on bistatic electromagnetic scattering models plays an important role in the analysis of these systems, in their simulation, and in the prediction of their performance. The two-scale model (TSM) is a widely used approach for the computation of scattering from rough surfaces, since it is able to account for depolarization effects due to surface tilting. However, in its original formulation, it requires a computationally intensive numerical integration, in order to perform appropriate average over surface random slopes. To overcome this limitation, a closed-form polarimetric TSM (PTSM) was developed, which has been also recently extended to the case of anisotropic rough surfaces (A-PTSM), with a focus on the sea surface. The A-PTSM can be efficiently used to compute the backscattering from anisotropic rough surfaces and can support the development and analysis of monostatic radar missions. In order to extend its scope to the general case of bistatic and multistatic configurations, in this article, we extend the A-PTSM to the case of bistatic electromagnetic scattering, presenting the evaluation of all the elements of the bistatic polarimetric covariance matrix. Due to the relevance of circularly polarized signals in opportunistic GNSS reflectometry applications, both the linear and the circular polarization bases are considered. The behavior of the obtained elements is discussed, and simplified expressions of the elements of the covariance matrix are provided for the case of scattering within the incidence plane. Relevant numerical examples are provided and compared to those obtained by the more refined, but more computationally intensive, second-order small-slope approximation (SSA2) method. In the examples, we consider both a wind-driven sea surface and a tilled soil, and both L-band and X-band frequencies. However, the presented method can be used at all frequencies of interest for microwave remote sensing and for all observation geometries, except for near grazing incidence and/or scattering.

Focusing Spotlight-Mode Bistatic GEO SAR With a Stationary Receiver Using Time-Doppler Resampling

Bistatic geosynchronous synthetic aperture radar (GEO SAR) system, with a geosynchronous illuminator and a stationary ground receiver, provides capability and flexibility of continuous observation and frequent revisit over certain area, which is of great significance for applications such as disaster monitoring. The Doppler frequency modulation (FM) rate in this configuration, however, varies along the azimuth direction, which increases difficulty in imaging. To equalize the Doppler FM rate, a new imaging method is proposed in this paper. By conducting time-Doppler resampling, the proposed method can remove the quadratic variance of Doppler FM rate at orbital positions where the Doppler FM rate is around zero. Validation results show that the proposed algorithm provides a better focusing quality compared with existing methods.

Bistatic Forward-Looking SAR MP-DPCA Method for Space–Time Extension Clutter Suppression

Echoes of bistatic forward-looking synthetic aperture radar (BFSAR) disperse to multiple range cells and exist spatial frequency extension as well as Doppler spectrum extension (i.e., namely space–time extension). Furthermore, the characteristics of BFSAR clutter are strongly nonstationary and spatial variants. Because of the abovementioned issues, clutter and moving targets are fully overlapped in the initial 3-D space–time–range raw data domain, and the clutter cannot be suppressed effectively. To solve this problem, a BFSAR multipulse displaced phase center antenna (MP-DPCA) method is proposed in this article. First, keystone transform without Doppler ambiguity is applied to remove the coupling between the space–time and range domains. Hence, the overall complex 3-D processing in the space–time–range domain is reduced to independent 2-D processing in each space–time domain. Subsequently, a spatial-dechirp processing is applied in the space–time domain to eliminate the spatial frequency extension. Meanwhile, Doppler parameters of clutter point scatterers are equalized by nonlinear chirp scaling processing in the frequency and time domains. Accordingly, the Doppler spectrum extension of point scatterers can be eliminated by a uniform azimuth dechirp processing. After aforesaid three steps, the clutter and moving targets are separated in the space–time domain. Finally, based on the linear phase difference of clutter between the channels, a multipulse canceller can be designed to suppress the clutter. Compared with the existing space–time adaptive procession (STAP) and DPCA methods, this method not only overcomes the nonstationary problem in BFSAR but also conquers the strict application conditions of DPCA. Simulation results are given to verify the effectiveness of the proposed method.

Joint Bi-Static Radar and Communications Designs for Intelligent Transportation

The cooperation of radar and communications becomes important in vehicular environments due to the demand for radar-assisted communications or communications-assisted radar. In this paper, the tradeoff between bi-static radar and communications in a joint radar-communications setting is studied. We propose three schemes by using time division, superposition or their mixture. For each scheme, three optimization problems are formulated to maximize either the probability of detection for radar subject to a minimum communications rate, the communications rate subject to a minimum probability of detection for radar, or a combined measure of tradeoff. Specifically, given a fixed amount of total time or power for both communications and radar, the optimal power allocation and/or time allocation between radar and communications are derived. Numerical results show that the superposition scheme outperforms the time division scheme and the mixture scheme with considerable performance gains. They also show that the surveillance channel in radar and the communications channel are more important than the direct channel in radar.

Sparse aperture bistatic ISAR imaging under low signal-to-noise ratio condition

A sparse representation-based bistatic inverse synthetic aperture radar (ISAR) imaging method can achieve a high-resolution image of a target with sparse aperture data. However, the bistatic ISAR system is more sensitive to noise than the monostatic one because of its nonmirror reflection geometry. To overcome this drawback, we propose the sparse aperture bistatic ISAR imaging method based on joint sparse model. Considering the joint sparse information of bistatic ISAR echo, a joint sparse imaging model is constructed. Then, the dechirped sparse aperture bistatic ISAR echo after translational compensation is transformed into range fast time and azimuth slow time domains by the joint sparse imaging model, and a corresponding azimuth sparse basis is constructed. Then a joint sparse complex approximate message passing algorithm is proposed to joint sparse imaging model. The joint sparse imaging problem is converted to a block sparse imaging problem by vectorization. Using the relationship between the vectorization of the matrix and the Kronecker product, a matrix iteration structure is proposed to solve the joint sparse model efficiently and accurately. The experimental results based on both scattering point model and electromagnetic calculation model data verify the effectiveness of the proposed imaging method.

Optimal Receiver Placement for K -barrier Coverage in Passive Bistatic Radar Sensor Networks

The improvement of coverage quality in the construction of multiple-barrier coverage is a critical problem in a wireless sensor network. In this article, we investigate the K -barrier coverage construction problem in passive bistatic radar sensor networks. In contrast to traditional bistatic radar networks, the transmitters in a passive bistatic radar network are predeployed and noncooperative. To construct K barriers, we need to deploy receivers that couple with predeployed transmitters to build continuous barriers. In this work, we focus on the minimum number of receivers problem of constructing K -barrier coverage, where the minimum number of receivers is based on the predeployed transmitters. To handle this problem, we first investigate the optimal placement of receivers between adjacent transmitters for a sub-barrier formation and then determine the optimal placement of receivers for the one-barrier construction. For multiple-barrier coverage construction, we introduce a weighted transmitter graph (WTG) to describe the relation among different transmitters, where the weight in the graph is the minimum number of receivers needed for these two transmitters for a sub-barrier formation. Based on WTG, the minimum receivers problem changes to a problem of how to find K -disjoint paths with the minimum total weight in the graph. For large-scale networks, we also propose two efficient heuristic algorithms to solve the corresponding problem. Finally, we conduct extensive experiments to validate the correctness and the efficiency of the proposed algorithms.

An Improved Frequency-Domain Image Formation Algorithm for Mini-UAV-Based Forward-Looking Spotlight BiSAR Systems

Mini-unmanned aerial vehicle (UAV)-based bistatic forward-looking synthetic aperture radar (SAR) (mini-UAV-based BFSAR) is much more attractive than the monostatic one because of the flexibility of the system geometry selection as well as its simplicity of system operation, especially with the mini-UAV platform. However, the trajectory of the mini-UAV needs to be accurately modeled since it is very sensitive to the external environment, and the forward-looking configuration results in more severe spatial variance in image formation processing. In the paper, an improved frequency-domain imaging algorithm based on a very accurate slant range model is proposed for mini-UAV-based BFSAR with spotlight illumination. First, a more accurate slant range expression considering the motion characteristics of the UAV and bistatic spotlight configuration is re-derived. Second, a new range nonlinear chirp scaling (NLCS) operator was derived based on the accurate bistatic slant range model. Third, an improved azimuth NLCS operator in the Doppler frequency domain was established for the spotlight illumination of the transmitter and receiver in mini-UAV based BFSAR systems. Finally, the proposed algorithm is validated by both simulations and real datasets.

Bistatic Radar Coincidence Imaging Based on Multiple Measurement Vectors for Rotating Cone-Shaped Targets

Bistatic radar imaging can overcome limitations of monostatic radar imaging and obtain abundant target feature information; thus, it is followed with interest. Different from bistatic inverse synthetic aperture radar (Bi-ISAR) imaging, bistatic radar coincidence imaging (Bi-RCI) provides a new tack on the bistatic radar imaging technique. In this paper, a Bi-RCI based on multiple measurement vectors (MMV) for rotating cone-shaped targets is proposed to realize Bi-RCI coherent processing and improve imaging performance. Based on the mixed mode signals, a MMV parametric model is established and measurement number coarse selection is proposed. Finally, a modified sparse Bayesian learning (MSBL) algorithm is introduced to reconstruct the target image. Simulation results demonstrate the validity and the superiority of the proposed method.

Martian Topographic Roughness Spectra and Its Influence on Bistatic Radar Scattering

There are few studies on predicting fully bistatic scattering from the rough surface of Mars, though some bistatic radar observations have been made, such as in the MARS EXPRESS mission. To better understand the interaction of radar signals with a planetary surface in bistatic radar observations, the topographic-scale roughness of Mars, characterized by a two-dimensional power spectrum density (2D-PSD), is examined in view of its global roughness variations and scale dependence on geological units. The analysis shows that the Martian 2D-PSD is strongly dependent on the geological units and that it lies between Gaussian and exponential functions, with a power index equal to 1.9. The bistatic scattering coefficients are calculated by an advanced integral equation model (AIEM) with the 2D-PSD as the input. It shows that the specific surface roughness spectrum and the dielectric inhomogeneity should be taken into account in interpreting the bistatic radar scattering response.

Using an Equivalence-Based Approach to Derive 2-D Spectrum of BiSAR Data and Implementation Into an RDA Processor

An equivalent range equation with a monostatic equivalent component and a bistatic synthetic aperture radar (BiSAR) compensation component was proposed. There were five monostatic equivalent parameters (MEPs) in the both components. With the MEPs, a BiSAR range equation can be expressed in a form similar to the monostatic SAR (MoSAR) expression. Then, by using the range equation and the principle of stationary phase (POSP), we analytically derive the 2-D spectrum of a point target, and this 2-D spectrum is implemented into the range Doppler algorithm (RDA) that processes the translational invariant (TI) BiSAR data. In our RDA, spatially variant range cell migration (RCM) correction and azimuth compression (AC), both of which are related to the spatially variant MEPs, are required to focus all targets in the whole scene of different range cells. Simulations under a wide range of imaging parameters are conducted to assess the equivalent range equation and the 2-D spectrums. Satisfactory results are obtained. In addition, traditional methods for motion compensation can be directly applied to our equivalent range equation. Finally, the RDA is evaluated through the analysis of acquired raw BiSAR data. Well-focused images are obtained. Therefore, the proposed equivalent range equation, derived 2-D spectrum, and RDA have been validated for forming imagery using raw BiSAR data.

A Novel Azimuth Spectrum Reconstruction and Imaging Method for Moving Targets in Geosynchronous Spaceborne–Airborne Bistatic Multichannel SAR

Geosynchronous spaceborne–airborne bistatic multichannel synthetic aperture radar (GEO-SABM SAR) is a form of bistatic SAR constructed by a GEO transmitter and an airborne multichannel receiver. The frequent coverage of earth observations in GEO-SABM SAR provides a great advantage in SAR-ground moving target indication (SAR-GMTI). However, the bandwidth of the azimuth spectrum in this configuration, which is larger than the pulse repetition frequency (PRF), makes the whole spectrum fold into several subsegments, i.e., azimuth spectrum aliasing (ASA) occurs. In addition, azimuth Doppler ambiguity (ADA) caused by the larger radial velocity of the moving target may occur simultaneously. To address these problems, an improved velocity SAR (VSAR)-based azimuth spectrum reconstruction method for moving targets is proposed. The influence of ASA and ADA on the signal of the moving targets is analyzed, and a signal model after coarse imaging with static target parameters is deduced. From the signal model, each subsegment has different Doppler frequencies and can be extracted based on improved VSAR. Meanwhile, the Doppler ambiguous integer has a definite relationship with the slope of the range migration of the subsegments after a range cell migration correction (RCMC) based on the static target parameters and can be estimated by this relationship. Furthermore, based on the extracted spectrum subsegments and estimated Doppler ambiguous integer, the azimuth spectrum can be reconstructed. Finally, the effectiveness of the proposed method is verified by the numerical experiments.

Bistatic Observations With SuperDARN HF Radars: First Results

AbstractSuper Dual Auroral Radar Network (SuperDARN) radars operate in a coordinated but monostatic configuration whereby high‐frequency (HF) signals scattered from ionospheric density irregularities or from the surface of the Earth return to the transmitting radar where Doppler parameters are then acquired. A bistatic arrangement has been developed for SuperDARN radars in which HF signals transmitted from one radar are received and analyzed by another radar that is separated by a large distance (>1,000 km). This new capability was developed and tested on radars located in Oregon and Kansas. Numerous 3‐day bistatic campaigns have been conducted over a period extending from September 2019 through March 2020. During these campaigns three distinct bistatic propagation modes have been identified including a direct mode in which signals are transmitted and received through the radar side lobes. Direct mode signals propagate along the great‐circle arc connecting the two bistatic radar sites, reflecting from the ionosphere at both E region and F region altitudes. Two additional modes are observed in which HF signals transmitted from one radar scatter from either ionospheric density irregularities or from the surface of the Earth before propagating to the bistatic receiving radar. Ray tracing simulations performed for examples of each mode show good agreement with observations and confirm our understanding of these three bistatic propagation modes. Bistatic campaigns continue to be scheduled in order to improve technical aspects of this new capability, to further explore the physical processes involved in the propagation and scattering of HF bistatic signals and to expand the coverage of ionospheric effects that is possible with SuperDARN.

Multibistatic Radar for Space Surveillance and Tracking

The ever increasingly resident space object density poses a challenge for current and future space missions and assets. Space debris in low Earth orbit (LEO) are of particular interest because they are present in the highest concentration with respect to the other orbits. Radio frequency systems, and particularly radar, prove to be suitable answers to the need of observing space object, especially at LEO. The reasons behind this statement are in the ability of RF sensors to operate independently of illumination and weather conditions. Radio telescopes are present in a relatively large number and are widely used for space observation. They have large antenna gain and highly sensitive receivers, which make them act as perfect receivers for bistatic radar systems. This article will present the architecture, system, and signal processing aspects related to a radar/telescope RF system for space surveillance and tracking applications.