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Ground moving target indication (GMTI) has been extensively applied in modern warfare. In this letter, a novel deceptive jamming technique for countering multichannel synthetic aperture radar (SAR)-GMTI is presented, which is implemented with the frequency diverse array (FDA). Different from the phased array (PA), FDA modulates the transmitting signal with multiple frequencies across its array elements, which, consequently, enables range-dimension false target deception for SAR imaging. Furthermore, to achieve effective deception for the GMTI, micromotion modulation is adopted to simulate dynamic features of the moving targets. Mathematical derivation and simulation results show that the proposed technique can efficiently produce massive false targets in both the range and azimuth dimensions.

Deep learning algorithms have been widely utilized for synthetic aperture radar (SAR) target detection. Nevertheless, the traditional feature extraction methods and deep learning methods achieve improved ship detection accuracy at a cost of increased complexity and lower detection speed. As detection speed also is meaningful, especially in real-time maritime rescue and emergency military decision-making applications, we propose a new framework of faster region-based convolutional neural network (R-CNN) detection method to handle this problem. A new lightweight basic network with feature relay amplification and multiscale feature jump connection structure is designed to extract the features of each scale target in the SAR images, so as to improve its recognition and localization task network. Moreover, the K-Means method is used to obtain the distribution of the target scale, which enables to select more appropriate preset anchor boxes to reduce the difficulty of network learning. Finally, RoIAlign instead of region of interest (RoI) Pooling is used to reduce the quantization error during positioning. Experimental results show that the detection performance of the proposed method achieves 0.898 average precision (AP), which is 2.78% better than the conventional Faster R-CNN and 800% faster detection speed.

In this letter, we propose a scattered-wave deceptive jamming approach using a frequency diverse array (FDA) radar against spaceborne synthetic aperture radars (SARs). As an emerging array radar, FDA transmits multiple carrier frequencies across its elements, and thus, a multiple deceptive jamming is potentially produced in the range dimension of the SAR image. Moreover, we consider the scattered-wave jamming, since it has low complexity when used to create spurious scenes and control the jammer locations. The theoretical analysis and numerical simulations show that the scattered-wave jamming with FDA can generate multiple fake targets with the number of targets being dependent on the number of FDA carrier frequencies.

Most of the existing deception jamming techniques focus on designing effective jamming signals for static targets or scenes. This paper proposes a multi-scene deception jamming against synthetic aperture radar (SAR) imaging with frequency diverse array (FDA) antenna. Different from traditional single-element and phased-array antennas, FDA antenna employs a small frequency offset across the array elements to produce angle-, range- and even time-dependent transmit beampattern, which brings bright prospect for the application of new jamming techniques against SAR imaging. Such a new method will generate many false targets or multiple deception scenes for the jammed SAR, which helps jam better on the static scene and moving target. Moreover, the location and number of false targets can be manipulated. This paper will illustrate the FDA-based deception jamming against SAR imaging, specially designed waveform and the relationship between the number of false targets or scenes and FDA parameters. The relationship between the location of false targets and the position of jammer will also be described in detail. All proposed methods are validated by extensive simulation results.

In conventional synthetic aperture radar (SAR) processing algorithms, it is generally assumed that the platform performs a uniform linear motion. However, if there is a three-dimensional acceleration during the flight, the motion trajectory will greatly increase the image processing complexity, especially in highly squinted scenarios. This paper proposes a high-precision imaging algorithm for highly squinted SAR with 3D acceleration. Firstly, the range history is extended by the Taylor series, and then a two-dimensional non-uniform fast Fourier transform (2D-NUFFT) is presented to focus the SAR image in range velocity domain. Moreover, as terrain matching is required in practice, the range-velocity image is further transformed into range-azimuth domain. The effectiveness of the proposed algorithm for highly squinted SAR imaging is verified with both simulation data for multi-point targets and experimental data for surface targets.

Spaceborne bistatic synthetic aperture radar (BiSAR) system with geosynchronous-earth-orbit (GEO) transmitter and a low-earth-orbit (LEO) receiver has many advantages which are fine resolution, higher signal-to-noise (SNR), shortest revisit cycle. However, BiSAR data are often azimuth variant because of the sum of two hyperbolic range equation which bring technical challenges to image focus. We address an improved nonlinear chirp scaling (NLCS) algorithm in this paper. The key is introduced a cubic perturbation function in the azimuth domain and used an modified NLCS algorithm to complete azimuth compression, the method of series of reversion (MSR) to obtain an accurate signal spectrum. Simulation results shows the effective of our proposed method.

This paper proposes a modified two-step processing approach to deal with the problem of azimuth time domain aliasing in processing high resolution spaceborne sliding spotlight synthetic aperture radar (SAR) data. The signal model of spaceborne SAR is formulated, which includes the geometric model, echo model and Doppler bandwidth. This paper proposes a modified approach through parameter design to avoid azimuth-time domain aliasing. The sliding factor has a critical value for the azimuth-time aliasing, which meet the requirement of azimuth resolution and large imaging scene. The effectiveness of the proposed approach for sliding-spotlight SAR imaging is verified with simulation data for point targets.

This paper proposes a method against bi-static synthetic aperture radar (SAR) jamming based on frequency diversity array (FDA). Firstly, we present the geometry model of the jamming signal of FDA-bistatic SAR. Then, we introduce two-dimensional non-uniform fast Fourier transform (2D-NUFFT) for FDA-bistatic SAR jamming imaging. Via simulation results, we find that the FDA has deceptive jamming effect on bi-static SAR.

In this paper, a novel jamming method for spaceborne synthetic aperture radar (SAR) based on convolution frequency shift using frequency diversity array (FDA) is proposed. Firstly, we introduce the principle of convolution frequency shift jamming method based on FDA. Next in importance, range doppler (RD) algorithm for jamming signal processing is introduced. Last but not least, numerical simulation experiments are carried out, and the simulation results further prove the correctness of the theoretical derivation.

Different from traditional single-element and phased-array antennas, frequency diverse array (FDA) uses a slight frequency offset across the elements to produce angle-, range- and even time-dependent transmit beampattern, which provides promising potentials to develop new jamming techniques on synthetic aperture radar (SAR) imaging. In this paper, we propose a novel deception jamming method against SAR imaging, which uses FDA to quickly generate false targets. Moreover, the position of the false target is controlled by the jammer, and the number of false targets is determined by the number of FDA elements. The proposed methods are validated by extensive simulation results with range-Doppler imaging algorithm.

Mosaic synthetic aperture radar (SAR) can flexibly steer its antenna beam, achieving high resolution wide swath (HRWS) imaging. Nevertheless, the conventional imaging algorithm may suffer from spectrum ambiguity and finally lead to defo-cused result due to data acquisition geometry. In this paper, the imaging geometry of mosaic SAR is introduced analyzed. An imaging algorithm based on the spectrum analysis technique is proposed to handel the mosaic SAR imaging. Simulation results validate the effectiveness of the proposed approach.

Compared to the monostatic geosynchronous synthetic aperture radar (GEO SAR), GEO bistatic SAR can provide finer spatial resolution and higher signal-to-noise ratio (SNR) with lower system complexity, which leads the GEO-LEO (low earth orbit) SAR be a hot research topic. In this paper, an imaging scheme using cooperative high-orbit and low-orbit satellites is proposed. Firstly, the bistatic range history is extended by Taylor series, and then two-dimensional non-uniform fast Fourier transform (2D-NUFFT) is presented to formulate a bistatic SAR image in the range-velocity domain. The effectiveness of the proposed imaging scheme for GEO-LEO bistatic SAR is verified by simulation data for multi-point targets.

Geosynchronous synthetic aperture radar (GEO SAR) data focusing is a more challenging and difficult task than the low earth orbit (LEO) SAR due to the strong 2-D coupling of echo signal induced by the orbital trajectory curvature. The range cell migration (RCM) in the GEO SAR configuration is space variant in both range and azimuth directions, hence standard RCM correction (RCMC) functions developed for LEO SAR are inadequate for GEO. In this letter, a curved trajectory model is proposed, taking into consideration the impacts of “stop-and-go” assumption. Based on the range model, a new data transform is derived to deal with the complicated coupling in GEO SAR. From the derivation, we find that the original Stolt mapping is a special case of the proposed “generalized Omega-k” algorithm. In comparison with the original Omega-k algorithm, this new algorithm can correct more complicated RCM effectively. Finally, simulation results show that the proposed imaging algorithm performs well for large scene focusing in an L-Band GEO SAR system.

A uniform linear motion is generally assumed in traditional synthetic aperture radar(SAR) processing algorithms. However, it is inevitable that if there is 3-D acceleration, the image formulation processing complexity will be significantly increased, especially in highly squinted situations. This paper aims to handle the imaging problems in the highly squinted SAR with three-dimensional acceleration, which utilizes the Taylor formula to expand the distance equation and further resolve it. Based on the formulated range formula, we further utilize the two- dimensional non-uniform Fast Fourier Transform (2D-NUFFT) to obtain focused SAR imagery. The proposed methods are verified with simulation results.

When synthetic aperture radar (SAR) imaging is applied to observe ground scene containing a moving target, the imagery of moving target will be typically smeared due to range cell migration and Doppler spectrum broadening caused by the target motions, especially for the accelerating targets within a long observation time. To eliminate these effects, a novel imaging algorithm using cooperative between SAR under high-orbit and low-orbit satellites is proposed. The range migration including range walk and range curvature within the coherent integration period has been corrected via the third-order keystone transform. Then, by estimating and compensating the phase errors and the fold factor terms, the target's resolution is improved and the motion parameters are correct-ly estimated. The effectiveness of the proposed algorithm is demonstrated by simulations.

Compared with stationary targets imaging, detection and imaging of moving targets becomes more difficult in Geosynchronous synthetic aperture radar (GEO SAR), especially when the moving target is drowned in strong ground clutter. In this paper, a scheme of moving target detection and imaging with three antennas is proposed for GEO SAR. Firstly, the displaced phase center antenna (DPCA) is used to eliminate stationary targets' echo. Then, the third-order keystone transform is applied to correct the range migration. Next, after coherent integration, the constant false alarm ratio (CFAR) is used to detect the moving target. Finally, simulation results demonstrate the effectiveness of the proposed scheme.

Based on the synthetic aperture radar (SAR) geometric model, a novel method of jamming space-borne SAR by utilizing the array beam-pattern characteristics of frequency diverse array (FDA) is proposed. A small frequency increment, as compared to the carrier frequency, is applied between the FDA elements to produce multiple false targets in the final space-borne SAR imaging. The separations between the false targets are determined by the frequency offset. Based on the imaging geometry in side-looking mode, this paper derives a range-Doppler (RD) algorithm for the space-borne SAR imaging under FDA jamming signals. Simulation results demonstrate the effectiveness of the proposed approach.

The theory of compressed sensing (CS) states that an unknown sparse signal can be accurately recovered from a limited number of measurements by solving a sparsity-constrained optimization problem. In this paper, we present a new framework of high-resolution bistatic inverse synthetic aperture radar (Bi-ISAR) imaging based on CS. A phase-preserved CS approach for high-range resolution imaging is proposed. The phase of a Bi-ISAR signal can be extracted by constructing a phase-preserved Fourier basis, which is crucial to azimuth processing of Bi-ISAR imaging. After performing CS reconstruction in range, we present an improved version of CS-based cross-range imaging by combining modified Fourier basis and weighting with CS optimization. Simulated data are used to test the robustness of the Bi-ISAR imaging framework with two-dimensional (2-D) CS method. The results show that the framework is capable of accurate reconstruction of Bi-ISAR image in both range and cross-range.

This letter proposes a Bayesian compressed sensing (BCS) method for high-resolution inverse synthetic aperture radar (ISAR) imaging when the basis matrix depends on an unknown rotation rate. In the proposed method, the radar transmits only a few probing frequencies instead of a wideband signal. In doing so, both the rotation rate and a high-resolution ISAR image can be simultaneously retrieved by jointly applying the BCS algorithm using Gaussian prior and a gradient-based search algorithm to exploit the sparse probing frequencies. The effectiveness of the proposed method is verified by experimental results with both simulated data and real data.

Translational-variant bistatic forward-looking synthetic aperture radar (TV-BFSAR) introduces three difficulties for the imaging algorithm, namely, large range cell migration (RCM), severe range–azimuth coupling and large azimuth spatial variance. To address these problems, an extended azimuth non-linear chirp scaling (EANLCS) algorithm is proposed. The essence is to remove the linear RCM and Doppler centroid and compensate the residual RCM and range–azimuth coupling terms with secondary range compression. Thereafter, the EANLCS operation is applied to eliminate the azimuth-dependent frequency-modulation rate and cubic phase terms. Experimental results demonstrate the effectiveness and superiority of the proposed algorithm in focusing TV-BFSAR data.

Compared with the monostatic geosynchronous synthetic aperture radar (GEO-SAR) system, GEO bistatic SAR (GEO-BiSAR) shows great advantages in finer spatial resolution and higher signal-to-noise ratio (SNR) with less system complexity. Many scholars have done researches on resolution of GEO-BiSAR, their models consist of a GEO transmitter and a low Earth orbit (LEO) receiver. The methods of improving the resolution by using two or more receivers are rare. In this paper, the system consists of a geosynchronous illuminator and two LEO receivers. The spectrum shift of SAR images could be introduced by multi-view angles of acquired images in the same coverage. We can widen the bandwidth of SAR images by combining the spectrum of two images to improve the resolution. The formation configuration design of two receivers is the crux of the matter. Then in this paper, an orbital design method of two receivers based on simulated-annealing (SA) algorithm is presented.

In geosynchronous (GEO) synthetic aperture radar (SAR), the satellite track is curvilinear and the typical assumption of ‘stop-and-go’ breaks down due to the increase of orbit altitude. Thus, standard imaging algorithms based on the conventional hyperbolic range equation (CHRE) become inadequate. A four-order range equation taking the ‘stop-and-go’ errors into consideration is adopted to improve the accuracy in the approximation of the range history for GEO SAR. Then, an accurate two-dimensional spectrum is analytically deduced under the curved trajectory model, and a modified nonlinear chirp scaling (NLCS) algorithm is proposed according to this new spectrum. Simulation results validate that the proposed algorithm has better performance than the CHRE-based NLCS algorithm in the GEO cases.

Simultaneous synthetic aperture radar (SAR) imaging and ground moving target indication (GMTI) is of great importance in remote sensing applications, but it is difficult to be implemented for existing methods due to the cross-interferences between stationary targets/clutter and moving targets. Generally, the imaged moving targets may be displaced in azimuth according to their radial velocities and superimposed upon clutter at a wrong location. In this paper, we proposes a simple simultaneous SAR and GMTI approach by exploiting the fractional Fourier transform (FrFT) algorithm, different from existing methods that perform first stationary clutter suppression and thereafter handle GMTI via Doppler parameters estimation. The feasibility is verified by simulation results.

Synthetic aperture radar (SAR) techniques are typically used to achieve a high azimuth resolution, but conventional monostatic SAR is not applicable in forward direction because of azimuth ambiguities and poor Doppler resolution. This paper focuses on SAR imaging processing in a novel forward-looking bistatic configuration that a pilotless plane transmits signals and a guided missile receives echo which can avoid image ambiguities and to improve the azimuth resolution. A fourth-order range equation and a fourth-order phase term are adopted to improve the accuracy in the approximation of the range history and two-dimensional spectrum for forward-looking bistatic SAR, respectively. The spectrum is used for high-order phase compensation, range compression, secondary range compression, range cell migration correction, and azimuth compression. Especially, the proposed algorithm is able to focus the translational variant bistatic configuration where the transmitter and receiver platforms are moving in parallel ...

High speed analog-to-digital (A/D) sampling and a large amount of echo storage are two basic challenges of high resolution synthetic aperture radar (SAR) imaging. In this paper, a novel SAR imaging algorithm which named CS-MTMAB is proposed based on compressed sensing (CS) and multiple transmitters multiple azimuth beams (MTMAB). In particular, this new algorithm, which respectively reconstructs the targets in range and azimuth directions via CS technique, simultaneously provides a high resolution and wide- swath two-dimensional map of the spatial distribution of targets with a signiflcant reduction in the number of data samples beyond the Nyquist theorem and with an implication in simpliflcation of radar architecture. The simulation results and analysis show that this new imaging scheme allows the aperture to be compressed and presents many important applications and advantages among which include reduced on-board storage constraints, higher resolution, lower peak side-lobe ratio (PSLR) and integrated side-lobe ratio (ISLR), less sampled data than the traditional SAR imaging algorithm, and also indicate that it has high robustness and strong immunity in the presence of serious noise. Finally, the real raw airborne SAR data experiment is performed to validate the proposed processing procedure.

Starting from airborne SAR image data, a method of simulating space-borne SAR raw received data is proposed, excluding the conventional method of simulating the targets’ back-scattering coefficients through the model of three-dimensional distributed targets. The airborne SAR image data are regarded as space-borne targets’ back-scattering coefficients, and raw data are generated by using space-borne SAR echo signal model. Raw data’s simulation of space-borne SAR can help us to optimum design of space-borne SAR system scheme, test and evaluate the performance of every imaging algorithm, and research motion error from satellite platform having influence on received data and image quality.

For high-precision synthetic aperture radar (SAR) processing, the estimation of Doppler centroid and Doppler frequency rate is essential for well-focused image. In this paper, we present a new method for estimation of Doppler parameters in bistatic forward-looking S AR (BFSAR). After range cell migration (RCM) of BFSAR is corrected by using the cross-correlation technique in inverse S AR, analog chirp-Fourier transform (ACFT) is applied to estimate the Doppler frequency rate. Afterwards, the unambiguous Doppler centroid is obtained by combining ACFT with resolving Doppler ambiguity. Experimental results show that the estimation errors of Doppler centroid and Doppler frequency rate are less than 0.2% and 0.15%, respectively.

The theory of compressed sensing (CS) indicates that the optimal reconstruction of an unknown ISAR signal with intrinsical sparsity can be achieved by solving a sparsity-driven optimization problem. Due to this property, a novel method to construct sparse basis is presented for ISAR image generation. We utilize discrete chirp fourier transform (dcft) and CLEAN to decompose the signal of interest into multiple LFM or chirp signals. The proposed method can generate adaptive sparse basis according to the frequencies and chirp rates of these chirp signals. Our proposed method which uses much fewer measured data can get almost the same image compared with the uncompressed conventional imaging algorithm and our proposal outperforms the CS-based method with standard Fourier basis. Both simulated and real experimental results can demonstrate the effectiveness and feasibility of the method.

The high-resolution imaging for high-squint synthetic aperture radar (SAR) is still a difficult issue due to large range migration and strong range dependence. An extended keystone transform (EKT) is introduced to correct more complex range cell migration and range-variant, then a two-dimensional non-uniform fast Fourier transform (2D NUFFT) is proposed to obtain the focused image. Simulation results are given to validate the effectiveness of the method.

Spaceborne/airborne hybrid bistatic SAR (SABSAR) has a special structure, its time synchronization system produces a great effect on the subsequent imaging processing. In view of the receiver, the impact of time synchronization errors is discussed in this paper, a time synchronization approach based on the direct signal is proposed. In this scenario, in order to compensate for time synchronization error in echo signal, it is necessary to extract the Doppler centroid from the direct signal timely. A novel method, which has small amount of computation, is put forward to estimate the Doppler centroid of the direct signal.

Spaceborne/airborne hybrid bistatic SAR(SABSAR) has a special structure, its time synchronization system produces a great effect on the subsequent imaging processing. In view of the receiver, the impact of time synchronization errors is discussed in this paper, a time synchronization approach based on the direct signal is proposed. In this scenario, in order to compensate for time synchronization error in echo signal, it is necessary to extract the Doppler centroid from the direct signal timely. A novel method, which has small amount of computation, is put forward to estimate the Doppler centroid of the direct signal.

Based on an advanced hyperbolic range equation (AHRE), this study presents an advanced Range Doppler (RD) algorithm for Synthetic aperture radar on geosynchronous satellites (GEO SAR) cases. Since the orbit altitude reaches up to about 36,000 km in GEO SAR, the integration time becomes longer and curved flight path is generated accordingly. Thus, the AHRE is introduced in this paper, which can compensate the error of the conventional hyperbolic range equation (CHRE) in GEO SAR. Then, the two dimensional (2-D) frequency spectrum (PTFS) expression of a point target is obtained by the method of series reversion (MSR). Finally the advanced RD algorithm based on the new spectrum is proposed. Point target simulation results show that the presented algorithm obtains fine performance in GEO SAR cases.

Focusing on the issue of echo data acquire approach in bistatic SAR system. In this paper, the key technology of echo sampling window synchronization is introduced, the effect of echo sampling window synchronization error to the echo data and image performance are analyzed, an adaptive echo sampling window synchronization approach based on amplitude demodulation and phase compare is proposed, which could automatically adapt for the echo pulse repeat interval(PRI), and establish a high accurate synchronized echo sampling window, then a high precise phase bias compare algorithm for the proposed approach is introduced. At last the performance and residual error for the presented approach are analyzed to illustrate the efficiency of the proposed approach. This paper provides a theoretical and engineering reference for the design of echo sampling window synchronization in bistatic SAR system.

High speed analog-to-digital (A/D) sampling and a large amount of echo storage are two basic challenges of high resolution synthetic aperture radar (SAR) imaging. To address these problems, a novel SAR imaging algorithm is proposed based on compressed sensing (CS) in this paper. In particular, this new algorithm provides the approach of receiving echo data via two-dimensional (2-D) random sparse sampling with a significant reduction in the number of sampled data beyond the Nyquist theorem and with an implication in simplification of radar architecture. Then CS technique is used to reconstruct the targets in range and azimuth directions, respectively. The simulation results and error analysis show that the proposed CS-based imaging method presents many important applications and advantages which include less sampled data, lower peak side-lobe ratio (PSLR) and integrated side-lobe ratio (ISLR) and higher resolution than the traditional SAR imaging algorithm.

Synthetic aperture radar on geosynchronous satellite (GEO SAR) has significant potential advantages over conventional low Earth orbit radars, albeit it also has challenges to overcome. In GEO SAR, the imaging geometry is more complicated and the range and azimuth variances are more severe. In order to deal with these problems, this paper presents an advanced equivalent slant range (AESR) model for the synthetic aperture radar undergoing an inclined circular orbit. Furthermore, the range and phase error between AESR model and conventional slant range model are also gauged in detail. Meanwhile, based on the AESR model, the accurate two dimensional (2-D) frequency spectrum (PTFS) expression of point target is obtained. And the modified algorithm and simulation results validate the AESR and show its advantages in image formation in GEO SAR cases.

Bistatic synthetic aperture radar (SAR) system separated its transmitter and receiver, the spatial separation mode provides many technical challenges. This paper addersses on the issue of antenna directing jitter error, the impact of antenna directing jitter including fast jitter and slow jitter are analyzed respectively. In the case of fast jitter, a generalized mathematic model is employed to analyze the impact of antenna directing error on the echo signal, and concluded that the antenna shaking may produce paired echo, the position and the amplitude of the paired echo are analyzed, in the other case, the modulating effect is ignored, and the illuminating region of antenna beam is mainly considered, the impact of echo signal partly misses is introduced. In the end, the simulation results are presented to verify the analyses.

The traditional phase compensation method based on parametric model always needs to make a tradeoff between the accuracy and the computational complexity. Given this, a new method for compensating phase based on Discrete Polynomial Transform (DPT) and CLEAN technique is proposed. To reduce the computation power further, the imaging region estimation is applied. Furthermore, the limitation and the restricted condition of DPT are analyzed for practical scenarios in this paper. In the end, simulation results are given to validate this method.

Synthetic aperture radar (SAR) techniques are typically used to achieve a high azimuth resolution, but conventional monostatic SAR is not applicable in forward direction because of azimuth ambiguities and poor Doppler resolution. In this paper, we present a new bistatic forward-looking SAR imaging algorithm based on point target reference spectrum using the two-dimensional(2-D) principle of stationary phase to improve the Doppler resolution and to avoid azimuth ambiguities. Based on the bistatic configuration and the novel algorithm, SAR not only can image the forward-looking terrain of the aerocraft, but also plays sufficient role in selflanding and navigation. Finally, simulations are used to validate the proposed spectrum and processing algorithm.

The Fourier transform has been widely used in ISAR signal and image processing. In most cases, ISAR signals exhibit time-varying behavior in the Doppler spectrum. Thus, a joint time-frequency analysis (JTFA) for ISAR signals is more useful. In this paper, we introduce a new WVD algorithm jointed CLEAN technique. Meanwhile, the simulations of LFM signal in ISAR are adapted to compare their performance. It is shown that our algorithm is better than typical WVD and SPWVD algorithms.

In geosynchronous synthetic aperture radar (GEO SAR), owing to the increase of signal propagation delay time and synthetic aperture time, the straight track approximation is inadequate. Most formulations and imaging algorithms based on the conventional hyperbolic range equation (CHRE) are not proper for GEO SAR directly. Thus, we tentatively aim to present an advanced range equation in this paper. The proposed equation is a fourth-order equation, which can improve the accuracy in the approximation of the range history for GEO SAR. Furthermore, the accurate two dimensional (2-D) frequency spectrum (PTFS) expression of a point target is obtained by the method of series reversion (MSR). It is found that the corresponding range cell migration correction (RCMC) reference function must be considered higher order term than the standard RD algorithm. Therefore, the modified Range Doppler (RD) algorithm is proposed based on the new spectrum. The simulation results validate the precision and efficiency of the improved range equation and the algorithm. (4 pages)

High speed A/D sampling and large scale data storage are two basic challenges of the high resolution SAR system. The developing of radar system is limited by these two challenges under the Nyquist sampling theory. Compressed sensing (CS) is a new approach of sparse signals recovered beyond the constraints of Nyquist sampling technique. With the consideration of these problems that might happen and the advantage of CS theory, a novel SAR image processing algorithm based on compressive sensing was proposed in this paper. Using the data whose sampling rate is lower than the required Nyquist sampling rate, the CS-based algorithm operates at range and azimuth dimensional respectively. Experimental results show the presented algorithm based on compressed sensing have a better performance than the conventional SAR algorithm even with only smaller samples, and also indicate that the presented algorithm is robustness with existence of serious noise

An improved CS imaging algorithm for SA-BSAR is proposed. The preprocessing method is adopted to correct the azimuth space-variant and the revised CS function used to improve the imaging quality. The simulation results demonstrate the validity of the algorithm.

Estimating cross-range motion parameter is one of the most important steps while using antenna array to get targets' 3-D ISAR images. A method which can estimate cross-range motion parameter based on DCFT is proposed in this paper. It can not only lower the amount of computation, but also insure the imaging precision. The validity of the method would be proved by simulation.

In this paper, we consider the problems of reconstructing the spectrum based on Fractional Fourier Transform (FrFT) from periodic non-uniformly sampled signal in multiple azimuth beams SAR system. First, based on the theory of the paired echoes, the influence of periodic non-uniform sampling for SAR imaging has been derived. Second, signal model of non-uniformly sampling in azimuth direction has been established. Finally, detailed analysis of spectrum reconstruction algorithm in the fractional Fourier domain has been performed. In addition, the simulations are carried out to verify the correctness of the results.

In multi-target ISAR imaging, if the returned signals are range non-separable and the relative radial velocity is large. We can neither resolve them in range domain nor the Doppler frequency domain. In order to solve this problem, the use of the Radon transform and a modified envelope correlation method for multi-target ISAR imaging is presented. The radon transform is used to align the range profiles coarsely. For more accuracy alignment, a modified envelope correlation method is proposed. After range alignment, phase compensation is fulfilled by Discrete chirp-Fourier transform (DCFT). The simulation results show that the method proposed in this paper is effective.

A novel algorithm for SAR(Synthetic Aperture Radar) raw signal simulation based on sub-aperture processing is proposed. The fundamental of the algorithm is analyzed, the signal model is deduced, as well as the simulation procedures are given. Simulation results of extended scene have shown that in the condition of meeting simulation precision, the simulation speed of the algorithm is higher than that of the echo simulation algorithm based on 1D FFT(Fast Fourier Transform).

A echo simulation algorithm for natural scene is presented. It is based on the model of equivalent scatterer for the scene, the approximate expression of SAR system transfer function, and one-dimensional fast Fourier transform (FFT) for data processing. The validity and correctness of the algorithm are verified through raw echo data simulation of point target and natural scene.

In pulse Doppler (PD) radar, a novel motion compensation method based on keystone transform is proposed for handling with the data of a low signal-to-noise ratio (SNR). The keystone transform is used to correct the linear range migration which results from the radial velocity of targets. The SNR is improved through coherently accumulating all pulses. The simulation results show that the performance of the method based on keystone transform is better than that of the conventional coherent integration method using fast Fourier transform (FFT).

In order to research imaging algorithm problems of space-borne bistatic SAR, it is necessary to simulate echo data of actual scene. On the basis of point target simulation, a method of simulating space-borne bistatic SAR raw echo data utilizing gray image data of airborne SAR is presented in this paper. First of all, gray data of airborne SAR image is added and averaged to compute different targets' RCS. Then, raw data of actual scene is generated using the model of scene echo signal of f space-borne bistatic SAR. Finally, imaging processing is fulfilled utilizing BP algorithm toward echo data. The imaging result verifies the correctness of this simulation method.

In this paper, a novel motion compensation method based on keystone transform is presented, which can correct range migration without the exact target velocity. As a result, the accumulation time isn't subject to the restriction due to target motion. Thus radar's system design turns more flexible. Keystone transform is a technique of range migration correction in the field of SAR. However, it hasn't reported to apply this method to PD radar. At the same, because of the increase of accumulation time, the Doppler resolution of radar is improved greatly, which provides an approach for mini-Doppler resolution. Therefore, it is hopeful to apply keystone transform to the field of decoy identification.