Due to existence of the long along-track baseline (ATB) among the different satellites in a distributed space-based radar (DSBR) system, a large number of grating lobes appear in radar returns, causing the non-continuous detection phenomenon of an air moving target (AMT). To solve this problem, in this paper, a novel approach for ATB distribution design in a DSBR system is proposed. In the proposed algorithm, to reduce the amount of spatial ambiguity points located at the main-lobe region and achieve the best air moving target indication (AMTI), the maximum target detectability ratio (TDR) in the main-lobe region is chosen to be the criteria for the optimal ATB design. The effectiveness of the proposed method is verified by the simulated multi-channel radar data in a DSBR system.

For a spaceborne bistatic early warning radar system with severe range dependence, the multi-channel division of the large-aperture antenna will bring about spatial under-sampling, which can lead to the spatial spectrum center estimation error and greatly influence the bistatic radar clutter suppression performance. To solve this problem, a novel bistatic clutter spectrum compensation method based on FFT range fitting is proposed in this paper. In the proposed method, the clutter Doppler and angle centers in different range gates are firstly estimated through Eigen decomposition. Then, the pseudo-single frequency complex sequence corresponding to the estimated spatial clutter center sequence is constructed, and the slope related to the angle centers is estimated after performing the FFT. Finally, the compensation matrix is constructed, so as to achieve the clutter non-stationary error compensation. The effectiveness of the proposed method is validated by the simulation experimental results.

To achieve tight beam coverage and obtain the optimal target detection performance for a space-based early warning radar (SBEWR) system, the reasonable radar beam design is prerequisite. In this paper, an optimal beam position design algorithm in a SBEWR system is proposed, where the beam position overlap rate (BPOR) choice is reasonably designed. In the proposed algorithm, the maximum signal-to-clutter and noise ratio (SCNR) of the targets located at the beam position edge is chosen as the criterion for the BPOR optimization design. The BPOR designment result provides important guidance and references for beam filling designment and guarantee the effective target detection capability of a SBEWR system.

Due to existence of the long along-track baseline (ATB) between the satellites in a distributed space-based early warning radar (DSBEWR) system, a large number of grating lobes appear in radar returns, causing the noncontinuous detection phenomenon of an aerial moving target (AMT). To solve this problem, in this paper, a novel approach for ATB distribution design in a muti-satellite DSBEWR system is proposed. In the proposed algorithm, to reduce the amount of spatial ambiguity points located at the main-lobe region, the main-lobe gain of the received antenna pattern in the azimuth dimension is designed to be maximum via the non-uniformly intersatellite ATB designment. The effectiveness of the proposed method is verified by the simulated multi-channel radar data in a DSBEWR system.

As one of the main statistical characteristics of clutter, the clutter amplitude distribution plays an important role in the accurate modeling of spaceborne multi-channel radar signal as well as the subsequent, maritime radar target detection. In this paper, considering that the space-time adaptive processing (STAP) technology is usually applied to accomplish the main-lobe clutter rejection in a space-borne surveillance radar, the influence of different clutter amplitude distributions on STAP in a spaceborne multichannel radar system are analyzed. Firstly, a spaceborne multi-channel clutter model is established based on radar equation and clutter space-time steering vector. Then, Rayleigh distribution, Weibull distribution, lognormal distribution, K distribution, generalized Pareto distribution, and IG-CG distribution are used to fit the clutter amplitude. Finally, the effects of these clutter amplitude distributions on STAP performance are analyzed, respectively. The simulation results show that in the case of the same clutter power, the influence of different clutter amplitude distributions on STAP performance is approximately the same.

The space-based surveillance radar system has a higher field of view and can overcome interference from Earth's atmosphere and terrain occlusion, which has been widely applied in high-threat near-Earth asteroid (NEA) warning and defense applications. Due to the limited power aperture product of the space-based system and the far distance between the radar and asteroid targets, the target signal is extremely weak. Prolonging the coherent accumulation time can effectively improve the radar detection capability of small asteroid targets, but the complex effects of range migration (RM) and Doppler frequency migration (DFM) will degrade the target coherent accumulation performance. To effectively solve this problem, an improved Keystone transform (KT) matched filtering banks method based on particle swarm optimization algorithm is proposed. Compared with traditional methods, the proposed method can not only ensure that the asteroid target detection performance is close to the theoretical optimum, but also reduce the system computation complexity. Simulation results verify the effectiveness of the proposed algorithm.

Due to the existence of the time synchronization error, the correlation coefficient between the main satellite and auxiliary satellite severely declines, thus deteriorating the clutter suppression ability and aerial moving target indication (AMTI) performance in a distributed space-based early warning radar (DSBEWR) system. In this paper, a novel algorithm is proposed to estimate and calibrate the linear time synchronization error. In the proposed algorithm, the rough linear time synchronization error range is firstly estimated according to the Doppler offset between the same spatial channel in the main satellite and the auxiliary satellite. After obtaining the searched rough error range, the linear time synchronization error can be accurately obtained by finding the max correlation coefficient between the main satellite and auxiliary satellite after performing time synchronization error compensation. The effectiveness of the proposed method is verified by the simulated multi-channel radar data in a DSBEWR system.

Due to existence of the long along-track baseline (ATB) in a distributed space-based early warning radar (DSBEWR) system, a large number of grating lobes appears in both main-lobe and side-lobe clutter regions, causing the discontinuously detectable phenomenon of an aerial moving target (AMT). To solve this problem, in this paper, a novel spatial ambiguity suppression algorithm is proposed. In the proposed algorithm, based on the prior information provided by the system parameters and the signal processing results from the single satellite radar data, after performing the multi-channel clutter rejection, the spatial ambiguity can be eliminated via the joint processing of residual clutter signals corresponding to the single satellite and the muti-satellites. Simulated processing results are provided to validate the effectiveness of the proposed method.

Geosynchronous spaceborne-airborne bistatic synthetic aperture radar (GEO-BiSAR) has the advantages of wide beam coverage, long exposure time, and superior system flexibility. However, it is a challenge for GEO-BiSAR to efficiently acquire SAR images both with high resolution and wide swath due to the severe range and azimuth spatial variances. To deal with this issue, a modified Omega-K method is proposed in this paper. In the proposed algorithm, an equivalent range model associated with GEO-BiSAR configuration is built, where the equivalent parameters of the airborne radar receiver absorb the phase parameters corresponding to the GEO transmitter. Then, the Stolt interpolation is performed to realize the range-azimuth decoupling, achieving the linearization between range and frequency variables. Finally, a well-focused SAR image could be obtained after residual spatial variance error compensation. Simulations are presented to demonstrate the effectiveness of the proposed method.

By transmitting the constant pulse repetition interval (PRI) sequence, the traditional synthetic aperture radar (SAR) system will suffer from the loss of coverage in elevation. Thus a staggered-SAR system is developed in recent years, which employs the continuously PRI-varied sequence, making the blind ranges locate at different regions in different receive instant. However, the nonuniformly sampled signal will cause ambiguities in the SAR imaging result. To deal with this issue, in this paper, a novel signal restoration method based on kernel regression is proposed to resample the nonuniform signal. Real-measured spaceborne SAR data is used to validate the proposed method.

Next-generation SAR imaging system demands wide-swath and high resolution to observe Earth's surface, promoting the development of the high-resolution and wide-swath (HRWS) synthetic aperture radar (SAR) system working in terrain observation by progressive scans (TOPS). However, Doppler ambiguities will occur in this system, causing the imaging performance severely degrading. To address this issue, in this paper, a novel Doppler ambiguous suppression method for an HRWS-TOPS SAR system based on the orthogonal projection subspace is developed. The effectiveness of the proposed method is verified by both the simulated and real SAR data.

The marine moving target detection is a very attractive research field in recent years. However, due to the existence of sea clutter with complex internal motion, the traditional space-time adaptive processing (STAP) methods may not obtain good processing performance. In this paper, the multichannel sea clutter is modeled and the time-varying and space-varying properties of sea clutter are analyzed. In addition, the time-frequency distribution characteristics of sea clutter are analyzed. Finally, a multichannel sea clutter suppression method based on short-time Fourier transform is proposed. The simulation results show that the proposed method can achieve better sea clutter suppression performance than that of the traditional STAP method.

In this letter, a novel method is proposed to suppress the terrain fluctuation clutter based on adaptive broadening processing. In the proposed algorithm, the flat interference phase is first compensated according to the priori radar system parameters. Then, according to the space-time trajectory distribution of clutter edge, the level of clutter Doppler spread in virtue of crab effect is estimated by a cost function related to the clutter eigenvector matrix. Finally, after calculating the clutter suppression weight vector according to the broadened clutter subspace, the non-stationary ground clutter can be robustly rejected. The validity of the proposed method is verified by both the simulated and real-measured multichannel radar data.

Phase synchronization is a key problem which has to be carefully considered in the distributed radar systems. In this letter, the use of a continuous duplex phase synchronization method for the distributed frequency modulated continuous wave synthetic aperture radar system is investigated. The bistatic raw signal model containing the phase difference due to the spatially separated oscillators is introduced. The continuous duplex phase synchronization procedure is proposed later and the synchronization method performance is predicted.

HRWS-SAR steers the antenna to increase the synthetic aperture which causes the radar changes beam squint angle gradually. The squint angle increases with the demanding of the resolution and swath width. With the squint increasing, the relative velocity between radar and lighting swath may reach several km/s. It causes the intra-pulse modulation on the echo. The traditional pulse compressing under the stop-go-stop assumption has bad performance including resolution decrease and PSLR increase. The paper established the echo model. The chirp rate is slightly changed because of the relative velocity. And velocity compensation method is put forward. The experiment results show that the pulse is well compressed. The PSLR and the resolution are restored to normal level.

For sparse signals (direct or indirect), sparse imaging methods can break through limitations of the conventional SAR methods. In this paper, we introduce the basic theory of sparse representation and reconstruction, and then implements several imaging algorithms including FFT and sparse methods. Through comparison, we conclude a good sparse reconstruction algorithm in SAR imaging. Besides, a new strategy of finding a better regularization parameter in sparse reconstruction is implemented. The imaging result of us has a higher resolution and much lower side lobe than the conventional algorithm based on matched filter theory.

With the observation distance of the radar increasing, the multichannel high-resolution synthetic aperture radar system may suffer from the reduction of the target signal-to-noise ratio, which leads to degradation in the detection performance for ground moving target indication (GMTI). Fortunately, the shadow feature, apart from the amplitude and interferometric phase of a moving target, may be available to improve the performance for target detection. In this letter, according to the geometric relationships between the moving object and its shadow in position and size, a shadow-aided method for GMTI is proposed. In addition, an efficient shadow detection method based on multifeature fusion is discussed to improve the shadow detection performance. Finally, numerical simulation results show that the shadow-aided method has a better detection performance, compared with the traditional detection algorithms.

A radar imaging algorithm named reciprocal spectrum algorithm (RSA) is proposed in this paper to get higher resolution in azimuth direction with frequency sampling waveform. Theoretical analysis and simulation results show that the algorithm can give better performance than the tradition range Doppler algorithm (RDA) at the cost of peak value reduction at the object points in radar image.

A progressive SAR imaging technique is proposed as a novel SAR raw data processing scheme in this paper. Different from the classic SAR imaging algorithms which focus the SAR raw data as a whole regardless of the backscattering signal, the novel scheme discriminate the backscattering signal and choose the proper ones to be focused progressively according to some application context while the others will be discarded. The new scheme makes the SAR imaging algorithm not only focus the energy back to the scattering points but also form an image more suitable for some special applications. In this paper, a realization of the scheme present via Atomic Decomposition (AD)[1]–[3]. AD helps estimate the parameters of backscattered signal of a scattering point and detach it from the raw data. With the parameters, the backscattering-signal can be reconstructed and focused. Targets or scatter-points in the scene will be imaged progressively in a sequence of their energy due to the greedy natural of matching pursuit employed during AD. Therefore, the contents in the final SAR image can be controlled by an energy threshold. Besides the interested targets can be extracted easily from the background clutter and this may be helpful for the SAR image understanding