Range ambiguity is a critical factor degrading the high-resolution and wide-swath (HRWS) imaging performance of spaceborne synthetic aperture radar (SAR), arising primarily from the antenna sidelobe characteristics. Recently, blind source separation (BSS) methods have shown promise in mitigating range ambiguity. However, existing studies have mainly focused on the determined scenario. In contrast, underdetermined cases are often more prevalent in practical settings. To address this gap, this article proposes a novel range ambiguity suppression scheme specifically designed for the underdetermined BSS (UBSS) scenario. Point and distributed targets simulation based on Sentinel-1 system is conducted to verify its effectiveness. The results indicate that for the point target imaging performance of two channels, peak sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) are improved by an average of 6.62 and 9.47 dB, respectively. In the distributed target case, the separation and recovery of the echo signals in the target region achieve an average similarity (pixel, structure, and cosine metrics) exceeding 94.27%, and demonstrate robustness at signal-to-noise ratios above 25 dB. These findings provide insight into the feasibility of UBSS-based strategies for range ambiguity suppression and offer valuable reference points for future investigations involving single-channel implementations.

Synthetic Aperture Radar (SAR) demonstrates advantages in continuous, all-weather, high-resolution Earth observation. However, barrage jamming in both the time and frequency domains can overwhelm SAR signals, leading to a significant overlap between interference and target signals, thus making separation challenging. In particular, barrage interference from multiple jammers can render SAR images almost indecipherable, substantially diminishing the quality of SAR image products. This paper introduces a barrage jamming suppression method for multiple jammers utilizing elevation multi-channel SAR. By first performing blind source separation on the mixed echoes, signals from different imaging bands are extracted, followed by imaging and other processes. Simulation experiments have confirmed that this approach offers benefits such as low system complexity and effective jamming suppression.

Digital beamforming (DBF) can provide high-gain narrow-beam scanning reception while transmitting wide-beam signals, which greatly improves the signal-to-noise ratio (SNR) of the corresponding systems. It is an effective technique for synthetic aperture radar (SAR) to obtain high-resolution wide-swath (HRWS) imaging capability. However, elevation changes in mountain area will lead to beam-pointing mismatch problems when using the ideal sphere model to calculate the beamforming weighting vector. As a result, the loss of receive gain and the deterioration of the SNR will occur. To solve this problem, adaptive DBF (ADBF) methods based on spectral estimation are typically used, such as Capon and MUSIC. However, the computational complexity of spectral estimation method is high, which is not conducive to on-satellite real-time processing. Therefore, a low complexity ADBF method based on beam-space phase-center cross correlation is proposed. In this method, the whole array is divided into several subarrays, and multiple phase centers are formed by beamforming so that the angle of arrival (AOA) of the signal source can be accurately estimated. Then, the weighted vector of the received beam is updated to mitigate the loss of receiver gain. The simulation results and airborne measured data validate the effectiveness of the proposed method. Compared with methods based on Capon and MUSIC, the proposed method can decrease the computational complexity without reducing the processing accuracy, thus providing a basis for the real-time processing of spaceborne DBF-SAR signals in the future.

The multiple elevation beam (MEB) mode is an effective technique for enhancing imaging width in spaceborne synthetic aperture radar (SAR) systems. This mode combines intra-pulse beam-steering during transmitting and digital beamforming (DBF) during receiving. By sequentially illuminating the far sub-swath followed by the near sub-swath, echoes from different sub-swaths can reach the antenna at the same time and overlap each other in the receiving window. To separate the overlapping echoes, the linear constrained minimum variance (LCMV) beamformer has been used, which is a single-null constrained beamformer. Additionally, a multi-null constraint beamformer has also been proposed on this basis. However, these two methods are insufficient for effectively separating the overlapping echoes when there is a significant energy difference between different sub-beams signals. To solve this problem, an advanced multi-null constrained beamformer with deepened nulls is proposed. Compared with other methods, the proposed method can flexibly adjust the width and depth of the nulls. The simulation results demonstrate that the proposed method can enhance echo separation quality. And the experimental results verify the effectiveness of the proposed method. All the results indicate that the proposed method is helpful to improve high-resolution and wide-swath imaging performance of future spaceborne SAR systems.

Insipred by the cocktail party effect, an advanced scheme based on blind source separation is put forward to suppress the range ambiguity of spaceborne SAR in this paper. In the scheme, multiple sub-antennas are used to collect multiple echo data sets, which are given different patterns. In this way, the echo signal of the desired region and that of the ambiguous region are weighted using different coefficients. During post-processing, a detailed flow with the blind source separation algorithm is proposed to separate the desired echoes from those data sets. To verify the scheme, the point targets simulation is carried out. The results indicate that range ambiguity can be reduced by more than 14 dB using the proposed scheme, the processing flow is effective, and the scheme has a good performance without increasing system complexity. The scheme has the potential to be applied to the future spaceborne SAR missions, such as LuTan-l (LT-l) misson.

Cocktail party effect is a fascinating thing about our amazing brains. Inspired by this, a new synthetic aperture radar (SAR) concept is first proposed for wide-swath imaging. Here, it is termed as IP-SAR, because this idea originally comes from voIce-seParation (IP). IP-SAR is a radar system with an array antenna divided into multi-channels along azimuth and/or el-evation directions, and it can image multiple sub-swaths at the same time. In order to verify the wide-swath imaging ability of IP-SAR, scene simulations are conducted, and the gener-ated echoes are processed according to a novel procedure.

Due to the minimum antenna area constrain of synthetic aperture radar (SAR), high-resolution and wide-swath (HRWS) imaging is difficult to be achieved using classical modes, such as scan, spotlight, and so on. Range ambiguity is one of the main technical challenges limiting HRWS imaging in spaceborne SAR. Insipred by the cocktail party effect, an advanced scheme based on blind source separation is put forward to suppress the range ambiguity of spaceborne SAR in this paper. In the scheme, multiple subantennas are used to collect multiple echo data sets, which are given different patterns. In this way, the echo signal of the desired region and that of the ambiguous region are weighted using different coefficients. During postprocessing, a detailed flow with the blind source separation algorithm is proposed to separate the desired echoes from those data sets. To verify the scheme, point target and scene simulations based on GF3 are carried out. The results indicate that the range ambiguity can be reduced by more than 15 dB using the proposed scheme, the processing flow is effective, and the scheme has a good performance without increasing the complexity of the system design under the current SAR system conditions. The scheme has the potential to be adopted in future spaceborne SAR missions.