Ground armored weapons have a high detection value in military operations. Satellite synthetic aperture radar (SAR) cannot accurately detect military targets with meter-level sizes limited by resolution of sensors. Airborne SAR have strict experimental conditions and cannot be applied in actual battlefield environments. MiniSAR sensors, which combine the advantages of submeter-level ultrahigh resolutions and flexible flight, play a crucial role in recognizing military targets. In this paper, various small military targets in real complex ground scenarios are detected with the MiniSAR of NUAA. However, there are still two difficulties. First, because of a limitation in the number of flight circles, the number of obtainable military target samples is not sufficient to adapt to the traditional deep learning methods that rely on a large number of image samples. Second, due to the imaging systems and different depression angle of MiniSAR, the SAR images of MiniSAR suffer from the same deformation challenge as the moving and stationary target acquisition and recognition (Mstar) with high depression angle. To address these two challenges, we propose a FASAR-Net framework based on few-shot learning with meta learning and adversarial domain learning, combined with the inherent scattering features of the SAR targets. Furthermore, we validate the reliability and accuracy of this algorithm on Mstar and our datasets, and the result of recognizing small SAR targets is compared with our algorithm and other classical algorithms. We conclude that the proposed algorithm has high accuracy in the recognition of the deformation small targets under the few sample condition.

The echo separation issue associated with different transmit antennas is the most technical challenge in realizing the Multiple-Input Multiple-Output (MIMO) Synthetic Aperture Radar (SAR) system. In this paper, a reconfigurable MIMO-SAR transmission scheme based on inter-pulse and intra-pulse joint phase modulation is proposed. The proposed scheme has many advantages. First, lots of monostatic waveforms can be directly employed in a MIMO-SAR system, which offers flexibility in waveform selection. Second, according to different MIMO-SAR applications, it is reconfigurable and can flexibly adjust the system Degree of Freedoms (DoFs) to accomplish echo separation, achieving the best system performance, which is the key for the multimodal operation of MIMO-SARs. Finally, due to the limited system resources in the real MIMO-SAR system, it is hard to separate echo in a single domain, and the proposed scheme jointly capitalizes DoFs of Doppler, time, and space domains to ensure the successful echo separation. In addition, detailed simulation experiments are carried out to verify the practicability and effectiveness of the newly proposed transceiver schemes.

The range ambiguity issue is a technical challenge in the radar community and has been widely discussed over the years. Researchers have given special attention to multiple-input and multiple-output (MIMO) radar to address the range ambiguity because this radar system can employ more equivalent degrees of freedom. Open studies on MIMO radar are generally based on the assumption of orthogonal waveforms, whereas radar performance is seriously limited by distributed targets due to mismatched energy. To this end, this paper deals with a novel MIMO radar transmission scheme called transmitter interpulse phase coding (TIPC) without using orthogonal waveforms. First, a set of well-designed TIPC codes are employed to modulate transmitter subarrays with the same modulated signal. Second, in the case of high pulse repetition frequency (PRF) ¹ , aliased echoes from different transmitted channels are directly separated by a group of simple Doppler filters; for normal PRF ² radar systems, a technique called digital beamforming in azimuth is exploited to ensure an effective multiple waveform separation. Third, a decoding processing is performed for a further derivation of the residual TIPC matrix that is related with ambiguity order. Next, the desired and ambiguous echoes are separated by a specifically designed spatial filter that absorbs the residual TIPC matrix. Particularly, the separated signal can be used for some further applications such as increasing the observation swath. Finally, point-like target and distributed targets simulation experiments are performed to verify the feasibility of the proposed TIPC MIMO radar.

Synthetic aperture radar (SAR) systems have the capacity for day-and-night and all-weather surveillance, which has become increasingly indispensable for military surveillance and global comprehensive environmental monitoring. With the development of the high-resolution SAR imaging technique, studies on SAR jamming have also received much interest. Traditional jamming methods are based on linear-frequency-modulated (LFM) signals, and this method can achieve high main-lobe jamming gain. However, its sidelobe jamming energy is very low. To solve this issue, a novel nonlinear frequency modulation (NLFM) waveform design method for SAR jamming is proposed in this paper. Compared with LFM waveforms, the designed waveforms have the same main-lobe jamming gain and very high sidelobes, which can significantly improve jamming performance. Moreover, detailed simulation experiments were carried out to verify the effectiveness of the newly proposed jamming scheme.

The problem of echo separation using digital beamforming (DBF) on receive for multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) is of notable importance to allow for practical systems. Regrettably, current DBF-MIMO-SAR schemes, such as the short-term shift-orthogonal (STSO) scheme, are computationally cumbersome, increasing the required hardware complexity. To alleviate this problem, we here propose an improved echo separation solution for realizing a low-cost MIMO-SAR system. We detail a generic waveform design scheme as well as optimized monostatic radar waveforms (e.g., nonlinear frequency modulation (NLFM) signal) showing how these can be directly adopted in the proposed scheme to improve the imaging performance. The proposed scheme enables the number of the interference segments generated by unmatched waveforms to be halved by the use of the fast time spectrum preprocessing and segment synthesis, dramatically simplifying the array configuration and reduces the system complexity. By exploiting inter-pulse phase coding techniques, the proposed method can provide a reconfigurable waveform transmitting scheme, allowing the system resources in range frequency, elevation space, and Doppler domains to be jointly exploited for the separation of aliased signal returns. The proposed scheme is evaluated using extensive numerical and measured data sets, demonstrating the feasibility and potential of the proposed method for resource-limited spaceborne/airborne MIMO-SAR systems.

Barrage jamming technique against spaceborne synthetic aperture radar (SAR) systems plays an important role in electronic countermeasures. Generally, it is crucial for the jammer to obtain a satisfactory SAR image corrupting performance with both low computational burden and low transmitting power. In this respect, a knowledge-aided precise jamming technique has been proposed to cope with the involved technical challenges. In our work, the generation of the jamming signal with two-dimensional (2-D) controllable coverage and high coherent integration gain is detailed using the range- Doppler algorithm (RDA) in linear frequency modulation (LFM) case. Moreover, the simple linear iterative clustering (SLIC) technique is also employed to segment the regions of interest (ROIs). Based on the 2-D controllable jamming modulation and the SLIC technique, the ROIs can be covered by a small amount of false scatterers, significantly reducing the signal modulation burden. Furthermore, the prior information of ROIs, i.e., the backscattering intensity information, is also exploited to achieve the optimal allocation of jammer power, allowing for further reduction of jamming energy. Finally, extensive numerical simulations are implemented to prove the feasibility of the proposed jamming technique against opponent's SARs.