In this letter, a method is proposed to suppress the interrupted sampling repeater jamming (ISRJ) by jointly designing the radar waveform and mismatch filter. Firstly, the joint design problem under multiple constraints is formulated with the optimization criterion of minimizing the integrated sidelobe levels (ISLs) of waveform mismatch filter output and integrated levels (ILs) of ISRJ signal mismatch filter output. An iterative algorithm is proposed to optimize the waveform and mismatch filter using Lagrange multiplier method and alternating direction multiplier method (ADMM), respectively. Simulation results show that the proposed method achieve good correlation performance between the waveform and mismatch filter, and demonstrate the effectiveness of anti-ISRJ.

The interrupted-sampling repeater jamming (ISRJ) is coherent and has the characteristic of suppression and deception to degrade the synthetic aperture radar (SAR) image quality. The anti-ISRJ methods are studied in this work in order to suppress the ISRJ based on the waveform and filter design for SAR. First, the relationship between the ISRJ and waveform is obtained by analyzing the principle of the ISRJ using the ambiguity function. The ISRJ produces multiple false targets based on the high Doppler tolerance of waveform and the characteristic of the matched filter. Next, a method is proposed to counter the ISRJ by transmitting a phase-coded (PC) waveform with low Doppler tolerance and designing the corresponding mismatched filter. The joint design method is then developed to improve the anti-ISRJ and imaging performance. In the proposed methods, the majorization minimization framework is introduced to solve the nonconvex waveform and filter design problem. Finally, several simulations are conducted to demonstrate the effectiveness of the proposed methods. Simulation results show that the joint design method shows better anti-ISRJ and imaging performance in comparison with the separate design method, but it is more sensitive to the ISRJ sampling duty ratio and period.

A joint waveform and filter design method is developed for suppressing radar pulse compression sidelobe level in this paper. The problem is formulated as the minimization of the integrated sidelobe level (ISL) under the constraint of waveform constant modular and filter energy. To control the loss-in-processing gain (LPG), an additional function is introduced to constrain the peak level based on penalty function method. The joint design algorithm is then derived based on the alternating minimization and majorization minimization (MM) schemes. The computation complexity is analyzed and the convergence analysis verifies that the algorithm can converge to a critical point. Specifically, the proposed method is extended to the waveform and filter design for suppressing the peak sidelobe level (PSL). Numerical simulations are carried out to analyze the key parameters, which demonstrate the feasibility of the proposed method. Simulation results show that the ISL and PSL can be significantly reduced with small LPG. Moreover, the proposed method exhibits faster running speed than the existing one and it thus can be applied to longer sequence designs.

Imaging of spatial-variant geosynchronous synthetic aperture radar (GEO SAR) in the L band with long integration time is discussed. To compensate for spatial variances in both range and azimuth directions, a new algorithm based on improved omega-K (ωK) and three-time azimuth chirp scaling (3ACS) is proposed. First, the integration time and the slant range model were analyzed. Second, the two-dimensional (2-D) spectrum was used for range cell migration correction (RCMC), secondary range compression (SRC), and azimuth compression, and the influences of spatial variances on each term were considered. Third, the improved ωK was used to compensate for the range variance, and 3ACS was used to compensate for the azimuth variance. The scope of 2-D focusing in high-resolution GEO SAR imaging was clearly enlarged. Finally, the performance of the algorithm was demonstrated using simulations based on a spaceborne radar advance simulator (SBRAS).

Frequency agility increases the difficulty of jammers to predict and estimate the carrier frequency and, thus, improves the radar electronic counter-countermeasures (ECCM) performance. In this article, frequency agility is introduced into synthetic aperture radar (SAR). The characteristic of the Doppler history of frequency-agile SAR (FASAR) is analyzed, which shows that the azimuth compression could not be achieved by the classic imaging algorithms. In order to reconstruct the images of interested targets, a three-channel sparse imaging method is proposed based on approximated observation model by using the echo data of different carrier frequencies. By deriving the equivalent observation model, it is concluded that the reconstruction performance can be enhanced by improving the coherence of match filter imaging results in different channels. The image characteristic of different channels in FASAR is analyzed based on the chirp scaling imaging operator. A phase compensation method is then proposed to improve the coherence of images of interested targets in different channels. Specifically, the SAR mode of random frequency agility is proposed to improve the reconstruction performance. Finally, simulations are carried out to demonstrate the effectiveness of imaging methods and ECCM performance. Theoretical analysis and simulation results demonstrate that images generated in random FASAR have better performance than those in stepped FASAR. By performing the phase compensation, the reconstruction performance of small targets can be significantly improved.