Research On Synthetic Aperture Radar Waveform Design For Countering Active Coherent Jamming

Synthetic aperture radar(SAR)has been widely applied in military filed,such as monitor of battlefield environment,reconnaissance of military targets,guidance of targets strike,and the damage assessment of military targets.However,due to the development of digital radio frequency memory and high-speed digital circuits,the active coherent jam-ming is increasingly abundant,which brings a great challenge to SAR.Improving SAR anti-jamming performance,especially countering the active coherent jamming,has been a hot issue in the SAR electronic counter counter measures filed.The goals of this disser-tation is to study the anti-jamming method against active coherent jamming by waveform deign.Aiming to suppress the typical coherent jamming,i.e.,shift-frequency jamming,active motion modulated jamming/interrupted sampling repeater jamming and convolu-tion modulated jamming,the dissertation focuses mainly on the basic principle of coherent jamming and anti-jamming waveform design,anti-jamming waveform design method and algorithms,imaging methods of the anti-jamming waveform and evaluation of the anti-jamming performance of the proposed methods.The main contents of this dissertation are as followsThe second chapter analyzes the principle of waveform design against active co-herent jamming,which provides the theoretical basis for the subsequent research on the anti-jamming waveform design methods.By analyzing the principle and electronic recon-naissance requirement of the typical coherent jamming,and imaging characteristic of the jamming signal,the relationship between the active coherent jamming and the intrapulse and interpulse waveform characteristics are obtained,respectively.Based on the above analysis,the following theory of anti-jamming waveform design is obtained.The intra-pulse and interpulse waveform design can be applied to counter shift-frequency jamming because it is dependent on the high Doppler tolerance of waveform,and the jamming echo always lags behind a pulse repetition interval.The interrupted sampling repeater jamming can be countered by the fast-time waveform and mismatched filter design since the jam-ming effect is determined by the waveform Doppler tolerance and smart use of matched filter.In addition,the interpulse characteristic of the waveform should be considered in order to suppress the convolution modulated jamming.The third chapter studies the waveform design method against the shift-frequency jamming.Due to the fact that the shift-frequency jamming is dependent on the high Doppler tolerance of the transmitted waveform,an anti-jamming method is proposed by designing waveform with low Doppler tolerance,which results in loss of processing gain of the jamming signal in the range direction,and thus suppress the shift-frequency jam-ming.By applying the interpulse random phase or waveform diversity method,the az-imuth processing gain of jamming signal is also suppressed,which further improves the shift-frequency jamming suppression performance.To meet the requirement of low pulse compression sidelobe in SAR imaging,a joint waveform and mismatched filter design algorithm is proposed to obtain high pulse compression performance.Fast joint design algorithms are then proposed based on block coordinate descent and majorization mini-mization tecniques,which can be used to design waveform with code length of 10~6.By simulation comparison,it is concluded that the integrated sidelobe level metric is more suitable than peak sidelobe level metric because it maintains a better balance between in-tegrated and peak sidelobe level are obtained by minimizing the integrated sidelobe level metric.In addition,a range Doppler imaging method is proposed for the anti-jamming waveform,and the Doppler compensation method is presented to improve the imaging performance in squint SAR.Finally,several simulations are conducted to evaluate the anti-jamming performance by assessing the signal-to-jamming ratio in the imaging re-sults.The fourth chapter proposes waveform and filter joint design method for suppress-ing the interrupted sampling jamming.Based on the jamming imaging characteristic,the proposed method concentrates on suppressing the peak interferences by designing the waveform with low Doppler tolerance and the mismatched filter,which aims to degrade the imaging processing gain of the jamming signal.Moreover,the pulse compression and integrated levels of the mismatch output of jamming signal are also considered in the joint design optimization problem to obtain good imaging performance and suppressing jam-ming energy.Then,the unimodular waveform and mismatched filter are proposed,and the corresponding joint design algorithm is derived based on the majorization minimization method.Moreover,the peak-to-average power ratio waveform and mismatched filter are then proposed to increase the degree of freedom of joint design method and thus enhance the anti-jamming performance.A joint design algorithm is then proposed based alternate direction minimization method to solve the nonconvex problem.Finally,the feasibility of the proposed methods is demonstrated by assessing the imaging results in the pres-ence of three interrupted sampling repeater jamming with different repeater mode,and micro motion and uniformly accelerated motion modulated interrupted sampling repeater jamming.The fifth chapter proposes an interpulse frequency coding waveform design method against the convolution modulated jamming.The anti-jamming principle of interpulse frequency is analyzed,the stepped frequency coding and random frequency coding wave-form is then proposed.By analyzing the Doppler history of the interpulse frequency cod-ing SAR,it is pointed out that the traditional imaging algorithm cannot obtain the focused images.Meanwhile,a microwave sparse imaging method is proposed for interpulse fre-quency coding SAR.The superiority of random frequency coding is also demonstrated by theoretical analysis and simulations.In addition,a three-channel microwave sparse imaging method and the corresponding phase compensation method are proposed to im-prove the coherence of the echo data from different carrier frequencies,and increase the downsampling rate in the sparse imaging method,which significantly improves the imag-ing performance.Finally,the imaging performance and anti-jamming performance of the proposed method is demonstrated by simulations.