Research On Radio Frequency Interference And Deceptive Jamming Suppression Approach In Synthetic Aperture Radar

Synthetic aperture radar,as an active microwave remote sensing device,offers advantages such as long detection range and excellent performance even in dark nights and harsh nat-ural environments,has been widely applied in various remote sensing systems.However,synthetic aperture radar is easily interferenced by numerous external signals in the current complex electromagnetic environment,leading to a sharp reduction of quality of the final ob-tained radar images.As two major external threats to synthetic aperture radar systems,radio frequency interference and deceptive jamming own the capability to significantly impact the ground detection performances of synthetic aperture radar.The characteristic of high-power makes the radio frequency interference can easily cover the information of ground scatters by forming extremely bright lines or blocks in radar images.On the other hand,deceptive jam-ming has the capacity to generate false scenes in radar images,consequently causing radar systems or technicians to make inaccurate judgments regarding the distribution of ground objects.Owing to the overlapping of radio frequency interference with radar signals in both time and frequency domains,coupled with its significantly higher power compared to radar echo signals,it is a big challenge and a hot research spot in finding an effectively way to suppress it.On the other hand,deceptive jamming shares the same form as radar echoes,and the false scene formed by it is very similar to the real scene.Therefore,it is also difficult to distinguish and suppress it.This dissertation focuses on studying how to effectively suppress the above-mentioned two interferences.The main content is summarized as follows:1.Many existing sparse recovery methods always face the problem of hyperparameter selec-tion difficulty when suppressing narrowband radio frequency interference,while hyperpa-rameters will affect the final interference suppression performance.More importantly,the number of interferences between different pulses may change,making the original hyper-parameter value no longer suitable.Aiming at this problem,a narrowband radio frequency interference suppression method based on frequency domain segmentation sparse search is proposed.The proposed method starts from the classic non-convex l₀norm LASSO model,combined with adaptive filter,determines the approximate range of interference frequency,and thus transforms the non-convex l₀problem into a convex one.After this transformation,hyperparameters no longer appear,and thus,the proposal avoids the problem of hyperparam-eter selection.Finally,by solving the transformed model,purified synthetic aperture radar data can be obtained.2.In the process of suppressing narrowband radio frequency interference,in the case that the interference frequency is mismatched with the divided grid frequency in prior,the interfer-ence energy will be diffused in the spectrum,reducing the performance of many existing interference suppression methods.Therefore,a narrowband radio frequency interference suppression method based on interference frequency mismatch reconstruction and rotation dictionary sparse recovery is proposed.In the proposed method,we first define the support set and construct null space projection operator.Based on the two definitions,we then by constructing and solving an optimization model to obtain mismatch between each interfer-ence and the corresponded frequency grid point.Secondly,by using the obtained mismatch,we are led to rotate the inverse Fourier matrix to form a rotated dictionary.It is shown that under the rotated dictionary,diffused interference energy can be refocused.Finally,one can construct a sparse recovery optimization model based on the above rotated dictionary and solve it to acquire synthetic aperture radar data after interference suppression.3.Aiming at the problem of quadratic coding based deceptive jamming suppression method cannot suppress deceptive jamming thoroughly under the case of low repetition frequency of radar,a deceptive jamming suppression method based on auxiliary channel slow time cod-ing is proposed.We propose to code every transmitted pulses on auxiliary channel,by the designed coding strategy.In this case,compared to the false scene in the main channel,it is shown that the false scene formed by deceptive jamming appears an offset in the obtained radar image of auxiliary channel radar images.Therefore,we propose to make use of the image change detection technology to form band-pass filter in the imagery domain to realize deceptive jamming filtering.4.Existing interference suppression methods always focus only on dealing with one kind of interference,but do not have ability to suppress the two kinds of interferences,namely,radio frequency interference or deceptive jamming.Therefore,it is undoubtedly a huge advance if an approach can suppress the above two interferences.Thus,a joint radio frequency inter-ference and deceptive jamming suppression method based on sub-pulse coding is proposed.By cleverly designing coding phase of transmitted pulses and combining sub-pulse transmis-sion mode,the proposed method can achieve narrow/wide band radio frequency interference suppression in the Doppler domain;on the other hand,after a decoding process,it is found that by using sub-pulse digital beamforming method combined with designed beamforming weights,deceptive jamming can also be well suppressed.