Research On ENLCS Imaging Algorithm For Airborne Synthetic Aperture Radar

The synthetic aperture radar system is mounted on mobile platforms such as airplanes and satellites.It uses synthetic aperture principles and microwave technology to perform real-time observations of all-weather and high-resolution imaging of designated areas on the ground.As an active monitoring system with strong anti-interference,the application of SAR system plays an impoitant role in military and civilian fields,and functions such as disaster warning,military investigation and resource exploration can all be realized by SAR system.Although the configuration of airborne SAR is relatively easy to deploy,the research of imaging algorithms will face more challenges.The squint mode of the radar beam increases the flexibility of the SAR geometry design,which not only causes severe range-azimuth coupling,but also causes complex azimuth-variant properties for the residual RCM and Doppler phase,seriously affecting the final focusing result.Aiming at the above problems,this paper proposes an imaging algorithm for airborne squint SAR imaging based on improved circular model.Firstly,the combination of LRWC and KT transform is used to remove the range-azimuth coupling,linear range walking and Doppler center frequency.According to the result of high-order RCMC,an improved circular model is constructed on the two-dimensional plane,and the azimuth-variant properties of the beam center range offset of the point target are accurately approximated.Based on the model,a new azimuth-variant residual RCMC is proposed,and the azimuth equalization and compression by the ENLCS are improved with the derivation results of the circle model.The simulation results show that the proposed algorithm based on the improved circular model accurately processes the residual high-order RCM and azimuth-variant Doppler phase,which greatly enhances the focusing performance.With the wide imaging scene,the range between the airborne radar platform and the target area is relatively small,and the change between the squint angles of the different point targets cannot be ignored.Therefore,the description of the signal characteristics of the point target by the traditional geometric configuration with a fixed squint angle is inaccurate,and characteristics of the wide imaging scene and smaller beam transmitting range make it more difficult to describe the azimuth-variant properties of the SAR signal by the analytical model.To solve the problem of wide imaging scene,this paper proposes a high-resolution imaging algorithm based on three-dimensional sphere model for airborne SAR with wide swath.Firstly,a more accurate geometric configuration is designed,and the characteristics of the changing squint angle of the signal are analyzed.After the preprocessing in range,a new three-dimensional sphere model is constructed according to the improved geometry configuration,which can accurately describe the azimuth-variant relationship of the range position offset of the point target.Then,the derivation results of the model are used to improve the procedure of the azimuth-variant residual RCMC and the azimuth equalization and compression by ENLCS.According to the resulte of the simlation experiments,the proposed airborne SAR imaging algorithm based on the three-dimensional sphere model can achieve better high-resolution focusing effect of the wide imaging scene compared to the traditional imaging method.