Research On Missile-Borne Synthetic Aperture Radar Imaging Algorithm With High-Resolution And High-Squint

Synthetic Aperture Radar(SAR)is a microwave active imaging system.Its working principle is: coherent processing of a small aperture antenna by the relative motion information of the platform and the imaging object is equivalent to a larger aperture antenna.Thereby obtaining high-resolution images.In addition to its high-resolution imaging capabilities,SAR is widely used in various fields because of its advantages of all-day and all-weather interference,real-time detection,and strong penetrating power.With the rapid development of radar technology,in order to adapt to the precise guidance in information warfare,various SAR imaging algorithms have been introduced into the field of missile guidance,missile-borne SAR develops rapidly.However,due to the high speed,complex and variable trajectory of the missile-borne SAR system,the imaging conditions are complicated due to the complicated configuration.Therefore,the traditional airborne and spaceborne SAR algorithms are no longer applicable.According to the different flight processes,such as the horizontal-flight section and the subduction section,this paper studies the high-resolution imaging algorithm based on the specific configuration of the missile-borne SAR and the characteristics of the flight path.In the horizontal-flight section,this paper finds that the squint angle is significantly different in the range spatial space under the condition of close-range and wide-area(close-range wide-sampling)imaging,which brings two-dimensional spatial variation of RCM and azimuth dependence of Doppler parameters.Therefore,firstly,the received echo is subjected to linear range walk correction(LRWC)processing in the range to remove most of the range cell migration(RCM).Then the KT(Keystone)operation is added to mitigate some of the range-azimuth coupling.The range pre-processing was completed by a bulk RCM correction(BRCMC).According to the result of the range pre-processing,an improved equidistant sphere model is constructed for the echo data of the spatial squint angle with the ground distance,so that the accurate two-dimensional space-varying characteristic analytical expression is obtained for the echo derivation.The remaining high-order RCM is compensated by deriving the analytical expression.In addition,in the azimuth direction,a frequency-domain extended nonlinear chirp scaling(FENLCS)imaging processing method is proposed based on the equidistant sphere model,which realizes the removal of the residual Doppler center and the equalization of the Doppler high-order frequency.In this process,a frequency domain high-order non-space-variant pre-filtering method is proposed to simplify the derivation process of FENLCS algorithm and improve the focus quality.The simulation results verify the validity of the orientation of this paper.In the subduction section,the missile-borne SAR platform has a large subduction velocity and acceleration,and the range-azimuth coupling is severe.However,under the condition of large squint angle,the range and azimuth spatial-denaturation problems increase,and the Doppler parameter estimation is difficult.It has a serious impact on motion compensation under motion.Therefore,the received echoes are first compensated for LRWC and acceleration in the range.Then combined with KT processing,the residual linear components of the two-dimensional space-varying characteristics are completely removed and the main range-azimuth coupling is removed.According to the result of the range processing,an equidistant sphere model is constructed,which completed the correction of high-order RCM and established the basis for the processing of azimuth.In the azimuth direction,the processing method of the flat flying segment is used,and the influence of the Doppler phase of the azimuth space is analyzed.Finally,the azimuth compression processing is completed with the help of FENLCS algorithm.