Research On Ship Target Imaging Method Of Airborne Bistatic Radar

Airborne bistatic Synthetic Aperture Radar（SAR）separates the transceiver system of the radar on different aircraft platforms,which can achieve high-precision imaging of the receiver’s forward-looking area in any weather and at any time.With the strong antiinterference ability,anti-reconnaissance and other advantages,it has very important application value in the military and civilian fields such as ground feature detection and ground/sea forward-looking area surveillance.Airborne bistatic radar ship target imaging technology refers to processing the ship target echo under the bistatic SAR system,overcoming the defocus problem caused by large range cell migration and spatial variant Doppler phase of the moving target echo and accurately reconstructing the two-dimensional scattering information of the ship target from the echo signals.High-precision imaging of ship targets is the premise for accurate classification and recognition of ship SAR images.This thesis focuses on the echo modeling,ship SAR image refocusing,high-precision time-frequency analysis imaging involved in bistatic SAR ship imaging.The main research contents are as follows:1.Established the motion model of the ship target and the echo model of the airborne bistatic radar ship target and analyzed the distance migration characteristics and spatialvariant Doppler characteristics of the ship moving target.Then,the difference between the echo characteristics of ship targets and ground targets is analyzed and compared,which lays a foundation for the follow-up research on high-precision imaging methods of ship targets.2.The defocus characteristics of ship moving targets and the limitations of the existing frequency-domain phase compensation methods in the time-domain Back Projection（BP）algorithm are studied and analyzed.According to the defocus characteristics of the ship target,a polar imaging model under any bistatic configuration is established.Then,based on the above research,a fast self-focusing method suitable for BP imaging method is proposed,which effectively solves the defocusing problem of ship target imaging.3.Proposed an airborne bistatic SAR ship target range instantaneous Doppler imaging method based on joint Fr FT-WVD time-frequency analysis.Firstly,a Doppler ambiguity number estimation method based on the criterion of minimum global average range profile entropy is proposed,which effectively solves the problem of echo data ambiguity.Then,through the joint Fr FT-WVD time-frequency processing,the problem of the two-dimensional spatial variant Doppler phase of the moving target echo is solved.Finally,the high-precision ship target image is obtained.The efficiency of the aforementioned methods is validated in this thesis through theoretical analysis and numerical experiments.The research findings suggest that the methods described above can effectively solve the problem of defocusing of ship SAR images and achieve high-precision imaging of ship targets.