Research On Radar Imaging In Microwave Anechoic Chamber Based On Compressed Sensing

The imaging radar actively transmits high-frequency electromagnetic wave signals to the detection target and performs inversion processing of the acquired backscattered energy,which can obtain the spatial position,fine scattering characteristics,motion state and other related parameter information of the observation target so as to meet the requirements for multi-level,high-precision,and time-efficient spatial information of the target in military,civilian and other application fields.Synthetic Aperture Radar(SAR)and Inverse Synthetic Aperture Radar(ISAR)are equivalently synthesized into a large antenna aperture through the relative motion between the radar platform and the observation target,which greatly improves the imaging resolution of the target without increasing the physical size of the antenna and has the advantages of long detection distance,unaffected by light and complex meteorological conditions,and rich target information.However,with the continuous development and iterative update of radar imaging technology,various application fields not only require radar equipment to have higher imaging resolution,wider mapping band and more timely computing and processing capacity,but also require it to continuously reduce the system complexity and reduce the carrying load of imaging radar.On the other hand,the imaging radar has limited imaging time and signal acquisition due to its own working mode and the complex and changeable motion state of the detection target,resulting in the frequency discontinuity of the effective sampling signal and the defect of the azimuth aperture data,which affects the imaging quality.In recent years,the emergence and development of Compressed Sensing/Compressive sensing(CS)theory has provided new solutions and ideas for low-cost transmission sampling and imaging processing of SAR/ISAR echo signals.CS theory breaks through the traditional limitation based on Shannon-Nyquist signal sampling criteria,simplifies the hardware design of the radar system,saves signal acquisition time,reduces the amount of data acquisition and storage and can effectively improve the imaging performance under the premise of ensuring the accurate reconstruction of radar echo signals,thereby achieving high-performance imaging of the detected target.In this dissertation,Compressed Sensing theory has been introduced into the radar imaging algorithm of microwave anechoic chamber.Under the premise of ensuring the high-precision reconstruction of the imaging target,the practical working efficiency of the overall imaging experimental system in microwave anechoic chamber has been greatly improved by studying the sparse representation relationship and sparse priori features of echo signals in the hardwarein-the-loop simulation.Finally,the high-resolution hardware-in-the-loop simulation imaging experimental results of SAR/ISAR target have been obtained.The main contributions of this dissertation are as follows:1.In the framework of CS theory,optimization of measurement matrices in sparse observation process has been studied in microwave anechoic chamber.Firstly,according to the scattering characteristics of the target and the imaging algorithms,a unified testing model of microwave anechoic chamber radar imaging has been constructed.Then,according to the needs of practical storage,matrices operation and performance improvement,the sparse band measurement matrices,sparse measurement chaotic sequence matrices and improved chaotic sequence cyclic shift measurement matrices with engineering significance and practical value have been constructed and improved.Finally,in the semi-physical experiment environment of the microwave anechoic chamber,the measured echo data is used to verify the correctness and validity of the measurement matrix proposed in the dissertation.2.In this dissertation,the sparse two-dimensional imaging algorithms based on Compressed Sensing is proposed.The sparse two-dimensional imaging of far-field turntable targets,near-field scanning targets and near-field array antenna targets is carried out by combining Compressed Sensing theory with two-dimensional imaging algorithms in microwave anechoic chamber.On the premise of ensuring the imaging quality,the amount of sampling data of azimuth-aperture echo signals is greatly reduced in ISAR imaging of far-field turntable;the scanning stroke of antenna probe and complexity of imaging system are greatly reduced,the testing time has been greatly shortened in near field scanning SAR imaging;the number of antenna elements is greatly reduce Near field array antenna SAR imaging.Moreover,in the two-dimensional imaging process of the near-field sparse array antenna,amplitude correction and phase error compensation are performed on the echo signals.At the same time,a diagonal sparse scanning method is proposed for the near-field planar scanning testing system in the dissertation,the complexity and computational amount of two-dimensional imaging has been reduced effectively and better imaging quality can be obtained.3.In this dissertation,the methods of echo signals acquisition about sparse planar aperture and high-resolution three-dimensional imaging algorithms of near-field targets are proposed based on CS theory,which combined with three-dimensional wavenumber domain imaging algorithm(3D-RMA)and time-domain imaging algorithm(3D-BPA).In the traditional planar scanning mode,the antenna detector of the scanning frame has the problems of long round-trip travel distance,a large number of scanning spots,more testing time,huge amount of data sampling and computation,and poor the efficiency of testing system.The sparse planar scanning method in the diagonal direction has been proposed in this dissertation based on CS theory echo signal model of three-dimensional imaging.Finally,the good focusing result of near-field 3D imaging is obtained and the energy efficiency of the whole testing system is also greatly improved.4.In this dissertation,the RID imaging method of non-cooperative maneuvering target in microwave anechoic chamber is proposed by combining Gabor transform time-frequency analysis and CS sparse reconstruction theory.Both the classic R-D imaging algorithm and the Compressed Sensing ISAR imaging algorithm fail to process the echo signal of non-stationary motion,while the Range-Instantaneous Doppler(RID)imaging algorithm requires complete target echo sequence data,so the imaging resolution is limited,as a result,the resolution of the three imaging algorithms is not good enough.To solve the above problem,the method of Gabor transform time-frequency analysis combined with CS sparse reconstruction theory is proposed to ensure the image quality of ISAR and achieve high-resolution ISAR imaging of maneuvering targets.