Research On Signal Processing And Imaging Of Curve Trajectory SAR

Along with the development of radar technology and the increasing demand for application,the curve trajectory synthetic aperture radar(CTSAR)should be born.It can solve the observation problems in some special areas and has more flexibility,mobility and autonomy.The existence of 3D acceleration makes the slant range of CTSAR more complicated,thus increasing the difficulty of CTSAR signal processing.Imaging algorithms under conventional linear trajectory synthetic aperture radar(LTSAR)are no longer applicable.This topic aims at CTSAR high-resolution imaging,based on the real-time imaging processing framework,combining frequency domain and time-frequency domain.The CTSAR signal characteristics are analyzed,with 3d spatial velocity and acceleration,and signal focusing techniques are explored.Firstly,the slant range expression is established according to the geometric model of the CTSAR system.Under the curve motion trajectory mode,combined with the motion characteristics of the SAR platform,according to the kinematics theory,the curve motion is divided into three components in the X,Y and Z directions,each of which has initial velocity and acceleration.Based on the 3D geometric model,the 3D mathematical model is built,and the function expression of the slant range is constructed.Since the complex slant range model of airborne CTSAR restricts the construction of subsequent imaging algorithms,the slant range model is approximately decomposed by Taylor,Legendre and Chebyshevpolynomials respectively,which reduces the complexity of imaging algorithm design and lays the foundation for the study of high-resolution imaging algorithm under CTSAR.Secondly,the echo signal model is established according to the slant range of the airborne CTSAR.The echo signal is transformed into two-dimensional frequency domain by phase of stationary principle and series inversion method,and the two-dimensional spectrum expression of echo signal is obtained.Curve course makes the coupling of range and azimuth direction of two-dimensional spectrum more complicated,which increases the difficulty of image processing of CTSAR.To this end,thethesis uses Legendre and Chebyshev polynomials to approximate the two-dimensional spectrum by orthogonal decompositionrespectively,in order to achieve the purpose of uncoupling and phase compensation.On this basis,two extended frequency domain imaging algorithms suitable for airborne CTSAR are proposed.The phase compensation functions of each order are derived to achieve high-resolution imaging under CTSAR and analyze the focusing quality.Finally,aiming at the present situation that the traditional Chirp Scaling imaging algorithm cannot achieve high-resolution imaging for CTSAR with 3D velocity and acceleration,an equivalent Chirp Scaling imaging algorithm is proposed,which is matched the slant range of 3D curve trajectory.The original slant range is equivalent to the hyperbolic slant range model of the traditional linear motion trajectory mode,and the slant range compensation term is added.This equivalent slant range ensures the resolution of SAR imaging.The echo signal and the corresponding phase functionare derived in the equivalent Chirp Scaling algorithm,matched with the equivalent slant range model.The simulation results show that this algorithm has good imaging quality and meets the imaging requirements.