Research On Bistatic SAR Signal Processing Method

Bistatic synthetic aperture radar(BiSAR)is a radar imaging system which the transmitting platform and the receiving platform work separately.Compared with the traditional monostatic SAR,it has more flexibility in application,longer range and more abundant information.In the meanwhile,challenges of technical are caused by the structure of separate transceiver platform.BiSAR slant function is the sum of two hyperbolas,which makes the solution of spectrum function more difficult and increases the complexity of imaging algorithm.A slant range model based on orthogonal decomposition is put forward in this issue.And then the high-resolution imaging algorithm is studied evolved in the linear motion trajectory and the curve motion trajectory of special scene requirements.The main contents of this issue are as follows:1.The slant range model as well as the orthogonal decomposition approximation method of slant range function are developed on the basis of the geometric configuration of BiSAR.According to the different geometry of BiSAR,the expression of slant distance function is established.In view of the particularity and complexity of BiSAR slant range,the traditional algorithm approximates it to Taylor series.However,the Legendre and Chebyshev orthogonal polynomials are applied to the slant range approximation processing by this article,which improves the accuracy of slant range approximation and lays the foundation for high-resolution imaging of BiSAR.2.Aiming at the edge defocusing problem of traditional Taylor series expansion offset method,the traditional Legendre series expansion algorithm is given by this thesis.Then,on account of the Legendre polynomials,the approximate analytical expressions of slant range function and coupling phase are derived.The two-dimensional spectrum of point target is deduced by using the principle of stationary phase and series inversion method,which improves the approximate accuracy of two-dimensional spectrum phase decomposition.The comparison shows that the algorithm ameliorates not only the focusing effect of the scene edge points,but also the focusing depth of the edge points,as it also has high accuracy without interpolation during the imaging process.3.In order to solve the complex problem of Legendre polynomial applied to the slant range function under acceleration,an improved Range Doppler(RD)algorithm based on orthogonal decoupling and motion compensation of BiSAR under acceleration is proposed.The approximate accuracy of the slant range as well as the spectral phase decomposition were improved by the analytical expressions of range function and coupling phase which are derived by Chebyshev polynomials,as it is more efficient than Legendre polynomials.The linear range migration correction reduces the range azimuth coupling and simplifies the imaging process.The comparison shows that the algorithm effectively compensates the motion error caused by acceleration,improves the imaging quality of point target,and has high computational respectively.4.In response to the special scene requirements of multi-angle observation targets,a Non-linear Chirp Scaling(NLCS)algorithm based on curvilinear motion BiSAR is raised.The algorithm decomposes the three-dimensional slant range function and coupling phase by Chebyshev polynomial.Aiming at the problem of azimuth time space variability caused by three-dimensional velocity and acceleration,the nonlinear scaling function is used to balance the Doppler modulation frequency of different point targets.Because of this,and the problem of azimuth spatial variability of Doppler modulation frequency is solved.The comparison illustrates that the algorithm enhances the image quality of edge points,and the application scene is more flexible.