Forward-looking Superresolution Imaging For Airborne Phased Array Radar

The range resolution of phased array radar can be increased by transmitting lin-ear frequency modulation signal while the Doppler bandwidth formed by the relative motion between the radar platform and the imaging targets is small in the area along the flight direction.Angular resolution is limited by physical aperture of antenna for phased array radar since the azimuth echo is the convolution of the antenna pattern and target azimuth backscatter coefficients,deconvolution algorithm can achieve forward-looking super-resolution to some extent.However,the linear range walk and Doppler center shift caused by the relative motion between the imaging scene and the carrier platform make the azimuth convolution model no longer valid;The phased array an-tenna pattern deviates from the design value or changes during the scanning process,which affects the deconvolution results;The ill-posed problem of deconvolution makes the result of single channel super-resolution sensitive to noise.Therefore,the follow-ing research work based on forward-looking deconvolution super-resolution imaging is utilized to deal with above intractable problems:I:We establish the imaging signal model for the moving platf-orm and target,ana-lyze the influence of linear range walk and Doppler center shift caused by relative mo-tion and compensate them.Furthermore,the formulation of airborne forward-looking scanning radar can be converted into a two dimensional(2D)convolution model,thus the 2D deconvolution without motion compensation for all the range cells together is conducted to obtain not only high angular resolution but also range resolution.More-over,simulation results preliminarily verify the feasibility of proposed motion compen-sation preprocessing framework and 2D deconvolution.2:In practical applications,antenna pattern can't be obtained accurately,which will deviate from the simulation or measurement result.This paper establishes the er-rors model for antenna pattern of phased array antenna and deduce the influence of above mismatch upon deconvolution by taking the least squares solution as an exam-ple.Considering the sparse distribution of strong scattering points in the imaging scene,the reweighted l1 minimization is utilized to limit the influence of the model error based on the traditional deconvolution algorithm.The simulation and measured results show that the proposed algorithm for pattern errors is superior to traditional methods in super-resolution performance.3:As a typical inverse problem,deconvolution can't ensure a reliable and robust imaging result because the highly ill-conditioned problem is noise sensitivity in prac-tical application.The ill-posed problem of single channel deconvolution can be alle-viated by using multi-channel deconvolution.Evaluation parameters are generalized to characterize the angular spectrum of antenna pattern and the singular value of the observation matrix to describe the performance improvement of the multi-channel sys-tem more effectively.Based on the multi-channel system,we propose multi-channel deconvolution algorithms to improve the imaging effect of airborne phased array for-ward looking sharpening via combining with traditional single channel deconvolution algorithm.Numerous simulations and experimental results illustrate the superiority of proposed multi-channel deconvolution methods.