Research On Key Technology Of Errors Calibration And Beamforming In Wideband Digital Array Radar

Digital array radar(DAR)has attracted much attention for the potential of achieving high dynamics,excellent anti-interference performance and providing multi-functions simultaneously.This dissertation is supported by the foundataion of National 863 Plan and the Twelfth Five-Year Pre-researching Plan,which makes effort to develop a dual-band digital array radar with both active and passive operation modes.Several key technologies of DAR,such as array errors calibration,digital beamforming(DBF)and the engineering implementation of receivers,are studied in the dissertation.The research aims to develop the next generation of digital,software-defined and smart radar.Major works are arranged as follows:1.A joint algorithm is proposed for the calibration of gain-phase and mutual coupling errors in narrowband arrays.According to the characteristics of uniform linear array(ULA),a simplified model of the array distortion matrix is developed,which has less unknown parameters.Then the least-square solutions can be obtained using time-disjoint calibration sources.This algorithm has the potential of achieving high precision without any prior information of the directions of calibration sources.Simulations and experiments verify the effectiveness of the proposed algorithm.2.The calibration technologies for wideband arrays is investigated.A STFT-based algorithm is proposed to calibrate wideband gain-phase errors,which can achive high performance in the presence of interferences and noise.Taking mutual coupling errors into consideration,a wideband DOA estimation algorithm for ULA based on auxiliary elements is presented.Based on the special structure of mutual coupling matrices,several elements are used as auxiliary elements to mitigate the mutual coupling effects.The proposed method can reach high estimation accuracy without any calibration sources.It has a low computational complexity because iterative processing is not required.Moreover,blind angles caused by mutual coupling may avoid.An FIR-filter-based algorithm is proposed to cope with the situations where both gain-phase errors and mutual coupling errors exist.Firstly,an active calibration approach is applied to calculate the calibration matrices at some discrete frequencies.Then a set of FIR filters are designed to fit the frequency characteristics of these matrices in the pass-band.Finally,a wideband calibration matrix is constructed using these FIR filters,which is capable to compensate array imperfections at any frequencies in the pass-band.The proposed algorithm has low computational complexity and can achieve high calibration accuracy.It is simple to implement and feasible for applications.3.A robust adaptive DBF algorithm is proposed for the wideband DAR which transmit linear frequency modulation signals.Firstly,digital stretch technology is employed to de-chirp received signals in each element.Then time-variant factors are generated to compensate phase perturbations induced by the digital stretch processing.In this way,the wideband signals can be treated as narrowband signals.Consequently,a narrowband DBF method based on uncertain set constraints is applied to suppress interferences.The proposed method is computational efficient and feasible for real-time applications.It behaves robustly in the presence of direction of arrival(DOA)estimation errors.4.The engineering implementation of the receiveing system of wideband DAR is discussed.Firstly,a digital receiver module and a DBF processing unit are designed.Then,an FPGA-based wideband array calibration module and a hierarchy DBF processing module are realized.Finally,experiments are carried out using the DAR test-bed and the results of measured data are presented.The research findings in the dissertation have been applied to XX wideband DAR test-bed,which will provide technical support for the practical implementation of DAR.