Research On Signal Processing Technology Of Airborne Conformal Array Antenna

Comparing with conventional planar arrays,conformal arrays tend to have less structural weight,better aerodynamic performance and larger aperture area.Therefore,it is expected to become an important antenna form in airborne radar system.However,the polarization characteristics and mutual coupling effects of the arrays are more complex due to the special surface structure.Different elements have different gesture and polarization direction.For the same scatterer,the received signal intensity of the array element is inconsistent,which makes the traditional clutter suppression method based on the plane array clutter model ineffective.Hence,it is of great significance to study the signal modeling and processing methods of airborne conformal array.This dissertation mainly studies three aspects: clutter characteristics,clutter suppression methods and target detection methods of airborne conformal array radar.Firstly,a clutter rank estimation method is given to estimate the rank of the clutter covariance matrix of polarization sensitive linear array.Then,an adaptive subspace detection method is given to solve the problem of signal subspace mismatch caused by array polarization inconsistency and mutual coupling.This method can compensate for the influence of polarization and mutual coupling,and improve the performance of radar target detection.Finally,a simplified covariance matrix construction method is proposed to reduce the computational complexity of signal processing.The main contents of this dissertation are summarized as follows:1.The pattern model,clutter model and clutter characteristics are studied.Considering the polarization and mutual coupling characteristics of conformal arrays,the universal array pattern model and clutter model are established.Meanwhile,the variations of polarization patterns of several typical conformal arrays are studied.In order to analyze the influence of polarization sensitivity on array more clearly,a clutter rank estimation method is given,which utilizes the difference of polarization direction between array elements and clutter patches to estimate the rank of clutter covariance matrix of polarization sensitive linear array accurately.Finally,the influence of mutual coupling and circular curvature on the degree of clutter freedom is analyzed.2.The target detection of airborne conformal array radar is studied.The polarization direction of different elements in conformal array may be different,so that the target steering vector changes with the polarization direction of the echo.Traditional space-time processing can not protect the target signal under the weight vector constraint criterion effectively.Therefore,this thesis studies a subspace detection method for target detection in clutter background.At the same time,aiming at the problem of mismatch between subspace and target signal caused by mutual coupling of array elements,a compensation method using transformation matrix is given.This method can be used as a pre-treatment of adaptive subspace detection to improve the performance of radar target detection.3.The clutter suppression and target detection of fully polarized conformal array are studied.The large number of elements of fully polarized conformal array increases the computational complexity and sample requirement of signal in adaptive processing.To solve this problem,a simplified covariance matrix construction method is proposed,which utilizes the weak correlation of received data between orthogonal arrays and calculates the covariance matrix of received data of horizontal polarization array and vertical polarization array separately.By combining the covariance matrices of received data,the data covariance matrix of fully polarized array is constructed,which reduces the computational complexity of estimating the statistical characteristics of clutter definitely.