Study On Error Calibration For Conformal Polarization Array Based On Signal Processing

Conformal array refers to the antenna array that is attached to the surface of the carrier and conforms to its shape.It not only can be used to sense multi-dimensional information including angular polarization domain of a target,but also has good stealth performance,aerodynamic performance and wider angle estimation performance.Thus,conformal array has been widely applied in the fields of radar,sonar,wireless communication and so on.In practice,the array has inevitable errors due to various non-ideal factors,such as the limited craftwork level,the varied temperature and humidity,and instruments aging,resulting in the performance deterioration of high resolution parameter estimation algorithms based on ideal steering vector.For planar array,we can use the classical algorithms to calibrate the array errors.However,the steering vector modeling of the conformal array is different from that of the planar array because of the complicated conformal structure and the special arrangement of array elements.Moreover,the antenna patterns of the elements in conformal array are usually not being the same in one coordinate.Therefore,modeling in conformal array becomes more difficult compared with planar array,and traditional error calibration methods for planar array cannot be applied in conformal array directly.To address the issues,the research content of this paper includes:Firstly,the basic theory of signal processing for conformal polarization sensitive arrays is introduced.For the arc-shaped conformal polarization array,an array model with channel gain and phase errors,array position errors and antenna response errors is established based on Euler rotation transformation.Secondly,with the error model,the influence of array error on parameter estimation is analyzed.Typical array error calibration techniques,including the error calibration with auxiliary source,the self-calibration based on echo data and the calibration with partial array response known precisely,are discussed.The array errors are various in sources and forms and closely related to the signal angle.The comprehensive influences of these errors are considered as the direction-dependent gain and phase errors of the antenna pattern and then a new gain and phase errors calibration algorithm is studied.In the algorithm,the gain and phase errors on the planes of j and q are estimated according to the polarization information difference of the source by transmitting the auxiliary source in a certain range of angles,and then the calibration matrix is calculated by applying the least squares approach.The array error within the angular range can be calibrated well.Compared to the existing error calibration methods,the algorithm studied can obtain a more accurate calibration matrix with less calibration signal sources,and is suitable for any conformal polarization sensitive array.Finally,based on the arc-shaped conformal polarization array system,the digital signal processing scheme,including digital down converter,error calibration and spatial spectrum estimation,is designed and implemented.We carry out a field test to collect and analyze the measured data.The single source channel data,the time diverse auxiliary sources calibration technique and the measured data of antenna pattern are used to obtain the corresponding error coefficients of the channel gain and phase errors,the position errors and the antenna response errors.The spatial spectrum estimation results with the discussional methods show the effectiveness of the designed error calibration algorithms.