Accurate Measurement Techniques For Fully Polarimetric Phased Array Radar

Along with the development of radar polarization theory and technology, polarization has became a very important techonique for modern radars, which are more and more accurate, higher dimensional, and more intelligent. Nowadays, a fully polarimetric phased array radar(PPAR) is the important trend of future multifunction phased array radar(MPAR), which has broad application prospect for meteorological observation missile defense. The measurement accuracy of target’s polarization scattering matrix(PSM) is the key factor of polarization techonique performance. There are very strict requrements for system design and signal processing of PPAR to obtain accurate polarization measurement. The spatial polarization characteristics of PPAR antenna changes along with the scanning angle. Specially, the cross polarization will increase obviously as the steered angle depart away form the normal direction of array plane. This intrinsical attribute will affect the signal processing of polarization information application in the data source. Therefore, it is also a great challenge for accurate measurent of PSM. Base on advanced signal processing techniques, the purpose of this paper is to solve the basic and common problems of accurate measurent for PPAR. The problems include four aspects, which are the spatial polarization characteristics analysis of the PPAR antenna, the technique of pattern synthesis and polarization control, polarization measurement and calibration for PPAR, and monopulse technique for PPAR. The proposed theory and methods is testified by PPAR antenna simulation data obtained from HFSS. The researches include following four aspects.1. The spatial polarization characteristics of PPAR antenna are studied. Firstly, two basic types of dual-polarized element are studied based on infinitesimal electric and magnetic current sources. The origin of cross polarization of the dual-polarized antenna element is revealed, then the spatial polarization characteristics of ideal dual-polarized element are analysed. Secondly, the effection of mutual coupling for the active element pattern and the radiation characteristics of synthesized array. A least square estimation of coupling coefficient for PPAR antennas is proposed. The mathematical model of the radiation characteristics of dual-polarized arrays is established, which provides theoretical support for continuing signal processing.2. The mehods for pattern synthesis and polarization control are reseached. Firstly, two methods of separated synthesis of power spatial pattern and polarization are propused. One of the pattern synthesis methods is based on mutual coupling compensation, and the other is based on the polarization control of array element. The performance of the two methos are analysed by simulation, and the limitation of the methods revealed. To overcome to the defects of these methods, a novel jointly synthesis of power pattern and polarization is presented. The power characteristics include beam width, sidelobe, and the nulling of pattern. Both the power and polarization characteristics are considered as a convex optimization problem, which can be solved by the numerical methods. Though the optimization of the coefficient of element, arbitrary sidelobe can be controlled and any polarization can be synthesized, which provides a technique to the obtain flexible beam scanning and accurate polarization. For the wideband array synthesis problem, a wideband pattern synthesis method based on FIR filter structure is propused. By this method, both the power and polarization characteristics satisfy the design requirements. At the same time, the frequency responses of the synthesized pattern are flattened at all relevant angles. As a result, the beam angle error and the pattern distortion are reduced by the wideband polarized beam pattern synthesis method.3. Polarization measurement and calibration methods for PPAR are presented. Firstly, according to the relationship between target and radar coordinate system, the change of the polarization basis along with the steering angle is analysed. Associate with the spatial polarization characteristics of PPAR antenna, the fully polarimetric target echo model is strictly established. The effection of cross-polarization, amptitude and phase of channels, and the waveform isolation on the polarization measurement performance is analysed for both ATSR and STSR modes. The definition of cross polarization isolation is presented, which provide guide lines for the PPAR antenna design. The cross polarization of antenna will induce polarization measurement error. To solve this problem, the jointly synthesis of power pattern and polarization is applied to calibrate the polarization of the orthogonal polarized beam pattern. Associate with the traits of transimitting and receiving array, the pattern synthesis and polarization calibration are jointly optimized based on partial elements of array. The performance is analysed and testified by antenna array data obtained from HFSS.4. The monoluse technique for PPAR is researched. The cross polarization of array antenna, polarization response difference almong array elements and the imbalance between channels will induce angle error in monopulse processing. To solve this problem, the jointly synthesis method of power pattern and polarization is used to improve the angle measurement accurance for monopulse technique. The polarization characteristics of sum patterns are in accordance to the ones of difference patterns. At the same time, the power characteristics of sum and difference patterns are satified to the design requirement, which can minish the angle bias error induced by antenna polarization and other radar system factors. Furthermore, a fully polarimetric monopulse technique based on polarization match receiving is proposed to maximize the signal to noise ratio(SNR), which can reduce the mean square error(MSE) induced by noise of receiver. The efficiency and potentiality are testified by dual polarized planar array data obtained from HFSS and the theory data of dual polarized cylindrical array.