| The main function of traditional airborne early warning radar is target detection and parameter estimation,which can complete the task with a narrow bandwidth.However,in future applications,after target detection,airborne radar needs to obtain high-resolution target range profile or ISAR image in order to achieve target classification and recognition,so a larger bandwidth is required.The increase of bandwidth means that the time or distance resolution of the system is improved,but it also brings problems to signal processing: In the spatial domain,the aperture transit time of the signal is no longer much less than the time resolution of the signal,and the range migration of the target signal and the clutter signal between the array elements cannot be ignored;In the time domain,the range migration of the high-speed target signal and the clutter between the pulses cannot be ignored.If the traditional space-time adaptive processing(STAP)method is used directly without considering the influence of range migration,the performance of clutter suppression and target detection will be significantly reduced.Therefore,it is of great significance to carry out special research on STAP methods and technologies for wideband applications.This thesis studies the echo signal of wideband airborne phased array radar,establishes the target signal model and clutter signal model of wideband phased array radar,and analyzes the problems caused by the use of wideband signals.In view of the significant drop in the output signal to clutter plus noise ratio of the traditional STAP method caused by the wideband signal envelope migration between array elements and pulses,two space-time adaptive processing methods suitable for wideband airborne phased array radar are proposed,which can effectively improve the output signal to clutter plus noise ratio and target detection performance.The main contents of this paper are summarized as follows:1.The signal model of wideband airborne phased array radar is established,and the difference between wideband signal model and narrowband model is analyzed.Firstly,the target signal model and clutter signal model of traditional narrowband airborne phased array radar are given,and the influence of bandwidth on echo signal is analyzed.Secondly,the signal form of wideband airborne phased array radar is obtained by derivation.Based on this,the target signal model and clutter signal model of wideband airborne phased array radar are established.Finally,the range migration of wideband target signal and the characteristics of wideband clutter are simulated and analyzed.2.The subband STAP method of wideband airborne phased array radar is studied.Firstly,according to the idea of subband processing,the subband method is divided into three steps:subband decomposition,subband clutter suppression and wideband target signal recovery.Secondly,the signal form after subband decomposition and the space time steering vector related to the subband center frequency are derived,and the subband space time adaptive processing method is obtained,which is different from the traditional method.Then,a method of wideband target signal recovery using discrete fourier transform is proposed.Finally,a complete subband STAP method for wideband signal is concluded,and the simulation results show that the subband method can improve the performance of wideband clutter suppression.3.The STAP method of range reconfiguration for wideband airborne phased array radar is studied.Aiming at the problem of wideband target signal's range migration between array elements and pulses,a STAP method of airborne radar range reconstruction with known target angle and velocity is proposed.The echo data is extracted and recombined according to the target distribution.After recombining,the peak point of the same target changes from scattered in several distance units to aggregated in the same distance unit,which reduces the target energy loss after coherent accumulation.The performance of target detection and clutter suppression is improved.Then,the target velocity search method in the range of interest velocity and the target angle search method in the range of beam width are studied,and the complete process of two-dimensional target angle and velocity search is summarized.Finally,the effectiveness of the method is verified by simulation experiments. |
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