Research On Radar Signal Processing Method Of Low Altitude Surveillance

When a low-altitude surveillance radar detects the low-altitude target,the direct signal and the multipath signal enter main antenna beam at the same time due to multipath effect,and the vector superposition of the two signals changes the amplitude and phase of echo signals.Moreover,direct signal and multipath signal is related strongly and difficult to distinguish,which affect seriously low-altitude surveillance radars on target detection and tracking performance,and even cause the target loss.Therefore,how to suppress the effect of multipath effect on target detection and tracking is very important for the improvement of low-altitude surveillance radars detection performance.Based on multipath effect,this thesis researches the geometric relationship between direct signal and multipath signal by establishing the low altitude multipath echo geometric model.Then,the reflection coefficients of the multipath signal and the echo model of the multipath array signal are analyzed.At the same time,the principle of single pulse angle measurement is introduced in detail,and the main factors influencing the detection probability and the low angle tracking accuracy are analyzed.Then,this thesis analyzes the influence of multipath effect on target detection,based on the ideal plane symmetric specular reflection model established previously.The main factors influencing the amplitude and power of low-altitude target echo signal under multipath are studied,and the relationship between low-altitude target echo signal and multipath propagation factor is deduced.Then,the detection method of multi-path low-altitude surveillance radar target is studied,and the detection performance curve of multi-frequency M/N detector using frequency diversity technique is deduced and simulated.Finally,the M value corresponding to the optimal detection performance of the multi-frequency M/N detector is obtained through a large number of experimental simulations.Afterwards,in order to reduce the influence of multi-path effect on the low-angle tracking accuracy of low-altitude surveillance radar,this thesis firstly designs the optimal symmetric beam by improving the antenna pattern based on the multi-path array signal model,and then realizes the symmetrical beam single pulse angle method.Then,by designing the double-pulse and beam and difference beam pattern,the double-zero single pulse angle method is realized.The effectiveness of the two algorithms in solving the low-angle tracking problem under multipath is simulated and verified respectively.The angular performance of the two algorithms is also analyzed.As the above two kinds of improved single pulse angle measurement algorithm have their own advantages and disadvantages and application scenarios,at the end of this thesis,the algorithmic flow,complexity and angle accuracy of the two algorithms are compared and analyzed,and the minimum SNR and minimum measurable elevation table of symmetric beam method and double zero method are given under different scenarios.Finally,the thesis summarizes and gives how to choose the appropriate low-angle tracking algorithm according to the different radar scene and accuracy requirements,so as to achieve the purpose of saving resources and improving the accuracy of low-altitude surveillance radar low-angle tracking accuracy,which provides a theoretical reference for practical engineering.