Filtering Technique For Low Elevation Target Tracking In The Presence Of Multipath Propagation

There is a great danger of low elevation targets penetration in modern war,so it is necessary to study the tracking strategy.The problem of multipath propagtion arises in the context of tracking low elevation targets on the sea and can cause severe degradation in the measured elevation angles of the targets,which is an urgent problem to be solved in the radar field.The problem is caused by specular reflection and diffuse reflection,and the interference effect of direct echo and specular reflection echo is especially serious.The total echo power is very small with only a little useful information in it,when the two echos are counterbalanced.For low elevation targets,both of the direct echo and the specular reflection echo may enter the antenna half-power lobe width.In view of the above problems,the following work is done for low elevation target tracking under multipath propogation.(1)The influence of multipath effect on monopulse ratio is simulated,the causes and effects of monopulse ratio spike are analyzed,and the limitation of narrow beam technique to eliminate multipath is analyzed.For the angle measurement problem of monopulse radar at low altitude which cannot be solved by high range resolution and high angle resolution technology,the radar data processing methods are studied in this paper.(2)Aiming at the problems of approximate periodic spike deviation and fixed deviation in the multipath scene,a tracking filtering algorithm based on monopulse ratio observation is proposed.The algorithm makes full use of the target position information contained in multipath effect and the target motion model information contained in time evolution.It combines with the static multiple-model unscented Kalman filter and through the real-time comparison of the estimation errors of the monopulse ratio in each model,the problem of height ambiguity is solved step by step.Compared with Interacting Multiple Model algorithm based on multipath error,the simulation results show that the proposed algorithm can effectively track the low elevation target under the multipath effect and reduce the error of the target height estimation.The performance of the algorithm in eliminating high ambiguity is compared under different range measurement noise variance.(3)The initialization methods of filters for low elevation target tracking is studied.The same monopulse ratio may correspond to several possible target height values,which leads to the problem of height ambiguity.Therefore,we proposed two initialization methods based on search traversal and dichotomy.The simulation results show that time complexity in the filter initialization is reduced byintroducing in dichotomy,which also reduces the possible missing target states.