Servo System Study For Shipborne Radar Tracking In The Whole Airspace

With the development of anti-ship missile and airplane,track radar that is used in the last-defense systems is demanded for tracking in the whole airspace. There are not only beam-slanting but also large blind zone near the zenith in the two-axes radar used in the present. So it is necessary to study the driving structure and control scheme of new system radar in order to track continuously in whole hemisphere without blind zone.Firstly,the methods to restrain the effect of ship swing are studied for two-axes shipbome radar. Two different methods based on ship rectangular frame and inertial frame are proposed separately according to consistence of radar base angle and beam angle. The paper points out the mistakes of the schemes and a new system scheme is given which is correspond with real system. The method combining digital filter and ship-dynamic compensation is used to realize the precise motion-target tracking on the condition of ship-motion which causes the target relative motion and the results coming from real system test prove the effectiveness.Second,structure of 3-axes perpendicular radar in which elevation axis is horizontal is proposed through analyzing carefully the shortages of two-axes radar. The paper corrects the errors of the international articles through discussing mathematics model of 3-axes track. 3-axes angle calculation formulae without medium parameters are deduced through analyzing the rotate principle and the results are proved by simulation. Considering the characters of 3-axes coordinate system that is not included in ship rectangular frame or inertial frame,Compensation conditions are deduced through studying the effects of ship-swing. The paper studies how to transfer line velocity and acceleration in the inertial frame to angular velocity and acceleration which correspond each axis,then gives the computer function scheme. Servo control scheme which can overcome ship swing and realize moving-target accurate tracking is designed according to inconsistency of radar base angle and beam angle. The results of computer simulation are proved.Thirdly,the paper analyze the angle error caused by elevation axis not in horizontal plane,make a conclusion that 3-axes perpendicular radar can not track in the whole airspace,propose the structure of slant 3-axes radar. The paper discuss the range of slant angle,deduce angle calculation formulae. The paper gives the calculation methods for three axes angular velocity and acceleration caused by ship swing and target moving. It is proved by computer simulation that the slant 3-axes radar can be used in target tracking in the whole air space without blind zone and beam slant. It is pointed out that the slant 3-axes radar can reduce the maximum angle for elevation axis compared with 3-axes perpendicular radar,then reduce the technique demand of angular velocity and acceleration of elevation axis.The last,taking into account of the nonlinear transformation from sphere frame to Cartesian frame,maneuvering target tracking is simulated by using current statistical model and converted measurement kalman filter (CMKF) without linearization bias in the statistical condition. The paper presents the converted measurement covariance that determines when to use the current measurements vs. the predicted state,and the simulation results are satisfied.