| In the modern warfare,airborne radar plays an important role in detecting long-range and low-altitude target and generating accurate early warning information.However,in the process of airborne radar target detection,it will inevitably be affected by the ground clutter.Due to the movement of the carrier relative to the ground,ground clutter echoes in different directions have different radial velocities relative to the carrier resulting in the broadening of the clutter echoes in the Doppler domain,which brings difficulties to target detection.As a mature method of clutter suppression,space-time adaptive processing(STAP)can effectively suppress clutter by forming a notch that matches the clutter on the two dimensional space-time plane.However,if the target velocity is low,it does not have a large Doppler frequency shift into the sidelobe clutter area,and the suppression of the mainlode clutter will be accompanied by a large loss of singal-tonoise ratio(SNR)of the target,which may lead to the target being unable to detect.Therefore,improving the detection performance of low-velocity target is an urgent problem to be solved.Taking the minimum detectable velocity(MDV)as the measurement index,this paper focuses on the STAP to improve the detection performance of low-velocity target in the model of single-base radar and bistatic radar.The main contents are summarized as follows:1.The method of reducing the minimum detectable velocity of airborne radar is studied.Aiming at the problem that the target angle is unknown and the position of the beam is fixed cannot obtain a low MDV,a method to reduce MDV using dense offset scanning is proposed.This method uses the received beam or the transmitted beam,received beam to perform offset scanning,improving the search accuracy of Doppler filter for target,changing the relative position of the target in the main lobe and reducing the radial velocity of target entrying into the sidelobe clutter area.Therefore,it can reduce MDV and improve the detection performance of low-velocity target.2.The method of using soft constraints and forming multiple beams to improve the gain of mismatched target is studied.Aiming at the problem that the target gain decreases after offset scanning and only constraining the beam center cannot effectively cover the velocity and angle of the mismatched target,two solutions are proposed.One is to add soft constraint at the target position to keep the target gain within a certain limit.The other is to form multiple beams within a certain the width of beam and process them through multiple groups of weight vectors to improve the target gain and improve MDV.3.The method of improving MDV by using bistatic mode is studied.In order to obtain a proper flight distance,the two carriers should be separated not only in the along-track but also in the altitude,forming a multibaseline.The different positions of the two platforms under the multibaseline will cause the misalignment of clutter Range-Doppler(R-D)units and the decorrelation of clutter signals.To solve this problem,a method of improving MDV by using bistatic mode called MP-STAP(Moving and PrefilteringSpace-time adaptive processing)is proposed,which aligns clutter R-D units by interpolated movement firstly,improves clutter correlation by range prefiltering secondly and uses space-time processing thirdly.In this paper,the theories and steps of these methods will be described in details,and their effectiveness is verified by simulation experiments. |
