Researches On Space-time Signal Processing For Airborne Phased Array Radar

The airborne phased array radar is operating in a down-looking mode,the intensity of the ground clutter is much larger than the target echo,it is also affected by active interference,the moving target echo is submerged in sidelobe clutter.Airborne phased array radar antennas have spatial adaptive filtering capabilities.Adaptive beamforming,the antenna pattern lobe is set to nulling in the direction of spatial interference,therefore,the jamming signal entering from the side-lobe direction can be suppressed.Space-time adaptive processing is applied to two-dimensional adaptive filtering of clutter and interference to detect moving targets.The space-time adaptive filter adopts the two-dimensional distribution along the clutter to form a filter notch,which filters out ground clutter,so that the target signal of adjacent main lobe clutter can also be detected.Fully adaptive beamforming requires a large amount of calculation and a large number of snapshots.The radar uses planar phased array antenna,and most adaptive beamforming algorithms are only applicable to linear phased array antenna.Fully space-time adaptive processing,inversion of high-order covariance matrix,it has a large amount of computation and cannot realize real-time processing.In an inhomogeneous clutter environment,it is difficult to get range gate sample data with independent and identical distribution.A high sidelobe level occurs in the space-time two-dimensional response of fully space-time processing.This paper proposes an algorithm to solve the above problems to improve the signal to interference noise ratio of the target echo,and target detection performance of phased array radar.1.A beam domain adaptive sidelobe canceller is proposed,in beam domain processing,conventional beamforming is performed on the output signal of the array element,then,the beam output is adaptively processed.The dimension of adaptive processing can be reduced,reduce the amount of calculation,direction information of the desired signal is not required.2.The planar phased array antenna is decomposed into linear phased array antenna,the idea of sidelobe cancellation in beam domain,an adaptive-adaptive interference cancellation algorithm is proposed,the degree of freedom after dimension reduction is determined by the number of beams.A wide notch can be formed in the side lobe,it is beneficial to suppress the interference in the space domain.The dimension reduction problem of two-dimensional adaptive beamforming is solved,the constrained optimization problem is transformed into an unconstrained adaptive filtering problem.3.This paper presents a reduced dimension STAP algorithm,post-Doppler STAP,beam-Doppler domain adaptive processing algorithm,a wide notch with beam is formed in the sidelobe clutter region.Each spatial channel is pre-filtering with a Doppler filter,space-time joint domain adaptive filtering is applied to the output data of adjacent multiple Doppler channels.The amount of computation is reduced by two orders of magnitude,and the performance is close to the optimum.But,the improvement factor curve fluctuates somewhat,slight performance degradation.Dimension reduction processing,reduce the requirement for range gate sample data with independent and identical distribution.