Study On Mainlobe Jammer Suppression Based On Transmit Modulation Design With Waveform Diversity Array Radar

Due to the advantage of being able to detect targets under all-weather conditions,radar systems have been widely applied in military and civilian fields.However,with the rapid development of electronic interference,radar faces increasingly severe problems.Among different types of interferences,mainlobe deception jammer can generate a large number of dense false targets,effectively reducing the detection performance of radar systems.In particular,the emergence of digital radio frequency memory(DRFM)has enhanced the performance of deception interference,posing great challenges to interference suppression.The improvement of controllable degrees-of-freedom(DOFs)often accompanies the innovation of radar systems.From the mechanical scanned radar system to phased array radar as well as the multiple-inputs and multiple-outputs(MIMO)radar,the ability to acquire information is becoming increasingly stronger.Therefore,frequency diversity array(FDA)radar can be considered as the new generation radar,which introduces minimal frequency increments across adjacent array elements to form a unique range-angle-dependent equivalent beampattern.By extracting the range dimension degrees of freedom through MIMO technology,the flexibility of signal processing is greatly enhanced,providing new ideas for the suppression of mainlobe deception interference.In the dissertation,based on the research focus and reinforcement of the key projects of the Natural Science Foundation and the Basic Enhancement Key Project,combined with the practical application requirements of the subject and the development trend of new system radars,a new system array radar transmission modulation and mainlobe interference suppression research is conducted for the yet unsolved global problem of mainlobe deception interference.By combining coding at the transmit array and information processing at the receiver,an effective solution is proposed for this problem using the controllable DOFs in the range domain and the extra DOFs in the Doppler domain to solve the problem of mainlobe deceptive jammer suppression.The main contents are summarized as follows:1.Focused on the problem of mainlobe deception interference suppression,the angle-range two-dimensional dependent beamparttern of FDA are utilized.Under the premise of rough estimation of the number of pulses or the range ambiguity number of true target,the differences in range dimensions between true and false targets are fully utilized to distinguish between the true target and interference.A sample selection method based on singular value analysis(SSA)is used to extract accurate interference and noise covariance matrices.Firstly,nonhomogeneous samples containing interference or target signals are selected through threshold detection,then the samples containing true target is filtered out through analysis of prior information.Finally,a transmit-receive data-dependent matched filter is designed and the interference is suppressed due to mismatch in the range dimension.2.Focused on the problem of interference suppression for dense false targets in the mainlobe,a quadratic phase encoding(QPC)method based on FDA-MIMO radar is proposed.In this system,extra DOFs in the range and Doppler domains can be obtained.In the receiver,QPC decoding and principle range compensation are used to differentiate between true and false targets in the joint Doppler and spatial frequency domains.Additionally,by performing datadependent transmit-receive-Doppler three-dimensional beamforming,false targets are suppressed in the joint transmit-receive-Doppler domain,achieving the suppression of false targets due to mismatch in range and Doppler.Then,the appropriate frequency increment and encoding coefficients are designed,and the number of suppressible mainlobe interference false targets is increased.3.Focused on the problem of performance degradation in the presence of mismatches for the false targets using data-independent beamforming,a quadratic element-pulse coding(QEPC)method based on MIMO radar system is studied.By encoding QEPC on the element dimension and slow-time pulse,different pulses have different equivalent spatial direction and additional Doppler frequency offsets to distinguish false targets from true targets.Range frequency compensation and Doppler compensation are performed to align the true targets with the nulls in the transmit-receive-Doppler domain.Appropriate encoding coefficients are designed to increase the number of suppressible interferences.Finally,interference is suppressed by nulls using transmit-receive-Doppler three-dimensional beamforming.The center-border-null broaden control(CBNBC)algorithm is developed.By applying artificial interference with preset power around the zero null in the equivalent beampattern,the null is broadened and deepened from the center to the preset border,resulting in a beampattern with low sidelobes,wide nulls,and flat mainlobe.4.Focused on the problem of suppression of the rapid generation of false targets by DRFM, an anti-jamming method based on secondary compensation for QPC-FDA-MIMO radar is proposed.Firstly,the Doppler degrees of freedom are obtained using coding and decoding techniques.Cross-period interference is differentiated from the true target and suppressed through Doppler compensation and Doppler filtering.Same-period false targets generated by DRFM are distinguished by spatial frequency compensation.A sample selection strategy using SSA technology is employed,and interference is suppressed through minimum variance distortionless response(MVDR).