| In the context of modern informationized warfare,radar countermeasure technology is becoming increasingly important.With the development of radar jammer technology,the main lobe deceptive jamming has a strong deception due to the highly coherent characteristics between the real echo and the jamming echo of the radar.the deceptive jammer can copy the intercepted radar waveform and modulate the false target information,which is a serious challenge to the radar anti-jamming ability.Multiple-input multiple-output(MIMO)radar is a new radar system that has attracted much attention since it was proposed.Compared with the conventional phased array radar,the MIMO radar can transmit orthogonal waveforms,so that MIMO radar can obtain the degrees-of-freedom(DOFs)of transmit domain by waveform diversity of receiver.The extra transmit degrees of freedom cause a larger virtual aperture,which can improve the detection and estimation performance of the radar.Furthermore,the information carried by the transmit domain provide a new spatial dimension for the interference and clutter suppression of the MIMO radar,which has great potential for radar signal processing.MIMO system provides promotes flexible design of radar,and the MIMO radar system based on frequency grading array(FDA)shows much advantage in recent years.The distance information of the scatterer is introduced into the transmit domain through the frequency increment between the transmit elements,plus the Doppler information of multi-pulses,the FDA-MIMO radar can distinguish targets and interference from the 3-D information of distance,angle and speed in the transmit domain,which provides great advantage of target detection in the interference or clutter environment.It is no wonder that waveform design is the key point to maintain the MIMO radar advantages in the real applications.And it is also an important guarantee of signal processing for MIMO radar.The existing orthogonal multi-channel radar waveform design still has the problem of high correlation sidelobes,which leads to the loss of DOFs in transmit domain.That will restrict the signal processing performance of radar.Therefore the waveform design of MIMO radar system is an urgent problem to be solved.In this dissertation,focusing on the problem of non-ideal orthogonality of multiwaveform under constant mode constraints and the problems introduced in FDA-MIMO radar applications,I have analyzed the influence mechanism of correlation sidelobe components on received data.Based on the classic orthogonal radar signal design,a new idea of waveform design based on phase response characteristic optimization is proposed.The main contributions of this dissertation are summarized as follows:1.Aiming at the problem that the spreading of correlation sidelobe power in the transmit domain is difficult to solved,the spatial spectral distribution characteristics of correlation sidelobe components is proposed based on the amplitude-phase response of waveform autocorrelation and cross-correlation functions.Studies show that the ideal steering vector of the autocorrelation sidelobe component points to the position of the corresponding scatterer,while the ideal steering vector of cross-correlation component points to the zero transmit spatial frequency.And the phase response difference of the multi-waveform causes the problem of spreading of correlation sidelobes.In theory,the problem that the correlation sidelobe component spread in the transmit domain can be solved by optimizing the phase response characteristics of the waveforms,thus the signal processing performance of radar can be improved.2.Focusing on the problem that the correlation sidelobe components can’t be effectively suppressed during main beam deceptive jammer suppression with the FDA-MIMO radar,a method called phase response similarity based on the coordinate descent framework is proposed to solve the problem of the phase response difference of the multi-waveform.With the proposed signal,the power of the autocorrelation sidelobe component is refocused in the transmit spatial domain,so that it is possible to suppress the correlation sidelobe power through digital beamforming.Therefore,the output signal-to-interference noise ratio(SINR)performance of FDA-MIMO radar to suppress main beam deceptive jamming is improved.3.Aiming at the problem that power of cross-correlation components is difficult to focus,a waveform optimization algorithm of cross-correlation phase response control is proposed.By studying the weighted forms of phase response sequence to the cross-correlation component,the phase response controlled compensation vector is designed,so that the crosscorrelation phase response of the proposed waveform can maintain a certain artificial phase difference,so that the actual steering vector of the cross-correlation component will point to controllable transmit spatial frequency.Furthermore,based on the proposed waveform,a deceptive jamming suppression method with FDA-MIMO radar is proposed.Because the cross-correlation component power is effectively focused,the proposed methods improve the anti-jamming performance of the FDA-MIMO radar compared with the traditional waveform algorithms.4.Focusing on the problem that the power of cross-correlation component is wasted during the signal processing of the FDA-MIMO radar,a waveform adaptive design method based on phase response controlled constraint of cognitive radar system is proposed.By designing the phase response controlled compensation vector to match the target,the correlation sidelobe power can adaptively contribute to the gain for target,which significantly improves the spatial spectrum estimation performance of the target.Thus the proposed method can also improve the performance of anti-jammer. |
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