Characteristic Analysis And Optimal Design Of Frequency Division-Phase Coded Linear Frequency Modulation Waveform For MIMO Radar

The Orthogonal Frequency Division Linear Frequency Modulation(OFD-LFM)waveform is a classic transmit waveform in Multiple Input Multiple Output(MIMO)radar with excellent target detection performance.However,the autocorrelation of the waveform spatial synthesis signal has discrete grating lobes,it is easy to cause radar false alarm or flooding weak targets,which seriously affects the radar detection performance.In order to solve this problem,this paper proposes a new solution based on the existing solutions,and combines the existing solutions with the proposed new methods to define a new waveform structure.That is,the Frequency Division-Phase Coded Linear Frequency Modulation(FD-PCLFM)waveform.In order to further improve the detection performance of FD-PCLFM waveform,based on the analysis of the temporal and spatial characteristics of the waveform,the space-time joint optimization design of FD-PCLFM waveform is carried out.The main work includes the following:(1)The problem that the autocorrelation function of OFD-LFM waveform spatial synthesis signal in MIMO radar has discrete grating lobes is introduced.The reasons for the existence of grating lobes are theoretically analyzed,and the existing methods for eliminating grating lobes are summarized.The analysis shows that the existing methods all adjust the OFD-LFM waveform structure to eliminate the grating lobes.(2)In order to eliminate the grating lobes,a new improved OFD-LFM waveform structure is proposed in this paper,that is,the phase encoding sequence is modulated on the OFD-LFM waveform.In this paper,the new waveform structure is defined as FD-PCLFM waveform,and the autocorrelation function of FD-PCLFM waveform spatial synthesis signal is deduced.Based on this,the inherent sidelobe property of the waveform autocorrelation function is analyzed,which further reveals the root cause of the FD-PCLFM waveform eliminating discrete grating lobes.(3)The FD-PCLFM waveform was analyzed in detail.The analysis shows that the FD-PCLFM waveform has the dual advantages of linear frequency modulation waveform and phase encoding waveform,and has the advantages of low side lobes,good Doppler tolerance,low interception and strong anti-interference ability.The temporal domain autocorrelation function and the spatial domain transmit beampattern of the FD-PCLFM waveform are deduced and theoretically analyzed.The analysis shows that the frequency interval,carrier baseband bandwidth and phase coding sequence of the FD-PCLFM waveform are important waveform parameters that affect the autocorrelation sidelobe level of the spatial synthesis signal and the shape of the transmit beampattern,which plays a decisive role in the detection performance of the waveform.(4)Based on the analysis of FD-PCLFM waveform temporal and spatial characteristics,this paper considers the optimization of the above three important parameters in the FD-PCLFM waveform to further improve the detection performance of the waveform.Therefore,in this paper,a bi-objective multivariable nonlinear optimization model is established by minimizing the peak sidelobe level of the autocorrelation function and minimizing the matching error between the waveform synthesis beampattern and the desired beampattern as two objective functions.The optimization model is simplified and analyzed.The solution of iterative optimization using sequential quadratic programming(SQP)and adaptive clonal selection(ACS)algorithm is proposed,and detailed algorithm steps are given.The simulation results show that the obtained optimized waveform can effectively approximate the desired pattern in the airspace while having the lower temporal domain autocorrelation sidelobes,thus effectively ensuring the target detection capability of the MIMO radar.