Researches On Radar Waveform Design And Several Techniques Of Mainlobe Active Interference Suppression

Radar waveform is the information carrier of a radar system,which is closely related to localization accuracy,resolution capability and anti-jamming performance of radar systems,so waveform design has been attracting much attention.Pulse compression plays an essential role in radar signal processing,which solves the contradiction between radar detection range and range resolution.But radar waveform after pulse compression inevitably produces undesirable outputs at shifted range bins(i.e.range sidelobes),and a high range sidelobe level may trigger false alarms or cause missing alarms.The range sidelobes of existing waveforms are still high,which are difficult to meet the needs of practical applications,especially under a complex and changeable electromagnetic environment.Consequently,for pulse compression radar,it is very important in practice to suppress range sidelobes through waveform optimization.In addition,modern warfare is guided by electronic warfare and we should enhance the viability of radar system under the complex electromagnetic countermeasure environment,which is one of the key factors to win a modern war.Hence,it is of great importance to study the anti-jamming technology in the presence of a complex and changeable electromagnetic environment.This dissertation falls into the field of radar waveform design,including range sidelobes suppression and raising Doppler robustness of monostatic radar system,enhancing the orthogonality of distributed Multiple-Input Multiple-Output(MIMO)radar waveform and several techniques of mainlobe active interference rejection.The main research contents done in this dissertation are summarized as follows.1.For the high sidelobes of monostatic radar waveform after pulse compression,waveform and mismatched filter simultaneous design for monostatic radar system is studied.Firstly,an approach of simultaneously optimizing Phase Coded Waveform(PCW)and a mismatched filter is studied,which establishes design criterion with the objective function to minimize Peak Sidelobe Level(PSL)and control Signal to Noise Ratio(SNR)loss,and we utilize a least-pth optimization algorithm to solve it.Compared with the existing literatures,this approach can obtain a lower PSL.Secondly,since the approach mentioned above does not take the Doppler mismatch into account,Doppler mismatch may cause mainlobe amplitude descending and range sidelobes rising when the waveform exists Doppler modulation.Therefore,this dissertation further studies another simultaneous optimization approach with Doppler concern,which can obtain good robustness within a specification of Doppler mismatch range.Thirdly,under fixed duration time of transmit waveform and keeping the same range resolution with the prescribed one based on the requirements of application scenarios,this chapter looks for more Degree Of Freedoms(DOFs)by expanding mainlobe and establishes a design criterion with the objective function to minimize PSL,control SNR loss and match desired mainlobe through simultaneously optimizing PCW and mismatched filter.Finally,the Doppler mismatch issue is considered during the waveform design process with expanded mainlobe mentioned above,which can ensure that the filter output results have robustness to Doppler mismatch.2.Since the waveform orthogonality of distributed MIMO radar in waveform domain can not satisfy the requirements of practical application,orthogonal waveforms and its mismatched filter bank design for distributed MIMO radar are studied.Firstly,a design criterion with the objective function to directly minimize Auto-correlation Peak Sidelobe Level(APSL),Peak Cross Correlation Level(PCCL)and control SNR loss is established and a double least-pth algorithm is exploited to simultaneously optimize orthogonal PCWs and mismatched filter bank.Compared with the separate design methods,this approach can further reduce APSL and PCCL.Secondly,in order to further enhance the waveform orthogonality,this chapter extends it to distributed MIMO radar based on the expanded mainlobe idea of the last chapter and an approach of orthogonal PCWs design with expanded mainlobe is proposed.Finally,based on the designed orthogonal PCWs with expanded mainlobe above,another design criterion with the objective function to control SNR loss,minimize APSL and PCCL of mismatched filter bank output and match a desired mainlobe is established,which can be effectively solved by using convex optimization algorithm.3.Some literatures of Digital Radio Frequency Memory(DRFM)repeat jammer rejection usually assume that the delay for a repeat jammer behind the radar lags is known,which is difficult for radar systems to obtain in practical applications.In addition,there exist many studies on conformal phased array,but conformal MIMO arrays are seldom studied.Based on the two problems mentioned above,waveform design for colocated MIMO radar is studied.Firstly,the differences between the transmit waveforms in the spatial direction(angular waveform)and the jamming signals transmitted by DRFM-based repeat jammer are analyzed.Then,a waveform design criterion with the objective function to suppress the peak cross correlation level between the angular waveforms and jamming signals,APSL and PCCL of angular waveforms,and match a desired transmit beampattern is established to reject the DRFM-based repeat jammer,which can be solved by sequential quadratic programming.Secondly,receiving beamforming is introduced into the waveform design process above,which can suppress the cross correlation level of the waveforms from different directions.Then,more DOFs can be utilized to suppress the jamming signals from same direction with that of real target returns.Therefore,a better performance of the DRFM-based repeat jammer rejection can be achieved.Finally,waveform design for colocated MIMO radar based on a cylindrical conformal array is studied and a good optimization result is obtained.4.Anti-jamming technologies based on frequency agility and pulse repetition interval(PRI)stagger modes are studied,which is primarily aimed at studying active anti-jamming at the transmitter and improving the performance of radar system at the same time.Firstly,an approach based on frequency agility technique is studied to reject the DRFM-based repeat jammer.The Doppler frequency difference between the real target echo and jamming signals are analyzed,which can be used to eliminate false targets.After eliminating false targets,a signal processing flow is provided for improving the detection performance of a radar system.Secondly,an anti-jamming approach based on the parameter modulation of PRI stagger pulses is studied,which has the ability of anti-sorting and count-discrimination and high detection performance and good range--Doppler estimation accuracies at the same time.