| With the increase of the complexity of radar environment,the strong clutter,jamming and other factors will have a serious impact on radar performance.Waveform is an important resource,and its construction,modulation pattern and excellent performance directly determine the capability of radar to detect targets and resist interference.Waveforms with good auto-correlation and cross-correlation performance can improve the capability of radar to detect weak targets.The agility of parameters such as the initial phase and frequency of the transmitting waveform can significantly improve the anti-jamming capability of the radar.The better the orthogonality of the Multi-Input Multi-Output(MIMO)radar waveform,the higher the range resolution of the system,and the easier it is to separate the signal after matched filtering.So how to select and design waveforms reasonably becomes the focus of modern radar research.Aiming at the problems of high range sidelobe,electronic interference and poor orthogonality of radar transmitting waveforms,this paper studies the design and optimization of radar transmitting waveforms under different systems.The main work is as follows:(1)In view of the problem that the high sidelobe level in the single-channel system will affect the performance of detecting targets,different transmitting signals are designed and different optimization algorithms are used to optimize the signals.Firstly,a method for designing Nonlinear Frequency Modulation(NLFM)signal is studied,which combines linear function with inverse proportional function to construct the time-frequency function of NLFM signal.By adjusting the parameters of linear and nonlinear intervals in timefrequency curves,a NLFM signal is designed,which can obtain the low peak sidelobe ratio without weighting.Then,based on Particle Swarm Optimization(PSO)Algorithm,the peak sidelobe ratio of pulse compression and the mainlobe-to-sidelobe ratio of ambiguity function are respectively used as objective functions to optimize NLFM signal.Finally,the phase codes are optimized based on Cyclic Algorithm-New(CAN).Simulation results have verified the capability of the sidelobe level suppression of the designed signal and the two optimization algorithms.(2)Aiming at the problem that single pulse is easy to be intercepted,the pulse agility waveforms are studied.Firstly,the stepped frequency waveform is designed.By changing the frequency and form of signal in different pulse repetition time,using the time difference between the interference signal and the target echo signal to suppress interference.Secondly,the waveform agility signal is designed,so that the radar transmits signals randomly in each pulse repetition time.Since the form of the transmitting signal is only mastered by ourself,the capability of the radar to suppress interference is effectively improved.In addition,the matching period grouping technique is also used to process the waveform agility signal at the receiving end.Simulation results have verified the effectiveness of the technique and the two waveforms designed to suppress interference.(3)Aiming at the problem of poor orthogonality property in the multi-channel system,the transmitting waveforms for MIMO radar based on frequency division orthogonality and code division orthogonality are proposed respectively.Firstly,OFDM-LFM signal is designed,and the orthogonality of the signal is analyzed.Secondly,the code division quadrature phase codes are studied,and the orthogonal continuous phase codes are optimized based on the PSO Algorithm and the Multi-Cyclic Algorithm-New(Multi-CAN),respectively.In addition,in order to meet the requirements of discrete phase in practical applications,the continuous phase is quantized to achieve phase discretization.Finally,the influence of the two optimization algorithms on the signal performance is compared and analyzed.Simulation experiments have verified the effectiveness of the two optimization algorithms in reducing sidelobe level and improving waveform orthogonality. |
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