Non-uniform Frequency Density Multi-carrier Radar Signal Waveform Design

High range resolution(HRR)radar adopt wideband signal as transmitted signal waveform of radar system.Traditional wideband signal is linear frequency modulation(LFM)pulse signal,which has disadvantages of simple waveform and intensive distribution of energy time-frequency.Therefore,LFM pulse signal is easy to be intercepted by time-frequency method of modern jammer.To improve performance of low probability of intercept(LPI)of wideband radar signal,multi-carrier signal is introduced into the radar field as a kind of wideband waveform.Due to its flat distribution of energy time-frequency,it is hard to be effectively intercepted by time-frequency method of modern jammer.The technique combining multicarrier,amplitude and phase coded and subcarrier frequency modulated can make the radar signal more complicated,unpredictability stronger,parameters estimation harder and accumulation efficiency of non-matched filtering(for interception reciever)lower than that of matched filtering(for radar reciever),which further improve LPI of multi-carrier signal.Orthogonal frequency division multiplexing(OFDM)pulse signal is just a typical multicarrier radar signal.Though it is in all its glory,its Doppler tolerance is low,which does not apply to guidance radar detecting hypersonic target in search patten.For the above problems,it is urgent to design a kind of multi-carrier radar signal with hign Doppler tolerance.As for the above application background,a new type of non-uniform frequency density multi-carrier(NUFD-MC)radar signal is proposed and the design method of subcarriers frequency based on nonlinear frequency modulation(NLFM)signal’s spectrum window function is given.Furthermore,the range resolution capability,the Doppler tolerance,the range-Doppler coupling characteristics and spectrum characteristics of the signal are analyzed in detail and the method of peak-to-average power ratio(PAPR)reduction of the signal is also studied.The main researches of the paper are as follows:(1)In order to overcome the disadvantage of OFDM signal’s low Doppler tolerance,a new type of multi-carrier radar signal with non-uniform frequency density is proposed and the design method of subcarriers frequency based on NLFM signal’s spectrum window function is given,and its AF is derived.At the same time,range resolution capability,the Doppler characteristics and spectrum characteristics are analyzed comparing with typical pseudo-noise OFDM(PN-OFDM)signal and subcarrier amplitude and phase weighted OFDM(SCAPW-OFDM).Theoretical analysis and numerical simulation result show that the new signal has advantages of higher utilization efficiency of signal energy,better pulse compression characteristics,no range-Doppler coupling and higher Doppler tolerance,which is suitable for wideband high resolution radar to search and detect high speed target.(2)For the disadvantage of NUFD-MC signal’s high PAPR,the method of PAPR reduction is proposed from the view of waveform design,which takes account of target detecting performance at the same time.For NUFD-MC signal basing on identical sequence coding,the method of PAPR reduction basing on window function amplitude weighting,phase weighting and combination weighting of both them are applied to it,in which best method is obtained,that is,combination weighting of Hamming window function amplitude and Schroeder phase,whose result of PAPR reduction is the most effective and simultaneously which can balance target detecting performance.For NUFD-MC signal basing on cyclic shift sequence coding,the reduction of signal PAPR is got by continuous cyclic shift of phase coded sequence and window function amplitude weighting in each subcarrier.To further reduce PAPR of NUFD-MC signal basing on cyclic shift sequence coding,NUFD-MC signal based on random shift coding sequence which is optimized by genetic algorithm is proposed,and the most optimal way of random shift coding is obtained,and according to reasonable PAPR constraint condition,appropriate signal is designed,whose peak sidelobe(PSL)of autocorrelation function(ACF)is largely decreased.