Research On The Complex Modulation Radar Waveform Design And Signal Processing

Radar is a vital information acquisition system in the complex modern information battlefield and its detection performance is weakened because of target stealthy technology,low/very low altitude penetration and complex clutter environment.The survival of radar is seriously threatened on account of the intercepted receivers' improving interception technology.Radar's detection performance depends on the range and velocity resolution and range resolution is determined by radar signal's bandwidth,velocity resolution is by pulses accumulation.It is not easy for enemy's electronic reconnaissance to intercept radar signals with modulation complexity and randomness.Even if a radar signal has been intercepted,its parameters and structures are difficult to analyze in this case,thus the living space of radar is expanded.Carrying out the research on complex modulation radar waveform design and processing is helpful to improve the low probability of intercept(LPI)performance and resolution of radar and has urgent military significance and application value.From single carrier to multicarrier,determinacy to chaos,single pulse to pulse train,inter-pulse constant frequency to random frequency hopping,and constant pulse position to random pulse position,this dissertation conducts a study on complex modulation radar waveform design and signal processing technology.The work and contributions in the dissertation can be summarized as follows:1.With comprhensive consideration of the length of chaotic sequence and truncation chaotic sequence,chaotic initial values and truncation starting point,a chaotic biphase code selection strategy based on autocorrelation's optimal peak side-lobe level is proposed.2.Chaos Based Multi-Carrier Phase Coded(CBMCPC)radar signal model and generation methods are proposed.For P4 MCPC signal,the influences of different P4 code sets on the signal's autocorrelation and Peak-to-Mean Envelope Power Ratio(PMEPR)performance are analyzed.The ambiguity functions and autocorrelation performance of CBMCPC signals are deduced and intensively analyzed.The influences of carrier number,phase-modulated bits and the carrier's complex weighting factor on the performance of the CBMCPC signal are also discussed.3.Different kinds of CBMCPC pulse train signals,including inter-pulse constant frequency,inter-pulse random frequency hopping,constant pulse position and random pulse position are designed.The ambiguity functions and autocorrelation performance of designed signals are deduced and analyzed.The influences of carrier,phase-modulated bit and period number on the autocorrelation performance are explicitly analyzed.Furthermore,intensive discussions are stretched on designed signals' Doppler tolerance and its improvement methods.Simulations results show that the signals designed in this dissertation perform wider bandwidths due to muticarrier property.Utilizing our designed signals hence improves radar's range resolution.The randomness,waveform diversity and agility capability of the designed signals are further increased due to the introduction of chaos and inter-pulse frequency hopping,which make it more difficult to be identified and intercepted by enemies.The inter-pulse frequency hopping of designed signals can achieve larger operating bandwidth by instantaneous bandwidth synthesis,which reducing the hardware requirement of receiving equipment.The random pulse position of designed signals not only increases the waveform agility capability but also improves the range and velocity ambiguity effectively.4.The signal processing methods of the designed complex modulation radar waveforms are provided.The CBMCPC signal processing is realized.Compared with LFM signal,the CBMCPC signals' detection performance of multiple targets in noise environment is analysed.For the requirement of low altitude,slow and small targets detection in strong clutter environment,a target detection method based on multi-channel threshold decision and mathematical morphology filtering is proposed.In addition,a target labeling method based on connected regions is presented to realize target position acquisition,which provided reliable targets data to tracking latter.The simulations results of the echo data processing of an early warning radar in strong clutter environment verified the effectiveness of the proposed methods.