Waveform Design And Signal Processing In Frequency Coded Radar

Frequency coded waveforms are widely used in modern radar systems because of its approximate ideal ambiguity function,low probability of intercept and strong anti-jamming ability.The design of frequency coded waveforms needs to consider the two main performances,namely,auto-correlation and cross-correlation.The former is to alleviate the masking effect of strong target on weak target,while the latter reduces the interference between different frequency coded waveforms.To solve the issue of high auto-correlation sidelobe peak and high cross-correlation peak of frequency coded waveforms,we investegate the waveform design and signal processing in frequency coded radar.Firstly,the model of frequency coded waveform is established.Its ambiguity function,especially delay ambiguity function are analyzed.The influences of frequency,phase and in-pulse signal on the ambiguity function are analyzed.The simulation results show that the auto-correlation and cross-correlation of frequency coded waveforms can be optimized by designing frequency,phase and in-pulse signals.Secondly,in the aspect of frequency coded waveform design,phase and LFM(linear frequency modulation)can be added to the baseband signal change the distribution of auto-correlation sidelobe.A frequency coded waveform with phase modulation is designed.The waveform optimization is established to minimize weighted sum of the auto-correlation sidelobe peak and cross-correlation peak.The genetic algorithm is designed to obtain the optimized frequency coded waveform.Simulation results show that the cross-correlation performance of the proposed frequency coded waveform is improved significantly,but the auto-correlation sidelobe peak is reduced slightly.Thus,the phase sequence,frequency sequence and frequency modulation slope sequence are optimized by adding LFM.Simulation results show that the auto-correlation sidelobe peak and cross-correlation peak of the designed frequency coded waveform are reduced dramatically.Thus,the target detection performance and anti-jamming ability of the frequency coded waveform are improved.Finally,in the aspect of the signal processing at receiver,the moving target detection method and range sidelobe suppressions method are studied.The Doppler tolerance of the designed frequency-coded waveform is analyzed.Then,the frequency compensation interval of the matched filter bank is designed according to the Doppler tolerance threshold with the aiming to eliminate the influence of the target Doppler frequency shift on the frequency coded waveform.Moreover,a rearrangement window based on frequency sequence is proposed to suppress the range sidelobe,which can greatly reduce the auto-correlation sidelobe peak value of frequency coded waveform and improve the detection performance of frequency-coded radar for weak target.