The Time-Domain Pulse Compression For LFM And NLFM Signals Based On FPGA

Pulse compression technology is widely used in radar detection system,which resolved the contradiction between the accuracy of velocity measurement and ranging,because the signal of the system with large time-wide and bandwidth at the same time.The speed and distance resolution of the system is incompatible,because of the FM signal is a good solution to this problem.Pulse compression is a kind of processing for echo signal,which ensured the speed resolution of the system,and at the same time,improved the resolution of the target.It has been widely used in modern radar system.This paper mainly studied the linear frequency modulated(LFM)signal and nonlinear frequency modulated(NLFM)signal for the transmitting signals of radar system,and the process of pulse compression that its echo as the input signal of a matched filter.LFM signal is studied earlier,its frequency is linear with time,and it's not sensitive to Doppler frequency shift.It has been widely used in all kinds of radar systems.LFM signal can be designed by direct frequency synthesis(DDS)chip and software programming based on DDS principle,two ways can produce stable linear FM signal.When the LFM signal as the transmitting pulse of the radar,the signal has high sidelobe when the echo is compressed,and it's easy to be misjudged by the strong noise.Therefore,the window function is usually used to suppress the sidelobe and improved the anti-interference ability of the signal.The design of NLFM signal usually adopted the function window base on the retention phase theorem,when as the transmit signal,the echo is matched filtering with Good sidelobe inhibition and narrow main lobe at the receiving end,which has strong target recognition and anti-interference ability.According to the LFM signal by window function weighting leads to mainlobe broadening,which reduced the ability of target recognition,and the complex process of producing NLFM and it is sensitive to Doppler shift and other issues,the article improved the Hamming window function.Through a variety of parameter settings and optimized results were analyzed to find out the best way of signal processing in radar system.The design adopted the popular digital signal processing chip FPGA to design the matched filter to realize the time domain pulse compression of LFM signal and NLFM signal.The circuit design of LFM signal pulse compression included the distributed algorithm circuit design,the window function weighting and the approximate model seeking circuit,etc.Among them,the distributed algorithm made full use of the advantages of FPGA structure and storage resources,transformed from multiplication operation to logical operation in convolution operation,which broke the limit of the order of IP checking the order of the filter.The chip selection was more diversified,and reduced the cost.The pulse compression processing of NLFM signal was the same as LFM signal,but no window function weighting.The whole flow of LFM and NLFM signal from design to pulse compression was introduced in detail,through the simulation tools such as MATLAB to compared the continuous waveform and discrete waveform of matched filter with different parameters,to verify the circuit design of LFM signal and NLFM signal in time domain pulse compression by FPGA.