Research And Implementation Of Direct Wave Suppression Technology For Co-location HF FMCW Radar

In recent years,high-frequency surface wave radar has been developed at a high speed.With the inherent advantages of over-the-horizon,low-cost,all-weather,and easily maintained,it has become one of the most important means of ocean monitoring,which have a high military civilian value.Due to the existence of direct wave interference,the co-located high-frequency ground wave radar mostly adopts the intermittent wave system,and the detection energy is difficult to reach high.The continuous wave system improves the detection energy effectively.It can reduce the hardware requirements,and reach farther detection distance,which is a trend of the development of high frequency surface wave radar.The direct wave interference is the primary problem in continuous wave system.Therefore,it is necessary to carry out research on direct wave interference inhibition technology based on the actual situation of co-located high frequency surface wave radar.This thesis focuses on the direct wave interference inhibition of the co-located HF surface wave radar under the FMCW system.By the use of theoretical reasoning,simulation analysis and actual measurement verification,the direct wave inhibition system is achieved.Firstly,the co-location HFSWR system analysis model is established from the actual situation.From the perspective of signal processing,the influence of direct wave interference on the actual system and target detection is analyzed.We determined two aspects of direct wave inhibition: radio frequency cancellation in the front of the receiver and inhibition in digital domain.Then,the basic idea of radio frequency cancellation is determined,and the influence of adjustment error on the cancellation depth is analyzed.Then,we discussed the differences of different delay,phase and amplitude measurement and adjustment methods in actual implementation.In this way,the appropriate measurement adjustment method is selected and a hardware implementation is given.After that,to analysis the feasibility of the actual implementation,the simulation analysis was carried out.We set up the RF cancellation experiment system and discussed the optimization of the RF cancellation system and the problems that needs to be paid attention to in this system.The depth of RF cancellation exceed 22.11 d B in the end.Finally,we discussed the feasibility of the mainstream direct wave inhibition algorithm applied to HF ground wave radar.Then,the problems that need to be paid attention to in the application of LMS adaptive interference cancellation algorithm are analyzed.We compared the difference between the fractional Fourier transform and solution distance algorithms and the limitation of the application of fractional Fourier transform in HFSWR was given.We do research on the inhibition of the residual of radio frequency cancellation in the digital domain,and derived the signal form of the radio frequency cancellation residual in the mixed low-pass output stage.In this paper,a new method for radio frequency cancellation residual inhibition using frequency domain LMS adaptive interference cancellation algorithm in the mixed low-pass output stage is proposed.The algorithm can achieve a cancellation depth of more than 43 d B through simulation analysis,and the measured data can be verified by more than 30 d B.Through the research of this thesis,the radio frequency cancellation of the receiver front-end direct wave and the inhibition of the residual in the digital domain are realized in the actual co-located high-frequency FMCW radar.The radio frequency cancellation can reach more than 22.11 d B,and the digital domain cancellation Up to 30 d B or more,the normal detection and target detection of high-frequency FMCW radar are successfully realized.