| When a non-linear target is irradiated by the radio frequency signal,it scatters the second and third harmonic signals to the surrounding.The function of the harmonic radar is to receive and process the second and third harmonic signals scattered by the non-linear target,so as to detect the specific location of the non-linear target.The common non-linear targets in real life are wiretaps,trackers and electronic detonators.Harmonic radar can effectively detect hidden electronic devices,electronic fuze mines and electronic explosives.Therefore,harmonic radar can be widely used in Metro stations,railway stations,airports and other public safety inspection,examination high-tech cheating prevention,personal privacy protection and other fields.Guided by the application requirements of harmonic radar and referring to the research status and development trend at home and abroad,the system functions and technical indicators are formulated,and a harmonic radar based on FPGA is designed,which has high detection sensitivity,strong anti-jamming ability,long detection distance,low false alarm rate and false alarm rate.In the process of designing harmonic radar,firstly,the basic theory and principle of existing radar are analyzed,as the theoretical basis of this research,the characteristics of non-linear target and its model theory are studied in detail,it mainly includes the study of volt-ampere characteristics of non-linear targets and the establishment of mathematical and physical models,the section area equation and radar equation of harmonic radar are derived.Based on the cross-sectional area equation and radar equation of harmonic radar,the system architecture of transmitter,receiver,digital signal processing and human-computer interaction platform is designed.The main function of the transmitter is to get the radio frequency signal between 2.412 GHz and 2.508 GHz from the zero-IF LFM analog signal through the IQ modulation circuit and radiate it through the antenna after the filter circuit.The main function of the receiver is to process the second and third harmonic signals received by the antenna.Because the power of the harmonic signals is small,the analog baseband signals are obtained through the IQ demodulation circuit after secondary amplification.The main function of digital signal processing is to use CORDIC algorithm to generate zero-IF LFM digital signal and process the received second and third harmonic signals.The human-computer interaction platform mainly completes the task of human-computer interaction,including setting the power and frequency band of the radio frequency signal,displaying the intensity of the received second and third harmonic signals.In practical application of harmonic radar,firstly,the receiver scans the existing frequency bands in the surrounding environment,and the transmitter chooses the best working frequency band of radio frequency signal,which effectively improves the anti-jamming ability of harmonic radar.This paper completes the design of hardware circuit and software driver of harmonic radar,and simulates with Modelsim and MATLAB to verify the feasibility of hardware and software design of the system.The actual function test shows that the design can detect the non-linear target,whether the target is in active or inactive state,shutdown or boot-up state.Compared with the current common security equipment,this design detects and locates non-linear targets,with automatic switching frequency function,strong anti-interference ability,high sensitivity,detection distance,false alarm rate and low leakage alarm rate. |
