Design And Implementation Of Frequency Hopping Wideband LFM Signal Echo Simulator

Radar echo simulator is an important radar equipment to test and verify the performance of radar.It avoids the shortcomings of high cost,long cycle and high cost brought by external field test,and has very important application value.As a commonly used radar waveform,linear frequency modulation(LFM)signals are relatively easy to generate and process,and have been widely studied and applied in the radar field.Wideband frequency hopping signals have high range resolution and anti-interference ability.It is of great significance to combine the two to perform target echo simulation.This thesis focuses on the design and implementation of a broadband frequencyhopping LFM signal echo simulator,analyzes the basic characteristics and the echo simulation methods of the frequency-hopping LFM signal,studies the method of undersampling frequency measurement of the broadband frequency-hopping LFM signal,and designs the overall scheme of the simulator system,which is implemented based on the field programmable gate array(FPGA)platform.The main work of this thesis includes:1.This thesis introduces and analyzes the basic characteristics of frequency-hopping coded signals and LFM pulse signals,the frequency-hopping coded signal is modulated by using the LFM signal,and the distance and velocity resolution of the frequencyhopping LFM signal are given by analyzing the fuzzy function.At the same time,the echo simulation of the frequency-hopping LFM signal is performed in the distance dimension and the velocity dimension,and finally the parameter index of the LFM signal echo simulator is given.2.This thesis introduces two common methods of undersampling frequency defuzzification,China remainder theorem and time-frequency analysis.Aiming at the problems of large errors in spectral peak search under low signal-to-noise ratio based on China remainder theorem and high complexity based on time-frequency analysis,an under-sampling defuzzification method based on multi-channel frequency partitioning is proposed to greatly reduce the realization complexity,and the fast frequency measurement is realized by the method of linear interpolation zero-crossing.3.The system scheme of the broadband frequency-hopping LFM signal echo simulator is designed.Based on the methods of LFM signal echo simulation,the undersampling frequency defuzzification,and the linear interpolation zero-crossing frequency measurement,the design of the echo generation module,RF module,undersampling non-fuzzy frequency measurement module,signal detection and processing module,and digital up-conversion module based on the multi-phase structure are completed.4.Based on the design scheme of the broadband frequency-hopping LFM signal echo simulator system,the overall architecture of the system hardware is given.Through the circuit analysis,the power module,digital-to-analog conversion module,FPGA module,digital signal processor(DSP)module and its interface circuits are implemented.At the same time,the design of the main control software is completed,and the communication between the host computer,DSP and FPGA is realized through the main control software.The methods proposed in this thesis have been verified through simulation and system testing.The results show that these methods can effectively solve the problem of ambiguity in frequency measurement when wideband frequency-hopping signals are under-sampled,and achieve fast and fuzzy-free frequency measurement and accurate target echo simulation.