Broadband Stepped Frequency Processing Technology For Millimeter Wave Inverse Synthetic Aperture Imaging Radar

Phased array inverse synthetic aperture imaging radar is an important development direction of ground-based space target detection.Based on the broadband characteristics of the transmitted signal,high-resolution fine detection and imaging of space targets can be realized.At the same time,based on the large-aperture phased array,it can realize functions such as longer operating distance,higher spatial resolution,beam agility,and multi-target detection.However,due to the influence of aperture fill time and aperture effect of large-aperture phased arrays,the instantaneous bandwidth of the transmitted signal is limited,and stepfrequency waveform synthesis is an effective solution.At present,there is relatively little research on broadband step-frequency processing technology for millimeter-wave phased array inverse synthetic aperture imaging radar.This thesis focuses on this problem.Firstly,the main research background of this thesis is introduced,the domestic and foreign development status of space target imaging radar and stepped frequency radar technology is analyzed and summarized,and the aperture effect of phased array antenna and the influence of aperture fill time on signal instantaneous bandwidth are discussed.The theory of step frequency signal processing is introduced,including step frequency signal model,key parameters,waveform generation,broadband synthesis,etc.Then,the waveform generation technology of broadband millimeter-wave stepped frequency radar is studied.The generation scheme of the combination of step frequency waveform baseband signal generation and tunable frequency source is analyzed and designed.The baseband waveform is generated based on DDS,and the baseband waveform is digitally up-converted to generate a C-band step frequency intermediate frequency signal.The C-band signal is further up-converted to the millimeter wave frequency band using the tunable analog local oscillator to realize broadband millimeter wave step frequency signal output.Then,the time-domain broadband synthesis algorithm and the frequency-domain broadband synthesis algorithm of the chirp waveform are studied.Taking the signal model as the starting point,the connotation of the construction of the speed compensation item in the frequency domain synthesis algorithm is focused on,The apparent envelope movement that appears in the wideband step frequency synthesis of 5 GHz bandwidth is compensated by the constructed speed compensation item,and the ideal synthesis result is obtained.Finally,a millimeter-wave step-frequency radar experimental verification system is constructed by using the RFSo C,which realizes step-frequency signal generation and processing based on DDS and PLL.The FPGA programming of the step frequency waveform frequency domain synthesis algorithm and the function test of each module have been completed,and the step frequency synthesis experiment verification of the maximum synthesis bandwidth 5 GHz has been realized.