Study On Distributed MIMO Radar Near-Field Detection Technology Based On Frequency Division Waveforms

Radar is the main detection means of battlefield perception in modern war.However,radar will face more complex detection environment in modern battlefield,such as the increasingly complex electromagnetic environment,the increasing number of types of targets and the continuous emergence of new combat modes.Traditional parabolic antenna radar and phased array radar,limited by carrier platform and cost-effectiveness index,is unable to distinguish cluster targets at a long distance.To overcome this limitation,Multiple-Input MultipleOutput(MIMO)radar is applied,which has the advantages of flexible working mode,multitask configuration on demand,strong survivability of decentralized battlefield and high efficiency of distributed computing.Compared with traditional monostatic radar,the aperture of distributed aperture MIMO radar is greatly increased,which makes the targets usually located in its near-field.Compared with bistatic/multistatic radar,the aperture of distributed aperture MIMO radar is the fusion aperture of multiple transmitter and multiple receiver signal level,and its processing results have the advantage of fine observation like magnifying glass.This thesis focuses on the near-field detection of distributed MIMO radar based on frequency division waveforms.Main accomplishments include:Since the near-field spherical wave model of distributed aperture MIMO radar is rarely reported,a Multiple-Input Multiple-Output three-dimensional near-field echo model is introduced.With frequency division multi-transmitting Linear Frequency Modulation(LFM)signal,the echo of near-field target by each receiving antenna is derived.The near-field echo model is established.The validity of the near-field three-dimensional echo model is verified by computer simulation.According to the requirements of the large number of distributed aperture transmitting waveforms and the high degree of isolation between transmitted waveforms,a MIMO signal transmitting scheme based on frequency division multi-transmitting LFM signal is studied.Firstly,the time-frequency relationship of frequency division multi-transmitting LFM signal is clarified.Secondly,the mathematical expressions of autocorrelation and cross-correlation among frequency division and multi-transmitting LFM signals are given.In view of the existence of high isolation degree with large bandwidth,medium isolation degree with medium bandwidth,small isolation degree with small bandwidth of the transmitted signals,three frequency division multi-transmitting waveform transmission schemes are proposed,which have frequency interval larger than signal bandwidth,frequency interval equal to signal bandwidth,and frequency interval smaller than signal bandwidth.The crosscorrelation performance of frequency division LFM signals under aforementioned scheme is studied.Finally,the performance of autocorrelation and cross-correlation of frequency division multi-transmitting LFM waveforms under various transmission schemes is verified by simulation.Aiming at the problem of getting transient high resolution of cluster targets,a near-field 3D matching detection method based on frequency-division multi-transmitting LFM waveform is proposed.This method does not require long-term phase-coherent accumulation and can realize the high transient resolution of multi-target flexible formation of clusters by the synthesis of multiple transmitting and multiple receiving pulses.Firstly,the spatial domain of interest is divided into three-dimensional grid points.Secondly,a digital frequency modulation(dechirp)preprocessing scheme based on distance segmentation is proposed to separate the transmitted signals.Then,the delay between each grid point and each transmitting/receiving array element is calculated by traversal.The echo signals separated from each array element are aligned to the reference time delay according to these delays.Finally,the synthesis of bandwidth and aperture can be achieved at the same time to realize the high resolution of range and space,through the synthesis of multiple transmitting and multiple receiving pulses.In this paper,three frequency-division multi-transmitting LFM signals with different frequency intervals are used to simulate the near-field threedimensional matching of single target and multi-target under two different structures of sparse linear array and sparse three-dimensional array,respectively.The simulation results verify the effectiveness of the proposed method.