The Resolution Analysis Of Active Millimeter Near-field Imaging System Based On CSAR And Circular MIMO

In recent years,terrorist attack has become a more and more severe challenge to the public safety,therefore the development of surveillance systems' capable of detecting concealed weapons and plastic explosives under clothing on human bodys has been seriously considered.Millimeter-wave systems are nonionizing and,therefore,pose no known health hazard at moderate power levels.Millimeter-wave imaging systems are capable of penetrating common clothing barriers to form an image of a person as well as any concealed items.Millimeter-wave systems can reach extremely high resolution due to the relatively short wavelength.Based on the above advantages,active millimeter-wave imaging systems gained extensive utilization in human security in recent years.The development of active millimeter-wave imaging systems experienced next several stages: single channel with two dimensional mechanical scanning,linear array with one dimensional mechanical scanning,area array with MIMO technology,and the balance between the cost and the performance is the everlasting pursuing goal.In recent years,an active millimeter-wave imaging system based on the principle of circular trace synthetic aperture radar(CSAR),which is called circular scanning near-field imaging system,is applied in body security imaging to get balance between the cost and the performance.The resolution analysis of circular scanning near-field imaging system is different from that of CSAR,which is studied in this thesis.In order to accelerate the imaging processing,a new imaging system called circular MIMO with multiple-receiver and multiple-transmitter distributing equally along a circle is proposed in this thesis.The contents researched in this thesis are as follows.Firstly,the normalized generalized ambiguity function under the near field conditions for the circular scanning near-field imaging system is derived.In consideration of the variation of the resolution according to the location of target points,A resolution evaluation criteria based on statistic analysis for the circular scanning near-field imaging system is proposed.The simulation and experiment is used to demonstrate the theoretical derivation.Secondly,the resolution analysis of the circular scanning near-field imaging system under cylindrical coordinate system is studied.The radial and tangential resolution is calculated and the trend of resolution variation is summarized.Finally,the circular MIMO system combining CSAR and MIMO is proposed.The circular MIMO system is composed of multiple receivers and multiple transmitters distributing equally along a circle.The back-projection algorithm and the normalized generalized ambiguity function is improved to adapt to circular MIMO system.It is confirmed that the circular MIMO system performs better on resolution than that of the circular scanning near-field imaging system by target point imaging with BP,wave-number domain analysis and normalized generalized ambiguity function calculation.