Design Of UWB MIMO Radar System And Research On The Method Of Through-wall Imaging

Ultra-wideband(UWB)multiple input multiple output(MIMO)radar technology is widely used in through-wall detection and imaging due to its good resolution and penetration ability,less antennas requirement and efficient data acquisition ability.UWB through-wall radar can penetrate the non-metallic shielding obstacles,and realize the non-destructive detection and positioning of hidden objects behind the wall or in complex environment,so it has a wide range of application prospects and important research significance in the fields of military operations,security monitoring,hostage rescue and disaster relief.In this paper,under the background of through-wall radar technology research,combined with the advantages of UWB technology and MIMO technology,we focus on how to design a UWB MIMO through-wall radar system with good performance and realize through-wall 2D multi-targets imaging.In the through-wall application,stepped-frequency-continuous-wave(SFCW)is one of the most commonly used signal forms of the frequency domain radar.Compared with the time-domain pulse radar system,the radar system adopting SFCW technology has more flexible frequency band control ability,can improve imaging resolution and adapt to the working frequency band range of radar antenna.In order to improve the resolution of radar system,realize through-wall imaging and save cost,this paper adopts the UWB SFCW signal model based on the vector network analyzer.Two-dimensional imaging is one of the most important signal processing steps in the through-wall MIMO radar system.When the electromagnetic wave penetrates the wall,it will produce reflection,refraction,velocity change,energy attenuation and other phenomena,which will result in the problems of displacement,defocus or false targets in the imaging results.In this paper,the cross-correlation based time domain back projection(CC-TDBP)algorithm is developed,which can speed up the calculation of the traditional BP algorithm,suppress the artifact clutter and improve the imaging quality.In addition,considering the influence of the wall on the refraction and velocity of electromagnetic wave,an improved through-wall BP algorithm based on ray tracing is proposed to correct the through-wall imaging results.The design of MIMO array structure is related to the complexity and cost of radar system,and directly affects the imaging quality,so a reasonable array topology design is very important.According to the principle of displaced phase center approximation and the method of polynomial factorization,this paper studies and designs a kind of linear sparse array structure with 8 transmitters and 8 receivers.The results of the sparse array topology design of MIMO radar system show that the larger array aperture and the smaller antenna cell spacing are obtained,and the better azimuth resolution and main and side lobe control are maintained.In this way,the number of antenna elements and the cost of the system are reduced while the aperture length is kept.Compared with the SAR system with the rail,the MIMO radar system can improve the speed of data acquisition by using electronic RF switch.In addition,in the MIMO through-wall radar system,the antenna is of great significance to radiate energy to the wall and detect the target signal.In order to balance the range resolution and the wall penetration ability,a new design of ultra-wideband low-frequency miniaturized Vivaldi antenna with the size of 250 mm × 200 mm × 1.6mm is selected.The actual working frequency band of the antenna is 0.5-2.5GHz,the directional performance is good,and the gain is stable with the change of frequency.It can be applied to the through-wall imaging.Finally,the design and integration of the MIMO through-wall radar system is completed.Theoretically,the range resolution of the system is 6.8cm,the actual aperture length of the array is about 1.1m,and the angle resolution is 0.101 rad.Different experiments are carried out with the designed radar system,and the imaging comparison results with different algorithms are applied.Simulation and experimental results show that the proposed imaging methods can effectively suppress the artifacts and focus on different targets in both the range direction and the azimuth direction.The designed MIMO through-wall radar system can detect and locate the human targets behind the wall accurately.The research results of this paper have great application potential for the future scientific research and experiments,and provide a good scientific experimental platform for the research of through-wall imaging technology.