Research On Ultra-wideband MIMO Radar High-resolution Though-the-wall Imaging Techniques

Through-wall imaging radar(TWIR) transmits ultra-wideband(UWB) electromagnetic wave and can detect and image concealed targets through walls and other obstacles. TWIR is widely applied both civilian and military field. Combined with multiple-input multiple-output(MIMO) arrays, radar systems can offer images with high imaging efficiency. In this thesis, based on the radar array model and through-wall imaging model, some critical techniques about spatial spectrum and factor weighting are studied focusing on how to improve imaging quality. The work can be summed up as the following three parts:The concepts of co-array and virtual array are extended to UWB near field condition. Use the concept of point spread function, the analysis proved that virtual array is equivalent to MIMO array. Based on virtual array, a MIMO array which has good performance is designed. Two MIMO radar imaging algorithms are extended to medium penetrating imaging as a basis for further research.The relationship between radar imaging and spatial spectrum filling is discussed. A non-orthogonal sidelobes reduction method based on sub-aperture imaging is adopted in MIMO radar through-wall imaging successfully. In order to solve the problem of huge sidelobes arising from gapped spatial spectrum of TWIR data, an approach is proposed based on spectral extrapolation technique. The high sidelobes is reduced efficiently.The characteristics of sidelobes and grating lobe in UWB MIMO radar through-wall imaging are analyzed. And the phase coherence factor(PCF) weighing method is extended to the stepped frequency signal system for the first time, adding additional phase diversity in frequency domain. The simulation and experimental data prove that PCF weighing method has a better sidelobes/grating lobe suppression effect than coherence factor(CF) weighing method. And when in the presence of array errors, PCF weighing method has good robustness.The methods mentioned in this thesis have been used in UWB MIMO radar successfully.