Near-Field Rotating Linear Array Imaging In The Terahertz Band

As a new kind of radar imaging mode,the near-field rotating linear array imaging in the terahertz band has the ability of realizing near-field target detection with high resolution and high frame rate,thus applicable to missile guidance,proximity fuze,security inspection and anti-terrorism.However,several difficulties actually exist in array system integration,balance between precision and efficiency of imaging algorithms,and side lobe avoidance.Centered on the problems above,this paper carries out in-depth study on the technique of near-field rotating linear array imaging in the terahertz band,mainly including system design,high-resolution imaging algorithms,efficient imaging methods,and side lobe suppression methods.In the introduction part,the background and significance of this research are firstly illuminated.And then the current development of terahertz radar systems,near field array systems and array imaging algorithms is overviewed.In Chapter 2,a near-field rotating linear array imaging system in the terahertz band is designed.Firstly,the signal frequency band and waveform,array configuration and scanning mode,working scenario and system structure are designed.Then several key indexes are calculated including radar transmit power,pulse repetition frequency,the amount and transmission rate of data.In addition,the theoretical resolution performance is analyzed.In Chapter 3,research on the terahertz near-field rotating linear array imaging method is carried out.Firstly,the feature on the echo signal with a rotating scanning trajectory is analyzed.Secondly,two high-resolution imaging algorithms-time domain correlation and back projection are analyzed in the rotating linear array mode by means of theoretical deduction and experimental verification.Finally,to increase the imaging efficiency,a fast back projection algorithm based on calculating the distance matrix in advance is proposed.In Chapter 4,methods of side lobe suppression in the imaging processing are studied.Firstly,the traditional time-windowing method is analyzed in the terahertz rotating linear array imaging system.Results show that time-windowing loses efficacy because of the special circular synthetic aperture and the circularly symmetric spectrum.Then a modified coherence weighting method is proposed,and its remarkable effect that it decreases the side lobe by almost 40 dB is demonstrated by experiments.In the last part of the thesis,the research work is summarized and directions of the future work are provided.