太赫兹频段粗糙面宽带一维距离像特性

Broadband one-dimensional range profiles characteristic of rough surface in terahertz band

基于太赫兹时域光谱技术搭建了近单站宽带太赫兹脉冲一维距离像的测量系统,其距离分辨率可达亚毫米量级.首先,利用该系统测量了多种形状目标的一维距离像,验证了测量系统的可靠性及通过目标的一维距离像中的散射特征位置分布来识别其外形特征的可行性.进而,通过测量不同粗糙度的铝板目标,结合粗糙表面散射基尔霍夫近似和微扰法理论,探究了目标表面粗糙度对于一维距离像强度及脉冲宽度的影响规律.此外,发现双站系统中一维距离像的时延与目标姿态的改变方向有关.相关研究结果对太赫兹雷达目标探测与识别具有一定的指导意义.

The one-dimensional(1D)range profile is an important back scattering characteristic of objective,which reveals the longitudinal distribution of radar cross section(RCS)along the detection beam.Since the shape and posture can be reflected by the 1D range profile,it is of great significance in military to determine the target orientation,velocity and whether it is armed.In this paper,broadband terahertz 1D-range-profile measurement system is built based on the time-domain spectroscopy(TDS)system.It is in bistatic configuration(bistatic angle of 9°)and the signal-to-noise ratio(SNR)is 34.5 dB,with a gold mirror used as a reflector.Benefiting from the ultrashort terahertz pulse width(full pulse width of 0.52 ps),the bandwidth covers the frequency range from 0.1 THz to 2.5 THz(peaked at 0.9 THz),corresponding to the range resolution on a submillimeter scale.Firstly,the 1D range profiles of several objects in different shapes are measured,including the step,cylinder,step cone and their combination,which indicates that the geometric profile of the target in the detection direction is adequate to identify the shape feature of the target and proves the reliability of the 1D range profile measuring system based on TDS.Secondly,aluminum plates with different surface roughness in a range of 0−25μm are also characterized.The Kirchhoff approximation theory and small perturbation method(SPM)are introduced to illustrate the characteristics of broadband terahertz 1D range profile related to the surface roughness of target.It is found that the scattering characteristic of metal object in the terahertz range is sensitive to surface roughness.If the surface roughness of the object is larger,the peak intensity of the 1D range profile will be weaker and the echo signal pulse width becomes wider.The rule is also applicable for the cases with different incident angles.Furthermore,it is revealed that the time delay of the 1D range profile in the bistatic system is related to the rotation direction of the target,which is useful in estimating the posture of the target.In summary,the characteristics of 1D range profile for metal objects relating to shape,surface roughness and posture are studied.The conclusions have certain guiding significance for the target detection and recognition of terahertz radar.