Investigation On Measurement Techniques Of Material Dielectric Constant And Target Scattering Characteristics In The Terahertz Range

Because of the characteristics of terahertz?THz?wave such as bandwidth,strong penetrability,low energy and high resolution,THz radar has broad application prospects in security and military fields.It has attracted worldwide attention.Studies of the dielectric constant and scattering characteristics of dielectric target and metal materials in the THz range is two important basic topics in the research field of THz radar.The two complement each other,which is the basis for research on key technologies such as military applications of THz active radar systems,determination of combat technology indicators,signal system and detection and identification.The measurement research work of the above two topics was carried out in this paper.In the measurement of the dielectric constant of materials in the THz range,the Far Infrared Fourier Spectrometer?FTIR?was improved to cover the 1¹0 THz range.A dielectric constant inversion method based on multi-beam interference in the THz band is proposed for dielectric materials that have transmittance in the THz range.The dielectric constant measurement of low-resistance silicon is taken as an example.The data obtained by the THz-TDS spectrometer were compared to verify the reliability of the method.For the metals and composites that cannot pass THz waves,the theory and method of using K-K relationship to calculate the dielectric constant of THz band are analyzed and expounded.The dielectric constants of high-resistance silicon,PTFE,copper,aluminum and other military commonly used materials were measured by FTIR.These data were compared with the measured values provided by THz-TDS to prove the reliability of the measured inversion data.In the measurement of target scattering characteristics in the THz range,the approximate solution of the typical target radar cross section?RCS?which is based on physical optics was firstly clarified,and the RCS measurement system based on THz laser that CO₂ laser pumped was built.RCS measurements of typical targets for different types and roughness were measured and compared with theoretical simulations of other units.Secondly,this paper studied the scattering characteristics of rough surface.Several metal aluminum plates with roughness of 0.3³0?m were processed as samples.The single-frequency scattering characteristic measurement system based on THz laser and the broadband reflection system based on FTIR were used for experimental measurement to verify rough surface scattering characteristics.The experimental results have good agreement with the Kirchhoff approximation in the effective range?1³.5THz?,which proves that the scattering intensity?reflectance?is negatively correlated with roughness and frequency,and positively correlated with the incident angle.