Terahertz Wide-Angle Imaging and Analysis on Plane-wave Criteria Based on Inverse Synthetic Aperture Techniques

This paper presents two parts of work around terahertz imaging applications. The first part aims at solving the problems occurred with the increasing of the rotation angle. To compensate for the nonlinearity of terahertz radar systems, a calibration signal acquired from a bright target is always used. Generally, this compensation inserts an extra linear phase term in the intermediate frequency (IF) echo signal which is not expected in large-rotation angle imaging applications. We carried out a detailed theoretical analysis on this problem, and a minimum entropy criterion was employed to estimate and compensate for the linear-phase errors. In the second part, the effects of spherical wave on terahertz inverse synthetic aperture imaging are analyzed. Analytic criteria of plane-wave approximation were derived in the cases of different rotation angles. Experimental results of corner reflectors and an aircraft model based on a 330-GHz linear frequency-modulated continuous wave (LFMCW) radar system validated the necessity and effectiveness of the proposed compensation. By comparing the experimental images obtained under plane-wave assumption and spherical-wave correction, it also showed to be highly consistent with the analytic criteria we derived.

[1]  F. Li,et al.  SAR Image Autofocus Utilizing Minimum-Entropy Criterion , 2013, IEEE Geoscience and Remote Sensing Letters.

[2]  Yiming Pi,et al.  Terahertz Imaging Radar With Inverse Aperture Synthesis Techniques: System Structure, Signal Processing, and Experiment Results , 2015, IEEE Sensors Journal.

[3]  K. Ajito,et al.  THz Chemical Imaging for Biological Applications , 2011, IEEE Transactions on Terahertz Science and Technology.

[4]  H. Roskos,et al.  Camera for High-Speed THz Imaging , 2015 .

[5]  Carlo Sirtori,et al.  Continuous-wave coherent imaging with terahertz quantum cascade lasers using electro-optic harmonic sampling , 2013, 1304.3207.

[6]  William D. Goodhue,et al.  Coherent imaging at 2.4 THz with a CW quantum cascade laser transmitter , 2010, OPTO.

[7]  Cun Lin Zhang,et al.  Experimental 0.22 THz Stepped Frequency Radar System for ISAR Imaging , 2014 .

[8]  Li Xi,et al.  Autofocusing of ISAR images based on entropy minimization , 1999 .

[9]  Ralf Henneberger,et al.  Fast Active THz Cameras with Ranging Capabilities , 2009 .

[10]  Patrick Lj Valdez,et al.  Active wideband 350GHz imaging system for concealed-weapon detection , 2009, Defense + Commercial Sensing.

[11]  J. M. Chamberlain,et al.  An introduction to medical imaging with coherent terahertz frequency radiation. , 2002, Physics in medicine and biology.

[12]  N. Llombart,et al.  Penetrating 3-D Imaging at 4- and 25-m Range Using a Submillimeter-Wave Radar , 2008, IEEE Transactions on Microwave Theory and Techniques.

[13]  R.J. Dengler,et al.  A Compact 600 GHz Electronically Tunable Vector Measurement System for Submillimeter Wave Imaging , 2006, 2006 IEEE MTT-S International Microwave Symposium Digest.

[14]  T. Loffler,et al.  Fast active THz-camera with global illumination , 2009, 2009 34th International Conference on Infrared, Millimeter, and Terahertz Waves.

[15]  W. Carrara,et al.  Spotlight synthetic aperture radar : signal processing algorithms , 1995 .

[16]  Helmut Essen,et al.  High-bandwidth 220 GHz experimental radar , 2007 .

[17]  Nuria Llombart,et al.  THz Imaging Radar for Standoff Personnel Screening , 2011, IEEE Transactions on Terahertz Science and Technology.

[18]  Cheng Wang,et al.  Real-Time Imaging With a 140 GHz Inverse Synthetic Aperture Radar , 2013, IEEE Transactions on Terahertz Science and Technology.

[19]  R. Panowicz,et al.  3D Non-destructive Imaging of Punctures in Polyethylene Composite Armor by THz Time Domain Spectroscopy , 2015 .

[20]  Viktor Krozer,et al.  TeraSCREEN: multi-frequency multi-mode Terahertz screening for border checks , 2014, Defense + Security Symposium.

[21]  Thomas E. Hall,et al.  Three-dimensional millimeter-wave imaging for concealed weapon detection , 2001 .

[22]  Guangyou Fang,et al.  Design, Analysis and Measurement of a Millimeter Wave Antenna Suitable for Stand off Imaging at Checkpoints , 2011 .

[23]  H.B. Wallace,et al.  Standoff Detection of Weapons and Contraband in the 100 GHz to 1 THz Region , 2007, IEEE Transactions on Antennas and Propagation.

[24]  Ken B. Cooper,et al.  Time-Delay Multiplexing With Linear Arrays of THz Radar Transceivers , 2014, IEEE Transactions on Terahertz Science and Technology.

[25]  Guangyou Fang,et al.  Minimum-Entropy-Based Adaptive Focusing Algorithm for Image Reconstruction of Terahertz Single-Frequency Holography With Improved Depth of Focus , 2015, IEEE Transactions on Geoscience and Remote Sensing.

[26]  B. Litvak,et al.  330 GHz FMCW Image Sensor for Homeland Security Applications , 2010 .