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

Abstract

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.

Experimental research on vehicle‐borne SAR imaging with THz radar

“…To avoid the impact of parameter errors on the following analysis, an optimum parameters estimation method based on the minimum entropy criterion is adopted firstly. When entropy is treated as a criterion of SAR image assessment, its physical meaning is that the better focusing degree of the image, the lower the entropy is . To facilitate the research of terahertz vehicle‐borne SAR imaging processing, two corner reflectors are chosen as targets, and their distances in range and azimuth are 1 and 2 m, respectively.…”

Efficient Terahertz Wide-Angle NUFFT-Based Inverse Synthetic Aperture Imaging Considering Spherical Wavefront

“…According to [27] and Table 1, we can conclude that the distance range within which the spherical correction is necessary is 200 m for ideal point targets. This 200 m constraint is also valid for more general targets in the following Experimental Section, although such looser (shorter) constraint exists.…”

Parameter Estimation of an Inhomogeneous Medium by Scattered Electromagnetic Fields Using Nonlinear Optics and Wavelets

“…Integrodifferential equation derived contains the derivatives of unknown functions [2]. Mathematical modelling can be done by functional equations, PDE, Integro differential equations (IDE), and stochastic equations [2]. These equations are used to solve problems of fluid dynamics, biological models, etc.…”

“…These equations are used to solve problems of fluid dynamics, biological models, etc. Wavelet method is one of the methods [3] to find approximate numerical solution to linear and nonlinear differential equations [2]. In this paper, algorithms to find parameters of the medium are obtained using least mean square estimation and inner product methods.…”

“…The nonlinearity and susceptibility of a medium play an important role in the generation of second harmonic and third harmonic waves, which is used in imaging [4][5][6]. Terahertz technology is also applied to image processing using a minimum entropy criterion for estimating and compensating linear phase error [2]. By the nonlinear interaction of light and matter, THz waves are produced.…”