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Remote Sens. 2017, 9(5), 449; doi:10.3390/rs9050449

Precision Near-Field Reconstruction in the Time Domain via Minimum Entropy for Ultra-High Resolution Radar Imaging

School of Integrated Technology, Yonsei Institute of Convergence Technology (YICT), Yonsei University, Incheon 21983, Korea
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Academic Editors: Francesco Soldovieri, Raffaele Persico, Zhong Lu and Prasad S. Thenkabail
Received: 12 December 2016 / Revised: 26 April 2017 / Accepted: 4 May 2017 / Published: 6 May 2017
(This article belongs to the Special Issue Radar Systems for the Societal Challenges)
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Abstract

Ultra-high resolution (UHR) radar imaging is used to analyze the internal structure of objects and to identify and classify their shapes based on ultra-wideband (UWB) signals using a vector network analyzer (VNA). However, radar-based imaging is limited by microwave propagation effects, wave scattering, and transmit power, thus the received signals are inevitably weak and noisy. To overcome this problem, the radar may be operated in the near-field. The focusing of UHR radar signals over a close distance requires precise geometry in order to accommodate the spherical waves. In this paper, a geometric estimation and compensation method that is based on the minimum entropy of radar images with sub-centimeter resolution is proposed and implemented. Inverse synthetic aperture radar (ISAR) imaging is used because it is applicable to several fields, including medical- and security-related applications, and high quality images of various targets have been produced to verify the proposed method. For ISAR in the near-field, the compensation for the time delay depends on the distance from the center of rotation and the internal RF circuits and cables. Required parameters for the delay compensation algorithm that can be used to minimize the entropy of the radar images are determined so that acceptable results can be achieved. The processing speed can be enhanced by performing the calculations in the time domain without the phase values, which are removed after upsampling. For comparison, the parameters are also estimated by performing random sampling in the data set. Although the reduced data set contained only 5% of the observed angles, the parameter optimization method is shown to operate correctly. View Full-Text
Keywords: inverse synthetic aperture radar (ISAR); minimum entropy; near-field; radar imaging; close–range; time domain; ultra-high resolution (UHR); ultra-wideband (UWB); vector network analyzer (VNA) inverse synthetic aperture radar (ISAR); minimum entropy; near-field; radar imaging; close–range; time domain; ultra-high resolution (UHR); ultra-wideband (UWB); vector network analyzer (VNA)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Yu, J.; Ka, M.-H. Precision Near-Field Reconstruction in the Time Domain via Minimum Entropy for Ultra-High Resolution Radar Imaging. Remote Sens. 2017, 9, 449.

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