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IMPROVEMENT OF PHASE GRADIENT autofocus algorithm

Chinese Journal of Aeronautics 1998年第3期11卷 33-39页

作者：李立伟毛士艺刘莹 Department of Electronic Engineering Beijing Univ. Aero. and Astronaut. Beijing 100083 China

The phase error estimated by phase gradient autofocus(PGA) is not based on a finite order polynomial mode, so PGA has a good autofocus property for arbitrary order phase error and is fit for high resolution airborne SAR. But PGA has two shortcomings: first, it has a worse estimation property for fast changing phase error; second, there exists a section of linear phase in the phase error estimated by this algorithm. This paper introduces the idea of rank one phase estimate (ROPE) autofocus technique, and improves PGA. The improved PGA(IPGA) can successfully overcome both these shortcomings of PGA.

关键词： high resolution airborne SAR autofocus algorithm phase gradient autofocus(PGA) rank one phase estimation(ROPE)

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An Effective autofocus algorithm for ISAR Imaging

An Effective Autofocus Algorithm for ISAR Imaging

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1996 CIE International Conference of Radar(ICR’96)

作者： Ye Wei Bao Zheng Key Laboratory for Radar Signal Processing EE Research InstituteXidian University

ISBN: (纸本)0780329147

＜正＞Motion compensation is a key step in inverse synthetic aperture radar（ISAR）*** paper first sets up the array model for ISAR imaging that clearly demonstrates the principle and possible methods for initial phase error *** effective autofocus method called calibrating source iteration algorithm（CASIA）is then presented to calibrate the initial phase ***, the real measured ISAR data of flying aircraft are processed to test the performance of CASIA and the imaging results confirm its validity.

关键词： synthetic aperture radar motion estimation radar imaging motion compensation aircraft calibration iterative methods array signal processing error analysis electromagnetic wave scattering inverse problems radar cross-sections radar clutter autofocus algorithm ISAR imaging motion compensation inverse synthetic aperture radar array model initial phase error calibration autofocus method calibrating source iteration algorithm measured ISAR data flying aircraft imaging results radar scattering radar clutter

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Implementation of autofocus in Alignment System for Layered Imprint Fabrication

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Transactions of Tianjin University 2009年第4期15卷 294-299页

作者：王权岱段玉岗卢秉恒向家伟杨连发 State Key Lab for Manufacturing Systems Engineering Xi'an Jiaotong University School of Mechanical and Electrical Engineering Guilin University of Electronic Technology

autofocus method based on the analysis of image content information is investigated to reduce the alignment error resulting from mark positioning uncertainty due to defocus in microstructure layered fabrication process based on multilevel imprint lithography. The applicability of several autofocus functions to the alignment mark images is evaluated concerning their uniformity, sharpness near peak, reliability and measure computation efficiency and the most suitable one based on power spectrum in frequency domain (PSFD) is adopted. To solve the problem of too much computation amount needed in PSFD algorithm, the strategy of interested region detection and effective image reconstruction is proposed and the algorithm efficiency is improved. The test results show that the computation time is reduced from 0.316 s to 0.023 s under the same conditions while the other merits of the function are preserved, which indicates that the modified algorithm can meet the mark image autofocusing requirements in response time, accuracy and robustness. The alignment error due to defocus which is about 0.5 μm indicated by experimental results can be reduced or eliminated by the autofocusing implementation.

关键词： autofocus algorithm alignment imprint lithography layered fabrication

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