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Sensors 2018, 18(2), 677; https://doi.org/10.3390/s18020677

Quadrature Errors and DC Offsets Calibration of Analog Complex Cross-Correlator for Interferometric Passive Millimeter-Wave Imaging Applications

School of Electronics and Information Engineering, Beihang University, Beijing 100191, China
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Received: 20 December 2017 / Revised: 15 February 2018 / Accepted: 20 February 2018 / Published: 24 February 2018
(This article belongs to the Special Issue Sensors for Microwave Imaging and Detection)
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Abstract

The design and calibration of the cross-correlator are crucial issues for interferometric imaging systems. In this paper, an analog complex cross-correlator with output DC offsets and amplitudes calibration capability is proposed for interferometric passive millimeter-wave security sensing applications. By employing digital potentiometers in the low frequency amplification circuits of the correlator, the outputs characteristics of the correlator could be digitally controlled. A measurement system and a corresponding calibration scheme were developed in order to eliminate the output DC offsets and the quadrature amplitude error between the in-phase and the quadrature correlating subunits of the complex correlator. By using vector modulators to provide phase controllable correlated noise signals, the measurement system was capable of obtaining the output correlation circle of the correlator. When injected with −18 dBm correlated noise signals, the calibrated quadrature amplitude error was 0.041 dB and the calibrated DC offsets were under 26 mV, which was only 7.1% of the uncalibrated value. Furthermore, we also described a quadrature errors calibration algorithm in order to estimate the quadrature phase error and in order to improve the output phase accuracy of the correlator. After applying this calibration, we were able to reduce the output phase error of the correlator to 0.3°. View Full-Text
Keywords: analog correlator; cross correlation; interferometric imaging; millimeter-wave imaging; security sensing analog correlator; cross correlation; interferometric imaging; millimeter-wave imaging; security sensing
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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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Wang, C.; Xin, X.; Liang, B.; Li, Z.; Miao, J. Quadrature Errors and DC Offsets Calibration of Analog Complex Cross-Correlator for Interferometric Passive Millimeter-Wave Imaging Applications. Sensors 2018, 18, 677.

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