A nontrivial phase noise analysis method is proposed for frequency synthesizer of a passive millimeter-wave synthetic aperture interferometric radiometer (SAIR) imager for concealed weapon detections on human bodies with high imaging rates. The frequency synthesizer provides local oscillator signals for both millimeter-wave front ends and intermediate frequency IQ demodulators for the SAIR system. The influence of synthesizer phase noise in different offset frequency ranges on the visibility phase errors has been systematically investigated with noise requirements drawn, and the integrated RMS phase error could represent uncorrelated phase noise effects in the most critical offset frequency range for visibility error control. An analytical phase noise simulation method is proposed to guide synthesizer design. To conclude, the phase noise effects on SAIR visibility errors have been concretized to noise design requirements, and good agreements have been observed between simulation and measurement results. The frequency synthesizer designed has been successfully in operation in BHU-2D-U system. 1. Introduction Various techniques in the area of concealed weapon detection on human bodies have been developed and widely applied for security checks. Compared with active detection systems, such as the X-ray sensors, the passive SAIR imaging system [1] provides several advantages. It only receives rather than emitting high frequency signals and does not result in human health concerns [2]. Moreover, any concealed hazards, including nonmetallic weapons, can be observed in the obtained image explicitly [3–5]. Visibility error is significant for a SAIR system. Frequency Synthesizer (FS) provides two local oscillators (LO) for mmW front ends and IF IQ demodulators, and its phase noise (PN) contributes to visibility errors. The PN analysis consists of 3 key problems: determining whether mmW or IF LO is the major cause of visibility errors from system-level analysis; finding the offset frequency range (OFR) whose PN is the main contributor of visibility errors and establishes proper SAIR FS phase noise design requirements; finding an accurate PN simulation method to realize FS design and fulfill the requirements. In Section 2, system configuration and PN system-level modeling are given, and the dominant source of visibility errors from FS is found. In Section 3, this risky PN is separated to three OFRs by visibility error analysis, and SAIR design requirements are proposed. In Section 4, an accurate PN simulation method is given, and FS design is realized. It is found
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