Performance Evaluation of a Passive Millimeter-Wave Imager
ABSTRACT A cross-correlating 186-GHz passive millimeter-wave imager has been built. The key components in the signal processing hardware are two 186-GHz receivers and a broadband complex correlator. To evaluate the performance of this imager, its point-spread function, beam pattern, baseline vector, and their variations with the scanning direction have been experimentally measured and derived. Some of these results are needed for optimizing the imager's parameter settings. Others are required for implementing the modulated-beam and modulated-scene algorithms proposed in a previous paper dealing with the imager's fringe in its point-spread function. These results will also reveal any problems in the construction process of the imager. The theoretical bases for these measurements are analyzed. Novel algorithms for deriving each antenna's point-spread function and beam pattern, as well as the imager's baseline vector from the measurement results of the imager's point-spread function and beam pattern are proposed and successfully applied in the measurements. Experimental results are presented and discussed.
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ABSTRACT: Passive millimeter-wave (PMMW) images often suffer common problems of noise and blurring. A new method is proposed to estimate the instrument response function (IRF) and desired image simultaneously. The proposed variational model integrates the adaptive weight data term, image smooth term, and IRF smooth term. The major novelty of this work is that Huber–Markov regularization is adopted for PMMW image restoration, which can preserve structural details as well as suppress noise effectively. The IRF is parametrically formulated as a Gaussian-shaped function based on experimental measurements through the utilized PMMW imaging system. The alternation minimization iterative method is applied to achieve the IRF width and desired image. Comparative experimental results with some real PMMW images reveal that the proposed approach can effectively suppress noise, reduce ringing artifacts, and improve the spatial resolution.Journal of Modern Optics 07/2013; 60(12):970-982. · 1.17 Impact Factor
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ABSTRACT: The design and testing of an active 190-GHz imaging system is presented. The system features two beam-scanning antennas, one of which transmits a vertical fan beam, and the other which receives a horizontal fan beam. By correlating the transmitted and received signals, an output is obtained that is proportional to the millimeter-wave reflectivity at the intersection of the two fan beams. Beam scanning is obtained by rotating a small subreflector within each antenna, allowing rapid scanning. The system has an angular resolution of 0.3 deg, a field of view of 14×14 deg, and operates at a standoff distance of 5 m.Journal of Electronic Imaging 01/2010; 19. · 0.85 Impact Factor
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ABSTRACT: We describe the design and application of a system for measuring the magnitude and phase of antenna radiation patterns in the 182-194 GHz frequency range. A heterodyne receiver comparing antenna and reference signals is designed from readily available components and incorporated into a 12-m anechoic chamber. The chamber is used with or without a compact-range reflector for compact-range or far-field measurement of antennas up to 0.6 m in diameter. The measured phase variation of the system, when idle, averages 0.3° over 227 s and 4.5° over 30 min. The amplitude stability is better than ±0.15 dB over a 63-h period. Verification of the system is obtained through comparison with other measurements and calculated results on horn and pillbox antennas. The applications of the system are illustrated through its use in characterizing the magnitude and phase radiation patterns of a new beam-scanning pillbox antenna for a 186-GHz imaging system.IEEE Transactions on Antennas and Propagation 01/2012; 60(4):1744-1757. · 2.46 Impact Factor