| All objects in nature generate outward thermal radiation in the form of electromagnetic waves, and the density of radiation is different when the emissivity of object is not the same. Passive millimeter wave(PMMW) imaging technology can be used to generate image with the radiation characteristics difference between objects by using MMW radiometer to receive the electromagnetic radiation of targets. Since the millimeter wave can easily penatrate through rain, fog, clothes and other materials, the technology has been widely used in the security check, remote sensing, blind landing of aircraft and other fields. PMMW imaging system should enhance the temperature sensitivity, spatial resolution and real-time characteristic to meet the practical requirements. The technology of passive millimeter wave focal plane array(FPA) imaging has the advantages mentioned above. It has become an important direction of the millimeter wave imaging technology. In this dissertation, based on the detailed analysis of the current development of domestic and foreign research on PMMW imaging technology, the key technologies of front-end for W-band PMMW focal plane array imaging are discussed by means of theoretical analysis, simulation and experimental testing. The research contents include the establishing and analysis of radiometric temperature transferring model, the method of MMW focal plane array antenna, the design of miniature highly-sensitive radiometer receiving channel and its integrated array, the study of image sampling and calibration, etc.For a start, the analysis model for radiometric temperature transferring in focused antenna and radiometer channel is established in this dissertation. According to the model, the relationships between the output voltage of MMW radiometer and the parameters such as object’s brightness temperature, antenna efficiency and radiometer’s noise temperature are analyzed. Based on that, a radiometric tempereture transferring model in two-layer medium is proposed. Then the changes of the temperature contrast between concealed metallic or nonmetallic object and the human body with ambient temperature, material’s transmissivity and emissivity are studied with the model. By comparing the radiometric temperature contrast in Ka and W-band, this dissertation concludes that the concealed objects will be more conducive for detection and imaging in the W-band because of the greater radiometric temperature contrast.As a key component of FPA passive millimeter wave imaging system, focal plane array antenna needs to form uniform closely-packed narrow multi-beam on the object plane with density satisfying the sampling criterion, so as to obtain a high imaging spatial resolution and enhance the system’s ability of detecting small size targets. This dissertation analyzes the radiation characteristics of parabolic reflector antenna by the aperture field integration method and the surface current integration method, and then discusses the beam deviation factor for lateral feed displacement and its effect on the beam uniformity. The arrangement of the feed array and its impact on the efficiency of antenna are also analyzed. Then a new type 16 elements full-sampling focal plane linear array antenna operating at W-band with large aperture parabolic reflector is developed, The antenna is designed to be able to sample the target area at Nyquist rate by optimizing the arrangement of the feed array. Experimental study shows that the antenna forms 16 stacked beams, and the gain fluctation between the beams is less than 0.4 dB, and the half-power beam widths(HPBW) in E-plane of the beams are in range of 0.4±0.03 o, and the. pointing directions of the beams shift regularly with interval of about 0.24o. The experimental results agree with theoretical analysis quite well, which verifies the effectivity of design method.Further, for the application of near-range FPA imaging, a method for accurate design and analysis of quasi-optical lens antenna is proposed in this dissertation. In the method, initially structure parameters of lens profile are obtained based on the Gaussian beam method and the geometrical optics, and then near field of the lens is calculated accurately by using an improved hybrid numerical method. The lens antenna is optimized according to the analysis results. This method is flexible and efficient for lens designing, which can be used for analysis of various lenses, including the electrically large lens antennas. Based on the method mentioned above, a hyperbolic lens and an aspheric lens are designed, both of which operate at W band. The focusing characteristics in near range of the lens are analyzed through theoretical simulation and experimental study. The test results show that beam width of the lens at distance of 3000 mm is less than 30 mm. The experimental results are in good agreement with the theoretical results, which shows that the method is correct and effective.As a key component of the focal plane array passive imaging system, MMW radiometer is required to have the characteristics of high temperature sensitivity, miniaturization and good channel uniformity. In this dissertation, a W-band adjustable miniaturized highly sensitive direct detection type radiometer is developed. Some key theoretical and technical problems have been resolved in the design process, including the optimal design of wideband transition between waveguide and coplanar line, broadband low noise amplifier, high sensitive detector, and electromagnetic compatibility design of miniaturization channel. By introducing some adjusting measures in the video amplifier, integrator and differential amplifier, the linearity parameters of the radiometer can be regulated, which will improve the consistency of receiving channels in a multi-channel radiometer system. A highly integrated two-channel radiometer module is developed, and experimental results indicate that its RF equivalent bandwidth is above 20 GHz, and its temperature sensitivity is better than 0.5 K when the integration time is 1 ms. The module has a regular structure with size of 82 mm * 12 mm * 12.1mm, which means that the module is quite suitable for dense arrangement of the focal plane array.For FPA passive millimeter wave imaging, this dissertation proposed a real-time calibration technology using back-ground radiometric temperature, which can wholly calibrate the consistency of all the radiometric channels in a FPA passive imaging system. The calibration algorithm is so simple and effective that calibration can be carried out for each frame without affecting the real-time capability of imaging, and it also helps to eliminate the impact of temperature drift on the quallity imaging in a long term. Finally, the first prototype of W-band 24 channel focal plane array short-range passive imaging system in China is developed in this dissertation. The imaging system has a field of view of 13.5 °(H) × 36 °(V), and its image statial resolution is better than 25 mm at distance of 3m and temperature sensitivity is better than 1K with a frame rate of 4Hz. Imaging experiments show that the imaging system can effectively detect concealed metallic and nonmetallic objects on human body.
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