W波段焦平面阵列被动成像前端关键技术研究

发布时间：2018-04-21 13:31

本文选题：W波段 + 被动成像　；参考：《电子科技大学》2016年博士论文

【摘要】：自然界中所有物体都以电磁波的形式向外产生热辐射,发射率不同的物体的辐射强度不相同。被动毫米波成像技术利用毫米波辐射计接收目标的电磁辐射,并根据物质的辐射特性差异生成图像。由于毫米波对雨雾、衣物等具有良好的穿透性,该技术在安全检查、遥感、飞机盲降等领域得到了广泛的应用。为满足应用需求,被动毫米波成像系统应具有高亮温灵敏度、高空间分辨率和高成像实时性的特点。毫米波焦平面阵列被动成像技术具备以上特点,是毫米波成像技术发展的重要方向之一。本文对国内外被动毫米波成像技术发展现状进行深入调研,采用理论分析、仿真和实验相结合的方法,研究了W波段焦平面阵列被动毫米波成像的前端关键技术,包括辐射温度传递模型的建立与分析、毫米波焦平面阵列天线理论、小型化高灵敏辐射计接收通道与阵列集成、成像采样及校准等。本文首先建立了聚焦天线和辐射计通道中辐射温度传递模型,利用该模型分析了辐射计输出电压与物体亮温、天线效率、辐射计噪声系数等的关系。在此基础上,本文建立了双层介质辐射温度传递模型,研究了人体隐匿的金属和非金属目标与人体之间的辐射亮温对比度随环境温度、介质透射率和发射率的变化关系,并通过对比Ka和W波段辐射亮温对比度,发现隐匿物与人体间的辐射温度在W波段差异更大,更有利于成像探测。作为焦面阵被动毫米波成像系统的关键部件,焦平面阵列天线需要在目标平面上形成密度满足采样定理要求的窄均匀堆积多波束,以提高系统的成像空间分辨率和探测细微目标的能力。本文采用口径场积分法和等效电流法分析了抛物反射面天线的辐射特性,讨论了馈源横向偏焦时的波束偏离系数及其对波束指向均匀性的影响,以及焦平面天线中馈源阵排列及其对天线效率的影响,并研制了一款基于大口径抛物面的新型W波段16阵元全采样焦平面线阵天线,通过馈源阵列优化排列,该天线实现了对目标区域奈奎斯特采样。实验研究表明:天线形成了16个堆积多波束,波束间增益波动小于0.4dB,E面半功率波束宽度约为0.4±0.03°,波束指向均匀,相邻波束间隔约为0.24°,测试结果与理论分析吻合良好,验证了设计方法的有效性。针对近程焦平面阵列被动成像应用,提出了一种准光透镜天线的精确设计和分析方法。该方法首先基于高斯波束法和几何光学法确定透镜天线轮廓,采用一种改进的混合数值计算法对透镜天线近场进行准确分析,并据此对透镜天线轮廓进行优化。这种设计方法灵活高效,可用于设计和分析各种形式的透镜天线,包括电大尺寸透镜天线。基于该方法,本文分别设计了W波段大口径双曲面透镜天线和非球面透镜天线,通过理论仿真与实验研究分析了透镜天线的近场区聚焦特性。结果表明,研制的透镜天线在距离透镜3000mm处,聚焦焦斑小于30mm,理论计算与实测结果吻合良好。毫米波辐射计作为焦面阵被动成像系统的关键部件,需具有亮温灵敏度高、结构尺寸小和通道一致性好的特点。本文研制了一款W波段参数可调小型化高灵敏直接检波式辐射计,解决了波导-共面线宽带过渡、宽带低噪声放大器、宽带高灵敏检波等的优化设计、小型化通道电磁兼容设计等关键理论和技术问题,并通过对视频放大、积分器、差分放大器引入调控方法,实现了辐射计通道参数可控,这种设计可改善多通道系统中的通道一致性。开展了高度集成的双通道辐射计模块的实验研究,结果表明,辐射计的射频等效带宽大于20GHz,积分时间为1ms时亮温灵敏度优于0.5K,双通道模块外形规则,尺寸仅为82mm*12mm*12.1mm,适用于焦平面阵列密集排列。本文针对焦平面阵被动成像系统应用,提出了一种基于背景辐射的辐射计通道实时校准方法。该方法可对焦平面阵列被动成像系统接收通道一致性进行整体校准,校准算法简单有效,能对每帧图像进行校准且不影响实时性,并克服了系统长时间工作时温度漂移对成像的影响。最后,本文研制了国内首台W波段24通道焦平面阵列近程被动成像系统,该系统成像视场范围为13.5°(H)×36°(V),成像距离为3m时的空间分辨率优于25mm,亮温灵敏度优于1K,成像速度达到4帧/秒,能有效探测人体携带隐匿金属和非金属目标。
[Abstract]:All objects in nature produce thermal radiation in the form of electromagnetic waves. The radiation intensity of objects with different emissivity is different. Passive millimeter wave imaging technology uses the millimeter wave radiometer to receive the electromagnetic radiation of the target and generates images according to the difference of the material's radiation characteristics. It has good wear by the millimeter wave to the rain fog and the clothing. In order to meet application requirements, the passive millimeter wave imaging system should have the characteristics of high brightness temperature sensitivity, high spatial resolution and high imaging real-time characteristics. The passive imaging technology of millimeter wave focal plane array has the above features, and it is a millimeter wave imaging technology. One of the important directions of the development is to investigate the development of passive millimeter wave imaging technology at home and abroad. By means of theoretical analysis, simulation and experiment, the key technology of the front end of the passive millimeter wave imaging of W band focal plane array is studied, including the establishment and analysis of the radiation temperature transfer model and the millimeter wave focal plane array. In this paper, the relationship between the output voltage of the radiometer and the temperature of the radiometer, the efficiency of the antenna and the noise coefficient of the radiometer is analyzed. In this paper, a radiative temperature transfer model of double-layer medium is established to study the relationship between the radiant temperature contrast between the human body and the human body and the radiation temperature between the human body and the human body with the ambient temperature, the transmittance and the emissivity of the medium. By comparing the radiant temperature contrast between the Ka and the W bands, the radiation temperature between the concealed objects and the human body is found in the W band. As the key component of the focal plane array passive millimeter wave imaging system, the focal plane array antenna needs to form a narrow uniform stacked multi beam in the target plane to meet the requirements of the sampling theorem, so as to improve the spatial resolution of the system and the ability to detect the fine targets. The radiation characteristics of the parabolic reflector antenna are analyzed by the method of separation and the equivalent current method. The beam deviation coefficient and its influence on the beam pointing uniformity are discussed, as well as the arrangement of the feed array in the focal plane antenna and its influence on the efficiency of the antenna, and a new W band 16 array element based on large aperture parabolic surface is developed. A fully sampled focal plane array antenna is optimized by an array of feed arrays. The antenna realizes the Nyquist sampling of the target area. The experimental study shows that the antenna has 16 stacked multi beams, the gain fluctuation of the beam is less than 0.4dB, the half power beam width of the E surface is about 0.4 + 0.03 degrees, the beam direction is uniform and the adjacent beam spacing is about 0.24 degrees. The experimental results are in good agreement with the theoretical analysis, which verifies the effectiveness of the design method. In view of the passive imaging application of the short range focal plane array, a precise design and analysis method of the quasi optical lens antenna is proposed. The method is based on the Gauss beam method and the geometric optics method to determine the contour of the lens sky line, and an improved hybrid numerical calculation is adopted. The method is used to accurately analyze the near field of the lens antenna and optimize the outline of the lens antenna. This method is flexible and efficient, and can be used to design and analyze various forms of the lens antenna, including the large size lens antenna. Based on this method, the W band large aperture hyperbolic lens antenna and the aspheric lens antenna are designed respectively. The focusing characteristics of the lens antenna near the field are analyzed by theoretical simulation and experimental study. The results show that the focused focal spot is less than 30mm at the distance from the lens 3000mm, and the theoretical calculation is in good agreement with the measured results. The millimeter wave radiometer, as the key component of the passive imaging system of the focal plane array, needs to have high brightness temperature sensitivity. In this paper, a W band parameter adjustable and highly sensitive direct detection radiometer is developed, which solves the key theory and technical problems of broadband transition of waveguide coplanar line, broadband low noise amplifier, broadband and high sensitive detection, and the key theory and technical problems of electromagnetically compatible design of miniaturized channels. After the video amplification, the integrator and the differential amplifier introduce the control method, the channel parameters of the radiometer are controlled. This design can improve the channel consistency in the multichannel system. The experimental research on the highly integrated dual channel radiometer module is carried out. The results show that the radiometer's radio frequency equivalent bandwidth is greater than 20GHz and the integration time is 1ms. The brightness temperature sensitivity is better than 0.5K, and the dual channel module has a regular shape and only 82mm*12mm*12.1mm. It is suitable for the dense array of focal plane arrays. In this paper, a real-time calibration method of the radiometer channel based on the background radiation is proposed. This method can be used for the reception channel of the passive imaging system of the focal plane array. Conformance is calibrated as a whole. The calibration algorithm is simple and effective. It can calibrate each frame without affecting real time, and overcomes the influence of temperature drift on imaging. Finally, the first W band 24 channel focal plane array close range imaging system is developed in this paper. The imaging field range is 13.5 (H). ) by 36 degree (V), the spatial resolution of the imaging distance of 3M is better than that of 25mm, the brightness temperature sensitivity is better than that of 1K, and the imaging speed reaches 4 frames per second, and the human body can be effectively detected with the hidden metal and non metal targets.

【学位授予单位】：电子科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN015

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