Research and Development of Millimeter Wave Imaging Technologies

当可见光和红外系统不可用时，毫米波焦平面成像能够通过云、烟雾和尘埃提供信息。它还可以用于等离子体测量、遥感等领域。传统的毫米波成像主要依赖于使用单个探测器，通过机械扫描光学元件来获得图像。然而，在成像阵列中使用多个探测器不需要机械扫描，并且使得实时成像成为可能。本研究的目的是研制一种用于成像阵列的元件。该单元由宽带天线、低噪声放大器(LNA)、检测器和低通滤波器组成。毫米波光学成像技术的发展也很重要。研究结果如下：1.考虑大气衰减是毫米波频率的函数，对被动成像阵元进行了理论分析，给出了阵元所需的特性和实验所需的频率为35 GHz。采用光线追踪法设计了像差较小的毫米波光学元件。用聚乙烯制作了直径为500 mm的非球面透镜。研制了一种具有费米-狄拉克函数锥度曲线的宽带锥槽天线(专利申请中)。用于35 GHz频段的低噪声放大器是使用商用MMIC设计和构造的，具有40分贝增益和7分贝NF.5的放大器。利用该成像元件，成功地在35 GHz频段观测到了天空、建筑物、树木等室外场景以及人脸、手等人体。毫米波被动成像的应用包括通过火焰探测机器人传感器、探测地雷等。

Millimeter(MM) wave focal plane imaging is able to provide information through clouds, smoke, and dust when visible and IR systems are unusable. It can also be used in the fields of plasma measurement remote sensing, etc. Conventional millimeter wave imaging relies mainly on the use of a single detector, with the optics mechanically scanned to obtain an image. The use of multiple detectors in an imaging array, however does not require mechanical scanning and makes real-time imaging possible. The object of this research is to develop an element for the imaging array. The element consists of a wide-band antenna, LNA (Low Noise Amplifier), a detector and a low-pass filter. The development of MM-wave optics to form images is also important. The results of this research are as follows :1. Considering atmospheric attenuation as a function of frequency of MM-waves, theoretical analyses for passive imaging array elements have been performed to give required characteristics of the elements and the frequency for the experiments to be 35 GHz.2. The ray-tracing method was used to design MM-wave optics with less aberration. An aspherical lens with a diameter of 500 mm was made using polyethylene.3. A wide-band tapered slot antenna with the taper curve of Fermi-Dirac function was developed for the elements (patents pending).4. LNA's for the 35 GHz band have been designed and constructed using commercially available MMIC's to have an amplifier of 40 dB gain and 7 dB NF.5. Using the imaging element, outdoor scenes such as sky, building and trees and also human body such as face and hand have been successfully observed at the 35 GHz band. The applications of the MM-wave passive imaging include robot sensors through flame, detection of land mines and so on.