根据毫米波光子成像辐射计成像系统要求,设计了一种基于光学上变频的被动毫米波扫描成像技术方案:使用电光调制器把毫米波信号加载到光载波的边频带中,利用光学滤波器滤掉载波分量;光电探测器把剩余边频带光信号转化为光电流,经过跨阻放大器后光电流变为电压信号,用锁相放大器读取输出电压信号,再通过计算机处理得到目标物体的亮温图。分析了该成像系统天线扫描速度和天线温度对比度关系、系统输出信号、噪声源、信噪比、灵敏度等工作性能指标及限制因素,讨论了成像系统灵敏度问题,找出改进成像系统灵敏度的方法,为毫米波辐射计实时成像系统的工程实现提供了理论依据。

A technique for passive millimeter-wave scanning imaging based on optical upconversion is designed for millimeter-wave photon imaging radiometer system. The millimeter-wave signal is transferred to the sidebands of the optical carrier by an electro-optical (EO) modulator,and filters are used to suppress the optical carrier. The optical signal of the remaining sideband is converted into a photocurrent by photodetector,and then the photocurrent is converted to the voltage signal by transimpedance amplifier. The lock-in amplifier is used to read the output voltage signal. The brightness temperature image of the objects is obtained by signal processing. We analysis the relationship between antenna scanning speed and antenna temperature contrast,system output signal,noise source,signal to noise ratio,and sensitivity etc. The sensitivity of imaging systems is discussed in detail. Several methods are proposed to improve the sensitivity of the imaging system,which provides a theoretical guidance for the realization of the millimeter-wave radiometer real-time imaging system project.