【作者】 张靖；

【导师】 朱耀庭； 李青侠；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2010， 博士

【摘要】 数字波束形成微波辐射计是近年来提出的一种新型辐射计,它能够以成像方式和非成像方式工作。它用于形成辐射图像时不需要机械扫描辐射计所使用的驱动设备和相控阵电扫描辐射计所使用的相控阵,简化了系统的硬件结构；与综合孔径辐射计相比它扫描波束的形状和方向都可以控制,还可以实现定位、跟踪、重复扫描,具有信号处理简单、波束方向灵活的优点,因此这种辐射计在海水盐度测量、射电天文观测、军事目标跟踪等方面都具有广阔的应用前景。为了分析这种新型辐射计的基本性能,本文从数字波束形成微波辐射计的基本系统结构出发,利用随机信号分析的方法,推导了数字波束形成微波辐射计主要性能指标的表达式；在此基础上,分析了系统各部分的非理想因素对数字波束形成微波辐射计性能的影响；并针对数字波束形成微波辐射计自身的特点,提出了部分冲击响应矩阵的校正算法,利用实际测量的实验数据进行了验证。主要内容包括：分析了数字波束形成微波辐射计的基本系统结构,并对数字波束形成微波辐射计和综合孔径辐射计形成的波束进行了比较,为数字波束形成微波辐射计建立了原理模型。利用随机信号分析理论,分析了热辐射信号在数字波束形成微波辐射计接收过程中的统计规律,从理论上推导了数字波束形成微波辐射计的基本性能指标：灵敏度和空间分辨率,给出了数字波束形成辐射计的灵敏度和空间分辨率的表达式。并且通过理论分析和实验比较了数字波束形成微波辐射计、实孔径辐射计和综合孔径辐射计的灵敏度和空间分辨率。从辐射计测量的基本原理出发,分析了数字波束形成微波辐射计的各个系统部件(天线、接收机、AD)引入的非理想因素,建立了这些非理想因素的误差模型。对于辐射计的天线部分,建立了考虑幅相误差的天线阵列方向图模型,并分析了天线阵列主波束的增益衰减因子、旁瓣电平和阵列指向误差。对于辐射计系统的接收机部分,重点对具有直接射频采样结构的辐射计接收机进行了分析,分析了带外噪声对辐射计接收机的影响。对于辐射计系统的AD部分给出了数字波束形成微波辐射计的信号量化噪声比与量化阶数之间的关系。以上的工作都为建立数字波束形成微波辐射计的校正模型奠定了基础。给出了考虑各种幅相误差影响的数字波束形成微波辐射计的系统输出表达式,并将已经应用在综合孔径辐射计中的冲击响应矩阵引入到数字波束形成微波辐射计的校正中。同时,针对冲击响应矩阵测量工作量大、部分信息冗余等缺点,利用数字波束形成微波辐射计自身的特点,提出了部分冲击响应矩阵校正算法。并利用实际测量得到的数据进行了验证,实验结果证明了部分冲击响应矩阵校正算法的有效性。更多还原

【Abstract】 The digital beam-forming microwave radiometer is a new type radiometer proposed recently, and it can be worked in imaging mode and in nonimaging mode. The digital beam-forming microwave radiometer can form radiation image without the driven mechanism of the mechanically scanning radiometer and the phase-shift array of the electronically scanning radiomter, simplifying the system hardware architecture. On the other hand, the pattern and direction of the radiometric beam can be controlled as it worked in nonimaging mode. Consequently the radiomter can be used for tracking, location and scanning specifical position repetitively. Having the merit of simple signal processing and the flexible beam, the digital beam-forming microwave radiometer can be widely used in the measurement of the sea surface salinity, detection in radio astronomy and tracking for military target.To analyze the characteristics of this new type radiometer, firstly the expression of the spatial resolution and sensitivity, the main characteristics of the digital beam-forming microwave radiometer, have been driven using the theory of random signal analysis. Secondly, on the basis of the expression, it is analyzed that the impact of the system imperfections on the radiometric characteristics. And then the calibration algorithm with partial-directional impulse response matrix is proposed for calibration the system imperfections, and the algorithm is validated by experimental data from a 16 elements digital beam-forming radiometer system. Main works are given below:The system architecture of the digital beam-forming microwave radiometer is analyzed, and the beams formed by digital beam-forming microwave radiometer and synthetic aperture microwave radiometer are compared.Using the theory of random signal analysis, the signal statistical characteristics of microwave radiation signals received, processed and outputed by digital beam-forming microwave radiometer are analyzed. The spatial resolution and sensitivity of the radiometer have been driven, and the expressions are given. The spatial resolution and sensitivity of the digital beam-forming microwave radiometer, total-power microwave radiometer and synthetic aperture microwave radiometer are compared by theory and experiments. The non-idealities of system components in antenna, receiver and AD are assessed, and the error models of some system imperfections have been built. In the antenna subsystem of the digital beam-forming microwave radiometer, the antenna radiation pattern with amplitude and phase errors is given, and the fractional loss in main-beam gain, the level of sidelobe and the pointing error of the array are discussed. In the receiver, the direct RF sampling radiometer channel is analyzed, and the effect of sensitivity by out-band noise is discussed. In the AD of the digital beam-forming microwave radiometer, the relationship between the signal-to-quantization-noise (SQNR) and the number of quantization bits is proposed.The system output including the error of amplitude and phase is expressed. The impulse response matrix used in synthetic aperture microwave radiometer already is introduced in digital beam-forming microwave radiometer. And using the trait of the digital beam-forming microwave radiometer, the partial-directional impulse response matrix is driven and the new calibration algorithm cut down the information redundancy of the impulse response matrix. Experimental results for scene show that the image blur is restrained by using the improved calibration algorithm.更多还原