Performance Analysis And Calibration Of Digital Beamforming Microwave Radiometer

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.