Microwave Imaging Technique And Its Application

This dissertation is focused on the study of microwave imaging system with real aperture antenna and its application. Significant results of the work include:1. A two-dimensional microwave imaging system in X band with stepped frequency signal and real aperture antenna is established. Two-dimensional super-resolution algorithm is applied in this system. The imaging system can be applied to the imaging of outdoor full-size target.2. A new angular superresolution technique called Phase Weighting Superresolution Method (PWSM) is proposed. The method combines a phase weighting method and a non-linear spectral estimation algorithm. It is used in conventional phased array radar for improving angle resolution. The motion compensation of radar target and an analysis of influence of component imperfection in the realization of the method are presented. To evaluate the performance of the proposed method. Monte Carlo simulation has been conducted to estimate the root mean square error of the angle estimates and the spatial resolution SNR threshold in the cases of both non-fluctuating targets and fluctuating targets. The simulation results have been compared to those of beam space MUSIC method and the Cramer Rao lower bound. Numerical and experimental results show that good angular superresolution and high estimation accuracy can be achieved provided that the radar pulse repetition time is small enough so that the echoes can be considered sufficiently correlated. For an X band conventional phased array radar with 139 antenna elements, by using PWSM. the angular resolution is improved by a factor of 2 when signal-to-noise ratio equals to 15dB.3. A new angular superresolution technique called Angle Weighting Superresolution Method (AWSM) is proposed. The method combines equivalent aperture normalization and a non-linear spectral estimation algorithm. It is used in conventional real aperture radar for improving angle resolution. Numerical and experimental results show that by using AWSM. the angular resolution is improved by a factor of 1.8 when signal-to-noise ratio equals to 15dB. The proposed AWSM method is also applied in a surveillant radar type LLQ09. The angular resolution is improved from 9?to 4?4. Based on the comparative study to the amplitude weighted and phase weighted time sequence phase measurement methods, the hybrid method is proposed. With the combination of automatic amplitude balance approach, in this method, the accuracy of the phase measurement has been improved significantly. Experimental results indicate that the maximum phase error is less than ?.5?5. A new data compression technique, called the threshold discrete Fourier transform (TDFT) method, is proposed to efficiently compress the scattered field data from complex targets. Compared with the matrix pencil (MP) method and CLEAN method, it is quite simple and time saving under the similar compression ratio and reconstruction error. In TDFT and CLEAN methods, the optimized segmentation is given which results in high compression ratio.