Study Of Interference Suppressing And Fast Imaging Method In Microwave Array Imaging System

Microwave array imaging (MAI) technology is widely used in national security, industrial measurement, medical diagnosis, and etc. It is playing an important role in variety applications. There are common technical features in the different areas, and there are also some unique technical problems in their respective field. This thesis focuses on the study of interference suppressing and fast imaging method to solve the problems encountered in through-wall-imaging and microwave medical tomography applications. The main contents and innovations of this thesis are as follows:1. To suppress ghost image brought in by backward projection (BP) imaging algorithm, the imaging probability function (IPF) method is proposed to reduce the ghost images. Due to the addition operation in target pixel unit is in phase, and the addition operation in non-target pixel unit is out of phase, we define the imaging probability function based on imaging addition operation, and suppress the ghost images using proper gate value of IPF to filter. In practice, there are calculation errors of IPF in part of pixel unit. These errors make part of ghost images can't be suppressed using IPF to filter. To solve this problem, using location inverse solution (LIS) method is proposed to reduce residual ghost images. The simulation results show that the proposed methods can't be affected by errors of wall parameters, and can effectively suppress ghost images.2. To reduce the effect of radio frequency interference (RFI) in microwave medical tomography system, according to the non-correlation feature between RFI sources and system illuminating source, a phase random coding method is proposed to transform RFI into zero mean random sequence, then the RFI can be suppressed simply using traditional mean-value filter algorithm. We conducted a set of 2D breast cancer imaging experiments using simulated data to test and verify the proposed method. Simulation results show that the proposed method is feasible and effective.3. Due to the measured data obtained by direct measurement pattern in circular antenna array is wide in dynamic range, unbalanced in parameter sensitivity and poor in signal to noise ratio (SNR), a difference measurement pattern is proposed to improve those deficiencies. Theoretical analysis and imaging experiments were conducted to evaluate the performance of proposed difference measurement pattern on 16-antenna microwave tomography system. Results demonstrate that difference measurement pattern have better performance of measured data.4. Analysis shows that the computational complexity and time-cost of imaging algorithm, based on nonlinear iterative method, will evidently increase with a speed of exponential progression while the density of computational mesh increases. To facilitate the spread of 2D microwave tomography for breast cancer detection, a fast imaging method is proposed in the realization of a personal computer, which uses a coarse mesh to image and locate the site of target firstly, then builds a locally refined fine mesh to image secondly. Imaging experiments were conducted using simulated and experimental data for breast cancer detection, the imaging results demonstrate that compared with the conventional imaging method using an overall fine mesh, the proposed twice imaging method can remarkably reduce the complexity of computation and save time-cost up to 80% while the equivalent image quality of target can be obtained.5. To detect finger arthritis using microwave tomography, an imaging method using priori information obtained from X-ray image is proposed, which optimize initial distribution of imaging parameters to improve quality of image. Imaging experiments were conduced using simulated data based on a simplified finger joint model. Experimental results show that a 2mm-wide finger joint can be quantitatively imaged based on its microwave property, and the pathological feature of finger joint can be detected from imaging result.