Reseach On Beamforming Methods At Subarray Level

The essence of the beamforming methods at subarray level is to partition the linear array into several subarrays. We can view each subarray as the receiving end and then we can adopt beamforming methods at subarray level. Different from traditional beamforming methods that are basically based on element level,beamforming methods at subarray level could reduce the algorithm complexity, cost and the difficulty of the system implementation. To overcome these disadvantages, the problems of robustness in beamforming methods at subarray level, diagnosis of subarray, the method of increasing the degree of freedom of the linear array and the beamforming method in frequency diversity array radar are investigated herein.The main contributions of this thesis are as follows.1. We studied two robust beamforming methods at subarray level. The problem of mismatch in traditional beamforming methods and the incompletion of the statistical characteristics will lead to a degraded beamforming performance. To resolve these problems, this thesis proposes two robust beamforming methods,which are diagonal loading beamforming method at subarray and linear constraint minimum variance beamforming method at subarray.2. An effective array failure diagnosis method is proposed. Useful information may be lost when the linear array is damaged. It will result in a bad beamforming performance. This thesis proposes an failure diagnosis method based on the difference co-array processing to make up possible degrees-of-freedom(DOFs) loss. The proposed method provides better accuracy and efficiency for the array diagnosis in the same environment.3. A novel nested phased-MIMO array structure is proposed herein, which can significantly increase DOFs. In practical applications, we often hope the array system can provides a dramatic increases of the DOFs then more number of sources can be resolved than the number of physical sensors. By exploiting the difference co-array processing, the proposed method can get DOFs from physical elements. And also,it can be obtained easily by combining two or more subarrays that have enlarged intersensor spacing.4. This thesis proposes a new adaptive beamforming method at subarray level for frequency diversity array radar. Instead of a linear phase shift in phased array radar,the frequency diversity array radar applies a small amount of frequency increment,compared to the carrier frequency, is applied to achieve range-dependent beam.The adaptive beamforming method at subarray level and the corresponding robust adaptive beamforming method are detailed.