中文摘要：

为了减小常规波束形成所需的庞大计算量以实现快速成像，本文提出了一种新的波束形成算法——分级聚焦波束形成。将基阵划分成各级子阵分级进行处理，对较短的子阵进行远场近似处理，逐级合并子阵进行子阵间的近场聚焦波束形成，并逐级进行波束插值。MATLAB仿真计算结果表明，分级聚焦法与常规波束形成相比，计算量和数据存储量大幅下降。该方法尤其适用于多焦点近场聚焦的场合。

英文摘要：

In order to reduce the huge computational task of conventional delay-sum beamforming so as to implement fast imaging, this paper describes a new algorithm of beamforming ——multistage-focusing beamforming. The array is divided into subarrays and multistage processing is implemented. Conventional far-field beamforming is done for these short subarrays. At successive stages the near-field beams for pairs of subarrays are combined and additional beams are developed. The simulation results using MATLAB demonstrate that the multistage-focusing beamforming shows great savings in the computational load and the data storage compared with the conventional beamforming. This method is especially fit for the situation of multifocus focusing in the near field.