For an imaging sonar mounted onto a small sonar carrier (e.g., unmanned underwater vehicles), the angular resolution is strictly restricted by the limited physical size. To solve the problem, we propose a high-resolution imaging approach utilizing a multiple-input multiple-output (MIMO) sonar. The MIMO sonar is composed of two transmitting transducers and a receiving uniform linear array (ULA). The two transmitting transducers and the receiving ULA are located on two neighboring parallel straight lines, respectively. And the spacing between the two transmitting transducers is equal to the product of the hydrophone number and the inter-hydrophone spacing of the receiving ULA. Simultaneously, a pair of up- and down-chirp linear frequency modulation (LFM) pulses with the same frequency band (producing the same auto-correlation function for multibeam processing) and a large time-bandwidth product (ensuring low cross-correlation functions for range sidelobe suppression) are employed as transmitting waveforms. Based on the designed array layout and the transmitting waveforms, an improved hybrid beamformer combining the subarray processing, the phase shift and the shifted sideband beamformers together, is given, which ensures a fine imaging resolution and a low computation load. Via theoretical analysis, numerical simulations and a tank experiment, we show that the angular resolution of the proposed MIMO sonar imaging method doubles that of the traditional single-input multiple-output (SIMO) imaging method using the same array physical size and the same working frequency band.

对于安装在小型声纳载体（例如无人水下航行器）上的成像声纳，其角分辨率受到有限的物理尺寸的严格限制。为了解决这个问题，我们提出了一种利用多输入多输出 (MIMO) 声纳的高分辨率成像方法。MIMO 声纳由两个发射换能器和一个接收均匀线性阵列 (ULA) 组成。两个发射换能器和接收ULA分别位于两条相邻的平行直线上。并且两个发射换能器之间的间距等于接收ULA的水听器数和水听器间距的乘积。同时地，一对具有相同频带（为多波束处理产生相同的自相关函数）和大时间带宽积（确保距离旁瓣的低互相关函数）的上调和下调线性调频 (LFM) 脉冲抑制）用作发射波形。基于所设计的阵列布局和发射波形，提出了一种将子阵处理、相移和移位边带波束形成器相结合的改进混合波束形成器，保证了良好的成像分辨率和较低的计算量。通过理论分析、数值模拟和坦克实验，