Abstract: Spread Doppler clutter (SDC) is a key problem on the slow ship detection of overthehorizon radar (OTHR). For the multiple input multiple output (MIMO) OTHR system, a multimode SDC suppression algorithm based on lowerrank approximation to weight matrix is proposed from the viewpoint of minimum variance distortionless (MVDR) weight vector. The block matrix is used for data preprocessing, then a multistage biiterative MVDR processor is addressed by taking advantage of the feature decomposition of transmitreceive weight matrix. This algorithm reduces the computational load and the requirement of sample support, while further improving the output signaltoclutterplusnoise ratio of elevation filtering, which is beneficial to low detectable slow ship target detection in OTHR. Theoretical analysis and simulation experiment are presented to verify the effectiveness of this algorithm.

Key words: overthehorizon radar (OTHR), spread Doppler clutter (SDC), multiple input multiple output (MIMO), lowerrank approximation, multimode propagation