A new correction method is proposed for the single RF channel digital beamforming (DBF) antenna array. In this array, each array element is followed by a $0/pi$ phase shifter, and the element outputs can be recovered by the single channel through the time sequence phase weighting (TSPW) technique. The outputs can be used to form desired beams through DBF. The performance of the DBF is influenced by the imperfection of the phase shifters. To obtain the errors in each phase shifter, the online test method based on a single known plane wave is introduced. The online test results are used to correct the element outputs using the relationship between the actual and the incorrect outputs. Compared with another previously proposed correction method, the new method is simpler and more suitable for real time correction. The factors that may influence the capability of the correction are analyzed. To validate the proposed method, an eight-element prototype is measured, and the data are used to synthesize low sidelobe patterns. Results show that the sidelobe level and gain improvements after correction are 11.1 and 2.6 dB, respectively.