We propose a general guideline on the design of a stimulated Brillouin scattering (SBS)-based microwave photonic filter (MPF) using a directly modulated pump. Filter gain profiles and passband ripples with waveform repetition periods of the driving current ranging from 2 to 100?ns are measured after the transmission of different fiber lengths. The results show that the filter performance has nothing to do with the fiber length, and the digital-to-analog converter bandwidth requirement for the dr