Abstract: By emitting H- and V-polarized pulses adjacently and receiving echoes with duo-polarized channels, multidimensional waveform encoding fully-polarimetric Synthetic Aperture Radar (SAR) can obtain all polarimetric components in one Pulse Repetition Interval (PRI). However, different polarized echoes will overlap under this mode, and thus should be separated effectively to realize fully-polarimetric remote sensing. To solve this problem, this paper proposes a new elevation Digital BeamForming (DBF) approach, which systematically integrates Finite Impulse Response (FIR) filters into the null-steering beamformer, to separate echoes. Compared with conventional null-steering beamfoming, FIR filters in the approach can deal with the issue of pulse extension well, thereby achieving better separation results. In the paper, detailed signal processing procedures, along with the block diagram of the new DBF, are provided. Simulation results are given to demonstrate the validation of the proposed approach.