High-resolution wide-swath (HRWS) imaging has always been a primary demand for synthetic aperture radar (SAR) remote sensing. Multiple-input multiple-output (MIMO) is a feasible scheme for achieving HRWS imaging and is a hot research topic among scholars. However, in contrast to classic single-input multiple-output (SIMO) SAR, MIMO-SAR schemes require the isolation of transmitted waveforms. The transmitted waveforms and the corresponding echo separation methods are essential techniques in MIMO-SAR. Orthogonal frequency-division multiplexing (OFDM)-chirp waveforms and an OFDM-beamforming (OB) method have been proposed, but have not been validated experimentally. In this letter, an airborne X-band digital beamforming (DBF)-SAR system is used to demonstrate MIMO-SAR with improved OFDM-chirp waveforms for the first time. Experimental results of frequency- and spatial-domain methods demonstrate that the mixed echoes can be effectively separated by OB scheme. The utilization of bandpass filters (BPFs) in OB scheme can conserve computation resources. Signal-to-interference ratio (SIR) is employed to test the performance of BPFs, where the indicator shows that the SIR loss is within 0.2 dB.