In this paper, we report a single-board integrated Doppler radar system (DRS) operating at 24 GHz. To verify the performance of the 24-GHz DRS, we make a comparison between the existing 5.8-GHz Doppler radar system (DRS) and the 24-GHz one about the ability to detect the bio-signals (heartbeats, respiration and human gait). In the experiment, DRSs are placed in the same experimental environment and working at the same time for the comparison purposes. Experimental results show that the 24-GHz DRS detects Doppler bio-signals of both the small-scale human cardiac motion and the large-scale human gait more accurately than the 5.8GHz one. The obtained results imply the great potential to implement the 24-GHz Doppler radar system for human bio-signals detection.