Accurate Doppler Cardiogram Sensing with Frequency-Domain Digital Beamforming Technique Based on a $K$-Band Biomedical Radar

Contactless Doppler cardiogram (DCG) detection provides critical and comprehensive health information by monitoring heart motion. However, existing techniques struggle to effectively eliminate respiratory interference. To address this challenge, a novel frequency-domain digital beamforming (FDDBF) technique is proposed, which efficiently and accurately retrieves the time-domain waveforms of both the fundamental and harmonic components of respiration, thereby enabling the effective removal of respiratory artifacts and resulting in a clean DCG signal, implemented using a custom-designed $K$-band continuous-wave (CW) biomedical radar system. Experiments were conducted to evaluate the performance of the proposed technique. Comparative results with electrocardiogram (ECG) measurements demonstrate that the differential DCG (D-DCG) achieves a root mean square error (RMSE) of 6.82 ms for the RR interval. This achievement highlights the potential of the proposed method for precise heartbeat characterization, paving the way for non-contact radar-based medical diagnostics.