Dual-band Noncontact Doppler Radar System for Pulse Measurement with K- and X-Band Frequencies

In this study, we developed a dual-frequency radar measurement system that exploits the Doppler effect and microdisplacement-induced echo phase variations.The system detects targets by using two frequency bands simultaneously: the 24 GHz (phased antenna array) and 12 GHz (conical antenna array) bands.This dual-frequency radar system enables the precise, noncontact measurement of physiological signals, including heartbeat and respiration, as well as minor variations in pulse and vascular contraction.Compared with single-frequency, unidirectional radar measurements, the proposed system's measurements showed inter-band agreement during repeated validation.Dual-frequency measurement enables the cross-comparison and verification of data, exhibiting high consistency while optimizing the trade-off among sensitivity, penetration, measurement range, and robustness to body motion.The proposed system demonstrates the feasibility of noncontact, dual-frequency radar-based physiological monitoring under minimal pulse variation.Pearson correlation coefficient (r) analysis was used to quantify the linear consistency between the 12 and 24 GHz measurements, yielding an r value of 0.82096, a 95% confidence interval of 0.80756-0.83351(estimated using Fisher's z-transform), and a twotailed p value considerably below 0.001.These results indicate that the dual-frequency radar sequences are highly synchronized in amplitude trends and exhibit strong linear consistency, providing a reliable basis for cross-validation and data fusion.