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Low-cost differential front-end for Doppler radar vital sign monitoring

We present a differential front end design for improving the performance of short-range low-cost Doppler radars for vital sign detection with application to automotive driver safety systems, health monitoring, and security screening. By using dual helical antennas each with a 40-degree beamwidth, it is possible to illuminate the body in two adjacent locations to perform a differential measurement. Since only one of the beams illuminates the heart, the baseband signal from the second radar is used for motion cancellation. We demonstrate this approach using a custom-designed dual helical antenna and simple direct-conversion radar circuits implemented in microstrip operating at 2.460 GHz and 2.510 GHz., respectively. Heart rate data is shown for detection distances of 0.5 meter showing reduction in background motion noise compared to data from traditional single radar unit design.