Null point elimination using RF phase shifter in continuous-wave Doppler radar system

A voltage-controlled tunable phase shifter is introduced in the architecture of a microwave Doppler radar to eliminate the null point problem in the non-contact vital sign detection. With a simple control mechanism, the phase of the demodulated signal can be effectively adjusted, providing an opportunity to always lock the radar system to the optimum point. Experiment demonstrates that such a method results in a significant improvement in measurement accuracy.