SMCW Radar for Low IF Sensing Applications

Quadrature monostatic direct conversion receivers (homodyne) have been extensively studied for detecting slow, small amplitude motions such as vital signs. The main advantage of direct conversion monostatic receivers is the straightforward coherent sensing that mitigates the oscillator phase noise. However, any imbalance between the two channels introduce significant errors in the recovered displacement and additional flicker noise is introduced during direct down-conversion to DC and in the baseband amplification circuit. To overcome these problems, low intermediate frequency radars have been proposed. Nevertheless, they exhibit increased hardware complexity and non-straightforward coherent detection. A sinusoidally modulated continuous wave radar is proposed to combine the benefits of the homodyne and heterodyne architectures. A theoretical analysis has been presented and experimentally verified. Measurements using mechanical targets demonstrate signal to noise ratio improvements of up to 21.45 dB, when a 10 µm motion was measured at a distance of 100 cm.