77-GHz active quasi-circulator based Doppler radar with phase evaluation for object tracking

A 77-GHz Doppler shift radar is demonstrated based on an Active Quasi-Circulator (QC) monostatic approach. The QC system includes a leakage canceler as well as a modulator for time division IQ switching. A flexible decimation chain, implemented in an FPGA, facilitates the use of a low cost ADC with moderate SNR performance. By analyzing the drift behavior of the system, the parameters for an appropriate high pass filter can be obtained. The system is capable of measuring Doppler shift frequencies from 0.05 Hz up to around 4 kHz. By means of a phase evaluation algorithm, it is possible to observe objects with varying velocities. Finally, the system has been verified with a breathing test, where the depth and the frequency of the breath can be determined accurately.