DC offset reduction in phase diversity heterodyne doppler radar system

Continuous wave Doppler radar systems have been used for non-contact detection of human cardiopulmonary activity, and these functions can be used in diverse applications including health care, emergency, military, or security. For reliable and robust sensing, several schemes are applied to overcome deleterious system sensitivity associated with the periodic phase relationship between the received signal and local oscillator. In previous work, arctangent demodulation was applied to a direct-conversion quadrature receiver in order to get a robust and accurate real-time data. As described, data related dc information must be separated from other dc offset, including those from radar hardware limitations and background clutter noise. This can sometimes be difficult to realize. In this paper a heterodyne system was used to eliminate internal dc offset caused mainly by self-mixing, while preserving the data related dc content for arctangent demodulation. Moreover, three antennas were used, one for transmitting and the others for receiving. Separation between receive antennas by a half wavelength results in minimum dc clutter noise while doubling the signal power through phase diversity. The concept of increasing SNR through phase diversity and related experimental results are described in this paper.