The design guidelines for non-contact vital sign detection are presented in this paper. Firstly, the choice of radio frequency and antenna beamwidth is demonstrated by numerical simulation based on ray-tracing technique and spectrum analysis. Guided by the numerical results of the first part, three typical radar architectures are recently built in one of the ISM bands (the 5.8 GHz band). The characteristics of each architecture are demonstrated and compared based on measurement results. Experiments show that direct-conversion non-quadrature architecture has DC offset and null detection point problem; direct-conversion quadrature architecture can eliminate null detection point but lead to complexity and higher power consumption in effectively combining two quadrature channels. Double-sideband indirect-conversion with simpler radio architecture and less baseband requirement can effectively alleviate the DC offset and null detection point problems.