A low-power and low-cost 5.8-GHz 2-port monostatic Doppler radar was designed, fabricated and tested for small motion detection. The implemented RF board is based on a new radar architecture that features a compact size and only one active device. Unlike conventional board level radar systems, it does not use separate Tx/Rx signal chains. With a single antenna for Tx/Rx, it does not use any low noise amplifier (LNA) or circulator in the RF front-end. Besides the local oscillator (LO), there is no more active device that consumes DC power. The fabricated radar system has dimensions of 20.6 mm × 26.5 mm (L×W) and a power consumption of 290 mW in continuous operation, which could be significantly reduced based on duty cycling. In addition, a low conversion loss of 3.6 dB was achieved. The high sensitivity of the proposed architecture was demonstrated by successfully measuring a 50 μm sinusoidal movement.