A compact Self-Injection Locked Oscillator based Doppler Radar (SILO-Radar) at 5 GHz has been studied, analytically and numerically. The SILO-Radar consists of just a cross-coupled oscillator and a Schottky diode baseband detector, with the help of the Hilbert transform at the baseband to extract the Doppler phase information. Both analytical analysis and PSpice simulation have been performed to verify the validity of the SILO-Radar. The compact, low-power and low-cost SILO-Radar has many potential consumer applications such as auto-driving radars, Unmanned Aerial Vehicle (UAV) navigation radars, remote heartbeat/respiration healthcare biomedical radars and so on.