An active phase switchable array includes a plurality of antenna elements and a bias circuit. Each of the radar elements includes an antenna, a power coupling network and an injection-locked oscillator (ILO), and each of the antenna elements is coupled with each other through the power coupling networks for operating the ILO of each of the antenna elements in self- and mutual-injection-locked states. The antenna elements in self-injection-locked state are utilized to detect the vital signs of subjects, and the antenna elements in mutual-injection-locked state are utilized to produce phase difference between the radiating signals of the antenna elements for forming a beam. As a result, the active phase switchable array can simultaneously detect the vital signs of multiple subjects.
