A microwave sensor is disclosed. The microwave sensor includes an active antenna module, a first low pass filter, a second demodulator, a modulation module, and a discrimination control module. The active antenna module is utilized for transmitting a first FMCW signal towards a target and receiving a second FMCW signal reflected back from the target according to a sweep period. The active antenna module includes a loop antenna and a radio frequency transistor. The first low pass filter and the radio frequency transistor form a first demodulator. The first demodulator and the second demodulator perform two-stage down converting and demodulating to extract information for calculating range and velocity, respectively. The present invention adjusts a radio frequency bandwidth of the FMCW signal by first adjusting an amplitude of a modulation signal generated by the modulation module to control various detection ranges.