Microwave sensor with range gate functions

TLDR: In this paper, the authors proposed a low power microwave sensor that includes an active antenna module for transmitting first FMCW signal toward a target and for receiving second FMCw signal reflected from the target.

Abstract: A low power microwave sensor includes an active antenna module for transmitting first FMCW signal toward a target and for receiving second FMCW signal reflected from the target. The active antenna module includes a loop antenna and a RF transistor having a second port coupled to a transmitting end of the loop antenna and a control port coupled to a receiving end of the loop antenna, the control port and the second port are coupled to inversed phase signals. The RF transistor is used for demodulating the first FMCW signal and the second FMCW signal to generate beat frequency. Then another demodulator is used to demodulate the beat frequency signal to generate a Doppler signal. The microwave sensor utilizes circuitry to demodulate the FMCW signals in two stages, determines a range between the sensor and the target based on the beat frequency, and determines velocity of the target according to frequency of a Doppler signal, in lieu of using software. The sensor also regulates detecting ranges by setting range gates relating to FMCW signals and triggers functions based on the velocity of the target.