RCWL-0516 Microwave Motion Detector

I found this module in our local electronic components store. The module was called Microwave radar motion detector which attracted my attention, so I decided to buy it (£2) and to perform some tests. I only connected pins VIN (5V), GND and OUT. When the chip detects a movement, pin OUT changes its state form logic low (0V) to logic high (3.3V). I wrote a piece of code to show the state of the sensor using an LCD display and an LED diode. (A short video presenting the motion detection can be found here: RCWL-0516 Microwave Sensor.) I noticed that the sensor is very sensitive as when I was close enough, my breathing was modulating the frequency response of the module (due to reflections). Furthermore, I meassured the spectrum. I used a short probe at a distance of about 5 - 10 cm away from the sensor. The measurements can be seen in the following figures.




The measured spectrum (near-field) can be seen in the following figures. The first measurement was made at home, the second one was taken at the university as I am a bit limited with the frequency range in this case.




I have found two nice videos explaining how such sensors work.