Rutronik System Solutions experts tested radar sensors from Infineon, MineW, and Nisshinbo that operate at 24 GHz and 60 GHz. The objective was twofold: first, to determine the effect of rainy weather conditions on the radars' presence detection function, and second, to select the optimal sensor. The exemplary customer's project involves outdoor mailboxes in the entrance area of a building. The mailboxes should unlock and the entrance area light should turn on when someone is within one meter of them. The customer assumed that rain could affect the presence detection function. This would be the case if there were a "wall" of rain between the mailboxes and a person. Rutronik System Solutions specialists conducted comparative tests to verify this assumption.
Test setup
The test conditions corresponded to mailboxes with a radar sensor located under a 0.7-meter-deep roof canopy. A person walks toward the mailboxes through the rain, outside the canopy, and passes the one-meter mark.
For comparison, the radars were also tested in "no rain" conditions, including when a person moved from left to right at a distance of two meters.
In total, each radar was tested under the following five conditions:
- Rain, no motion
- Rain, frontal motion
- No rain, no motion
- No rain, frontal motion
- No rain, lateral motion
Test results
In the absence of rain or motion, most radars only detect a small amount of noise. When a person approaches a radar, there is an initial period of no movement, followed by periods of approach and departure (2 m – 1 m – 2 m). After these periods, there is another initial period of no movement. Both 60 GHz and 24 GHz radars clearly detect movement.
In the absence of movement, "rain" is interpreted as intense noise. We also observed slight noise caused by water droplets falling from the sprayers after the pumps stopped. At this stage, we see that 24 GHz radars are more sensitive to rain.
In simulated rain conditions, 60 GHz radars can detect an approaching person with high accuracy. In this case, however, the readings of some 24 GHz radars were ambiguous.
Download the App Note for more details about the Rain Test and explore sensor comparisons, and recommendations for reliable radar presence detection in outdoor environments.