24 GHz Radar
Understanding 24 GHz Radar
If you want to build a smart car that can detect a vehicle in its blind spot, you cannot use a camera. A camera is completely blinded by fog, heavy rain, and darkness. You must use radar.
| Characteristic | 24 GHz | 77 GHz | 79 GHz |
|---|---|---|---|
| Bandwidth | 250 MHz | 1 GHz | 4 GHz |
| Range Resolution | 60 cm | 15 cm | 3.75 cm |
| Antenna Size | Moderate | Small | Small |
| Regulation | ISM (global) | Licensed | Licensed (UWB) |
However, you cannot use a massive, spinning military radar dish on a Honda Civic. The solution is the microscopic, solid-state 24 GHz Radar.
The Magic of FMCW
Military radars shoot massive, high-power pulses and listen for the echo. 24 GHz automotive radars use a much smarter, lower-power technique called Frequency Modulated Continuous Wave (FMCW).
- The radar chip continuously transmits a 24 GHz signal, but it "sweeps" the frequency up and down like a siren (a chirp).
- The wave hits the car in the blind spot and bounces back to the receiver.
- Because the transmitted frequency is constantly changing, by the time the echo returns, the transmitter is already broadcasting a different frequency.
- The computer instantly compares the frequency it is transmitting right now to the frequency of the echo that just arrived. The mathematical difference between the two frequencies tells the computer exactly how far away the target is, and the Doppler shift tells the computer exactly how fast the target is moving relative to the sensor.
The Shift to 77 GHz
While 24 GHz radar revolutionized the automotive industry, it has a fatal flaw: Resolution.
The global 24 GHz ISM band is incredibly narrow (only 250 MHz wide). In radar physics, your ability to distinguish two targets standing close together (Range Resolution) is entirely dependent on how wide your frequency sweep is. Because the 24 GHz band is so narrow, the radar can tell there is a "large metal object" in the blind spot, but it cannot tell if it is a motorcycle next to a guardrail or a single large truck.
To achieve the high-resolution required for self-driving cars, the automotive industry is actively abandoning 24 GHz and moving to the massive, multi-gigahertz wide 77 GHz Band, which provides the bandwidth required to 'paint' a highly detailed 3D radar image of the road.
Frequently Asked Questions
Is 24 GHz radar dangerous to humans?
No. Because it operates in the unlicensed ISM band, the FCC strictly limits the transmit power (EIRP) to less than a fraction of a Watt. The radar beam is so weak that it poses zero thermal heating threat to human tissue, even if you are standing directly in front of the sensor.
Can 24 GHz radar detect a human?
Yes. Unlike PIR (Passive Infrared) motion sensors that only detect body heat and can be fooled if a person stands perfectly still, a 24 GHz radar detects physical mass. Advanced 24 GHz 'Vital Sign' radars can actually detect the microscopic, millimeter-level movement of a human chest expanding and contracting, sensing a person's breathing rate through a solid wall.
Does 24 GHz radar interfere with Wi-Fi?
No. Standard Wi-Fi operates at 2.4 GHz and 5 GHz. Even the new Wi-Fi 6E only operates up to 7 GHz. The 24 GHz band is massively separated from consumer data networks, making it a completely clean, interference-free environment for safety sensors.