Automotive Radar
Understanding Automotive Radar
Automotive radar operates at 77 GHz (E-band), where the atmosphere is relatively transparent and the short wavelength (3.9 mm) allows physically small antennas to achieve narrow beamwidths. A single-chip radar transceiver (like the TI AWR2243 or NXP TEF82xx) integrates the transmitter, receiver, synthesizer, and ADC into a package smaller than a postage stamp. The antenna array is typically printed directly on the PCB, making the complete radar module small enough to hide behind the bumper fascia paint.
FMCW Radar Signal Processing
R = (fb × c × Tchirp) / (2 × BW)
Range Resolution:
ΔR = c / (2 × BW) = 3×108 / (2 × 4×109) = 3.75 cm
Velocity from Phase Change Across Chirps:
v = (Δφ × λ) / (4π × Tchirp)
Maximum Unambiguous Velocity:
vmax = λ / (4 × Tchirp)
With λ = 3.9 mm and Tchirp = 60 μs:
vmax = 16.25 m/s (58.5 km/h per chirp; extended by phase unwrapping)
Automotive Radar Module Types
| Type | Range | FoV (Azimuth) | Typical Placement | ADAS Function |
|---|---|---|---|---|
| Long Range (LRR) | 200 to 300 m | ±15° | Front center (behind badge) | ACC, AEB, Forward Collision Warning |
| Medium Range (MRR) | 80 to 150 m | ±40° | Front corners | Cross-traffic alert, intersection assist |
| Short Range (SRR) | 20 to 80 m | ±75° | Rear corners | Blind spot detection, parking assist |
| 4D Imaging | 200+ m | ±60° az, ±15° el | Front center | Freespace mapping, height classification |
Frequently Asked Questions
How does FMCW radar measure range and velocity simultaneously?
The radar transmits a frequency-ramping chirp. The echo returns with a time delay proportional to range, producing a beat frequency when mixed with the transmit chirp. Velocity is measured by comparing beat phase across successive chirps. A 2D FFT across fast-time and slow-time produces a range-Doppler map resolving both dimensions simultaneously.
What is 4D imaging radar?
Traditional automotive radar resolves range, velocity, and azimuth angle. 4D imaging radar adds elevation angle resolution using a 2D antenna array. This lets the radar distinguish a vehicle on the road from an overhead sign, solving the phantom braking problem in AEB systems. Leading chips like TI AWR2944 provide 192 virtual channels for simultaneous azimuth and elevation beamforming.
How many radar modules does a typical new vehicle have?
A mid-range 2025 model has 5 radars: one long-range forward (ACC/AEB, 200+ m), two rear corner short-range (blind spot/cross-traffic, 80 m), and two front corner short-range (parking/intersection assist). Premium vehicles with Level 2+ autonomy may have 6 to 8 radars for 360-degree coverage.