Spectrum & Regulation

Automotive Radar Band

Q: Why is the 77 GHz band used for automotive radar?

77 GHz offers three advantages. First, the short wavelength (3.9 mm) allows physically small antennas with narrow beamwidths, fitting behind bumper fascia paint. Second, the band is globally harmonized (ITU, FCC, ETSI, and MIC Japan all allocate it for vehicular radar). Third, up to 4 GHz of bandwidth is available (77 to 81 GHz), providing range resolution of 3.75 cm, enough to separate a pedestrian from a nearby vehicle.

Q: What is the difference between 76-77 GHz and 77-81 GHz?

The 76-77 GHz segment provides 1 GHz bandwidth (15 cm range resolution) and is allocated for long-range radar with higher EIRP limits. The 77-81 GHz segment provides up to 4 GHz bandwidth (3.75 cm range resolution) for short-range, high-resolution applications like parking assist and 4D imaging radar. Modern radar chips typically sweep across the full 76-81 GHz band in a single chirp, using the entire 4-5 GHz bandwidth.

Q: Will automotive radar face interference as more vehicles have radar?

Yes, mutual interference is a growing concern. With 5+ radar modules per vehicle and millions of vehicles on the road, the probability of two radars illuminating each other increases significantly. The interference manifests as ghost targets or elevated noise floor. Mitigation techniques include randomized chirp start times, frequency hopping across the band, and interference detection algorithms that blank corrupted chirps. ETSI is developing standards for cooperative radar coexistence.

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The 76 to 81 GHz frequency allocation designated by the ITU, FCC, ETSI, and MIC (Japan) for vehicular radar applications. The band is divided into a 76 to 77 GHz long-range segment with 1 GHz bandwidth and higher EIRP limits, and a 77 to 81 GHz segment with up to 4 GHz bandwidth for high-resolution short-range sensing. Modern automotive radar chips sweep across the full 5 GHz span in a single chirp, achieving range resolution as fine as 3 cm.

Category: Spectrum & Regulation

Allocation: 76 to 81 GHz (globally harmonized)

Max BW: 4 to 5 GHz

Understanding the Automotive Radar Band

The choice of 76 to 81 GHz for automotive radar was not arbitrary. Below 30 GHz, antennas are too large for bumper integration. Above 100 GHz, atmospheric attenuation increases sharply, and semiconductor technology becomes prohibitively expensive. The 77 GHz sweet spot offers manageable atmospheric loss (~0.4 dB/km in clear air), compact antenna size, wide bandwidth, and global regulatory harmony.

Frequency Allocation Comparison

Sub-Band	Range	Bandwidth	Range Resolution	Application	EIRP Limit
76-77 GHz	76.0 to 77.0 GHz	1 GHz	15 cm	Long-range radar (ACC, AEB)	+55 dBm (ETSI)
77-81 GHz	77.0 to 81.0 GHz	4 GHz	3.75 cm	Short-range radar (parking, BSM, 4D imaging)	+55 dBm (ETSI)
Full sweep	76.0 to 81.0 GHz	5 GHz	3 cm	Combined LRR+SRR on single chip	Region dependent

Range Resolution:
ΔR = c / (2 × BW)

1 GHz BW: ΔR = 15 cm
4 GHz BW: ΔR = 3.75 cm
5 GHz BW: ΔR = 3 cm

Legacy 24 GHz ISM Band (being phased out):
200 MHz BW: ΔR = 75 cm (too coarse for modern ADAS)

The legacy 24 GHz ISM band (24.05 to 24.25 GHz) was used by early automotive radars but has been phased out in Europe since January 2022 due to its narrow 200 MHz bandwidth and interference with other ISM users. All new radar designs now operate exclusively in the 76 to 81 GHz band.

Common Questions

Frequently Asked Questions

Why is the 77 GHz band used for automotive radar?

77 GHz offers a short wavelength (3.9 mm) for compact antennas, is globally harmonized across all major regulatory bodies, and provides up to 4 GHz of bandwidth for 3.75 cm range resolution. This combination of small size, global availability, and high resolution makes it the ideal frequency for vehicle-integrated sensing.

What is the difference between 76-77 GHz and 77-81 GHz?

76-77 GHz provides 1 GHz bandwidth (15 cm resolution) for long-range radar. 77-81 GHz provides up to 4 GHz bandwidth (3.75 cm resolution) for high-resolution short-range applications. Modern chips sweep across the full 76-81 GHz band in a single chirp.

Will automotive radar face mutual interference?

Yes. With 5+ radars per vehicle and millions on the road, the probability of mutual illumination is increasing. Interference appears as ghost targets or elevated noise floor. Mitigation includes randomized chirp timing, frequency hopping, and interference blanking algorithms. ETSI is developing cooperative coexistence standards.

Related Terms

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