Millimeter Wave Specific Challenges mmWave Radar and Sensing Informational

What is the difference between 24 GHz and 77 GHz automotive radar in terms of resolution and range?

24 GHz and 77 GHz are the two primary frequency bands used in automotive radar, with fundamentally different performance characteristics: (1) Range resolution: determined by the radar bandwidth (BW). Range resolution = c / (2 × BW). At 24 GHz: the allocated bandwidth is 200 MHz (ISM band, 24.0-24.25 GHz) or 5 GHz (UWB, 21.65-26.65 GHz, now sunset in EU). With 200 MHz: range resolution = 3e8 / (2 × 200e6) = 0.75 m (cannot distinguish objects separated by less than 0.75 m). At 77 GHz: the allocated bandwidth is 4 GHz (76-81 GHz in the EU and US). Range resolution = 3e8 / (2 × 4e9) = 0.0375 m = 3.75 cm. The 77 GHz radar has 20× better range resolution than 24 GHz (narrowband). This allows distinguishing between closely spaced objects (e.g., a pedestrian next to a vehicle). (2) Angular resolution: determined by the antenna aperture (D). Angular resolution = lambda / D (radians) = (lambda / D) × (180/pi) (degrees). For the same physical aperture D = 30 mm: at 24 GHz (lambda = 12.5 mm): theta = 12.5/30 = 0.417 rad = 24° (poor). At 77 GHz (lambda = 3.9 mm): theta = 3.9/30 = 0.13 rad = 7.4° (3× better). For the same angular resolution at 24 GHz: the antenna must be 3× larger. This makes 77 GHz much more suitable for compact automotive form factors. (3) Maximum range: for the same TX power and antenna gain: maximum range is determined by the radar equation: R_max ∝ (P × G² × lambda² × sigma)^(1/4). The lambda² term favors lower frequencies: 24 GHz has 10 dB advantage in Friis equation per the FSPL. However: 77 GHz can use a physically smaller antenna with higher gain (more elements in the same aperture). For the same antenna size: the higher gain at 77 GHz compensates for the higher FSPL. Net: 77 GHz achieves similar or better range than 24 GHz with smaller antennas. (4) Regulatory status: 24 GHz narrowband (200 MHz): still allowed but being phased out. Not suitable for high-resolution applications. 77 GHz (76-81 GHz): the globally allocated automotive radar band. 4-5 GHz bandwidth. All new automotive radars use 77 GHz. 24 GHz UWB (21.65-26.65 GHz): sunset in the EU (ETSI regulation, expired 2022). Phased out globally.

Category: Millimeter Wave Specific Challenges

Updated: April 2026

Product Tie-In: Radar ICs, Antennas, Signal Processors

24 vs 77 GHz Automotive Radar

The automotive industry is migrating entirely from 24 GHz to 77 GHz. All new radar designs should target 77 GHz (76-81 GHz) exclusively.

Resolution Comparison

(1) Range resolution: 24 GHz (200 MHz BW): Δr = 0.75 m. 77 GHz (4 GHz BW): Δr = 3.75 cm. 77 GHz (1 GHz BW, reduced for lower-cost sensors): Δr = 15 cm. Even at 1 GHz BW: 77 GHz is 5× better than 24 GHz at 200 MHz. At the full 4 GHz: 20× better. (2) Angular resolution (for a given antenna size): aperture D = 50 mm (a typical automotive radar module). 24 GHz: theta = 14.3° (3 dB beamwidth). 77 GHz: theta = 4.5° (3 dB beamwidth). The 77 GHz radar can separate two objects at 100 m that are separated by 7.8 m. The 24 GHz radar requires 25 m separation for the same resolution. (3) Velocity resolution: determined by the chirp duration (T_chirp) and the number of chirps per frame (N_chirps). Velocity resolution = lambda / (2 × N_chirps × T_chirp). For N = 128 chirps, T = 50 us per chirp: at 24 GHz: Δv = 0.0125 / (2 × 128 × 50e-6) = 0.98 m/s. At 77 GHz: Δv = 0.0039 / (2 × 128 × 50e-6) = 0.30 m/s. 77 GHz has 3× better velocity resolution (proportional to lambda).

Sensor Types

(1) Long-range radar (LRR): 77 GHz, 4 GHz BW, narrow beam (3-5°), range 200-300 m. Used for: adaptive cruise control (ACC), autonomous emergency braking (AEB), and highway pilot. Antenna: 12-24 TX + 12-24 RX elements (MIMO virtual array for angular resolution). (2) Medium-range radar (MRR): 77 GHz, 1-4 GHz BW, moderate beam (10-20°), range 80-150 m. Used for: cross-traffic alert, lane change assist, and cyclist/pedestrian detection. (3) Short-range radar (SRR): 77 GHz (previously 24 GHz UWB), 2-4 GHz BW, wide beam (30-60°), range 20-50 m. Used for: parking assist, blind spot detection, and door opener safety. (4) Imaging radar (4D radar): 77 GHz, 4 GHz BW, large virtual antenna array (hundreds of virtual channels via MIMO). Provides: range, velocity, azimuth, AND elevation information. The elevation resolution allows distinguishing between objects at different heights (e.g., a vehicle on a bridge from one on the road below). This is the emerging category for L3+ autonomous driving.

IC Solutions

Integrated 77 GHz radar ICs: (1) Texas Instruments AWR series: AWR1843 (3TX/4RX, single-chip radar with ARM MCU + DSP), AWR2243 (4TX/4RX cascade-capable for imaging radar). (2) NXP TEF series: TEF8102 (4TX/4RX), TEF822x (cascade for imaging radar). (3) Infineon RASIC: BGT60LTR11 (1TX/1RX, simple presence sensor), BGT60TR13C (3TX/4RX, full-featured radar). These ICs integrate: TX PA (77 GHz), RX LNA + mixer, chirp synthesizer (PLL + VCO at 77 GHz), ADC (for digitizing the beat frequency), and digital processing (MCU, DSP, or hardware accelerator). Single-chip radar sensor cost: $5-$15 at high volume. This enables the proliferation of radar sensors (4-8 per vehicle for current ADAS, 12+ for L3+ autonomy).

Radar Resolution Comparison

Range res: Δr = c/(2×BW)
77GHz @4GHz BW: Δr = 3.75 cm
24GHz @200MHz: Δr = 75 cm
Angular res: θ = λ/D
Vel res: Δv = λ/(2×N×T_chirp)

Common Questions

Frequently Asked Questions

Are 24 GHz radars still being manufactured?

Yes, but production is declining rapidly: (1) Narrowband 24 GHz (200 MHz, ISM band) sensors are still manufactured for: simple presence detection (motion sensors, door openers, security), industrial level sensing, and traffic monitoring. These applications do not require the resolution of 77 GHz and benefit from the lower cost of 24 GHz ICs. (2) UWB 24 GHz (5 GHz bandwidth) is being phased out entirely. The EU sunset the allocation in 2022 (ETSI EN 302 288). Units installed before the sunset can continue operating, but no new certifications are issued. The US still permits UWB 24 GHz but the industry has moved to 77 GHz. (3) For automotive: all new ADAS radar designs target 76-81 GHz. No major Tier 1 supplier (Continental, Bosch, ZF, Aptiv) is developing new 24 GHz automotive radar products.

Can 77 GHz radar detect pedestrians?

Yes, but with challenges: (1) Pedestrian radar cross-section (RCS): approximately 0.5-2 m² at 77 GHz (the human body is a moderate reflector). Compared to a car: 10-100 m² RCS. The pedestrian has 10-50× lower RCS. (2) Detection range: for a radar designed to detect a car (10 m² RCS) at 200 m: the same radar detects a pedestrian (1 m²) at: R_ped = R_car × (sigma_ped/sigma_car)^(1/4) = 200 × (1/10)^0.25 = 200 × 0.56 = 112 m. Adequate for urban driving (the stopping distance at 60 km/h is approximately 40 m). (3) Classification: the range resolution of 3.75 cm (at 4 GHz BW) allows the radar to resolve features on the pedestrian (limbs, torso). Combined with Doppler information (walking speed, arm swing): the radar can classify the target as a pedestrian (vs a car, bicycle, or static object) with > 95% accuracy using machine learning algorithms.

What about 60 GHz radar for consumer devices?

60 GHz (V-band, 57-71 GHz) is used for short-range radar sensing in consumer devices: (1) Google Pixel Soli (Project Soli): 60 GHz radar for gesture recognition (detect hand and finger movements at 0-2 m distance). (2) Smart home presence sensors: detect human presence in a room for lighting, HVAC, and security (range: 5-10 m). (3) Health monitoring: contactless vital signs sensing (heart rate, respiration) using the Doppler shift of the 60 GHz radar off the chest wall. The 60 GHz band has 14 GHz of bandwidth (57-71 GHz): range resolution = 1.1 cm. Very high resolution for fine-grained sensing. Advantages over 77 GHz for consumer: lower regulatory barriers (60 GHz is in the ISM band; no automotive-specific certification required), and lower power (the short range allows very low TX power, < 10 mW).

Keep Reading