How the 77 GHz radar sensor works and why it is indispensable for modern ADAS

HELLA 77 GHz radar sensor in workshop environment next to diagnostic unit – cutting-edge automotive radar sensor for driver assistance systems and ADAS applications

HELLA TECH WORLD – The workshop's friend

77 GHz radar technology – the crucial part in ADAS: Cutting-edge radar sensors enable reliable environment detection for functions including ACC, automatic emergency braking, lane change and cross-traffic assist – even in rainy, foggy and dark conditions.
Compact design, rugged technology: The HELLA 77 GHz radar sensor combines RF-CMOS technology, integrated signal processing and self-diagnostics in a rugged housing for tough vehicle applications.
FMCW principle for accurate measurements: Frequency-modulated continuous wave radar simultaneously and highly accurately detects the distance and relative speed of several objects.
Versatile areas of application: From front radar to corner radar as well as parking, off-highway and autonomous applications – 77 GHz sensors offer flexible use.
Crucial diagnostics and calibration: Vehicle-specific calibration using the diagnostic unit is essential to guarantee safe system functionality following its removal and installation, work on the vehicle's body or chassis.

The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.

Using 77 GHz radar sensors in cutting-edge driver assistance systems

Radar sensors with various ranges are used in cutting-edge vehicle architectures to provide various driver assistance functions. Short-range radars (typically 24 GHz or 77 GHz with small antenna aperture) detect objects at close range and support parking assistance systems. Medium-range radars detect vehicles to the side and are used for lane change and cross-traffic assist systems. Long-range radars with a long range and narrow opening angle enable functions, such as adaptive cruise control (ACC) and automatic emergency braking. Thanks to their rugged performance in rainy, foggy and dark conditions, radar sensors provide accurate distance and relative speed measurements. Integrating them into camera and lidar systems enables sensor-fusion-based environment perception for highly automated driving functions.

Radar sensor frequency ranges in automotive applications

Radar sensors operating across various frequency ranges are used in a host of vehicles, depending on the respective application and range.

The following section provides an overview of the frequency ranges and their typical areas of application:

Frequency range	Typical range	Area of application
24 GHz (24.05 - 24.25 GHz)	Up to approx. 30 m	Parking aid, blind spot assistance systems
77 GHz (76.0 - 77.0 GHz)	Up to approx. 250 m	Adaptive cruise control (ACC), lane change assistant, cross-traffic warning
77.0 - 81.0 GHz	Up to approx. 300 m	High-resolution applications, automated driving, emergency braking, ACC

HELLA 77 GHz radar sensor – design and functionality

Exploded view of HELLA 77 GHz radar sensor featuring housing, printed circuit board, shielding and radome – automotive radar sensor design — Hella 77 GHz radar sensor design: 1. Connector housing; 2. Shielding heat sink; 3. Printed circuit board (PCB); 4. Housing cover/radome; 5. Fastening screw; 6. Thermal decoupler/heat conducting paste; 7. Adhesive

HELLA 77 GHz radar sensor design

The HELLA 77 GHz radar sensor is a compact, high-frequency sensor specially developed for demanding environments. Its centrepiece is the radar system chip, which is based on RF-CMOS technology. This circuit technology combines radio frequency (RF), analogue and digital electronics on a single CMOS chip to enable and improve wireless communication.

This architecture allows the integration of:

Transmitting and receiving components
Digital processing units
Self-diagnostics systems

A rugged housing accommodates the sensors, meeting IP 6K7 and IP X9K protection classes, meaning they are resistant to water, dust and high-pressure cleaning. It is installed using three eyelets for M6 screws. With a weight of less than 100 g and a supply voltage of 12 V/24 V, they are easy and flexible to integrate.

Signal curve of an FMCW radar – frequency modulation illustration to measure distance and speed in 77 GHz radar sensors — Sample of a frequency-modulated continuous wave radar signal curve

Function

The radar sensor is based on the principle of frequency-modulated continuous wave (FMCW) radar. In this process, a continuous signal (carrier frequency) is transmitted and modulated within a bandwidth.

As soon as an object reflects the signal, the distance and relative speed of the object can be calculated by comparing the frequencies.

The calculation takes into account what is known as chirp time, the bandwidth of the signal and the speed of light. A chirp is a signal with a frequency that changes, increases or decreases over time. Modern FMCW systems utilise very short chirps (less than 100 µs) to enable high measuring frequencies and accurate object tracking – even if there are several targets at the same time.

A major advantage of FMCW technology is its insensitivity to weather conditions such as rain, snow, fog or darkness. As radar is based on electromagnetic waves, it works regardless of the light conditions and can even measure through certain materials, such as plastic covers. FMCW radar also makes it possible to simultaneously detect distance and speed, which is essential for driver assistance systems, such as adaptive cruise control (ACC), emergency brake assistants or lane change assistants.

Areas of application and technical properties

Application in ADAS and autonomous driving functions

HELLA 77 GHz radar sensors are designed for use in demanding environments and offer high-resolution detection capability. They are suitable for operation in on-highway and off-highway vehicles and, depending on the sensor type, comply with protection classes including IP 6K7 and IP X9K.

Typical areas of application:

ADAS (Advanced Driver Assistance Systems): Front radar for automatic emergency braking, ACC (Adaptive Cruise Control), collision avoidance
Corner radar: for blind spot monitoring systems, lane change assistants, cross-traffic detection systems
Parking and manoeuvring aids: accurately detect obstacles at low speeds
Autonomous systems: Environment sensor systems for navigation and object classification
Specialised vehicles: Agricultural and forestry equipment, construction machinery, mobile robots

Connector and pin assignment of a HELLA 77 GHz radar sensor – CAN bus, power supply and ground connections

Technical data and performance characteristics (*)

Centre frequency: 76.5 GHz
FOV azimuth: ± 75° (at 10 dBsm @ 20 m)
FOV elevation: ± 10° (at 10 dBsm @ 20 m)
Communication interface: CAN
12 V/24 V supply voltage
100 μA maximum quiescent current
Power: < 4 W
Operating temperature: -40 °C to +85 °C

*Technical data is exemplary and may vary.

System integration and diagnostics

Lane change assistant system overview – networking of radar sensors, control units and CAN bus for driver assistance systems in vehicles — Sample illustration of lane change assistant communication and system integration featuring two radar sensors.

Communication and system integration of in-vehicle radar sensor systems

Internal communication between radar sensors and other BUS participants via the connection to the central system control unit and individual driver assistance system control units. The radar control units continuously and reliably exchange information required for the respective system application via the data bus. This data forms the basis for accurate and situation-appropriate functionality of the assistance systems, for instance measuring the distance, warning of collisions or automatic cruise control. The networking structure shown may differ from other models depending on vehicle model and system architecture.

Diagnostics view in HELLA Gutmann Tester – reading out a fault code for lane change assistant radar sensors — Reading out a fault code. In this function, fault codes stored in the fault memory can be read out and used for further diagnostics. As shown here by way of example, fault code 729605 "Faulty or missing calibration" has been stored in the control unit.

Live parameter indication of a 77 GHz radar sensor in the diagnostics unit – ADAS system voltage and status values — Reading out parameters. In this function, the current measured values of the sensor in the control unit can be displayed and evaluated.

Basic setting and calibration of radar sensors using the diagnostics unit – setting up the lane change assistant in the vehicle — Basic settings – this function can be used to configure a basic setting or calibrate radar sensors. The diagnostic unit takes you through the calibration process step-by-step and indicates required special tools and operations.

Testing and control unit diagnostics

The radar sensor function is monitored by the respective higher-level system control unit and thus via the on-board diagnostics (OBD). Component-related faults such as incorrect operational readiness, electrical short circuits or cable interruptions are recognised directly and logged in the fault memory. Therefore, initially read out the assistance system fault memory using a suitable diagnostic device. The respective test depth and variety of functions can differ from vehicle manufacturer to vehicle manufacturer and depend on the respective system configuration of the control unit. The data from control unit communication forms the basis for actual troubleshooting and for successful repair work. Depending on the system, additional parameters can be displayed and used for troubleshooting.

In certain vehicle models, the radar sensor holder is fixed and does not allow mechanical adjustment. Instead, fine adjustments are made electronically using the diagnostics system. In this process, it determines a correction angle and stores it in the control unit to safeguard correct functionality.

Radar sensor calibration is necessary if:

The installation position of the sensor has been changed as a result of work on the vehicle body
The radar sensor has been removed, installed or replaced
The vehicle level has been changed as a result of a chassis modification or repair
An adjustment error has been stored in the fault memory

Maintenance and repair instructions

Observe the following instructions during maintenance and repair to ensure that driver assistance systems featuring radar sensors operate properly:

Exclusively trained specialists are permitted to carry out repair and maintenance.
After installation of the radar sensor, it may be necessary to carry out a vehicle-specific adjustment and also a system calibration by using a suitable diagnostic device.
Bumper panelling must exclusively be repainted in compliance with the painting instructions specified by the vehicle manufacturer.
Do not attach stickers to bumper panelling within the radar sensor transmission range.
Work on hybrid and electric vehicles may only be carried out by persons who have been instructed in electrical engineering and who are appropriately qualified.
Improper handling can lead to life-threatening situations.

In this context, it is essential to observe removal, installation and safety instructions of the respective vehicle manufacturer and the respective country-specific laws and regulations regarding work on high-voltage systems!

Further information on driver assistance system maintenance and repair is available on the following pages that deal individually with particular topics:
Lane change assistant | HELLA
Adaptive Cruise Control – adjusting sensor | HELLA

Exemplary representations, pictures and descriptions serve to explain and illustrate the document text and cannot be used as a basis for vehicle-specific repairs.

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