Millimetre wave radar is a precision detection device operating in the 30–300 GHz millimetre wave band. Its wave length lies between that of microwaves (1–100 mm) and far-infrared waves (0.75–1 mm), combining characteristics of both. As one of the core sensors in intelligent driving perception systems, millimetre wave radar emits high-frequency millimetre-wave signals and receives echoes from targets, enabling precise measurement of a target’s distance, speed and angle, thereby providing reliable data for system decision-making and control.
Compared to traditional microwave radar,millimetre wave radar offers advantages such as higher resolution, greater penetration capability (able to penetrate light obstacles), a narrower beam and better directionality.Crucially, it is unaffected by adverse weather conditions such as rain, snow, fog or strong sunlight, and is capable of stable operation in all weather and at all times, occupying an irreplaceable position in Advanced Driver Assistance Systems (ADAS). In addition to autonomous driving, millimetre wave radar is also widely used in industrial automation, drone obstacle avoidance, smart home applications and medical health monitoring.
Core Characteristics of Millimetre Wave Technology
Extremely Wide Spectrum Bandwidth
Millimetre wave technology offers an available spectrum bandwidth of approximately 270 GHz, far exceeding that of the microwave band.This characteristic gives it a natural advantage in the field of communications when used for communication, it can achieve extremely high data transmission rates. For example, the millimetre wave band (FR2) in 5G communications can easily reach 10-gigabit (10 Gbps) downlink speeds, meeting the high-speed demands of high-definition video transmission, VR and AR, and other applications. Currently, some countries such as the United States and Japan have already achieved commercial deployment of the millimetre-wave band, whilst China is in the pilot verification phase and is gradually advancing industrial applications.
Outstanding Sensing Capabilities
Due to their extremely short wave lengths, millimetre waves are highly sensitive to minute displacements and deformations, possessing excellent distance resolution and the ability to accurately detect movements or deformations at the millimetre level. This characteristic endows millimetre waves with powerful sensing capabilities, which is the core reason for their widespread application in fields such as autonomous driving and security monitoring.
Significant Advantages in Antennas and Beamforming
According to electromagnetic theory and practical experience, the transmission and reception conversion efficiency of an antenna is highest when its length is one-quarter of the signal wavelength. As millimetre wave lengths are extremely short, antennas can be fabricated at the millimetre scale, thereby significantly reducing equipment size and allowing for the integration of more antenna elements within the same space. A greater number of antenna elements can form narrower, more precise beams at the same size,the beam width of millimetre-wave signals is only one-tenth that of microwave signals. This offers advantages such as excellent directivity, concentrated energy and strong resistance to interference, significantly enhancing target positioning accuracy.
Inherent limitations
Due to their high frequency and short wave length,millimetre wave signals have poor diffraction capabilities.Although they can easily penetrate non metallic materials such as plastic and clothing, signals are significantly attenuated when encountering hard obstacles such as metal or walls,thereby limiting the coverage range.This limitation means that millimetre wave radar is more suitable for short to medium range detection;in long range detection scenarios,it must work in conjunction with other sensors.
Classification of millimetre wave radar
By beam scanning method:
Mechanical scanning radar: Scanning is achieved by rotating the antenna via a motor. This method is low cost and technically mature, but has a slow scanning speed and relatively long response latency. It is primarily used in low-speed scenarios, such as vehicle reversing radar.
Phased array radar: Electronic scanning is achieved via phase shifters in the array antenna, eliminating the need for mechanical rotation. It offers fast scanning speeds, strong multi-target tracking capabilities and rapid response times, and is widely used in forward-looking radar for autonomous driving, supporting functions such as adaptive cruise control and emergency braking.
By application scenario:
Short range radar (SRR): Detection range of 0–50 metres, used for blind spot monitoring, automated parking and side collision warning. For example, the short-range radar on the front bumper of a Tesla can identify pedestrians, non-motorised vehicles and obstacles at close range.
Medium-range radar (MRR): Detection range of 50–200 metres, primarily used for adaptive cruise control (ACC) at high speeds, monitoring the speed and distance of the vehicle ahead in real time and automatically adjusting the vehicle’s speed. Most car manufacturers install medium-range radar in the front grille.
Long-range radar (LRR): Detection range of 200–300 metres, suitable for high-speed collision warning and long-range target identification. Some luxury models are equipped with long-range radar to provide the driver with ample reaction time.
By function:
Frequency Modulated Continuous Wave (FMCW) Radar: Emits millimetre wave signals with continuously varying frequencies, utilising the Doppler effect to calculate speed and distance. It offers strong interference resistance and high measurement accuracy, and is the mainstream technology in the current autonomous driving sector.
Pulse Doppler Radar (PD): Emits pulsed signals and determines the target’s motion state by analysing changes in the echo frequency. It offers strong resistance to clutter and is suitable for adverse weather or complex environments, and is commonly used in aerospace and security applications.
By Antenna Structure:
Microstrip Antenna Radar: Highly integrated, compact, lightweight and cost effective, suitable for in vehicle systems and portable devices, such as millimetre wave radar modules for mobile phones and obstacle avoidance radars for small drones.
Horn Antenna Radar: Offers good beam directivity, high gain and low transmission loss, and is commonly used for long range detection, such as airport security radars and long range meteorological detection radars.
By Detection Target:
Under body radar: Installed beneath the vehicle chassis to detect road surface protrusions, potholes or obstacles, thereby enhancing the manoeuvrability of autonomous vehicles.
Side view radar: Positioned on both sides of the vehicle body to monitor vehicles, pedestrians and obstacles in adjacent lanes, assisting in functions such as lane change assistance and side collision warning.
Applications of millimetre wave radar
Intelligent Driving
Millimetre wave radar serves as the core sensor in intelligent driving perception systems. It can accurately detect the distance, speed and relative position of vehicles, pedestrians and non motorised vehicles ahead, providing critical data for functions such as Adaptive Cruise Control (ACC), Automatic Emergency Braking (AEB), Lane Keeping Assist (LKA) and automated parking.
In Level 2–4 autonomous driving systems, millimetre wave radar works in conjunction with cameras and lidar to compensate for the latter’s limitations in recognition under adverse weather conditions such as rain, snow and fog, forming an all weather, all round perception system that enhances the safety and reliability of autonomous driving.
Security and Surveillance
Millimetre wave radar is used in security and surveillance applications such as intrusion detection, crowd density counting and abnormal behaviour recognition. Compared to traditional cameras, it is unaffected by environmental factors such as night time conditions, smoke or heavy rain, operates reliably and has a low false alarm rate. It is widely deployed in airports, stations, industrial sites and residential estates.
Other Expanding Application Areas
Millimetre wave radar also plays a significant role in industrial automation (material inspection on production lines, equipment fault monitoring), drone obstacle avoidance (precise detection of obstacles), smart homes (human presence detection, gesture control), and healthcare monitoring (breathing and heart rate monitoring), gradually permeating various aspects of production and daily life.
