Classification, Principle and Test Method of Vehicle-mounted Millimeter-wave Radar

The realization of vehicle autonomous driving is inseparable from the "eyes" that can see the surrounding environment. The vehicle-mounted millimeter-wave radar is such a "smart eye". It can not only see far, but also penetrate clouds, fog, smoke and dust, and is not afraid of the night. It has become the most widely used intelligent environmental perception sensor in pre-installed mass production. Today, we will take you to get closer to millimeter-wave radar, understand its classification and principle, and test experimental methods.

1 Classification of millimeter-wave radar and ADAS applications

Vehicle-mounted millimeter-wave radar is a detector that measures the distance, direction and speed of a target by emitting electromagnetic waves and receiving the reflected echo of the target. At present, the electromagnetic waves emitted by vehicle-mounted millimeter-wave radars are in the frequency bands of 24GHz, 77GHz to 79GHz, and the wavelength is between 1mm and 0.1cm, also known as millimeter waves. The use of electromagnetic waves in this frequency band can form a narrower beam with better directivity, improve the radar's resolution of the target, and at the same time have a strong ability to penetrate dust, smoke, rain and fog.

Based on the detection distance and installation location, vehicle-mounted millimeter-wave radars can be divided into forward radars and corner radars. The detection range of the forward radar is within 200 meters, and the field of view angle can reach ±45°. It is installed on the rear side of the front bumper of the vehicle. The detection distance of the corner radar is about 70 meters, and the field of view angle can reach ±60°. It is usually installed on the four corners of the vehicle. Currently, the automatic driving functions based on millimeter-wave radar include adaptive cruise control, automatic emergency braking, forward collision warning, blind spot detection, lane change assistance, etc.

2 Principle of millimeter wave radar

The hardware of vehicle-mounted millimeter-wave radar can be divided into two parts: the RF front end and the low-frequency substrate. The RF front end transmits electromagnetic waves modulated in a frequency-modulated continuous wave mode. After being reflected by the target, the electromagnetic waves are received again by the RF front end. By comparing the frequency changes between the transmitted waveform and the received waveform, the time difference between the transmission and reception of the electromagnetic wave can be calculated, and then the distance of the target can be calculated. At the same time, since the moving target will cause Doppler frequency deviation, the received signal is Fourier transformed by the signal processing unit of the low-frequency substrate to obtain the speed information of the target. The vehicle-mounted millimeter-wave radar detects the target azimuth based on the phase difference of the radar wave reflected by the target reaching different receiving antennas. Through the multi-transmit and multi-receive MIMO antenna array setting, the vehicle-mounted millimeter-wave radar can detect the horizontal azimuth and even the vertical azimuth of the target.

3. Testing of vehicle-mounted millimeter-wave radar

The electromagnetic waves emitted by vehicle-mounted millimeter-wave radars are invisible and intangible, so how can their performance be tested? The testing of millimeter-wave radars can be divided into laboratory simulation testing, scene simulation testing, and field or open road testing according to the product development cycle. The testing of vehicle-mounted millimeter-wave radar components covers radio frequency performance, detection performance, and electronic and electrical characteristics. Shanghai Automotive Inspection is one of the few national quality inspection centers in the country that supports the testing of all categories of vehicle-mounted millimeter-wave radars.

Laboratory simulation testing is a common method for testing the RF performance and detection performance of vehicle-mounted millimeter-wave radars. The test system consists of an anechoic chamber, a turntable, a radar target simulator, and a spectrum analyzer. The radar target simulator simulates targets of different distances, directions, and speeds, and has the characteristics of high precision, high stability, and high repeatability. Shanghai Automotive Inspection has an advanced whole-machine test system and has carried out test verification on the mainstream vehicle-mounted millimeter-wave radars in the current market.

Shanghai Automotive Inspection also has the only dedicated traffic and vehicle-mounted millimeter-wave radar in China that can evaluate the dynamic response performance of traffic scenes based on point target and volume target simulation. Through the large transceiver antenna array wall and the target simulation system at the back end, common road traffic participants and typical traffic scenes are simulated to evaluate the dynamic performance of vehicle-mounted millimeter-wave radars. The simulation distance range can reach 500 meters, and the speed range can cover (-500~500) km/h. Shanghai Automotive Inspection has also innovatively established a radar reflection cross-section library for common traffic participants, which can extract target strong scattering points in real time and synthesize more accurate volume targets based on the relative position of the target and the radar.