Millimeter radar wave overview

millimeter wave radar

1. Applications and characteristics of millimeter-wave radar
   1) Research significance of vehicle-mounted millimeter-wave radar
   With the rapid development of modern science and technology and people’s living standards has increased significantly, the use of vehicles has increased sharply, and the corresponding traffic accidents have also increased sharply. A large amount of traffic accident data shows that more than 80% of car accidents are caused by driver errors, 65% of vehicle collisions are rear-end collisions, and the rest are side or frontal collisions. Relevant research shows that if car drivers have 0.5 seconds of extra reaction time, 60% of rear-end collisions and crashes can be avoided, and if there is 1 second of extra reaction time, 90% of rear-end collisions and crashes can be avoided. Such significant functions and effects have effectively promoted the development and application of automobile anti-collision systems. As one of the core components of the automobile anti-collision system, automobile anti-collision radar has become a research hotspot in recent years.
   2) Characteristics of automotive millimeter wave radar
   Automobile anti-collision radar mainly includes ultrasonic radar, lidar, millimeter wave radar and other types. Compared with other types of radar, millimeter-wave radar has a strong ability to penetrate fog, smoke, and dust, and has the advantage of being available all-weather (except heavy rain). Its disadvantages are that it cannot identify the color of objects; the field of view is small and multiple radars are required to be used in combination; the reflected waves of pedestrians are weak and difficult to identify.

2. Working Principle of Millimeter Wave Radar
   Millimeter wave radar emits millimeter waves (frequency modulated continuous waves) through a microstrip array antenna, receives the target reflection signal, and processes it to obtain the surrounding environment of the car body. Physical environment information (such as the relative distance, relative speed, azimuth angle, etc. between the car and other objects), and then identification and target tracking based on the detected object information, and then combined with the vehicle body dynamic information for data processing. After reasonable decision-making, the driver will be warned in various ways such as sound, light and touch, or proactive intervention in the car will be made in a timely manner to reduce the chance of accidents. The working principle diagram is shown in Figure 1 below.
   Figure 1: Working principle of radar
   1) Principle of radar ranging and speed measurement
   Millimeter wave radar emits continuous frequency modulation through the antenna Wave (triangular wave), receive the target reflected signal as shown in Figure 2, mix it with the local transmit frequency to produce an intermediate frequency signal IF, and process the intermediate frequency signal IF to obtain target distance and speed information. The reflected wave has the same shape as the transmitted wave: there is a time difference Δt and a Doppler shift fd. The radar transmitted signal and reflected signal are shown in Figure 3, and the reflected signals of moving targets and stationary targets identified by the radar are shown in Figure 4.
   According to the distance formula, find the distance to the target:
   According to the Doppler principle, find the relative speed relative to the target:

Figure 3: Principle of radar speed measurement

Figure 4: Transmitted signal and reflected signal
Figure 5: Reflected signal of moving target and stationary target
2) Principle of radar ranging and angle measurement
Angle measurement is to detect the angle between the "line connecting the target and the center line of the antenna" and the normal line, which is used for target positioning to obtain position information of the target and the vehicle. The antenna generally needs to be set to one transmitter and two receivers, and the phase comparison method is used to achieve the angle measurement function. The principle diagram of millimeter wave radar angle measurement is shown in Figure 6. The distance between the receiving antennas is d, causing the echo signals to arrive at the receiving antenna one after another, resulting in a phase difference of Δφ between the signals received by the two antennas at the same time. θ is the angle to be measured. It is calculated:
Figure 6: Principle of millimeter wave radar angle measurement
3) Radar target recognition
Basic principles of millimeter wave radar target recognition It is: using the target characteristic information such as amplitude, phase, spectrum and polarization in the radar echo, through various mathematical multi-dimensional space transformations to estimate the size, shape and other physical parameters of the target, and finally determined based on a large number of training samples. The identification function is used to make recognition decisions in the classifier, including modules such as target recognition preprocessing, feature signal extraction, feature space transformation, pattern classifier, and sample learning. Among them, characteristic signal extraction refers to the millimeter wave radar collecting and extracting various information generated by the interaction between the electromagnetic waves it emits and the target, including: RCS (radar scattering cross-section area) and other characteristic parameters. Commonly used characteristic parameters include the structural shape characteristics of the target, The dynamic characteristics of the target and the echo waveform characteristics, etc.; and the purpose of the feature space transformation is to: change the original data distribution structure, compress the dimensionality of the feature space (reduce), and remove redundant features. The commonly used feature transformation technology: K-L transformation (to remove Redundancy) and Walsh transformation (dimensionality reduction), etc. The principle diagram of target recognition of millimeter wave radar is shown in Figure 7.
Figure 7: Principle of target recognition by millimeter wave radar
There are two methods of target recognition by millimeter wave radar: template-based method and model-based method. The template-based method refers to: millimeter wave radar directly extracts features with intuitive physical meaning or target images from the target echo as templates, and classifies them by comparing the measured templates with the template library; the model-based method refers to: in a large number of training Based on the samples, a mathematical model of the target echo or image is established, and classification is performed by comparing the measured echo characteristics with the model predicted characteristics.
4) Radar target tracking
The target tracking system consists of target information preprocessing, target tracking processing, target filtering processing and other modules. The target information preprocessing mainly includes target echo processing, target detection, point trace aggregation, parameter calculation, etc. The relevant definitions are as follows.
①Echo processing: mainly includes echo demodulation, signal FFT transformation, etc.;
②Target detection: target threshold detection, false alarm rate control Processing;
③Point trace condensation: mainly calculate the center of gravity, center of mass, etc. of multiple echo signals to estimate the target position;
④Parameter calculation: through various The processing model algorithm calculates the target's position and motion parameter information.
Target tracking processing and filtering mainly include target prediction, target correlation, target filtering, etc. Target prediction refers to predicting the status of the current moment based on the value of the previous moment; target correlation refers to the calculation of correlation judgment parameters (distance, speed, orientation, etc.) between the predicted information and the existing target information; target filtering refers to the prediction based on the measurement results. The results are corrected, and the main filter function is Kalman filter.

3. Millimeter wave radar hardware composition
   Millimeter wave radar mainly consists of three parts: antenna, radio frequency MMIC, and baseband signal processing, of which radio frequency MMIC is the core component. Today's millimeter-wave radar uses "microstrip patch antennas" to make the antenna smaller and lighter. The radar RF front-end monolithic microwave integrated circuit (MMIC) is used to generate and receive RF signals. The current mainstream chip is the SiGe process. However, companies such as Fujifilm and Texas Instruments have developed millimeter-wave radio frequency chips using CMOS technology, which has significantly reduced costs. The baseband signal processing part is mainly algorithms, which is the core of the stability and reliability of millimeter wave radar. Digital processing includes beam forming algorithms for array antennas, signal detection, measurement algorithms, classification and tracking algorithms, etc.

1) Radar antenna high-frequency PCB board
The antenna is one of the key designs for the effective operation of automotive millimeter wave radar, and it is also the key to whether millimeter wave automotive radar can win the market. The mainstream solution for millimeter-wave radar antennas is microstrip array. Simply put, the high-frequency PCB board is integrated on an ordinary PCB substrate to realize the function of the antenna. It is necessary to maintain sufficient signal strength of the antenna in a small integration space. 77Ghz radar has higher specifications of high-frequency PCB boards. The wide-scale application of 77GHz radar will bring huge demand for corresponding high-frequency PCB boards. For example, Bosch's LRR3. Compared with the second-generation LRR, which requires several gallium arsenide chips to generate, amplify and detect 77GHz microwaves, Bosch's third-generation LRR greatly simplifies the radar antenna PCB board, using only 1 or 2 InfraStructures. Ling silicon germanium chip.

2) MMIC (Monolithic Microwave Integrated Circuit)
MMIC has the characteristics of low circuit loss, low noise, wide frequency range, large dynamic range, high power, and strong anti-electromagnetic radiation ability. . It includes a variety of functional circuits, such as low-noise amplifiers (LNA), power amplifiers, mixers, detectors, modulators, voltage-controlled oscillators (VCO), phase shifters, etc. The front-end monolithic microwave integrated circuit (MMIC) technology, a key component of millimeter wave radar, is controlled by foreign semiconductor companies, while high-frequency MMIC is only in the hands of a very few foreign chip manufacturers such as Infineon and Freescale. Domestic MMIC is still in its infancy. Xiamen Yixing and Nanjing Miller are developing radar MMIC, and the relevant performance still needs to be verified. In addition, Southeast University, the only State Key Laboratory of Haomi Wave Radar, has also been developing 77GHz millimeter wave integrated circuits.

The 77GHz millimeter wave automotive radar technology solutions used by the entire automotive industry are diverse, and their core radio frequency chips mainly come from companies such as Infineon, NXP/Freescale, and STMicroelectronics. Among them, Infineon adopts millimeter wave radar technology of multi-chip radio frequency system. The transceiver channel is 2T/4R. The system features are: 2 transmitters and 4 receivers. The transmitter module and the receiver module are separated. The integration level is high. This solution is used to design 77GHz radio frequency. The front-end circuit has a certain degree of flexibility, but because it involves a lot of control circuit design, the later debugging workload is relatively large, and it is not currently open to the country. Freescale adopts millimeter-wave radar technology of multi-chip radio frequency system. The transceiver channel is 2T/3R. The system features are: 2 transmitters and 3 receivers. The transmitter module and the receiver module are separated. The integration level is high. This solution is used to design the 77GHz RF front-end. The circuit has a certain degree of flexibility, but because it involves a lot of control circuit design, the later debugging workload is also large. STMicroelectronics adopts millimeter-wave radar technology with a single-chip radio frequency system. The transceiver channel is 3T/4R. System features: 3 transmitters and 4 receivers. Integrated design of transmitter module, receiver and other modules. Supplemented by MCU and other partial circuits, the radar system can be constructed. The degree of integration is High, this solution is used to design the 77GHz RF front-end circuit. The internal configuration is flexible. Since there are few control circuits involved, the later debugging workload is less and the cost is low. It is now open to the country.
The comprehensive situation analysis is as follows:
It can be seen from the above comparative analysis that the development and application of 77GHz millimeter wave radar mainly depends on the performance of the front-end radio frequency chip. There are many high-frequency bands. The chip solution makes the design and debugging complex, making development more difficult. At present, ST integrated chip is the core architecture for the development of 77Ghz millimeter wave radar. It has high integration, multiple channels, good performance and high degree of technical openness, which is conducive to rapid development.

4. Millimeter wave radar actual vehicle matching
   Millimeter wave radar has high requirements for the layout on the whole vehicle. Only by meeting the relevant layout requirements can the functions and performance of millimeter wave radar be obtained. For better protection, the following table lists the layout requirements of millimeter wave radars (different millimeter wave radars have different assembly requirements, the following table is for reference only).
   Meeting the vehicle installation layout of millimeter-wave radar is only the most basic requirement for its function. In order to ensure that millimeter-wave radar can realize functions such as automatic emergency braking or adaptive cruise of the vehicle, millimeter-wave radar is also required. The wave radar completes relevant signal communication with the vehicle. Among them, the vehicle signals required by millimeter wave radar include: wheel speed signal, yaw angular velocity signal, steering wheel angle signal, steering wheel angular velocity signal, ABS/TCS/VDC status signal, accelerator pedal signal, etc.
   In order to realize functions such as automatic emergency braking or adaptive cruise of the vehicle, in addition to installing millimeter wave radar to provide display and control signals for the vehicle, other related parts of the vehicle also need to meet the corresponding design Require.
   The design requirements for the vehicle hardware structure include: First, meet the requirements of the ESP (body stability system) based on the adaptive cruise system and automatic emergency braking system in terms of life and brake pressure build-up speed. and noise requirements, ① ESP motor low-frequency control ECU hardware needs to be upgraded to medium-frequency control ECU, ② ESP needs to replace hardware such as normally-open valve filter with half-filled design structure, normally-open valve base with higher hardness; secondly, add self- Adapt the cruise function operation hardware control switch; Third, make design changes to the shape of the vehicle's front bumper.
   The design requirements for the vehicle software include: first, ESP is required to provide wheel speed, yaw angular velocity, braking pressure and other signals to the millimeter-wave radar; second, EMS (engine electronic control) is required Unit) provides engine speed signals and accelerator pedal position signals, etc., and must meet the requirements of timely response to torque requests according to millimeter wave radar instructions; third, the TCU (transmission control unit) is required to provide gear information; fourth, the instrument needs to be added The adaptive cruise system, automatic emergency braking system working indicator light and alarm indicator light increase the display information required by related systems. Fifth, set the setting soft switch of related functions on the navigation.
   Layout requirements of a domestic radar

5. Millimeter wave radar market
   According to research from Mamus Consulting, the number of pre-installed millimeter wave radars in Chinese cars reached 1.05 million in 2016, of which 24GHz radars accounted for 63.8%. 77GHz radar accounts for 36.2%. 24GHz radar is now mainly used in blind spot detection (BSD), with market demand coming from Chinese brand car models; 77GHz radar is mainly used in adaptive cruise control systems (ACC), and some companies also use it for forward collision warning (FCW) and automatic Emergency braking (AEB). According to the China New Car Assessment Program (C-NCAP), the automatic emergency braking system (AEBS) will be included in the scoring system in 2018, so the demand for 77GHz radar will increase.
   The global millimeter wave radar presents a monopolistic competition pattern. The main market for 77GHz millimeter wave radar is basically occupied by international parts giants. In 2016, Bosch and Continental’s global market share reached 35%, followed by Hella, Fujitsuten, Denso, ZF, etc.

At present, China's millimeter wave radar is developing rapidly. Many manufacturers have the ability to mass produce 24GHz millimeter wave radar (see attachment). It is expected that domestic 24GHz millimeter wave radar will show substantial growth in the short term, while 77GHz millimeter wave radar The large-scale application of radar will be slightly delayed due to factors such as design difficulty and the RF chip supply chain system. From a mid- to long-term perspective, 77GHz millimeter-wave radar will have the opportunity to break through the bottlenecks of design and supply chain and enter the peak of domestic substitution. Expect. At the same time, many independent companies have begun to deploy next-generation millimeter-wave radars at 79-81GHz. In the future, a pattern of 77GHz radar for long-distance detection and 79GHz radar for short-distance detection is likely to be formed.
Comparison of 77GHz radar parameters from foreign manufacturers

6. Future Development Direction
   1) Market Prospects
   China is the world’s largest automobile producer and consumer. In 2015, China’s automobile market reached 170 million The number of vehicles in existence (including 125 million private cars) will grow rapidly at an annual growth rate of nearly 20 million vehicles in the future. The Chinese automobile market accounts for more than 30% of global automobile sales, but the share of ADAS is significantly less than 30%. With the upgrading of the consumption structure and the increasing demand for car purchases by the middle class, the demand for ADAS based on millimeter wave radar will show explosive growth in the future. The global millimeter wave automotive radar market size was approximately US$1.94 billion in 2015, and is expected to reach US$3.47 billion in 2018. By 2020, the global millimeter wave radar market size will exceed US$5 billion.
   According to surveys, domestic automotive millimeter wave radar sales in 2014 were approximately 1.2 million units, and in 2015 they were approximately 1.8 million units. The main application is short- and medium-range radar (24Ghz) for blind spot detection and rear vehicle reminder. Each vehicle requires two. In 2016, China's automobile sales volume was 28.0282 million units. If my country's passenger car compound growth rate is 4% from 2015 to 2020, the annual passenger car sales volume in 2020 will be approximately 30 million units. Car sales are expected to peak at 42 million units. The upgrade of domestic automobile consumption structure and the expansion of market demand for driverless cars will drive the explosive growth of domestic market demand for millimeter-wave radar front and rear components. In 2015, China's millimeter-wave radar market size was approximately 1.8 billion yuan, and it is expected to reach 4.14 billion yuan in 2018. By 2020, China's millimeter-wave radar market may exceed 7.21 billion yuan.
   2) Development Trend
   Currently, in the millimeter wave frequency band, the bands open to civilian use are 24GHz\60GHz\77GHz\120GHz, among which 24GHz and 77GHz are used in automobiles. They are all used in 24GHz. 24GHz was the earliest to be opened and is currently more commonly used. 24GHz is mainly for medium and short range detection of 5-70m, and its main applications include BSD\LDW\LKA\LCA\PA, etc. 77GHz is mainly for medium and long-range detection of 100-250 meters, such as ACC\FCW\AEB, etc. However, as the accuracy requirements of automotive radar systems increase, 77GHz will be the mainstream in the future. Many companies have begun to launch 77GHz mid-range radars to replace 24GHz radars in BSD and other systems. Therefore, looking to the future, 77GHz radars with smaller size and longer detection range will squeeze the market space of 24GHz radars.