What is Millimeter Wave Radar?
Millimeter - wave refer to the electromagnetic wave wavelength between 1-10MM. Shorter wavelength bandwidth. Millimeter - wave radar has high resolution and is not susceptible to interference. It is a high-Precision sensor to measure the relative distance of the measured object and its speed and azimuth. IT was used in the military field in the early days.
At present, each country has different frequency bands allocated for on-board Millimeter - wave radars. But they are mainly concentrated in 24GHz and 77GHz. A few countries (such as Japan) adopt the 60GHz band. Due to the advantages of 77G over 24G. The global on-board Millimeter-wave radars will converge to the 77GHz band (76-81GHz) in the future.
Theory of Automobile of Millimeter - wave radars.
Principle of Automobile Millimeter - wave radars.
The automobile Millimeter - wave radar transmits the millimeter - wave outward through the antenna to receive the reflected signal from the target. After the rear processing, the information of the physical environment around the automobile body can be obtained quickly and accurately. (Such as the relative distance between the car and other objects, relative speed, angular direction of motion, and so on.
Target tracking and recognition classification based on the information of the detected objects. Then combine the dynamic information of the car body for data fusion.
Finally, intelligent processing through the central processing unit (ECU)and rational decision making. Inform or warn the driver by sound, light, touch and other ways, or make an active intervention to the car time, to ensure the safety and comfort of the driving process and reduce the probability of accidents.
Millimeter – wave radars path diagram.
Depending on how the electromagnetic waves are radiated. Millimeter – wave radars mainly has a pulse system and continuous wave system. The continuous wave can be divided into FSK (Frequency Shift Keying) PSK (Phase Shift Keying) CW (Constant Frequency Continuous wave) FMCW (Frequency Modulation Continuous Wave)
Because it can measure multiple targets, high resolution, low signal processing complexity, low cost, mature technology, the FWCW radar became the most commonly used vehicle-mounted millimeter - wave radar, Delphi, Bosch, and other Tier 1 suppliers adopt FMCW modulation. The FWCW radar system mainly includes transceiver antenna, radio frequency front end, modulation signal, signal processing module, and another millimeter - wave radar, which realize the detection range, azimuth, and relative velocity of the target through the correlation processing of the received signal and the transmitted signal.
Development status of millimeter wave radar
1. Radio Frequency Front end
The radio - frequency front obtains the signal by transmitting and receiving the millimeter - wave, and extracts the information such as range and speed. Therefore, the radio frequency front end directly determines the performance of the radar system.
At present, the radio frequency front end of Millimeter - wave radar is mainly plane integrated circuit. There are two forms of hybrid microwave integrated circuit (HMIC) and monolithic microwave integrated circuit (MMIC). Radio - frequency front-end in monolithic microwave integrated circuit form has low cost and high yield.
Suitable for mass production in the production process, generally adopted epitaxial MESFET HEMT and HBT device process. GaAs- based HEMT process is the most mature with excellent noise performance.
2. Signal Handling Equipment
The signal handling equipment system is importance part of millimeter - wave radar. By embedding different signal processing algorithms. The if signals collected from the radio frequency front end are extracted to obtain specific types of target information signal processing systems, which generally take DSP as the core, and realize complex digital signal processing algorithms to meet the real-time requirements of radar.
3. The Back-end Algorithm
The Back – end Algorithm takes the highest proportion of the whole millimeter - wave radar cost.
For millimeter - wave radar, the domestic researchers from frequency domain time-frequency analysis of multiple points of view put forward a lot of time - domain algorithms, off-line experimental accuracy is higher also, however, the domestic radar products are mainly based on fast furrier transform of frequency domain and its improved algorithm were analyzed, and the measuring precision and scope of application has certain limitations and patent protection strictly, the price is very expensive.
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