1. What is radar？
Radar finds targets by radio and determines their spatial location. Therefore, radar is also known as “radio positioning”. Radar is an electronic device that detects targets by means of electromagnetic waves. Radar emits electromagnetic wave to illuminate the target and receives its echo. From this, the information of distance, range change rate (radial velocity), azimuth and altitude from the target to the emitter of electromagnetic wave can be obtained.
The advantage of radar is that it can detect long-range targets day and night, and is not obstructed by fog, cloud and rain. It has the characteristics of all-weather and all-time, and has certain penetration ability. Therefore, it has not only become an indispensable military electronic equipment, but also widely used in social and economic development (such as weather forecasting, resource detection, environmental monitoring, etc.) and scientific research (astronomical research, atmospheric physics, ionospheric structure research, etc.). Spaceborne and airborne SAR have become very important sensors in remote sensing. Radar targeting the ground can detect the precise shape of the ground. Its spatial resolution can reach several to tens of meters, and is independent of distance. Radar also shows great potential in flood monitoring, sea ice monitoring, soil moisture survey, forest resources inventory and geological survey.
2. Military radar and civil radar
Radar can be divided into military radar and civil radar according to its use.
Military radar is a military electronic equipment which uses electromagnetic wave to detect targets. The electromagnetic wave emitted by the radar illuminates the target and receives its echo, thus finding the target and determining its position, moving direction, velocity and other characteristics.
Civil radar includes navigation radar, weather radar, velocity radar and so on.
3. Examples of civilian radar
(1). Meteorological radar
Meteorological radar is mainly used to detect meteorological conditions and trends. It has been widely used in weather forecasting and professional meteorological services in agriculture, hydrology, forestry, transportation, energy, ocean, aviation, aerospace, national defense, construction, tourism, medical and other fields. It is an aviation electronic product developed by people to guard against meteorological risks and ensure flight safety. It is based on the principle that electromagnetic waves are reflected back from obstacles when they pass through the antenna. The higher the conductivity of the target is, the larger the reflector is, the stronger the echo is. It can continuously provide the pilots with the weather conditions in front of the flight path and on both sides. In addition, it also provides a map display of the ground surface characteristics in front of the aircraft. The pilots can choose safe routes, avoid dangerous weather areas or other obstacles, identify landmarks and determine the position of the aircraft.
(2). Speed measuring radar
Radar velocity measurement is mainly based on the principle of Doppler effect: when the target approaches the radar antenna, the frequency of the reflected signal will be higher than that of the transmitter; otherwise, when the target moves away from the antenna, the frequency of the reflected signal will be lower than that of the transmitter. Thus, the relative velocity of the target and radar can be calculated by changing the value of the frequency (the Doppler frequency is positive when the target is flying towards the radar, and the Doppler frequency is negative when the target is flying towards the radar). Now it has been widely used in police overspeed testing and other industries.
(3). Reversing radar
Reversing Radar, which is called “Reversing Anti-collision Radar”, is also called “Parking Assistant Device”. It mainly consists of ultrasonic sensors, controllers and monitors.
Reversing radar is a safety assistant device when parking or reversing a car. It can inform the driver about obstacles by sound or more intuitive display, relieve the trouble caused by the driver’s left and right visits when parking, reversing and starting the car, and help the driver to clear the dead angle of vision and blurred vision. Sink.
When reversing the car, the radar uses the principle of ultrasound to transmit the sound wave from the probe installed on the rear bumper after it strikes the obstacle, calculates the actual distance between the car body and the obstacle, and then prompts the driver to make parking or reversing easier and safer.
(4). Marine radar
Navigation radar is a kind of radar installed on ships for navigation avoidance, ship positioning and narrow channel pilotage, also known as marine radar. Navigation radar provides necessary observation means for navigators when visibility is poor. Its appearance is an important milestone in the development of navigation technology.
From the late World War II to the early 1950s, the navigational radar equipped by warships was a relative motion display radar. Since the late 1970s, the performance of radar automatic plotter has been improved continuously, such as acquisition and tracking ability of target, image and data display ability, anti-clutter jamming ability, trial operation function, etc., and the functions of automatic drift compensation, channel display and chart display have been added. Navigation radar will further combine with other positioning and navigation technology, digital technology and automatic control technology to form a closed-loop automatic navigation and collision avoidance system through automatic steering system and host remote control system.
4. Future Development of Civil Radar
Because of the high frequency of radar signal, it is easy to avoid the complex call-off, large environmental noise interference, and it is easy to obtain stable and reliable detection results. The centimeter wave (such as 24GHz) gradually replaces the traditional detection equipment (sensors) in the field of civil consumption, and obtains the opportunity of universal application, such as intelligent light control, underground garage car. Vehicle detection, speed detection, trajectory detection and so on.
Radar working in other frequency bands has a wider range of intelligent applications, such as the most popular smart car, driverless technology, intelligent assistant driving technology (ADAS) in which radar technology is widely used, can be said to be “radar without intelligence”.
