Doppler radar, also known as pulse Doppler radar, is a radar that uses the Doppler effect to detect the position and relative velocity of moving targets.In 1842, Austrian physicist J. C. Doppler found that when the wave source and the observer have a relative motion, the frequency of the wave received by the observer is different from the frequency sent by the wave source. This phenomenon is called the Doppler effect.When the wave source and the observer are close to each other, the received frequency increases;When the two leave each other, it decreases.Doppler radar is a kind of pulse radar made of this Doppler effect.pulseDoppler radar includes range gate circuit, single sideband filter, main beam clutter suppression circuit and detection filter bank, which can suppress ground object interference well.Pulse Doppler radar can be used for airborne early warning, airborne interception, airborne navigation, low altitude defense, fire control, battlefield reconnaissance, missile guidance, range measurement, satellite tracking and weather detection.[1]
In 1842, Austrian physicist J. C. Doppler found that when the wave source and the observer have a relative motion, the frequency of the wave received by the observer is different from the frequency sent by the wave source. This phenomenon is called the Doppler effect.When the wave source and the observer are close to each other, the received frequency increases;When the two leave each other, it decreases.For example, when the wave source moves away from us, the interval between two successive peaks is larger than that when they leave the source, because each subsequent peak has to travel a little more than the previous one to reach us.Therefore, the receiving frequency will be lower than the transmitting frequency. At this time, we will feel that the wavelength of the wave emitted from a moving wave source away from us is longer than the wavelength emitted when the wave source is stationary.Similarly, the wavelength of the wave emitted from a wave source moving towards us is shorter than that emitted when the wave is stationary.An example of the Doppler effect is the change in the tone of the whistle when a train passes a station.In astronomy, the movement of spectral lines in the spectrum emitted by the celestial body can be used to predict the speed of the celestial body approaching or leaving the observer: according to the Doppler effect, when the spectral lines emitted by the celestial body shift to the longer end of the wavelength (i.e. red shift), it indicates that the celestial body is leaving the observer;When the spectral line emitted by the celestial body shifts to the shorter end of the wavelength (i.e., purple shift), it indicates that the celestial body is coming to the observer.[2]
Operating principle of radar
The working principle of Doppler radar can be described as follows: when the radar transmits a pulse wave with a fixed frequency to scan in the air, if it encounters a moving target, the frequency difference between the echo frequency and the transmitted wave frequency is called Doppler frequency.According to the size of Doppler frequency, the radial relative velocity of the target to the radar can be measured;According to the transmitted pulse and receivedtime difference, the distance of the target can be measured.At the same time, Doppler frequency of target is detected by frequency filtering methodSpectral lineFiltering the spectral lines of jamming clutter can enable the radar to distinguish target signals from strong clutter.Therefore, Doppler radar has stronger anti clutter ability than ordinary radar, and can detect moving targets hidden in the background.
Doppler radar
developing process
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Pulse Doppler radar was successfully developed and put into use in the 1960s.Since the 1970s, with the development of large-scale integrated circuits and digital processing technology, pulse Doppler radar has been widely used in airborne early warning, navigation, missile guidance, satellite tracking, battlefield reconnaissance, range measurement, weapon fire control and weather detection, and has become an important military equipment.Early warning aircraft equipped with pulse Doppler radar have become effective military equipment against low altitude bombers and cruise missiles.For example, the airborne fire control system mainly uses pulse Doppler radar.For example, the APG-68 radar equipped by American fighter planes represents the advanced level of airborne pulse Doppler fire control radar.It has 18 working modes, which can search and track air, ground and sea targets, with good anti-interference performance. When the aircraft is flying at low altitude, it can also guide the aircraft to track terrain fluctuations to avoid collision with the ground.This kind of radar is small in size, light in weight and high in reliability.
In addition, the radar is also used for meteorological observation.The signal measurement of conventional weather radar is limited to the strength of meteorological targets.Doppler weather radar can not only provide all functions of conventional weather radar, but also provide signals of atmospheric wind field.Through Doppler velocity resolution of meteorological echoes, the distribution of various air turbulence movements in the atmosphere at different altitudes can be obtained.The development of Doppler weather radar technology in China started late. At the end of the 1980s, the development of Doppler weather radar and its trial in meteorological operations began.In the 1990s, 714CD and 714SD inter pulse coherence have been produced.In 1997, the first imported WSR88D new generation Doppler weather radar was settled in Shanghai.In 1999, the WSR-88D was transformed, and the first advanced S-band all coherent pulse Doppler mine CINRAD/CC 3824 was built.The significant improvement of CINRAD/CC is to use the Doppler effect in physics to measure the radial velocity of precipitation particles, and infer the wind speed distribution, wind field structure characteristics, vertical airflow velocity, etc. of precipitation clouds through the velocity information.At present, it is the leading ground-based meteorological detection equipment in the United States, Western Europe and other developed countries.Doppler radar is the most advanced radar system in the world, known as "super clairvoyance", with a maximum detection range of 460km.Compared with the traditional weather radar, the Doppler radar can monitor the generation and change of convective cloud layer in the high altitude of 8-12km from the vertical ground, judge the moving speed of the cloud, with 72 kinds of product information, and the accuracy of weather forecast will be greatly improved than before.A new generation of weather radar network is under construction to improve the timeliness and accuracy of disastrous weather forecasting, such as sudden rainstorm, coastal typhoon and heavy rainfall warning of large rivers in China.By the end of 2010, 126 new generation weather radar stations had been built in China, accounting for 73% of the 158 planned stations nationwide.There are two bands, S band and C band. There are three different types of radars in S band (CINRAD/SA, CINRAD/SB, CINRAD/SC), which are mainly distributed along the coast of the Yangtze River.C-band type radars (CINRAD/CC, CINRAD/CB, CINRAD/CD, CINRAD/CJ) are mainly distributed inland.
Structure composition
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Airborne pulse Doppler radar mainly consists of antenna, transmitter, receiverservo system、digital signal processing Computer, radar data processor, data bus, etc.Airborne pulse Doppler radar usually adopts coherent system, with extremely high carrier frequency stability, spectral purity and extremely low antenna sidelobe, and adopts advanced digital signal processing technology.Pulse Doppler radar usually adopts high and multiple repetition rates and multiple transmission signal forms to use algebraic methods in the data processor, and can apply filtering theory to further filter or predict the target coordinate data in the data processor.
characteristic
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One difference between Doppler radar and traditional radar is that its transmitter is always on
Radar is called continuous wave or CW radar.The reason why the transmitter must always be turned on is that unlike traditional radars, it needs to calculate the time between transmission and reception, and Doppler radars look for frequency changes.The frequency change will not last for a long time, so the transmitter must always be on.
Doppler radar
Pulse Doppler radar has the following characteristics:
① The programmable signal processor is used to increase the processing capacity, speed and flexibility of radar signals and improve the reusability of equipment, so that the radar can search while tracking and can change or increase the working state of the radar, so that the radar has the ability to deal with various interferencesBeyond visual rangeThe ability to identify targets;
② The programmable grid controlled traveling wave tube is used to enable the radar to work at different pulse repetition rates, with the ability to adapt the waveform. The waveform of low, medium or high pulse repetition rates can be selected according to different tactical states, and the best performance of various working states can be obtained;
③ AdoptDoppler beam sharpeningThe technology can achieve high resolution, provide high resolution mapping and high resolution local amplification mapping in air to ground applications, and can distinguish group targets in dense formation in air to air enemy situation judgment state.
application
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Military applications
Doppler radar is widely used in airborne early warning, navigation, missile guidance, satellite tracking, battlefield reconnaissance, range measurement, weapons and other aspects.
Meteorological observation
Doppler radar is also used for weather detection and other occasions.Through Doppler velocity resolution of meteorological echoes, the distribution of various air turbulence movements in the atmosphere at different altitudes can be obtained, and thus the relevant meteorological information can be obtained.
