Radar, a transliteration of English Radar, is derived from the abbreviation of radio detection and ranging, which means "radio detection and ranging", that is, using radio methods to find targets and determine their spatial positions.Therefore, radar is also called "radio positioning".Radar is an electronic device that uses electromagnetic waves to detect targets.The radar emits electromagnetic waves to illuminate the target and receive its echo, thus obtaining the distance, distance change rate (radial velocity), azimuth, altitude and other information from the target to the electromagnetic wave emission point.
Chinese name
radar
Foreign name
Radar[1]
Full English name
radio detection and ranging
Chinese full translation
Radio Detection and Ranging
Fundamentals
Detection of target range, azimuth, velocity, etc. by electromagnetic wave
application area
Military battle command and civil navigation guidance
The emergence of radar was due to the fact that during World War I, when Britain and Germany were engaged in war, Britain needed a radar (technology) that could detect metal objects in the air to help search for German aircraft in anti air raids.During World War II, radar technology with ground to air, air to ground (search) bombing, air to air (interception) fire control, and identification of friend or foe functions has appeared.
After World War II, radar developed new radar systems such as monopulse angle tracking, pulse Doppler signal processing, high resolution synthetic aperture and pulse compression, combined system combined with identification of friend or foe, automatic fire control system combined with computer, terrain avoidance and terrain following, passive or active phase array, frequency agility, multi-target detection and tracking.
Later, with the scientific progress in various fields such as microelectronics and the continuous development of radar technology, its connotation and research content are constantly expanding.The detection method of radar has developed from radar to infrared, ultraviolet, laser and other optical detection methods.
The simultaneous multi-function capability of modern radars enables battlefield commanders to scan targets in various search/tracking modes and automatically correct jamming errors, and most control functions are completed within the system.
Automatic target recognition can make the weapon system play its role to the maximum extent. In fact, integrated radar systems such as airborne early warning aircraft and JSTARS, which have the ability to identify enemy and friend in the battlefield, have become the information command center in the future battlefield.
Development history
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Subgrade radar
In 1842, Christian Andreas Doppler, an Austrian physicist, first proposed a Doppler radar using the Doppler effect.
In 1864, the British physicist James Clerk Maxwell deduced the formula that can calculate the characteristics of electromagnetic waves.
In 1886, German physicist Heinerich Hertz launched a series of experiments to study radio waves.
In 1888, Hertz successfully used instruments to generate radio waves.
In 1897, JJ Thomson began to study cathode rays in vacuum tubes.
In 1904, Christian H ü lsmeyer invented the electric mirror, which is a device that uses radio echo detection to prevent ships from colliding at sea.
Mobile radar
In 1906, De Forest Lee invented the vacuum triode, which is the first active electronic component in the world that can amplify signals.
In 1916, Marconi and Franklin began to study the reflection of short wave signals.
In 1917, Robert Watson Watt successfully designed the thunderstorm location device.
In 1922, Marconi delivered a speech at the American Institutes of Electrical and Radio Engineers on the topic of plane angle radar that can prevent ships from colliding.
In 1922, Taylor and Yang of the United States proposed to equip two warships with high-frequency transmitters and receivers to search for enemy ships.
Sea based radar
In 1924, Britain's Appleton and Barnett measured the height of the ionosphere by reflecting radio waves from the ionosphere.Blair and Duff of the United States used pulse waves to measure the Havessel layer.
In 1925, John L. Baird invented mobile television (the predecessor of modern television).
In 1925, Gregory Breit cooperated with Merle Antony Tuve to successfully use radar for the first time, displaying the short radio pulse reflected from the ionosphere on the cathode ray tube.
In 1931, the US Naval Research Laboratory developed radar based on the beat frequency principle, and began to let the transmitter transmit continuous waves. Three years later, it switched to pulse waves.
Marine radar
In 1935, French Gooden developed a magnetron to generate signals with a wavelength of 16cm, which can be used to find other ships in foggy days or at night.This is the beginning of the peaceful use of radar.
In 1935, Robert Watson Watt of England invented the first practical radar.
In January 1936, Robert Watson Watt of England set up the first radar station in Britain on the coast of Sofk.The British Air Force added five more, which played an important role in the Second World War.
In 1937, Marconi Company built 20 additional chain direction radar stations for Britain.
In 1937, the first US warship radar XAF test was successful.
In 1937, Russell and Sigurd Varian developed a high-power microwave oscillator, also known as klystron.
Strategic early warning radar
In 1939, Henry Boot and John T. Randall invented the electron tube, also known as the resonant cavity magnetron.
In 1941, the Soviet Union first equipped an early warning radar on an aircraft.
In 1943, Massachusetts Institute of Technology developed the airborne radar plane position indicator and early warning radar.
In 1944, Marconi Company successfully designed, developed and produced Bagful system and Carpet radar jamming system.The former was used to intercept German radio communications, while the latter was used to equip the RAF bombing fleet.
After the end of World War II in 1945, the Allied forces were able to defeat Germany only by the radar equipped with a specially designed vacuum tube magnetron.
airborne radar
In 1947, Bell Telephone Laboratory developed a linear frequency modulation pulse radar.In the mid-1950s, the United States was equipped with a super range early warning radar system, which can explore supersonic aircraft.The pulse Doppler radar was soon developed.
In 1959, General Electric Company of the United States developed a ballistic missile early warning radar system, which can track missiles 3000 miles away and 600 miles high, and the early warning time is 20 minutes.
In 1964, the United States installed the first space orbit surveillance radar to monitor man-made earth satellites or space vehicles.
In 1971, three people, including Ijuka of Canada, invented holographic matrix radar.At the same time, digital radar technology appeared in the United States.
In 1993, Dreel McGill of Manchester, United States, invented the super intelligent radar of Dotchart.
working principle
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The specific uses and structures of various radars are different, but the basic forms are the same, including transmitter, transmitting antenna, receiver, receiving antenna, processing part and display.There are also auxiliary equipment such as power supply equipment, data recording equipment, anti-interference equipment, etc.
FMCW speed measurement and distance measurement principle
The role of radar is similar to that of eyes and ears. Of course, it is no longer a masterpiece of nature. At the same time, its information carrier is radio waves.In fact, both visible light and radio waves are essentially the same thing, which are electromagnetic waves. The speed of propagation in vacuum is the speed of light C. The difference lies in their respective frequencies and wavelengths.The principle is that the transmitter of the radar equipment shoots the electromagnetic wave energy to a certain direction in space through the antenna, and the objects in this direction reflect the electromagnetic wave encountered;The radar antenna receives the reflected wave, sends it to the receiving equipment for processing, and extracts some information about the object (the distance between the target object and the radar, the rate of distance change or the radial speed, azimuth, height, etc.).
The principle of velocity measurement is the frequency Doppler effect generated by the relative motion between the radar and the target.The target echo frequency received by the radar is different from the radar transmission frequency, and the difference between the two is called Doppler frequency.One of the main information that can be extracted from Doppler frequency is the range change rate between radar and target.When the target and jamming clutter exist in the same spatial resolution unit of the radar at the same time, the radar can detect and track the target from the jamming clutter by using the difference of Doppler frequency between them.The principle of measuring target azimuth is to use the sharp azimuth beam of the antenna to measure the elevation beam with narrow elevation angle, so that the target height can be calculated according to the elevation angle and distance.
The principle of distance measurement is to measure the time difference between the transmitted pulse and the echo pulse. Since the electromagnetic wave propagates at the speed of light, it can be converted into the accurate distance between the radar and the target.
classification
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radar
There are many kinds of radar, and the classification method is also very complex.Generally, it is military radar.Generally, it can be classified according to the use of radar, such as early warning radar, search alert radar, guidance and command radar, gun aiming radar, height finding radar, battlefield surveillance radar, airborne radar, radio height finding radar, radar fuze, weather radar, navigation control radar, collision avoidance and friend or foe identification radar, etc.
1. According to the type of radar signal, there are pulse radar, continuous wave radar, pulse compression radar and frequency agile radar.
2. According to the angle tracking mode, there are monopulse radar, conical scanning radar and concealed conical scanning radar.
3. According to the parameter classification of target measurement, there are height finding radar, two coordinate radar, three coordinate radar, friend or foe identification radar, multi station radar, etc.
4. According to the technology and signal processing methods adopted by the radar, there are coherent integration and non coherent integration, moving target display, moving target detection, pulse Doppler radar, synthetic aperture radar, and tracking while scanning radar.
5. It is classified into mechanical scanning radar and phased array radar according to antenna scanning mode.
6. According to radar frequency band, it can be divided into over the horizon radar, microwave radar, millimeter wave radar and laser radar.
Among them, phased array radar, also known as phase array radar, is a kind of radar that changes the beam direction by changing the radar wave phase. Because the beam is controlled electronically rather than the traditional mechanical rotation of the antenna surface, it is also called electronic scanning radar phased array technology, which has appeared as early as the late 1930s.In 1937, the United States first began this research work.However, it was not until the mid-1950s that two practical shipborne phased array radars were developed.In the 1980s, phased array radar was further applied due to its many unique advantages.Multi functional phased array radar is widely used in the new generation of medium and long range air defense missile weapon systems that have been equipped and are being developed. It has become an important symbol of the third generation of medium and long range air defense missile weapon systems.Thus, the combat performance of air defense missile weapon system is greatly improved.In the 21st century, with the continuous development of science and technology and the characteristics of modern war weapons, the manufacture and research of phased array radar will reach a higher level.
Waveband division
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Radar sensor
The length of the electromagnetic wave used to search radar was 23cm at the earliest. This band was defined as L-band (the beginning of Long in English). Later, the center wave length of this band became 22cm.When the electromagnetic wave with a wavelength of 10cm is used, its wave band is defined as S-band (short means shorter than the original wavelength).
After the emergence of fire control radar which mainly uses 3cm electromagnetic wave, the 3cm wavelength electromagnetic wave is called X-band, because X represents a point on the coordinate.
In order to combine the advantages of X-band and S-band, a radar with a central wavelength of 5cm has gradually emerged, which is called C-band (C is the prefix of the word "combination" in English).
After the British, the Germans also began to develop their own radar independently. They chose 1.5cm as the central wavelength of their radar.This wavelength of electromagnetic wave is called K-band (K=Kurz, the German word for "short").
Unfortunately, the wavelength chosen by the Germans can be strongly absorbed by water vapor because of their unique "accuracy" of the Germanic nation.As a result, this band of radar cannot be used in rainy and foggy weather.In order to avoid this absorption peak, radar designed after the war usually uses Ka band (Ka, abbreviation for K-above, meaning above the K-band) and Ku band (abbreviation for K-under, meaning below the K-band) with a frequency slightly higher than the K-band.
Finally, because the earliest radar used meter wave, this band is called P-band (P is the abbreviation of Previous, which is the prefix of "past" in English).
The system is very cumbersome and inconvenient to use.Finally, it was replaced by a wavelength division band system divided by actual wavelength. The conversion of these two systems is as follows.
Original P-band=current A/B band
Original L-band=current C/D-band
Original S-band=current E/F band
Original C-band=current G/H band
Original X band=current I/J band
Original K band=current K band
Band standard
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There are three standards for radar band after World War II: German standard, American standard and European standard.Since German and American standards were proposed earlier, most of them are new European standards:
Some waveband tables under new European standards
band
type
Wavelength [cm]
Frequency [GHz]
A
Mibo
<0.25
B
Mibo
0.25-0.5
C
Decimeter wave
30-60
0.5-1
D
Decimeter wave
15-30
1-2
E
Decimeter wave
10-15
2-3
F
Decimeter wave
7.5-10
3-4
G
Decimeter wave
5-7.5
4-6
H
Centimeter wave
4-5
6-8
I
Centimeter wave
3-4
8-10
J
Centimeter wave
1.5-3
10-20
K
Centimeter wave
0.75-1.5
20-40
L
Millimeter wave
0.5-0.75
40-60
M
Millimeter wave
0.3-0.5
60-100
Current microwave band code
Band code
Nominal wavelength (cm)
Frequency range (GHz)
Wavelength range (cm)
L
twenty-two
1-2
30-15
S
ten
2-4
15-7.5
C
five
4-8
7.5-3.75
X
three
8-12
3.75-2.5
Ku
two
12-18
2.5-1.67
K
one point two five
18-27
1.67-1.11
Ka
zero point eight
27-40
1.11-0.75
U
zero point six
40-60
0.75-0.5
V
zero point four
60-80
0.5-0.375
W
zero point three
80-100
0.375-0.3
Frequency division method in China
name
Symbol
frequency
band
wavelength
Propagation characteristic
Main purpose
VLF
VLF
3-30KHz
Ultralong wave
1kkm-100km
Space wave dominated
Coastal submarine communication;Long-distance communication;Ultra long range navigation
Marine communication;Amateur radio communication;Mobile communication;Mid range navigation
high frequency
HF
3-30MHz
shortwave
100m-10m
Sky wave and ground wave
Long-distance short wave communication;International fixed point communication
VHF
VHF
30-300MHz
Mibo
10m-1m
Space wave
Ionospheric scattering (30-60MHz);Meteor trail communication;Artificial ionospheric communication (30-144MHz);Communication with space flying bodies;mobile communication
extra-high frequency
UHF
0.3-3GHz
Decimeter wave
1m-0.1m
Space wave
Small capacity microwave relay communication;（352-420MHz）；Tropospheric scatter communication (700-10000MHz);Medium capacity microwave communication (1700-2400MHz)
UHF
SHF
3-30GHz
Centimeter wave
10cm-1cm
Space wave
Large capacity microwave relay communication (3600-4200MHz);Large capacity microwave relay communication (5850-8500MHz);Digital communication;Satellite communication;International Maritime Satellite Communication (1500-1600MHz)
Extremely high frequency
EHF
30-300GHz
Millimeter wave
10mm-1mm
Space wave
Communication when loading the atmosphere;Waveguide communication
application
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The advantage of radar is that it can detect distant targets in the daytime and at night, and is not blocked by fog, clouds and rain. It has the characteristics of all-weather and all-weather, and has a certain penetration ability.Therefore, it has not only become an essential electronic equipment in military affairs, but also widely used in socio-economic development (such as weather forecasting, resource detection, environmental monitoring, etc.) and scientific research (celestial 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 meters to tens of meters, and is independent of distance.Radar also shows good application potential in flood monitoring, sea ice monitoring, soil moisture survey, forest resource inventory, geological survey, etc.
