The concept of radar was formed in the early 20th century. Radar is a transliteration of radar, abbreviated as radio Detection and Ranging. It is an electronic device that uses microwave band electromagnetic waves to detect targets.
The specific use and structure of various radars are different, but the basic form is the same, including five basic components: the transmitter, the transmitting antenna, the receiver, the receiving antenna and the display. There are power supply equipment, data admission equipment, anti-interference equipment and other auxiliary equipment.
The transmitter of a radar device transmits the electromagnetic wave energy to a certain direction of space through an antenna, and the electromagnetic wave is reflected by an object in this direction. The radar antenna receives the reflected wave and sends it to the receiving device for processing, extract some information about the object (distance from the target object to the radar, distance change rate or radial speed, orientation, height, etc ).
The measurement distance is actually the time difference between the emission pulse and the echo pulse. Because the electromagnetic wave is transmitted at the speed of light, it can be converted into the precise distance of the target.
The measurement target orientation is measured using the sharp azimuth beam of the antenna. Measuring the elevation angle is measured by a narrow elevation angle beam. The target height can be calculated based on the elevation and distance.
The measurement speed is the frequency doppler effect produced by radar based on relative motion between itself and the target. The target echo frequency received by a radar is different from the radar transmitting frequency. The difference between the two is the Doppler frequency. One of the main information that can be extracted from the Doppler frequency is the distance change rate between the Radar and the target. When the target and the interference clutter exist in the same spatial resolution unit of the radar, the radar can detect and track the target from the interference clutter using different Doppler frequencies between them.
The advantage of radar is that it can detect long-distance targets during the day and night, and is not blocked by fog, clouds, and rain. It has the characteristics of around-the-clock and full-day weather, and has a certain Penetration ability. Therefore, it is not only an essential electronic equipment for military purposes, but also widely used in social and economic development (such as meteorological forecasts, resource detection, environmental monitoring, etc) and scientific research (Research on celestial bodies, atmospheric physics, and the structure of the ionic, etc ). Satellite and airborne synthetic aperture radar 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 dozens of meters, and it has nothing to do with distance. The radar shows good application potential in flood monitoring, sea ice monitoring, soil humidity survey, forest resource check, and geological survey.
There are many types of radar, which can be classified by multiple methods: (1) the positioning method can be divided into: active radar, semi-active radar and passive radar. (2) the installation location can be divided into ground radar, onboard radar, aerial radar, and satellite radar. (3) Pulse Radar and continuous wave radar can be divided by radiation types. (4) The operating wavelength band can be divided into two types: radar at the worker wavelength, radar at the shard interval, radar at the worker wavelength, and radar at other bands. (5) Target Detection Radar, reconnaissance radar, weapon control radar, flight support radar, meteorological radar, and navigation radar.
- Pulse measuring radar (pulse instrumentation radar)
Radio devices that track and precisely measure aircraft. It provides measurement information for Spacecraft Orbit Determination and target feature measurement. Common pulse measurement radars include Cone Scanning radar and single pulse radar.
Working principle pulse measurement radar obtains the distance information of the target by measuring the round-trip time delay of the pulse electromagnetic wave, and measures the radial speed of the target according to the Doppler frequency in the received pulse carrier, obtain the target's Azimuth and elevation angle data using the same signal method. The Tracking Principle of a Cone Scanning radar is that the antenna beam deviates from a small angle from the radar target axis (equal signal axis) and quickly rotates around the target axis, A cone is scanned at the maximum beam gain direction to form a sine modulation of the target echo amplitude. The angle error signal between the target and the target can be obtained through signal demodulation and phase identification, which is used to control the rotation of the antenna to reduce the angle of the target and achieve angle tracking. A single pulse radar receives ECHO at the same time using four receivers in an equal-signal symmetric configuration □, and the upper and lower pairs are compared with the signals received by □ on the left and right sides, the error signal is obtained to control the rotation of the antenna. The angle tracking is completed when the signal is equal to the signal received by the □ pairs. In addition to radar tracking, the azimuth and elevation angles can be read from the Angle Encoder of the antenna base. The single pulse method has higher accuracy, high data rate, and strong anti-interference ability than the Cone Scanning Method. Measurement, analysis and processing of the target echo signal waveform can obtain information about the target reflection cross section, rolling speed, polarization characteristics, and so on.
There are three modes of work for pulse measurement radar: ① reflection: Radar receives the reflected signal of the target. This method is often used for tracking close targets to obtain rocket power segment information and reentrant Target Feature data. ② Response type: the radar receives signals forwarded by the responder on the aircraft. This method has a strong forwarding signal, long radar distance, and strong anti-interference ability. It is used for the measurement of long-distance targets. The response type can be divided into two types: the response type of the phase parameter and the response type of the phase parameter. When the phase parameter response is used, the receiving and sending frequency of the server must be strictly multiple. ③ Beacon
Type: The radar only receives signals sent by the signal receiver on the aircraft, and can only capture the target.
In order to expand the measurement range of the flight area, multiple radars are often configured along the navigation area column to achieve the tracking and measurement of the target, which is called the radar chain, that is to say, the current one-station radar has captured it before it can continue to track or "not see" the target. Various radars are synchronized to provide real-time data interception. (See Pulse Doppler radar and Radio Tracking Measurement System)
- Pulse Doppler radar (pulsed Doppler radar)
Use the Doppler effect and spectrum Separation Technology to suppress various background clutter pulse radars. The Airborne Pulse Doppler radar has the lower view function, and can improve the capabilities of early warning, Air Combat, low-altitude penetration targets and attacks against ground targets. Pulse Doppler radar is an important part of the fire control system of the interceptor. In addition to air navigation, airborne fire control, air warning and command systems, this radar can also be used as an active missile seeker and a landing device in a moon landing ship.
In 1842, Austrian physicist C. Doppler found that the relative motion of the source and observer changes the observed frequency, which is called the Doppler effect. It was not until 1938 that people began to research and apply this effect to radio devices. In 1950s, the Airborne Pulse Doppler navigation radar and the airborne phase parameter Pulse Doppler fire control interception radar were successfully developed for air navigation. Since 1960s, in order to combat low-altitude penetration and improve the effectiveness of the strategic defense system, a new air warning and command system has been developed. The background radar using the Pulse Doppler system has expanded its monitoring horizon, it can discover low-altitude intrusion targets hundreds of kilometers away and provide timely air intelligence.
Basic principle when an airborne radar transmitter emits high-frequency energy pulses at a specific frequency, different radial velocity target echoes received within the same distance have different Doppler frequencies. Therefore, the pulse Doppler radar has the ability of accurate speed measurement and speed resolution. The emission pulse signal spectrum consists of several discrete spectral lines on the carrier frequency □□□and edge frequency □□dangercode; □□□□□which is the recurrence frequency of the emission pulse, □which is an integer. The envelope of the spectrum is determined by the shape of the emission pulse. Generally, a rectangular pulse is used, and the spectral envelope is sin □□/ □.
The receiving station must extract useful target spectral lines from the background of the main wave bundle, the vertical line, and the side-lobe clutter. There are multiple parallel distance doors in the receiver. Each distance door corresponds to a distance unit and a corresponding distance channel. Each distance channel has a single-band filter, and a spectral line of the target echo is obtained through the spectrum after the filter and the narrowband filter group. In this way, Pulse Doppler radar not only has the ability to measure and distinguish distance, but also has the ability to measure and distinguish speed.
The Airborne Pulse Doppler radar consists of antennas, transmitters, receivers, servo systems, digital signal processors, radar data processors, and data bus. Airborne Pulse Doppler radar usually uses a coherent system. In order to improve the ability of radar to detect useful signals in the complex spectrum, it is necessary to have extremely high carrier frequency stability and spectrum purity, it also requires extremely low antenna sides and advanced digital signal processing technology. Generally, Pulse Doppler radar uses a high repetition frequency to reduce the amplitude of the primary clutter and the relative range of the primary clutter in the frequency field. In order to provide better performance in all aspects of the lower view and upper view, the radar uses a variety of repetition frequencies and a variety of transmit signal forms. In order to eliminate the fuzzy problem (that is, the multi-value problem) in Speed Measurement and ranging caused by high repetition frequency, multiple signals with different repetition frequencies can be sent, use algebra to eliminate fuzzy data in a data processor. In addition, the filter theory can be applied to further filter or predict the target coordinate data in the data processor.
Diagram of Airborne Pulse Doppler Radar
Features modern Airborne Pulse Doppler radar has the following features: Program To increase the processing capacity, speed, and flexibility of radar signals and improve the reusability of devices, so that the radar can be searched while tracking and can change or increase the working state of the radar, so that the radar has the ability to deal with various kinds of interference and the ability to recognize targets beyond the horizon; ② The use of programmable gate-controlled traveling wave tube enables the radar to operate at different pulse repetition frequencies and has the ability to adapt waveforms, low, Medium, or high pulse repetition frequency waveforms can be selected based on different tactical states, and the optimal performance of various working states can be obtained; ③ High Resolution can be obtained through Doppler beam sharpening technology, in the air-to-ground application, high-resolution map ing and high-resolution local amplification ing can be provided. In the air-to-ground application, the air-to-air enemy condition judgment status can identify the group targets of dense formations.
- Target Acquisition and identification radar
A radar that intercepts, tracks, and recognizes an incoming target in a broad search space. It is usually an integral part of early warning radar networks. It accepts guidance Data from Early Warning Radar and searches for and intercepts targets in the specified airspace. Filters, classifies, and identifies various suspicious targets through automatic tracking (see Target Recognition Technology ). Then, the actual attacking targets (ballistic missile warhead, bomber and air-ground missiles) are allocated to the anti-ballistic missile defense system and the Guided radar of the Air Defense System. The target interception and recognition radar was developed from the beginning of 400. It adopts a phased array system (see phased array radar) and works in the p-band ~ 500 MHz), the distance is 3000 ~ 4500 km. It features short search cycles, high probability of interception, fast response, changeable emission waveforms, and strong recognition capabilities. The probability of interception is equal to the probability that the target exists in the search airspace multiplied by the probability of discovery. The latter probability is completely determined by the radar capability and the performance of the detection device. Based on the guidance data of Early Warning Radar, the target interception and recognition radar performs rapid search at the specified Two-Dimensional Angle and radial distance. Needle-shaped antennas have multiple scanning modes, such as spiral, slice, and grating. The distance search wave door generally performs constant motion. After the target is intercepted, the radar immediately enters the automatic tracking status. After the radar is transferred to the Automatic Tracking State, it can conduct ranging, speed measuring, and angle measuring for multiple targets, calculate their positions and motion parameters, and perform polarization state transformation and emission Waveform Transformation at the same time, and calculate the Target Feature signal for identification and judgment. Although the intercepted targets have passed the Early Warning Radar primary election, due to the development of electronic confrontation, the real targets will be accompanied by many false targets (such as bullet fragments, foil bait and hot bait ). The target interception and recognition radar can identify suspicious targets, exclude false targets, and leave only real targets.
- Meteorological radar)
Radar that detects Meteorological Elements and various weather phenomena. The weather radar can provide accurate and continuous images of weather conditions in front of the aircraft and display them in the form of distance and orientation to ensure the plane's change of channels, avoiding bumpy areas and flight safety; provide necessary meteorological data for weather forecasts, launch and flight of rockets, missiles and spacecraft, and provide information for meteorological support and meteorological research at airports. Meteorological radar can be divided into rain radar, cloud radar and wind radar.
Rain radar, also known as weather radar, is used to detect the concentration, distribution, movement and evolution of precipitation in the atmosphere or large drops in the cloud by scattering electromagnetic waves by raindrops, cloud drops, ice crystals, and snow, understand the structure and features of the weather system. Rain radar can detect typhoons, strong winds in some regions □, hail, □rain and strong convective clouds, and monitor weather changes.
The working principle of the radar is the same as that of the rain radar.
Test the height of the cloud top and bottom. In the case of multi-layer clouds in the air, the height of each layer can also be measured. Because cloud particles are smaller than precipitation particles, the working wavelength of the cloud radar is shorter. Cloud radar testing can only detect high-layer and Middle-layer clouds with few clouds. For low-layer clouds with large water content, such as the accumulation clouds and hail clouds, the beams of cloud radar are difficult to penetrate. Therefore, they can only be detected by rain monitoring.
Wind radar is used to detect the horizontal wind direction, wind speed, air pressure, temperature, humidity, and other meteorological elements in different atmospheres at high altitude. Generally, the detection methods of wind radar are to constantly locate the balloon by using the reflection target or responder mounted on the balloon. The horizontal wind direction and wind speed of different atmosphere can be determined based on the displacement of the balloon within the unit time. A probe is mounted on a balloon to remotely measure the air pressure, temperature, and humidity at a height.
Meteorological radar has been deployed in most countries into a network, and the detection scope can cover their own land. Advanced Aircraft are also equipped with airborne weather radar.
- Phased Array Radar (phased array radar)
The array antenna is used to implement the radar for the electromagnetic scanning of beam in space. The emergence of high-speed aircraft, missiles, and man-made earth satellites requires a radar with higher detection capability, greater airspace coverage, higher data rates, and adaptability to multi-target environments. Mechanical scanning radar has a large inertia and limited target capacity, which cannot meet such requirements. The beam of a phased array radar can jump in the whole airspace in several microseconds. The beam shape is flexible and changeable. The computer can directly process the signal and control the radar, compared with the traditional mechanical scanning radar, there has been a fundamental change.
Phased Array Radar
Features the main features of phased array radar are: ① multi-function, large airspace, and multi-target: A phased array radar not only can search, intercept, identify, track and provide the RF radiation energy required by a semi-active guidance system for multiple targets in the airspace, in addition, multiple missiles can be tracked and corresponding Guidance instructions can be sent. The planar array can scan up to 120 dangercode in the airspace, and the spherical or cylindrical array can cover the hemisphere airspace. You can monitor and track hundreds of targets in the airspace. ② Large power-aperture product: use multiple transmitters for power synthesis in space (one transmitter can be used for each antenna array unit) to increase the radiation power. At the same time, a fixed electrical scanning array can use a large aperture to form an extremely high power-aperture product, so that the radar has a greater distance. ③ High data rate: beam scanning is non-inertial. It has a high data rate for several key targets in the airspace, and the lowest data rate required for monitoring other targets in the airspace. ④ Perfect Adaptability: it can adapt to complex external target environments. ⑤ Strong anti-interference ability: it can form a number of beam points in the space, automatically aligning the interference direction of the space, can effectively suppress the active interference.
Composition and working principle phased array radar consists of a transmitting system, an antenna array and A wave controller, a receiving and signal processing system, a central computer, a data processing and display system, etc. Compared with ordinary radar, the most fundamental difference is that it * controls the phase of each radiation unit of the array antenna to change the angle before the phase wave to change the beam direction. The transmitting system generates high-power RF signals with certain waveforms and feeds them to all antenna units for air radiation. The central computer calculates the phase difference between the adjacent units directed by the specified beam, and then the wave controller calculates the phase corresponding to the Phase Shifters of each radiation unit and controls the driver to make the Phase Shifters reach this phase, in this way, the antenna beam is accurate to the specified direction. The maximum speed of a beam hop is determined by the computing time required by the computer-wave controller and the minimum time required for Phase Shifting-drive conversion. The number of elements of the antenna arrays that form the beam can be changed, so the beam shape can be controlled. Each antenna unit receives the echo signal from the target and sends it to the data processing and display system after coherent addition, amplification, and detection. The receiving and receiving antennas can be arrays or arrays. Because the beam motion has no inertia, it can achieve optimal energy allocation in space and time under the control of a computer. Computer plays a key role in phased array radar. It controls the work of the entire radar and participates in signal processing, data processing, information display, and automated radar monitoring. Therefore, flexible computers, high computing speed, and large capacity are required. The feed mode of phased array radar is generally divided into two types: spatial feed and branch forced feed.
- Phased Array Radar (phased array radar)
The array antenna is used to implement the radar for the electromagnetic scanning of beam in space. The emergence of high-speed aircraft, missiles, and man-made earth satellites requires a radar with higher detection capability, greater airspace coverage, higher data rates, and adaptability to multi-target environments. Mechanical scanning radar has a large inertia and limited target capacity, which cannot meet such requirements. The beam of a phased array radar can jump in the whole airspace in several microseconds. The beam shape is flexible and changeable. The computer can directly process the signal and control the radar, compared with the traditional mechanical scanning radar, there has been a fundamental change.
Phased Array Radar
Features the main features of phased array radar are: ① multi-function, large airspace, and multi-target: A phased array radar not only can search, intercept, identify, track and provide the RF radiation energy required by a semi-active guidance system for multiple targets in the airspace, in addition, multiple missiles can be tracked and corresponding Guidance instructions can be sent. The planar array can scan up to 120 dangercode in the airspace, and the spherical or cylindrical array can cover the hemisphere airspace. You can monitor and track hundreds of targets in the airspace. ② Large power-aperture product: use multiple transmitters for power synthesis in space (one transmitter can be used for each antenna array unit) to increase the radiation power. At the same time, a fixed electrical scanning array can use a large aperture to form an extremely high power-aperture product, so that the radar has a greater distance. ③ High data rate: beam scanning is non-inertial. It has a high data rate for several key targets in the airspace, and the lowest data rate required for monitoring other targets in the airspace. ④ Perfect Adaptability: it can adapt to complex external target environments. ⑤ Strong anti-interference ability: it can form a number of beam points in the space, automatically aligning the interference direction of the space, can effectively suppress the active interference.
Composition and working principle phased array radar consists of a transmitting system, an antenna array and A wave controller, a receiving and signal processing system, a central computer, a data processing and display system, etc. Compared with ordinary radar, the most fundamental difference is that it * controls the phase of each radiation unit of the array antenna to change the angle before the phase wave to change the beam direction. The transmitting system generates high-power RF signals with certain waveforms and feeds them to all antenna units for air radiation. The central computer calculates the phase difference between the adjacent units directed by the specified beam, and then the wave controller calculates the phase corresponding to the Phase Shifters of each radiation unit and controls the driver to make the Phase Shifters reach this phase, in this way, the antenna beam is accurate to the specified direction. The maximum speed of a beam hop is determined by the computing time required by the computer-wave controller and the minimum time required for Phase Shifting-drive conversion. The number of elements of the antenna arrays that form the beam can be changed, so the beam shape can be controlled. Each antenna unit receives the echo signal from the target and sends it to the data processing and display system after coherent addition, amplification, and detection. The receiving and receiving antennas can be arrays or arrays. Because the beam motion has no inertia, it can achieve optimal energy allocation in space and time under the control of a computer. Computer plays a key role in phased array radar. It controls the work of the entire radar and participates in signal processing, data processing, information display, and automated radar monitoring. Therefore, flexible computers, high computing speed, and large capacity are required. The feed mode of phased array radar is generally divided into two types: spatial feed and branch forced feed.
- Meteorological Doppler radar (meteorological Doppler radar)
In addition to weather radar functions, it can also use Doppler effects to measure the radial velocity (Doppler velocity) of clouds and precipitation particles relative to radar. Pulse Doppler radar was developed in the early 1960s S. It is an important tool for studying cloud and precipitation physics, Cloud dynamics, and small and medium scale weather systems (especially for monitoring the dragon volume.
Principle when the radar transmitter and receiver are at the same position, if the radial velocity of the target relative to the radar is □□□, the frequency difference between the transmitting wave and the echo (also called Doppler frequency offset) = □= 2 □□/ □. □Is the wavelength of the radar transmitting wave. Therefore, the speed can be determined □□□. The Doppler velocity of precipitation particles is not only affected by the flow of precipitation clouds (including turbulence), but also by the falling velocity of precipitation particles. Therefore, under reasonable assumptions, it can be used to obtain information such as Horizontal Atmospheric Wind Field, vertical flow velocity, atmospheric turbulence, and precipitation drops. When clearing the sky, you can also use the clear air echo (see the meteorological radar echo) or the echo of the scattered metal foil to obtain information about the atmospheric flow field.
Working principle of Pulse Doppler Radar
Early Performance Doppler radar, the antenna is directed directly to the lead, and the Doppler velocity measured is the sum of the falling velocity of precipitation particles relative to the air and the velocity of the lead flow. Under various assumptions, based on the known relationship between the Falling Velocity of water drops and the diameter of water drops, we can use the direct direction of lead to detect and obtain information about the volume of rain and the direct velocity of the air flow. In the future, the elevation angle of the radar antenna is fixed to a certain value for azimuth scanning. In this way, the radial velocity of the target is distributed along with the azimuth at a certain elevation. The corresponding display method is speed-orientation display (VAD ). The resulting information,
Through mathematical operations, the wind direction, wind speed, and horizontal divergence at various heights over the radar station can be obtained. This method can quickly measure the distribution of wind with height within several kilometers to dozens of kilometers. The measurement error of wind speed is about 0.5 meters/second. If the orientation of the radar antenna is fixed and the elevation angle is constantly changed, the distance-height-speed displayed by this scanning method is rhv ), the direct profile of the wind speed component in the scanning azimuth is provided (Figure 2 vertical profile of the relative velocity component in the storm ). When the antenna performs a azimuth scan near the horizontal level, the corresponding display mode is the planar shear display (PSI), which can display the strong wind shear and the area where the vortex exists. For monitoring volumes (see color map Doppler radar detection of Tornado Storm color display chart echo intensity display speed unit: meter/second, observation elevation angle: 0.01 □, distance ring distance: 16 km Doppler radar detection of Tornado Storm color display diagram Doppler Speed Display Speed Unit: meter/second, observation elevation: 0.01 dangercode;, distance: 16 km) severe weather such as hail is very useful. The combined detection test of dual Doppler radar or three Doppler radar can also obtain the detailed structure of three-dimensional motion of the precipitation system.
One of the important problems in the development and application of Doppler radar is the conflict between the distance of Doppler radar and the maximum measurable velocity. Therefore, you can only choose a compromise between the maximum measured speed and the maximum effective distance based on actual needs. However, because Doppler radar can determine the detailed structure of the three-dimensional motion of the precipitation system and effectively detect the strong weather such as the dragon volume, it is increasingly widely used.
- very high frequency and ultra high frequency doppler radar (very high frequency and ultra high frequency doppler radar)
working in 30 ~ Meteorological Doppler radar in the 3000 MHz band. Generally, it has a high detection sensitivity. The detection height ranges from 1 to 1 ~ It is also known as the middle-layer-to-the-ground radar (MST radar), which is 100 kilometers ). It is mainly used to detect the direct distribution of atmospheric dynamics parameters such as wind, atmospheric turbulence, and atmospheric stability (see atmospheric static stability) in the clear air.
principle this type of radar uses the interaction between electromagnetic waves and the atmosphere to detect the Clear Air Atmosphere: ① scattering of electromagnetic waves by the refractive index uneven structure caused by atmospheric turbulence; ② Stable Atmospheric stratified structure partial reflection of the incident electromagnetic wave; ③ sometimes the free electrons in the Middle Atmosphere scatter the electromagnetic wave; ④ the meteor debris scattering in the middle atmosphere. Scattering the air movement in the volume, so that the radar echo has a Doppler frequency deviation.
the structure of the structured MST radar is roughly the same as that of the meteorological Doppler radar. They are generally equipped with large antennas (antenna arrays), and some antenna arrays of high frequency radar, with a scale of 30 ~ 200 meters, beam scanning is implemented using a half-wave vibrator array or an eight-wood antenna vibrator array in a phase-controlled manner. Ultra-high frequency radar uses a movable parabolic antenna with a diameter of dozens of meters. The launch power of these radars ranges from several hundred kilowatts to Two megawatts, and the product of the transmit power and the antenna area is 10 □ ~ Between 10 □□w dangercode and meters. In addition, in order to obtain high sensitivity and high spatial resolution, some technical measures are also taken in terms of the pulse emission system and echo data processing.
the use of the Echo Doppler spectrum can be used for the following measurements: ① To detect the direct distribution of the atmospheric wind field. At the same elevation, the spatial resolution is about 150 ~ 1000 meters. After pulse compression technology, the resolution can reach 15 meters. ② Detect the atmospheric turbulence structure. The direct distribution of the mean refractive index turbulence structural constant (C □) can be given. After some atmospheric turbulence models are introduced, the direct distribution of turbulence dissipation rate can be calculated. ③ Detect the height and thickness of the top and back-temperature layers of the trotters. At present, very high frequency and ultra-high frequency doppler radar can only determine the vertical line of the preceding Meteorological Elements and
their time changes, rather than providing three-dimensional spatial distribution data.
- very high frequency and ultra high frequency doppler radar (very high frequency and ultra high frequency doppler radar)
working in 30 ~ Meteorological Doppler radar in the 3000 MHz band. Generally, it has a high detection sensitivity. The detection height ranges from 1 to 1 ~ It is also known as the middle-layer-to-the-ground radar (MST radar), which is 100 kilometers ). It is mainly used to detect the direct distribution of atmospheric dynamics parameters such as wind, atmospheric turbulence, and atmospheric stability (see atmospheric static stability) in the clear air.
principle this type of radar uses the interaction between electromagnetic waves and the atmosphere to detect the Clear Air Atmosphere: ① scattering of electromagnetic waves by the refractive index uneven structure caused by atmospheric turbulence; ② Stable Atmospheric stratified structure partial reflection of the incident electromagnetic wave; ③ sometimes the free electrons in the Middle Atmosphere scatter the electromagnetic wave; ④ the meteor debris scattering in the middle atmosphere. Scattering the air movement in the volume, so that the radar echo has a Doppler frequency deviation.
the structure of the structured MST radar is roughly the same as that of the meteorological Doppler radar. They are generally equipped with large antennas (antenna arrays), and some antenna arrays of high frequency radar, with a scale of 30 ~ 200 meters, beam scanning is implemented using a half-wave vibrator array or an eight-wood antenna vibrator array in a phase-controlled manner. Ultra-high frequency radar uses a movable parabolic antenna with a diameter of dozens of meters. The launch power of these radars ranges from several hundred kilowatts to Two megawatts, and the product of the transmit power and the antenna area is 10 □ ~ Between 10 □□w dangercode and meters. In addition, in order to obtain high sensitivity and high spatial resolution, some technical measures are also taken in terms of the pulse emission system and echo data processing.
the use of the Echo Doppler spectrum can be used for the following measurements: ① To detect the direct distribution of the atmospheric wind field. At the same elevation, the spatial resolution is about 150 ~ 1000 meters. After pulse compression technology, the resolution can reach 15 meters. ② Detect the atmospheric turbulence structure. The direct distribution of the mean refractive index turbulence structural constant (C □) can be given. After some atmospheric turbulence models are introduced, the direct distribution of turbulence dissipation rate can be calculated. ③ Detect the height and thickness of the top and back-temperature layers of the trotters. At present, very high frequency and ultra-high frequency doppler radar can only determine the vertical line of the preceding Meteorological Elements and
their time changes, rather than providing three-dimensional spatial distribution data.
- multi-Base radar (Multistatic Radar)
a radar system consists of transmitters and receivers in different bases. It may consist of multiple forms. The transmitters and receivers on each base can be one or more, and the number does not have to be equal. Multi-Base radar is suitable for precise positioning of long-range targets. Like a single base radar, it can detect, locate, track, and speed the target. However, it uses the distance, angle, and distance of the target base to represent the coordinates of the target. Multi-Base radar can also be used to measure the distance between pulse signals or continuous wave frequency modulation signals. To measure the frequency shift, transmit the transmit signal from the transmitting base to the receiving base as a reference signal. However, when the receiving base measures the angle of the target, the direct signal may interfere with the target echo signal, and the direct signal must be isolated from the echo signal. Here, the Doppler frequency is used to identify whether the target is static, but the radial velocity of the target cannot be determined. Compared with single-base radar, the Data Processing System of Multi-Base radar is much more complex and has a false target phenomenon. Other auxiliary information and corresponding data processing methods should be used to eliminate or reduce the data processing system. In addition to precise targeting of intrusion targets and precise missile guidance, multi-Base radar can also be used as a precise trajectory measurement system for space vehicles.
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