Let's start at the beginning - what is radar and why is it needed? First of all, I would like to note that radar is a certain branch of radio engineering, which helps in determining the various characteristics of surrounding objects. The action of radar is directed to the supply of radio waves by an object to the device.
Radar, radar station is a certain set of various devices and devices that allow you to monitor objects. The radio waves that are fed by the radar can detect the target under investigation and make a detailed analysis of it. Radio waves are refracted and, as it were, "draw" the image of the object. Radar stations can operate in all weather conditions and perfectly detect any objects on the ground, in the air or in the water.
Principles of operation of the radar
The action system is simple. Radio waves from the station are sent to objects, when they meet with them, the waves are refracted and reflected back to the radar. This is called radio echo. To detect this phenomenon, radio transmitters and radio receivers are installed in the station, which have high sensitivity. Previously, a couple of years ago, radar stations required huge costs. But not now. For the correct operation of devices and the definition of objects, it takes very little time.
All radar operations are based not only on the reflection of waves, but also on their dispersion.
Where can radar be used?
The scope of radar systems is quite wide.
- The first branch will be the military. Used to identify ground, water and air targets. Radars perform control and survey of the territory.
- Agriculture and forestry. With the help of such stations, specialists conduct research to study the soil and vegetation, as well as to detect various kinds of fires.
- Meteorology. Studying the state of the atmosphere and making forecasts based on the data obtained.
- Astronomy. Scientists use radar stations to study distant objects, pulsars and galaxies.
Radar in the automotive industry
Since 2017, developments have been underway at the MAI, which are aimed at creating a small-sized radar station for unmanned vehicles. Such small on-board vehicles could be installed in every car in the near future. In 2018, non-standard radars for unmanned aerial vehicles are already being tested. It is planned that such devices will be able to detect terrestrial objects at a distance of up to 60 kilometers, sea ones - up to 100 km.
It is worth recalling that in 2017 a small-sized airborne dual-band radar was also introduced. The unique device was designed to detect various kinds of objects and objects under any conditions.
Device I - indicator. Purpose:
Playback on the screen of primary information about the environment coming from the radar equipment.
Determining the coordinates of surface objects and solving navigation problems graphically.
Synchronization and control of station operating modes.
Formation of trigger pulses of the transmitting device.
Formation of impulses for starting auxiliary devices.
Formation of pulses of the course signal for auxiliary devices.
Providing autonomous power supply of own blocks and devices.
Device and principle of operation:
Device I consists of the following paths and nodes:
Time synchronization path.
Timebase path.
The path of the sight and range marks.
Path of the direction finder.
Information entry path.
True motion path.
Digital display of range and direction.
Cathode-ray tube and deflection systems.
The principle of operation of the device And consider its block diagram(Fig. 1).
The time synchronization path has a master oscillator (3G), which generates master pulses with a repetition rate of 3000 pulses / sec - for range scales of 1 and 2 miles; 1500 imp/sec for 4 and 8 mile scales; 750 imp/sec - for scales 16 and 32 miles; 500 pulses/sec for 64 miles scale. The master pulses from 3G are fed to the output of the device to trigger functionally connected devices (in the P-3 device); to start the sawtooth voltage generator (in the time synchronization path);
In turn, from Device P-3, secondary synchronization pulses enter the synchronization path of the device, due to which the start of the sweep in range and direction is synchronized with the beginning of the emission of probing pulses by device A (radar antenna) and the path of the sight and range marks is launched.
The timebase path, using a sweep generator, forms and generates a sawtooth voltage, which, after a series of transformations, is supplied to the deflecting system of relative motion in the cathode-ray tube and to the path of the direction sight.
The path of the sight and range marks is intended for the formation of a mobile range sight (PVD), through which objects are sighted in range, and the range is measured by an electronic digital counter. Distance information is displayed on a digital display TsT-3.
The rotor of the rotating transformer of the sweep generator rotates synchronously and in phase with the antenna, which ensures synchronous rotation of the sweep and the antenna, as well as obtaining a mark for the start of the sweep at the moment the maximum of the antenna pattern crosses the center plane of the vessel.
The direction finder path consists of an angle sensor, readout and decoding signal generators, a rotating transformer for the direction finder sweep. The angle of rotation of the rotating transformer generated in the path of the direction sight, formed in the form of an encoded signal, after decoding, is fed to the digital indicator-tableau TsT-4.
The information input path is designed to enter information on the range and direction to the object on the CRT, as well as display on the CRT the video signal coming from the P-3 device.
The true motion mode path is designed to input data on the speed V s - from the log, the course K s from the gyrocompass, according to which the components of the velocity vector are generated on a scale in the directions N - S and E - W; to ensure the movement of the own ship mark on the CRT screen in accordance with the selected scale, as well as the path, automatic and manual return of the own ship mark to the starting point is provided.
The P-3 device is a transceiver. Purpose:
P-3 device (transceiver) is intended for:
Formation and generation of probing microwave pulses;
Receiving, amplifying and converting reflected radar signals into a video signal.
Ensuring synchronous and in-phase operation in time of all blocks and units of devices: And; P - 3; A.
The composition of the device:
· Microwave unit - 3 (unit of ultra-high frequency).
MP block (transmitter modulator).
FM block (modulator filter).
block AFC (automatic frequency control unit)
block UR (adjustable amplifier)
UG block (main amplifier)
Block NK - 3 (block settings and control)
ACS unit (automatic stabilization and control unit)
FS subblock (sync pulse shaper)
4 rectifier devices providing power to the blocks and circuits of the device P - 3.
We will consider the operation of the device on its block diagram.
The stabilization signal generation path is designed to generate secondary synchronization pulses entering the device AND as well as to launch the transmitter modulator through the automatic control stabilization unit. With the help of these sync pulses, the probing pulses are synchronized with the start of the sweep on the CRT of the I device.
The probing pulse generation path is designed to generate microwave pulses and transmit them through the waveguide to device A. This occurs after the voltage modulator generates a pulse modulation of the microwave generator, as well as control and synchronization pulses of the mating blocks and nodes.
The video signal generation path is designed to convert reflected microwave pulses into intermediate frequency pulses using a local oscillator and mixers, form and amplify the video signal, which then enters device I. To transmit probing pulses to device A and reflected pulses to the video signal generation path, a common waveguide is used.
The control and power setting path is designed to generate supply voltages for all blocks and circuits of the device, as well as to monitor the performance of power sources, functional blocks and units of the station, magnetron, local oscillator, arrester, etc.
Device A is an antenna device. Purpose:
Device A is designed to emit and receive microwave energy pulses and output data on the heading angle of the antenna and mark the course to device I. It is a horn-type slot antenna.
Basic device data A.
Beam Width:
In the horizontal plane - 0.7 ° ± 0.1
Vertical - 20° ± 0.1
Antenna rotation frequency 19 ± 4 rpm.
Operating temperature ranges from - 40°С to + 65°С
Dimensions:
Length - 833 mm
Width - 3427 mm
Height - 554 mm
Weight - 104 kg.
Structurally, the device is made in the form of 2 detachable blocks;
PA block - rotary part of the antenna
block AR - is carried out: the formation of microwave energy in the form of a radio beam of the required shape; directed radiation of energy into space and its directed reception after reflection from irradiated objects.
Device operation a.
An electric motor with a gearbox is installed in the PA unit of the device. The electric motor is powered by the ship's network and provides circular rotation of the AR unit of device A. The electric motor, through the gearbox, also rotates the rotor of the rotating transformer from which the signal about the angular position of the antenna relative to the ship's DP (heading angle) is supplied to the device And through the tracking system, and also a ship's heading signal. The PA block also contains a rotating microwave junction designed to connect a rotating emitter (AR block) to a fixed waveguide path.
The AR block, which is a slot antenna, forms a directional radio beam of the required shape. The radio beam radiates microwave energy into space and provides directional reception of part of this microwave energy reflected from the irradiated objects. The reflected signal, through a common waveguide, enters the P-3 device, where, after a series of transformations, it turns into a video signal.
A thermal electric heater (TEN) is also installed in the PA block, designed to prevent the danger of icing of the moving parts of the device A and a filter to eliminate industrial radio interference.
The KU device is a contactor device. Purpose:
The KU device (contactor device) is designed to connect the radar to the onboard network, switch the output voltage of the machine unit, protect the antenna drive from overloads and protect the radar in case of violation of the order to turn it off, as well as protect the station in case of emergency shutdown of the onboard network.
The device supplies alternating current voltage 220V with a frequency of 400 Hz to the radar devices in 3 ÷ 6 seconds after turning on the machine unit.
In the event of an emergency shutdown of the on-board network, the device switches off consumers within 0.4 ÷ 0.5 s.
The device switches off the antenna drive after 5 ÷ 20 s. with incorrect phase sequence, with a break in one of the phases and with an increase in the load current of the antenna drive.
Converter ALL - 1.5m. Purpose:
The converter is designed to convert a three-phase current with a frequency of 50 Hz into a single-phase alternating current voltage 220 V, frequency 427 Hz. It is a machine unit, on the shaft of which there is a three-phase synchronous motor and a single-phase synchronous generator.
The converter provides local and remote start and stop of the power unit.
RADAR OPERATION CONTROL.
Control radar operation carried out from the panel and control panel of the device I.
The governing bodies are divided into operational and support.
By using operational governing bodies:
The station turns on and off. (27)
The range scales are switched. (14)
Distances to targets are measured using a rangefinder. (15)
Heading angles and bearings of targets are determined using electronic and mechanical direction sights. (28), (29)
Heading marker is disabled. (7)
They control the visibility (amplification) of radar signals and noise protection. (8, 9, 10, 11, 12, 13)
The brightness of the backlight of the panel and scales is adjustable. (2)
By using auxiliary governing bodies:
Turns the antenna rotation on and off. (26)
The connection of the indicator with the log and the gyrocompass is switched on.
The indications of the movable scale of the direction finder are coordinated. (29)
Adjusts the brightness of the sweep and course mark. (22, 23)
The AFC is turned off and the manual mode for adjusting the local oscillator frequency is turned on. (27)
The center of rotation of the sweep is aligned with the geometric center of the direction finder. (20)
The local oscillator of the P-3 device is tuned.
The control mode of the overall performance of the radar is switched on. (16, 17, 18, 19)
The power supply of the P-3 device modulator is turned off.
The brightness of the CRT screen is set and the beam is focused.
The antenna rotator is turned on. (26)
Antenna heating is switched on on the KU device
The location of the controls on the remote control and the indicator panel is shown in the figure.
Rice No. 3. Radar indicator control panel "Naiad - 5":
1-“Illumination of scales”; 2-"Panel illumination"; 3-"Degrees"; 4-"Scale - interval"; 5-"Miles"; 6-"PZ"; 7-"Course mark"; 8-"Rain"; 9-“VN brightness”; 10-"VD brightness"; 11-"Brightness MD"; 12-“Waves”; 13-"Gain"; 14-"Range scale switch"; 15-"Range"; 16-"Blocks"; 17-"Rectifiers"; 18-"Control"; 19-"Dial indicator"; 20-"Setting the center"; 21-“RPC-Off”; 22-"Brightness OK"; 23-"Sweep brightness"; 24-"False signals"; 25-"Radar control"; 26-"Antenna - Off"; 27-"Radar-Off"; 28-"Mechanical sight"; 29-"Direction"; 30-"Kurs-North-North-ID"; 31-"Reset to the center"; 32-"Reset"; 33-"Offset of the center"; 34-"Accounting for demolition"; 35-"Speed manually"
RADAR MAINTENANCE.
Before turning on the radar, you must:
Produce visual inspection and make sure that there is no external damage to the devices and the unit.
Set the controls to the position indicated in the table.
| Name of the governing body | The position of the controls before the indicator turns on |
| Toggle switch "Radar - Off." “Rain” knob “HV brightness” knob “VD brightness” knob “MD brightness” knob “Waves” knob “Gain” knob Reset to Center" "Center Offset" knobs "Drift Accounting: Speed, Direction" knobs "Manual Speed" knob "False Signals" button "Gyrocompass - Off" toggle switch Toggle switch "Antenna - Off." | "Off" Leftmost Average Average Average Leftmost Average Average In the factory-fixed "Course" Enabled Average 0 on a digitized scale 0 on a digitized scale Enabled "Off" "Off" |
The rest of the controls can remain in any position.
Switching on the station.
The on-board network voltage switch is set to the “On” position (the power unit starts)
On the indicator:
Switch "Radar - off." set to the position of the radar
Toggle switch "Antenna - off." set to Antenna.
Turn on the operational button P - 3 (in this case, the scale mechanism and explanatory inscriptions should be illuminated).
After 1.5 ÷ 2.5 min. on the screen of the CRT should appear a rotating scan, a course mark, range marks and a line of sight of the direction.
After 4 minutes, a probing pulse mark and marks of objects in the radar field of view should appear.
Using the appropriate controls, choose the optimal brightness of the HV; VD; MD; and the position of the Wave.
The transceiver is turned on with a push button switch. (6)
Orientation of the image relative to the true meridian (north) or relative to the center plane of the ship (heading) in the relative motion mode is carried out by switch 30, setting it to the "north" or "heading" position. The same switch, setting it to the "North - ID" position, provides a mode of true movement on a scale of scales 1; 2; 4; 8 miles.
The sweep center is shifted to the selected point by potentiometers (33)
The beginning (center) of the sweep is returned to the center of the CRT with buttons 31 and 32.
Own ship speed data can be entered manually (35)
Drift correction for current is entered by potentiometer (35)
To eliminate false marks due to overreaction, a change in the frequency of probing pulses is provided (24)
The handle of the resistor "panel illumination" (1) adjusts the brightness of the indication: "reset to the center"; "false signals"; "miles"; "degrees".
The handle of the resistor "scale illumination" adjusts the brightness of the "scale - interval" indication.
Digital indication of the distance measured to the target and direction indication is carried out on digital displays TsT - 3 and TsT - 4 (3; 5)
Radar performance monitoring is carried out by a built-in system that provides general performance monitoring and troubleshooting (16; 17; 18; 19;)
They are convinced of the possibility of: controlling the VD range finders and the VN direction, as well as turning off the course mark and changing the scale by switching the range scales.
Check: alignment of the beginning of the sweep with the center of the screen (according to two mutually perpendicular positions of the direction finder on the 4-mile scale). The operability of the image orientation scheme (the gyrocompass is turned off, the switch "heading - north - north ID" is set alternately in the "heading" and "north" positions, making sure that the heading mark, at the same time, changes its position). After that, set the toggle switch to the “gyrocompass” position and make sure that the position of the course line corresponds to the readings of the GK repeater.
They check the shift of the center of rotation of the sweep in the OD mode (the "reset to center" handle is set to the off position, the "centre shift" handle smoothly moves the center of the sweep to the left and right by 2/3 of the CRT radius, all this is done by 1; 2; 4; 8 mile range scales when oriented alternately along the "course" and "north").
Using the "reset to center" button, I again combine the scan center with the center of the "CRT screen".
They check the indicator for operation in ID mode for which: set the switch to the "north - ID" mode, the range scale is 1 mile, turn off the log and gyrocompass, the "drift accounting" knob to zero position, manually set an arbitrary speed value, using the "reset" button to the center” make sure that the start of the sweep on the screen moves along the course at the set speed. When the movement reaches 2/3 of the CRT radius, the sweep center should automatically return to the center of the screen. The return of the beginning of the sweep to the starting point must also be ensured manually by pressing the "reset" button.
Using the “drift accounting” knobs, enter an arbitrary value of corrections for the course and speed, and make sure that the parameters for moving the start of the sweep on the CRT screen change.
The switch "course - north - north ID" is set to the position "course" or "north". In this case, the beginning of the sweep should move to the center of the screen and the OD mode should turn on. The same should happen when setting the range scales to 16; 32; 64 miles.
They check the manual offset of the start of the sweep in ID mode: turn off the "reset to center" button, set the "center offset" controls to a position that provides a shift of the start of the sweep by less than 2/3 of the CRT radius, press the "reset" button, and make sure that the center sweep moved to the selected point, and began to move to given direction. Having shifted by 2/3 of the screen radius, the sweep center automatically returns to the selected point.
Station health monitoring is carried out by a built-in system that provides monitoring and troubleshooting. The system consists of elements that are separate nodes in the devices and the station unit.
The operability of the device P - 3 is controlled using the block NK - 3 located in it, which checks the serviceability of power sources and functional blocks and assemblies.
The control of the operability of the AND device, the search for a faulty power source or functional block is carried out using the built-in control unit located on the control panel of the AND device.
THE STATION IS SHUT DOWN:
Removing power with the toggle switch "Radar - off."
Turning off the voltage of the on-board network (button "stop" of the starter)
· Disconnection of voltage from communication elements with log and gyrocompass.
Radar station
Request "Radar" is redirected here; for the register of medicinal products, see Register of medicinal products.
Radar station(radar) or radar(English) radar from RA dio D etection A nd R anging- radio detection and ranging) - a system for detecting air, sea and ground objects, as well as for determining their range, speed and geometric parameters. It uses a method based on the emission of radio waves and the registration of their reflections from objects. The English term-acronym appeared in 1941, subsequently, in its spelling, uppercase letters were replaced by lowercase ones.
Story
In the USSR and Russia
In the Soviet Union, the realization of the need for means of detecting aircraft, free from the shortcomings of sound and optical observation, led to the development of research in the field of radar. The idea proposed by the young artilleryman Pavel Oshchepkov was approved by the high command: the People's Commissar of Defense of the USSR K. E. Voroshilov and his deputy - M. N. Tukhachevsky.
In 1946, American specialists - Raymond and Hucherton, former employee the US Embassy in Moscow, wrote: "Soviet scientists successfully developed the theory of radar several years before the radar was invented in England."
Classification
According to the scope of application, there are- military;
- civil;
- detection radar;
- control and tracking radar;
- Panoramic radars;
- side-looking radar;
- Meteorological radars;
- targeting radar;
- Situation review radar;
- Coastal radars
- Marine radars
- Airborne radar
- Mobile radars
- Primary or passive
- Secondary or active
- Combined
- Over-the-horizon radar
- Meter
- decimeter
- centimeter
- Millimeter
The device and principle of operation of the Primary radar
Primary (passive) radar mainly serves to detect targets by illuminating them with an electromagnetic wave and then receiving reflections (echoes) of this wave from the target. Because the speed electromagnetic waves constant (the speed of light), it becomes possible to determine the distance to the target based on the measurement of various signal propagation parameters.
At the heart of the device of the radar station are three components: transmitter, antenna and receiver.
Transmitter(transmitting device) is a high power electromagnetic signal source. It can be a powerful pulse generator. For centimeter-range pulse radars, it is usually a magnetron or a pulse generator operating according to the scheme: a master oscillator is a powerful amplifier that most often uses a traveling wave lamp as a generator, and for a meter-range radar, a triode lamp is often used. Depending on the design, the transmitter either operates in a pulsed mode, generating repetitive short powerful electromagnetic pulses, or emits a continuous electromagnetic signal.
Antenna performs focusing of the transmitter signal and beamforming, as well as receiving the signal reflected from the target and transmitting this signal to the receiver. Depending on the implementation, the reception of the reflected signal can be carried out either by the same antenna, or by another, which can sometimes be located at a considerable distance from the transmitting device. In the event that transmission and reception are combined in one antenna, these two actions are performed alternately, and so that a powerful signal leaking from the transmitting transmitter to the receiver does not blind the weak echo receiver, a special device is placed in front of the receiver that closes the receiver input at the moment the probing signal is emitted.
Receiver (receiving device) performs amplification and processing of the received signal. In the very simple case the resulting signal is fed to a ray tube (screen), which displays an image synchronized with the movement of the antenna.
Different radars are based on different methods of measuring the reflected signal:
frequency method
The frequency method of distance measurement is based on the use of frequency modulation of emitted continuous signals. In this method, a frequency is emitted over a period, changing linearly from f1 to f2. The reflected signal will arrive modulated linearly at a point in time preceding the present by the delay time. That. the frequency of the reflected signal received at the radar will depend proportionally on time. The lag time is determined by the abrupt change in frequency of the difference signal.
Advantages:
- allows you to measure very short ranges;
- a low-power transmitter is used;
Flaws:
- two antennas are required;
- deterioration of the receiver sensitivity due to leakage through the antenna into the receiving path of the radiation of the transmitter, subject to random changes;
- high requirements for linearity of frequency change;
These are its main shortcomings.
Phase Method
The phase (coherent) radar method is based on the selection and analysis of the phase difference between the sent and reflected signals, which occurs due to the Doppler effect, when the signal is reflected from a moving object. In this case, the transmitting device can operate both continuously and in a pulsed mode. Main advantage this method is that it "allows you to observe only moving objects, and this excludes interference from stationary objects located between the receiving equipment and the target or behind it."
Since ultrashort waves are used in this case, the unambiguous range of measuring range is about a few meters. Therefore, in practice, more complex circuits are used, in which there are two or more frequencies.
Advantages:
- low-power radiation, since undamped oscillations are generated;
- accuracy does not depend on the Doppler shift of the reflection frequency;
- a fairly simple device;
Flaws:
- lack of range resolution;
- deterioration of the sensitivity of the receiver due to penetration through the antenna into the receiving path of the radiation of the transmitter, subject to random changes;
Pulse Method
Modern tracking radars are built as impulse radars. Pulse radar only transmits an emitting signal for a very short time, in a short pulse (usually about a microsecond), after which it goes into receive mode and listens for an echo reflected from the target, while the emitted pulse propagates in space.
Since the pulse travels far from the radar at a constant speed, the time elapsed from the moment the pulse was sent until the moment the echo was received is a direct relationship to the distance to the target. The next pulse can be sent only after some time, namely after the pulse comes back (this depends on the radar detection range, transmitter power, antenna gain, receiver sensitivity). If the pulse is sent earlier, then the echo of the previous pulse from a distant target may be confused with the echo of the second pulse from a close target.
The time interval between pulses is called pulse repetition interval, its reciprocal is an important parameter, which is called pulse repetition frequency(PPI) . Long range low frequency radars typically have a repetition interval of several hundred pulses per second. The pulse repetition frequency is one of the hallmarks by which it is possible to remotely determine the radar model.
Advantages of the pulsed ranging method:
- the possibility of building a radar with one antenna;
- simplicity of the indicator device;
- convenience of measuring the range of several targets;
- the simplicity of the emitted pulses, lasting a very short time, and the received signals;
Flaws:
- The need to use large transmitter pulse powers;
- the impossibility of measuring short ranges;
- large dead zone;
Elimination of passive interference
One of the main problems of pulse radars is getting rid of the signal reflected from stationary objects: earth's surface, high hills, etc. If, for example, the aircraft is against the background of a high hill, the reflected signal from this hill will completely block the signal from the aircraft. For ground-based radars, this problem manifests itself when working with low-flying objects. For airborne pulse radars, it is expressed in the fact that the reflection from the earth's surface obscures all objects lying below the aircraft with the radar.
Interference elimination methods use, one way or another, the Doppler effect (the frequency of a wave reflected from an approaching object increases, from a departing object it decreases).
The simplest radar that can detect a target in interference is moving target radar(MPD) - pulsed radar that compares reflections from more than two or more pulse repetition intervals. Any target that appears to be moving relative to the radar produces a change in the signal parameter (stage in serial SDM), while the clutter remains unchanged. Interference is eliminated by subtracting reflections from two successive intervals. In practice, the elimination of interference can be carried out in special devices - through period compensators or algorithms in software.
FCRs operating at a constant pulse repetition rate have a fundamental weakness: they are blind to targets with specific circular velocities (which produce phase changes of exactly 360 degrees), and such targets are not displayed. The speed at which the target disappears for the radar depends on the operating frequency of the station and on the pulse repetition rate. Modern MDCs emit multiple pulses at different repetition rates - such that the invisible speeds at each pulse repetition rate are covered by other PRFs.
Another way to get rid of interference is implemented in pulse-doppler radar, which use significantly more complex processing than SDC radars.
An important property of pulse-Doppler radars is signal coherence. This means that the sent signals and reflections must have a certain phase dependence.
Pulse-Doppler radars are generally considered better than MDS radars in detecting low-flying targets in multiple ground clutter, this is the preferred technique used in modern fighter aircraft for aerial interception/fire control (AN/APG-63, 65, 66, 67 and 70 radars). In modern Doppler radar, most of the processing is done by a separate processor in digital form with the help of digital signal processors, usually using the high performance Fast Fourier Transform algorithm to convert the digital reflection sample data into something more manageable by other algorithms. Digital signal processors are very flexible, since the algorithms used in them can be quickly replaced by others, by changing only the program in the device’s memory (“ROM firmware”), thus, if necessary, quickly adapting to the enemy’s jamming technique.
Radar ranges
| Range | Etymology | Frequencies | Wavelength | Notes |
|---|---|---|---|---|
| HF | English high frequency | 3-30 MHz | 10-100 m | Coast Guard radars, "over-the-horizon" radars |
| P | English previous | < 300 МГц | > 1 m | Used in early radars |
| VHF | English very high frequency | 50-330 MHz | 0.9-6 m | Long range detection, Earth exploration |
| UHF | English ultra high frequency | 300-1000 MHz | 0.3-1 m | Detection at long ranges (for example, artillery shelling), forest surveys, the Earth's surface |
| L | English Long | 1-2 GHz | 15-30 cm | air traffic surveillance and control |
| S | English short | 2-4 GHz | 7.5-15 cm | air traffic control, meteorology, maritime radar |
| C | English Compromise | 4-8 GHz | 3.75-7.5 cm | meteorology, satellite broadcast, intermediate range between X and S |
| X | 8-12 GHz | 2.5-3.75 cm | weapons control, missile guidance, maritime radar, weather, medium resolution mapping; in the US, the 10.525 GHz ± 25 MHz band is used in airport radar | |
| K u | English under K | 12-18 GHz | 1.67-2.5 cm | mapping high definition, satellite altimetry |
| K | German kurz- "short" | 18-27 GHz | 1.11-1.67 cm | use is limited due to strong absorption by water vapor, so the K u and K a ranges are used. The K band is used for cloud detection, in police traffic radars (24.150 ± 0.100 GHz). |
| K a | English above K | 27-40 GHz | 0.75-1.11 cm | Mapping, short range air traffic control, special radars controlling traffic cameras (34.300 ± 0.100 GHz) |
| mm | 40-300 GHz | 1-7.5mm | millimeter waves are divided into two following ranges | |
| V | 40-75 GHz | 4.0-7.5mm | EHF medical devices used for physiotherapy | |
| W | 75-110 GHz | 2.7-4.0mm | sensors in experimental automatic vehicles, high-precision weather research |
secondary radar
"Secondary radar" is used in aviation to identify aircraft. The main feature is the use of an active transponder on aircraft.
The principle of operation of the secondary radar is somewhat different from the principle of the Primary radar. The device of the Secondary Radar Station is based on the components: transmitter, antenna, azimuth mark generators, receiver, signal processor, indicator and aircraft transponder with antenna.
Transmitter- serves to emit request pulses to the antenna at a frequency of 1030 MHz
Antenna- serves to emit and receive the reflected signal. According to ICAO standards for secondary radar, the antenna transmits at a frequency of 1030 MHz and receives at a frequency of 1090 MHz.
Bearing marker generators- serve to generate azimuth marks (Azimuth Change Pulse or ACP) and generating marks of the North (Azimuth Reference Pulse or ARP). For one turn radar antennas 4096 small azimuth marks are generated (for older systems) or 16384 small azimuth marks (for new systems, they are also called improved small azimuth marks (Improved Azimuth Change pulse or IACP), as well as one mark of the North. The north mark comes from the generator of azimuth marks at in such a position of the antenna when it is directed to the North, and small azimuth marks serve to read the angle of rotation of the antenna.
Receiver- serves to receive pulses at a frequency of 1090 MHz.
signal processor- serves to process the received signals.
Indicator- serves to display the processed information.
Aircraft transponder with antenna- serves to transmit a pulsed radio signal containing additional information back to the side of the radar upon receipt of a request radio signal.
The principle of operation of the secondary radar is to use the energy of the aircraft transponder to determine the position of the aircraft. The radar irradiates the surrounding area with interrogation pulses at a frequency of P1 and P3, as well as a P2 suppression pulse at a frequency of 1030 MHz. Transponder-equipped aircraft located in the interrogation beam coverage area, upon receiving interrogation pulses, if the condition P1,P3>P2 is in effect, respond to the requesting radar with a series of coded pulses at a frequency of 1090 MHz, which contain Additional Information about the side number, height and so on. The response of the aircraft transponder depends on the radar request mode, and the request mode is determined by the time interval between the request pulses P1 and P3, for example, in request mode A (mode A), the time interval between the request pulses of the station P1 and P3 is 8 microseconds and upon receipt of such a request, the transponder aircraft encodes its aircraft number in the response pulses.
In interrogation mode C (mode C), the time interval between the interrogation pulses of the station is 21 microseconds, and upon receipt of such a request, the transponder of the aircraft encodes its height in the response pulses. The radar can also send an interrogation in a mixed mode, such as Mode A, Mode C, Mode A, Mode C. The azimuth of the aircraft is determined by the angle of rotation of the antenna, which in turn is determined by counting small azimuth marks.
The range is determined by the delay of the incoming response. If the aircraft is in the coverage area of the side lobes, and not the main beam, or is behind the antenna, then the aircraft transponder, upon receiving a request from the radar, will receive at its input the condition that pulses P1, P3 The signal received from the transponder is processed by the radar receiver, then it goes to the signal processor, which processes the signals and outputs information to the end user and (or) to the control indicator. Advantages of a secondary radar: Radio waves sent into space propagate in it at the speed of light. But as soon as they meet some object on their way, for example, an airplane or a ship, they are reflected from it and come back. Therefore, they can be used to detect various remote objects, observe them and determine their coordinates and parameters. Detecting the location of objects using radio waves is called radar. Alexander Stepanovich Popov
In 1897, during experimental radio communication sessions between the sea transport "Europe" and the cruiser "Africa", conducted by the Russian physicist Alexander Stepanovich Popov, an interesting phenomenon was discovered. It turned out that the correctness of the propagation of an electromagnetic wave was distorted by all metal objects - masts, pipes, tackle both on the ship from which the signal was sent, and on the ship where it was received. When the cruiser Lieutenant Ilyin appeared between these ships, the radio communication between them was broken. So the phenomenon of reflection of radio waves from the hull of the ship was discovered. But if radio waves are capable of being reflected from a ship, then ships can be detected with their help. And also other goals. And already in 1904, the German inventor Christian Hülsmeier applied for the first radar, and in 1905 he received a patent for using the effect of reflection of radio waves to search for ships. And a year later, in 1906, he proposed using this effect to determine the distance to an object that reflects radio waves. Christian Hülsmeier
In 1934, the Scottish physicist Robert Alexander Watson-Watt received a patent for the invention of a system for detecting airborne objects and demonstrated one of the first such devices the following year. Robert Alexander Watson-Watt
Locating something called location. For this, a device called locator. The locator emits some form of energy, such as sound or an optical signal, towards the intended object, and then receives the signal reflected from it. Radar uses radio waves for this purpose. In fact, a radar, or radar station (RLS), is a complex system. The designs of different radars may vary, but the principle of their operation is the same. A radio transmitter sends radio waves into space. Having reached the goal, they are reflected from it, as from a mirror, and come back. Such radar is called active. The main components of the radar (RLS) - transmitter, antenna, antenna switch, receiver, indicator. According to the method of radiation of radio waves, radars are divided into pulsed and continuous action. How does a pulse radar station work? The radio wave transmitter turns on for a short time, so radio waves are emitted in pulses. They enter the antenna, which is located at the focus of a paraboloid-shaped mirror. This is necessary in order for the radio waves to propagate in a certain direction. The work of the radar is similar to the work of a spotlight, the rays of which are directed in the same way into the sky and, illuminating it, look for the desired object. But the work of the spotlight is limited to this. And the radar not only sends radio waves, but also receives a signal reflected from the found object (radio echo). This function is performed by the receiver. The pulse radar antenna works either for transmitting or for receiving. It has a switch for that. Once the radio signal is sent, the transmitter turns off and the receiver turns on. There comes a pause, during which the radar, as it were, “listens” to the air and waits for a radio echo. And as soon as the antenna picks up the reflected signal, the receiver immediately turns off and the transmitter turns on. And so on. Moreover, the pause time can be many times greater than the pulse duration. Thus, the emitted and received signals are separated in time. The received radio signal is amplified and processed. The indicator, which in the simplest case is a display, displays processed information, for example, the size of an object or the distance to it, or the target itself and its surroundings. Radio waves travel through space at the speed of light. Therefore, knowing the time t
from emitting a radio signal pulse to returning it, you can determine the distance to an object. R=
cˑ
t/2
, Where With
is the speed of light. Continuous radar
emits high frequency radio waves continuously. Therefore, the antenna also captures a continuous reflected signal. In their work, such radars use the Doppler effect. The essence of this effect is that the frequency of the signal reflected from an object moving towards the radar is higher than the frequency of the signal reflected from an object moving away from it, despite the fact that the frequency of the emitted signal is constant. Therefore, such radars are used to determine the parameters of a moving object. An example of a radar based on the Doppler effect is a radar used by traffic police to determine the speed of a moving car. In search of an object, the directional beam of the radar antenna scans the space, describing a full circle, or choosing a specific sector. It can be directed along a helix, in a spiral. The view can also be conical or linear. It all depends on the task he has to perform. If it is necessary to constantly monitor the selected moving target, the radar antenna is constantly directed at it and rotates after it with the help of special tracking systems. For the first time, radar stations began to be used during the Second World War to detect military aircraft, ships and submarines. So at the end of December 1943, the radars installed on British ships helped to detect the Nazi battleship, which left the port of Altenfjord in Norway at night to intercept warships. The fire on the battleship was carried out very accurately, and soon she went to the bottom. The first radars were not very perfect, unlike modern ones, which reliably protect airspace from air raids and missile attacks, recognizing almost any military installations on land and at sea. Radar guidance is used in homing missiles for terrain recognition. Radars monitor the flights of intercontinental missiles. Radars have found their application in civilian life. Pilots guiding ships through narrow straits, airport dispatchers directing the flights of civil aircraft cannot do without them. They are indispensable when sailing in conditions of limited visibility - at night or in bad weather. With their help, the relief of the bottom of the seas and oceans is determined, and pollution of their surfaces is studied. They are used by meteorologists to determine thunderstorm fronts, measure wind and cloud speeds. On fishing boats, radar helps locate schools of fish. Very often, radars, or radar stations (RLS), are called radars. And although now this word has become independent, in fact it is an abbreviation that arose from the English words " radiodetectionandranging », which means "radio detection and ranging" and reflects the essence of radar. The radar consists of the following main elements: transmitting device; receiving device; Antenna switch and antenna device; terminal device; Synchronizer. The block diagram of the radar is shown in Figure 5.2. Fig.5.2 Structural diagram of the radar station. Transmitting device The radar is designed to generate a probing signal and transmit it to the antenna. receiving device The radar is designed for preliminary processing of the reflected signal received by the antenna. It extracts a useful signal from a mixture of signal and interference, converts the radio signal into a video signal and transmits it to the terminal device. Antenna switch designed to connect the transmitter to the antenna when emitting a probing signal and connect the receiver to the antenna when receiving the reflected signal. terminal device to analyze the useful signal. The type of terminal device depends on the type of signal (analogue or digital), the recipient of the radar information (operator, automatic positioning device, computer, etc.) and the type of radar information. Synchronizer provides a given sequence of operation of the radar elements. So, for example, in the most common radars with a pulsed mode of operation, the synchronizer performs the following functions: Coordination of the moment of formation of the probing pulse with the moment of the start of the time base of the indicator or the zero count of the computing device; Coordination of the position of the antenna pattern in space with the sweep of the indicator or the zero reading of the computing device; Determination of the moment of opening the receiver and the interval of its operation. In this case, the following synchronization methods are fundamentally possible: 1. Synchronization from the transmitter to the terminal device. In such radars, the moment of formation of the probing pulse determines the moment of the start of the time sweep of the indicator or the moment of resetting the computing device. The advantage of this method of synchronization is that the instability of the repetition rate of the probing pulses of the transmitter does not affect the accuracy of radar measurements. However, such radars are characterized by the instability of the launch of the terminal device, which is difficult to completely eliminate. 2. Synchronization from the terminal device to the transmitter. In this case, the operation of the terminal and transmitter is controlled by a highly stable generator, which is part of the terminal. Due to this, high accuracy of radar measurements is achieved. However, problems arise when changing the repetition rate of probing pulses. 3. Synchronization using a separate high-stability crystal oscillator that is not part of the transmitting or terminal device. This synchronization method is used in most modern radars, which usually provide for the possibility of changing the repetition rate of probing pulses during the operation of the station. This is necessary to ensure the noise immunity of the radar when operating in conditions of passive or active radar interference. The block diagram of the radar mainly depends on its purpose, the type of probing signal (pulse or continuous) and the modulated parameter of the radio signal. However, in the general case, the procedure for processing a radio signal in a radar station must be consistent not only with the type of probing signal, but also with the type of interference. Therefore, the block diagram of the radar should take into account the sources of active and passive electronic interference. This task complicates the work of any radar, because. interference causes distortion of the signal reflected from the target and leads to the loss of useful radar information. Therefore, in the process of processing the reflected signal, they seek to suppress interference, which is achieved by introducing electronic interference protection devices into the radar block diagram.see also
Literature
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Notes
Soviet and Russian radar stations
Radar of the Radio Engineering Troops
"RUS-1" "RUS-2" "P-3" P-8 Volga "P-10 Volga-A" P-14 P-18 Terek P-20 P-30 P-35 Drainage P-37 P-40 P-70 Lena-M "Resonance-N(E)" "Ring" "Casta" "5N59.19ZH6.35D6 / 36D6""Casta-2E" "Gamma-C1E" "Gamma-DE" "Defense-14""5N87" "Desna-M" "Enemy-GE"
radio altimeters
"PRV-9" "PRV-10" "PRV-11" "PRV-13" "PRV-16""PRV-17"
Special SAM radars
P-15 P-19 1L117M Desna-M 76N6 96L6E
Long range radar stations
Dnepr Dnestr-M Daryal Krona Danube Don-2N Duga 1 Volga Voronezh-M/DM Vitim
Aviation radars
Gneiss-2 Gneiss-5 RP-5 Izumrud-5 Liana Vega-M Bumblebee E-801 Oko N007 Barrier N010 Zhuk ( 8-II / 27 / M(S)(E) / (M)F(E) / A(E)) H011 Bars ( M/29) H035 Irbis H050
Shipborne radars
Redoubt-K Guys-1 Guys-2 Neptun Fut-N Reef Don P-500 Frigate Boletus Fourke Monument-A Pal-N 3Р41 3Р95 Flag Tackle
Counter-battery and other radars
Zoo Stork Farah Credo
Coastal radars
How did radiolocation come about?
How Radar Works
The use of radar
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