The purpose of the radar. Radar stations: history and basic principles of work. Accuracy of determination of coordinates by range

Modern wars are distinguished by their swiftness and transience. Often the winners in combat encounters are those who were the first to detect potential threats and react accordingly. For eighty years now, radar methods have been used for reconnaissance and recognition of the enemy at sea and on land, as well as in airspace.

They are based on the emission of radio waves with the registration of their reflections from a wide variety of objects. Installations that send and receive such signals are modern radar stations or radars. The concept of "radar" comes from the English abbreviation - RADAR. It appeared in 1941 and has long been included in the languages ​​of the world.

The advent of radar was a landmark event. In the modern world, it is almost impossible to do without radar stations. Aviation, navigation, hydrometeorological center, traffic police, etc. cannot do without them. Moreover, the radar complex is widely used in space technologies and in navigation systems.

Radar in military service

Yet most of all, the military liked the radars. Moreover, these technologies were originally created for military use and were practically implemented before the Second World War. All major states actively used radar to detect enemy ships and aircraft. Moreover, their use decided the outcome of many battles.

To date, new radar stations are used in a very wide range of military tasks. This includes tracking intercontinental ballistic missiles and artillery reconnaissance. All planes, helicopters, warships have their own radar. Radars are generally the basis of air defense systems.

How Radars Work

Location is the definition of where something is. Thus, radar is the detection of objects or objects in space using radio waves that are emitted and received by a radar or radar. The principle of operation of primary or passive radars is based on the transmission into space of radio waves reflected from objects and returned to them in the form of reflected signals. After analyzing them, radars detect objects at certain points in space, their main characteristics in the form of speed, height and size. All radars are complex radio engineering devices made up of many elements.

Modern radar complex

Any radar consists of three main elements:

• signal transmitters;
• Antennas;
• Receivers.

Of all the radar stations, there is a special division into two large groups:

• Pulse;
• Continuous action.

Pulse radar transmitters emit electromagnetic waves for short periods of time (fractions of a second). The next signals are sent only when the first pulses come back and hit the receivers. The pulse repetition rates are also the most important characteristics. So low-frequency radars send more than one hundred pulses within a minute.

Pulse radar antennas work like transmitters and receivers. As soon as the signals are gone, the transmitters turn off for a while and the receivers turn on. Following their reception, reverse processes occur.

Pulse radars have their own advantages and disadvantages. They can determine the range of several targets at the same time. Such radars may have one antenna each, and their indicators are quite simple.

However, the emitted signals must be of high power. All modern tracking radars have a pulse circuit. Pulse radar stations usually use magnetrons or traveling wave tubes as signal sources.

Pulse radar systems

Radar antennas focus and direct electromagnetic signals, as well as pick up reflected pulses and transmit them to receivers. In some radars, signals can be received and transmitted using different antennas located at large distances from one another. Radar antennas can emit electromagnetic waves in a circle or operate in certain sectors.

Radar beams can be directed spirally or have cone shapes. If necessary, radars can track moving targets, and all the time direct antennas at them using special systems. The receivers process the received data and transfer it to the screens of the operators.

One of the main shortcomings in the operation of pulsed radars is interference coming from immovable objects, from the earth's surface, mountains, hills. Thus, airborne pulsed radars, in the course of their operation in aircraft, will receive shadows from signals reflected by the earth's surface. Ground-based or shipborne radar systems identify these problems in the process of detecting targets that fly at low altitudes. To eliminate such interference, the Doppler effect is used.

Continuous radar

Continuous radars operate by constantly emitting electromagnetic waves and use the Doppler effect. Its principle is that the frequencies of electromagnetic waves reflected from objects approaching signal sources will be higher than from receding objects. In this case, the frequencies of the emitted pulses remain unchanged. Such radars do not detect stationary objects; their receivers pick up only waves with frequencies above or below those emitted.

The main disadvantage of continuous action radars is their inability to determine distances to objects. However, during their operation, there is no interference from stationary objects between the radars and targets, or behind them. Also, Doppler radars have a relatively simple device, which will have enough signals with low power to function. In addition, modern continuous-wave radars have the ability to determine distances to objects. To do this, changes in the frequencies of the radars in the course of their action are applied.

It is also known about the so-called secondary radars used in aviation to identify aircraft. In such radar systems, there are also aircraft transponders. During the exposure of aircraft to electromagnetic signals, the transponders provide additional data, such as altitude, route, aircraft number, and nationality.

Varieties of radar stations

Radars can be separated by the length and frequency of the waves they operate on. In particular, when the earth's surface is being studied and when working at long distances, waves of 0.9-6 m and 0.3-1 m are used. In air traffic control, radars with a wavelength of 7.5-15 cm are used, and in over-the-horizon radars at stations for detecting missile launches, 10-100-meter waves are used.

From the history of the development of radar

The idea of ​​using radar arose after the discovery of radio waves. So, in 1905, an employee of Siemens, Christian Hülsmeyer, created a device that, using radio waves, could detect the presence of large metal objects. The inventor proposed to install such devices on ships in order to avoid collisions, for example, in fogs. However, no interest in the new device was expressed in the shipping companies.

Radar studies were also carried out on the territory of Russia. So, at the end of the 19th century, the Russian scientist Popov discovered that the presence of metal objects prevents the propagation of radio waves.

In the early twenties, American engineers Albert Taylor and Leo Young discovered a passing ship using radio waves. However, due to the fact that the radio engineering industry of that time was undeveloped, it was not possible to create radar stations on an industrial scale.

The production of the first radar stations, with the help of which practical problems would be solved, began in England in the 30s. This equipment was extremely bulky and could be installed either on the ground or on large ships. It was only in 1937 that the first miniature radar was created that could be installed on aircraft. As a result, before the Second World War, the British had an extensive network of radar stations called Chain Home.

Cold War Radars

At times cold war in the United States and in the Soviet Union, a new type of destructive weapon appeared. Of course, this was the appearance of intercontinental ballistic missiles. Timely detection of launches of such missiles was vital.

Soviet scientist Nikolai Kabanov proposed the idea of ​​using short radio waves to detect enemy aircraft at considerable distances (up to 3,000 km). Everything was simple enough. The scientist was able to find that 10-100-meter radio waves have a predisposition to reflection from the ionosphere.

Thus, when irradiating targets on the earth's surface, they also return back to the radars. Later, based on this idea, scientists were able to develop radars with over-the-horizon detection of ballistic missile launches. An example of such installations can be "Daryal" - a radar station. For decades, it was at the heart of Soviet missile launch warning systems.

To date, the most promising direction in the development radar systems considered to be the creation of radar stations with phased antenna arrays (PAR). Such devices have not one, but hundreds of radio wave emitters. All their functioning is controlled by powerful computers. The radio waves emitted by different sources in the PAR can be amplified one by one, or vice versa, when they are in phase or attenuated.

Phased array radar signals can be given any desired shape. They can move in space in the absence of changes in the positions of the antennas themselves, and also operate at different radiation frequencies. Phased array radars are considered more reliable and more sensitive than the same devices with conventional antennas.

However, such radars also have disadvantages. by the most big problems in radar stations with HEADLIGHTS are their cooling systems. Moreover, such radar installations are extremely complex in the production process, as well as very expensive.

Radar complexes with PAR

What is known about the new phased array radars is that they are already being installed on fifth-generation fighters. Such technologies are used in American systems with early warning of missile attacks. Radar systems with HEADLIGHTS are supposed to be installed on "Armata" - newest tanks Russian production. Many experts note that the Russian Federation is one of the world leaders successfully developing radar stations with phased array.

The principle of operation of a pulse radar can be understood by considering the “Simplified block diagram of a pulse radar (Fig. 3.1, slide 20, 25 ) and graphs explaining the operation of a pulse radar (Fig. 3.2, slide 21, 26 ).

The operation of a pulse radar is best considered from the synchronization unit (launch unit) of the station. This block sets the “rhythm” of the station operation: it sets the frequency of repetition of probing signals, synchronizes the operation of the indicator device with the operation of the station transmitter. The synchronizer generates short-term spiked pulses And zap with a certain repetition rate T P. Structurally, the synchronizer can be made in the form of a separate unit or represent a single unit with the station modulator.

Modulator controls the operation of the microwave generator, turns it on and off. The modulator is triggered by synchronizer pulses and generates powerful rectangular pulses of the required amplitude U m and duration τ and. The microwave generator is switched on only in the presence of modulator pulses. The switching frequency of the microwave generator, and, consequently, the repetition frequency of the probing pulses is determined by the frequency of the synchronizer pulses T P. The duration of the microwave generator operation each time it is turned on (that is, the duration of the probing pulse) depends on the duration of the pulse shaping in the modulator τ and. Modulator pulse duration τ and usually amounts to units of microseconds, and the pauses between them are hundreds and thousands of microseconds.

Under the action of the modulator voltage, the microwave generator generates powerful radio pulses U gene, the duration and shape of which is determined by the duration and shape of the modulator pulses. High-frequency oscillations, that is, probing pulses from the microwave generator, enter the antenna through the antenna switch. The oscillation frequency of radio pulses is determined by the parameters of the microwave generator.

Antenna switch (AP) provides the ability to operate the transmitter and receiver on one common antenna. During the generation of the probing pulse (µs), it connects the antenna to the transmitter output and blocks the receiver input, and for the rest of the time (pause time - hundreds, thousands of µs) it connects the antenna to the receiver input and disconnects it from the transmitter. In a pulse radar, automatic high-speed switches are used as antenna switches.

The antenna converts microwave oscillations into electromagnetic energy (radio waves) and focuses it into a narrow beam. Signals reflected from the target are received by the antenna, pass through the antenna switch and are fed to the input of the receiver U With, where they are selected, amplified, detected and fed through the anti-interference equipment to indicator devices.

Anti-interference equipment is activated only if there are passive and active interference. This equipment will be studied in detail in topic 7.

The indicator device is the terminal device of the radar and serves to display and read radar information. The electrical circuit and design of indicator devices is determined by the practical purpose of the station and can be very different. For example, for radar detection using indicator devices, the air situation should be reproduced and the coordinates of targets D and β should be determined. These indicators are called Around View Indicators (PPIs). Altitude indicators are used in target altitude measurement radars (altimeters). Range indicators measure only the range to the target and are used for control purposes.

To accurately determine the range, it is necessary to measure the time interval t h(tens and hundreds of microseconds) with high accuracy, that is, devices with a very low inertia are required. Therefore, in range indicators, cathode ray tubes (CRTs) are used as measuring instruments.

Note. The principle of range measurement was studied in lesson 1, therefore, when studying this issue, the main attention should be paid to the formation of a sweep on the PPI.

The essence of range measurement (delay time t h) using a CRT can be explained by the example of using a linear sweep in a tube with an electrostatically controlled electron beam.

With a linear sweep in a CRT, an electron beam under the action of a sweep voltage U R periodically moves at a constant speed in a straight line from left to right (Fig. 1.7, slide 9, 12 ). The sweep voltage is generated by a special sweep generator, which is triggered by the same synchronizer pulse as the transmitter modulator. Therefore, the motion of the beam across the screen begins each time the probing pulse is sent.

When using the target height mark, the reflected signal coming from the output of the receiver causes the beam to deviate in a perpendicular direction. Thus, the reflected signal can be seen on the screen of the tube. The farther the target is, the more time passes until the reflected pulse appears and the farther to the right the beam has time to move along the scan line. Obviously, each point of the scan line corresponds to a certain moment of arrival of the reflected signal and, consequently, a certain range value.

Radars operating in all-round view mode use all-round view indicators (PICO) and CRT with electromagnetic beam deflection and brightness mark. The radar antenna with a narrow beam (DN) is moved by the antenna rotation mechanism in the horizontal plane and "views" the surrounding space (Fig. 3.3, slide,

At the PPI, the range sweep line rotates in azimuth synchronously with the antenna, and the beginning of the electron beam movement from the center of the tube in the radial direction coincides with the moment of emission of the probing pulse. Synchronous rotation of the sweep on the IKO with the radar antenna is carried out using a power synchronous drive (SSP). The response signals are displayed on the indicator screen in the form of a brightness mark.

PPI allows you to simultaneously determine the range D and azimuth β goals. For convenience of counting on the PPI screen electronically distance scale marks are applied, having the form of circles and azimuth scale marks in the form of bright radial lines (Fig. 3.3, slide, 8, 27 ).

Note. Using a television set and a TV card, invite students to determine the coordinates of the targets. Specify the scale of the indicator: range marks follow after 10 km, azimuth marks - after 10 degrees.

CONCLUSION

(slide 28)

Determining the distance to an object with the impulse method is reduced to measuring the delay time t h of the reflected signal relative to the probing pulse. The moment of emission of the probing pulse is taken as the origin of the radio wave propagation time.

Advantages of pulse radar:

convenience of visual observation simultaneously of all targets irradiated by the antenna in the form of marks on the indicator screen;

alternate operation of the transmitter and receiver allows you to use one common antenna for transmission and reception.

Second study question.

Key indicators of the impulse method

The main indicators of the impulse method are (slide 29) :

Unambiguously determined maximum range, D;

range resolution, δD;

minimum detectable range, D min .

Let's take a look at these metrics.

Unambiguous maximum range

The maximum range of the radar is determined by the basic radar formula and depends on the parameters of the radar.

The unambiguity of determining the distance to the object depends on the repetition period of the probing pulses T P. Further, this question is stated as follows.

The maximum range of the radar is 300 km. Determine the delay time to a target located at this range

The repetition period of the probing pulses is chosen to be 1000 μs. Determine the range to the target, the delay time to which is equal to T P

There are two targets in the airspace: target No. 1 at a range of 100 km and target No. 2 at a range of 200 km. What will the marks from these targets look like on the radar indicator (Fig. 3.4, slide 22, 30 ).

When sounding space with pulses with a repetition period of 1000 μs, the mark from target No. 1 will be displayed at a distance of 50 km, since after a range of 150 km a new sweep period will begin and the distant target will give a mark at the beginning of the scale (at a distance of 50 km). The measured range does not correspond to the real one.

How to eliminate ambiguity in determining the range?

After summarizing the students' answers, conclude:

To unambiguously determine the range, it is necessary to choose the repetition period of the probing pulses in accordance with the specified maximum range of the radar, that is

For a given range of 300 km, the repetition period of the probing pulses must be greater than 2000 μs, or the repetition frequency must be less than 500 Hz.

In addition, the maximum determined range depends on the width of the beam, the speed of rotation of the antenna, and the required number of pulses reflected from the target in one revolution of the antenna.

Range resolution (δD) is the minimum distance between two targets located at the same azimuth and elevation angle at which the signals reflected from them are observed on the indicator screen still separately(Fig. 3.5, slide 23, 31, 32 ).

For a given duration of the probing pulse τ and and distance between targets ∆D 1 targets #1 and #2 are irradiated separately. With the same pulse duration, but with a distance between targets ∆D 2 targets #3 and #4 are irradiated simultaneously. Therefore, in the first case, the PPI will be visible on the screen separately, and in the second case, they will be seen together. It follows from this that for separate reception of impulse signals, it is necessary that the time interval between the moments of their reception be greater than the pulse duration τ and (∆ t > τ and )

Minimum difference (D 2 – D 1 ), at which the targets are visible on the screen separately, by definition there is a range resolution δD, Consequently

In addition to the pulse duration τ and the range resolution of the station is affected by the resolution of the indicator, which is determined by the sweep scale and the minimum diameter of the luminous spot on the CRT screen ( d P ≈ 1 mm). The larger the range sweep scale and the better the focusing of the CRT beam, all the better resolution of the indicator.

In the general case, the range resolution of the radar is equal to

where δD and is the resolution of the indicator.

The less δD , the better the resolution. Typically, the range resolution of a radar is δD= (0.5...5) km.

In contrast to the resolution in range, the resolution in angular coordinates (in azimuth δβ and elevation δε ) not depends from the radar method and is determined by the width of the antenna pattern in the corresponding plane, which is customarily measured at the half power level.

Radar resolution in azimuth δβ about is equal to:

δβ about = φ 0.5r about + δβ and about ,

where φ 0.5r about– beamwidth at half power in the horizontal plane;

δβ and about- azimuth resolution of the indicator equipment.

The high resolution capabilities of the radar make it possible to separately observe and determine the coordinates of closely spaced targets.

The minimum detectable range is the smallest distance at which the station can still detect a target. Sometimes the space around the station, in which targets are not detected, is called the "dead" zone. ( slide 33 ).

The use of a single antenna in a pulse radar for transmitting sounding pulses and receiving reflected signals requires turning off the receiver for the duration of the sounding pulse τ u. Therefore, the reflected signals coming to the station at the moment when its receiver is not connected to the antenna will not be received and registered on the indicators. The length of time during which the receiver cannot receive reflected signals is determined by the duration of the probing pulse τ u and the time required to switch the antenna from transmission to reception after exposure to the probe pulse of the transmitter t in .

Knowing this time, the value of the minimum range D min pulse radar can be determined by the formula

where τ u- duration of the radar probe pulse;

t in- receiver turn-on time after the end of the transmitter probing pulse (units - μs).

For example. At τ u= 10µs D min = 1500 m

at τ u= 1 µs D min = 150 m.

It should be borne in mind that with an increase in the radius of the "dead" zone D min leads to the presence on the screen of an indicator reflected from local objects and the limited limits of antenna rotation in elevation.

CONCLUSION

The impulse method of radar is effective in measuring the distances of objects located at large distances.

Third study question

Continuous radiation method

Along with the use of the pulse method, radar can be carried out using installations with continuous energy radiation. With the continuous method of radiation, it is possible to send a large amount of energy towards the target.

Along with the advantage of the energy order, the method of continuous radiation is inferior to the pulsed method in a number of indicators. Depending on which parameter of the reflected signal serves as the basis for measuring the distance to the target, with a continuous radar method, there are:

phase (phase-metric) method of radar;

frequency method of radar.

Combined methods of radar are also possible, in particular, pulse-phase and pulse-frequency.

With the phase method radar about the distance to the target to the target is judged by the phase difference of the emitted and received reflected oscillations. The first phase-metric methods for measuring distance were proposed and developed by academicians L.I. Mandelstam and N.D. Papaleksi. These methods have found application in long-wave long-range aviation radio navigation systems.

With the frequency method In radar, the distance to the target is judged by the beat frequency between the direct and reflected signals.

Note. Students study these methods independently. Literature: Slutsky V.Z. Pulse technique and fundamentals of radar. pp. 227-236.

CONCLUSION

Determining the distance to an object with the pulse method is reduced to changing the delay time t rec of the reflected signal relative to the probing pulse.

For the unambiguous determination of the distance to the object, it is necessary that t zap.max ≤ T p.

The range resolution δD is the better, the shorter the duration of the probing pulse τ u .

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 right 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 - 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.

Modern warfare is swift and fleeting. Often the winner in a combat encounter is the one who is the first to be able to detect a potential threat and respond adequately to it. For more than seventy years, to search for the enemy on land, sea and in the air, a radar method has been used, based on the emission of radio waves and the registration of their reflections from various objects. Devices that send and receive such signals are called radar stations or radars.

The term "radar" is an English abbreviation (radio detection and ranging), which was put into circulation in 1941, but has long since become an independent word and entered most of the world's languages.

The invention of radar is, of course, a landmark event. Modern world it is difficult to imagine without radar stations. They are used in aviation, in maritime transport, with the help of radar the weather is predicted, violators of the rules are identified. traffic, the earth's surface is scanned. Radar systems (RLK) have found their application in the space industry and in navigation systems.

However, radars are most widely used in military affairs. It should be said that this technology was originally created for military needs and reached the stage of practical implementation just before the start of World War II. All the major countries participating in this conflict actively (and not without result) used radar stations for reconnaissance and detection of enemy ships and aircraft. It can be confidently asserted that the use of radars decided the outcome of several significant battles both in Europe and in the Pacific theater of operations.

Today, radars are used to solve an extremely wide range of military tasks, from tracking the launch of intercontinental ballistic missiles to artillery reconnaissance. Each aircraft, helicopter, warship has its own radar system. Radars are the backbone of the system air defense. The newest radar system with a phased array antenna will be installed on a promising Russian tank "Armata". In general, the variety of modern radars is amazing. These are completely different devices that differ in size, characteristics and purpose.

It can be said with confidence that today Russia is one of the recognized world leaders in the development and production of radars. However, before talking about the trends in the development of radar systems, a few words should be said about the principles of operation of radars, as well as the history of radar systems.

How Radar Works

Location is a method (or process) of determining the location of something. Accordingly, radar is a method of detecting an object or object in space using radio waves that are emitted and received by a device called a radar or radar.

The physical principle of operation of the primary or passive radar is quite simple: it transmits radio waves into space, which are reflected from surrounding objects and return to it in the form of reflected signals. Analyzing them, the radar is able to detect an object at a certain point in space, as well as show its main characteristics: speed, height, size. Any radar is a complex radio engineering device consisting of many components.

The structure of any radar includes three main elements: a signal transmitter, an antenna and a receiver. All radar stations can be divided into two large groups:

• impulse;
• continuous action.

The pulse radar transmitter emits electromagnetic waves for a short period of time (fractions of a second), the next signal is sent only after the first pulse returns back and hits the receiver. The pulse repetition frequency is one of the most important characteristics of a radar. Low frequency radars send out several hundred pulses per minute.

The pulse radar antenna works for both reception and transmission. After the signal is emitted, the transmitter turns off for a while and the receiver turns on. After receiving it, the reverse process occurs.

Pulse radars have both disadvantages and advantages. They can determine the range of several targets at once, such a radar can easily do with one antenna, the indicators of such devices are simple. However, in this case, the signal emitted by such a radar should have a fairly high power. It can also be added that all modern tracking radars are made according to a pulsed scheme.

Pulse radar stations usually use magnetrons, or traveling wave tubes, as the signal source.

The radar antenna focuses the electromagnetic signal and directs it, picks up the reflected pulse and transmits it to the receiver. There are radars in which the reception and transmission of a signal are carried out by different antennas, and they can be located at a considerable distance from each other. The radar antenna is capable of emitting electromagnetic waves in a circle or working in a certain sector. The radar beam can be directed in a spiral or be shaped like a cone. If necessary, the radar can follow a moving target by constantly pointing the antenna at it with the help of special systems.

The functions of the receiver include processing the received information and transferring it to the screen, from which it is read by the operator.

In addition to pulse radars, there are also continuous-wave radars that constantly emit electromagnetic waves. Such radar stations use the Doppler effect in their work. It lies in the fact that the frequency of an electromagnetic wave reflected from an object that approaches the signal source will be higher than from a receding object. The frequency of the emitted pulse remains unchanged. Radars of this type do not fix stationary objects, their receiver picks up only waves with a frequency above or below the emitted one.

A typical Doppler radar is the radar used by traffic police to determine the speed of vehicles.

The main problem of continuous radars is the inability to use them to determine the distance to the object, but during their operation there is no interference from stationary objects between the radar and the target or behind it. In addition, Doppler radars are quite simple devices, which require low-power signals to operate. It should also be noted that modern radar stations with continuous radiation have the ability to determine the distance to the object. To do this, use the change in the frequency of the radar during operation.

One of the main problems in the operation of pulse radars is the interference that comes from stationary objects - as a rule, this is the earth's surface, mountains, hills. During the operation of airborne pulsed aircraft radars, all objects located below are “obscured” by the signal reflected from the earth's surface. If we talk about ground-based or shipborne radar systems, then for them this problem manifests itself in the detection of targets flying at low altitudes. To eliminate such interference, the same Doppler effect is used.

In addition to primary radars, there are so-called secondary radars that are used in aviation to identify aircraft. The composition of such radar systems, in addition to the transmitter, antenna and receiver, also includes an aircraft transponder. When irradiated with an electromagnetic signal, the transponder issues Additional information about altitude, route, board number, its nationality.

Also, radar stations can be divided by the length and frequency of the wave on which they operate. For example, to study the surface of the Earth, as well as to work at considerable distances, waves of 0.9-6 m (frequency 50-330 MHz) and 0.3-1 m (frequency 300-1000 MHz) are used. For air traffic control, a radar with a wavelength of 7.5-15 cm is used, and over-the-horizon radars of missile launch detection stations operate at waves with a wavelength of 10 to 100 meters.

History of radar

The idea of ​​radar arose almost immediately after the discovery of radio waves. In 1905, Christian Hülsmeyer, an employee of the German company Siemens, created a device that could detect large metal objects using radio waves. The inventor suggested installing it on ships so that they could avoid collisions in conditions of poor visibility. However, ship companies were not interested in the new device.

Experiments with radar were also carried out in Russia. As early as the end of the 19th century, the Russian scientist Popov discovered that metal objects prevent the propagation of radio waves.

In the early 1920s, American engineers Albert Taylor and Leo Young managed to detect a passing ship using radio waves. However, the state of the radio engineering industry of that time was such that it was difficult to create industrial models of radar stations.

The first radar stations that could be used to solve practical problems appeared in England around the mid-1930s. These devices were very large and could only be installed on land or on the deck of large ships. It was not until 1937 that a miniature radar prototype was created that could be installed on an aircraft. By the start of World War II, the British had an deployed chain of radar stations called Chain Home.

Engaged in a new promising direction in Germany. And, I must say, not without success. Already in 1935, the Commander-in-Chief of the German Navy, Raeder, was shown a working radar with a cathode-beam display. Later, production models of the radar were created on its basis: Seetakt for the naval forces and Freya for air defense. In 1940, the Würzburg radar fire control system began to enter the German army.

However, despite the obvious achievements of German scientists and engineers in the field of radar, the German army began to use radar later than the British. Hitler and the top of the Reich considered radars to be exclusively defensive weapons, which the victorious German army did not really need. It is for this reason that by the beginning of the Battle of Britain, the Germans had deployed only eight Freya radar stations, although in terms of their characteristics they were at least as good as their British counterparts. In general, it can be said that it was the successful use of radar that largely determined the outcome of the Battle of Britain and the subsequent confrontation between the Luftwaffe and the Allied Air Force in the skies of Europe.

Later, the Germans, based on the Würzburg system, created an air defense line, which was called the Kammhuber Line. Using special forces units, the Allies were able to unravel the secrets of the German radar, which made it possible to effectively jam them.

Despite the fact that the British entered the "radar" race later than the Americans and Germans, at the finish line they managed to overtake them and approach the beginning of World War II with the most advanced radar detection system for aircraft.

Already in September 1935, the British began to build a network of radar stations, which already included twenty radar stations before the war. It completely blocked the approach to the British Isles from the European coast. In the summer of 1940, British engineers created a resonant magnetron, which later became the basis of airborne radar stations installed on American and British aircraft.

Work in the field of military radar was also carried out in the Soviet Union. The first successful experiments on detecting aircraft using radar stations in the USSR were carried out as early as the mid-1930s. In 1939, the first RUS-1 radar was adopted by the Red Army, and in 1940 - RUS-2. Both of these stations were launched into mass production.

Second World War clearly demonstrated the high efficiency of the use of radar stations. Therefore, after its completion, the development of new radars became one of the priority areas for development military equipment. Over time, airborne radars were received by all military aircraft and ships without exception, radars became the basis for air defense systems.

During the Cold War, the United States and the USSR acquired a new destructive weapon - intercontinental ballistic missiles. Detecting the launch of these missiles became a matter of life and death. Soviet scientist Nikolai Kabanov proposed the idea of ​​using short radio waves to detect enemy aircraft at long distances (up to 3,000 km). It was quite simple: Kabanov found out that radio waves 10-100 meters long are capable of being reflected from the ionosphere, and irradiating targets on the earth's surface, returning the same way to the radar.

Later, based on this idea, radars for over-the-horizon detection of ballistic missile launches were developed. An example of such radars is Daryal, a radar station that for several decades was the basis of the Soviet missile launch warning system.

Currently, one of the most promising areas for the development of radar technology is the creation of a radar with a phased antenna array (PAR). Such radars have not one, but hundreds of radio wave emitters, which are controlled by a powerful computer. Radio waves emitted by different sources in the phased array can amplify each other if they are in phase, or, conversely, weaken.

The phased array radar signal can be given any desired shape, it can be moved in space without changing the position of the antenna itself, and work with different radiation frequencies. A phased array radar is much more reliable and sensitive than a conventional antenna radar. However, such radars also have disadvantages: the cooling of the radar with phased array is a big problem, in addition, they are difficult to manufacture and expensive.

New phased array radars are being installed on fifth-generation fighters. This technology is used in the US missile attack early warning system. Radar complex with PAR will be installed on the newest Russian tank "Armata". It should be noted that Russia is one of the world leaders in the development of PAR radars.

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Radar stations are classified according to the following criteria:

The origin of the radio signal received by the radar receiver - active radars (with active and passive response), semi-active and passive radars;

The used range of radio waves (radar decameter, meter, decimeter, centimeter and millimeter ranges);

Type of probing signal [radar with continuous (unmodulated or frequency-modulated) and pulsed (non-coherent, coherent-pulse with large and small duty cycles, with intra-pulse frequency or phase modulation) radiation];

The number of channels used for emitting and receiving signals (single-channel and multi-channel with frequency or spatial division of channels);

The number and type of measured coordinates (one-, two- and three-coordinate);

Method of measurement, display and removal of object coordinates;

Place of installation of the radar (ground, ship, aircraft, satellite);

The functional purpose of the radar [from small-sized portable radars for measuring the speed of vehicles to huge ground-based radars of air defense (air defense) and missile defense (ABM) systems]. We list the main types of ground, ship and aircraft radars for various purposes.

Main types ground radars :

Detection of air targets and guidance of fighters on them;

Air traffic control (surveillance and control rooms);

Detection and determination of the coordinates of ballistic missiles (BR) and artificial Earth satellites (AES);

Target designation for anti-aircraft artillery control stations and guidance of anti-aircraft guided missiles (SAM);

Control of anti-aircraft artillery and missiles;

Mortar detection;

Meteorological;

Overview of the port water area;

Overview of the airfield;

Detection and determination of the speed of ground moving objects.

Main types shipborne radars :

Navigation support;

Detection of surface objects and low-flying aircraft, determination of their coordinates;

Detection and determination of the coordinates of high-flying aircraft;

Management of missiles and anti-aircraft artillery;

detection and determination of the coordinates of BR and AES.

Main types aircraft radar :

Radar rangefinders;

radio altimeters;

Doppler ground speed and drift angle meters;

Aircraft detection and collision avoidance radar;

Panoramic radar survey of the earth's surface;

side-looking radar (including those with a synthesized antenna opening);

radar interception and aiming;

guided missile guidance radar;

Radar fuses.

The above classification does not include all types of radar used. However, the listed types are sufficient to characterize the breadth and diversity of the use of radar facilities.

1.6. Tactical characteristics of the radar.

tactical name the characteristics of the system, the requirement that the system must meet in order to solve the problem. These requirements are set for the developer of radio-electronic equipment. Based on tactical requirements, the developer further determines the technical characteristics of the system as a whole and the individual devices of its constituents.

The main tactical characteristics of the radar include:

Purpose of the system ;

Installation location ;

The composition of the measured coordinates ;

Zone (area) of the review or the working area of ​​the system, specified by the sector of view (search) according to the measured parameters of the object;

view area called the area of ​​space in which the system reliably performs the functions corresponding to its purpose. So, for a detection radar, the field of view is a region of space in which objects with given reflection characteristics are detected with a probability not less than a given one.

When working with the view area, the following parameters are set: R max , R min ,  max ,  min ,  max ,  min .

5) review time (search) for a given sector or review speed; review time(search) is the time required for a single review of a given system coverage area. The choice of survey time is related to the maneuverability of observed or controlled objects, the volume of the survey space, the level of signal and interference, as well as a number of tactical and technical characteristics of the system.

Coordinate measurement accuracy ;

Accuracy The system is characterized by errors in measuring the coordinates and parameters of the object's motion. The reasons for the errors are the imperfection of the applied measurement method and equipment, the influence of external conditions and radio interference, the subjective qualities of the operator, if the processes of obtaining and implementing information are not automated. The accuracy requirements of the system depend on its purpose. An unjustified overestimation of the requirements for accuracy leads to a complication of the system, a decrease in its efficiency, and sometimes even reliability of operation.

Measurement of signal parameters is always accompanied by errors:

Systematic (appear when measuring parameters on instruments);

Random (they appear from factors that are not subject to accounting. Therefore, these errors obey the normal distribution law).

where  X is the root mean square error.

a) Range resolution- numerically characterized by the minimum distance between two fixed targets located in the radial direction relative to the radar, the signals of which are still recorded by the station separately. With a smaller distance between the targets, their separate radar observation becomes impossible.

For example, we have two objects 1 and 2. The distance between them is respectively R 1 and R 2 (Fig.I.1.6)

The delay time of one t of the second object (Fig. I.1.7):
,
.

R the distance between the objects began to decrease (Fig. I.1.8), i.e.

;
;
,

where With is a measure of resolution.

b) Directional resolution is numerically characterized by the minimum angle between the directions to two stationary targets equidistant relative to the radar, at which their signals are still recorded separately. Often the resolution is estimated separately in azimuth and elevation.

Those.
and
(the directional resolution is equal to half of the antenna pattern).

c) Speed ​​resolution is estimated by the minimum difference in the speeds of two targets that are not resolved by coordinates, at which their signals are still recorded separately.

Bandwidth characterized by the number of objects serviced by the system simultaneously or per unit of time. Throughput depends on the principle of operation of the system and a number of its tactical and technical parameters and in particular, working area, accuracy and resolution.

The throughput of ranging systems based on the principle of request and active response (two communication lines) is limited by the transponder, in which some time is required to generate a response signal for each request. In this case, the throughput is characterized by the probability of serving a given number of objects for a given period of repetition of requests by each of the objects located in the working area of ​​the system;

9) Noise immunity Radar - the ability to reliably perform the specified functions under the influence of unintentional and organized interference. Noise immunity is determined by the secrecy of the system and its noise immunity.

Under secrecy systems understand the indicator that characterizes the difficulty of detecting its operation and measuring the main parameters of the emitted radio signal, and, consequently, the creation of specially organized (targeted) interference. Stealth is ensured by the use of highly directional radiation, the use of noise-like signals with a low power level, and the change in the main signal parameters over time.

Quantifying noise immunity The radar is the signal-to-noise ratio at the receiver input, at which the measurement error of a given parameter does not exceed the allowable one with the required probability; for radar detection, in this case, detection of a signal with a given R" 0 at admissible values ​​of the false alarm probability. The required noise immunity is achieved by a rational choice of the radio signal parameters of the system, as well as the characteristics of the beam and devices for receiving and processing the signal.

10) Reliability - the property of the object to keep in time within the established limits the values ​​of the parameters that characterize the ability to perform the required functions in the specified modes and conditions of use, storage and transportation.

Depending on the reasons causing failures in the system, the following types of reliability are distinguished:

Hardware related to the state of the hardware;

Software, due to the state of the programs of computing devices used in the system;

Functional, i.e., the reliability of the performance of individual functions assigned to the system, and, in particular, the extraction and processing of information. In this sense, noise immunity can also be related to the functional reliability of the radio system.

11) Mass-dimensional characteristics – the volume and mass of the equipment are set;

12) Power consumption .